Quantitative analysis of dinuclear manganese(II) EPR spectra

Golombek, Adina; Hendrich, Michael P.

doi:10.1016/j.jmr.2003.07.001

Cited by 104 publications

(104 citation statements)

References 64 publications

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“…2) 21,22 . Simulation of the EPR signals of 4 using the SpinCount software 26 shows that this species is formed in B20% yield, an amount that is higher than that reported by Talsi, but still not high enough to determine its oxidation state reliably via Mössbauer spectroscopy.…”

Section: Resultsmentioning

confidence: 70%

“…4) (Fig. 2, inset) that represents 47% of the Fe in the sample based on a SpinCount simulation 26 , as indicated by the red line. The fraction of Fe represented by this species is 3-7 times higher than that reported for the g ¼ 2.7 species by Lyakin et al 21,22 There are also two additional S ¼ 5/2 signals that arise from high-spin (S ¼ 5/2) iron(III): a major component (purple curve, E30% of Fe) that originates from the upper Kramers doublet of a species with DE À 0.8 cm À 1 and E/DE0.10 and a minor fraction (green curve, B5 % of Fe) with E/DE1/3 that gives rise to the resonance at g ¼ 4.3.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, the spin-dipolar and (large) orbital contributions along z are positive, yielding a positive A z . Using the model of Oosterhuis and Lang 35 implemented in SpinCount 26 , we obtained D ¼ 1,015 cm À 1 and V ¼ 1,157 for the tetragonal and rhombic crystal field splittings, respectively (using lE380 cm À 1 for the spin-orbit coupling constant). Using the scaling factors P ¼ 2g n b n /r À 3 S ¼ 85 MHz and k ¼ 0.35 (see equation (10) The Mossbauer assignment of 4* as a low-spin iron(III) species and the requirement that 4* must have the two oxidising equivalents to carry out olefin epoxidation lead us to propose 4* as a low-spin acylperoxoiron(III) complex.…”

Section: Resultsmentioning

confidence: 99%

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Identification of a low-spin acylperoxoiron(III) intermediate in bio-inspired non-heme iron-catalysed oxidations

et al. 2014

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Synthetically useful hydrocarbon oxidations are catalysed by bio-inspired non-heme iron complexes using hydrogen peroxide as oxidant, and carboxylic acid addition enhances their selectivity and catalytic efficiency. Talsi has identified a low-intensity g ¼ 2.7 electron paramagnetic resonance signal in such catalytic systems and attributed it to an oxoiron(V)-carboxylate oxidant. Herein we report the use of Fe II (TPA*) (TPA* ¼ tris (3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) to generate this intermediate in 50% yield, and have characterized it by ultraviolet-visible, resonance Raman, Mössbauer and electrospray ionization mass spectrometric methods as a low-spin acylperoxoiron(III) species. Kinetic studies show that this intermediate is not itself the oxidant but decays via a unimolecular rate-determining step to unmask a powerful oxidant. The latter is shown by density functional theory calculations to be an oxoiron(V) species that oxidises substrate without a barrier. This study provides a mechanistic scenario for understanding catalyst reactivity and selectivity as well as a basis for improving catalyst design.

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Section: Resultsmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Identification of a low-spin acylperoxoiron(III) intermediate in bio-inspired non-heme iron-catalysed oxidations

et al. 2014

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“…EPR simulations were performed using SpinCount, which was written by and obtained from Prof. Michael P. Hendrich. 4 In order to obtain a reasonable fit for the trimer, the transitions from both ms states (|±1/2⟩ & |±3/2⟩) were included. Magnetic susceptibility measurements were obtained using a Quantum Designs SQUID magnetometer running MPMSR2 software.…”

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confidence: 99%

The Cobalt Hydride that Never Was: Revisiting Schrauzer’s “Hydridocobaloxime”

