Disproportionation of Aquachromyl(IV) Ion by Hydrogen Abstraction from Coordinated Water

Nemes, Attila; Bakač, Andreja

doi:10.1021/ic0013577

Cited by 26 publications

(20 citation statements)

References 43 publications

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“…[3] This unexpected result cannot be explained by any classical ET mechanism and some alternative explanation should be considered. Similar unusual behaviour has been reported for cobalt, [4] manganese [5,6] and chromium [7] self-exchange reactions in aqueous media. [8] Understanding these apparent anomalies is important because aquo or hydroxo complexes of transition metals are, in many cases, the heart of redox centres in enzymes such as horseradish peroxidase, [9] ribonucleotide reductase [10,11] and Chlamydia trachomatis ribonucleotide reductase.…”

supporting

confidence: 84%

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

Campaña

Buñuel

Cuerva

et al. 2013

Chemistry A European J

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supporting

confidence: 84%

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

Campaña

Buñuel

Cuerva

et al. 2013

Chemistry A European J

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“…HAT to metal-oxo complexes, the reverse of the latter part of equation 14, is well known (Mayer 1998;Meyer and Huynh 2003). However, the ability of aquo or hydroxo complexes to act as H-atom donors is less common (see Binstead et al 1995;Nemes and Bakac 2001;Jensen et al 2001). To our knowledge there are no clear examples of concerted H + and e ) transfer from an aquo complex to different acceptors, a process that would resemble the PCET in HOAr-NH 2 described above.…”

Section: Toward a Model For Proton-coupled Electron Transfer From A Mmentioning

confidence: 99%

Models for Proton-coupled Electron Transfer in Photosystem II

et al. 2006

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The coupling of proton and electron transfers is a key part of the chemistry of photosynthesis. The oxidative side of photosystem II (PS II) in particular seems to involve a number of proton-coupled electron transfer (PCET) steps in the S-state transitions. This mini-review presents an overview of recent studies of PCET model systems in the authors' laboratory. PCET is defined as a chemical reaction involving concerted transfer of one electron and one proton. These are thus distinguished from stepwise pathways involving initial electron transfer (ET) or initial proton transfer (PT). Hydrogen atom transfer (HAT) reactions are one class of PCET, in which H(+) and e (-) are transferred from one reagent to another: AH + B --> A + BH, roughly along the same path. Rate constants for many HAT reactions are found to be well predicted by the thermochemistry of hydrogen transfer and by Marcus Theory. This includes organic HAT reactions and reactions of iron-tris(alpha-diimine) and manganese-(mu-oxo) complexes. In PS II, HAT has been proposed as the mechanism by which the tyrosine Z radical (Y(Z)*) oxidizes the manganese cluster (the oxygen evolving complex, OEC). Another class of PCET reactions involves transfer of H(+) and e (-) in different directions, for instance when the proton and electron acceptors are different reagents, as in AH-B + C(+) --> A-HB(+) + C. The oxidation of Y(Z) by the chlorophyll P680 + has been suggested to occur by this mechanism. Models for this process - the oxidation of phenols with a pendent base - are described. The oxidation of the OEC by Y(Z)* could also occur by this second class of PCET reactions, involving an Mn-O-H fragment of the OEC. Initial attempts to model such a process using ruthenium-aquo complexes are described.

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“…5 The mechanisms of the subsequent steps in the reduction leading eventually to Cr(III) are not too well characterized, but a number of studies on synthetic models suggest that disproportionation pathways are involved. [17][18][19][20][21][22] There have been a number of structural studies yielding information related to the reduction of Cr(VI) by cytochrome c 7 , e.g. X-ray studies of the binding site of redox-inert oxyanions such as MoO 4 2À revealing interactions with nearby lysine residues.…”

Section: Introductionmentioning

confidence: 99%

How do enzymes reduce metals? The mechanism of the reduction of Cr(vi) in chromate by cytochromec₇proteins proposed from DFT calculations

2011

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Various bacteria are effective in metal reduction, and there is an increasing use of such micro-organisms for decontaminating polluted environments. Iron-containing electron transfer proteins, particularly those of the cytochrome c7 family, can bind a number of toxic metals in their high oxidation states, and can reduce them via electron transfer mechanisms. We report a computational investigation of the binding of CrO4(2-) to the cytochrome c7 of Desulfuromonas acetoxidans and explore possible mechanisms for the subsequent reduction of Cr(VI) to Cr(III). Our modelling strategy is to identify the binding site of D. acetoxidans for the chromate di-anion, and to use this structure as a starting point to generate realistic models for DFT calculations of the structures and energetics of species along the pathway for reduction. We address the following aspects of the mechanism: (i) How do the neighbouring residues, particularly the nearby lysines, modulate the reduction process? (ii) What is the speciation of chromium as the oxidation state is reduced from VI? (iii) How is the electron transfer made energetically feasible, considering the initial species (chromate) has a high negative charge? We suggest that both electron transfer from the heme and proton transfer from the lysines occur, followed by a disproportionation mechanism involving Cr(V). This mechanism is compared with our proposed mechanism for the reduction of actinyl species.

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Disproportionation of Aquachromyl(IV) Ion by Hydrogen Abstraction from Coordinated Water

Cited by 26 publications

References 43 publications

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

Models for Proton-coupled Electron Transfer in Photosystem II

How do enzymes reduce metals? The mechanism of the reduction of Cr(vi) in chromate by cytochromec₇proteins proposed from DFT calculations

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Disproportionation of Aquachromyl(IV) Ion by Hydrogen Abstraction from Coordinated Water

Cited by 26 publications

References 43 publications

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the FeII–FeIII Self‐Exchange and Related Systems

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the FeII–FeIII Self‐Exchange and Related Systems

Models for Proton-coupled Electron Transfer in Photosystem II

How do enzymes reduce metals? The mechanism of the reduction of Cr(vi) in chromate by cytochromec7proteins proposed from DFT calculations

Contact Info

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The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

The Role of Water‐Based Hydrogen Atom Wires in Long‐Range Electron‐Transfer Reactions in Aqueous Media for the Fe^II–Fe^III Self‐Exchange and Related Systems

How do enzymes reduce metals? The mechanism of the reduction of Cr(vi) in chromate by cytochromec₇proteins proposed from DFT calculations