CHARGE TRANSFER ACROSS INTERFACES OF BIOLOGICAL SYSTEMS

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The aim of this research is to increase our understanding of charge transfer across biological interfaces, a process vital to all living cells. The planar lipid bilayer is used as the model of cellular inter- faces. The transfer of charge across the lipid bilayer-water interface and across the bilayer itself will be studied by fast photoelectric methods and by the photogating effect developed during previous studies. These methods allow direct measure of kinetics on the subnanosecond time scale. The photogating method uses photogeneration of charge within the membrane and allows ion movement to be observed without interfering capacitative artefacts. These measurements and electrostatic calculations of interactions within the membrane will be used to disentangle the various stages of charge movement: interfacial, transmembrane,and reverse interfacial. We will use the fullerence C60 as a novel hydrophobic anion charge carrier. In particular we will aim at verifying our Ion Chain hypothesis of hydrophobic ion conductance across bilayers. A chain of alternating cations and anions may allow an ion to cross the membrane by a single hop at each end, analagous to the Grotthuss mechanism for excess proton or hydroxyl ion mobilities in water. Proof of this mechanism would have implications for the origin of ion channels: the Ion Chain can be looked upon as a prototype of these channels. Synthesis of analogues of channel forming peptides such as cecropins and melittins will be used to understand the molecular determinants of channel formation and of ion gating. The methodology of wide band, time resolved, pulsed photoacoustics developed during previous studies, will be applied to bacteriorhodopsin and to charge transfer reactions in solution and at interfaces. A major aim will be to ascertain the importance of entropic effects or "conformational changes" in bacteriorhodopsin and of solvation effects in charge transfer reactions.