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arXiv 0810.0015cond-mat.softcond-mat.stat-mech
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过冷水中的压力效应:二维水模型与蛋白质表面水实验的比较

Pressure Effects in Supercooled Water: Comparison between a 2D Model of Water and Experiments for Surface Water on a Protein

Giancarlo Franzese, Kevin Stokely, Xiang-qiang Chu, Pradeep Kumar, Marco G. Mazza, Sow-Hsin Chen, H. Eugene Stanley

摘要:

在大量水中的实验证实了具有不同密度的水分子的两种局部排列的存在,但是,由于在低温$T$下不可避免的冻结,不能确定这两种排列是否在两个阶段中分离。为了避免冻结,新的实验测量了蛋白质表面上低$T$时的水动力学,发现了从高$T$时的非阿耳忒弥斯状态到低$T$时近似阿耳忒弥斯状态的交叉。受这些实验的启发,Kumar等人[Phys. Rev. Lett. 100,105701(2008)]通过Monte Carlo模拟和平均场计算,研究了在水的细胞模型中动态交叉与两个液相共存的关系,并预测:(i)动态交叉是等时的,即交叉时间$τ_{\rm L}$的值近似与压力$P$无关;(ii)低- $T$状态的Arrhenius活化能$E_{\rm A}(P)$随着$P$的增加而降低;(iii)$τ$达到固定宏观时间$τ^*\geq τ_{\rm L}$时的温度$T^*(P)$随着$P$的增加而降低;特别地,这对于$τ=τ_{\rm L}$达到固定宏观时间时的交叉温度$T_{\rm L}(P)$也是如此。在这里,我们将这些预测与最近的准弹性中子散射(QENS)实验进行比较。Q. Chu { \it等}在不同的$P$值下对水合蛋白质的影响。我们发现,实验与这三个预测一致。

英文摘要:

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 $T$, can not ascertain whether the two arrangements separate in 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. [Phys. Rev. Lett. 100, 105701 (2008)] investigated, by Monte Carlo simulations and mean field calculations, the relation of the dynamic crossover with the coexistence of two liquid phases in a cell model for water and predict that: (i) the dynamic crossover is isochronic, i.e. the value of the crossover time $τ_{\rm L}$ is approximately independent of pressure $P$; (ii) the Arrhenius activation energy $E_{\rm A}(P)$ of the low-$T$ regime decreases upon increasing $P$; (iii) the temperature $T^*(P)$ at which $τ$ reaches a fixed macroscopic time $τ^*\geq τ_{\rm L}$ decreases upon increasing $P$; in particular, this is true also for the crossover temperature $T_{\rm L}(P)$ at which $τ=τ_{\rm L}$. Here, we compare these predictions with recent quasi elastic neutron scattering (QENS) experiments performed by X.-Q. Chu {\it et al.} on hydrated proteins at different values of $P$. We find that the experiments are consistent with these three predictions.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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