Stephen Blanksby

Rapid quantification of free cholesterol in tears using direct insertion/electron ionization-Mass spectrometry

Publisher: Association for Research in Vision and Ophthalmology (ARVO)

Date: 09-12-2013

DOI: 10.1167/IOVS.13-12786

Abstract: To establish a simple and rapid analytical method, based on direct insertion/electron ionization-mass spectrometry (DI/EI-MS), for measuring free cholesterol in tears from humans and rabbits. A stable-isotope dilution protocol employing DI/EI-MS in selected ion monitoring mode was developed and validated. It was used to quantify the free cholesterol content in human and rabbit tear extracts. Tears were collected from adult humans (n = 15) and rabbits (n = 10) and lipids extracted. Screening, full-scan (m/z 40-600) DI/EI-MS analysis of crude tear extracts showed that diagnostic ions located in the mass range m/z 350 to 400 were those derived from free cholesterol, with no contribution from cholesterol esters. DI/EI-MS data acquired using selected ion monitoring (SIM) were analyzed for the abundance ratios of diagnostic ions with their stable isotope-labeled analogues arising from the D6-cholesterol internal standard. Standard curves of good linearity were produced and an on-probe limit of detection of 3 ng (at 3:1 signal to noise) and limit of quantification of 8 ng (at 10:1 signal to noise). The concentration of free cholesterol in human tears was 15 ± 6 μg/g, which was higher than in rabbit tears (10 ± 5 μg/g). A stable-isotope dilution DI/EI-SIM method for free cholesterol quantification without prior chromatographic separation was established. Using this method demonstrated that humans have higher free cholesterol levels in their tears than rabbits. This is in agreement with previous reports. This paper provides a rapid and reliable method to measure free cholesterol in small-volume clinical s les.

Direct Observation of Photodissociation Products from Phenylperoxyl Radicals Isolated in the Gas Phase

Publisher: American Chemical Society (ACS)

Date: 07-06-2013

DOI: 10.1021/JA402610S

Abstract: Gas phase peroxyl radicals are central to our chemical understanding of combustion and atmospheric processes and are typically characterized by strong absorption in the UV (λ(max) ≈ 240 nm). The analogous maximum absorption feature for arylperoxyl radicals is predicted to shift to the visible but has not previously been characterized nor have any photoproducts arising from this transition been identified. Here we describe the controlled synthesis and isolation in vacuo of an array of charge-substituted phenylperoxyl radicals at room temperature, including the 4-(N,N,N-trimethylammonium)methyl phenylperoxyl radical cation (4-Me3N([+])CH2-C6H4OO(•)), using linear ion-trap mass spectrometry. Photodissociation mass spectra obtained at wavelengths ranging from 310 to 500 nm reveal two major photoproduct channels corresponding to homolysis of aryl-OO and arylO-O bonds resulting in loss of O2 and O, respectively. Combining the photodissociation yields across this spectral window produces a broad (FWHM ≈ 60 nm) but clearly resolved feature centered at λ(max) = 403 nm (3.08 eV). The influence of the charge-tag identity and its proximity to the radical site are investigated and demonstrate no effect on the identity of the two dominant photoproduct channels. Electronic structure calculations have located the vertical B ← X transition of these substituted phenylperoxyl radicals within the experimental uncertainty and further predict the analogous transition for unsubstituted phenylperoxyl radical (C6H5OO(•)) to be 457 nm (2.71 eV), nearly 45 nm shorter than previous estimates and in good agreement with recent computational values.

Desorption electrospray ionisation mass spectrometry of stabilised polyesters reveals activation of hindered amine light stabilisers

Publisher: Elsevier BV

Date: 2014

DOI: 10.1016/J.POLYMDEGRADSTAB.2013.10.026

Prenylated bisresorcinols from Grevillea floribunda

Publisher: Elsevier BV

Date: 02-2009

DOI: 10.1016/J.PHYTOL.2008.11.004

Structural elucidation of hydroxy fatty acids by photodissociation mass spectrometry with photolabile derivatives

Publisher: Wiley

Date: 13-03-2020

DOI: 10.1002/RCM.8741

An opto-magneto-mechanical quantum interface between distant superconducting qubits

Publisher: Springer Science and Business Media LLC

Date: 04-07-2014

DOI: 10.1038/SREP05571

Fragmentations of Deprotonated Alkyl Hydroperoxides (ROO− Upon Collisional Activation: A Combined Experimental and Computational Study

Publisher: CSIRO Publishing

Date: 2003

DOI: 10.1071/CH03039

Abstract: The collision-induced dissociation (CID) mass spectra of the [M − H]– anions of methyl, ethyl, and tert-butyl hydroperoxides have been measured over a range of collision energies in a flowing afterglow–selected ion flow tube (FA-SIFT) mass spectrometer. Activation of the CH3OO– anion is found to give predominantly HO– fragment anions whilst CH3CH2OO− and (CH3)3COO– produce HOO– as the major ionic fragment. These results, and other minor fragmentation pathways, can be rationalized in terms of unimolecular rearrangement of the activated anions with subsequent decomposition. The rearrangement reactions occur via initial abstraction of a proton from the α-carbon in the case of CH3OO– or the β-carbon for CH3CH2OO– and (CH3)3COO–. Electronic structure calculations suggest that for the CH3CH2OO– anion, which can theoretically undergo both α- and β-proton abstraction, the latter pathway, resulting in HOO– + CH2CH2, is energetically preferred.

Production and isolation of ligated metal(IV)‐oxo ions by tandem mass spectrometry

Publisher: Wiley

Date: 19-03-2010

DOI: 10.1002/RCM.4493

Abstract: High valent metal(IV)-oxo species, [M(==O)(MeIm)(n)(OAc)](+) (M = Mn-Ni, MeIm = 1-methylimidazole, n = 1-2), which are relevant to biology and oxidative catalysis, were produced and isolated in gas-phase reactions of the metal(II) precursor ions [M(MeIm)(n)(OAc)](+) (M = Mn-Zn, n = 1-3) with ozone. The precursor ions [M(MeIm)(OAc)](+) and [M(MeIm)(2)(OAc)](+) were generated via collision-induced dissociation of the corresponding [M(MeIm)(3)(OAc)](+) ion. The dependence of ozone reactivity on metal and coordination number is discussed.

Exercise alters the profile of phospholipid molecular species in rat skeletal muscle

Publisher: American Physiological Society

Date: 11-2004

DOI: 10.1152/JAPPLPHYSIOL.00344.2004

Abstract: We have determined the effect of two exercise-training intensities on the phospholipid profile of both glycolytic and oxidative muscle fibers of female Sprague-Dawley rats using electrospray-ionization mass spectrometry. Animals were randomly ided into three training groups: control, which performed no exercise training low-intensity (8 m/min) treadmill running or high-intensity (28 m/min) treadmill running. All exercise-trained rats ran 1,000 m/session for 4 days/wk for 4 wk and were killed 48 h after the last training bout. Exercise training was found to produce no novel phospholipid species but was associated with significant alterations in the relative abundance of a number of phospholipid molecular species. These changes were more prominent in glycolytic (white vastus lateralis) than in oxidative (red vastus lateralis) muscle fibers. The largest observed change was a decrease of ∼20% in the abundance of 1-stearoyl-2-docosahexaenoyl-phosphatidylethanolamine [PE(18:0/22:6) P 0.001] ions in both the low- and high-intensity training regimes in glycolytic fibers. Increases in the abundance of 1-oleoyl-2-linoleoyl phopshatidic acid [PA(18:1/18:2) P 0.001] and 1-alkenylpalmitoyl-2-linoleoyl phosphatidylethanolamine [plasmenyl PE (16:0/18:2) P 0.005] ions were also observed for both training regimes in glycolytic fibers. We conclude that exercise training results in a remodeling of phospholipids in rat skeletal muscle. Even though little is known about the physiological or pathophysiological role of specific phospholipid molecular species in skeletal muscle, it is likely that this remodeling will have an impact on a range of cellular functions.

Preparation of an ion with the highest calculated proton affinity: ortho-diethynylbenzene dianion

Publisher: Royal Society of Chemistry (RSC)

Date: 2016

DOI: 10.1039/C6SC01726F

Abstract: Owing to the increased proton affinity that results from additional negative charges, multiply-charged anions are shown as a route to preparing powerful ‘superbases’.

Photoelectron spectroscopy of HCCN− and HCNC− reveals the quasilinear triplet carbenes, HCCN and HCNC

Publisher: AIP Publishing

Date: 13-08-2002

DOI: 10.1063/1.1496473

Abstract: Negative ion photoelectron spectroscopy has been used to study the HCCN− and HCNC− ions. The electron affinities (EA) of cyanocarbene have been measured to be EA(HCCN X̃ 3Σ−=2.003±0.014 eV and EA(DCCN X̃ 3Σ−)=2.009±0.020 eV. Photodetachment of HCCN− to HCCN X̃ 3Σ− shows a 0.4 eV long vibrational progression in ν5, the H–CCN bending mode the HCCN− photoelectron spectra reveal excitations up to 10 quanta in ν5. The term energies for the excited singlet state are found to be T0(HCCN ã 1A′)=0.515±0.016 eV and T0(DCCN ã 1A′)=0.518±0.027 eV. For the isocyanocarbene, the two lowest states switch and HCNC has a singlet ground state and an excited triplet state. The electron affinities are EA(HCNC X̃ 1A′)=1.883±0.013 eV and EA(X̃ 1A′ DCNC)=1.877±0.010 eV. The term energy for the excited triplet state is T0(HCNC ã 3A″)=0.050±0.028 eV and T0(DCNC ã 3A″)=0.063±0.030 eV. Proton transfer kinetics in a flowing afterglow apparatus were used to re-measure the enthalpy of deprotonation of CH3NC to be ΔacidH298(CH3NC)=383.6±0.6 kcal mol−1. The acidity/EA thermodynamic cycle was used to deduce D0(H–CHCN)=104±2 kcal mol−1 [ΔfH0(HCCN)=110±4 kcal mol−1] and D0(H–CHNC)=106±4 kcal mol−1 [ΔfH0(HCNC)=133±5 kcal mol−1].

Intersubject and Interday Variability in Human Tear and Meibum Lipidomes: A Pilot Study

Publisher: Elsevier BV

Date: 2016

DOI: 10.1016/J.JTOS.2015.08.005

Abstract: Our aim was to quantitate day-to-day changes in the tear and meibum lipid profile of in idual subjects in a pilot study of healthy humans. Matched tear and meibum s les were obtained from four subjects on three consecutive days. Quantitative lipid profiles of human basal tears and meibum were compared using multivariate analysis by principal components. Substantial differences in the lipid profile between subjects were observed, while lipid profiles were steady across the three consecutive days of s ling. Multivariate principal component analysis demonstrated that lysophosphatidylcholine was the largest variant lipid class between subjects in tears, while wax esters comprised the most variation between subjects in meibum secretions. Interday variability is shown to be much smaller than interpatient variability, suggesting that tears and meibum subjects both have unique profiles in humans.

Isolation and characterization of charge-tagged phenylperoxyl radicals in the gas phase: direct evidence for products and pathways in low temperature benzene oxidation

Publisher: Royal Society of Chemistry (RSC)

Date: 2012

DOI: 10.1039/C2CP43507A

Abstract: The phenylperoxyl radical has long been accepted as a critical intermediate in the oxidation of benzene and an archetype for arylperoxyl radicals in combustion and atmospheric chemistry. Despite being central to many contemporary mechanisms underpinning these chemistries, reports of the direct detection or isolation of phenylperoxyl radicals are rare and there is little experimental evidence connecting this intermediate with expected product channels. We have prepared and isolated two charge-tagged phenyl radical models in the gas phase [i.e., 4-(N,N,N-trimethylammonium)phenyl radical cation and 4-carboxylatophenyl radical anion] and observed their reactions with dioxygen by ion-trap mass spectrometry. Measured reaction rates show good agreement with prior reports for the neutral system (k(2)[(Me(3)N(+))C(6)H(4)˙ + O(2)] = 2.8 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 4.9% k(2)[((-)O(2)C)C(6)H(4)˙ + O(2)] = 5.4 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 9.2%) and the resulting mass spectra provide unequivocal evidence for the formation of phenylperoxyl radicals. Collisional activation of isolated phenylperoxyl radicals reveals unimolecular decomposition by three pathways: (i) loss of dioxygen to reform the initial phenyl radical (ii) loss of atomic oxygen yielding a phenoxyl radical and (iii) ejection of the formyl radical to give cyclopentadienone. Stable isotope labeling confirms these assignments. Quantum chemical calculations for both charge-tagged and neutral phenylperoxyl radicals confirm that loss of formyl radical is accessible both thermodynamically and entropically and competitive with direct loss of both hydrogen atom and carbon dioxide.

Mass Spectrometry Imaging with Isomeric Resolution Enabled by Ozone‐Induced Dissociation

Publisher: Wiley

Date: 19-06-2018

DOI: 10.1002/ANGE.201802937

Variation in the Relative Isomer Abundance of Synthetic and Biologically Derived Phosphatidylethanols and Its Consequences for Reliable Quantification

Publisher: Oxford University Press (OUP)

Date: 04-04-2020

DOI: 10.1093/JAT/BKAA034

Abstract: Phosphatidylethanol (PEth) in human blood s les is a marker for alcohol usage. Typically, PEth is detected by reversed-phase liquid chromatography coupled with negative ion tandem mass spectrometry, investigating the fatty acyl anions released from the precursor ion upon collision-induced dissociation (CID). It has been established that in other classes of asymmetric glycerophospholipids, the unimolecular fragmentation upon CID is biased depending on the relative position (known as sn-position) of each fatty acyl chain on the glycerol backbone. As such, the use of product ions in selected-reaction-monitoring (SRM) transitions could be prone to variability if more than one regioisomer is present in either the reference materials or the s le. Here, we have investigated the regioisomeric purity of three reference materials supplied by different vendors, labeled as PEth 16:0/18:1. Using CID coupled with ozone-induced dissociation, the regioisomeric purity (% 16:0 at sn-1) was determined to be 76, 80 and 99%. The parallel investigation of the negative ion CID mass spectra of standards revealed differences in product ion ratios for both fatty acyl chain product ions and ketene neutral loss product ions. Furthermore, investigation of the product ion abundances in CID spectra of PEth within authentic blood s les appears to indicate a limited natural variation in isomer populations between s les, with the cannonical, PEth 16:0/18:1 (16:0 at sn-1) predominant in all cases. Different reference material isomer distributions led to variation in fully automated quantification of PEth in 56 authentic dried blood spot (DBS) s les when a single quantifier ion was used. Our results suggest caution in ensuring that the regioisomeric compositions of reference materials are well-matched with those of the authentic blood s les.

Tandem mass spectrometry of deprotonated iodothyronines

Publisher: Wiley

Date: 14-07-2005

DOI: 10.1002/RCM.2061

Abstract: In order to assist with the development of more selective and sensitive methods for thyroid hormone analysis the [M-H]- anions of the iodothyronines T4, T3, rT3, (3,5)-T2 and the non-iodinated thyronine (T0) have been generated by negative ion electrospray mass spectrometry. Tandem mass spectra of these ions were recorded on a triple-quadrupole mass spectrometer and show a strong analogy with the fragmentation pathways of the parent compound, tyrosine. All iodothyronines also show significant abundances of the iodide anion in their tandem mass spectra, which represents an attractive target for multiple reaction monitoring (MRM) analysis, given that iodothyronines are the only iodine bearing endogenous molecules. Characteristic fragments are observed at m/z 359.7 and 604.5 for rT3 but are absent in the spectrum of T3, thus differentiating the two positional isomers. The striking difference in the fragmentation patterns of these regioisomeric species is attributed to the increased acidity of the phenol moiety in rT3 compared with T3.

Sphingolipid distribution changes with age in the human lens

Publisher: Elsevier BV

Date: 09-2010

DOI: 10.1194/JLR.M007716

Detection and quantification of tear phospholipids and cholesterol in contact lens deposits: The effect of contact lens material and lens care solution

Publisher: Association for Research in Vision and Ophthalmology (ARVO)

Date: 06-2010

DOI: 10.1167/IOVS.09-4609

Abstract: To examine the deposition of tear phospholipids and cholesterol onto worn contact lenses and the effect of lens material and lens care solution. Lipids were extracted from tears and worn contact lenses using 2:1 chloroform:methanol and the extract washed with aqueous ammonium acetate, before analysis by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Twenty-three molecular lipids from the sphingomyelin (SM) and phosphatidylcholine (PC) classes were detected in tears, with total concentrations of each class determined to be 5 +/- 1 pmol/microL ( approximately 3.8 microg/mL) and 6 +/- 1 pmol/microL ( approximately 4.6 microg/mL), respectively. The profile of in idual phospholipids in both of these classes was shown to be similar in contact lens deposits. Deposition of representative polar and nonpolar lipids were shown to be significantly higher on senofilcon A contact lenses, with approximately 59 ng/lens SM, 195 ng/lens PC, and 9.9 microg/lens cholesterol detected, whereas balafilcon A lens extracts contained approximately 19 ng/lens SM, 19 ng/lens PC, and 3.9 microg/lens cholesterol. Extracts from lenses disinfected and cleaned with two lens care solutions showed no significant differences in total PC and SM concentrations however, a greater proportion of PC than SM was observed, compared with that in tears. Phospholipid deposits extracted from worn contact lenses show a molecular profile similar to that in tears. The concentration of representative polar and nonpolar lipids deposited onto contact lenses is significantly affected by lens composition. There is a differential efficacy in the removal of PC and SM with lens care solutions.

Characterization of acyl chain position in unsaturated phosphatidylcholines using differential mobility-mass spectrometry

Publisher: Elsevier BV

Date: 08-2014

DOI: 10.1194/JLR.M046995

Identification of phospholipids in human meibum by nano-electrospray ionisation tandem mass spectrometry

Publisher: Elsevier BV

Date: 03-2011

DOI: 10.1016/J.EXER.2010.12.012

Abstract: Meibum is believed to be the major source of tear film lipids, which are vital in the prevention of excess evaporation of the aqueous phase. The complete lipid composition of meibum has yet to be established. While earlier studies reported the presence of phospholipids in human meibum, recent mass spectrometric studies have not detected them. In this study we use electrospray ionisation tandem mass spectrometry to investigate the presence of phospholipids in meibum and provide comparison to the phospholipid profile of tears. Lipids were extracted from human meibum and tear s les using standard biphasic methods and analysed by nano-electrospray ionisation tandem mass spectrometry using targeted ion scans. A total of 35 choline-containing phospholipids were identified in meibum and the profile of these was similar to that observed in tears, suggesting tear lipids are derived from meibum. The results shown here highlight the need for a combination of optimised techniques to enable the identification of the large range of lipid classes in meibum.

