Long-range orientational order of branched chain phospholipid monolayers

Abstract

Two-dimensional phase behaviour and ordering of branched chain glycerophosphoethanolamines (n-16PEs) having a 2-branched hexadecanoyl chain (the side chains are methyl, ethyl, pentyl and tetradecyl) at the sn-1 position of the glycerol backbone and an unbranched hex-adecyl residue at the sn-2 position, are systematically studied. The ordering of the alkyl chains is increasingly disturbed by short side chains of increasing length so that at n = 5 a condensed monolayer phase cannot be formed. Further side chain elongation enhanced again the ordering with the consequence that a tetradecyl side chain leads to texture and thermodynamic properties of the monolayer which correspond to those of a triple-chain phospholipid. Texture and shape of the dendritic or fractal-like condensed phase domains are similar to that known from double-chain phosphatidyl-amine monolayers. However, in agreement with the ordering, individual differences in the inner textures are observed at different side chain lengths.