title: Dependence of interfacial film organization on lipid molecular structure.
abstract: Combination of surface analytical techniques was employed to investigate the interfacial behavior of the two designed lipids-N-stearoylglycine (1) and its bulky neutral headgroup-containing derivative N-stearoylvaline ethyl ester (2)-at the air-solution interface and as transferred layers on different substrates. Formation of monolayers at the air-water interface was monitored on pure water and on aqueous solutions of different pH. Crystallization effects were visualized at pure water by recording the hystereses in the Langmuir-Blodgett (LB) isotherms and by transferring the layers onto mica, gold (111), and ITO (indium-tin oxide on glass) electrodes. Subphase pH affects the morphology and patch formation in monolayers of 1, as evidenced by BAM measurements. At pH 8.2, formation of well-ordered crystallites is observed, which upon compression elongate according to predominantly 1-D growth mechanism to form a dense layer of crystallites. This effect is not observed in monolayers of 2, whose headgroup is not protonated. The orientation of layers of 1 transferred to the solid supports is also pH dependent, and their stability can be related to formation of a hydrogen-bonded networks. AFM images of 1 exhibited platelets of multilayer phase. The IR spectra of the ITO substrates covered by 1 indicated formation of hydrogen bonds between the amide groups. The nature of the adsorption layer and its organization as a function of potential were studied in-depth by EC STM using Au(111) as the substrate. A model showing the arrangement of hydrogen bonds between adsorbed molecules is presented and related to the observed organization of the layer.
authors.affiliation: Faculty of Chemistry, University of Warsaw , Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: Dorota
authors.initials: D
authors.lastname: Matyszewska
authors.forename: Slawomir
authors.initials: S
authors.lastname: Sek
authors.forename: Elżbieta
authors.initials: E
authors.lastname: Jabłonowska
authors.forename: Barbara
authors.initials: B
authors.lastname: Pałys
authors.forename: Jan
authors.initials: J
authors.lastname: Pawlowski
authors.forename: Renata
authors.initials: R
authors.lastname: Bilewicz
authors.forename: Fabian
authors.initials: F
authors.lastname: Konrad
authors.forename: Yazmin M
authors.initials: YM
authors.lastname: Osornio
authors.forename: Ehud M
authors.initials: EM
authors.lastname: Landau