EFFECT OF VESICULAR INTERFACIAL POTENTIAL ON ELECTRON-TRANSFER BETWEEN N,N,N',N'-TETRAMETHYLBENZIDINE AND QUINONES

Photoinduced electron transfer reactions between N,N,N',N'-tetramethylbenzidine (TMB) and various quinones (duroquinone (DQ), benzoquinone (BQ)) and vitamin K1(VK1) embedded in the lipidic phase of dihexadecylphosphate vesicles (DHP), and the corresponding back electron transfer reactions, are studied by laser flash spectroscopy. The results show that TMB+ cation and Q- anion formation are principally a result of the direct electron transfer between the TMB singlet excited state and Q. The back reaction between TMB+ cation and Q- anion takes place by two decays. The fast decay, corresponding to a reaction site located in the bilayer, is independent of the interfacial electrical potential-DELTA-PSI, and depends on the redox potential of the quinone. The best electron acceptor (VK1) yields the slowest rate. A slow back-reaction rate is observed when the two reactants are separated by the vesicular interface after migration of Q- anions towards the aqueous phase, and the transfer rate constant turns out to be an exponential function of DELTA-PSI.