Chemical and structural modifications in multilayer liposomes of synthetic phosphatidylcholine induced by gamma irradiation are investigated with different techniques. Fluorescence anisotropy of the DPH probe and differential scanning calorimetry reveal a broadening of the main lipid transition and the disappearance of pretransition. Fluorescence anisotropy is shown to be higher in the irradiated sample and particularly so at low temperatures. NMR and TLC results show that lysolecithin and palmitic acid are formed with a consequent change in bilayer organization. The possibility that these modifications may account for the permeability variations observed in irradiated natural membranes is discussed.

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Multilayer membraoes of l,MipaImitoyl-sn-glycer+~phorylchorylcho~~ were prepared in D,Q and exposed to y-radiation. Changa in the chemical structure due to irradiation were studied by 'H, "C and "P NMR after lyophilization and dissolution in chloroform-methanol (1 : 2, vjv). Qne-and two-dimensional techniques were used. l-Palmitoyl-sn-glycei+~pb~pbo~~choline, 2-palmitoyl-sn-glycero-3-pbosphorylcboli, glycer+lphos-phorylcholiw and palmitic acid were identified as new componen&. Their development during irradiation was quantitatively determined. The results were discussed in terms of possible reaction steps responsible for the radiolytic decomposition.