Alkyl chain ordering of asymmetric phosphatidylcholines adsorbed at a liquid-liquid interface

Vibrational spectroscopic investigations of hydrocarbon chain ordering in phosphatidylcholines (PCs) adsorbed from aqueous solution to a carbon tetrachloride-water interface presented here examine on a molecular level the organization pertinent to the surface characteristics displayed by these films. In a series of saturated symmetric and asymmetric chain PCs, both symmetric PCs with 16 or fewer carbons per acyl chain and highly asymmetric PCs produced relatively disordered films at the liquid-liquid interface. The longest chain PCs studied, 1,2-distearoyl-sn-glycero-3-PC (C-18/C-18), 1-stearoyl-2-palmitoyl-sn-glycero-3-PC (C-18/C-16) and 1-palmitoyl-2-stearoyl-sn-glycero-3-PC (C-16/C-18), formed well-ordered layers at room temperature. The results can be explained in terms of enhanced chain-chain interactions among the longer, nearly symmetric hydrocarbon chains. Properties of the neat liquid-liquid interface that may influence the formation of these well-ordered two-dimensional phases are discussed.