GAMMA-IRRADIATION AND UV-C LIGHT-INDUCED LIPID-PEROXIDATION - A FOURIER TRANSFORM-INFRARED ABSORPTION SPECTROSCOPIC STUDY

Fourier transform-infrared spectroscopy of dry, multibilayer films has been used to study gamma-radiation and UV-C light induced lipid perox idation in 1,2-dilinoleoyl-sn-glycero-3-phosphocholine liposomes. The observed spectral changes were compared with the results obtained from measurement of hydroperoxides, conjugated dienes and to the formation of thiobarbituric acid reactive substances, such as malondialdehyde ( MDA) or MDA-like substances. Upon irradiation a decrease in intensity of the asymmetric C-H stretching vibration (nu(a)(CH2)) of the isolate d cis C=C-H groups (3010 cm(-1)) was observed. Directly correlated wit h the decrease of the nu(a)(CH2) absorption was a shift of the asymmet ric phosphate ester stretching vibration (nu(a)(P=O)) towards smaller wavenumbers (1260 --> 1244 cm(-1)), indicating that the lipid peroxida tion induced molecular alterations in the fatty acid chains influence the packing of the phospholipids in dry multibilayer films. In additio n, the formation of a new absorption band at 1693 cm(-1) could be dete cted, the intensity of which was comparable with the formation of thio barbituric acid reactive substances and, therefore, attributed to the (C=O) stretching of alpha,beta unsaturated aldehydes. Dose-dependent s tudies using ionizing radiation showed that the decrease of nu(a)(CH2) was directly correlated with an increase in absorption of the conjuga ted dienes at 234 nm and with the formation of hydroperoxides suggesti ng that the absorption at 3010 cm(-1) is solely due to isolated cis C= C-H groups and hence subject to the early stages of the radical chain reaction. UV-C light induced lipid peroxidation revealed a non-linear decrease of I-3010 which was directly correlated with the formation of hydroperoxides. The observed early saturation of the conjugated diene s was attributed to an early photodecomposition of the conjugated doub le bonds.