STRUCTURE OF AN ADSORBED DIMYRISTOYLPHOSPHATIDYLCHOLINE BILAYER MEASURED WITH SPECULAR REFLECTION OF NEUTRONS

Using specular reflection of neutrons, we investigate for the first time the structure of a single dimyristoylphosphatidylcholine bilayer adsorbed to a planar quartz surface in an aqueous environment. We demonstrate that the bilayer is strongly adsorbed to the quartz surface and is stable to phase state changes as well as exchange of the bulk aqueous phase. Our results show that the main phase transition is between the L-alpha-phase and the metastable L-beta*, phase, with formation of the P-beta, ripple phase prevented by lateral stress on the adsorbed bilayer. By performing contrast variation experiments, we are able to elucidate substantial detail in the interfacial structure. We measure a bilayer thickness of 43.0 +/- 1.5 angstrom in the L-alpha-phase (T = 31-degrees-C) and 46.0 +/- 1.5 angstrom in the L-beta*, phase (T = 20-degrees-C). The polar head group is 8.0 +/- 1.5 angstrom thick in the L-alpha-phase. The water layer between the quartz and bilayer is 30 +/- 10 angstrom for the lipid in both the L-alpha and L-beta*, phase. Our results agree well with those previously reported from experiments using lipid vesicles and monolayers, thus establishing the feasibility of our experimental method.