近红外光谱用于低温水结构的分析

采用近红外光谱分析并结合拉曼光谱和分子动力学模拟研究了二甲基亚砜(DMSO)-水混合物中水在低温时的结构,对DMSO降低水冰点的机理进行了讨论.通过对不同DMSO含量混合物的近红外和拉曼光谱分析,发现了DMSO与水相互作用的光谱信息,表明DMSO与水在混合物中主要以摩尔比1∶2和2∶1的氢键结构(DW2和D2W)的形式存在,结构形式主要取决于DMSO和水在混合物中的比例.通过对水和30%(摩尔分数)DMSO-水混合物的温控近红外光谱分析,发现DW2结构抑制四面体水结构的形成是混合物冰点降低的主要原因.采用分子动力学模拟对DMSO-水混合物体系进行的模拟进一步证明了结论的可靠性.

Near Infrared Spectroscopy for Low-temperature Water Structure Analysis

The structure of water and its flexibility have been widely studied due to the mysterious behavior in biological and chemical process. Under supercooled conditions, water may have special properties, such as the thermodynamic response and phase transformation. In this study, water structure in dimethyl sulfoxide(DMSO)-water mixture at low temperature was studied by near infrared spectroscopy combined with Raman spectroscopy and molecular dynamics simulation for understanding the mechanism of DMSO in reducing the freezing point of water. Through the analysis of the near-infrared and Raman spectra of the mixtures with diffe- rent DMSO contents, the spectral feature reflecting the interaction of DMSO and water was found, and two hydrogen-bonded DMSO-water structures(DW2 and D2W) were determined in the mixture of different DMSO/ water ratio. Analyzing the spectra obtained by temperature-dependent near-infrared spectroscopy for a 30%DMSO-water mixture over the temperature range from 20 ^oC to -70 ^oC, it was found that DW2 structure inhibits the formation of tetrahedral water structure at low temperature and this founding can be used to explain the reason for DMSO reducing the freezing point of the mixture. The result of molecular dynamics simulation also gave a proof for the reliability of the conclusion.