The helix—coil transition of poly-N5-(2-hydroxyethyl)L-glutamine (PHEG) in aqueous mixtures of 2-propanol was followed by means of light-scattering measurements. For each of the two samples investigated, the curve for the root-mean-square radius of gyration ‹S2›1/2 vs. helical fraction fN exhibited a broad minimum. This behavior was consistent with the previous optical rotatory dispersion data, which had indicated that the transition of PHEG was characterized by very low cooperativity. The data for ‹S2› were analyzed by the method of Teramoto et al., to give 14.7A for the effective bond length of the randomly coiled portions and 1.97A for the pitch of the helix per monomer residue. The disparity of the latter value from the 1.5A expected for the α-helix was attributed to short-range interactions between the helical sections and the neighboring random coil residues. The Flory viscosity constant Φ was found to stay almost constant (about 2×1021) over the range of fN up to 0.9. This fact was taken to suggest that, for substantial portions of the transition, the average shape of a high molecular weight PHEG molecule is spherically symmetric like random coil.
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Ohta, T., Norisuye, T., Teramoto, A. et al. Solution Properties of Synthetic Polypeptides. XX. Light-Scattering Study of Poly-N5-(2-hydroxyethyl)L-glutamine in the Helix—Coil Transition Region. Polym J 8, 281–287 (1976). https://doi.org/10.1295/polymj.8.281
- Helix—Coil Transition
- Light Scattering
- Mean-Square Radius of Gyration
- Flory Viscosity Constant
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