Characterization of monomeric and gemini cationic amphiphilic molecules by fluorescence intensity and anisotropy

Pyrene fluorescence intensity and conductivity measurements were used to determine the cmc of two monomeric surfactants namely, dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide as well as two gemini surfactants, 16-3-16 2Br and 16-4-16 2Br of the alkanediyl-alpha,omega-bis(alkyldimethyl ammonium bromide) type. Cmc measurements were confirmed using fluorescence anisotropy measurements employing fluorescein as probe. Anisotropy-concentration plots showed sigmoidal behaviour and the obtained values for cmc were in good agreement with those determined using conductivity and pyrene fluorescence intensity. Also, the anisotropy of both fluorescein and another fluorescent probe. perylene, were used to provide information on the micellar structure.