title: Sum frequency generation spectroscopic study of the condensation effect of cholesterol on a lipid monolayer.
abstract: Sum frequency generation (SFG) spectra and surface pressure-molecular area (pi-A) isotherms have been obtained for mixed cholesterol-DPPC monolayers with cholesterol mole fractions, x(chol.), from 0 to 1.0, at the air-water interface, under same conditions, at 22 degrees C. Analysis of the spectra indicated that incorporation of cholesterol into the monolayers at 3 mN m-1 greatly increases the conformational and orientational order of the alkyl chains of DPPC, maximizing these properties at x(chol.)=0.4. Analysis also indicated that order in the mixed monolayers at 15 and 35 mN m-1 is not affected by incorporation of cholesterol. The pi-A isotherms measured at 3 mN m-1 for the mixed monolayer with x(chol.)=0.4 have the largest negative deviation of the molecular area relative to those of ideal mixtures (the so-called "condensation effect" of cholesterol), indicating the most thermodynamically stable state. Comparison of results from SFG spectra and pi-A isotherms explicitly proved that the condensation effect can be interpreted in terms of conformational and orientational ordering of the alkyl chains of DPPC.
authors.affiliation: Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, 169-8555, Japan.
authors.forename: C
authors.initials: C
authors.lastname: Ohe
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
authors.forename: M
authors.initials: M
authors.lastname: Noi
authors.forename: Y
authors.initials: Y
authors.lastname: Goto
authors.forename: K
authors.initials: K
authors.lastname: Itoh
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D008567:Membranes, Artificial; D010767:Phosphorylcholine / Q000737:chemistry*; D013057:Spectrum Analysis; D013499:Surface Properties
chemical_list: D008567:Membranes, Artificial; D010767:Phosphorylcholine; C038151:1,2-dipalmitoyl-sn-glycero-3-thiophosphocholine; D002784:Cholesterol