MAGNETIC-FIELD EFFECTS ON THE DYNAMICS OF RADICAL PAIRS - THE PARTITION EFFECT IN VESICLES

A combination of product studies and laser flash photolysis (LFP) was used to study the recombination of radical pairs derived from dibenzyl ketone (DBK) and its methyl derivative. Two sizes of vesicles consist ing of dioctadecyldimethylammonium chloride (DODAC) were generated. In the product studies, irradiation of the ketone led to a substantial o verall cage effect both above and below the phase-transition temperatu re. However, LFP results demonstrate that no geminate reactions, that correspond to the reactions of radicals generated from the same precur sor molecule are occurring even at room temperature. The results are d iscussed in terms of the partition effect where the cage effect is det ermined by the differences in the solubility of the radical inside the vesicle bilayer and in the aqueous phase. In small (30 mn diameter) v esicles, most of the random recombination occurs after re-entry of the radicals into the bilayer, whereas in large (similar to 150 nm) lipos omes, a significant proportion of the recombination reactions takes pl ace in the hulk water. This work demonstrates that magnetic fields can efficiently alter the reactivity of radicals involved in nongeminate pathways and further supports the use of the radical pair mechanism to explain possible effects of magnetic fields in biological systems.