ORCID Profile
0000-0003-3944-7427
Current Organisations
Oklahoma State University
,
Karlsruhe Institute of Technology
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Publisher: Wiley
Date: 02-09-2010
Publisher: American Chemical Society (ACS)
Date: 30-10-2012
DOI: 10.1021/IC301347T
Abstract: Two new dinucleating ligands (H3L(2) and HL(3)), derivatives of a well-known dinucleating ligand (HL(1)) with two bis-picolylamine sites connected to a bridging phenolate, with hydrogen-bonding donor groups at two of the pyridine moieties were designed and synthesized. Design of these ligands suggests that they will lead to dinuclear complexes with potential to stabilize phosphoester substrates as monodentate rather than bridging ligands. We report the diferric complexes [Fe(III)2(H2L(2))(OH)](4+) and [Fe(III)2(L(3))(OH)(OH2)2](4+), which have been characterized by spectrophotometric titrations, UV-vis, IR, NMR, EPR, and Mössbauer spectroscopy. The phosphatase activity of the diferric systems, in addition to the partially reduced heterovalent [Fe(III)Fe(II)(L(3))(OH)(OH2)2](3+) complex, has been investigated, and the complexes are shown to catalytically hydrolyze the activated phosphodiester substrate BDNPP (bis-dinitrophenylphosphate) as well as the corresponding phosphomonoester substrate DNPP (dinitrophenylphosphate). The results indicate that indeed the secondary interactions lead to an increase of the phosphatase activity and to active phosphomonoesterase catalysts. Interestingly, the heterovalent form of the HL(3)-based complex is more efficient than the diferric complex, and this is also discussed.
Publisher: Royal Society of Chemistry (RSC)
Date: 1993
DOI: 10.1039/P19930002317
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA90142D
Publisher: Routledge
Date: 11-09-2002
Publisher: Wiley
Date: 03-06-2022
Abstract: Four new heterometallic trinuclear essentially linear (“in‐line”) M II 2 Dy III complexes (M=Cd II ( 1 ), Co II ( 2 ), Cu II ( 3 , 4 ) were synthesised using the ligand 3,5‐di‐ tert ‐butylbenzoic acid (dtbbaH) in a MeCN : i PrOH ( 1–3 ) or in a MeOH : i PrOH : DMF ( 4 ) mixture. Single crystal structure analyses revealed the formation of [Cd 2 Dy(dtbba) 6 ( i PrOH) 2 (H 2 O) 2 NO 3 ] ⋅ i PrOH ( 1 ), [Co 2 Dy(dtbba) 6 ( i PrOH) 2 (H 2 O) 2 NO 3 ] ⋅ i PrOH ( 2 ), [Cu 2 Dy(dtbba) 6 (MeCN) 4 NO 3 ] ⋅ MeCN ( 3 ) and [Cu 2 Dy(dtbba) 6 ( i PrOH) 1.68 (DMF) 1.32 (H 2 O)NO 3 ] ⋅ 3 i PrOH ⋅ H 2 O ( 4 ). The M−Dy−M angles become more acute from ( 1 ) to ( 3 ) leading to decreased M⋅⋅M distances. The Dy III ions are 8‐coordinate with a distorted triangular dodecahedron geometry and a D 2d symmetry whereas the geometry of the 5‐coordinate terminal M II ions can best be described as either distorted vacant octahedra or as spherical square pyramids with a C 4v symmetry. Magnetic susceptibility measurements were performed on ( 1 ), ( 2 ) and ( 3 ) which allows a comparison of the effect of replacing highly anisotropic Co II with the quantum spin of Cu II . Both ( 2 ) and ( 3 ) show effects of ferromagnetic interactions at low temperatures.
