Helix formation in poly(Nε,Nε,Nε‐trimethyl‐L‐lysine) and poly(L‐lysine): Dependence on concentration and molecular weight

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Abstract
Helix formation in (Lys)n · HClO4 and poly(Nε, Nε, Nε–trimethyl-L-lysine) · HClO4 [(LysMe3)n · HClO4] is dependent on peptide concentration and on molecular weight. For (LysMe3)n · HClO4 of degree of polymerization (DP) 2510 the midpoint of the coil-to-helix transition is 2 mM and for DP of 190 it is 5 mM. For (Lys)n · HC1O4 the peptide concentration for half-helix is 30–60 times as high, and is only weakly dependent, if at all, on molecular weight. Helix formation is an intermolecular process. The use of methylated (Lys)n as the perchlorate permits study of the intermolecular coil-helix transition at low concentration, instead of the high concentration (ca. 1–2M) required for (Lys)n · HBr. At constant peptide concentration helix content increases with added NaClO4. The higher the peptide concentration, the less NaClO4 is needed to induce helix.