【作者】 杨博；

【导师】 孙成林；

【作者基本信息】 吉林大学 ， 光学， 2023， 博士

【摘要】 水是人类赖以生存的物质,在自然界中广泛存在。虽然水分子构成很简单,但是液态水的研究却极具挑战性。水之所以如此神秘,与其复杂的氢键网络密切相关。水与其他物质相互作用形成的二元溶液在物理、化学和生物过程中扮演着重要角色。复杂相互作用不仅会影响水结构,而且会影响水分子的动力学性质。因此,水溶液中微观结构和分子动力学过程的变化一直是水-有机化学领域的研究热点。本论文主要使用二维相关拉曼光谱（2D Raman-COS）研究外扰作用下有机分子诱导水结构变化,并阐明氢键和疏水效应在有机分子诱导水的氢键网络增强中的作用。具体研究结果如下:（1）通过拉曼光谱对浓度和温度外扰作用下乙二醇（EG）诱导水结构转变进行研究。O-H伸缩振动模式的光谱变化表明当EG/水摩尔比小于1/28时,EG诱导水的氢键网络结构增强,这是亚甲基基团的疏水效应引起的。当进一步增加EG浓度时,水的氢键网络结构会逐渐变弱。降低EG水溶液的温度,位于3120cm^-1处会出现出冰Ih的拉曼峰。保持温度外扰不变,冰Ih的拉曼峰强度随EG浓度增加而减弱,这是由于EG与水分子之间形成强氢键,打破了水的氢键网络结构,导致水的冰点降低。此外,温度降低导致3200 cm^-1左右的拉曼峰强度增加,代表水分子的有序性增加。2D Raman-COS对外扰作用下EG诱导水结构转变的分析结果显示,水的强氢键结构优先响应温度或浓度外扰,并诱导水的弱氢键结构发生转变。最后,采用密度泛函理论（DFT）探究EG诱导水结构转变,为实验结果提供理论支持。（2）采用拉曼光谱研究氢键和疏水效应在有机醇诱导水的氢键网络增强中的作用。H-O-H弯曲振动模式的光谱变化显示在整个浓度变化范围内,正丙醇（NPA）会诱导H-O-H弯曲振动模式蓝移,而甲醇则诱导其红移。与它们不同的是,当乙醇/水摩尔比低于1/5时,H-O-H弯曲振动模式蓝移,进一步增加乙醇浓度则红移。这些结果显示随着烷基链长度的延长,醇诱导水的氢键网络增强程度不断增大。对乙醇与EG水溶液进行比较研究,结果证实醇诱导增强水的氢键网络主要源于烷基链的疏水效应。使用2D Raman-COS探究醇诱导水结构变化的细节,结果表明:水的自由O-H和强氢键结构优先响应醇含量的变化,并诱导水的弱氢键结构发生转变;与其他C-H振动模式相比,CH₃伸缩振动模式优先响应水含量变化,这意味着疏水效应优先发生在醇的甲基基团周围。最后,使用DFT对醇诱导水结构转变进行理论分析,与实验结果基本一致。（3）利用拉曼光谱结合导数光谱法研究浓度外扰作用下,二甲基亚砜（DMSO）、丙酮和异丙醇（IPA）诱导水结构转变的过程。结果显示在疏水效应近似的情况下,有机分子诱导水的氢键网络增强主要归因于亲水基团的强氢键作用。此外,导数光谱法证实O-H伸缩振动光谱分解为三个子谱带更合理,分别位于3225,3450和3625 cm^-1。最后,O-H伸缩振动模式的同谱系2D Raman-COS结果表明,水的强氢键结构比弱氢键结构优先响应有机分子的浓度变化。O-H和C-H伸缩振动模式相关形成的异谱系2D Raman-COS结果显示,水结构优先C-H伸缩振动模式响应DMSO浓度变化,表明DMSO水溶液中可能存在弱氢键C-H…O。相反,丙酮和IPA水溶液的异谱系2D Raman-COS结果则暗示甲基基团不会与周围水分子形成氢键。（4）采用自发拉曼和受激拉曼光谱研究浓度外扰作用下,N,N-二甲基甲酰胺（DMF）水溶液中分子间相互作用的变化。结果表明当DMF/水摩尔比达到1/6.5时,DMF诱导水的氢键网络结构发生转变,形成DMF-3H₂O和DMF-2H₂O团簇。同谱系2D Raman-COS结果显示水的自由O-H和强氢键结构都优先水的弱氢键结构响应DMF浓度变化。异谱系2D Raman-COS结果则显示CH₃对称及反对称伸缩振动模式比水结构优先响应DMF浓度变化,这表明DMF的疏水基团不会与周围水分子形成氢键。本论文所选择的研究对象从独特的EG分子延伸至一系列的醇分子,再拓展到一般的有机分子,最后聚焦到特殊有机分子DMF,证实了研究结果对有机分子水溶液具有普适性。本论文所取得的研究结果有助于理解有机分子水溶液中分子间相互作用的微观物理机制,从而推动其他复杂水-有机化学体系的研究。更多还原

