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

ROSA, ANTONIO SEBASTIAN; CEJAS, JIMENA DEL PILAR; DISALVO, EDGARDO ANIBAL; FRÍAS, M. DE LOS ÁNGELES; HUGO A. PÉREZ

San Luis

Encuentro; VIII Encuentro de Física y Química de Superficies EFyQS 2018; 2018

Física y Química de Superficies

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.