Dielectric relaxations of ice and uncrystallized water in partially crystallized bovine serum albumin-water mixtures.

To investigate the dielectric relaxations of ice in low-concentration protein-water mixtures, broadband dielectric spectroscopy measurements were performed on partially crystallized bovine serum albumin (BSA)-water mixtures with BSA concentrations of 1-10 wt% at temperatures in the range of 123-298 K. The temperature dependence of the relaxation time of ice observed in all these mixtures changes twice at T C1 (∼240 K) and T C2 (200-160 K) ( T C1 > T C2 ), i.e. , at which the apparent activation energy, E a , changes. Below 200 K, the relaxation of ice separates as 3-4 relaxations with different T C2 and E a values. The presence of the multiple ice relaxations is the same as that observed for the gelatin-water mixtures (T. Yasuda, K. Sasaki, R. Kita, N. Shinyashiki and S. Yagihara, J. Phys. Chem. B , 2017, 121 , 2896), but the concentration dependences of T C1 and T C2 are different. The relaxation interpreted to be due to uncrystallized water in 20 wt% and 40 wt% BSA-water mixtures reported (N. Shinyashiki, W. Yamamoto, A. Yokoyama, T. Yoshinari, S. Yagihara, R. Kita, K. L. Ngai and S. Capaccioli, J. Phys. Chem. B , 2009, 113 , 14448) was re-examined and concluded to be due to one of the multiple relaxations of ice.