The contribution of water to the specific heat change at the glass-to-rubber transition of the ternary system BSA-water-NaCl

We studied the glass-to-rubber transition of a BSA-water-NaCl system using DSC. The T-g was 178-187 K and decreased with increasing NaCl content from 1:9 to 6:4 NaCl:BSA. The specific heat change (DeltaC(p)*, J/((g BSA)K)) at T-g increased as the weight ratio increased from 1:9 to 5:5 NaCl:BSA, as did the change in calculated unfrozen water (UFW). The UFW was also correlated with the amount of NaCl in the glassy region with a correlation coefficient of approx. 6 (mol H2O)/(mol NaCl), which is comparable, to the hydration number of Na+. These results suggest that UFW could contribute to the DeltaC(p) at T-g of the BSA-water system.