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Model PC membranes in seawater media as studied by force- and transmission IR spectroscopy

Biophysical behaviour of lipid membranes is of fundamental importance due to their role of flexible boundary which enables controlled exchange of information and energy between the cell interior and its environment [1]. Lipid membranes are also involved in a number of mechanical events such as cell adhesion, fusion, growth, and migration. Due to the high complexity of cellular membranes, model membranes such as liposomes and supported lipid bilayers (SLB) have been extensively used. How the lipid membrane properties like the surface potential, the dipole potential, the phase transitions and the structure and dynamics of lipid molecules in general are affected by the surrounding medium is to a great extent determined by the medium ionic composition [2]. The ion mixture effect in seawater, particularly the contribution of Mg2+ and Ca2+ as dominant divalent cations on the thermotropic phase behaviour and the nanomechanical response of DMPC as a model neutral (zwitterionic) lipid membrane have been studied by transmission IR spectroscopy and force spectroscopy. By considering both the electrostatic and the chemical equilibrium contributions, it has been shown that the membrane mechanical stability in seawater was unproportionally increased by the cooperative and competitive ion binding processes [3] in both the gel and the liquid phase. The correlation between the ionic strength and the ionic composition of the media with membrane mechanical stability helped us to emphasize the specific characteristics of SW as naturally occurring complex ion mixture. Finally an overview of the on-going investigations will be given with particular emphasis on the challenges and possible solutions the field of nanobiotechnology is faced with.

AFM; Force spectroscopy; Ion binding; Ion mixture; IR spectroscopy; Lipid bilayers; Nanomechanics; Seawater

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