Statistical Thermodynamic Analysis of Helix-Coil Transitions in Polypeptides

Synthetic polypeptides distinguish themselves from common polymer substances in the characteristic feature that a majority, though not all of them, have molecular chains capable of maintaining a partially or entirely helical secondary structure called a-helix in appropriate solvents over a certain range of temperature. Thus with a helix-forming polypeptide it is possible to observe (for example, by measurement of specific rotation) a change in molecular conformation from a-helix to random coil if either the temperature or the solvent composition is continuously varied. Since the discovery by Doty and collaborators [l–3] in the mid-1950s with poly(y-benzyl L-glutamate) and poly(L-glutamic acid), this thermally or solvent-induced helix-coil transition in polypeptide has created great interest in the field of macromolecular science and biophysical chemistry [4–10].