Reentrant phase transitions of DNA-surfactant complexes

Abstract

Complexes of double-stranded DNA with the cationic surfactant cetyltrimethylammonium bromide have been studied using small angle X-ray diffraction at varying concentrations of DNA and the cosurfactant hexanol. At low DNA concentrations, an intercalated hexagonal (H_I^c)→lamellar (L_α^c)→inverted hexagonal (H_II^c) transformation is found on increasing hexanol content. The H_II^c structure is converted into L_α^c on adding more DNA. Further increase in hexanol content leads to a phase separation in the surfactant solution, and a reentrant L_α^c→H_II^c→L_α^c transition is observed as DNA concentration is increased. Such structural transformations of DNA-surfactant complexes, driven by DNA concentration, have not been reported until now.