Thermal unfolding curves of high concentration bovine IgG measured by FTIR spectroscopy.

The purpose of this research is to study the thermal unfolding of high concentration bovine Immunoglobulin G (IgG) under 26 different experimental conditions by Fourier Transform Infrared spectroscopy with improved purge conditions and software calculations. When bovine IgG (25-200 mg/mL) was thermally denatured between pH 4.0 and 8.0, it was observed that at 25 mg/mL concentration, the protein exhibited maximum thermal stability at pH 6.0 and 7.0 as evident from the apparent T(m) values. Increasing the concentration from 25 to 100 mg/mL at those pH values increased the thermal resistance of the protein by 2-3 °C. But, at 200 mg/mL, IgG showed a small decrease in its transition temperature. Presence of 100 mM Trehalose enhanced the T(m) values at all conditions and possibly prevented the complete loss of IgG as insoluble aggregates at higher temperatures. Second derivative plots were constructed to explain the conformational changes of IgG during thermal unfolding.