Conformation of poly( L -glutamic acid) in aqueous solutions of linear amphiphiles with a cationic group at both ends

Abstract

The conformations of poly(l-glutamic acid) [P(Glu)] in solutions of the bipolar amphiphile 1,20-icosanediylbis(alkylammonium chloride) [C20(RA)2], where RA includes trimethylammonium (TMA), dimethylammonium (DMA), or methylammonium (MA), were investigated with measurements of the circular dichroism spectra at 10–35 °C. All C20(RA)2 induced an α-helix of P(Glu) in the aqueous solutions. The residue molar ellipticity at 222 nm showed a similar dependence on the amphiphile concentration (Cs) below 0.5 of the ratio of 2Cs to the residue concentration (Cp) of P(Glu), but it separated into three directions at 2Cs/Cp>0.5. C20(MA)2 induced an α-helix of P(Glu) at 2Cs/Cp 0.5. C20(DMA)2 and C20(TMA)2 also induced an α-helix, but a helix aggregate. C20(TMA)2 indicated a strong temperature dependence and did not induce a complete α-helix at 35 °C.