G. D’Angelo1, V. Conti Nibali2, U. Wanderlingh1, C. Crupi1, C. Branca1
1 Dipartimento di Scienze matematiche ed Informatiche, scienze Fisiche e scienze della Terra, Università degli Studi di Messina, Messina, Italy
2 RuhrUniversity Bochum, Institute for Physical Chemistry II, Bochum, Germany
Water is a key element that controls the self-assembly and the function of lipid bilayers in cell. Through its interaction with lipid moieties at the interface, water modifies the electrostatic charges of the membrane affecting vital processes, such as the transport of ions, biomolecules or drugs across the membrane, as well as the signal transduction. Although the structural organization and dynamics of the lipid-water system are being extensively studied from a long time, many of the properties of lipid membranes and the details of the membrane hydration and interaction are very far from being well understood.
In this contribution the results of a FTIR study in aligned DMPC phospholipid multibilayer under conditions of low hydrations are shown. Relevant information on the water/phospholipid interactions in the interfacial region were gathered by analysing the OH stretching band. Three water molecule populations were identified and attributed to water molecules in between the hydrocarbon lipid chains, water molecules interacting with the positive charge in the choline groups and molecules forming strong hydrogen bonds with the positive interfacial groups. Interestingly, it was deduced that at very low hydration a small amount of water is embedded in confined spaces within the hydrocarbon region. The frequency changes of lipid moieties were also investigated and correlated with the OH stretching band mirroring the water molecule environments. The obtained results can be useful for understanding how changes in the degree of hydration can threaten the stability and biological function of lipid membrane.