FREE RADICALS DETECTED BY ESR FROM PHENYLHEPTATRIYNE IN LIPOSOMES IRRADIATED WITH UV-A

Abstract— When irradiated with UV-A liposome bilayers composed of distearoyl phosphatidylcholine and containing phenylheptatriyne produced a free radical signal detected by electron spin resonance spectroscopy. The spectrum contained one broad peak characterized by a linewidth of 19 G and a g value of 2.0017. The rate of formation of the signal amplitude was dependent upon light intensity, concentration of PHT within the bilayer and concentration of the PHT-liposome suspension. Enhancement of the signal under an anaerobic atmosphere indicated a non-photodynamic mechanism for free radical formation. Once formed however, the free radical was stable to the presence of oxygen and decayed very slowly with a half-life of 8 h. Formation of the free radical species was demonstrated to be dependent upon a highly ordered lipid environment since incorporation of lysophosphatidylcholine, stearoyl which perturbs lipid packing, decreased the levels of the free radical species. On the other hand, when PHT was present in a liposome with a more fluid bilayer such as egg yolk phosphatidylcholine, the levels of free radical species were even lower. Conversely, the levels increased when cholesterol which increases lipid order, was incorporated into the egg yolk phosphatidylcholine liposomes. Cells of E. coli, B , containing PHT, produced a similar free radical signal upon irradiation demonstrating in vivo generation of free radicals from PHT.