Effect of temperature and pH on the β–helix transition of poly( L ‐lysine) in sodium dodecyl sulfate solution

The conformational phase diagram of poly( L ‐lysine) (4.6 × 10 −4 M , residue) in sodium dodecyl sulfate (1.6 × 10 −2 M ) solution was constructed from circular dichroism results at various temperatures and pH's. Poly( L ‐lysine)–sodium dodecyl sulfate complexes undergo a β–helix transition upon raising the pH of the solution. The transition pH tends to shift downward at elevated temperatures. No helix–β transition can be detected for poly( L ‐lysine) in sodium dodecyl sulfate solution (pH > 11) even after 1‐hr heating at 70°C. This is in marked contrast with uncharged poly( L ‐lysine) solution without sodium dodecyl sulfate, which is converted into the β‐form upon mild heating of the solution above 50°C.