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

IF 2.3 2区物理与天体物理 Q3 CHEMISTRY, PHYSICAL Structural Dynamics-Us 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。

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来源期刊

Structural Dynamics-Us CHEMISTRY, PHYSICALPHYSICS, ATOMIC, MOLECU-PHYSICS, ATOMIC, MOLECULAR & CHEMICAL

CiteScore

5.50

自引率

3.60%

发文量

审稿时长

16 weeks

期刊介绍： Structural Dynamics focuses on the recent developments in experimental and theoretical methods and techniques that allow a visualization of the electronic and geometric structural changes in real time of chemical, biological, and condensed-matter systems. The community of scientists and engineers working on structural dynamics in such diverse systems often use similar instrumentation and methods. The journal welcomes articles dealing with fundamental problems of electronic and structural dynamics that are tackled by new methods, such as: Time-resolved X-ray and electron diffraction and scattering, Coherent diffractive imaging, Time-resolved X-ray spectroscopies (absorption, emission, resonant inelastic scattering, etc.), Time-resolved electron energy loss spectroscopy (EELS) and electron microscopy, Time-resolved photoelectron spectroscopies (UPS, XPS, ARPES, etc.), Multidimensional spectroscopies in the infrared, the visible and the ultraviolet, Nonlinear spectroscopies in the VUV, the soft and the hard X-ray domains, Theory and computational methods and algorithms for the analysis and description of structuraldynamics and their associated experimental signals. These new methods are enabled by new instrumentation, such as: X-ray free electron lasers, which provide flux, coherence, and time resolution, New sources of ultrashort electron pulses, New sources of ultrashort vacuum ultraviolet (VUV) to hard X-ray pulses, such as high-harmonic generation (HHG) sources or plasma-based sources, New sources of ultrashort infrared and terahertz (THz) radiation, New detectors for X-rays and electrons, New sample handling and delivery schemes, New computational capabilities.