Resolving Sphingolipid Isomers Using Cryogenic Infrared Spectroscopy

Publisher: Wiley

Date: 18-05-2020

DOI: 10.1002/ANIE.202002459

Bond Dissociation Energies of Organic Molecules

Publisher: American Chemical Society (ACS)

Date: 28-01-2003

DOI: 10.1021/AR020230D

Abstract: In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

Cumulenic and heterocumulenic anions: potential interstellar species?

Publisher: Oxford University Press (OUP)

Date: 11-2001

DOI: 10.1046/J.1365-8711.2001.04836.X

Reaction of ionised steryl esters with ozone in the gas phase

Publisher: Elsevier BV

Date: 07-2019

DOI: 10.1016/J.CHEMPHYSLIP.2018.12.013

Abstract: Cholesterol is an ubiquitous membrane lipid, that also serves as a precursor to many steroid hormones. The 5,6 carbon-carbon double bond on the tetracyclic carbon backbone of cholesterol is an attractive target for ozone with the reaction giving rise to a wide range of possibly bioactive molecules. Despite this, little is known about the ozonolysis of cholesterol esters, which often possess an additional double bond(s) on the fatty acyl chain. Understanding the intrinsic gas phase reaction of ozone with the two disparate double bond positions on cholesteryl esters can inform our understanding of these processes in vivo, particularly reactions occurring at the air-water interface (e.g., tear film lipid layer) and on the surfaces of the body where these cholesterol and cholesteryl esters may be present (e.g., sebum). In the present work we describe the gas phase ozonolysis of lithium and sodium cations formed from three steryl esters: two isomeric for double bond position (cholestanyl oleate and cholesteryl stearate), and a third with carbon-carbon double bonds present in both the sterol ring system and fatty acyl chain (cholesteryl oleate). We confirm the enhanced reactivity of the endocyclic carbon-carbon double bond with ozone over double bonds present in the acyl chain, and elucidate competitive interactions between the two double bond positions during ozonolysis. Elucidation of the mechanisms underlying this interaction is important for both understanding these processes in vivo and for deploying ozonolysis chemistry in analytical strategies for lipidomics.

Identification of abundant alkyl ether glycerophospholipids in the human lens by Tandem mass spectrometry techniques

Publisher: American Chemical Society (ACS)

Date: 02-02-2009

DOI: 10.1021/AC802395D

Abstract: Previous studies have shown that the human lens contains glycerophospholipids with ether linkages. These lipids differ from conventional glycerophospholipids in that the sn-1 substituent is attached to the glycerol backbone via an 1-O-alkyl or an 1-O-alk-1'-enyl ether rather than an ester bond. The present investigation employed a combination of collision-induced dissociation (CID) and ozone-induced dissociation (OzID) to unambiguously distinguish such 1-O-alkyl and 1-O-alk-1'-enyl ethers. Using these methodologies the human lens was found to contain several abundant 1-O-alkyl glycerophosphoethanolamines, including GPEtn(16:0e/9Z-18:1), GPEtn(11Z-18:1e/9Z-18:1), and GPEtn(18:0e/9Z-18:1), as well as a related series of unusual 1-O-alkyl glycerophosphoserines, including GPSer(16:0e/9Z-18:1), GPSer(11Z-18:1e/9Z-18:1), GPSer(18:0e/9Z-18:1) that to our knowledge have not previously been observed in human tissue. Isomeric 1-O-alk-1'-enyl ethers were absent or in low abundance. Examination of the double bond position within the phospholipids using OzID revealed that several positional isomers were present, including sites of unsaturation at the n-9, n-7, and even n-5 positions. Tandem CID/OzID experiments revealed a preference for double bonds in the n-7 position of 1-O-ether linked chains, while n-9 double bonds predominated in the ester-linked fatty acids [e.g., GPEtn(11Z-18:1e/9Z-18:1) and GPSer(11Z-18:1e/9Z-18:1)]. Different combinations of these double bond positional isomers within chains at the sn-1 and sn-2 positions point to a remarkable molecular ersity of ether-lipids within the human lens.

Electrospray Ionization-Mass Spectrometry of Synthetic Polymers Functionalized with Carboxylic Acid End-Groups

Publisher: American Chemical Society (ACS)

Date: 09-07-2021

DOI: 10.1021/JASMS.1C00085

Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1CP20784A

Abstract: α-Carboxylate radical anions are potential reactive intermediates in the free radical oxidation of biological molecules (e.g., fatty acids, peptides and proteins). We have synthesised well-defined α-carboxylate radical anions in the gas phase by UV laser photolysis of halogenated precursors in an ion-trap mass spectrometer. Reactions of isolated acetate (˙CH(2)CO(2)(-)) and 1-carboxylatobutyl (CH(3)CH(2)CH(2)˙CHCO(2)(-)) radical anions with dioxygen yield carbonate (CO(3)˙(-)) radical anions and this chemistry is shown to be a hallmark of oxidation in simple and alkyl-substituted cross-conjugated species. Previous solution phase studies have shown that C(α)-radicals in peptides, formed from free radical damage, combine with dioxygen to form peroxyl radicals that subsequently decompose into imine and keto acid products. Here, we demonstrate that a novel alternative pathway exists for two α-carboxylate C(α)-radical anions: the acetylglycinate radical anion (CH(3)C(O)NH˙CHCO(2)(-)) and the model peptide radical anion, YGGFG˙(-). Reaction of these radical anions with dioxygen results in concerted loss of carbon dioxide and hydroxyl radical. The reaction of the acetylglycinate radical anion with dioxygen reveals a two-stage process involving a slow, followed by a fast kinetic regime. Computational modelling suggests the reversible formation of the C(α) peroxyl radical facilitates proton transfer from the amide to the carboxylate group, a process reminiscent of, but distinctive from, classical proton-transfer catalysis. Interestingly, inclusion of this isomerization step in the RRKM/ME modelling of a G3SX level potential energy surface enables recapitulation of the experimentally observed two-stage kinetics.

Bisresorcinol Derivatives from Grevillea glauca

Publisher: Wiley

Date: 10-2011

DOI: 10.1002/HLCA.201100089

Time to face the fats: What can mass spectrometry reveal about the structure of lipids and their interactions with proteins?

Publisher: American Chemical Society (ACS)

Date: 06-06-2012

DOI: 10.1007/S13361-012-0410-2

Abstract: Since the 1950s, X-ray crystallography has been the mainstay of structural biology, providing detailed atomic-level structures that continue to revolutionize our understanding of protein function. From recent advances in this discipline, a picture has emerged of intimate and specific interactions between lipids and proteins that has driven renewed interest in the structure of lipids themselves and raised intriguing questions as to the specificity and stoichiometry in lipid-protein complexes. Herein we demonstrate some of the limitations of crystallography in resolving critical structural features of ligated lipids and thus determining how these motifs impact protein binding. As a consequence, mass spectrometry must play an important and complementary role in unraveling the complexities of lipid-protein interactions. We evaluate recent advances and highlight ongoing challenges towards the twin goals of (1) complete structure elucidation of low, abundant, and structurally erse lipids by mass spectrometry alone, and (2) assignment of stoichiometry and specificity of lipid interactions within protein complexes.

Antibacterial anthranilic acid derivatives from Geijera parviflora

Publisher: Elsevier BV

Date: 03-2014

DOI: 10.1016/J.FITOTE.2013.12.008

Abstract: Five anthranilic acid derivatives, a mixture I of three new compounds 11'-hexadecenoylanthranilic acid (1), 9'-hexadecenoylanthranilic acid (2), and 7'-hexadecenoylanthranilic acid (3), as well as a new compound 9,12,15-octadecatrienoylanthranilic acid (4) together with a new natural product, hexadecanoylanthranilic acid (5), were isolated from Geijera parviflora Lindl. (Rutaceae). Their structures were elucidated by extensive spectroscopic measurements, and the positions of the double bonds in compounds 1-3 of the mixture I were determined by tandem mass spectrometry employing ozone-induced dissociation. The mixture I and compound 5 showed good antibacterial activity against several Gram-positive strains.

Functional mass spectrometry imaging maps phospholipase-A2 enzyme activity during osteoarthritis progression

Publisher: Ivyspring International Publisher

Date: 2023

DOI: 10.7150/THNO.86623

Revolutions in Lipid Isomer Resolution: Application of Ultrahigh-Resolution Ion Mobility to Reveal Lipid Diversity

Publisher: American Chemical Society (ACS)

Date: 17-10-2023

DOI: 10.1021/ACS.ANALCHEM.3C02658

Structural Lipidomics

Publisher: Wiley

Date: 17-10-2012

DOI: 10.1002/9783527655946.CH6

Formation of neutral molecules of potential stellar interest by neutralisation of negative ions in a mass spectrometer

Publisher: Elsevier BV

Date: 03-2003

DOI: 10.1016/S1093-3263(02)00182-1

Abstract: This paper is a modified version of a lecture which describes the synthesis, structure and reactivity of some neutral molecules of stellar significance. The neutrals are formed in the collision cell of a mass spectrometer following vertical Franck-Condon one electron oxidation of anions of known bond connectivity. Neutrals are characterised by conversion to positive ions and by extensive theoretical studies at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory. Four systems are considered in detail, viz (i) the formation of linear C(4) and its conversion to the rhombus C(4), (ii) linear C(5) and the atom scrambling of this system when energised, (iii) the stable cumulene oxide CCCCCO, and (iv) the elusive species O(2)C-CO. This paper is not intended to be a review of interstellar chemistry: ex les are selected from our own work in this area.

Direct detection of brominated flame retardants from plastic e‐waste using liquid extraction surface analysis mass spectrometry

Publisher: Wiley

Date: 20-04-2014

DOI: 10.1002/RCM.6889

Abstract: The worldwide generation of plastic electronic waste (e-waste) is reaching epic proportions. The presence of toxic brominated flame retardants (BFRs) within these materials limits their ability to be recycled, resulting in large amounts of e-waste reaching landfills. Liquid extraction surface analysis mass spectrometry (LESA-MS) employing a chip-based nanoelectrospray coupled to a triple quadrupole mass spectrometer represents a novel control technology for directing e-waste streams for recycling. LESA-MS allows direct s ling and analysis of solid material, capable of detecting BFRs including polybrominated diphenyl ethers (PBDEs) and tetrabromobisphenol A (TBBP-A), the two most common flame retardant additives currently in circulation. Authentic PBDE congeners and TBBP-A were deposited on glass and characterised by LESA-MS analysis. PBDEs are notoriously difficult to detect via electrospray however, they were detected with ease by utilising a combination of nanoelectrospray and solvent doped with ammonium acetate. In situ detection of TBBP-A within plastic e-waste was also possible by performing LESA-MS on the surface of granulated material provided by a commercial waste depot. E-waste s le analysis was completely automated, with each s le analysed in less than 1 min. LESA-MS is fast, simple, and robust allowing unambiguous detection of a range of additives through tandem mass spectrometry. LESA-MS does not require dissolution of the solid matrix nor the s le to be present under vacuum and the use of separative techniques prior to analysis is not necessary.

Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation.

Publisher: AIP Publishing

Date: 05-01-2015

DOI: 10.1063/1.4904267

Abstract: The S1←S0 electronic transition of the N-pyridinium ion (C5H5NH+) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N2-tagged complex. Gas-phase N-pyridinium ions photodissociate by the loss of molecular hydrogen (H2) in the photon energy range 37 000–45 000 cm−1 with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculations are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum.

Highly efficient gas-phase reactivity of protonated pyridine radicals with propene

Publisher: Royal Society of Chemistry (RSC)

Date: 2017

DOI: 10.1039/C7CP06644A

Abstract: Reaction of the three dehydro- N -pyridinium radical cation isomers with propene is highly efficient. Vinylpyridinium is the major product.

A rapid ambient ionization-mass spectrometry approach to monitoring the relative abundance of isomeric glycerophospholipids

Publisher: Springer Science and Business Media LLC

Date: 02-04-2015

DOI: 10.1038/SREP09243

Abstract: Glycerophospholipids with two, non-equivalent fatty acyl chains can adopt one of two isomeric forms depending on the relative position of substitutions on the glycerol backbone. These so-called sn -positional isomers can have distinct biophysical and biochemical behaviors making it desirable to uniquely assign their regiochemistries. Unambiguous assignment of such similar molecular structures in complex biological extracts is a significant challenge to current analytical technologies. We have recently reported a novel mass spectrometric method that combines collision- and ozone-induced dissociation in series (CID/OzID) to yield product ions characteristic of acyl chain substitution patterns in glycerophospholipids. Here phosphatidylcholines are examined using the CID/OzID protocol combined with desorption electrospray ionization (DESI) to facilitate the rapid exploration of s le arrays comprised of a wide variety of synthetic and biological sources. Comparison of the spectra acquired from different extracts reveals that the sn -positional isomers PC 16:0/18:1 and PC 18:1/16:0 (where the 18:1 chain is present at the sn- 2 and sn- 1 position of the glycerol backbone, respectively) are most often found together in lipids of either natural or synthetic origin. Moreover, the proportions of the two isomers vary significantly between extracts from different organisms or even between adjacent tissues from the same organism.

Mapping the Compaction of Discrete Polymer Chains by Size Exclusion Chromatography Coupled to High-Resolution Mass Spectrometry

Publisher: American Chemical Society (ACS)

Date: 15-03-2019

DOI: 10.1021/ACS.MACROMOL.9B00203

Formation of the heterocumulene anion SCCCN? by a cyano migration from the radical anion of 1,2-dicyanoethylenedithiolateDedicated to Professor John H. Bowie on the occasion of his 65th Birthday and in recognition to his pioneering work on the gas phase chemistry of anions.

Publisher: Royal Society of Chemistry (RSC)

Date: 2004

DOI: 10.1039/B311151B

Abstract: The anionic heterocumulene SCCCN(-) was generated in the gas phase by collisional activation of the radical anion of 1,2-dicyanoethylenedithiolate. The mechanism of this reaction, as well as the structures of neutral and anionic products, was investigated by hybrid density functional theory (DFT) calculations. Dissociation to form SCCCN(-) and SCN is proposed to occur by a radical directed cyano migration reaction, with calculations suggesting this is the lowest energy fragmentation pathway available to the precursor anion. In contrast, the even-electron protonated 1,2-dicyanoethylenedithiolate anion fragmented by loss of HCN.

Stepwise reduction of interlocked viologen-based complexes in the gas phase

Publisher: Royal Society of Chemistry (RSC)

Date: 2020

DOI: 10.1039/D0CC05115B

Abstract: Thinking outside the (blue)box: electron transfer mass spectrometry as a dual-purpose synthetic and analytical tool for supramolecular complexes.

Gas phase reactions of iodide and bromide anions with ozone: evidence for stepwise and reversible reactions

Publisher: Royal Society of Chemistry (RSC)

Date: 2020

DOI: 10.1039/D0CP01498B

Abstract: Ion-trap mass spectrometry maps the discrete steps in the reaction of I − and Br − with gaseous ozone.

OzFAD: Ozone-enabled fatty acid discovery reveals unexpected diversity in the human lipidome

Publisher: Cold Spring Harbor Laboratory

Date: 25-10-2022

DOI: 10.1101/2022.10.24.513604

Abstract: Fatty acid isomers are responsible for an under-reported lipidome ersity across all kingdoms of life. Isomers of unsaturated fatty acid are often masked in contemporary analysis by incomplete separation and the absence of sufficiently diagnostic methods for structure elucidation. Here, we introduce a comprehensive workflow to discover new unsaturated fatty acids through coupling liquid chromatography and mass spectrometry with gas-phase ozonolysis of double bonds. The workflow encompasses semi-automated data analysis and enables de novo identification in complex media including human plasma, cancer cell lines and human sebaceous wax (i.e., vernix caseosa). The targeted analysis including ozonolysis enables structural assignment over a dynamic range of five orders of magnitude, even in instances of incomplete chromatographic separation. Thereby we expand the number of identified plasma fatty acids two-fold, including non-methylene interrupted fatty acids. Detection, without prior knowledge, allows discovery of non-canonical double bond positions. Changes in relative isomer abundances reflect underlying perturbations in lipid metabolism.

Gas-Phase Chemical Separation of Phosphatidylcholine and Phosphatidylethanolamine Cations via Charge Inversion Ion/Ion Chemistry

Publisher: American Chemical Society (ACS)

Date: 27-10-2015

DOI: 10.1021/ACS.ANALCHEM.5B02243

A Theoretical Study of C₄B Isomers. The Interconversion of CCBCC and CCCCB via Cyclic C₄B

Publisher: American Chemical Society (ACS)

Date: 11-2003

DOI: 10.1021/JP030717J

Direct detection of additives and degradation products from polymers by liquid extraction surface analysis employing chip-based nanospray mass spectrometry

Publisher: Wiley

Date: 15-01-2012

DOI: 10.1002/RCM.6116

Abstract: Polymer-based surface coatings in outdoor applications experience accelerated degradation due to exposure to solar radiation, oxygen and atmospheric pollutants. These deleterious agents cause undesirable changes to the aesthetic and mechanical properties of the polymer, reducing its lifetime. The use of antioxidants such as hindered amine light stabilisers (HALS) retards these degradative processes however, mechanisms for HALS action and polymer degradation are poorly understood. Detection of the HALS TINUVIN®123 (bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate) and the polymer degradation products directly from a polyester-based coil coating was achieved by liquid extraction surface analysis (LESA) coupled to a triple quadrupole QTRAP® 5500 mass spectrometer. The detection of TINUVIN®123 and melamine was confirmed by the characteristic fragmentation pattern observed in LESA-MS/MS spectra that was identical to that reported for authentic s les. Analysis of an unstabilised coil coating by LESA-MS after exposure to 4 years of outdoor field testing revealed the presence of melamine (1,3,5-triazine-2,4,6-triamine) as a polymer degradation product at elevated levels. Changes to the physical appearance of the coil coating, including powder-like deposits on the coating's surface, were observed to coincide with melamine deposits and are indicative of the phenomenon known as polymer 'blooming'. For the first time, in situ detection of analytes from a thermoset polymer coating was accomplished without any s le preparation, providing advantages over traditional extraction-analysis approaches and some contemporary ambient MS methods. Detection of HALS and polymer degradation products such as melamine provides insight into the mechanisms by which degradation occurs and suggests LESA-MS is a powerful new tool for polymer analysis.

