PREHISTORY IN THE PRETRANSITION RANGE OF DIPALMITOYLPHOSPHATIDYLCHOLINE WATER SYSTEM/

Transitional states in multilamellar fully hydrated dipalmitoylphospha tidylcholine (DPPC) liposomes were studied by using small and wide ang le X-ray scattering. The incubation technique was applied to achieve c onditions as close as possible to equilibrium. The structures formed i n the wide temperature range (30-37 degrees C) of the pretransition ar e very different depending on the starting temperatures, 28 and 38 deg rees C, respectively. The difference weakens with time but does not co mpletely vanish even after one week of incubation. The parent phases, the gel (L-beta') and the rippled gel (P-beta') are present in the who le temperature range. The amounts of the phases do not change during t he pretransition simultaneously. When the samples are cooled down from the narrower transitional temperature range, a previously existing L- beta' with destroyed layer structure is reformed. However, when heated from this stage up to above the transitional temperature into the pha se P-beta', 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 reveale d that the structures formed in the critical transition temperature do main produce extreme variety and this feature may have importance in t he regulation of membrane transport properties. (C) 1998 Elsevier Scie nce B.V. All rights reserved.