Conformation changes in the nonionizable water-soluble synthetic polypeptide poly-N5-(3-hydroxypropl)-1-glutamine.

Abstract

AbstractPoly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) samples of molecular weights from 20,000 to 140,000 were synthesized by the action of 3‐amino‐1‐propanol on poly‐γ‐benzyl‐L‐glutamate. PHPG is freely soluble in water and in a variety of organic solvents and was shown to be devoid of functional groups ionizing in the pH range 2–12. From hydrodynamic data (viscosity, sedimentation, diffusion) and optical rotatory measurements (ORD in the range 289–650 mμ, circular dichroism and Cotton effects in the range 210–280 mμ) on samples of different molecular weight it was concluded that PHPG is largely helical in methanol, ethylene glycol, formamide, dimethylform‐amide, n‐butylamine, and acetic acid, and randomly coiled in dichloroacetic acid and formic acid. In water the polymer is partly helical, the degree of helicity increasing with decreasing temperature and increasing molecular weight. The following solutes were found to decrease the helicity in the order indicated: NaOH > guanidinium chloride > urea > HCl > LiBr > NaBr > NaCl > H2O. Detergents do not destroy the helical conformation. Helix–coil transition curves were obtained for the solvent pairs: methanol–water, acetic acid–water, and chloroform–dichloroacetic acid. Thermal transitions were observed in water, water–methanol (70:30 v/v), and dichloroacetic acid–ethylene dichloride (22:78 v/v), the latter being of the “inverted” type. Heats of helix formation were calculated and their significance is discussed.