TEMPERATURE-VARIATION OF LIPID-MEMBRANE STRUCTURE AND THE HYDRATION FORCE IN FLUID LAMELLAR PHASE - EXPERIMENTAL STUDIES WITH DIMYRISTOYLPHOSPHATIDYLCHOLINE MULTIBILAYERS

Results of X-ray small-angle scattering experiments with dimyristoyl-p hosphatidylcholine multibilayers show that the lipid packing parameter s in such a system have an anomalous temperature dependence. Critical fluctuations in the lipid membranes cause the lamellar repeat distance and membrane thickness to decrease with the relative temperature appr oximately as (T - T(m))-1, up to approximately 10 degrees above the li pid chain-melting transition temperature. Above 40-degrees-C and espec ially above 70-degrees-C the interlamellar water layer thickness start s to increase non-linearly, however. This is probably due to the tempe rature-induced swelling of the interfacial region which goes along wit h enhanced lipid headgroup fluctuations and gives rise to anomalously strong <<hydration force>> at high temperatures.