NMR evidence for asymmetric radiation damage of bilayer liposomes

Abstract

In aqueous solutions of irradiated sonicated egg yolk lecithin vesicles the 1H relaxation times T 1 and T 2 were determined for the outer and inner (CH 3) 3N +-groups at 250 MHz and at room temperature. After a γ irradiation up to a dose of 13.5 kGy, T 1 remains constant T 1=(0.33±0.01)s, T 2 is a sensitive parameter in detecting radiation induced changes of slow reorientations for the lipid molecules. While T 2=0.10 s for the outer head group signal decreases by 25% after irradiation, the effect is significantly smaller for the inner head group. This preferred radiation damage of the outer lipid layer may be a consequence of the indirect radiation action and/or due to the geometric packing constraints in small vesicles. The spectroscopic results were derived from partially relaxed NMR spectra. This method seems to be useful for the detection of the effects of different agents on the radiation damage of the liposome, as demonstrated with the partially relaxed head group spectra in the presence of NaCl.