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 c = 0.2-0.25 and becomes more visible as h increases. When h is lower than h 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.

Dynamical behaviors of structural, constrained and free water in calcium- and magnesium-silicate-hydrate gels

“…Therefore, as temperature decreases, the relaxation time of the free water molecules increases more rapidly than that of the constrained water, due to the stronger local order of the former. A similar phenomenon is also observed in studies on hydration dependence of systems such as rutile [39], MCM-41 [44] and lysozyme [31]. Here we define the quantity CLR as the constrained to liquid water ratio (where liquid means the sum of the constrained and free water fractions).…”

“…The sample with lower CLR exhibits a stronger super-Arrhenius behavior. Its characteristic relaxation time results faster at high temperatures and slower at low temperatures since at low temperatures the "cage-breaking" translational jumps of free water molecules in a tetrahedral hydrogen bonded network requires longer time [31,39,44]. Applying this evidence, we conjectured that M-S-H with ASN additives has higher CLR than pure M-S-H and that C-S-H sample has higher CLR than all the M-S-H samples.…”

“…This transition in 〈 〉 of the hydration water molecule from an Arrhenius (linear) behavior at low-temperature to a super-Arrhenius (non-linear) behavior at high-temperature is called the dynamic crossover. For pure M-S-H at ambient pressure, the dynamic crossover takes place at T L = 2261 K. This is also a common feature in various other hydrated systems [11,31,32,43]. The non-linear super-Arrhenius behavior happens for hydration water when an adequate fraction of free water molecules enables the "cage-breaking" translational jumps.…”

“…Fig. 4 shows the Arrhenius plot of the mean characteristic relaxation time 〈 〉 for the pure M-S-H. At high temperature data exhibits super-Arrhenius behavior, which can be fit by the Vogel-Fulcher-Tammann relation 〈 〉 , ( )-, while at low temperature data exhibits Arrhenius behavior, which follows the Arrhenius relation 〈 〉 ( ) [31]. In this experiment, our focus is the high temperature region from 280 K to 230 K. As shown in Fig.…”

“…Theoretical [24,25], computer simulation [26,27] and experimental studies [11,[27][28][29][30][31][32] suggest that in the supercooled regime, the relaxation of the translational motion of water molecules is highly stretched. Therefore, the stretched exponential decay with was previously used by us to replace the Lorentzian functions thus representing the translational contribution of the liquid water under confinement [10,31,32]. This model can fit the measured QENS spectra of cement paste well and thus the structural and liquid water (constrained water and free water) can be studied in detail [10].…”