Surface analysis of lipids by mass spectrometry: More than just imaging

Publisher: Elsevier BV

Date: 10-2013

DOI: 10.1016/J.PLIPRES.2013.04.005

Abstract: Mass spectrometry is now an indispensable tool for lipid analysis and is arguably the driving force in the renaissance of lipid research. In its various forms, mass spectrometry is uniquely capable of resolving the extensive compositional and structural ersity of lipids in biological systems. Furthermore, it provides the ability to accurately quantify molecular-level changes in lipid populations associated with changes in metabolism and environment bringing lipid science to the "omics" age. The recent explosion of mass spectrometry-based surface analysis techniques is fuelling further expansion of the lipidomics field. This is evidenced by the numerous papers published on the subject of mass spectrometric imaging of lipids in recent years. While imaging mass spectrometry provides new and exciting possibilities, it is but one of the many opportunities direct surface analysis offers the lipid researcher. In this review we describe the current state-of-the-art in the direct surface analysis of lipids with a focus on tissue sections, intact cells and thin-layer chromatography substrates. The suitability of these different approaches towards analysis of the major lipid classes along with their current and potential applications in the field of lipid analysis are evaluated.

Isomeric lipid signatures reveal compartmentalized fatty acid metabolism in cancer

Publisher: Elsevier BV

Date: 06-2022

DOI: 10.1016/J.JLR.2022.100223

Membrane-active peptides escape drug-resistance in cancer

Publisher: Cold Spring Harbor Laboratory

Date: 28-10-2022

DOI: 10.1101/2022.10.27.513961

Abstract: Acquired drug-resistance is a recurring problem in cancer treatment, and this is particularly true for patients with metastatic melanoma that carry a BRAF V600E mutation. In the current study, we explored the use of membrane-active peptides as an alternative therapeutic modality to target drug-resistant melanoma cells. We produced slow-cycling and drug-resistant melanoma cells using dabrafenib, a small molecule drug that targets tumor cells with BRAF V600E mutation, and characterised their lipidome and proteome to investigate the role of membrane lipids in acquired drug-resistance. Despite some changes in the lipid composition, tested anti-melanoma membrane-active cyclic peptides (cTI and cGm) killed melanoma cells that are sensitive, tolerant, or resistant to dabrafenib. Importantly, melanoma cells did not develop resistance to cTI or cGm, nor changed their lipid composition with long-term peptide treatment. Therefore, these peptides are well suited as templates to design therapeutic leads to target drug-resistant metastatic melanoma cells and/or as co-treatment with small molecule drugs.

Ultraviolet photodissociation action spectroscopy of gas-phase protonated quinoline and isoquinoline cations

Publisher: Royal Society of Chemistry (RSC)

Date: 2015

DOI: 10.1039/C5CP02035B

Abstract: Gas-phase two-photon UV action spectra of protonated quinoline and isoquinoline cations are reported revealing two broad, vibrationally-structured electronic bands and multiple photoproduct channels.

Characterising in situ activation and degradation of hindered amine light stabilisers using liquid extraction surface analysis-mass spectrometry

Publisher: Elsevier BV

Date: 2014

DOI: 10.1016/J.ACA.2013.09.039

Abstract: Changes in the molecular structure of polymer antioxidants such as hindered amine light stabilisers (HALS) is central to their efficacy in retarding polymer degradation and therefore requires careful monitoring during their in-service lifetime. The HALS, bis-(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate (TIN123) and bis-(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate (TIN292), were formulated in different polymer systems and then exposed to various curing and ageing treatments to simulate in-service use. S les of these coatings were then analysed directly using liquid extraction surface analysis (LESA) coupled with a triple quadrupole mass spectrometer. Analysis of TIN123 formulated in a cross-linked polyester revealed that the polymer matrix protected TIN123 from undergoing extensive thermal degradation that would normally occur at 292°C, specifically, changes at the 1- and 4-positions of the piperidine groups. The effect of thermal versus photo-oxidative degradation was also compared for TIN292 formulated in polyacrylate films by monitoring the in situ conversion of N-CH3 substituted piperidines to N-H. The analysis confirmed that UV light was required for the conversion of N-CH3 moieties to N-H - a major pathway in the antioxidant protection of polymers - whereas this conversion was not observed with thermal degradation. The use of tandem mass spectrometric techniques, including precursor-ion scanning, is shown to be highly sensitive and specific for detecting molecular-level changes in HALS compounds and, when coupled with LESA, able to monitor these changes in situ with speed and reproducibility.

Does Addition of NO₂ to Carbon-Centered Radicals Yield RONO or RNO₂? An Investigation Using Distonic Radical Ions

Publisher: American Chemical Society (ACS)

Date: 23-02-2013

DOI: 10.1007/S13361-012-0549-X

Abstract: Nitrogen dioxide is used as a "radical scavenger" to probe the position of carbon-centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M + NO2](+) adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro- (RNO2) or nitrosoxy- (RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion-trap mass spectrometry. In each case, stabilized [M + NO2](+) adduct ions are observed and isolated. The structure of these adducts is probed by collision-induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro- and nitrosoxy-benzenes. We demonstrate unequivocally that for the phenyl radical cations studied here, all stabilized [M + NO2](+) adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low-pressure conditions, the nitrosoxy-isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical with NO2. The combined experimental and theoretical results lead to the prediction that stabilization of the nitrosoxy-isomer will only be possible for systems wherein the energy required for dissociation of the RO-NO bond (or other low energy fragmentation channels) rises close to, or above, the energy of the separated reactants.

Localization of Carbon–Carbon Double Bond and Cyclopropane Sites in Cardiolipins via Gas-Phase Charge Inversion Reactions

Publisher: American Chemical Society (ACS)

Date: 28-12-2020

DOI: 10.1021/JASMS.0C00348

Phospholipid composition of the rat lens is independent of diet

Publisher: Elsevier BV

Date: 12-2008

DOI: 10.1016/J.EXER.2008.08.009

Abstract: Dietary fatty acids are known to influence the phospholipid composition of many tissues in the body, with lipid turnover occurring rapidly. The aim of this study was to investigate whether changes in the fatty acid composition of the diet can affect the phospholipid composition of the lens. Male Sprague-Dawley rats were fed three diets with distinct profiles in both essential and non-essential fatty acids. After 8 weeks, lenses and skeletal muscle were removed, and the lenses sectioned into nuclear and cortical regions. In these experiments, the lens cortex was synthesised during the course of the variable lipid diet. Phospholipids were then identified by electrospray ionisation tandem mass spectrometry, and quantified via the use of internal standards. The phospholipid compositions of the nuclear and cortical regions of the lens differed slightly between the two regions, but comparison of the equivalent regions across the diet groups showed remarkable similarity. In contrast, the phospholipid composition of skeletal muscle (medial gastrocnemius) in these rats varied significantly. This study provides the first direct evidence to show that the phospholipid composition of the lens is tightly regulated and thus appears to be independent of diet. As phospholipids determine membrane fluidity and influence the activity and function of integral membrane proteins, regulation of their composition may be important for the function of the lens.

Reactions of a distonic peroxyl radical anion influenced by SOMO–HOMO conversion: an example of anion-directed channel switching

Publisher: Royal Society of Chemistry (RSC)

Date: 2020

DOI: 10.1039/C9CP05989J

Abstract: Deprotonation of a remote site in a peroxyl radical energetically buries the singly occupied molecular orbital, suppressing radical-driven oxidation and promoting reactions involving the anion site.

Unimolecular reaction chemistry of a charge-tagged beta-hydroxyperoxyl radical

Publisher: Royal Society of Chemistry (RSC)

Date: 2014

DOI: 10.1039/C4CP02981J

Abstract: The study of unimolecular isomerization and decomposition of a charge-tagged β-hydroxyperoxyl radical anion ˙CH 2 C(OH)(CH 3 )CH 2 C(O)O − using mass spectrometry, quantum mechanical calculations and master equation kinetic simulations.

Superoxide Does React with Peroxides: Direct Observation of the Haber–Weiss Reaction in the Gas Phase

Publisher: Wiley

Date: 15-06-2007

DOI: 10.1002/ANIE.200700219

Unterscheidung von isomeren Sphingolipiden mittels kryogener Infrarotspektroskopie

Publisher: Wiley

Date: 18-05-2020

DOI: 10.1002/ANGE.202002459

Next-generation derivatization reagents optimized for enhanced product ion formation in photodissociation-mass spectrometry of fatty acids

Publisher: Royal Society of Chemistry (RSC)

Date: 2021

DOI: 10.1039/D0AN01840F

Abstract: Next-generation derivatives for photodissociation-mass spectrometry for fatty acids generating photoproduct yields of up to 97% at 266 nm.

Radical Generation from the Gas-Phase Activation of Ionized Lipid Ozonides

Publisher: American Chemical Society (ACS)

Date: 08-05-2017

DOI: 10.1007/S13361-017-1649-4

Direct Detection of a Persistent Carbonyloxyl Radical in the Gas Phase

Publisher: Wiley

Date: 14-07-2013

DOI: 10.1002/ANIE.201304316

Gas-Phase Oxidation of the Protonated Uracil-5-yl Radical Cation

Publisher: American Chemical Society (ACS)

Date: 17-01-2018

DOI: 10.1021/ACS.JPCA.7B09411

Abstract: This study targets the kinetics and product detection of the gas-phase oxidation reaction of the protonated 5-dehydrouracil (uracil-5-yl) distonic radical cation using ion-trap mass spectrometry. Protonated 5-dehydrouracil radical ions (5-dehydrouracilH

Enhancement of 1,2-dehydration of alcohols by alkali cations and protons: a model for dehydration of carbohydrates

Publisher: Elsevier BV

Date: 2003

DOI: 10.1016/S0165-2370(02)00103-1

Gas-Phase Syntheses of Three Isomeric C₅H₂ Radical Anions and Their Elusive Neutrals. A Joint Experimental and Theoretical Study

Publisher: American Chemical Society (ACS)

Date: 11-1998

DOI: 10.1021/JP982780S

Polarized Infrared Absorption Spectrum of Matrix-Isolated Methylperoxyl Radicals, CH₃OO X̃ ²A‘ ‘

Publisher: American Chemical Society (ACS)

Date: 19-12-2001

DOI: 10.1021/JP0126816

Generation of three isomers of C7H– in the gas phase. A joint experimental and theoretical study

Publisher: SAGE Publications

Date: 1999

DOI: 10.1255/EJMS.290

Establishing carbon–carbon double bond position and configuration in unsaturated fatty acids by gas-phase infrared spectroscopy

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D2SC06487A

Abstract: 3-Pyridylcarbinol ester derivatization introduces a universal probe for cryogenic gas-phase infrared spectroscopy of fatty acids that enables assignment of the position and configuration of carbon–carbon double bonds even in the presence of isomers.

Conversion of neutral C2COC2 to C4CO. potential interstellar molecules

Publisher: Elsevier BV

Date: 2000

DOI: 10.1016/S1387-3806(99)00188-8

High-Pressure Ozone-Induced Dissociation for Lipid Structure Elucidation on Fast Chromatographic Timescales

Publisher: American Chemical Society (ACS)

Date: 15-03-2017

DOI: 10.1021/ACS.ANALCHEM.7B00268

Abstract: Ozone-induced dissociation (OzID) is a novel ion activation technology that exploits the gas-phase reaction between mass-selected ions and ozone inside a mass spectrometer to assign sites of unsaturation in complex lipids. Since it was first demonstrated [ Thomas et al. Anal. Chem. 2008 , 80 , 303 ], the method has been widely deployed for targeted lipid structure elucidation but its application to high throughput and liquid chromatography-based workflows has been limited due to the relatively slow nature of the requisite ion-molecule reactions that result in long ion-trapping times and consequently low instrument duty cycle. Here, the implementation of OzID in a high-pressure region, the ion-mobility spectrometry cell, of a contemporary quadrupole time-of-flight mass spectrometer is described. In this configuration, a high number density of ozone was achieved and thus abundant and diagnostic OzID product ions could be observed even on the timescale of transmission through the reaction region (ca. 20-200 ms), representing a 50-1000-fold improvement in performance over prior OzID implementations. Collisional activation applied prereaction was found to yield complementary and structurally informative product ions arising from ozone- and collision-induced dissociation. Ultimately, the compatibility of this implementation with contemporary ultrahigh performance liquid chromatography is demonstrated with the resulting hyphenated approach showing the ability to separate and uniquely identify isomeric phosphatidylcholines that differ only in their position(s) of unsaturation.

Ultraviolet Photodissociation of the N-Methylpyridinium Ion: Action Spectroscopy and Product Characterization

Publisher: American Chemical Society (ACS)

Date: 15-10-2013

DOI: 10.1021/JP4075515

Abstract: The ultraviolet photodissociation of gas-phase N-methylpyridinium ions is studied at room temperature using laser photodissociation mass spectrometry and structurally diagnostic ion-molecule reaction kinetics. The C5H5N-CH3(+) (m/z 94), C5H5N-CD3(+) (m/z 97), and C5D5N-CH3(+)(m/z 99) isotopologues are investigated, and it is shown that the N-methylpyridinium ion photodissociates by the loss of methane in the 36,000 - 43,000 cm(-1) (280 - 230 nm) region. The dissociation likely occurs on the ground state surface following internal conversion from the S1 state. For each isotopologue, by monitoring the photofragmentation yield as a function of photon wavenumber, a broad vibronically featured band is recorded with origin (0-0) transitions assigned at 38 130, 38 140 and 38 320 cm(-1) for C5H5N-CH3(+) C5H5N-CD3+ and C5D5N-CH3(+), respectively. With the aid of quantum chemical calculations (CASSCF(6,6)/aug-cc-pVDZ), most of the observed vibronic detail is assigned to two in-plane ring deformation modes. Finally, using ion-molecule reactions, the methane coproduct at m/z 78 is confirmed as a 2-pyridinylium ion.

Characterization of [M–H] cations, radicals and anions of glycine in the gas phase: a combined experimental and ab initio study

Publisher: Elsevier BV

Date: 03-1999

DOI: 10.1016/S1387-3806(98)14249-5

Imaging of human lens lipids by desorption electrospray ionization mass spectrometry

Publisher: American Chemical Society (ACS)

Date: 12-2010

DOI: 10.1016/J.JASMS.2010.09.003

Abstract: The lipid composition of the human lens is distinct from most other tissues in that it is high in dihydrosphingomyelin and the most abundant glycerophospholipids in the lens are unusual 1-O-alkyl-ether linked phosphatidylethanolamines and phosphatidylserines. In this study, desorption electrospray ionization (DESI) mass spectrometry-imaging was used to determine the distribution of these lipids in the human lens along with other lipids including, ceramides, ceramide-1-phosphates, and lyso 1-O-alkyl ethers. To achieve this, 25 μm lens slices were mounted onto glass slides and analyzed using a linear ion-trap mass spectrometer equipped with a custom-built, 2-D automated DESI source. In contrast to other tissues that have been previously analyzed by DESI, the presence of a strong acid in the spray solvent was required to desorb lipids directly from lens tissue. Distinctive distributions were observed for [M + H](+) ions arising from each lipid class. Of particular interest were ionized 1-O-alkyl phosphatidylethanolamines and phosphatidylserines, PE (18:1e/18:1), and PS (18:1e/18:1), which were found in a thin ring in the outermost region of the lens. This distribution was confirmed by quantitative analysis of lenses that were sectioned into four distinct regions (outer, barrier, inner, and core), extracted and analyzed by electrospray ionization tandem mass spectrometry. DESI-imaging also revealed a complementary distribution for the structurally-related lyso 1-O-alkyl phosphatidylethanolamine, LPE (18:1e), which was localized closer to the centre of the lens. The data obtained in this study indicate that DESI-imaging is a powerful tool for determining the spatial distribution of human lens lipids.

The fragmentation pathways of protonated Amiton in the gas phase: towards the structural characterisation of organophosphorus chemical warfare agents by electrospray ionisation tandem mass spectrometr

Publisher: Wiley

Date: 22-05-2006

DOI: 10.1002/RCM.2535

Abstract: Amiton (O,O-diethyl-S-[2-(diethylamino)ethyl] phosphorothiolate), otherwise known as VG, is listed in schedule 2 of the Chemical Weapons Convention (CWC) and has a structure closely related to VX (O-ethyl-S-(2-diisopropylamino)ethylmethylphosphonothiolate). Fragmentation of protonated VG in the gas phase was performed using electrospray ionisation ion trap mass spectrometry (ESI-ITMS) and revealed several characteristic product ions. Quantum chemical calculations provide the most probable structures for these ions as well as the likely unimolecular mechanisms by which they are formed. The decomposition pathways predicted by computation are consistent with deuterium-labeling studies. The combination of experimental and theoretical data suggests that the fragmentation pathways of VG and analogous organophosphorus nerve agents, such as VX and Russian VX, are predictable and thus ESI tandem mass spectrometry is a powerful tool for the verification of unknown compounds listed in the CWC.

Isomer-Resolved Mass Spectrometry Imaging of Acidic Phospholipids

Publisher: American Chemical Society (ACS)

Date: 15-08-2023

DOI: 10.1021/JASMS.3C00192

Pushing the limits of single chain compaction analysis by observing specific size reductions via high resolution mass spectrometry

Publisher: Royal Society of Chemistry (RSC)

Date: 2020

DOI: 10.1039/C9PY01910C

Abstract: Herein, we push the limits of single chain nanoparticle analysis to directly observe the specific compaction of defined single chains dependent on the number of compaction steps.

Polyselenoureas via Multicomponent Polymerizations Using Elemental Selenium as Monomer

Publisher: American Chemical Society (ACS)

Date: 11-07-2018

DOI: 10.1021/ACSMACROLETT.8B00428

Toward Complete Structure Elucidation of Glycerophospholipids in the Gas Phase through Charge Inversion Ion/Ion Chemistry

Publisher: American Chemical Society (ACS)

Date: 25-11-2019

DOI: 10.1021/ACS.ANALCHEM.9B04376

Instability of the cellular lipidome with age

Publisher: Springer Science and Business Media LLC

Date: 06-09-2011

DOI: 10.1007/S11357-011-9293-6

Mass Spectrometry Imaging of Lipids with Isomer Resolution Using High-Pressure Ozone-Induced Dissociation

Publisher: American Chemical Society (ACS)

Date: 06-07-2021

DOI: 10.1021/ACS.ANALCHEM.1C01377

Using ambient ozone for assignment of double bond position in unsaturated lipids

Publisher: Royal Society of Chemistry (RSC)

Date: 2012

DOI: 10.1039/C1AN15864C

Abstract: Unsaturated lipids deposited onto a range of materials are observed to react with the low concentrations of ozone present in normal laboratory air. Parent lipids and ozonolysis cleavage products are both detected directly from surfaces by desorption electrospray ionisation mass spectrometry (DESI-MS) with the resulting mass spectra providing clear evidence of the double bond position within these molecules. This serendipitous process has been coupled with thin-layer chromatography (TLC) to provide a simple but powerful approach for the detailed structural elucidation of lipids present in complex biological extracts. Lipid extracts from human lens were deposited onto normal phase TLC plates and then developed to separate components according to lipid class. Exposure of the developed plates to laboratory air for ca. 1 h prior to DESI-MS analysis gave rise to ozonolysis products allowing for the unambiguous identification of double bond positions in even low abundant, unsaturated lipids. In particular, the co-localization of intact unsaturated lactosylceramides (LacCer) with products from their oxidative cleavage provide the first evidence for the presence of three isomeric LacCer (d18:0/24:1) species in the ocular lens lipidome, i.e., variants with double bonds at the n-9, n-7 and n-5 positions.

