Use of the Ising model for doubly ordered macromolecules

We developed a statistical model, based on a one-dimensional Ising model, for a recently studied polypeptide which displays an endothermic helix-to-coil transition with an “anomalous” behavior in the heat of solution. The model supports the assumption of an ordering of the chains due to a specific hydrogen bond interaction among them, beside the helical ordering of the backbone; this double ordering of the macromolecule produces the “anomalous” experimental behavior. With the hypothesis of a highly coopertive interaction among amide groups and side chains, we find that the backbone cooperation increases the chains cooperation, but not vice versa; this influence when the cooperation in the backbone increases.