Interaction of Guanidine-type Surfactants with Biological Substances

The interaction of guanidine-type cationic surfactants with bovine serum albumin (BSA) and liposome were investigated. Dodecylguanidine hydrochloride (C12A0G) and several dodecanoylamide alkylguanidine hydrochlorides (C12AmG, m = 2, 3, 4, 6) were used as the guanidine-type surfactants. In the interaction of these surfactants with BSA as a model protein, the binding isotherms of the surfactants to BSA were analysed. The structural change of the protein was also examined on the basis of circular dichroism and UV absobance data. In the interaction of these surfactants with liposome as a lipid bilayer model, we studied the effects of the surfactants on the solubilisation of liposomes and the release of carboxyfluorescein from liposomes. In addition, the effect of the surfactant molecular structure on the skin irritation was evaluated in connection with the interactions of the surfactants with BSA and liposome. It was found that small amounts of binding of C12A0G caused both a partial destruction of a-helix and an aggregation of BSA. C12A0G also induced the aggregation of liposomes, whereas C12AmG showed no such action. The presence of Am group in C12AmG appeared to reduce the skin irritation in parallel with the weakening of the interaction of the guanidine group with the protein and the lipid bilayer.