Electron-proton transfer

Of course, proton transfer can also occur between two reactants in the solution. As such, it is not an electrochemical reaction, unless it is combined with an electron exchange with the electrode. Such a combined electron-proton transfer can be represented by the scheme of squares shown in Fig. 2.8. Both electron and proton transfer... 

Sobolewski AL, Domcke W (2003) Ab initio study of the excited-state coupled electron-proton-transfer process in the 2-aminopyridine dimer. Chem Phys 294 2763... 

R. Hille and R.F. Anderson, Coupled electron/proton transfer in complex flavoproteins — solvent kinetic isotope effect studies of electron transfer in xanthine oxidase and trimethylamine dehydrogenase. J. Biol. Chem. 276, 31193-31201 (2001). 

Borgis, D. (1992) Proton transfer reactions in solutions a molecular approach,in Electron Proton Transfer Chem. Biol., 345-362. 

More complicated reactions that combine competition between first- and second-order reactions with ECE-DISP processes are treated in detail in Section 6.2.8. The results of these theoretical treatments are used to analyze the mechanism of carbon dioxide reduction (Section 2.5.4) and the question of Fl-atom transfer vs. electron + proton transfer (Section 2.5.5). A treatment very similar to the latter case has also been used to treat the preparative-scale results in electrochemically triggered SrnI substitution reactions (Section 2.5.6). From this large range of treated reaction schemes and experimental illustrations, one may address with little adaptation any type of reaction scheme that associates electrode electron transfers and homogeneous reactions. 

As discussed in Section 2.5.1, aryl radicals are easily reduced at the potential where they are generated. This reduction that can take place at the electrode surface (ECE) or in the solution (DISP) opposes the substitution process. This three-cornered competition between substitution (SUBST) electron + proton transfer (ECE or DISP) depends on two competition parameters that are closely similar to the HAT-ECE-DISP parameters described in the preceding section ... 

The competition between H-atom transfer and electron + proton transfer, exemplified by the reduction of aryl halides in Section 2.5.5, corresponds to the symbolic Scheme 6.4. 

Coupled electron-proton transfer, reactions of oxo-molybdenum centers, 40 57-59 Coupled-ring nitrides molecular structure of, 15 401-6 preparation of, 15 400 properties and reactions of, 15 402-403 purification of, 15 400-401 Covalent bonding... 

Oxo-molybdenum centers, 40 48-61 coupled electron-proton transfer reactions, 40 57-59... 

This reactivity suggests that although these complexes effectively catalyze a reaction that likely proceeds by a coupled electron proton transfer, they appear to be relatively poor oxygen atom donors. 

VI.D. Coupled Electron Proton Transfer with Concomitant Water Activation or Elimination... 

The cathodic reduction of naphthalene (40) has been the topic of numerous studies 58 60). However, most were concerned with the mechanism of the initial electron-proton transfers. For example, in 0.5 M (C4Hg)4NBF4 in DMF — 1.8% HzO naphthalene exhibited 61) one polarographic wave, Ei/Z = —2.56 V(SCE). 

The ET processes under discussion here correspond by definition to pure ET, in which molecular or medium coordinates may shift (the polaron response) [17], but no overall bonding rearrangements occur. More complex ET processes accompanied by such rearrangements (e.g., coupled electron/proton transfer and dissociative ET) are of great current interest, and many theoretical approaches have been formulated to deal with them, including quantum mechanical methods based on DC treatment of solvent [31,32],... 

With adequate hydronium-ion fluxes, HOO- is transformed to HOOH via a second electron-proton transfer (HOO1 + H30+ + e — - HOOH E°, +0.8 V vs. NHE). Achievement of a full two-electron peak height for the process of Eq. (9.33) requires a ratio of at least four (DMF)H30+ ions per 02 molecule in DMF. This results because (H30)C104 forms (DMF)H30+, and the diffusion coefficient for the latter is much smaller than that for 02. Furthermore, the flux of (DMF)H30+ to the electrode must be twice that for 02 to achieve the second cycle of Eq. (9.33) with the products of Eq. (9.34). 

Stowell, M.H.B., McPhillips, T.M., Rees, D.C., Solitis, S.M., Abresch, E. and Feher, G. (1997) Light-induced structural changes in photosynthetic reaction center implications for mechanism of electron-proton transfer, Science (Washington, D. C.) 276, 812-816. 

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