Conformation of Poly( l -glutamic acid) in Solutions of a Cationic Surfactant with an ω-Hydroxyl Group

The conformation of poly(l-glutamic acid) was examined based on the circular dichroism spectra in solutions of ω-hydroxyalkylammonium bromides with the dodecyl or undecyl chain and the methyl-, dimethyl- or trimethylammonium moiety, as well as in normal surfactant solutions of dodecylammonium bromides with a corresponding cationic group used as a reference. The conformational change from a random coil to an α-helix was observed, depending on the chain length and head group of the surfactant. A surfactant with a longer chain length induced the α-helix at a lower concentration. A surfactant with more methyl groups has less ability for inducing an ordered conformation, presumably due to a steric hindrance, though it is more hydrophobic. No ordered conformation of poly(l-glutamic acid) was observed in surfactants with the trimethylammonium cationic group.