Dept. of Chemistry and Biochemical Sciences
Oregon Graduate Institute of Science & Technology
The ability of alkyl viologens (C[subscript]nMV[superscript]2+) to mediate electron transfer across dihexadecylphosphate (DHP) bilayers was studied. DHP vesicles were prepared in weakly alkaline buffers and reduction of viologen molecules adsorbed on the inner and/or outer vesicle surface(s) was monitored after the anaerobic addition of dithionite (S[subscript]2O[subscript]4[superscript]2-) ion. In the absence of external viologen the reduction of inner viologen was extremely slow, with half-lives on the order of hours. In the presence of external C[subscript]nMV[superscript]2+ reduction of inner viologen proceeded over the course of minutes with the general trend that second-order rates decreased as n increased. For methyl viologen (MV[superscript]2+,n=l) the reduced product was spectroscopically observed to be characteristic of dimers in cases where the initial concentration of viologen inside the vesicles exceeded that outside. It was also determined that under these conditions most of the reduced viologen had migrated into the vesicles. These phenomena were observed to lesser extents as the viologen alkyl chain length increased. It is hypothesized that electron transfer, as well as viologen migration, is controlled in part by transmembrane electrical potentials. Transmembrane oxidation-reduction leads to polarization of the membrane. The migration of viologen cations inward compensates for this charge buildup. The addition of other lipophilic ions was studied to help clarify this notion. Various other transmembrane redox systems were briefly studied. The charge recombination rates of a photochemical system containing ZnTPPS[superscript]4- and alkyl viologens adsorbed to DHP vesicles were studied using laser flash photolysis. Conditions were varied to determine which factors affected the rates. The recombination reaction was found to be first-order and possible mechanisms are proposed.
Patterson, Brian Clay, "Viologen-mediated electron transfer across dihexadecylphosphate bilayer membranes" (1990). Scholar Archive. 132.