Effect of cationic surfactants on the conformation and aggregation of poly(L‐glutamic acid)

Abstract

AbstractThe effects of three cationic surfactants, dodecylammonium chloride (DAC), dodecyldimethylammonium chloride (DDAC), and dodecyldimethylammonium chloride (DTDAC), on the conformation of poly(L‐glutamic acid) and at neutral pH were examined by CD. The maximum extent of the α‐helix induction occurs for each surfactant when the mixing ration is about unity. Different effects specific to each surfactant, as described below, appear in the range of mixing ratios larger than that required for the maximum induction. In the case of DTAC, the α‐helices disintegrate into random coils. In the case of DDAC, the aggregation of α‐helices takes place eventually leading to precipitation. Solubilization of the precipitates occurs at high mixing ratios. The most complex behavior is seen in the case of DAC; aggregation of α‐helices occurs only to a small extent and the formation of a small complex predominates over aggregation takes place again as DAC concentration increases further. Induction of the α‐helix is favored by dilution at a constant mixing ratio but is suppressed by the addition of NaCl.