Base-Induced Decomposition of Alkyl Hydroperoxides in the Gas Phase. Part 3. Kinetics and Dynamics in HO⁻ + CH₃OOH, C₂H₅OOH, and tert-C₄H<

Publisher: American Chemical Society (ACS)

Date: 21-06-2008

DOI: 10.1021/JP800702Z

Abstract: The E(CO)2 elimination reactions of alkyl hydroperoxides proceed via abstraction of an alpha-hydrogen by a base: X(-) + R(1)R(2)HCOOH --> HX + R(1)R(2)C=O + HO(-). Efficiencies and product distributions for the reactions of the hydroxide anion with methyl, ethyl, and tert-butyl hydroperoxides are studied in the gas phase. On the basis of experiments using three isotopic analogues, HO(-) + CH3OOH, HO(-) + CD3OOH, and H(18)O(-) + CH3OOH, the overall intrinsic reaction efficiency is determined to be 80% or greater. The E(CO)2 decomposition is facile for these methylperoxide reactions, and predominates over competing proton transfer at the hydroperoxide moiety. The CH3CH2OOH reaction displays a similar E(CO)2 reactivity, whereas proton transfer and the formation of HOO(-) are the exclusive pathways observed for (CH3)3COOH, which has no alpha-hydrogen. All results are consistent with the E(CO)2 mechanism, transition state structure, and reaction energy diagrams calculated using the hybrid density functional B3LYP approach. Isotope labeling for HO(-) + CH3OOH also reveals some interaction between H2O and HO(-) within the E(CO)2 product complex [H2O...CH2=O...HO(-)]. There is little evidence, however, for the formation of the most exothermic products H2O + CH2(OH)O(-), which would arise from nucleophilic condensation of CH2=O and HO(-). The results suggest that the product dynamics are not totally statistical but are rather direct after the E(CO)2 transition state. The larger HO(-) + CH3CH2OOH system displays more statistical behavior during complex dissociation.

Selecting and identifying gas-phase protonation isomers of nicotineH+ using combined laser, ion mobility and mass spectrometry techniques

Publisher: Royal Society of Chemistry (RSC)

Date: 2019

DOI: 10.1039/C8FD00212F

Abstract: Protonation isomers of gas-phase nicotineH + are separated and assigned using a combination of FAIMS and UV photodissociation action spectroscopy.

Direct Evidence for Base-Mediated Decomposition of Alkyl Hydroperoxides (ROOH) in the Gas Phase

Publisher: American Chemical Society (ACS)

Date: 06-03-2002

DOI: 10.1021/JA017658C

Abstract: The reaction of F(-) with CH(3)OOH has been studied in the gas phase using a tandem flowing afterglow-selected ion flow tube apparatus. The reaction is rapid (k = 1.23 x 10(-9) cm(3) s(-1), 49% efficiency), and formation of HO(-) + CH(2)O + HF is the major reaction channel observed (85%). Isotopic labeling, reactions of F(-) with larger alkyl hydroperoxides, and computational studies demonstrate that the major product ion, HO(-), is formed via a concerted elimination mechanism that appears to be general to all alkyl hydroperoxides possessing an alpha-hydrogen. This mechanism represents a base-mediated decomposition of alkyl hydroperoxides in the gas phase that may have important implications for solution and biochemical reactions. The reverse reaction, CH(3)OO(-) + HF is also efficient (k = 2.43 x 10(-9) cm(3) s(-1)). The major product ensemble HO(-) + CH(2)O + HF (81%) is identical to that of the forward reaction, and represents a novel neutral-catalyzed decomposition of the anion.

Differential-Mobility Spectrometry of 1-Deoxysphingosine Isomers: New Insights into the Gas Phase Structures of Ionized Lipids

Publisher: American Chemical Society (ACS)

Date: 02-04-2018

DOI: 10.1021/ACS.ANALCHEM.8B00469

Abstract: Separation and structural identification of lipids remain a major challenge for contemporary lipidomics. Regioisomeric lipids differing only in position(s) of unsaturation are often not differentiated by conventional liquid chromatography-mass spectrometry approaches leading to the incomplete, or sometimes incorrect, assignation of molecular structure. Here we describe an investigation of the gas phase separations by differential-mobility spectrometry (DMS) of a series of synthetic analogues of the recently described 1-deoxysphingosine. The dependence of the DMS behavior on the position of the carbon-carbon double bond within the ionized lipid is systematically explored and compared to trends from complementary investigations, including collision cross-sections measured by drift tube ion mobility, reaction efficiency with ozone, and molecular dynamics simulations. Consistent trends across these modes of interrogation point to the importance of direct, through-space interactions between the charge site and the carbon-carbon double bond. Differences in the geometry and energetics of this intramolecular interaction underpin DMS separations and influence reactivity trends between regioisomers. Importantly, the disruption and reformation of these intramolecular solvation interactions during DMS are proposed to be the causative factor in the observed separations of ionized lipids which are shown to have otherwise identical collision cross-sections. These findings provide key insights into the strengths and limitations of current ion-mobility technologies for lipid isomer separations and can thus guide a more systematic approach to improved analytical separations in lipidomics.

1-Azahomocubane

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D3SC00001J

Abstract: 1-Azahomocubane has been prepared 56 years after the parent hydrocarbon. Introduction of a nitrogen atom into this constrained polycyclic environment resulted in minimal changes to the framework geometry, with s-character of the nitrogen lone pair increasing due to strain.

Discrimination of isobaric and isomeric lipids in complex mixtures by combining ultra-high pressure liquid chromatography with collision and ozone-induced dissociation

Publisher: Elsevier BV

Date: 08-2018

DOI: 10.1016/J.IJMS.2018.05.016

Differentiation of complex lipid isomers by radical-directed dissociation mass spectrometry

Publisher: American Chemical Society (ACS)

Date: 22-08-2012

DOI: 10.1021/AC301652A

Abstract: Contemporary lipidomics protocols are dependent on conventional tandem mass spectrometry for lipid identification. This approach is extremely powerful for determining lipid class and identifying the number of carbons and the degree of unsaturation of any acyl-chain substituents. Such analyses are however, blind to isomeric variants arising from different carbon-carbon bonding motifs within these chains including double bond position, chain branching, and cyclic structures. This limitation arises from the fact that conventional, low energy collision-induced dissociation of even-electron lipid ions does not give rise to product ions from intrachain fragmentation of the fatty acyl moieties. To overcome this limitation, we have applied radical-directed dissociation (RDD) to the study of lipids for the first time. In this approach, bifunctional molecules that contain a photocaged radical initiator and a lipid-adducting group, such as 4-iodoaniline and 4-iodobenzoic acid, are used to form noncovalent complexes (i.e., adduct ions) with a lipid during electrospray ionization. Laser irradiation of these complexes at UV wavelengths (266 nm) cleaves the carbon-iodine bond to liberate a highly reactive phenyl radical. Subsequent activation of the nascent radical ions results in RDD with significant intrachain fragmentation of acyl moieties. This approach provides diagnostic fragments that are associated with the double bond position and the positions of chain-branching in glycerophospholipids, sphingomyelins and triacylglycerols and thus can be used to differentiate isomeric lipids differing only in such motifs. RDD is demonstrated for well-defined lipid standards and also reveals lipid structural ersity in olive oil and human very-low density lipoprotein.

Ultraviolet Action Spectroscopy of Iodine Labeled Peptides and Proteins in the Gas Phase

Publisher: American Chemical Society (ACS)

Date: 20-08-2012

DOI: 10.1021/JP305470J

Abstract: Structural investigations of large biomolecules in the gas phase are challenging. Herein, it is reported that action spectroscopy taking advantage of facile carbon-iodine bond dissociation can be used to examine the structures of large molecules, including whole proteins. Iodotyrosine serves as the active chromophore, which yields distinctive spectra depending on the solvation of the side chain by the remainder of the molecule. Isolation of the chromophore yields a double featured peak at ~290 nm, which becomes a single peak with increasing solvation. Deprotonation of the side chain also leads to reduced apparent intensity and broadening of the action spectrum. The method can be successfully applied to both negatively and positively charged ions in various charge states, although electron detachment becomes a competitive channel for multiply charged anions. In all other cases, loss of iodine is by far the dominant channel which leads to high sensitivity and simple data analysis. The action spectra for iodotyrosine, the iodinated peptides KGYDAKA, DAYLDAG, and the small protein ubiquitin are reported in various charge states.

UV photodissociation action spectra of protonated formylpyridines

Publisher: AIP Publishing

Date: 07-10-2022

DOI: 10.1063/5.0113107

Abstract: The first ππ* transition for protonated 2-, 3-, and 4-formylpyridine (FPH

Mass Analysis

Publisher: Wiley

Date: 07-12-2012

DOI: 10.1002/9783527641826.CH1

Evaluation of hindered amine light stabilisers and their N-chlorinated derivatives as antibacterial and antifungal additives for thermoset surface coatings

Publisher: Elsevier BV

Date: 10-2016

DOI: 10.1016/J.PORGCOAT.2016.06.009

Advances in mass spectrometry for lipidomics

Publisher: Annual Reviews

Date: 06-2010

DOI: 10.1146/ANNUREV.ANCHEM.111808.073705

Abstract: Recent expansion in research in the field of lipidomics has been driven by the development of new mass spectrometric tools and protocols for the identification and quantification of molecular lipids in complex matrices. Although there are similarities between the field of lipidomics and the allied field of mass spectrometry (e.g., proteomics), lipids present some unique advantages and challenges for mass spectrometric analysis. The application of electrospray ionization to crude lipid extracts without prior fractionation—the so-called shotgun approach—is one such ex le, as it has perhaps been more successfully applied in lipidomics than in any other discipline. Conversely, the erse molecular structure of lipids means that collision-induced dissociation alone may be limited in providing unique descriptions of complex lipid structures, and the development of additional, complementary tools for ion activation and analysis is required to overcome these challenges. In this article, we discuss the state of the art in lipid mass spectrometry and highlight several areas in which current approaches are deficient and further innovation is required.

Forensic analysis of water‐based lubricants using liquid extraction surface analysis high‐resolution tandem mass spectrometry

Publisher: Wiley

Date: 12-08-2018

DOI: 10.1002/RCM.8220

Abstract: Analysis of water-based personal lubricants can provide pivotal information to law enforcement regarding sexual assault allegations, particularly in the absence of biological evidence. Traditional methodology for the extraction and analysis of water-based lubricants is cumbersome, time-consuming, and is often not sufficiently selective or sensitive to fully characterise the wide range of chemical components present within complex formulations. Liquid extraction surface analysis (LESA) was deployed in combination with high-resolution mass spectrometry (HRMS) and tandem mass spectrometry (MS/MS) to screen a range of water-based lubricants directly from contaminated cotton fabric. Rehydration of the fabric was the only s le preparation required. Analysis of ten different water-based lubricants by nano-electrospray ionisation mass spectrometry in negative ion mode enabled discrimination based on the presence or absence of nine compounds, which were identified by comparison of their MS/MS spectra with those of available standards. Lubricants were successfully detected by LESA from stained fabric surfaces even following extended periods of time between deposition and s ling. A library encompassing the common components of water-based lubricants has been established using HRMS and tandem mass spectrometry to enable identification of personal lubricant formulations and differentiation between suppliers.

Ion−Molecule Reactions of O,S-Dimethyl Methylphosphonothioate: Evidence for Intramolecular Sulfur Oxidation during VX Perhydrolysis

Publisher: American Chemical Society (ACS)

Date: 17-11-2009

DOI: 10.1021/JO901944P

Abstract: The alkaline perhydrolysis of the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) was investigated by studying the ion-molecule reactions of HOO(-) with O,S-dimethyl methylphosphonothioate in a modified linear ion-trap mass spectrometer. In addition to simple proton transfer, two other abundant product ions are observed at m/z 125 and 109 corresponding to the S-methyl methylphosphonothioate and methyl methylphosphonate anions, respectively. The structure of these product ions is demonstrated by a combination of collision-induced dissociation and isotope-labeling experiments that also provide evidence for their formation by nucleophilic reaction pathways, namely, (i) S(N)2 at carbon to yield the S-methyl methylphosphonothioate anion and (ii) nucleophilic addition at phosphorus affording a reactive pentavalent intermediate that readily undergoes internal sulfur oxidation and concomitant elimination of CH(3)SOH to yield the methyl methylphosphonate anion. Consistent with previous solution phase observations of VX perhydrolysis, the toxic P-O cleavage product is not observed in this VX model system and theoretical calculations identify P-O cleavage to be energetically uncompetitive. Conversely, intramolecular sulfur oxidation is calculated to be extremely exothermic and kinetically accessible explaining its competitiveness with the facile gas phase proton transfer process. Elimination of a sulfur moiety deactivates the nerve agent VX and thus the intramolecular sulfur oxidation process reported here is also able to explain the selective perhydrolysis of the nerve agent to relatively nontoxic products.

9‐Azahomocubane

Publisher: Wiley

Date: 12-10-2023

DOI: 10.1002/CHEM.202303133

Formation and Fragmentation of Unsaturated Fatty Acid [M – 2H + Na]^– Ions: Stabilized Carbanions for Charge-Directed Fragmentation

Publisher: American Chemical Society (ACS)

Date: 13-12-2013

DOI: 10.1007/S13361-013-0760-4

Abstract: Fatty acids are long-chain carboxylic acids that readily produce [M - H](-) ions upon negative ion electrospray ionization (ESI) and cationic complexes with alkali, alkaline earth, and transition metals in positive ion ESI. In contrast, only one anionic monomeric fatty acid-metal ion complex has been reported in the literature, namely [M - 2H + Fe(II)Cl](-). In this manuscript, we present two methods to form anionic unsaturated fatty acid-sodium ion complexes (i.e., [M - 2H + Na](-)). We find that these ions may be generated efficiently by two distinct methods: (1) negative ion ESI of a methanolic solution containing the fatty acid and sodium fluoride forming an [M - H + NaF](-) ion. Subsequent collision-induced dissociation (CID) results in the desired [M - 2H + Na](-) ion via the neutral loss of HF. (2) Direct formation of the [M - 2H + Na](-) ion by negative ion ESI of a methanolic solution containing the fatty acid and sodium hydroxide or bicarbonate. In addition to deprotonation of the carboxylic acid moiety, formation of [M - 2H + Na](-) ions requires the removal of a proton from the fatty acid acyl chain. We propose that this deprotonation occurs at the bis-allylic position(s) of polyunsaturated fatty acids resulting in the formation of a resonance-stabilized carbanion. This proposal is supported by ab initio calculations, which reveal that removal of a proton from the bis-allylic position, followed by neutral loss of HX (where X = F(-) and (-)OH), is the lowest energy dissociation pathway.

Oxidation of 4-substituted TEMPO derivatives reveals modifications at the 1- and 4-positions

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1OB05037K

Abstract: Potenital pathways for the deactivation of hindered amine light stabilisers (HALS) have been investigated by observing reactions of model compounds--based on 4-substituted derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)--with hydroxyl radicals. In these reactions, dilute aqueous suspensions of photocatalytic nanoparticulate titanium dioxide were irradiated with UV light in the presence of water-soluble TEMPO derivatives. Electron spin resonance (ESR) and electrospray ionisation mass-spectrometry (ESI-MS) data were acquired to provide complementary structural elucidation of the odd- and even-electron products of these reactions and both techniques show evidence for the formation of 4-oxo-TEMPO (TEMPONE). TEMPONE formation from the 4-substituted TEMPO compounds is proposed to be initiated by hydrogen abstraction at the 4-position by hydroxyl radical. High-level ab initio calculations reveal a thermodynamic preference for abstraction of this hydrogen but computed activation barriers indicate that, although viable, it is less favoured than hydrogen abstraction from elsewhere on the TEMPO scaffold. If a radical is formed at the 4-position however, calculations elucidate two reaction pathways leading to TEMPONE following combination with either a second hydroxyl radical or dioxygen. An alternate mechanism for conversion of TEMPOL to TEMPONE via an alkoxyl radical intermediate is also considered and found to be competitive with the other pathways. ESI-MS analysis also shows an increased abundance of analogous 4-substituted piperidines during the course of irradiation, suggesting competitive modification at the 1-position to produce a secondary amine. This modification is confirmed by characteristic fragmentation patterns of the ionised piperidines obtained by tandem mass spectrometry. The conclusions describe how reaction at the 4-position could be responsible for the gradual depletion of HALS in pigmented surface coatings and secondly, that modification at nitrogen to form the corresponding secondary amine species may play a greater role in the stabilisation mechanisms of HALS than previously considered.

Ozone-induced dissociation: Elucidation of double bond position within mass-selected lipid ions

Publisher: American Chemical Society (ACS)

Date: 07-12-2008

DOI: 10.1021/AC7017684

Abstract: Ions formed from lipids during electrospray ionization of crude lipid extracts have been mass-selected within a quadrupole linear ion trap mass spectrometer and allowed to react with ozone vapor. Gas-phase ion-molecule reactions between unsaturated lipid ions and ozone are found to yield two primary product ions for each carbon-carbon double bond within the molecule. The mass-to-charge ratios of these chemically induced fragments are diagnostic of the position of unsaturation within the precursor ion. This novel analytical technique, dubbed ozone-induced dissociation (OzID), can be applied both in series and in parallel with conventional collision-induced dissociation (CID) to provide near-complete structural assignment of unknown lipids within complex mixtures without prior fractionation or derivatization. In this study, OzID is applied to a suite of complex lipid extracts from sources including human lens, bovine kidney, and commercial olive oil, thus demonstrating the technique to be applicable to a broad range of lipid classes including both neutral and acidic glycerophospholipids, sphingomyelins, and triacylglycerols. Gas-phase ozonolysis reactions are also observed with different types of precursor ions including [M+H]+, [M+Li]+, [M+Na]+, and [M-H]-: in each case yielding fragmentation data that allow double bond position to be unambiguously assigned. Within the human lens lipid extract, three sphingomyelin regioisomers, namely SM(d18:0/15Z-24:1), SM(d18:0/17Z-24:1), and SM(d18:0/19Z-24:1), and a novel phosphatidylethanolamine alkyl ether, GPEtn(11Z-18:1e/9Z-18:1), are identified using a combination of CID and OzID. These discoveries demonstrate that lipid identification based on CID alone belies the natural structural ersity in lipid biochemistry and illustrate the potential of OzID as a complementary approach within automated, high-throughput lipid analysis protocols.

