ORCID Profile
0000-0001-9443-0834
Current Organisation
UNSW Sydney
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Publisher: Cambridge University Press (CUP)
Date: 03-09-2021
DOI: 10.33774/CHEMRXIV-2021-XPP8V
Abstract: The measured changes in self-diffusion of small molecules during reactions have been attributed “boosted mobility”. We demonstrate the critical role of changing concentrations of paramagnetic ions on nuclear magnetic resonance (NMR) signal intensities, which lead to erroneous measurements of diffusion coefficients. We present simple methods to overcome this problem. The use of shuffled gradient litudes allows accurate diffusion NMR measurements, even with time-dependent relaxation rates caused by changing concentrations of paramagnetic ions. The addition of a paramagnetic relaxation agent allows accurate determination of both diffusion coefficients and reaction kinetics during a single experiment. We analyze a copper-catalyzed azide-alkyne cycloaddition ‘click’ reaction, for which boosted mobility has been claimed. With our methods, we accurately measure the diffusive behavior of solvent, starting materials and product, and find no global increase in diffusion coefficients during the reaction. We overcome NMR signal overlap using an alternative reducing agent to improve the accuracy of the diffusion measurements. The alkyne reactant diffuses slower as the reaction proceeds, due to binding to the copper catalyst during the catalytic cycle. The formation of this intermediate was confirmed by complementary NMR techniques and density functional theory calculations. Our work calls into question recent claims that molecules actively propel or swim during reactions, and establishes that time-resolved diffusion NMR measurements can provide valuable insight into reaction mechanisms.
Publisher: American Chemical Society (ACS)
Date: 05-10-2020
DOI: 10.26434/CHEMRXIV.13023164.V1
Abstract: The apparent “boosted mobility” observed by nuclear magnetic resonance (NMR) diffusion measurements is the result of a known artefact. When signal intensities are changing during an NMR diffusion measurement for reasons other than diffusion, the use of monotonically increasing gradient litudes produces erroneous diffusion coefficient values. We show that no boosted molecular mobility is observed when shuffled gradient litudes are applied.
Publisher: American Chemical Society (ACS)
Date: 25-11-2020
DOI: 10.26434/CHEMRXIV.12950858
Abstract: Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a Rhodamine B dye encapsulated in gels formed from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.
Publisher: American Chemical Society (ACS)
Date: 11-01-2022
DOI: 10.1021/ACSMACROLETT.1C00719
Abstract: Online, high-throughput molecular weight analysis of polymerizations is rare, with most studies relying on tedious s ling techniques and batchwise postanalysis. The ability to track both monomer conversion and molecular weight evolution in real time could underpin precision polymer development and facilitate study of rapid polymerization reactions. Here, we use a single time-resolved diffusion nuclear magnetic resonance (NMR) experiment to simultaneously study the kinetics and molecular weight evolution during a photopolymerization, with in situ irradiation inside the NMR instrument. As a model system, we used a photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The data allow diffusion coefficients and intensities to be calculated every 14 s from which the polymer size and monomer conversion can be extracted. Key to this approach is (1) the use of shuffled gradient litudes in the diffusion NMR experiment to access reactions of any rate, (2) the addition of a relaxation agent to increase achievable time resolution and, (3) a sliding correction that accounts for viscosity changes during polymerization. Diffusion NMR offers a uniquely simple, translatable handle for online monitoring of polymerization reactions.
Publisher: Wiley
Date: 13-04-2023
Abstract: Polydopamine (PDA) is a synthetic model for melanin and has a wide range of opto‐electronic properties that underpin its utility in applied and biological settings, from broadband light absorbance to possessing stable free radical species. Here, we show that PDA free radicals are photo‐responsive under visible light irradiation, enabling PDA to serve as a photo‐redox catalyst. Steady‐state and transient electron spin resonance spectroscopy reveals a reversible lification in semiquinone radical population within PDA under visible light. This photo‐response modifies the redox potential of PDA and supports sensitisation of exogenous species via photoinduced electron transfer (PET). We demonstrate the utility of this discovery by employing PDA nanoparticles to photosensitise a common diaryliodonium photoinitiator and initiate free‐radical polymerisation (FRP) of vinylic monomers. In situ 1 H nuclear magnetic resonance spectroscopy reveals an interplay between PDA‐driven photosensitising and radical quenching during FRP under blue, green, and red light. This work provides crucial insights into the photoactive free radical properties of melanin‐like materials and reveals a promising new application for polydopamine as a photosensitiser.
