Phase Transitions in the Lyotropic System Dipalmitoyl Phosphatidyl Choline (DPPC) Doped with the Antileprosy Drug, Dapsone

Abstract

We have carried out DSC investigations of the ice-water [iw, wi and (wi)¹], chain-melting (CM) and chain ordering (CO) transitions in DPPC-water (model membrane) systems for a range of water concentrations for both pure and DDS-doped samples. The temperatures, T _CM and T _co, are hardly affected by the inclusion of DDS, showing that DDS does not get embedded in the acyl chain layers. Increase in CM and CO transition widths indicates varied environments for the DPPC molecules in the presence of DDS. The enthalpies for the ice-water transitions point to the fact that DDS (a) reduces “free” water content of the membrane, (b) affects the population of the different bound water differently, perturbing the structure of the vicinal water. X-ray diffraction results show that the chain-melting transition which is strongly first order for the pure system is broadened by the inclusion of DDS, supporting the DSC data.