Structure and dynamics of supercooled water in the hydration layer of poly(ethylene glycol).

Pub Date : 2022-09-08 eCollection Date: 2022-09-01 DOI:10.1063/4.0000158
Yuqing Li, Zehua Han, Changli Ma, Liang Hong, Yanwei Ding, Ye Chen, Junpeng Zhao, Dong Liu, Guangai Sun, Taisen Zuo, He Cheng, Charles C Han
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Abstract

The statics and dynamics of supercooled water in the hydration layer of poly(ethylene glycol) (PEG) were studied by a combination of quasi-elastic neutron scattering (QENS) and molecular dynamics (MD) simulations. Two samples, that is, hydrogenated PEG/deuterated water (h-PEG/D2O) and fully deuterated PEG/hydrogenated water (d-PEG/H2O) with the same molar ratio of ethylene glycol (EG) monomer to water, 1:1, are compared. The QENS data of h-PEG/D2O show the dynamics of PEG, and that of d-PEG/H2O reveals the motion of water. The temperature-dependent elastic scattering intensity of both samples has shown transitions at supercooled temperature, and these transition temperatures depend on the energy resolution of the instruments. Therefore, neither one is a phase transition, but undergoes dynamic process. The dynamic of water can be described as an Arrhenius to super-Arrhenius transition, and it reveals the hydrogen bonding network relaxation of hydration water around PEG at supercooled temperature. Since the PEG-water hydrogen bond structural relaxation time from MD is in good agreement with the average relaxation time from QENS (d-PEG/H2O), MD may further reveal the atomic pictures of the supercooled hydration water. It shows that hydration water molecules form a series of pools around the hydrophilic oxygen atom of PEG. At supercooled temperature, they have a more bond ordered structure than bulk water, proceed a trapping sites diffusion on the PEG surface, and facilitate the structural relaxation of PEG backbone.

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聚乙二醇水化层中过冷水的结构与动力学。
采用准弹性中子散射(QENS)和分子动力学(MD)相结合的方法研究了聚乙二醇(PEG)水化层中过冷水的静力学和动力学。比较了乙二醇(EG)单体与水摩尔比为1:1的氢化PEG/氢化水(h-PEG/D2O)和完全氘化PEG/氢化水(d-PEG/H2O)两种样品。h-PEG/D2O的QENS数据显示了PEG的动力学,d-PEG/H2O的QENS数据显示了水的运动。两种样品的弹性散射强度均在过冷温度下发生转变,而这些转变温度取决于仪器的能量分辨率。因此,两者都不是相变,而是一个动态过程。水的动力学可以描述为Arrhenius到超Arrhenius的转变,它揭示了PEG周围水化水在过冷温度下氢键网络的松弛。由于MD得到的PEG-water氢键结构弛豫时间与QENS (d-PEG/H2O)得到的平均弛豫时间吻合较好,MD可以进一步揭示过冷水化水的原子图像。结果表明,水合水分子在聚乙二醇的亲水性氧原子周围形成一系列的池。在过冷温度下,它们具有比散装水更有序的键结构,在PEG表面进行捕获位点扩散,促进PEG主链的结构松弛。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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