Publisher: American Chemical Society (ACS)
Date: 29-03-2021
DOI: 10.26434/CHEMRXIV.14306771
Abstract: A study reported in The Journal of Physical Chemistry Letters (12 (2021) 2370) of “boosted mobility” measured by diffusion NMR experiments contains significant errors in data analysis and interpretation. We carefully reanalyzed the same data and find no evidence of boosted mobility, and we identify several sources of error.
Publisher: Wiley
Date: 12-04-2023
Abstract: Polydopamine (PDA) is a synthetic model for melanin and has a wide range of opto‐electronic properties that underpin its utility in applied and biological settings, from broadband light absorbance to possessing stable free radical species. Here, we show that PDA free radicals are photo‐responsive under visible light irradiation, enabling PDA to serve as a photo‐redox catalyst. Steady‐state and transient electron spin resonance spectroscopy reveals a reversible lification in semiquinone radical population within PDA under visible light. This photo‐response modifies the redox potential of PDA and supports sensitisation of exogenous species via photoinduced electron transfer (PET). We demonstrate the utility of this discovery by employing PDA nanoparticles to photosensitise a common diaryliodonium photoinitiator and initiate free‐radical polymerisation (FRP) of vinylic monomers. In situ 1 H nuclear magnetic resonance spectroscopy reveals an interplay between PDA‐driven photosensitising and radical quenching during FRP under blue, green, and red light. This work provides crucial insights into the photoactive free radical properties of melanin‐like materials and reveals a promising new application for polydopamine as a photosensitiser.
Publisher: American Chemical Society (ACS)
Date: 05-10-2020
DOI: 10.26434/CHEMRXIV.13023164
Abstract: The apparent “boosted mobility” observed by nuclear magnetic resonance (NMR) diffusion measurements is the result of a known artefact. When signal intensities are changing during an NMR diffusion measurement for reasons other than diffusion, the use of monotonically increasing gradient litudes produces erroneous diffusion coefficient values. We show that no boosted molecular mobility is observed when shuffled gradient litudes are applied.
Publisher: American Chemical Society (ACS)
Date: 26-07-2022
Publisher: American Association for the Advancement of Science (AAAS)
Date: 15-01-2021
Abstract: The apparent “boosted mobility” observed by Wang et al . (Reports, 31 July 2020, p. 537) is the result of a known artifact. When signal intensities are changing during a nuclear magnetic resonance (NMR) diffusion measurement for reasons other than diffusion, the use of monotonically increasing gradient litudes produces erroneous diffusion coefficients. We show that no boosted molecular mobility is observed when shuffled gradient litudes are applied.
Publisher: Wiley
Date: 19-02-2022
Abstract: A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self‐assembled metallosupramolecular structures. The photoswitching ligand is an ortho ‐fluoroazobenzene with appended pyridyl groups. Combining the E ‐isomer with palladium(II) salts affords a double‐walled triangle with composition [Pd 3 L 6 ] 6+ and a distorted tetrahedron [Pd 4 L 8 ] 8+ (1 : 2 ratio at 298 K). Irradiation with 410 nm light generates a photostationary state with approximately 80 % of the E‐ isomer of the ligand and results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the more kinetically inert product. The triangle is then slowly transformed back into the tetrahedron over 2 days at 333 K. The Z ‐isomer of the ligand does not form any well‐defined structures and has a thermal half‐life of 25 days at 298 K. This approach shows how a thermodynamically preferred self‐assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non‐destructive visible light.
Publisher: American Chemical Society (ACS)
Date: 03-08-2022
DOI: 10.1021/JACS.2C02830
Abstract: In their Comment (DOI: 10.1021/jacs.2c02965) on two related publications by our groups (
Publisher: American Chemical Society (ACS)
Date: 03-09-2021
DOI: 10.26434/CHEMRXIV-2021-XPP8V
Abstract: The measured changes in self-diffusion of small molecules during reactions have been attributed “boosted mobility”. We demonstrate the critical role of changing concentrations of paramagnetic ions on nuclear magnetic resonance (NMR) signal intensities, which lead to erroneous measurements of diffusion coefficients. We present simple methods to overcome this problem. The use of shuffled gradient litudes allows accurate diffusion NMR measurements, even with time-dependent relaxation rates caused by changing concentrations of paramagnetic ions. The addition of a paramagnetic relaxation agent allows accurate determination of both diffusion coefficients and reaction kinetics during a single experiment. We analyze a copper-catalyzed azide-alkyne cycloaddition ‘click’ reaction, for which boosted mobility has been claimed. With our methods, we accurately measure the diffusive behavior of solvent, starting materials and product, and find no global increase in diffusion coefficients during the reaction. We overcome NMR signal overlap using an alternative reducing agent to improve the accuracy of the diffusion measurements. The alkyne reactant diffuses slower as the reaction proceeds, due to binding to the copper catalyst during the catalytic cycle. The formation of this intermediate was confirmed by complementary NMR techniques and density functional theory calculations. Our work calls into question recent claims that molecules actively propel or swim during reactions, and establishes that time-resolved diffusion NMR measurements can provide valuable insight into reaction mechanisms.
