title: Composition of supported model membranes determined by neutron reflection.
abstract: We have investigated the formation of supported bilayers by coadsorption of dipalmitoyl phosphatidylcholine (DPPC) with the nonionic surfactant beta-D-dodecyl maltoside. The adsorption of mixed phospholipid-surfactant micelles on hydrophilic silica surfaces at 25 degrees C was followed as a function of bulk concentration by neutron reflection. Using chain-deuterated d(25)-beta-D-dodecyl maltoside and d(62)-DPPC, we demonstrate that it is possible to determine the composition of the bilayers at each stage of a sequential dilution process, which enriches the adsorbed layer in phospholipid and leads to complete elimination of the surfactant. The final supported bilayers have thicknesses of 51 +/- 3 A and are stable to heating to 37 degrees C once all surfactant has been removed, and the structures agree well with other published data on DPPC supported bilayers. The coadsorption of cholesterol in a DPPC-surfactant mixture was also achieved, and the location and volume fraction of cholesterol in the DPPC bilayer was determined. Cholesterol is located in a 18 +/- 1 A thick layer below the lipid headgroup region and leads to an increased bilayer thickness of 58 +/- 2 A at 26 mol % of cholesterol.
authors.affiliation: Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom.
authors.forename: Hanna P
authors.initials: HP
authors.lastname: Vacklin
authors.forename: Fredrik
authors.initials: F
authors.lastname: Tiberg
authors.forename: Giovanna
authors.initials: G
authors.lastname: Fragneto
authors.forename: Robert K
authors.initials: RK
authors.lastname: Thomas
mesh_terms: D000042:Absorption; D002784:Cholesterol / Q000737:chemistry; D005960:Glucosides / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D009502:Neutrons; D010713:Phosphatidylcholines / Q000737:chemistry*
chemical_list: D005960:Glucosides; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C040358:dodecyl maltoside; D002784:Cholesterol