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. Author manuscript; available in PMC: 2011 Dec 8.
Published in final edited form as: Chem Rev. 2010 Nov 4;110(12):6939–6960. doi: 10.1021/cr1001436

Fig. 2.

Fig. 2

Four-state model for coupled electron and proton transfer reactions. In the initial state (OU), the electron is on the donor site O (Oxidized acceptor), and the proton is on the U site (Unprotonated acceptor). In the final state (RP), the electron is on the acceptor site R (Reduced acceptor), and the proton is on the P site (Protonated acceptor). Intermediate states (OP) and (RU) correspond to activated states for sequential PT/ET and ET/PT reactions. The concerted reaction corresponds to an (OU) to (RP) transition. Figure reprinted with permission from Ref. 42. Copyright 2003 World Scientific.