Publisher: American Chemical Society (ACS)
Date: 29-03-2021
DOI: 10.26434/CHEMRXIV.14306771.V1
Abstract: A study reported in The Journal of Physical Chemistry Letters (12 (2021) 2370) of “boosted mobility” measured by diffusion NMR experiments contains significant errors in data analysis and interpretation. We carefully reanalyzed the same data and find no evidence of boosted mobility, and we identify several sources of error.
Publisher: American Chemical Society (ACS)
Date: 11-04-2022
DOI: 10.1021/JACS.2C02073
Abstract: Modifying surfaces using free radical polymerization (FRP) offers a means to incorporate the erse physicochemical properties of vinyl polymers onto new materials. Here, we harness the universal surface attachment of polydopamine (PDA) to "prime" a range of different surfaces for free radical polymer attachment, including glass, cotton, paper, sponge, and stainless steel. We show that the intrinsic free radical species present in PDA can serve as an anchor point for subsequent attachment of propagating vinyl polymer macroradicals through radical-radical coupling. Leveraging a straightforward, twofold soak-wash protocol, FRP over the PDA-functionalized surfaces results in covalent polymer attachment on both porous and nonporous substrates, imparting new properties to the functionalized materials, including enhanced hydrophobicity, fluorescence, or temperature responsiveness. Our strategy is then extended to covalently incorporate PDA nanoparticles into organo-/hydrogels via radical cross-linking, yielding tunable PDA-polymer composite networks. The propensity of PDA free radicals to quench FRP is studied using in situ
Publisher: Wiley
Date: 03-02-2021
Publisher: American Chemical Society (ACS)
Date: 22-09-2020
DOI: 10.26434/CHEMRXIV.12950858.V3
Abstract: Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a Rhodamine B dye encapsulated in gels formed from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.
Publisher: American Chemical Society (ACS)
Date: 25-11-2020
DOI: 10.26434/CHEMRXIV.12950858.V4
Abstract: Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a Rhodamine B dye encapsulated in gels formed from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.
Publisher: Wiley
Date: 03-02-2021
Publisher: American Chemical Society (ACS)
Date: 15-09-2020
DOI: 10.26434/CHEMRXIV.12950858.V1
Abstract: Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron macroscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a Rhodamine B dye encapsulated in gels formed from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.
Publisher: American Chemical Society (ACS)
Date: 02-12-2021
DOI: 10.1021/JACS.1C09455
Abstract: The reported changes in self-diffusion of small molecules during reactions have been attributed to "boosted mobility". We demonstrate the critical role of changing concentrations of paramagnetic ions on nuclear magnetic resonance (NMR) signal intensities, which led to erroneous measurements of diffusion coefficients. We present simple methods to overcome this problem. The use of shuffled gradient litudes allows accurate diffusion NMR measurements, even with time-dependent relaxation rates caused by changing concentrations of paramagnetic ions. The addition of a paramagnetic relaxation agent allows accurate determination of both diffusion coefficients and reaction kinetics during a single experiment. We analyze a copper-catalyzed azide-alkyne cycloaddition "click" reaction, for which boosted mobility has been claimed. With our methods, we accurately measure the diffusive behavior of the solvent, starting materials, and product and find no global increase in diffusion coefficients during the reaction. We overcome NMR signal overlap using an alternative reducing agent to improve the accuracy of the diffusion measurements. The alkyne reactant diffuses slower as the reaction proceeds due to binding to the copper catalyst during the catalytic cycle. The formation of this intermediate was confirmed by complementary NMR techniques and density functional theory calculations. Our work calls into question recent claims that molecules actively propel or swim during reactions and establishes that time-resolved diffusion NMR measurements can provide valuable insight into reaction mechanisms.
Publisher: American Chemical Society (ACS)
Date: 16-09-2020
DOI: 10.26434/CHEMRXIV.12950858.V2
Abstract: Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a Rhodamine B dye encapsulated in gels formed from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.
No related grants have been discovered for Lucy Fillbrook.