Lipid bilayers adhesion forces

Fig. VI-6. The force between two crossed cylinders coated with mica and carrying adsorbed bilayers of phosphatidylcholine lipids at 22°C. The solid symbols are for 1.2 mM salt while the open circles are for 10.9 roM salt. The solid curves are the DLVO theoretical calculations. The inset shows the effect of the van der Waals force at small separations the Hamaker constant is estimated from this to be 7 1 x 10 erg. In the absence of salt there is no double-layer force and the adhesive force is -1.0 mN/m. (From Ref. 66.)...

Some lipid bilayers adhere to each other when they get into close contact. Attractive electrostatic forces between the positively charged ammonium groups and negatively charged phosphate groups in the opposing lipid molecules lead to an adhesion [1263]. In addition, hydrogen bonds between the lipid molecules contribute to the attraction. 

Shear of a liquid-crystalline lipid phase which is in equilibrium with a water phase can result in exposure of hydrocarbon chains to water which results in a strong tendency to fuse with other bilayers with exposed hydrocarbon chains. The formation of liposomes, discussed in the next paragraph, is a consequence of such rupture and fusion behaviour. Recently, the first experimental measurements of the force behind such adhesion, the hydrophobic force, were reported (Israelachvili and Paskey, 1982). It was found to be a long-range force with the same range of existence as the van der Waals interaction and shows an exponential fall-off with a decay length of 10 A. 

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