Fourier transform ir spectroscopy of collagen and gelatin solutions: Deconvolution of the amide I band for conformational studies

The ir spectra of lathyritic rat skin collagen and calf skin gelatin solutions at a variety of temperatures were obtained using Fourier transform ir spectroscopy and a 9‐reflection, 2‐pass ZnSe prism sample cell. The spectra were then deconvolved (based on Kauppinnen's method) and the behavior of the amide I band at ∼ 1650 cm⁻¹ observed in detail. Throughout the temperature range studied (4–50°C), three component absorption peaks within the amide I band (at 1633, 1643, and 1660 cm⁻¹) are common to the spectra irrespective of the degree of triple helix content of the sample. Changes in the relative intensities of these component peaks are, however, conformationally dependent. During denaturation of the triple helix, the dominant 1660‐cm⁻¹ component in the native collagen spectrum diminishes and the 1633‐cm⁻¹ peak becomes relatively intensified. The inherently strong basicity of the carbonyl group of the proline residues together with the frequent occurrence of this imino acid in the X position of the Gly‐X‐Y triplet of collagen largely accounts for the −30‐cm⁻¹ shift of the amide I band during denaturation. Temperature and conformationally dependent changes in the fine structure of the amide I band from dilute solutions of collagen can be monitored in a reproducible and quantitative fashion.