The response of collagen molecules in acid solution to temperature

The response of collagen molecules in acid solution (0.25, 0.50 and 1.0 mg/mL) to temperature (20–50 °C) was studied by ultra-sensitive differential scanning calorimeter (US-DSC), atomic force microscopy (AFM) and fluorescence spectrophotometer. The enthalpy changes (ΔH) for collagen varied with collagen concentrations, indicating that the aggregation state of collagen molecules was correlated with its thermal effect. Fluorescence measurements of pyrene in collagen solutions, which showed the polarity of the microenvironment in collagen molecules, suggested different behaviors: aggregation (20–32 °C) and disaggregation (38–50 °C), which was manifested by the changes in morphology of collagen fibers as observed by AFM. Furthermore, emission intrinsic fluorescence spectra of collagen at different temperatures showed that the fluorescence intensity of collagen decreased with increasing temperature, and the dynamic response of collagen molecules to temperature was further explored from the corresponding two-dimensional correlation fluorescence spectra.