Interactive forces between phosphatidylcholine bilayers in monovalent salt solutions

Abstract

We have used X-ray diffraction and the osmotic force technique to investigate the effect of monovalent salts on the interactive forces between dipalmitoylphosphatidylcholine (DPPC) bilayers, distearoylphosphatidylcholine (DSPC) bilayers, dilauroylphosphatidylcholine (DLPC) bilayers, and dioleoylphosphatidylcholine (DOPC) bilayers. The Hamaker constant of the van der Waals force and the decay equation of the hydration force were determined by both the analysis technique of W. Tamura-Lis, L. J. Lis, and J. M. Collins ( J. Colloid Interface Sci. 114, 214 (1986)) and that of D. M. LeNeveu, R. P. Rand, V. P. Parsegian, and D. Gingell ( Biophys. J. 18, 209 (1977)). The majority of monovalent cations had little effect on the net force between phosphatidylcholine bilayers. However, the presence of monovalent anions caused an increase in the attractive force between DPPC bilayers. The electrostatic force between DPPC bilayers in 1 M KBr was analyzed and a binding ratio of one ion per 20 lipid headgroups at maximum hydration was inferred.