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

Abstract

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.