The thermal induced helix—β transition of poly(Nε‐methyl‐ L ‐lysine) and poly(Nδ‐ethyl‐ L ‐ornithine) in aqueous solution

Uncharged poly(Nε‐methyl‐L‐lysine) (PMLL) and its isomer, poly(Nδ‐ethyl‐L‐ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix‐to‐β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L‐lysine) (PLL). The rate of conversion follows the order: PMLL < PELO < PLL. The helix can be regenerated upon cooling near zero degrees, for instance, after more than 12 hr at 2°C. At concentrations less than 0.02% the β form is intramolecular, but at higher concentrations both intra‐ and intermolecular β forms are generated. Poly(Nδ‐methyl‐L‐ornithine) (PMLO), an isomer of PLL, behaves like poly(L‐ornithine); uncharged PMLO in alkaline solution is partially helical and becomes disordered at elevated temperatures.