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Flash illumination of a lipid bilayer containing a positively charge pigment: chlorophyll h cholyl hydrazone and separating two salt solutions. one of which contained ferricyanide. resulted in a photovoltage of -30mV. acceptor side negative. The positive charge on the pigment resulted in several novel effects. ( I ) The photo-emf is twice that of chlorophyll a and five times that of chlorophyll h at a given concentration. A higher surface concentration of the charged derivative is the likely cause of this effect.( 2 ) The pheophytin of chlorophyll b cholyl hydrazone produces about one-half the photo emf of the magnesium derivative whereas pheophytin a o r b produced only one-tenth the signal. This may be a reflection of the changed redox potential of the cation chlorophyll b cholyl hydrazone. (3) A voltage drop of 100 mV across the membrane, the acceptor side negatively biased, causes a >+fold increase in the charge recombination rate. Biasing the acceptor side 100 mV positive ha5 no effect. Chlorophyll n o r h do not show this field effect. This asymmetric effect is explained as a movement of the more polar chlorophyll dication towards the water interface, leading to more rapid reaction with donor. Thus the kinetics of the charge reversal are a sensitive and specific probe of the polar interfacial region of the lipid bilayer-water interface.

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