A comparison of the gas phase acidities of phospholipid headgroups: Experimental and computational studies

Publisher: American Chemical Society (ACS)

Date: 06-2005

DOI: 10.1016/J.JASMS.2005.02.019

Abstract: Proton-bound dimers consisting of two glycerophospholipids with different headgroups were prepared using negative ion electrospray ionization and dissociated in a triple quadrupole mass spectrometer. Analysis of the tandem mass spectra of the dimers using the kinetic method provides, for the first time, an order of acidity for the phospholipid classes in the gas phase of PE < PA << PG < PS < PI. Hybrid density functional calculations on model phospholipids were used to predict the absolute deprotonation enthalpies of the phospholipid classes from isodesmic proton transfer reactions with phosphoric acid. The computational data largely support the experimental acidity trend, with the exception of the relative acidity ranking of the two most acidic phospholipid species. Possible causes of the discrepancy between experiment and theory are discussed and the experimental trend is recommended. The sequence of gas phase acidities for the phospholipid headgroups is found to (1) have little correlation with the relative ionization efficiencies of the phospholipid classes observed in the negative ion electrospray process, and (2) correlate well with fragmentation trends observed upon collisional activation of phospholipid [M - H](-) anions.

Formation of Neutrals of Interstellar Significance in the Gas Phase by One- Electron Oxidation of Precursor Anions of Known Bond Connectivity

Publisher: Bentham Science Publishers Ltd.

Date: 10-2003

DOI: 10.2174/1385272033486323

Direct lipid profiling of single cells from inkjet printed microarrays

Publisher: American Chemical Society (ACS)

Date: 07-11-2012

DOI: 10.1021/AC302634U

Abstract: The on-demand printing of living cells using inkjet technologies has recently been demonstrated and allows for the controlled deposition of cells in microarrays. Here, we show that such arrays can be interrogated directly by robot-controlled liquid microextraction coupled with chip-based nanoelectospray mass spectrometry. Such automated analyses generate a profile of abundant membrane lipids that are characteristic of cell type. Significantly, the spatial control in both deposition and extraction steps combined with the sensitivity of the mass spectrometric detection allows for robust molecular profiling of in idual cells.

Formation of Two Isomeric C₃HO Radicals from Charged Precursors in the Gas Phase. Potential Interstellar Molecules

Publisher: American Chemical Society (ACS)

Date: 26-05-2000

DOI: 10.1021/JP994229G

Reactivity Trends in the Gas-Phase Addition of Acetylene to the N-Protonated Aryl Radical Cations of Pyridine, Aniline, and Benzonitrile

Publisher: American Chemical Society (ACS)

Date: 14-01-2021

DOI: 10.1021/JASMS.0C00386

Reactions of the hydroperoxide anion with dimethyl methylphosphonate in an ion trap mass spectrometer: evidence for a gas phase α-effect

Publisher: Royal Society of Chemistry (RSC)

Date: 2008

DOI: 10.1039/B803734E

Abstract: The gas phase degradation reactions of the chemical warfare agent (CWA) simulant, dimethyl methylphosphonate (DMMP), with the hydroperoxide anion (HOO(-)) were investigated using a modified quadrupole ion trap mass spectrometer. The HOO(-) anion reacts readily with neutral DMMP forming two significant product ions at m/z 109 and m/z 123. The major reaction pathways correspond to (i) the nucleophilic substitution at carbon to form [CH(3)P(O)(OCH(3))O](-) (m/z 109) in a highly exothermic process and (ii) exothermic proton transfer. The branching ratios of the two reaction pathways, 89% and 11% respectively, indicate that the former reaction is significantly faster than the latter. This is in contrast to the trend for the methoxide anion with DMMP, where proton transfer dominates. The difference in the observed reactivities of the HOO(-) and CH(3)O(-) anions can be considered as evidence for an alpha-effect in the gas phase and is supported by electronic structure calculations at the B3LYP/aug-cc-pVTZ//B3LYP/6-31+G(d) level of theory that indicate the S(N)2(carbon) process has an activation energy 7.8 kJ mol(-1) lower for HOO(-) as compared to CH(3)O(-). A similar alpha-effect was calculated for nucleophilic addition-elimination at phosphorus, but this process--an important step in the perhydrolysis degradation of CWAs in solution--was not observed to occur with DMMP in the gas phase. A theoretical investigation revealed that all processes are energetically accessible with negative activation energies. However, comparison of the relative Arrhenius pre-exponential factors indicate that substitution at phosphorus is not kinetically competitive with respect to the S(N)2(carbon) and deprotonation processes.

Characterisation of sphingolipids in the human lens by thin layer chromatography-desorption electrospray ionisation mass spectrometry

Publisher: Elsevier BV

Date: 09-2014

DOI: 10.1016/J.BBALIP.2014.05.006

Abstract: The lipidome of the human lens is unique in that cholesterol and dihydrosphingomyelin are the dominant classes. Moreover, the lens lipidome is not static with dramatic changes in several sphingolipid classes associated with both aging and cataract. Accordingly, there is a clear need to expand knowledge of the molecular species that constitute the human lens sphingolipidome. In this study, human lens lipids have been extracted and separated by thin-layer chromatography (TLC). Direct analysis of the TLC plates by desorption electrospray ionisation-mass spectrometry (DESI-MS) allowed the detection over 30 species from 11 classes of sphingolipids. Significantly, novel classes of lens lipids including sulfatides, dihydrosulfatides, lactosylceramide sulfates and dihydrolactosylceramide sulfates were identified.

Solvent-Mediated Proton-Transfer Catalysis of the Gas-Phase Isomerization of Ciprofloxacin Protomers

Publisher: American Chemical Society (ACS)

Date: 11-01-2022

DOI: 10.1021/JASMS.1C00331

Abstract: Understanding how neutral molecules become protonated during positive-ion electrospray ionization (ESI) mass spectrometry is critically important to ensure analytes can be efficiently ionized, detected, and unambiguously identified. The ESI solvent is one of several parameters that can alter the dominant site of protonation in polyfunctional molecules and thus, in turn, can significantly change the collision-induced dissociation (CID) mass spectra relied upon for compound identification. Ciprofloxacin─a common fluoroquinolone antibiotic─is one such ex le whereby positive-ion ESI can result in gas-phase [M + H]

Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations

Publisher: Royal Society of Chemistry (RSC)

Date: 2013

DOI: 10.1039/C3CP53690D

Abstract: The reactions of distonic 4-(N,N,N-trimethylammonium)-2-methylphenyl and 5-(N,N,N-trimethylammonium)-2-methylphenyl radical cations (m/z 149) with O2 are studied in the gas phase using ion-trap mass spectrometry. Photodissociation (PD) of halogenated precursors gives rise to the target distonic charge-tagged methylphenyl radical whereas collision-induced dissociation (CID) is found to produce unreactive radical ions. The PD generated distonic radicals, however, react rapidly with O2 to form [M + O2]˙(+) and [M + O2- OH]˙(+) ions, detected at m/z 181 and m/z 164, respectively. Quantum chemical calculations using G3SX(MP3) and M06-2X theories are deployed to examine key decomposition pathways of the 5-(N,N,N-trimethylammonium)-2-methylphenylperoxyl radical and rationalise the observed product ions. The prevailing product mechanism involves a 1,5-H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates ˙OH to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O2 reaction, thus serving as a plausible source of ˙OH radicals in combustion environments.

Ambient ionisation mass spectrometry for the characterisation of polymers and polymer additives: A review

Publisher: Elsevier BV

Date: 2014

DOI: 10.1016/J.ACA.2013.10.001

Abstract: The purpose of this review is to showcase the present capabilities of ambient s ling and ionisation technologies for the analysis of polymers and polymer additives by mass spectrometry (MS) while simultaneously highlighting their advantages and limitations in a critical fashion. To qualify as an ambient ionisation technique, the method must be able to probe the surface of solid or liquid s les while operating in an open environment, allowing a variety of s le sizes, shapes, and substrate materials to be analysed. The main sections of this review will be guided by the underlying principle governing the desorption/extraction step of the analysis liquid extraction, laser ablation, or thermal desorption, and the major component investigated, either the polymer itself or exogenous compounds (additives and contaminants) present within or on the polymer substrate. The review will conclude by summarising some of the challenges these technologies still face and possible directions that would further enhance the utility of ambient ionisation mass spectrometry as a tool for polymer analysis.

Introduction of a Fixed-Charge, Photolabile Derivative for Enhanced Structural Elucidation of Fatty Acids

Publisher: American Chemical Society (ACS)

Date: 12-07-2019

DOI: 10.1021/ACS.ANALCHEM.9B01566

Abstract: Fatty acids are a structurally erse category of lipids with a myriad of biochemical functions, which includes their role as building blocks of more complex lipids (e.g., glycerophospholipids and triacylglycerols). Increasingly, the analysis of fatty acids is undertaken using liquid chromatography-mass spectrometry (LC-MS), due to its versatility in the detection of lipids across a wide range of concentrations and ersity of molecular structures and masses. Previous work has shown that fixed-charge pyridinium derivatives are effective in enhancing the detection of fatty acids in LC-MS workflows. Herein, we describe the development of two novel pyridinium fixed-charged derivatization reagents that incorporate a photolabile aryl iodide that is selectively activated by laser irradiation inside the mass spectrometer. Photodissociation mass spectra of fatty acids conjugated to 1-(3-(aminomethyl)-4-iodophenyl)pyridin-1-ium (4-I-AMPP

Innentitelbild: Unterscheidung von isomeren Sphingolipiden mittels kryogener Infrarotspektroskopie (Angew. Chem. 32/2020)

Publisher: Wiley

Date: 22-06-2020

DOI: 10.1002/ANGE.202007701

Influence of Meibomian Gland Expression Methods on Human Lipid Analysis Results

Publisher: Elsevier BV

Date: 2016

DOI: 10.1016/J.JTOS.2015.10.001

Abstract: To compare the lipid composition of human meibum across three different meibum expression techniques. Meibum was collected from five healthy non-contact lens wearers (aged 20-35 years) after cleaning the eyelid margin using three meibum expression methods: cotton buds (CB), meibomian gland evaluator (MGE) and meibomian gland forceps (MGF). Meibum was also collected using cotton buds without cleaning the eyelid margin (CBn). Lipids were analyzed by chip-based, nano-electrospray mass spectrometry (ESI-MS). Comparisons were made using linear mixed models. Tandem MS enabled identification and quantification of over 200 lipid species across ten lipid classes. There were significant differences between collection techniques in the relative quantities of polar lipids obtained (P<.05). The MGE method returned smaller polar lipid quantities than the CB approaches. No significant differences were found between techniques for nonpolar lipids. No significant differences were found between cleaned and non-cleaned eyelids for polar or nonpolar lipids. Meibum expression technique influences the relative amount of phospholipids in the resulting s le. The highest amounts of phospholipids were detected with the CB approaches and the lowest with the MGE technique. Cleaning the eyelid margin prior to expression was not found to affect the lipid composition of the s le. This may be a consequence of the more forceful expression resulting in cell membrane contamination or higher risk of tear lipid contamination as a result of reflex tearing.

Generating Fatty Acid Profiles in the Gas Phase: Fatty Acid Identification and Relative Quantitation Using Ion/Ion Charge Inversion Chemistry

Publisher: American Chemical Society (ACS)

Date: 14-06-2019

DOI: 10.1021/ACS.ANALCHEM.9B01333

Characterisation of the ionic products arising from electron photodetachment of simple dicarboxylate dianions

Publisher: Elsevier BV

Date: 10-2013

DOI: 10.1016/J.IJMS.2013.06.008

Differences in membrane acyl phospholipid composition between an endothermic mammal and an ectothermic reptile are not limited to any phospholipid class

Publisher: The Company of Biologists

Date: 10-2007

DOI: 10.1242/JEB.007286

Abstract: This study examined questions concerning differences in the acyl composition of membrane phospholipids that have been linked to the faster rates of metabolic processes in endotherms versus ectotherms. In liver, kidney, heart and brain of the ectothermic reptile, Trachydosaurus rugosus, and the endothermic mammal, Rattus norvegicus, previous findings of fewer unsaturates but a greater unsaturation index (UI) in membranes of the mammal versus those of the reptile were confirmed. Moreover, the study showed that the distribution of phospholipid head-group classes was similar in the same tissues of the reptile and mammal and that the differences in acyl composition were present in all phospholipid classes analysed, suggesting a role for the physical over the chemical properties of membranes in determining the faster rates of metabolic processes in endotherms. The most common phosphatidylcholine (PC) molecules present in all tissues (except brain) of the reptile were 16:0/18:1, 16:0/18:2, 18:0/18:2,18:1/18:1 and 18:1/18:2, whereas arachidonic acid (20:4), containing PCs 16:0/20:4, 18:0/20:4, were the common molecules in the mammal. The most abundant phosphatidylethanolamines (PE) used in the tissue of the reptile were 18:0/18:2, 18:0/20:4, 18:1/18:1, 18:1/18:2 and 18:1/20:4, compared to 16:0/18:2, 16:0/20:4, 16:0/22:6, 18:0/20:4, 18:0/22:6 and 18:1/20:4 in the mammal. UI differences were primarily due to arachidonic acid found in both PC and PEs, whereas docosahexaenoic acid (22:6) was a lesser contributor mainly within PEs and essentially absent in the kidney. The phospholipid composition of brain was more similar in the reptile and mammal compared to those of other tissues.

Photoinduced intermolecular cross-linking of gas phase triacylglycerol lipid ions

Publisher: SAGE Publications

Date: 06-2015

DOI: 10.1255/EJMS.1344

Abstract: Complex mixtures of plant-derived triglycerol (TG) lipids are commonly used as feedstock components for the production of industrial polymers. However, there remains a need for the development of analytical strategies to investigate the intrinsic intermolecular cross-linking reactivity of in idual TG molecules within these mixtures as a function of their structures and physicochemical properties, and for the characterization of the resultant products. Here, to address this need, we describe a novel multistage tandem mass spectrometry based method for intermolecular cross-linking and subsequent structural characterization of TG lipid ions in the gas phase. Cross-linking reactions were initiated using 266 nm ultraviolet photodissociation tandem mass spectrometry (UVPD-MS/MS) of saturated or unsaturated TG dimers introduced via electrospray ionization into a linear ion trap mass spectrometer as noncovalent complexes with protonated 3,4-, 2,4- or 3,5-diiodoaniline (diIA). UVPD resulted in the initial formation of an anilinyl biradical via the sequential loss of two iodine radicals, which underwent further reaction to yield multiple cross-linked TG products along with competing noncross-linking processes. These chemistries are proposed to occur via sequential combinations of hydrogen abstraction (H-abstraction), radical addition, and radical recombination. Multistage collision-induced dissociation tandem mass spectrometry (CID-MS n ) was used to obtain evidence for the structures and mechanisms of formation for these products, as a function of both the TG lipid and diIA ion structures. The efficiency of the UVPD reaction was shown to be dependent on the number of unsaturation sites present within the TG lipids. However, when unsaturation sites were present, the formation of the cross-linked and noncross-linked product ions via H-abstraction and radical addition mechanisms was found to be competitive. Finally, the identity of the anilinyl biradical (e.g., 3,4- versus 2,4-substituted) was found to significantly affect the distribution of these two types of product ions. Importantly, owing to the observed propensity for cross-linking to occur via H-abstraction-initiated processes, this novel gas-phase cross-linking reaction provides a convenient method to link two molecules covalently without the requirement of any specific functional group, and therefore could be applied to examine the gas-phase intermolecular interactions and cross-linking of a wide range of biomolecular classes.

Proton Transfer Reactions for the Gas-Phase Separation, Concentration, and Identification of Cardiolipins

Publisher: American Chemical Society (ACS)

Date: 08-07-2020

DOI: 10.1021/ACS.ANALCHEM.0C02545

Direct Observation of the Gas Phase Reaction of the Cyclohexyl Radical with Dioxygen Using a Distonic Radical Ion Approach

Publisher: American Chemical Society (ACS)

Date: 29-12-2009

DOI: 10.1021/JP9073398

Abstract: Alkylperoxyl radicals are intermediates in the oxidation of hydrocarbons. The reactive nature of these intermediates, however, has made them elusive to direct observation and isolation. We have employed ion trap mass spectrometry to synthesize and characterize 4-carboxylatocyclohexyl radical anions (*C(6)H(10)-CO(2)(-)) and observe their reactivity in the presence of dioxygen. The resulting reaction is facile (k = 1.8 x 10(-10) cm(3) molecule(-1) s(-1) or 30% of calculated collision rate) and results in (i) the addition of O(2) to form stabilized 4-carboxylatocyclohexylperoxyl radical anions (*OO-C(6)H(10)-CO(2)(-)), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO(2)* and HO* radicals consistent with recent laser-induced fluorescence studies of the reaction of neutral cyclohexyl radicals with O(2). Electronic structure calculations at the B3LYP/6-31+G(d) level of theory reveal viable pathways for the observed reactions showing that formation of the peroxyl radical is exothermic by 37 kcal mol(-1) with subsequent transition states as low as -6.6 kcal mol(-1) (formation of HO(2)*) and -9.1 kcal mol(-1) (formation of HO*) with respect to the entrance channel. The combined computational and experimental data suggest that the structures of the reaction products correspond to cyclohexenes and epoxides from HO(2)* and HO* loss, respectively, while alternative pathways leading to cyclohexanone or ring-opened isomers are not observed. Activation of the charged peroxyl radical *OO-C(6)H(10)-CO(2)(-) by collision induced dissociation also results in the loss of HO(2)* and HO* radicals confirming that these products are directly connected to the peroxyl radical intermediate.

Switching radical stability by pH-induced orbital conversion

Publisher: Springer Science and Business Media LLC

Date: 21-04-2013

DOI: 10.1038/NCHEM.1625

Abstract: In most radicals the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO) however, in a small number of reported compounds this is not the case. In the present work we expand significantly the scope of this phenomenon, known as SOMO-HOMO energy-level conversion, by showing that it occurs in virtually any distonic radical anion that contains a sufficiently stabilized radical (aminoxyl, peroxyl, aminyl) non-π-conjugated with a negative charge (carboxylate, phosphate, sulfate). Moreover, regular orbital order is restored on protonation of the anionic fragment, and hence the orbital configuration can be switched by pH. Most importantly, our theoretical and experimental results reveal a dramatically higher radical stability and proton acidity of such distonic radical anions. Changing radical stability by 3-4 orders of magnitude using pH-induced orbital conversion opens a variety of attractive industrial applications, including pH-switchable nitroxide-mediated polymerization, and it might be exploited in nature.

