X-ray diffractometry and calorimetry studies of structural modifications induced by γ-irradiation in phosphatidylcholine multilamellar liposomes

Experimental results are reported on structural and thermodynamic modifications induced by γ-irradiation in model membranes. Differential scanning calorimetry (DSC) and X-ray diffraction were used to study the different phases and associated transitions of dipalmitoylphosphatidylcholine after 60Co γ-irradiation. Changes were observed in the shape of calorimetric peaks and in the corresponding enthalpy. The repetition distance of the layers increases while the distances related to the aliphatic chains decrease as a function of γ-irradiation time. Moreover, an increase in the hexagonal symmetry with increasing dose was detected. No disappearance of a pre-transition was detected even at high doses. (author)