LYOTROPIC MESOMORPHISM OF ALKYL ESTERS OF ACYL-L-CARNITINES

The lyotropic polymorphism of a series of alkyl esters of acyl-L-carni tine has been studied by optical polarizing microscopy and X-ray diffr action. The different structures observed as a function of concentrati on and temperature have been characterized and their topology determin ed. As a result, two different phase sequence patterns have been detec ted: esters of normal alcohols bearing an alkyl chain of 6 or more car bon atoms in the acyl substituent display only a lamellar phase, while compounds which bear a relatively short alkyl chain (4 or less carbon atoms) show in addition non-lamellar type I hexagonal and cubic Q(230 ) phases. From the analysis of the areas-per-molecule at the polar/apo lar interface, the ability of the compounds investigated to form not o nly non-lamellar phases, but also direct micelles in isotropic solutio n has been related to the structural characteristics of the molecules. Curved, convex interfaces (in micelles and in non-lamellar phases) ar e possible only for the most polar acylcarnitines which have a relativ ely short alkyl chain, so that they behave like single chain surfactan ts; the most paraffinic derivatives, which have a relatively long alky l chain, are effective double chain surfactants and then generate only quasi-planar interfaces.