Thermal analysis of protein-metallic ion systems

Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal TMDSC were used to analyze the protein-metallic ion interactions in silk fibroin proteins. The precise heat capacities were measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the silk-metallic salts system. Results show that K+ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (T-g) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca2+ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein structure. This indicates that the thermal analysis methods offer a new pathway to study protein-metallic ion systems, yielding very fruitful information for the study of protein structures in the future.