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Abstract Infrared absorption and x‐ray diffraction measurements have been made of D , L ‐copoly‐γ‐benzylglutamate fibers (cast from dioxane solutions) with various D / L ratios and with various degrees of polymerization. It was found that each chain of these copolymers consists of a random coil portion and an α‐helix portion and that the conformation of the latter is similar to the α‐helix of pure poly‐γ‐benzyl‐ L ‐glutamate. It was also found that the fraction of the α‐helix portion increases with the degree of polymerization of the copolymer. A simplified polymerization mechanism has been proposed for mixtures of D ‐ and L ‐amino acid N ‐carboxyanhydrides. A model of the molecular conformation of the D , L ‐copolypeptide chains derived from this proposed polymerization mechanism is in good agreement with infrared, x‐ray, and other measurements. Based on the results of these observations, we discuss the number of L ‐ or D ‐residues linked in succession that is required for initiating the formation of an α‐helix during the course of polymerization.
Tsuboi et al. (Thu,) studied this question.