Experimental and theoretical study of the effect of temperature on collagen in aqueous solution

Abstract

Background and Objectives: An experimental andtheoretical study ofthe effect oftemperature onthe vibrational spectra of an aqueous collagen solution in the range of 60–90°C was carried out. Results: According to the performed experiment, at first at a temperature of 60°C, an increase in the intensity of the absorption bands of the IR spectra of collagen is observed compared to room temperature, and then, with further heating of the aqueous collagen solution, the intensity of the absorption bands decreases. To explain this effect, a molecular modeling method was used, when the oligopeptide Gly-Pro-Hyp-Gly, the most frequently repeated in the structure of collagen of any type, was selected as the main structural fragment. The interpretation of the vibrational spectra of the selected molecular fragment of collagen showed qualitative and quantitative agreement with the experimental spectra, which made it possible to use it to explain the temperature dependence. Conclusion: An increase in the intensity of the absorption bands of the experimental IR spectrum of collagen at 60°C is associated with a change in the conformation of the zwitter-ion form of the oligopeptide Gly-Pro-Hyp-Gly, which occurs due to the rotation of the bipolar groups N+H3 and CO− relative to each other. A further increase in temperature leads to a decrease in the pH of the medium, and, as a consequence, to the formation of protonated Gly ionic forms located at the ends of the Gly-Pro-Hyp-Gly molecular fragment in an aqueous solution, which is confirmed by the calculation of theoretical spectra and their comparison with experiment.

Keywords

• collagen
• modeling of ir and raman spectra
• aqueous solution
• conformers
• dependence of vibrational spectra on temperature