Proton and electron-transfer

Barbara P F, Walker G C and Smith T P 1992 Vibrational modes and the dynamic solvent effect in electron and proton transfer Science 256 975-81... 

The mechanism of the light-promoted reaction involves a series of electron and proton transfers from water to Q. 

The Clemmensen reduction can be formulated to proceed by a sequence of one-electron and proton transfer reactions. It is a heterogenous reaction, taking place at the zinc surface. Initially an electron is transferred from zinc to the carbonyl group of ketone 1, leading to a radical species 3, which is presumed to react further to a zinc-carbenoid species 4 ... 

A large red shift observed in polar solvents was indicative of the intramolecular charge transfer character of the triplet state. The change of dipole moment accompanying the transition Tj - Tn, as well as rate constants for electron and proton transfer reactions involving the T state of a-nitronaphthalene, were determined. The lower reactivity in polar solvents was attributed to a reduced n-n and increased charge transfer character of the triplet state... 

Paradoxically, all these significant recent contributions to the theory of the ORR, together with most recent experimental efforts to characterize the ORR at a fuel cell cathode catalyst, have not led at aU to a consensus on either the mechanism of the ORR at Pt catalysts in acid electrolytes or even on how to properly determine this mechanism with available experimental tools. To elucidate the present mismatch of central pieces in the ORR puzzle, one can start from the identification of the slow step in the ORR sequence. With the 02-to-HOOads-to-HOads route appearing from recent DFT calculations to be the likely mechanism for the ORR at a Pt metal catalyst surface in acid electrolyte, the first electron and proton transfer to dioxygen, according to the reaction... 

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... 

Figure 2.8 Reaction scheme for combined electron and proton transfer.

Figure 2.9 Model potential energy surface for combined electron and proton transfer. is the solvent coordinate for electron transfer and Q2 that for proton transfer. (See color insert.)...

Grimminger J, Bartenschlager S, Schmickler W. 2005. A model for combined electron and proton transfer in electrochemical systems. Chem Phys Lett 416 316-320. 

Marcus, R. A., Similarities and differences between electron and proton transfers at electrodes and in solution, Theory of hydrogen evolution reaction, Proc. Electrochem. Soc., 80-3, 1 (1979). 

It should be noted that recent work has not been devoted only to the application of the theory to new processes and phenomena but has also been concerned with the basis of the theory. Therefore, new important results have been obtained also for processes which have been under theoretical investigation for many years, in particular, for electron and proton transfer reactions. These results open new directions for further investigations. 

Muller A, Ratajack H, Junge W et al (1992) Studies in physical and theoretical chemistry electron and proton transfer in chemistry and biology, vol 78. Elsevier, Amsterdam, The Netherlands... 

The reaction-center proteins for Photosystems I and II are labeled I and II, respectively. Key Z, the watersplitting enzyme which contains Mn P680 and Qu the primary donor and acceptor species in the reaction-center protein of Photosystem II Qi and Qt, probably plastoquinone molecules PQ, 6-8 plastoquinone molecules that mediate electron and proton transfer across the membrane from outside to inside Fe-S (an iron-sulfur protein), cytochrome f, and PC (plastocyanin), electron carrier proteins between Photosystems II and I P700 and Au the primary donor and acceptor species of the Photosystem I reaction-center protein At, Fe-S a and FeSB, membrane-bound secondary acceptors which are probably Fe-S centers Fd, soluble ferredoxin Fe-S protein and fp, is the flavoprotein that functions as the enzyme that carries out the reduction of NADP+ to NADPH. 

EPR, ENDOR, Mossbauer, EXAFS, and MCD spectroscopies to further elucidate intimate details of electron and proton transfer within nitrogenase are difficult... 

Figure 13.14 Structural basis for electron and proton transfer at centre P part a shows ubiqunol hydrogen bonded to Hisl81 of ISP and Glu272 of cytochrome b. Part b shows the ubiquinol-binding pocket after movement of Glu272. (From Hunte et al., 2000. Copyright 2003, with permission from Elsevier.)...

E. M. KosowerandD. Huppert, Excited state electron and proton transfers, Ann. Rev. Phys. Chem. 37, 127(1986). 

A. Muller, H. Ratajczak, W. lunge, and E. Diemann, Eds., Electron and Proton Transfer in Chemistry, Elsevier, New York, 1992... 

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