Ozone-enabled fatty acid discovery reveals unexpected diversity in the human lipidome

Publisher: Springer Science and Business Media LLC

Date: 04-07-2023

DOI: 10.1038/S41467-023-39617-9

Abstract: Fatty acid isomers are responsible for an under-reported lipidome ersity across all kingdoms of life. Isomers of unsaturated fatty acids are often masked in contemporary analysis by incomplete separation and the absence of sufficiently diagnostic methods for structure elucidation. Here, we introduce a comprehensive workflow, to discover unsaturated fatty acids through coupling liquid chromatography and mass spectrometry with gas-phase ozonolysis of double bonds. The workflow encompasses semi-automated data analysis and enables de novo identification in complex media including human plasma, cancer cell lines and vernix caseosa. The targeted analysis including ozonolysis enables structural assignment over a dynamic range of five orders of magnitude, even in instances of incomplete chromatographic separation. Thereby we expand the number of identified plasma fatty acids two-fold, including non-methylene-interrupted fatty acids. Detection, without prior knowledge, allows discovery of non-canonical double bond positions. Changes in relative isomer abundances reflect underlying perturbations in lipid metabolism.

Mass Spectrometry Imaging with Isomeric Resolution Enabled by Ozone-Induced Dissociation.

Publisher: Wiley

Date: 19-06-2018

DOI: 10.1002/ANIE.201802937

UV Photodissociation Action Spectroscopy of Haloanilinium Ions in a Linear Quadrupole Ion Trap Mass Spectrometer

Publisher: American Chemical Society (ACS)

Date: 23-04-2013

DOI: 10.1007/S13361-013-0615-Z

Abstract: UV-vis photodissociation action spectroscopy is becoming increasingly prevalent because of advances in, and commercial availability of, ion trapping technologies and tunable laser sources. This study outlines in detail an instrumental arrangement, combining a commercial ion-trap mass spectrometer and tunable nanosecond pulsed laser source, for performing fully automated photodissociation action spectroscopy on gas-phase ions. The components of the instrumentation are outlined, including the optical and electronic interfacing, in addition to the control software for automating the experiment and performing online analysis of the spectra. To demonstrate the utility of this ensemble, the photodissociation action spectra of 4-chloroanilinium, 4-bromoanilinium, and 4-iodoanilinium cations are presented and discussed. Multiple photoproducts are detected in each case and the photoproduct yields are followed as a function of laser wavelength. It is shown that the wavelength-dependent partitioning of the halide loss, H loss, and NH3 loss channels can be broadly rationalized in terms of the relative carbon-halide bond dissociation energies and processes of energy redistribution. The photodissociation action spectrum of (phenyl)Ag2 (+) is compared with a literature spectrum as a further benchmark.

Negative-Ion Photoelectron Spectroscopy, Gas-Phase Acidity, and Thermochemistry of the Peroxyl Radicals CH₃OO and CH₃CH₂OO

Publisher: American Chemical Society (ACS)

Date: 07-09-2001

DOI: 10.1021/JA010942J

Abstract: Methyl, methyl-d(3), and ethyl hydroperoxide anions (CH(3)OO(-), CD(3)OO(-), and CH(3)CH(2)OO(-)) have been prepared by deprotonation of their respective hydroperoxides in a stream of helium buffer gas. Photodetachment with 364 nm (3.408 eV) radiation was used to measure the adiabatic electron affinities: EA[CH(3)OO, X(2)A' '] = 1.161 +/- 0.005 eV, EA[CD(3)OO, X(2)A' '] = 1.154 +/- 0.004 eV, and EA[CH(3)CH(2)OO, X(2)A' '] = 1.186 +/- 0.004 eV. The photoelectron spectra yield values for the term energies: Delta E(X(2)A' '-A (2)A')[CH(3)OO] = 0.914 +/- 0.005 eV, Delta E(X(2)A' '-A (2)A')[CD(3)OO] = 0.913 +/- 0.004 eV, and Delta E(X(2)A' '-A (2)A')[CH(3)CH(2)OO] = 0.938 +/- 0.004 eV. A localized RO-O stretching mode was observed near 1100 cm(-1) for the ground state of all three radicals, and low-frequency R-O-O bending modes are also reported. Proton-transfer kinetics of the hydroperoxides have been measured in a tandem flowing afterglow-selected ion flow tube (FA-SIFT) to determine the gas-phase acidity of the parent hydroperoxides: Delta(acid)G(298)(CH(3)OOH) = 367.6 +/- 0.7 kcal mol(-1), Delta(acid)G(298)(CD(3)OOH) = 367.9 +/- 0.9 kcal mol(-1), and Delta(acid)G(298)(CH(3)CH(2)OOH) = 363.9 +/- 2.0 kcal mol(-1). From these acidities we have derived the enthalpies of deprotonation: Delta(acid)H(298)(CH(3)OOH) = 374.6 +/- 1.0 kcal mol(-1), Delta(acid)H(298)(CD(3)OOH) = 374.9 +/- 1.1 kcal mol(-1), and Delta(acid)H(298)(CH(3)CH(2)OOH) = 371.0 +/- 2.2 kcal mol(-1). Use of the negative-ion acidity/EA cycle provides the ROO-H bond enthalpies: DH(298)(CH(3)OO-H) = 87.8 +/- 1.0 kcal mol(-1), DH(298)(CD(3)OO-H) = 87.9 +/- 1.1 kcal mol(-1), and DH(298)(CH(3)CH(2)OO-H) = 84.8 +/- 2.2 kcal mol(-1). We review the thermochemistry of the peroxyl radicals, CH(3)OO and CH(3)CH(2)OO. Using experimental bond enthalpies, DH(298)(ROO-H), and CBS/APNO ab initio electronic structure calculations for the energies of the corresponding hydroperoxides, we derive the heats of formation of the peroxyl radicals. The "electron affinity/acidity/CBS" cycle yields Delta(f)H(298)[CH(3)OO] = 4.8 +/- 1.2 kcal mol(-1) and Delta(f)H(298)[CH(3)CH(2)OO] = -6.8 +/- 2.3 kcal mol(-1).

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

Publisher: Wiley

Date: 10-08-2009

DOI: 10.1002/RCM.4192

Abstract: 2,3-Dimethyl-2,3-dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour-phase detection systems. In this study, the formation and detection of gas-phase [M+H](+), [M+Li](+), [M+NH(4)](+) and [M+Na](+) adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H](+) ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50 degrees C. In contrast, the [M+Na](+) ion demonstrated increasing ion abundance at source temperatures up to 105 degrees C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision-induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source-formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na](+) adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry.

Investigation of the microbial communities colonizing prepainted steel used for roofing and walling

Publisher: Wiley

Date: 20-12-2017

DOI: 10.1002/MBO3.425

Development of a Miniature Mass Spectrometry System for Point-of-Care Analysis of Lipid Isomers Based on Ozone-Induced Dissociation

Publisher: American Chemical Society (ACS)

Date: 29-09-2022

DOI: 10.1021/ACS.ANALCHEM.2C03112

Abstract: Disorder of lipid homeostasis is closely associated with a variety of diseases. Although mass spectrometry (MS) approaches have been well developed for the characterization of lipids, it still lacks an integrated and compact MS system that is capable of rapid and detailed lipid structural characterization and can be conveniently transferred into different laboratories. In this work, we describe a novel miniature MS system with the capability of both ozone-induced dissociation (OzID) and collision-induced dissociation (CID) for the assignment of sites of unsaturation and sn- positions in glycerolipids. A miniature ozone generator was developed, which can be operated at a relatively high pressure. By maintaining high-concentration ozone inside the linear ion trap, OzID efficiency was significantly improved for the identification of C═C locations in unsaturated lipids, with reaction times as short as 10 ms. Finally, the miniature OzID MS system was applied to the analysis of C═C locations and sn- positions of lipids from biological s les. Direct s ling and fast detection of changes in phospholipid isomers were demonstrated for the rapid discrimination of breast cancer tissue s les, showing the potential of the miniature OzID MS system for point-of-care analysis of lipid isomer biomarkers in complex s les.

Actinic Wavelength Action Spectroscopy of the IO^– Reaction Intermediate

Publisher: American Chemical Society (ACS)

Date: 08-12-2021

DOI: 10.1021/ACS.JPCLETT.1C03456

Abstract: Iodinate anions are important in the chemistry of the atmosphere where they are implicated in ozone depletion and particle formation. The atmospheric chemistry of iodine is a complex overlay of neutral-neutral, ion-neutral, and photochemical processes, where many of the reactions and intermediates remain poorly characterized. This study targets the visible spectroscopy and photostability of the gas-phase hypoiodite anion (IO

Gas-Phase Transformation of Phosphatidylcholine Cations to Structurally Informative Anions via Ion/Ion Chemistry

Publisher: American Chemical Society (ACS)

Date: 21-03-2013

DOI: 10.1021/AC400190K

A comparison of patient matched meibum and tear lipidomes

Publisher: Association for Research in Vision and Ophthalmology (ARVO)

Date: 11-11-2013

DOI: 10.1167/IOVS.13-12916

Abstract: To quantify the molecular lipid composition of patient-matched tear and meibum s les and compare tear and meibum lipid molecular profiles. Lipids were extracted from tears and meibum by bi-phasic methods using 10:3 tert-butyl methyl ether:methanol, washed with aqueous ammonium acetate, and analyzed by chip-based nanoelectrospray ionization tandem mass spectrometry. Targeted precursor ion and neutral loss scans identified in idual molecular lipids and quantification was obtained by comparison to internal standards in each lipid class. Two hundred and thirty-six lipid species were identified and quantified from nine lipid classes comprised of cholesterol esters, wax esters, (O-acyl)-ω-hydroxy fatty acids, triacylglycerols, phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylserine. With the exception of phospholipids, lipid molecular profiles were strikingly similar between tears and meibum. Comparisons between tears and meibum indicate that meibum is likely to supply the majority of lipids in the tear film lipid layer. However, the observed higher mole ratio of phospholipid in tears shows that analysis of meibum alone does not provide a complete understanding of the tear film lipid composition.

Identification of Monomethyl Branched-Chain Lipids by a Combination of Liquid Chromatography Tandem Mass Spectrometry and Charge-Switching Chemistries

Publisher: American Chemical Society (ACS)

Date: 11-10-2022

DOI: 10.1021/JASMS.2C00225

Abstract: While various mass spectrometric approaches have been applied to lipid analysis, unraveling the extensive structural ersity of lipids remains a significant challenge. Notably, these approaches often fail to differentiate between isomeric lipids─a challenge that is particularly acute for branched-chain fatty acids (FAs) that often share similar (or identical) mass spectra to their straight-chain isomers. Here, we utilize charge-switching strategies that combine ligated magnesium dications with deprotonated fatty acid anions. Subsequent activation of these charge inverted anions yields mass spectra that differentiate

Five vs. six membered-ring PAH products from reaction of o-methylphenyl radical and two C3H4 isomers

Publisher: Royal Society of Chemistry (RSC)

Date: 2021

DOI: 10.1039/D1CP01764K

Abstract: Gas-phase o -methylphenyl reactions with propyne and allene form PAHs: with preferences for either six–six or five–six bicyclic products.

Modelling reaction kinetics of distonic radical ions: a systematic investigation of phenyl-type radical addition to unsaturated hydrocarbons

Publisher: Royal Society of Chemistry (RSC)

Date: 2022

DOI: 10.1039/D2FD00045H

Abstract: We measure second-order rate coefficients for a suite of radical-ion reactions involving unsaturated hydrocarbons (C 2 H 2 and C 2 H 4 ), and report our efforts to develop an accurate modelling framework using a Rice–Ramsperger–Kassel–Marcus theory Master Equation approach.

Online Ozonolysis Combined with Ion Mobility-Mass Spectrometry Provides a New Platform for Lipid Isomer Analyses

Publisher: American Chemical Society (ACS)

Date: 21-12-2017

DOI: 10.1021/ACS.ANALCHEM.7B04091

Elucidation of double bond position in unsaturated lipids by ozone electrospray ionization mass spectrometry

Publisher: American Chemical Society (ACS)

Date: 05-06-2007

DOI: 10.1021/AC0702185

Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: a combined neutral and distonic radical study

Publisher: Royal Society of Chemistry (RSC)

Date: 2016

DOI: 10.1039/C5CP02953H

Abstract: The o -hydroxyphenyl radical reacts with O 2 to form o -benzoquinone + OH and cyclopentadienone is assigned as a secondary product.

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Publisher: Elsevier BV

Date: 2011

DOI: 10.1016/J.IJMS.2010.09.031

Molecular Weight Growth in the Gas-Phase Reactions of Dehydroanilinium Radical Cations with Propene

Publisher: American Chemical Society (ACS)

Date: 19-09-2019

DOI: 10.1021/ACS.JPCA.9B04088

Abstract: Protonated aniline-one of the simplest nitrogen-bearing aromatic molecules-is speculated to be present within Titan's atmosphere, where it could play a role in molecular weight growth chemistry. To investigate this possibility, this paper examines the reactions of propene with distonic radical cations derived from protonated aniline. The reaction kinetics, products, and branching ratios of these distonic radical cations (i.e., 2-, 3-, and 4-dehydroanilinium radical cations) are measured in the gas phase using ion-trap mass spectrometry, and calculations (M06-2

Potential interstellar molecules. Formation of neutral C6CO from C6CO?� in the gas phase

Publisher: Wiley

Date: 16-01-2000

DOI: 10.1002/(SICI)1097-0231(20000130)14:2<118::AID-RCM848>3.0.CO;2-Z

Mechanisms of Glycerol Dehydration

Publisher: American Chemical Society (ACS)

Date: 18-04-2006

DOI: 10.1021/JP060597Q

Abstract: Dehydration of neutral and protonated glycerol was investigated using quantum mechanical calculations (CBS-QB3). Calculations on neutral glycerol show that there is a high barrier for simple 1,2-dehydration, E(a)=70.9 kcal mol(-1), which is lowered to 65.2 kcal mol(-1) for pericyclic 1,3-dehydration. In contrast, the barriers for dehydration of protonated glycerol are much lower. Dehydration mechanisms involving hydride transfer, pinacol rearrangement, or substitution reactions have barriers between 20 and 25 kcal mol(-1). Loss of water from glycerol via substitution results in either oxirane or oxetane intermediates, which can inter-convert over a low barrier. Subsequent decomposition of these intermediates proceeds via either a second dehydration step or loss of formaldehyde. The computed mechanisms for decomposition of protonated glycerol are supported by the gas-phase fragmentation of protonated glycerol observed using a triple--quadrupole mass spectrometer.

Combining liquid chromatography with ozone-induced dissociation for the separation and identification of phosphatidylcholine double bond isomers

Publisher: Springer Science and Business Media LLC

Date: 05-03-2015

DOI: 10.1007/S00216-014-8430-3

Abstract: Revealing the inherent molecular ersity of lipid biology requires advanced analytical technologies. Distinguishing phospholipids that differ in the position(s) of carbon-carbon double bonds within their acyl chains presents a particular challenge because of their similar chromatographic and mass spectral behaviours. Here-for the first time-we combine reversed-phase liquid chromatography for separation of isomeric phospholipids with on-line mass spectral analysis by ozone-induced dissociation (OzID) for unambiguous double bond position assignment. The customised tandem linear ion-trap mass spectrometer used in our study is capable of acquiring OzID scans on a chromatographic timescale. Resolving the contributions of isomeric lipids that are indistinguishable based on conventional mass spectral analysis is achieved using the combination of liquid chromatography and OzID. Application of this method to the analysis of simple (egg yolk) and more complex (sheep brain) extracts reveals significant populations of the phosphatidylcholine PC 16:0_18:1(n-7) alongside the expected PC 16:0_18:1(n-9) isomer.

Laser Photodissociation Action Spectroscopy for the Wavelength-Dependent Evaluation of Photoligation Reactions

Publisher: American Chemical Society (ACS)

Date: 21-05-2021

DOI: 10.1021/ACS.ANALCHEM.1C01584

Generation and characterization of ionic and neutral dihydroxy boron B(OH)2+/0 in the gas phase

Publisher: Elsevier BV

Date: 02-2000

DOI: 10.1016/S1387-3806(99)00223-7

Isomeric lipid signatures reveal compartmentalised fatty acid metabolism in cancer

Publisher: Cold Spring Harbor Laboratory

Date: 03-11-2021

DOI: 10.1101/2021.11.01.466716

Abstract: 1.0 Cellular energy and biomass demands of cancer drive a complex dynamic between uptake of extracellular fatty acids (FA) and de novo synthesis. Given that oxidation of de novo synthesised FAs for energy would result in net-energy loss, there is an implication that FAs from these two sources must have distinct metabolic fates - however hitherto FAs were considered part of a common pool. To probe FA metabolic partitioning, cancer cells were supplemented with stable-isotope labelled FAs. Structural analysis of the resulting glycerophospholipids revealed that labelled FAs from uptake were largely incorporated to canonical ( sn -)positions on the glycerol backbone. Surprisingly, labelled FA uptake disrupted canonical isomer patterns of the unlabelled lipidome and induced repartitioning of n -3 and n -6 polyunsaturated-FAs into glycerophospholipid classes. These structural changes evidence differences in the metabolic fate of FAs derived from uptake or de novo sources and demonstrate unique signalling and remodelling behaviours usually hidden to conventional lipidomics. Lipid isomers reveal discrete metabolic compartmentalisation in cancer FAs derived from uptake and de novo synthesis have different metabolic fates Stearate uptake signals for PUFA ( n -3 and n -6) repartitioning between lipid classes sn -positional isomers are a marker for aberrant lipid metabolism

Desorption electrospray ionisation mass spectrometry reveals in situ modification of a hindered amine light stabiliser resulting from direct N-OR bond cleavage

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C0AN00656D

Abstract: Detection and characterisation of structural modifications of a hindered amine light stabiliser (HALS) directly from a polyester-based coil coating have been achieved by desorption electrospray ionisation mass spectrometry (DESI-MS) for the first time. In situ detection is made possible by exposing the coating to an acetone vapour atmosphere prior to analysis. This is a gentle and non-destructive treatment that allows diffusion of analyte to the surface without promoting lateral migration. Using this approach a major structural modification of the HALS TINUVIN®123 (bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate) was discovered where one N-ether piperidine moiety (N-OC(8)H(17)) is converted to a secondary piperidine (N-H). With the use of 2-dimensional DESI-MS imaging the modification was observed to arise during high curing temperatures (ca. 260 °C) and under simulated physiological conditions (80 °C, full solar spectrum). It is proposed that the secondary piperidine derivative is a result of a highly reactive aminyl radical intermediate produced by N-O homolytic bond cleavage. The nature of the bond cleavage is also suggested by ESR spin-trapping experiments employing α-phenyl-N-tert-butyl nitrone (PBN) in toluene at 80 °C. The presence of a secondary piperidine derivative in situ and the implication of N-OR competing with NO-R bond cleavage suggest an alternative pathway for generation of the nitroxyl radical-an essential requirement in anti-oxidant activity that has not previously been described for the N-ether sub-class of HALS.

