Synthesis of Ion-Pair Amphiphiles and Calorimetric Study on the Gel to Liquid-Crystalline Phase Transition Behavior of Their Bilayers

Abstract

In this work, nine homologous ion-pair amphiphiles (IPAs) were successfully prepared by the precipitation or ion-exchange methods. This demonstrated the feasibility of designing and synthesizing lipid-like amphiphiles from cheap and abundant single-chained cationic and anionic amphiphiles. The thermotropic transition behavior from gel phase (Lβ) through rippled phase (Pβ′) to liquid-crystalline phase (Lα) of these IPA bilayers in water was thereafter systematically studied by using differential scanning calorimetry. A database of pretransition temperature, main transition temperature, and the corresponding transition enthalpy/entropy of the nine IPA bilayers was documented. Different phase transition behavior is exhibited by IPA bilayers with different hydrocarbon chain lengths and symmetry. The main phase transition temperature (Tm) is consistently higher for IPAs with higher total number of carbon atoms in the hydrocarbon chains. For IPAs with the same total number of carbon atoms in the hydrocarbon cha...