Pressure Dependence of the Dynamic Crossover Temperatures in Protein and its Hydration Water (original) (raw)
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Observation of fragile-to-strong dynamic crossover in protein hydration water
Proceedings of The National Academy of Sciences, 2006
At low temperatures proteins exist in a glassy state, a state which has no conformational flexibility and shows no biological functions. In a hydrated protein, at and above 220 K, this flexibility is restored and the protein is able to sample more conformational sub-states, thus becomes biologically functional. This 'dynamical' transition of protein is believed to be triggered by its strong coupling with the hydration water, which also shows a similar dynamic transition. Here we demonstrate experimentally that this sudden switch in dynamic behavior of the hydration water on lysozyme occurs precisely at 220 K and can be described as a Fragile-to-Strong dynamic crossover (FSC). At FSC, the structure of hydration water makes a transition from predominantly high-density (more fluid state) to low-density (less fluid state) forms derived from existence of the second critical point at an elevated pressure.
The Journal of …, 2008
A super-Arrhenius-to-Arrhenius dynamic crossover phenomenon has been observed in the translational R-relaxation time and in the inverse of the self-diffusion constant both experimentally and by simulations for lysozyme hydration water in the temperature range of T L ) 223 ( 2 K. MD simulations are based on a realistic hydrated powder model, which uses the TIP4P-Ew rigid molecular model for the hydration water. The convergence of neutron scattering, nuclear magnetic resonance and molecular dynamics simulations supports the interpretation that this crossover is a result of the gradual evolution of the structure of hydration water from a high-density liquid to a low-density liquid form upon crossing of the Widom line above the possible liquid-liquid critical point of water.
Two dynamic crossovers in protein hydration water and their thermodynamic interpretation
2009
Studies of liquid water in its supercooled region have led to many insights into the structure and behavior of water. While bulk water freezes at its homogeneous nucleation temperature of approximately 235 K, for protein hydration water, the binding of water molecules to the protein avoids crystallization. Here we study the dynamics of the hydrogen bond (HB) network of a percolating layer of water molecules, comparing measurements of a hydrated globular protein with the results of a coarse-grained model that has been shown to successfully reproduce the properties of hydration water. With dielectric spectroscopy we measure the temperature dependence of the relaxation time of protons charge fluctuations. These fluctuations are associated to the dynamics of the HB network of water molecules adsorbed on the protein surface. With Monte Carlo (MC) simulations and mean-field (MF) calculations we study the dynamics and thermodynamics of the model. In both experimental and model analyses we find two dynamic crossovers: (i) one at about 252 K, and (ii) one at about 181 K. The agreement of the experiments with the model allows us
We investigate, for two water models displaying a liquid-liquid critical point, the relation between changes in dynamic and thermodynamic anomalies arising from the presence of the liquid-liquid critical point. We find a correlation between the dynamic fragility transition and the locus of specific heat maxima C max P ("Widom line") emanating from the critical point. Our findings are consistent with a possible relation between the previously hypothesized liquid-liquid phase transition and the transition in the dynamics recently observed in neutron scattering experiments on confined water. More generally, we argue that this connection between C max P and dynamic crossover is not limited to the case of water, a hydrogen bonded network liquid, but is a more general feature of crossing the Widom line. Specifically, we also study the Jagla potential, a spherically symmetric two-scale potential known to possess a liquid-liquid critical point, in which the competition between two liquid structures is generated by repulsive and attractive ramp interactions. Using molecular dynamics simulations, we also investigate the relation between the dynamic transitions of biomolecules (lysozyme and DNA) and the dynamic and thermodynamic properties of hydration water. We find that the dynamic transition of the macromolecules, sometimes called a "protein glass transition", occurs at the temperature of dynamic crossover in the diffusivity of hydration water, and also coincides with the maxima of the isobaric specific heat C P and the temperature derivative of the orientational order parameter. We relate these findings to the hypothesis of a liquid-liquid critical point in water. Our simulations are consistent with the possibility that the protein glass transition results from a change in the behavior of hydration water, specifically from crossing the Widom line.
Journal of Physics: Condensed Matter, 2008
Water's behavior differs from that of normal fluids, having more than sixty anomalies. Simulations and theories propose that many of these anomalies result from the coexistence of two liquid phases with different densities. Experiments in bulk water confirm the existence of two local arrangements of water molecules with different densities, but, because of inevitable freezing at low temperature T , cannot ascertain whether the two arrangements separate into two phases. To avoid the freezing, new experiments measure the dynamics of water at low T on the surface of proteins, finding a crossover from a non-Arrhenius regime at high T to a regime that is approximately Arrhenius at low T . Motivated by these experiments, Kumar et al (2008 Phys. Rev. Lett. 100, 105701) investigated, by Monte Carlo simulations and mean field calculations on a cell model for water in two dimensions (2D), the relation of the dynamic crossover with the coexistence of two liquid phases. They show that the crossover in the orientational correlation time τ is a consequence of the rearrangement of the hydrogen bonds at low T , and predict that: (i) the dynamic crossover is isochronic, i.e. the value of the crossover time τ L is approximately independent of pressure P; (ii) the Arrhenius activation energy E A (P) of the low-T regime decreases upon increasing P; (iii) the temperature T * (P) at which τ reaches a fixed macroscopic time τ * τ L decreases upon increasing P; in particular, this is true also for the crossover temperature T L (P) at which τ = τ L .
The Journal of Chemical Physics, 2009
The diffusive dynamics of hydration water in lysozyme is studied by high-resolution incoherent quasielastic neutron scattering spectroscopy and molecular dynamics ͑MD͒ simulations in a temperature range of 290 K Ͻ T Ͻ 380 K. The hydration level of the protein powder sample is kept at h = 0.35 gram of water per gram of dry protein to provide monolayer of water coverage on the protein surfaces. Two lysozyme samples, the H 2 O hydrated and the D 2 O hydrated, are measured in the experiments. The difference spectra of the two are used to extract the diffusive dynamics of the hydration water. The self-diffusion constant D of the hydration water is obtained from the analyses of the low-Q spectra. The Arrhenius plot of the inverse diffusion constant ͓i.e., log͑1 / D͒ versus 1 / T͔ shows a dynamic crossover from a super-Arrhenius behavior at low temperatures to an Arrhenius behavior at high temperatures bordered at T D = 345Ϯ 5 K. We also observe a pronounced increase in the migration distance d of the hydration water molecules above T D . We present evidence from the neutron scattering experiment that this dynamic crossover temperature in the hydration water coincides with that of the reversible denaturation of lysozyme determined by specific heat measurements. We further performed MD simulations of hydrated lysozyme powder to offer a plausible reason for this coincidence of the crossover phenomenon with the reversible denaturation of the protein.
Glass Transition in Biomolecules and the Liquid-Liquid Critical Point of Water
Using molecular dynamics simulations, we investigate the relation between the dynamic transitions of biomolecules (lysozyme and DNA) and the dynamic and thermodynamic properties of hydration water. We find that the dynamic transition of the macromolecules, sometimes called a ''protein glass transition,'' occurs at the temperature of dynamic crossover in the diffusivity of hydration water and also coincides with the maxima of the isobaric specific heat C P and the temperature derivative of the orientational order parameter. We relate these findings to the hypothesis of a liquid-liquid critical point in water. Our simulations are consistent with the possibility that the protein glass transition results from crossing the Widom line, which is defined as the locus of correlation length maxima emanating from the hypothesized second critical point of water.