Human lens lipids differ markedly from those of commonly used experimental animals

Publisher: Elsevier BV

Date: 06-2008

DOI: 10.1016/J.BBALIP.2008.04.002

Abstract: Electrospray ionisation tandem mass spectrometry has allowed the unambiguous identification and quantification of in idual lens phospholipids in human and six animal models. Using this approach ca. 100 unique phospholipids have been characterised. Parallel analysis of the same lens extracts by a novel direct-insertion electron-ionization technique found the cholesterol content of human lenses to be significantly higher (ca. 6 times) than lenses from the other animals. The most abundant phospholipids in all the lenses examined were choline-containing phospholipids. In rat, mouse, sheep, cow, pig and chicken, these were present largely as phosphatidylcholines, in contrast 66% of the total phospholipid in Homo sapiens was sphingomyelin, with the most abundant being dihydrosphingomyelins, in particular SM(d18:0/16:0) and SM(d18:0/24:1). The abundant glycerophospholipids within human lenses were found to be predominantly phosphatidylethanolamines and phosphatidylserines with surprisingly high concentrations of ether-linked alkyl chains identified in both classes. This study is the first to identify the phospholipid class (head-group) and assign the constituent fatty acid(s) for each lipid molecule and to quantify in idual lens phospholipids using internal standards. These data clearly indicate marked differences in the membrane lipid composition of the human lens compared to commonly used animal models and thus predict a significant variation in the membrane properties of human lens fibre cells compared to those of other animals.

Electron capture of tetracyanoethylene oxide in the gas phase. Rearrangement of the parent radical anion to form [(NC)3C]−. A joint experimental and ab initio study

Publisher: Elsevier BV

Date: 2000

DOI: 10.1016/S1387-3806(99)00124-4

Ion–molecule reactions reveal facile radical migration in peptides

Publisher: Royal Society of Chemistry (RSC)

Date: 2009

DOI: 10.1039/B907833A

Abstract: Ion-molecule reactions between molecular oxygen and peptide radicals in the gas phase demonstrate that radical migration occurs easily within large biomolecules without addition of collisional activation energy.

Elucidating the chemical structure of native 1-deoxysphingosine

Publisher: Elsevier BV

Date: 07-2016

DOI: 10.1194/JLR.M067033

Comment on the Ionization Energy of B₂F₄

Publisher: American Chemical Society (ACS)

Date: 28-08-2012

DOI: 10.1021/JP306150U

The Lowest Singlet and Triplet States of the Oxyallyl Diradical

Publisher: Wiley

Date: 20-10-2009

DOI: 10.1002/ANIE.200904417

Experimental evidence for competitive N-O and O-C bond homolysis in gas-phase alkoxyamines

Publisher: Elsevier BV

Date: 02-2015

DOI: 10.1016/J.IJMS.2014.06.030

Ozone-induced dissociation of conjugated lipids reveals significant reaction rate enhancements and characteristic odd-electron product ions

Publisher: American Chemical Society (ACS)

Date: 05-01-2013

DOI: 10.1007/S13361-012-0521-9

Abstract: Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for [M + X](+) ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.

Structural identification of hindered amine light stabilisers in coil coatings using electrospray ionisation tandem mass spectrometry

Publisher: Wiley

Date: 18-03-2010

DOI: 10.1002/JMS.1730

Abstract: Hindered amine light stabilisers (HALS) are the most effective antioxidants currently available for polymer systems in post-production, in-service applications, yet the mechanism of their action is still not fully understood. Structural characterisation of HALS in polymer matrices, particularly the identification of structural modifications brought about by oxidative conditions, is critical to aid mechanistic understanding of the prophylactic effects of these molecules. In this work, electrospray ionisation tandem mass spectrometry (ESI-MS/MS) was applied to the analysis of a suite of commercially available 2,2,6,6-tetramethylpiperidine-based HALS. Fragmentation mechanisms for the [M + H](+) ions are proposed, which provide a rationale for the product ions observed in the MS/MS and MS(3) mass spectra of N-H, N-CH(3), N-C(O)CH(3) and N-OR containing HALS (where R is an alkyl substituent). A common product ion at m/z 123 was identified for the group of antioxidants containing N-H, N-CH(3) or N-C(O)CH(3) functionality, and this product ion was employed in precursor ion scans on a triple quadrupole mass spectrometer to identify the HALS species present in a crude extract from of a polyester-based coil coating. Using MS/MS, two degradation products were unambiguously identified. This technique provides a simple and selective approach to monitoring HALS structures within complex matrices.

Identification of Carbon-Carbon Double Bond Stereochemistry in Unsaturated Fatty Acids by Charge-Remote Fragmentation of Fixed-Charge Derivatives

Publisher: American Chemical Society (ACS)

Date: 07-11-2022

DOI: 10.1021/ACS.ANALCHEM.2C03625

Abstract: Separation and identification of fatty acid (FA) isomers in biological s les represents a challenging problem for lipid chemists. Notably, FA regio- and stereo-isomers differing in the location or (

Analysis of unsaturated lipids by ozone-induced dissociation

Publisher: Elsevier BV

Date: 11-2011

DOI: 10.1016/J.BBALIP.2011.04.015

Abstract: Recent developments in analytical technologies have driven significant advances in lipid science. The sensitivity and selectivity of modern mass spectrometers can now provide for the detection and even quantification of many hundreds of lipids in a single analysis. In parallel, increasing evidence from structural biology suggests that a detailed knowledge of lipid molecular structure including carbon-carbon double bond position, stereochemistry and acyl chain regiochemistry is required to fully appreciate the biochemical role(s) of in idual lipids. Here we review the capabilities and limitations of tandem mass spectrometry to provide this level of structural specificity in the analysis of lipids present in complex biological extracts. In particular, we focus on the capabilities of a novel technology termed ozone-induced dissociation to identify the position(s) of double bonds in unsaturated lipids and discuss its possible role in efforts to develop workflows that provide for complete structure elucidation of lipids by mass spectrometry alone: so-called top-down lipidomics.

Wavelength-gated photoreversible polymerization and topology control

Publisher: Royal Society of Chemistry (RSC)

Date: 2020

DOI: 10.1039/C9SC05381F

Abstract: We exploit the wavelength dependence of [2 + 2] photocycloadditions and -reversions of styrylpyrene to exert unprecedented control over the photoreversible polymerization and topology of telechelic building blocks.

Clinical dyslipidaemia is associated with changes in the lipid composition and inflammatory properties of apolipoprotein-B-containing lipoproteins from women with type 2 diabetes

Publisher: Springer Science and Business Media LLC

Date: 18-01-2012

DOI: 10.1007/S00125-011-2444-6

Abstract: The aim of this study was to use lipidomics to determine if the lipid composition of apolipoprotein-B-containing lipoproteins is modified by dyslipidaemia in type 2 diabetes and if any of the identified changes potentially have biological relevance in the pathophysiology of type 2 diabetes. VLDL and LDL from normolipidaemic and dyslipidaemic type 2 diabetic women and controls were isolated and quantified with HPLC and mass spectrometry. A detailed molecular characterisation of VLDL triacylglycerols (TAG) was also performed using the novel ozone-induced dissociation method, which allowed us to distinguish vaccenic acid (C18:1 n-7) from oleic acid (C18:1 n-9) in specific TAG species. Lipid class composition was very similar in VLDL and LDL from normolipidaemic type 2 diabetic and control participants. By contrast, dyslipidaemia was associated with significant changes in both lipid classes (e.g. increased diacylglycerols) and lipid species (e.g. increased C16:1 and C20:3 in phosphatidylcholine and cholesteryl ester and increased C16:0 [palmitic acid] and vaccenic acid in TAG). Levels of palmitic acid in VLDL and LDL TAG correlated with insulin resistance, and VLDL TAG enriched in palmitic acid promoted increased secretion of proinflammatory mediators from human smooth muscle cells. We showed that dyslipidaemia is associated with major changes in both lipid class and lipid species composition in VLDL and LDL from women with type 2 diabetes. In addition, we identified specific molecular lipid species that both correlate with clinical variables and are proinflammatory. Our study thus shows the potential of advanced lipidomic methods to further understand the pathophysiology of type 2 diabetes.

Unusual cross‐ring S_N2 reactions of [MH]⁻ ions of methoxyacetanilides

Publisher: Wiley

Date: 1995

DOI: 10.1002/RCM.1290090214

Dissociation of proton-bound complexes reveals geometry and arrangement of double bonds in unsaturated lipids

Publisher: Elsevier BV

Date: 11-2015

DOI: 10.1016/J.IJMS.2015.07.006

Ozone-induced dissociation on a modified tandem linear ion-trap: Observations of different reactivity for isomeric lipids

Publisher: American Chemical Society (ACS)

Date: 12-2010

DOI: 10.1016/J.JASMS.2010.08.011

Abstract: Ozone-induced dissociation (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to determine the position(s) of unsaturation. In this contribution, we describe the modification of a tandem linear ion-trap mass spectrometer specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides spatial separation between mass-selection, the ozonolysis reaction, and mass-analysis steps in the OzID process and thus delivers significant enhancements in speed and sensitivity (ca. 30-fold). These improvements allow spectra revealing the double-bond position(s) within unsaturated lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput lipidomic protocols. The stable ozone concentration afforded by this modified instrument also allows direct comparison of relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution position on the glycerol backbone, and (3) stereochemistry. For cis- and trans-isomers, differences were also observed in the branching ratio of product ions arising from the gas-phase ozonolysis reaction, suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Additional activation energy applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra containing both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsaturated phosphatidylcholine within a cow brain lipid extract provided evidence for up to four structurally distinct phospholipids differing in both double-bond position and sn-substitution.

Syntheses of NCN and NC₃N from Ionic Precursors in the Gas Phase and an Unusual Rearrangement of Neutral NC₃N:  A Joint Experimental and Theoretical Study

Publisher: American Chemical Society (ACS)

Date: 11-2000

DOI: 10.1021/JP001590Q

Photodissociation of TEMPO-modified peptides: new approaches to radical-directed dissociation of biomolecules

Publisher: Royal Society of Chemistry (RSC)

Date: 2014

DOI: 10.1039/C3CP54825B

Abstract: Radical-directed dissociation of gas phase ions is emerging as a powerful and complementary alternative to traditional tandem mass spectrometric techniques for biomolecular structural analysis. Previous studies have identified that coupling of 2-[(2,2,6,6-tetramethylpiperidin-1-oxyl)methyl]benzoic acid (TEMPO-Bz) to the N-terminus of a peptide introduces a labile oxygen-carbon bond that can be selectively activated upon collisional activation to produce a radical ion. Here we demonstrate that structurally-defined peptide radical ions can also be generated upon UV laser photodissociation of the same TEMPO-Bz derivatives in a linear ion-trap mass spectrometer. When subjected to further mass spectrometric analyses, the radical ions formed by a single laser pulse undergo identical dissociations as those formed by collisional activation of the same precursor ion, and can thus be used to derive molecular structure. Mapping the initial radical formation process as a function of photon energy by photodissociation action spectroscopy reveals that photoproduct formation is selective but occurs only in modest yield across the wavelength range (300-220 nm), with the photoproduct yield maximised between 235 and 225 nm. Based on the analysis of a set of model compounds, structural modifications to the TEMPO-Bz derivative are suggested to optimise radical photoproduct yield. Future development of such probes offers the advantage of increased sensitivity and selectivity for radical-directed dissociation.

Determination of ester position in isomeric (O-acyl)-hydroxy fatty acids by ion trap mass spectrometry

Publisher: Wiley

Date: 25-09-2016

DOI: 10.1002/RCM.7715

Abstract: (O-acyl)-hydroxy fatty acids (OAHFAs) are a recently discovered class of endogenous lipids, generating significant interest for their correlation with enhanced glucose tolerance. Structural variants that differ in the position of the ester linkage have been described, including the ω-OAHFA sub-class, that plays a key role in stabilizing the human tear film. Developing analytical tools for rapid and unambiguous structural elucidation of OAHFAs is essential to understanding their erse physiological functions. Commercially available and synthesized OAHFA standards were dissolved in chloroform and subsequently diluted into methanol with 1.5 mM ammonium acetate. Negative ion collision-induced dissociation (CID) MS Major product ions observed during CID of [OAHFA - H] A mechanistic rationale is provided to explain the unimolecular dissociation of [OAHFA - H]

Fatty acid uptake and incorporation into phospholipids in the rat lens

Publisher: Association for Research in Vision and Ophthalmology (ARVO)

Date: 09-02-2011

DOI: 10.1167/IOVS.10-5830

Rapid differentiation of isomeric lipids by photodissociation mass spectrometry of fatty acid derivatives

Publisher: Wiley

Date: 18-02-2013

DOI: 10.1002/RCM.6503

Abstract: Both traditional electron ionization and electrospray ionization tandem mass spectrometry have demonstrated limitations in the unambiguous identification of fatty acids. In the former case, high electron energies lead to extensive dissociation of the radical cations from which little specific structural information can be obtained. In the latter, conventional collision-induced dissociation (CID) of even-electron ions provides little intra-chain fragmentation and thus few structural diagnostics. New approaches that harness the desirable features of both methods, namely radical-driven dissociation with discrete energy deposition, are thus required. Herein we describe the derivatization of a structurally erse suite of fatty acids as 4-iodobenzyl esters (FAIBE). Electrospray ionization of these derivatives in the presence of sodium acetate yields abundant [M + Na](+) ions that can be mass-selected and subjected to laser irradiation (λ = 266 nm) on a modified linear ion-trap mass spectrometer. Photodissociation (PD) of the FAIBE derivatives yields abundant radical cations by loss of atomic iodine and in several cases selective dissociation of activated carbon-carbon bonds (e.g., at allylic positions) are also observed. Subsequent CID of the [M + Na - I](•+) radical cations yields radical-directed dissociation (RDD) mass spectra that reveal extensive carbon-carbon bond dissociation without scrambling of molecular information. Both PD and RDD spectra obtained from derivatized fatty acids provide a wealth of structural information including the position(s) of unsaturation, chain-branching and hydroxylation. The structural information obtained by this approach, in particular the ability to rapidly differentiate isomeric lipids, represents a useful addition to the lipidomics tool box.

Generation and characterization of ionic and neutral (CH3OBH)+/· and (CH3BOH)+/· in the gas phase by tandem mass spectrometry

Publisher: Elsevier BV

Date: 10-2000

DOI: 10.1016/S1387-3806(00)00256-6

Structural characterization of glycerophospholipids by combinations of ozone- and collision-induced dissociation mass spectrometry: The next step towards “top-down” lipidomics

Publisher: Royal Society of Chemistry (RSC)

Date: 2014

DOI: 10.1039/C3AN01712E

Abstract: The complete structural elucidation of complex lipids, including glycerophospholipids, using only mass spectrometry represents a major challenge to contemporary analytical technologies. Here, we demonstrate that product ions arising from the collision-induced dissociation (CID) of the [M + Na](+) adduct ions of phospholipids can be isolated and subjected to subsequent gas-phase ozonolysis - known as ozone-induced dissociation (OzID) - in a linear ion-trap mass spectrometer. The resulting CID/OzID experiment yields abundant product ions that are characteristic of the acyl substitution on the glycerol backbone (i.e., sn-position). This approach is shown to differentiate sn-positional isomers, such as the regioisomeric phosphatidylcholine pair of PC 16:0/18:1 and PC 18:1/16:0. Importantly, CID/OzID provides a sensitive diagnostic for the existence of an isomeric mixture in a given s le. This is of very high value for the analysis of tissue extracts since CID/OzID analyses can reveal changes in the relative abundance of isomeric constituents even within different tissues from the same animal. Finally, we demonstrate the ability to assign carbon-carbon double bond positions to in idual acyl chains at specific backbone positions by adding subsequent CID and/or OzID steps to the workflow and that this can be achieved in a single step using a hybrid triple quadrupole-linear ion trap mass spectrometer. This unique approach represents the most complete and specific structural analysis of lipids by mass spectrometry demonstrated to date and is a significant step towards comprehensive top-down lipidomics.

Accelerating Ozonolysis Reactions Using Supplemental RF-Activation of Ions in a Linear Ion Trap Mass Spectrometer

Publisher: American Chemical Society (ACS)

Date: 24-02-2022

DOI: 10.1021/ACS.ANALCHEM.1C04915

Abstract: Gas-phase ion-molecule reactions provide structural insights across a range of analytical applications. A hindrance to the wider use of ion-molecule reactions is that they are relatively slow compared to other ion activation modalities and can thereby impose a bottleneck on the time required to analyze each s le. Here we describe a method for accelerating the rate of ion-molecule reactions involving ozone, implemented by supplementary RF-activation of mass-selected ions within a linear ion trap. Reaction rate accelerations between 15-fold (for ozonolysis of alkenes in ionised lipids) and 90-fold (for ozonation of halide anions) are observed compared to thermal conditions. These enhanced reaction rates with ozone increase s le throughput, aligning the reaction time with the overall duty cycle of the mass spectrometer. We demonstrate that the acceleration is due to the supplementary RF-activation surmounting the activation barrier energy of the entrance channel of the ion-molecule reaction. This rate acceleration is subsequently shown to aid identification of new, low abundance lipid isomers and enables an equivalent increase in the number of lipid species that can be analyzed.

Trapping of a tert-adamantyl peroxyl radical in the gas phase

Publisher: Royal Society of Chemistry (RSC)

Date: 2006

DOI: 10.1039/B516408G

Abstract: A bridgehead adamantyl peroxyl radical has been prepared and isolated in the gas phase by the reaction of a distonic radical anion with dioxygen in a quadrupole ion-trap mass spectrometer.

Investigation of the gas phase reactivity of the 1-adamantyl radical using a distonic radical anion approach

Publisher: Royal Society of Chemistry (RSC)

Date: 2007

DOI: 10.1039/B711156H

Abstract: The gas phase reactions of the bridgehead 3-carboxylato-1-adamantyl radical anion were observed with a series of neutral reagents using a modified electrospray ionisation linear ion trap mass spectrometer. This distonic radical anion was observed to undergo processes suggestive of radical reactivity including radical-radical combination reactions, substitution reactions and addition to carbon-carbon double bonds. The rate constants for reactions of the 3-carboxylato-1-adamantyl radical anion with the following reagents were measured (in units 10(-12) cm(3) molecule(-1) s(-1)): (18)O(2) (85 +/- 4), NO (38.4 +/- 0.4), I(2) (50 +/- 50), Br(2) (8 +/- 2), CH(3)SSCH(3) (12 +/- 2), styrene (1.20 +/- 0.03), CHCl(3) (H abstraction 0.41 +/- 0.06, Cl abstraction 0.65 +/- 0.1), CDCl(3) (D abstraction 0.035 +/- 0.01, Cl abstraction 0.723 +/- 0.005), allyl bromide (Br abstraction 0.53 +/- 0.04, allylation 0.25 +/- 0.01). Collision rates were calculated and reaction efficiencies are also reported. This study represents the first quantitative measurement of the gas phase reactivity of a bridgehead radical and suggests that distonic radical anions are good models for the study of their elusive uncharged analogues.

