?Effect of water polarized at the carbonyl groups of phosphatidylcholines on the dipole potential of lipid bilayers?

DIAZ, S.; AMALFA, F.; BIONDI DE LOPEZ, A.C.; DISALVO, E.A.

LANGMUIR

AMER CHEMICAL SOC

Año: 1999 vol. 15 p. 5179 - 5182

0743-7463

Lipids are amphiphilic molecules that stabilize in a bilayer when dispersed in water as a consequence of their hydration above the transition temperature. Water hydrating the lipids in the lamellar structure organizes around the polar head groups at the membrane interface.1 Calorimetry, sedimentation, equilibrium dialysis, and X-ray diffraction haveshownthat around 18-24 molecules of water are associated with phosphatidylcholines.4,7,8 The different values obtained with each methodology are a consequence of the fact that not all the water molecules are linked to the chemical groups of the lipid molecules with the same strength. Therefore, those numbers are averaged in time; that is, the residence times of different water molecules will be different. On average, X-ray diffraction studies have been able to demonstrate that water not only locates at the well-defined polar region but also may penetrate into the region of the ester bonds between the glycerol backbone and the fatty acid residues.7 It has been established that water organization determines important membrane properties such as the excluded volume, the hydration forces, and the dipole potential.2,3,6 The excluded volume contributes to the barrier of permeability and to the membrane structure.2,5 The hydration water also accounts for the repulsion energy between surface membranes, thus counteracting the adhesion, adsorption, and aggregation processes.3 The hydration forces determine a physical and electrical barrier to the interaction between membranes or of membranes with proteins. It corresponds to a steric effect of excluded volume and an electrical field repulsion due to the orientation of the dipoles normal to the bilayer interface.