Coupling of Surface pressure and osmotic stress. A new model for lipid monolayers/bilayers base on thermodynamics of irreversible processes

DISALVO E.A.; PINTO O. A

Salto, Uruguay

Congreso; Latin American Crosstalk in Biophysics and Physiology. SBF.uy-SAB; 2015

The principal feature of lipid monolayers is that a surface pressure/area per lipid curve can be obtained in a Langmuir balance that resembles thePV isotherms of gases.The problem is that meanwhile the gas molecules occupy a threedimensional volume in vacuum, lipids occupy a bidimensional surface interactingwith water. In other words, when a monolayer is compressed the work is not onlyto force the molecules to condense interacting with each other but also a workagainst water/lipid interaction should be considered.It may be possible that compression under a lateral force produces achange in the excess lipid concentration and hence modifying the water-lipidinteraction. On the other way round, when lipids are subjected to a watergradient i.e. osmosis, water may be extruded from the interphase modifying thelateral pressure.The analysis of the coupling of these two processes, that may help tointerrelate processes in monolayers and bilayers, will be the purpose of thiscommunication.With this aim we first present the basis of coupled phenomena in abidimensional system as the lipid monolayer to make afterwards an analogy witha bilayer.The influence of water on the lipids and the influence of lipids onthe water, respectively, is considered by crossed coefficients one consideringthe compression or expansion due to change in the water activity and the secondthe change in water activity due to surface pressure (exchange of water byextrusion or penetration). Both coefficients may be considered equal in idealconditions reducing the equation to those generally applied in literature.  References: [1] Damodaran, S., (1998) Wateractivity at interfaces and its role in regulation of interfacial enzymes: Ahypothesis, Colloids and Surfaces B: Biointerfaces, 11, 231-237.[2] Disalvo, E. A., Hollmann, A.,Semorile L. and Martini, M. F., (2013) Evaluation of the Defay-Prigogine modelfor the membrane interphase in relation to biological response inmembrane-protein interactions, Biochimica et Biophysica Acta, 1828, 1834-1839.10)