Disentangling Lipid Isomers by High-Resolution Differential Ion Mobility Spectrometry/Ozone-Induced Dissociation of Metalated Species

Publisher: American Chemical Society (ACS)

Date: 09-11-2021

DOI: 10.1021/JASMS.1C00251

Abstract: The preponderance and functional importance of isomeric biomolecules have become topical in biochemistry. Therefore, one must distinguish and identify all such forms across compound classes, over a wide dynamic range as minor species often have critical activities. With all the power of modern mass spectrometry for compositional assignments by accurate mass, the identical precursor and often fragment ion masses render this task a steep challenge. This is recognized in proteomics and epigenetics, where proteoforms are disentangled and characterized employing novel separations and non-ergodic dissociation mechanisms. This issue is equally pertinent to lipidomics, where the lack of isomeric depth has thwarted the deciphering of functional networks. Here we introduce a new platform, where the isomeric lipids separated by high-resolution differential ion mobility spectrometry (FAIMS) are identified using ozone-induced dissociation (OzID). Cationization by metals (here K

PCCP does exist

Publisher: Royal Society of Chemistry (RSC)

Date: 2000

DOI: 10.1039/B000225I

Separation and identification of phosphatidylcholine regioisomers by combining liquid chromatography with a fusion of collision- and ozone-induced dissociation

Publisher: SAGE Publications

Date: 06-2015

DOI: 10.1255/EJMS.1300

Abstract: The differentiation of closely related lipid isomers is increasingly important to our evolving understanding of lipid biochemistry but it is equally challenging to contemporary chromatographic and mass spectral analyses. Recently, we described a novel ion-activation approach based on combining collision- with ozone-induced dissociation (CID/OzID) for the identification of the relative acyl chain substitution positions in glycerophospholipids. Here we demonstrate, for the first time, that CID/OzID can be effectively combined with reversed-phase chromatography to enable the separation and unambiguous identification of regioisomeric pairs of phosphatidylcholines that differ only in the arrangement of acyl chains on the glycerol backbone.

Gas-Phase Ion/Ion Reactions Involving Tris-Phenanthroline Alkaline Earth Metal Complexes as Charge Inversion Reagents for the Identification of Fatty Acids

Publisher: American Chemical Society (ACS)

Date: 27-09-2018

DOI: 10.1021/ACS.ANALCHEM.8B03441

Ethylenedione: An Intrinsically Short-Lived Molecule

Publisher: Wiley

Date: 04-12-1998

DOI: 10.1002/(SICI)1521-3765(19981204)4:12<2550::AID-CHEM2550>3.0.CO;2-E

Photoelectron Spectroscopic Study of the Oxyallyl Diradical

Publisher: American Chemical Society (ACS)

Date: 16-02-2011

DOI: 10.1021/JP111311K

Abstract: The photoelectron spectrum of the oxyallyl (OXA) radical anion has been measured. The radical anion has been generated in the reaction of the atomic oxygen radical anion (O(•-)) with acetone. Three low-lying electronic states of OXA have been observed in the spectrum. Electronic structure calculations have been performed for the triplet states ((3)B(2) and (3)B(1)) of OXA and the ground doublet state ((2)A(2)) of the radical anion using density functional theory (DFT). Spectral simulations have been carried out for the triplet states based on the results of the DFT calculations. The simulation identifies a vibrational progression of the CCC bending mode of the (3)B(2) state of OXA in the lower electron binding energy (eBE) portion of the spectrum. On top of the (3)B(2) feature, however, the experimental spectrum exhibits additional photoelectron peaks whose angular distribution is distinct from that for the vibronic peaks of the (3)B(2) state. Complete active space self-consistent field (CASSCF) method and second-order perturbation theory based on the CASSCF wave function (CASPT2) have been employed to study the lowest singlet state ((1)A(1)) of OXA. The simulation based on the results of these electronic structure calculations establishes that the overlapping peaks represent the vibrational ground level of the (1)A(1) state and its vibrational progression of the CO stretching mode. The (1)A(1) state is the lowest electronic state of OXA, and the electron affinity (EA) of OXA is 1.940 ± 0.010 eV. The (3)B(2) state is the first excited state with an electronic term energy of 55 ± 2 meV. The widths of the vibronic peaks of the X̃ (1)A(1) state are much broader than those of the ã (3)B(2) state, implying that the (1)A(1) state is indeed a transition state. The CASSCF and CASPT2 calculations suggest that the (1)A(1) state is at a potential maximum along the nuclear coordinate representing disrotatory motion of the two methylene groups, which leads to three-membered-ring formation, i.e., cyclopropanone. The simulation of b̃ (3)B(1) OXA reproduces the higher eBE portion of the spectrum very well. The term energy of the (3)B(1) state is 0.883 ± 0.012 eV. Photoelectron spectroscopic measurements have also been conducted for the other ion products of the O(•-) reaction with acetone. The photoelectron imaging spectrum of the acetylcarbene (AC) radical anion exhibits a broad, structureless feature, which is assigned to the X̃ (3)A'' state of AC. The ground ((2)A'') and first excited ((2)A') states of the 1-methylvinoxy (1-MVO) radical have been observed in the photoelectron spectrum of the 1-MVO ion, and their vibronic structure has been analyzed.

Product detection study of the gas-phase oxidation of methylphenyl radicals using synchrotron photoionisation mass spectrometry

Publisher: Royal Society of Chemistry (RSC)

Date: 2019

DOI: 10.1039/C9CP01935A

Abstract: Reactions of ortho and meta -methylphenyl radicals with oxygen form products that depend acutely on the position of the methyl group.

Experimental evidence for long-range stabilizing and destabilizing interactions between charge and radical sites in distonic ions

Publisher: Elsevier BV

Date: 2019

DOI: 10.1016/J.IJMS.2018.10.031

Systematic differences in membrane acyl composition associated with varying body mass in mammals occur in all phospholipid classes: An analysis of kidney and brain

Publisher: The Company of Biologists

Date: 10-2008

DOI: 10.1242/JEB.019968

Abstract: The acyl composition of membrane phospholipids in kidney and brain of mammals of different body mass was examined. It was hypothesized that reduction in unsaturation index (number of double bonds per 100 acyl chains)of membrane phospholipids with increasing body mass in mammals would be made-up of similar changes in acyl composition across all phospholipid classes and that phospholipid class distribution would be regulated and similar in the same tissues of the different-sized mammals. The results of this study supported both hypotheses. Differences in membrane phospholipid acyl composition (i.e. decreased omega-3 fats, increased monounsaturated fats and decreased unsaturation index with increasing body size) were not restricted to any specific phospholipid molecule or to any specific phospholipid class but were observed in all phospholipid classes. With increase in body mass of mammals both monounsaturates and use of less unsaturated polyunsaturates increases at the expense of the long-chain highly unsaturated omega-3 and omega-6 polyunsaturates, producing decreases in membrane unsaturation. The distribution of membrane phospholipid classes was essentially the same in the different-sized mammals with phosphatidylcholine (PC) and phosphatidylethanolamine (PE) together constituting ∼91% and ∼88% of all phospholipids in kidney and brain, respectively. The lack of sphingomyelin in the mouse tissues and higher levels in larger mammals suggests an increased presence of membrane lipid rafts in larger mammals. The results of this study support the proposal that the physical properties of membranes are likely to be involved in changing metabolic rate.

ZnO Colloid Crystal Facet-Type Determines both Au Photodeposition and Photocatalytic Activity

Publisher: American Chemical Society (ACS)

Date: 03-12-2019

DOI: 10.1021/ACSANM.9B01864

Identification of double bond position in lipids: From GC to OzID

Publisher: Elsevier BV

Date: 09-2009

DOI: 10.1016/J.JCHROMB.2009.01.017

Abstract: Recent developments in mass spectrometry and chromatography provide new possibilities for the identification and in some instances quantification of a wide range of lipids in complex matrices. These advances in analytical technologies have provided a tantalizing glimpse of the true structural ersity of lipids in nature and have reinvigorated interest in the role of lipids in biology. While technological advances have been impressive, difficulties in the ready identification of sites of unsaturation (i.e., double bond position) within these molecules presents a significant impediment to understanding lipid biochemistry. This is of particular importance given the growing body of literature suggesting that the presence of naturally occurring lipid double bond isomers can have a significant influence, both positive and negative, on the development of pathologies such as cancer, cardiovascular disease and type 2 diabetes. This article provides a critical review of the current suite of analytical approaches to the challenge of identification of the position of carbon-carbon double bonds in intact lipids.

Sex-specific triacylglycerides are widely conserved in Drosophila and mediate mating behavior

Publisher: eLife Sciences Publications, Ltd

Date: 11-03-2014

DOI: 10.7554/ELIFE.01751

Abstract: Pheromones play an important role in the behavior, ecology, and evolution of many organisms. The structure of many insect pheromones typically consists of a hydrocarbon backbone, occasionally modified with various functional oxygen groups. Here we show that sex-specific triacylclyerides (TAGs) are broadly conserved across the subgenus Drosophila in 11 species and represent a novel class of pheromones that has been largely overlooked. In desert-adapted drosophilids, 13 different TAGs are secreted exclusively by males from the ejaculatory bulb, transferred to females during mating, and function synergistically to inhibit courtship from other males. Sex-specific TAGs are comprised of at least one short branched tiglic acid and a long linear fatty acyl component, an unusual structural motif that has not been reported before in other natural products. The ersification of chemical cues used by desert-adapted Drosophila as pheromones may be related to their specialized diet of fermenting cacti.

Gas-Phase Internal Proton-Transfer of Protonated para-Aminobenzoic Acid Catalyzed by One Methanol Molecule

Publisher: American Chemical Society (ACS)

Date: 08-06-2023

DOI: 10.1021/JASMS.3C00118

Automated surface sampling of lipids from worn contact lenses coupled with tandem mass spectrometry

Publisher: Royal Society of Chemistry (RSC)

Date: 2013

DOI: 10.1039/C2AN36189B

Abstract: The deposition of biological material (biofouling) onto polymeric contact lenses is thought to be a major contributor to lens discomfort and hence discontinuation of wear. We describe a method to characterize lipid deposits directly from worn contact lenses utilizing liquid extraction surface analysis coupled to tandem mass spectrometry (LESA-MS/MS). This technique effected facile and reproducible extraction of lipids from the contact lens surfaces and identified lipid molecular species representing all major classes present in human tear film. Our data show that LESA-MS/MS is a rapid and comprehensive technique for the characterization of lipid-related biofouling on polymer surfaces.

Mapping Enzyme Activity on Tissue by Functional Mass Spectrometry Imaging

Publisher: Wiley

Date: 23-01-2020

DOI: 10.1002/ANIE.201911390

Concerted HO2 Elimination from alpha-Aminoalkylperoxyl Free Radicals: Experimental and Theoretical Evidence from the Gas-Phase NH2 center dot CHCO2- + O-2 Reaction

Publisher: American Chemical Society (ACS)

Date: 07-03-2012

DOI: 10.1021/JZ300118K

Abstract: We have investigated the gas-phase reaction of the α-aminoacetate (glycyl) radical anion (NH2(•)CHCO2(-)) with O2 using ion trap mass spectrometry, quantum chemistry, and statistical reaction rate theory. This radical is found to undergo a remarkably rapid reaction with O2 to form the hydroperoxyl radical (HO2(•)) and an even-electron imine (NHCHCO2(-)), with experiments and master equation simulations revealing that reaction proceeds at the ion-molecule collision rate. This reaction is facilitated by a low-energy concerted HO2(•) elimination mechanism in the NH2CH(OO(•))CO2(-) peroxyl radical. These findings can explain the widely observed free-radical-mediated oxidation of simple amino acids to amides plus α-keto acids (their imine hydrolysis products). This work also suggests that imines will be the main intermediates in the atmospheric oxidation of primary and secondary amines, including amine carbon capture solvents such as 2-aminoethanol (commonly known as monoethanolamine, or MEA), in a process that avoids the ozone-promoting conversion of (•)NO to (•)NO2 commonly encountered in peroxyl radical chemistry.

The Loss of Carbon Dioxide from Activated Perbenzoate Anions in the Gas Phase:  Unimolecular Rearrangement via Epoxidation of the Benzene Ring

Publisher: American Chemical Society (ACS)

Date: 22-09-2006

DOI: 10.1021/JO060730A

Abstract: The unimolecular reactivities of a range of perbenzoate anions (X-C6H5CO3-), including the perbenzoate anion itself (X = H), nitroperbenzoates (X = para-, meta-, ortho-NO2), and methoxyperbenzoates (X = para-, meta-OCH3) were investigated in the gas phase by electrospray ionization tandem mass spectrometry. The collision-induced dissociation mass spectra of these compounds reveal product ions consistent with a major loss of carbon dioxide requiring unimolecular rearrangement of the perbenzoate anion prior to fragmentation. Isotopic labeling of the perbenzoate anion supports rearrangement via an initial nucleophilic aromatic substitution at the ortho carbon of the benzene ring, while data from substituted perbenzoates indicate that nucleophilic attack at the ipso carbon can be induced in the presence of electron-withdrawing moieties at the ortho and para positions. Electronic structure calculations carried out at the B3LYP/6-311++G(d,p) level of theory reveal two competing reaction pathways for decarboxylation of perbenzoate anions via initial nucleophilic substitution at the ortho and ipso positions, respectively. Somewhat surprisingly, however, the computational data indicate that the reaction proceeds in both instances via epoxidation of the benzene ring with decarboxylation resulting--at least initially--in the formation of oxepin or benzene oxide anions rather than the energetically favored phenoxide anion. As such, this novel rearrangement of perbenzoate anions provides an intriguing new pathway for epoxidation of the usually inert benzene ring.

Discrimination between Protonation Isomers of Quinazoline by Ion Mobility and UV-Photodissociation Action Spectroscopy

Publisher: American Chemical Society (ACS)

Date: 05-05-2001

DOI: 10.1021/ACS.JPCLETT.0C01009

Mass spectrometry as a tool to advance polymer science

Publisher: Springer Science and Business Media LLC

Date: 06-03-2020

DOI: 10.1038/S41570-020-0168-1

Ozonolysis of phospholipid double bonds during electrospray ionization: A new tool for structure determination

Publisher: American Chemical Society (ACS)

Date: 14-12-2006

DOI: 10.1021/JA056797H

Abstract: Ozonolysis of double bonds is observed during the negative ion electrospray ionization of unsaturated phospholipids under conditions that produce a corona discharge. Ionic products of the ozonolysis are detected and characterized by mass spectrometry, and the mass-to-charge ratio of these species can be used to unambiguously assign the double bond position within the unsaturated fatty acid radyls. The reaction products are consistent with the gas-phase ozonolysis of desolvated phospholipid ions in an atmosphere rich in volatilized solvent. Reactions may be carried out in a conventional electrospray ionization mass spectrometer and provide a new method for the structural characterization of phospholipids.

Inside Cover: Resolving Sphingolipid Isomers Using Cryogenic Infrared Spectroscopy (Angew. Chem. Int. Ed. 32/2020)

Publisher: Wiley

Date: 22-06-2020

DOI: 10.1002/ANIE.202007701

Conversion of Linear to Rhombic C₄ in the Gas Phase:  A Joint Experimental and Theoretical Study

Publisher: American Chemical Society (ACS)

Date: 11-07-2000

DOI: 10.1021/JA000951C

Heat of Formation of the Hydroperoxyl Radical HOO Via Negative Ion Studies

Publisher: American Chemical Society (ACS)

Date: 18-07-2002

DOI: 10.1021/JP014614H

Analytical separations for lipids in complex, nonpolar lipidomes using differential mobility spectrometry

Publisher: Elsevier BV

Date: 11-2019

DOI: 10.1194/JLR.D094854

Mapping Enzyme Activity on Tissue by Functional Mass Spectrometry Imaging

Publisher: Wiley

Date: 23-01-2020

DOI: 10.1002/ANGE.201911390

Queensland University Of Technology

Location: Australia

View Organisation

University Of Adelaide

Location: Australia

View Organisation

Linkage Projects - Grant ID: LP0989883

Start Date: 09-2009

End Date: 09-2012

Amount: $303,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE100100087

Start Date: 2010

End Date: 12-2010

Amount: $450,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0882289

Start Date: 2008

End Date: 12-2008

Amount: $520,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0452849

Start Date: 2004

End Date: 12-2007

Amount: $330,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP110200648

Start Date: 02-2012

End Date: 12-2015

Amount: $267,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0453832

Start Date: 2004

End Date: 12-2005

Amount: $550,910.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP150101715

Start Date: 2015

End Date: 12-2017

Amount: $434,700.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP170101596

Start Date: 06-2017

End Date: 12-2021

Amount: $365,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0989078

Start Date: 09-2009

End Date: 12-2009

Amount: $400,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0668374

Start Date: 2006

End Date: 12-2006

Amount: $470,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP140100711

Start Date: 06-2015

End Date: 06-2019

Amount: $450,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0986738

Start Date: 2009

End Date: 12-2011

Amount: $320,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE130100096

Start Date: 2013

End Date: 01-2014

Amount: $235,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP180100238

Start Date: 09-2019

End Date: 09-2022

Amount: $293,985.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP190101486

Start Date: 2019

End Date: 12-2024

Amount: $655,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0455472

Start Date: 09-2004

End Date: 08-2007

Amount: $150,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE190100106

Start Date: 03-2019

End Date: 12-2019

Amount: $334,425.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP110200322

Start Date: 02-2012

End Date: 04-2015

Amount: $300,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0775032

Start Date: 11-2007

End Date: 12-2011

Amount: $117,354.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE120100059

Start Date: 01-2012

End Date: 12-2012

Amount: $220,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0453771

Start Date: 2004

End Date: 12-2005

Amount: $148,246.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE110100093

Start Date: 2011

End Date: 11-2011

Amount: $600,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE220100031

Start Date: 06-2022

End Date: 05-2023

Amount: $630,880.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP140101237

Start Date: 06-2014

End Date: 12-2017

Amount: $360,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP120102922

Start Date: 2012

End Date: 12-2016

Amount: $380,000.00

Funder: Australian Research Council

ARC Centres Of Excellence - Grant ID: CE0561607

Start Date: 12-2005

End Date: 10-2015

Amount: $21,800,000.00

Funder: Australian Research Council