Physical chemical properties of lipid membrane interphases: new and old paradigms

DISALVO, E.A.; A.S. ROSA; CEJAS, J.P.; H.A. PÉREZ

San Luis

Congreso; VIII Encuentro de Fisica y Quimica de Superficies; 2018

Lipids organized as a bilayer constitute the structural backbone of biological membranes. From a mechanical, thermodynamic and electrochemical behaviour it is considered a peculiar material that cannot be mimicked by other materials. However, the studies of these systems from the physical chemistry and thermodynamic point of view are usually interpreted along laws and formalisms applicable to tridimensional macroscopic systems and the deviations are mostly explained by introducing geometrical arrangements and structures that are controversial. A critical point in the failure of classical paradigms is that they consider the membrane as a solubility (partition) phase disregarding the interphasial phenomena. Although water is considered to be the solvent by which lipids stabilize as a bilayer due to entropic and energetic contributions, it is not considered as a structural component that determines the response of the bilayer as a surface thermodynamic system.In this work, the failures of the old paradigms are discussed and a new approach within the frame of thermodynamics of irreversible process is applied to monolayers/bilayer as open systems with the ability to exchange water with the surroundings coupled to mechanical stress that explains the responses of the membranes to perturbations by biologically significant effectors.The approach is valid to explain surface pressure /area isotherms and swelling and shrinkage processes in monolayers and bilayers, respectively and the link between them. The thermodynamic picture is corroborated by changes in membrane structure at mesoscopic and microscopic level by studies by FTIR and fluorescence spectroscopy, surface pressure isotherms and kinetics.