Modulation of bilayer structures derived from diacetylenic phosphocholines containing oxygen linker β to diacetylene

Abstract

Phospholipids with diacetylenes present in the acyl chains form tubules and helices in aqueous dispersions. In order to modulate the morphology of bilayer structures and to understand the role of diacetylene in lipid-bilayer assembly, two diacetylenic phosphocholines, 1,2-bis(9,16-dioxa-hexacosa-11,13-diynoyl)- sn-3-phosphocholine and 1,2-bis(15-oxa-pentacosa-10,12-diynoyl)- sn-3-phosphocholine, in which the diacetylene is linked to the acyl chain by an oxygen spacer have been synthesized. Lipid dispersions were characterized by calorimetric, film balance and microscopic techniques. Placement of oxygen spacer influences the morphology of the bilayer assemblies formed in aqueous solution. When both ends of the diacetylene were linked to the acyl chain by oxygen atoms, liposomes (diameters ranging from 0.3–3.4 μm) were observed by optical microscopy. Linking only the terminal portion of the acyl chain to the diacetylene with an oxygen atom resulted in a lipid which formed tubular microstructures as well as vesicles. Diameter of the tubular structures ranged from 0.4–4.7 μm. Transmission electron microscopic (TEM) analysis of replicas of a freeze fractured sample of the dispersion revealed that the tubular structures were hollow cylinders consisting of an aqueous core surrounded by a wall of lipid.