LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL AND QUINONE IN ELECTRICALLY‐CHARGED VESICLES: EFFECTS OF COUNTERIONS LOCATED IN EITHER THE INNER OR OUTER AQUEOUS PHASES ON RADICAL FORMATION AND DECAY*

Abstract

Abstract— The presence of relatively low concentrations of counterions (millimolar in the case of univalent ions and micromolar in the case of polyvalent ions) in either the inner or outer aqueous compartments of electrically charged lipid bilayer vesicles containing chlorophyll in the presence of benzoquinone has been shown to produce large effects on radical formation and decay as measured by laser flash photolysis. With negatively charged vesicles having no added salt inside, salt ions added to the external phase caused radical yields to markedly decrease, with no change in decay kinetics. When salt was present only in the interior phase, radical decay became biphasic and the ability of externally added salt to affect radical yields was greatly diminished.With positively charged vesicles having no added salt inside, salt addition to the external medium caused both the radical decay rate and yield to decrease. The presence of interior salt, however, caused radical decay to become faster and, as was the case with negative vesicles, greatly reduced the effects of salt added externally.These results have been interpreted in terms of electrostatic and structural effects of charge neutralization by counterions on the dynamics of radical‐ion separation and recombination.