Effects of added urea and alkylureas on gel to liquid-crystal transitions in DOAB vesicles

The gel to liquid-crystal transition for vesicles in aqueous solution forme d by dimethyldi-n-octadecylammonium bromide (DOAB) occurs at 44.7 degrees C . Moreover, the shapes of the scans recorded by a sensitive DSC microcalori meter are very similar when the vesicular solutions are prepared starting w ith solid DOAB and comparable amounts of either solid urea or solid alkylur eas. Therefore, the DOAB vesicles in aqueous solution accommodate this clas s of solutes without marked changes in the melting temperature and the enth alpy of the transition. The contrast with effects of added surfactants and simple organic solutes such as THF and ethanol is particularly significant.