Prehistory in the pretransition range of dipalmitoylphosphatidylcholine/water system

Abstract

Transitional states in multilamellar fully hydrated dipalmitoylphosphatidylcholine (DPPC) liposomes were studied by using small and wide angle X-ray scattering. The incubation technique was applied to achieve conditions as close as possible to equilibrium. The structures formed in the wide temperature range (30–37°C) of the pretransition are very different depending on the starting temperatures, 28 and 38°C, respectively. The difference weakens with time but does not completely vanish even after one week of incubation. The parent phases, the gel (L β′) and the rippled gel (P β′) are present in the whole temperature range. The amounts of the phases do not change during the pretransition simultaneously. When the samples are cooled down from the narrower transitional temperature range, a previously existing L β′ with destroyed layer structure is reformed. However, when heated from this stage up to above the transitional temperature into the phase P β′, a more disordered layer structure is formed. This complex thermal prehistory can be interpreted by a memory effect with respect to the one-dimensional lattice structure. The present work has revealed that the structures formed in the critical transition temperature domain produce extreme variety and this feature may have importance in the regulation of membrane transport properties.