Electron-transfer catalysis

Clark, T. Ab Initio Calculations on Electron-Transfer Catalysis by Metal Ions. 177, 1-24 (1996). 

Research was done with redox systems incorporated into Nafion-modified electrodes51 because of interesting possible applications of such systems, e.g., for electron-transfer catalysis. 

FIGURE 4.15. a Cyclic voltammetric response of a monolayer catalytic coating for the reaction scheme in Figure 4.10 with a slow P/Q electron transfer. Catalysis kinetic parameter kr°/ /DAFv/TIT — 5. Same electrode electron transfer MHL law as in Figure 1.18. Dotted line Nemstian limiting case. Solid lines From left to right, F(>k 1/sjD Fv/ lZT = 1, 0.1, 0.01. b Convoluted current, c Derivation of the catalytic rate constant (return curve have been omitted, d Derivation of the kinetic law. 

Ab Initio Calculations on Electron-Transfer Catalysis by Metal Ions... 

The concepts of electron-transfer catalysis and so-called hole-catalysis [1] are closely related. It is now generally accepted that many organic reactions that are slow for the neutral reaction system proceed very much more easily in the radical cation. Although hole-catalysis is now well documented experimentally [2], there is surprisingly little mention of the corresponding reductive process, in which a reaction is accelerated by addition of an electron to the reacting system. Although the concept of electron-catalysis is not as well known as hole-catalysis, there are experimental examples of electrocyclic reactions that proceed rapidly in the radical anion, but slowly or not at all in the neutral system [3], For reasons that will be outlined below, we can expect that, in many cases, difficult or forbidden closed-shell reactions will be very much easier if an unpaired electron is introduced into the system by one-electron oxidation or reduction. Thus, if a neutral reaction A - B proceeds slowly or not at all, the radical cation (A" -> B" ) or radical anion (A" B" ) may be facile... 

In order to understand the principles involved in electron-transfer catalysis and also in order to appreciate the historical development of the subject, we must treat hole catalysis and electron transfer between metal atoms and ions and organic substrates before examining catalytic reactions in more detail. This review is intended to cover the basic principles involved in these three areas and to provide a conceptual framework for electron-transfer catalysis. 

One of the surprising aspects of this and other studies using naked metal ions as models for electron-transfer catalysis are the many analogies found to known transition metal chemistry, either in the gas phase with naked ions or for complexes under more normal conditions. Clearly, such simple models as the beryllium cation cannot account for transition metal reactivity, but they do have the advantage that, because of their very simplicity, the reasons for their effects are relatively clear. The fact that Be can catalyze a given reaction does not necessarily mean that, for instance, a transition metal does not use d-orbitals to catalyze the same reaction but it does mean that d-orbitals are not a prerequi-... 

In the mid-1960s, Dessy and coworkers [12, 13] provided an extensive survey of the anodic and cathodic reactions of transition metal organometallic species, including binary (homoleptic) carbonyls, and this provided a stimulus for many later detailed studies. Whereas the electrochemistry of heteroleptic transition metal carbonyls is covered elsewhere in this volume, that of the binary carbonyls, which is covered here, provides paradigms for the electrochemistry of their substituted counterparts. A key aspect is the generation of reactive 17-electron or 19-electron intermediates that can play key roles in the electrocatalytic processes and electron-transfer catalysis of CO substitution by other ligands. 

The consequences of such a conformational change could be dramatic for the physical and chemical properties of the protein and would explain the cytochrome c behavior. Related effects on electron transfer catalysis of the protein have been discussed elsewhere.40... 

Ciolowski J (1990) Scaling Properties of Topological Invariants. 153 85-100 Clark T (1996) Ab Initio Calculations on Electron-Transfer Catalysis by Metal Ions. 777 1-24 Cohen MH (1996) Strenghtening the Foundations of Chemical Reactivity Theory. 183 143-173... 

In studies of analogs of the redox cofactor pyrroloquinoline quinone (PQQ), synthetic efforts have focused initially on isosteric, isomeric structures that reflect on important mechanisms of electron-transfer catalysis mediated by PQQ. These studies provide insight into the choice of PQQ as an electron-transfer catalyst in nature, and bear directly on pharmaceutical applications of this vitamin-like nutritional factor. 

Cyclic Water Cleavage — Hydrogen and Oxygen Production via Electron Transfer Catalysis 523... 

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