Publisher: American Chemical Society (ACS)
Date: 21-07-2015
DOI: 10.1021/ACS.INORGCHEM.5B00628
Abstract: The active site of mammalian purple acid phosphatases (PAPs) have a dinuclear iron site in two accessible oxidation states (Fe(III)2 and Fe(III)Fe(II)), and the heterovalent is the active form, involved in the regulation of phosphate and phosphorylated metabolite levels in a wide range of organisms. Therefore, two sites with different coordination geometries to stabilize the heterovalent active form and, in addition, with hydrogen bond donors to enable the fixation of the substrate and release of the product, are believed to be required for catalytically competent model systems. Two ligands and their dinuclear iron complexes have been studied in detail. The solid-state structures and properties, studied by X-ray crystallography, magnetism, and Mössbauer spectroscopy, and the solution structural and electronic properties, investigated by mass spectrometry, electronic, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and Mössbauer spectroscopies and electrochemistry, are discussed in detail in order to understand the structures and relative stabilities in solution. In particular, with one of the ligands, a heterovalent Fe(III)Fe(II) species has been produced by chemical oxidation of the Fe(II)2 precursor. The phosphatase reactivities of the complexes, in particular, also of the heterovalent complex, are reported. These studies include pH-dependent as well as substrate concentration dependent studies, leading to pH profiles, catalytic efficiencies and turnover numbers, and indicate that the heterovalent diiron complex discussed here is an accurate PAP model system.
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A704388K
Publisher: Wiley
Date: 10-01-2012
Abstract: The synthesis and characterization of a novel dinucleating ligand L (L=4,11-dimethyl-1,8-bis{2-[N-(di-2-pyridylmethyl)amino]ethyl}cyclam) and its μ-oxo-bridged diferric complex [(H(2)L){Fe(III)(2)(O)}(Cl)(4)](2+) are reported. This diiron(III) complex is the first ex le of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4-dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)-bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)-bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time.
Publisher: American Chemical Society (ACS)
Date: 08-11-2011
DOI: 10.1021/IC201157M
Abstract: Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl(3)·(H(2)O)(m)] with dibenzoylmethane (Ph(2)acacH) and a base. Using cesium carbonate (Cs(2)CO(3)) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph(2)acac)(4)}](n) (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl(3)·(H(2)O)(6)] with Ph(2)acacH resulted in [K{Nd(Ph(2)acac)(4)}](n) (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph(2)acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1-5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the in idual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump robe experiments with DMF solutions of 1-5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S(1) to T(1) level of the ligands. Magnetic studies show that [Cs{Dy(Ph(2)acac)(4)}](n) (4) has slow relaxation of the magnetization arising from the single Dy(3+) ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.
Publisher: Wiley
Date: 15-04-2009
Abstract: By deprotonation of the corresponding tris(pyrazolyl)methane ((Me)Tpm) precursor complexes [M((Me)Tpm)(2)][(OTf)(2)] (1 and 2), the zwitterionic tris(pyrazolyl)methanide iron(II) (3) and cobalt(II) (4) "sandwich" complexes of the general formula [M((Me)Tpmd)(2)] are easily accessible. The structurally characterised complexes 3 and 4 are the first such homoleptic 3d transition metal species to feature two "naked", outward pointing pyramidal carbanions. Density functional theory calculations show metal-centred HOMOs and LUMOs with the destabilised carbanion orbitals in the energy region of the filled transition-metal-centred frontier orbitals. The electronic structures of these complexes have been investigated in detail by various spectroscopic techniques such as NMR, EPR, SQUID, Mössbauer, etc. Both complexes adopt a high-spin (HS) configuration at room temperature in solution and in the solid state. A thermally induced high-spin to low-spin (HS-LS) transition is observed for the iron(II) complex 3. The HS-LS transition temperature of 3 in solution differs from that in the solid state, which in turn strongly depends on the amount of solvent molecules in the crystal lattice. Electrochemical studies on the corresponding cobalt(II) complex 4 provide evidence for a HS-Co(II) LS-Co(III) transition upon oxidation, which was confirmed by preliminary synthetic oxidation reactions. Overall, it can be concluded that the related kappa(3)N-donor ligands tris(pyrazolyl)hydroborates (Tp(R)) and (R)Tpmd ligands have similar bonding properties and that the metal cations experience more or less the same ligand environment.
No related grants have been discovered for Annie Powell.