Infrared spectroscopy of collagen and collagen‐like polypeptides

Abstract The set of synthetic polytripeptides and polyhexapeptides which can adopt a triple‐helical form constitute a good model system for investigating collagen structure. Here we consider previous and new infrared spectroscopic studies on collagen and present the infrared spectra of a number of polymers with collagen‐like features. The amide A band position for all triple‐helical polypeptides is higher than that observed for most proteins and polypeptides, and this high frequency appears to be related to the degree of supercoiling of the triple helix. It is possible that with increased supercoiling of the three chains the angles between the groups involved in the intramolecular hydrogen bonds become less favorable, or these bonds may become unusually long. The frequency of the amide I band varies considerably for triple‐helical polypeptides with different amino acid sequences, and often minor bands are observed. This finding contrasts with the observations for polypeptides in a pleated sheet or α‐helical form, where the same amide I frequency is observed regardless of the amino acid composition. An explanation for this variation is proposed in terms of the hydrogen bonding properties of imino acids. Significant spectral changes in the amide I region are observed on hydration in the spectra of some triple‐helical polypeptides, but corresponding changes have not been found in the collagens examined.