Reentrant phase transitions of DNA-surfactant complexes

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-alpha(c))-->inverted hexagonal (H-II(c)) transformation is found on increasing hexanol content. The H-II(c) structure is converted into L-alpha(c) on adding more DNA. Further increase in hexanol content leads to a phase separation in the surfactant solution, and a reentrant L-alpha(c)-->H-II(c)-->L-alpha(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.