Conformation Analyses of Poly( l -lysine) Induced by Various Surfactants

The relative proportion of α-helix, β, and random-coil structures in each conformation of poly(l-lysine) (PLL) caused by surfactants was computed by simulating a mixed spectrum of typical circular dichroism(CD) spectra for these structures to the experimentally obtained spectrum. Simulation was done in both the 190–250 nm and 200–250 nm regions at 1-nm intervals. The results show that PLL assumed 52 and 75% α-helix (at largest) in sodium octyl sulfate (SOS) and sodium 1-octanesulfonate solutions, respectively. The α-helical structure was found to coexist with considerable amounts of β and random-coil structures in these surfactant solutions. For instance, 51% α-helical structure coexisted with 29% β-structure and 20% random-coil structure in 6.0 mmol dm−3 SOS. In contrast, PLL did not assume any α-helical structure in the concentration range of 0 to 10 mmol dm−3 sodium dodecyl sulfate(SDS). Rather, the random-coil structure was transformed to a β-structure when SDS was added to PLL. The effects of NaCl and of 1-octanol on the relative proportions of the three structures in PLL were also examined.