SYNTHESIS, THERMOTROPIC BEHAVIOR, AND PERMEABILITY PROPERTIES OF VESICULAR MEMBRANES COMPOSED OF CATIONIC MIXED-CHAIN SURFACTANTS

In order to elucidate the role of the linkage region that connects pol ar headgroups with hydrophobic segments in a lipid monomer, cationic m ixed-chain amphiphiles containing acyl and alkyl hydrophobic segments connected at the level of Me(2)N(+) headgroups 2a-d were synthesized. Related dialkyldimethyl-ammonium ion surfactants 1a-e and diacyl syste ms 3a-c were also synthesized. Despite mismatch in the connector regio n, amphiphiles 2a-d form bilayer vesicles like their dialkyl and diacy l counterparts, as revealed by electron microscopy. Introduction of an ester connector function between the polar and hydrophobic parts rais es the phase transition temperature (T-m), transition enthalpies, and resistance to ion permeation. Consideration of energy minimized confor mations points toward the importance of differences in the depth of ch ain penetration into the putative bilayer.