Layer formations of dipalmitoylphosphatidylcholine liposomes in the pretransition range

Destroyed lamellar and chain packing arrangements of the dipalmitoylphospho choline-water (30% w/w) system are formed in the pretransition range (31-35 .5 degrees C) under quasi-equilibrium conditions observed by means of simul taneous small- and wide-angle X-ray scattering method. The peak profiles of the scattering curves detected in the pretransition range were modeled as the superpositions of the fitted profiles of the L-beta' and P-beta' phases corresponding to the one-dimensional layer arrangements and the subcells i n the chain packing. On the basis of the fitted profiles the ratios of the phases can be given as a function of the temperature. It can be stated that (i) both the L-beta' and P-beta' phases are present in the temperature ran ge of the pretransition and (ii) in the P-beta' phase the layer arrangement s and chain packing do not change to the same extent. The maximum loss in t he layer arrangement was observed around 33 degrees C. The accumulation of the defect structures appears to be highly permanent as it was observed aft er sequential heat treatments, i.e., quenching to the temperature domain of the L-beta' phase (28 degrees C) and then reheating above the pretransitio n range to the temperature domain of the P-beta' phase (38 degrees C). A me mory effect occurs in the sense that the destroyed structures are restored in the temperature range of phase P-beta' after the formation of a largely reconstructed phase L-beta' The destroyed layer structures formed in the pr etransition and in the rippled phase temperature domains are not identical, as observed by freeze-fracture electron microscopy.