Eur. Phys. J. B 11, 127-130 (1999)
https://doi.org/10.1007/s100510050923

Bilayers of neutral lipids bear a small but significant charge

¹ Laboratoire de Physique Statistique de l'École Normale Supérieure (Associé au CNRS et aux Universités Paris VI et Paris VII) , 24 rue Lhomond, 75231 Paris Cedex 05, France
² Laboratoire de Physico-Chimie Moléculaire des Membranes Biologiques, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France

Corresponding author: ^a pincet@physique.ens.fr

Received: 18 December 1998
Published online: 15 September 1999

Abstract

Many experiments done on neutral lipid bilayers in pure water show weak repulsions. These weak forces prevent vesicles from adhering and are generally overcome by adding some salt in the aqueous medium. They also appear as stray repulsions in surface forces measurements made on lipid bilayers. Using a surface forces apparatus in pure water and in salt solution, we have measured the forces between two stearoyl-oleoyl-phosphatidyl-choline (SOPC) bilayers and between two dimiristoyl-phosphatidyl-ethanolamine (DMPE) bilayers. The results show that the repulsions are due to a small amount of negative charges coming from impurities in SOPC. This was quantitatively confirmed by electrophoretic measurements. There are 3 times less charges in the case of DMPE layers. The effect of these charges which is negligible at high salt concentration may significantly affect the adhesion energy and behaviour of neutral lipid bilayers between 0 and salt.