title: Hydration in Lipid Monolayers: Correlation of Water Activity and Surface Pressure.
abstract: In order to give a physical meaning to each region of the membrane we define the interphase as the region in a lipid membrane corresponding to the polar head groups imbibed in water with net different properties than the hydrocarbon region and the water phase. The interphase region is analyzed under the scope of thermodynamics of surface and solutions based on the definition of Defay-Prigogine of an interphase and the derivation that it has in the understanding of membrane processeses in the context of biological response. In the view of this approach, the complete monolayer is considered as the lipid layer one molecule thick plus the bidimensional solution of the polar head groups inherent to it (the interphase region). Surface water activity appears as a common factor for the interaction of several aqueous soluble and surface active proteins with lipid membranes of different composition. Protein perturbation can be measured by changes in the surface pressure of lipid monolayers at different initial water surface activities. As predicted by solution chemistry, the increase of surface pressure is independent of the particle nature that dissolves. Therefore, membranes give a similar response in terms of the determined surface states given by water activity independent of the protein or peptide.
authors.affiliation: Laboratorio de Biointerfases y Sistemas Biomimeticos, Centro de Investigacion y Transferencia de Santiago del Estero, Universidad Nacional de Santiago del Estero-Consejo Nacional de Investigaciones Científicas y Técnicas, 4200, Santiago del Estero, Argentina. disalvoanibal@yahoo.com.ar.
authors.forename: E Anibal
authors.initials: EA
authors.lastname: Disalvo
authors.affiliation: Laboratorio de Biointerfases y Sistemas Biomimeticos, Centro de Investigacion y Transferencia de Santiago del Estero, Universidad Nacional de Santiago del Estero-Consejo Nacional de Investigaciones Científicas y Técnicas, 4200, Santiago del Estero, Argentina.
authors.forename: Axel
authors.initials: A
authors.lastname: Hollmann
authors.affiliation: Instituto de Química y Metabolismo del Fármaco, IQUIMEFA UBA-CONICET, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 PP (1113), Buenos Aires, Argentina. flormartini@yahoo.com.ar.
authors.forename: M Florencia
authors.initials: MF
authors.lastname: Martini
mesh_terms: D008055:Lipids / Q000737:chemistry*; D008962:Models, Theoretical; D011312:Pressure; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D008055:Lipids; D014867:Water
keywords: Defay-Prigogine model; Lipid monolayers; Peptide interaction; Surface pressure; Water activity