Conformation of random polypeptide chains

Abstract

The characteristic ratios C_of and C_∞ are calculated for infinitely long poly(L-amino acid) chains having a-CH₂-R' substitution at the C^α atom, as functions of the valence angle τ at the C^α atom. The value of C_of is found to increase from 1.6 to 2.3 as τ varies from 105 to 115°. On the other hand, C^α decreases with increasing τ in the range 105-111°, passes through a minimum at 111°, and then increases slowly. Since, C_∞ is much less dependent on τ in the most commonly observed range (110-115°), any variation in τ in this range due to solvent would not appreciably affect C_∞. The calculated temperature coefficient of C_∞ is negative and increases significantly in absolute magnitude even for small deviations in τ from 110°.