Charge proton-coupled electron transfer

Under the advisement of PhD mentor Professor Joseph T. Hupp, the PI successfully used spectroelectrochemical quartz crystal microgravimetry to elucidate the mechanism of charge transport... for both aqueous and nonaqueous sytems. This was the first demonstration of proton-coupled electron transfer at oxide semiconductor interfaces. These findings were then successfully applied to a new interpretation of photoinduced electron transfer at similar interfaces, which are of importance in the field of solar energy conversion. ... 

For oxidation of G in duplex DNA, Steenken concluded that the proton on N-1 of G shifts spontaneously to N-3 of the cytosine in the normal Watson-Crick base pair to generate [C+(H)/G ]. Consistent with this proposal, calculations indicate that charge transfer in oxidized DNA is coupled with proton transfer from G to Experiments carried out in D2O also reveal a kinetic isotope effect for G oxidation, implicating a concerted proton-coupled electron transfer mechanism. However, density functional theory (DFT) calculations in the gas phase predict that the structure with a proton on G N-1 [C/HG ] is more stable than [C (H)/G ] by 1.4kcal/mol. " ... 

Hammes-Schiffer S. Theoretical perspectives on proton-coupled electron transfer reactions. Acc. Chem. Res. 2001 34 273-281. Khoshtariya DE, Wei J, Liu H, Yue H, Waldeck DH. Charge-transfer mechanism for cytochrome c adsorbed on nanometer thick films, distinguishing frictional control from conformational gating. J. Am. Chem. Soc. 2003 125 7704-7714. 

Proton-coupled electron transfer (pcet) is an important mechanism for charge transfer in biology. In a pcet reaction, the electron and proton may transfer consecutively (et/pt or pt/et) or conceitedly (etpt). These mechanisms are analyzed and expressions for their rates presented. Features that lead to dominance of one mechanism over another are outlined. Dissociative etpt is also discussed, as well as a new mechanism for highly exergonic proton transfer. 

Hu YZ, Tsukiji S, Shinkai S, Oishi S, Hamachi I (2000) Construction of artificial photosynthetic reaction centers on a protein surface vectorial, multistep, and proton-coupled electron transfer for long-lived charge separation. J Am Chem Soc 122 241-253... 

Figure lb exemplifies a system where excited-state electron transfer triggers proton-coupled electron transfer. The initial charge shift occurs from the photoexcited Ru —trisbipyridine unit... 

Proton-coupled electron transfer (PCET) is a ubiquitous process in biology and chemistry and plays an essential role in multi-electron, multi-proton transfer processes of biological relevance, such as photosynthesis and respira-tion. The coupling between proton and electron motions stabilizes reaction intermediates, by preventing charge build-up during the accumulation of redox equivalents. The key role of PCET natural photosynthesis is probably the major contributor to this effect. 

As outlined in the Introduction, a couple of suggested pathways have been proposed for the first electron transfer step (a) dissociative chemisorption of O2 (rds) probably accompanied by e-transfer and followed by proton transfer (b) simultaneous proton and electron transfer to a weakly adsorbed O2 molecule. We have recently shown through CPMD [21,69] and DFT [75] results that both pathways may take place under different conditions of the interfadal structure i.e., proton transfer may be involved in the first reduction step depending on the relative location of the O2 molecule with respect to the surface and to the proton, on the degree of proton hydration, and on the surface charge which is dependent on the electrode potential. Moreover, it was shown that proton transfer may precede or follow the first electron transfer, but in most cases the final product of the first step is an adsorbed HOO. ... 

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