Hydration-dependent dynamic crossover phenomenon in protein hydration water

Abstract

The characteristic relaxation time τ of protein hydration water exhibits a strong hydration level h dependence. The dynamic crossover is observed when h is higher than the monolayer hydration level h[subscript c] =0.2–0.25 and becomes more visible as h increases. When h is lower than h[subscript c], τ only exhibits Arrhenius behavior in the measured temperature range. The activation energy of the Arrhenius behavior is insensitive to h, indicating a local-like motion. Moreover, the h dependence of the crossover temperature shows that the protein dynamic transition is not directly or solely induced by the dynamic crossover in the hydration water.