Abstract
The helix–coil transition of poly(Nγ-carbobenzoxy-L-α,γ-diaminobutyric acid) (PCLB) in mixtures of dichloroacetic acid (DCA) and 1,2-dichloroethane (EDC) was studied by optical rotatory dispersion (ORD) measurement. At DCA contents between 55 and 58 vol%, the Moffitt parameter b0 increased with increasing temperature, passed through a maximum, and gradually decreased above 40°C. This result indicates that in mixtures of DCA and EDC of appropriate compositions, PCLB undergoes a dual transition: one which is normal (helix to coil) at lower temperatures and one which is inverse (coil to helix) at higher temperatures. The ORD data were analyzed theoretically to evaluate the equilibrium constant s for the helix formation as a function of temperature T and solvent composition. A plot of In s at a fixed solvent composition against 1/T followed a curve convex downward, corresponding to the dual transition. The conformation of PCLB in a helicogenic solvent, dimethyl sulfoxide, was investigated by light scattering and viscometry, and it was found from the observed relation between the mean-square radius of gyration ‹S2› and molecular weight that PCLB takes on the form of an interrupted helix in this solvent. The molecular weight dependence of ‹S2› and intrinsic viscosity indicates that the helix of PCLB is as stable as those of poly(Nε-carbobenzoxy-L-lysine) and poly(Nδ-carbobenzoxy-L-ornithine), but less stable than that of poly(γ-benzyl L-glutamate).
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Saruta, S., Einaga, Y. & Teramoto, A. Solution Properties of Synthetic Polypeptides. XXII. Helix–Coil Transition of Poly(Nγ-carbobenzoxy-L-α,γ-diaminobutyric acid). Polym J 12, 161–170 (1980). https://doi.org/10.1295/polymj.12.161
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DOI: https://doi.org/10.1295/polymj.12.161