Evidence For Transfer of Radicals between Oil-in-Water Emulsion Droplets as Detected by the Probe (E,E)-3,5-Bis(4-phenyl-1,3-butadienyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY665/676

(E,E)-3,5-Bis(4-phenyl-1,3-butadienyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY665/676, is a lipophilic radical-sensitive fluorescent probe that can be used to study radical-driven lipid autoxidation. The sensitivity of BODIPY665/676 was studied in the presence of radical initiators di-tert-butyl peroxide and 2,2'-azobis(2,4-dimethyl)valeronitrile (AMVN). In both cases the fluorescence of BODIPY665/676 changed more in saturated medium-chain triglyceride oil than in linseed or sunflower oils, where the high degree of unsaturation is expected to give more pronounced radical-derived lipid oxidation. It was suggested that BODIPY665/676, as the only available oxidizable substance in the saturated oil, was directly attacked by radicals, resulting in high rates of probe oxidation, while in the unsaturated oils, radicals attacked either unsaturated fatty acids or BODIPY665/676, resulting in lower rates of probe oxidation. Confocal microscopy studies with BODIPY665/676 as a radical-sensitive probe combined with oxygen consumption measurements of mixtures of oil-in-water emulsions showed that radicals could be transferred between oil droplets and thereby spread radical-driven oxidation between neighboring droplets.