2015

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Molecular cobalt-dmg (dmg = dimethylglyoxime) complexes are an important class of electrocatalysts used heavily in mechanistic model studies of the hydrogen evolution reaction (HER). Schrauzer’s early isolation of a phosphine-stabilized “[H-CoIII(dmgH)2P(nBu)3]” complex has long provided circumstantial support for the plausible intermediacy of Co(III)-H species in HER by cobaloximes in solution. Our investigation of this complex has led to a reassignment of its structure as [CoII(dmgH)2P(nBu)3], a complex that contains no hydride ligand and dimerizes to form an unsupported Co–Co bond in the solid state. A paramagnetic S = 3/2 impurity that forms during the synthesis of [CoII(dmgH)2P(nBu)3] when exposed to adventitious oxygen has also been characterized. This impurity features a 1H NMR resonance at −5.06 ppm that was recently but erroneously attributed to the hydride resonance of “[H-CoIII(dmgH)2P(nBu)3]”. We draw attention to this reassignment because of its relevance to cobaloxime hydrides and HER catalysis and because Schrauzer’s “hydridocobaloxime” is often cited as the primary example of a bona fide hydride that can be isolated and characterized on this widely studied HER platform.

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“…20,21 Many proteins contain binuclear manganese centers (catalases, thiosulfate oxidase, dinitrogen reductase regulatory protein, and aminopeptidases and λ protein phosphatase). 22 Divalent manganese is also an active Arginase is one of the best-studied non-redox enzymes, which structure is shown in Figure 4. Two Mncenters are bridged through hydroxide which hydrogen forms H-bond with uncoordinated oxygen atom of Asp-128 residue.…”

Section: Introductionmentioning

confidence: 99%

"SYNTHESIS AND SPECTRAL CHARACTERIZATION OF Fe(II) AND Mn(II) COMPLEXES WITH ORAL FLUOROURACIL PRO-DRUG CAPECITABINE "

2017

RJC

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Malignant neoplasms are today one of the leading causes of death in the world. Their treatment is extremely complex and requires the application of various chemical compounds which leads to disruption of homeostasis in the human body. During a treatment, there is a possibility of complex formation with important bioelements, such as copper, iron, cobalt, manganese, and others in the biological system. This paper presents the results of possible formation of complexes between Fe(II) and Mn(II) ions and capecitabine (IUPAC name: pentyl 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-methyl-tetra-hydrofuran-2-yl)-5-fluoro-2-oxo-1,2-dihydropyrimidin-4-yl carbamate). This chemotherapeutic agent is often used for the treatment of different solid tumors including breast, colon, prostate, liver and gastrointestinal tract carcinoma. Spectroscopic methods (UV/Vis and FT-IR spectroscopy) were used in order to research specific compounds between CPC and metal ions that may be formed in human body under physiological and approximately physiological conditions. In addition, microscopic characterization and comparison of solid samples of capecitabine and products of interactions of CPC as a ligand with Fe(II) and Mn(II) ions have been performed. FT-IR spectra indicate the existence of interaction of these two divalent bio cations with CPC, i.e. their coordination through nitrogen and oxygen atoms of CPC. When UV spectra of pure ligand and model systems M(II)-CPC were compared, similar absorption bands were observed with absorption maxima at the same wavenumbers but lower absorbance values for model systems M(II)-CPC.

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Quantitative analysis of dinuclear manganese(II) EPR spectra

Cited by 104 publications

References 64 publications

Identification of a low-spin acylperoxoiron(III) intermediate in bio-inspired non-heme iron-catalysed oxidations

Identification of a low-spin acylperoxoiron(III) intermediate in bio-inspired non-heme iron-catalysed oxidations

The Cobalt Hydride that Never Was: Revisiting Schrauzer’s “Hydridocobaloxime”

"SYNTHESIS AND SPECTRAL CHARACTERIZATION OF Fe(II) AND Mn(II) COMPLEXES WITH ORAL FLUOROURACIL PRO-DRUG CAPECITABINE "

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