【Abstract】 Water is fundamental to human existence and is widespread in nature.Despite the simplicity of its elemental composition,the study of liquid water was challenging.The mysterious nature of water is closely related to its complex hydrogen bond（H-bond）network.Binary solutions formed by the interaction of water with other substances play an important role in physical,chemical and biological processes.Complex interactions affect not only the structure of water,but also the dynamic properties of water molecules.Therefore,changes in microstructure and molecular dynamics processes in aqueous solutions have been a hot topic in the field of water-organic chemistry.This paper focuses on the structural changes in water induced by organic molecules using two-dimensional Raman correlation spectroscopy（2D Raman-COS）,and elucidates the roles of H-bond and hydrophobic effects in organic molecule-induced the enhancement of water structure.The specific results were as follows:（1）The ethylene glycol（EG）-induced water structural transformation under external perturbations of concentration and temperature were investigated by Raman spectroscopy.The spectral change in the O-H stretching mode indicated that when the molar ratio of EG/water is less than 1/28,EG-induced enhancement of water structure,resulting from the hydrophobic effect around the methylene groups of EG.Further increase in EG concentration,the H-bond structure of water was gradually weakened.Decreasing the temperature of the aqueous EG solution,the Raman peak of ice Ih was observed at 3120 cm^-1.Keeping the external temperature perturbation constant,the Raman peak of ice Ih decreases with increasing EG concentration due to the strong H-bonding between EG and water molecules,which breaks the H-bonding network structure of water,resulting in a lower freezing point of water.In addition,the decrease in temperature induces an enhancement of the Raman peak at about 3200cm^-1,representing an increase in the orderliness of the water molecules.Further analysis of the EG-induced water structural transformation by 2D Raman-COS reveals that the strong H-bond structure of water preferentially responds to external perturbations,and induces a transition to the weak H-bond structure of water.Finally,the EG-induced water structural transition was analyzed using density functional theory（DFT）to provide evidence for the spectroscopic study.（2）The role of H-bonding and hydrophobic effects in the enhancement of the H-bonding network of water induced by organic alcohols was investigated using Raman spectroscopy.The spectral changes in the H-O-H bending mode demonstrated that n-propanol（NPA）induced a blue shift and methanol caused a red shift over their entire range of compositions,while ethanol exhibited a blue shift only when the ethanol/water molar ratio was below 1/5.These results indicated that the extent of alcohol-induced water structure enhancement increased as the length of the alkyl chain increased.Further comparison with aqueous EG solution revealed that the enhanced water structure stemmed mainly from the hydrophobic effect rather than the hydrophilic effect of hydrophilic hydroxyl groups.Alcohol-induced water structural transitions were further analyzed using 2D Raman-COS,which showed that the free O-H and strong H-bond structure of water respond preferentially to changes in alcohol content,inducing a transition in the weak H-bond structure of water.In addition,the CH₃ stretching mode of alcohol responds preferentially to variations in water content compared to other C-H vibrational modes,which implies that hydrophobic effects occur predominantly around the methyl group of the alcohol.Finally,the alcohol-induced structural transitions of water were analyzed using DFT,which was consistent with the experimental results.（3）The structural changes in water induced by dimethyl sulfoxide（DMSO）,acetone,and isopropanol（IPA）were investigated by Raman spectroscopy combined with derivative spectroscopy under external perturbation of concentration.The results show that the organic molecules induce water structure enhancement mainly from the strong H-bonding of hydrophilic groups in the approximate agreement of hydrophobic effects.In addition,the second-order derivative spectral results suggested that the spectral decompositions of the O-H stretching mode into three sub-bands are more reasonable,located at 3225,3450 and 3625 cm^-1,respectively.Finally,the homospectral 2D Raman-COS in the O-H stretching mode showed that the strong H-bond structure of water responds preferentially to changes in the concentration of organic molecules than the weak H-bond structure.The heterospectral 2D Raman-COS formed by the correlation of O-H and C-H stretching modes indicated that the spectral peaks of the water structure change in preference to those of the C-H stretching mode as the DMSO concentration increases,suggesting that weak H-bond C-H…O may be present in aqueous DMSO solution.In contrast,the heterospectral 2D Raman-COS of binary solutions of water with acetone or IPA demonstrated that the methyl group does not H-bond with the surrounding water molecules.（4）Spontaneous and stimulated Raman spectra were used to study the changes in intermolecular interactions in aqueous solutions of N,N-dimethylformamide（DMF）at different concentrations.The results showed that when the DMF/water molar ratio reached 1/6.5,DMF induced a transition in the H-bond network structure of water,forming DMF-3H₂O and DMF-2H₂O complexes.The homospectral 2D Raman-COS showed that the free O-H and strong H-bond structure of water respond preferentially to the increase in DMF content than the weak H-bond structure of water.The heterospectral 2D Raman-COS indicated that the CH₃ symmetric and asymmetric stretching mode respond preferentially to the increase in DMF content,suggesting that the hydrophobic group of DMF does not H-bond with water molecules.The subjects chosen for this paper extend from unique EG molecules to a range of alcohol molecules,then to general organic molecules,and to the specific DMF molecule,confirming the universality of these results for aqueous solutions of organic molecules.Our results contribute to understanding the microphysical mechanisms of intermolecular interactions in aqueous solutions of organic molecules,thus advancing the study of other complex water-organic chemistry.更多还原