title: Functional role of water in membranes updated: A tribute to Träuble.
abstract: The classical view of a cell membrane is as a hydrophobic slab in which only nonpolar solutes can dissolve and permeate. However, water-soluble non-electrolytes such as glycerol, erythritol, urea and others can permeate lipid membranes in the liquid crystalline state. Moreover, recently polar amino acid's penetration has been explained by means of molecular dynamics in which appearance of water pockets is postulated. According to Träuble (1971), water diffuses across the lipid membranes by occupying holes formed in the lipid matrix due to fluctuations of the acyl chain trans-gauche isomers. These holes, named "kinks" have the molecular dimension of CH2 vacancies. The condensation of kinks may form aqueous spaces into which molecular species of the size of low molecular weight can dissolve. This molecular view can explain permeability properties considering that water may be distributed along the hydrocarbon chains in the lipid matrix. The purpose of this review is to consolidate the mechanism anticipated by Träuble by discussing recent data in literature that directly correlates the molecular state of methylene groups of the lipids with the state of water in each of them. In addition, the structural properties of water near the lipid residues can be related with the water activity triggering kink formation by changes in the head group conformation that induces the propagation along the acyl chains and hence to the diffusion of water.
authors.affiliation: Laboratory of Biointerphases and Biomimetic Systems, (CITSE) University of Santiago del Estero and CONICET RN 9, Km 1125, 4206 El Zanjón, Santiago del Estero, Argentina. Electronic address: disalvoanibal@yahoo.com.ar.
authors.forename: E A
authors.initials: EA
authors.lastname: Disalvo
authors.affiliation: Laboratory of Nanostructured System and Electrochemistry, (CITSE) University of Santiago del Estero and CONICET RN 9, Km 1125, 4206 El Zanjón, Santiago del Estero, Argentina.
authors.forename: O A
authors.initials: OA
authors.lastname: Pinto
authors.affiliation: IQUIMEFA, University of Buenos Aires, CONICET, Buenos Aires, Argentina.
authors.forename: M F
authors.initials: MF
authors.lastname: Martini
authors.affiliation: Laboratory of Biointerphases and Biomimetic Systems, (CITSE) University of Santiago del Estero and CONICET RN 9, Km 1125, 4206 El Zanjón, Santiago del Estero, Argentina.
authors.forename: A M
authors.initials: AM
authors.lastname: Bouchet
authors.affiliation: Laboratory of Biointerphases and Biomimetic Systems, (CITSE) University of Santiago del Estero and CONICET RN 9, Km 1125, 4206 El Zanjón, Santiago del Estero, Argentina; Laboratory of Molecular Microbiology, Institute of Basic and Applied Microbiology, University of Quilmes, Bernal, Argentina.
authors.forename: A
authors.initials: A
authors.lastname: Hollmann
authors.affiliation: Laboratory of Biointerphases and Biomimetic Systems, (CITSE) University of Santiago del Estero and CONICET RN 9, Km 1125, 4206 El Zanjón, Santiago del Estero, Argentina.
authors.forename: M A
authors.initials: MA
authors.lastname: Frías
mesh_terms: D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D002463:Cell Membrane Permeability; D004058:Diffusion; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D008563:Membrane Lipids; D014867:Water
keywords: Kinks-water pocket; Lipid membrane; Permeability; Water diffusion