HELIX COIL TRANSITION IN MULTICOMPONENT RANDOM COPOLYPEPTIDES IN WATER .3. INCLUSION OF NEAREST-NEIGHBOR INTERACTIONS AND APPLICATION TO RANDOM COPOLYMERS OF (HYDROXYBUTYL)-L-GLUTAMINE, L-ALANINE, L-PHENYLALANINE, L-LYSINE, AND GLYCINE

Water-soluble random copolymers, poly[N5-(hydroxybutyl)-L-glutamine-co-L-alanine-co-L- phenylalanine-co-L-lysine-co-glycine], were synthesized, fractionated, and characterized, and the thermally induced helix-coil transitions of these five-component copolymers in water were determined by optical rotatory dispersion measurements. The melting behavior of the copolymers was analyzed with the theory reported earlier. To account for the discrepancies between the experimental and theoretical melting curves, the helix-coil transition theory for multicomponent random copolymers was extended by considering the effects of specific nearest-neighbor interactions on the melting curves, i.e., by assuming that the statistical weight of a residue depends not only on the chemical structure of the residue but also on that of its nearest-neighbor residue. By optimization of two independent parameters in the statistical weights, the extended theory accounts for the experimental results. The implications of these statistical weights for the five-component random copolymers are discussed. © 1990, American Chemical Society. All rights reserved.