Study Of Hydrogen Bond-driven Structural Changes In Aqueous Solutions By Raman Spectroscopy

Water is widely recognized as the primary source of life and the site of most chemical and biological reactions.It plays an essential role in various fields,including physical chemistry,earth science,and biomedicine.Therefore,the structure and properties of water have always been hot topics of research interest.However,as research progresses,numerous abnormal physical properties of water continue to emerge.Understanding how water interacts with other substances in solutions can be advantageous for delving deeper into these anomalous properties and the changes in hydrogen-bonding network structure.In this paper,we investigate three representative aqueous systems by Raman spectroscopy,namely alcohol-water system,water in salt-organic solvent system,and silicon quantum dots-water system.Firstly,we clarify the intermolecular interactions and changes of hydrogen-bonding network structure in alcohol solutions and silicon quantum dot solutions under different conditions by analyzing the shift and intensity of Raman characteristic peaks.Secondly,we conduct Raman spectrum measurement and molecular dynamics simulation of water-in-salt-γ-butyrolactone ternary system and elucidate the microphysical mechanisms of the interaction between molecules and the hydrogen-bonding structure transition.The results are obtained as follows:（1）The impact of varying volume fractions methanol/ethanol on the hydrogen bonding network structure in water is investigated using spontaneous and stimulated Raman spectroscopy combination.The results indicate that the addition of a small quantity of alcohol strengthens the O-H vibration peak intensity of water,and make it shifts towards a lower wavenumber,indicating that the hydrogen bond structure in water is enhanced.This is attributed to the enhanced hydrogen bond structure in the hydration shell around the hydrophobic groups and the compression between H2?:?:?:H^-.However,as the alcohol volume fraction increases,the O-H vibration Raman peaks shift to higher wavenumber,and the peak intensity gradually become weaker until it disappears,indicating that the hydrogen bonding network structure in water is destroyed.This is because of self-association between alcohol molecules that deforms or even destructs the cage structure of liquid water around hydrophobic groups,thereby destroying the hydration shell structure around the alcohol molecules.At the same time,the C-H⁺in alcohol molecule is attracted by the lone electron pair on the oxygen atom in water molecule to form H₃O⁺,and then interacts with adjacent water molecules through the H?H repulsion,weakening the hydrogen bonding network structure of water molecules.Furthermore,the presence of ice Ih-like structure at low alcohol concentrations is discovered using stimulated Raman scattering.This research provides insights into the effect of hydrophilic and hydrophobic groups in alcohol on water molecules,which has implications in the fields of physical chemistry,food processing,and biomedicine.（2）The hydrogen bond dynamics and microstructure changes in water-in-salt（Na Cl O₄-H₂O）-organic solvent（γ-butyrolactone:GBL）ternary system are studied using Raman spectroscopy combined with molecular dynamics simulation.Through the analysis of water characteristic peaks,it is found that the hydrogen bonding network structure in water can be destroyed by both Na Cl O₄ and GBL,and Na Cl O₄ is stronger than GBL in the destruction of water.Through the analysis of the C=O characteristic peak of GBL,it is found that the interaction between GBL and water molecules is the strongest,and the interaction between GBL and sodium ions is the weakest.Using molecular dynamics simulation,it is found that with the increase concentration of GBL in water-in-salt system,the structure of salt and water can be dispersed,and the clusters of salt and water become smaller in size and more in number.But during this process,the salt and water maintain the same structure,indicating that even at high concentrations of GBL,the salt remains bound to the water.In addition,as the GBL concentration increased,the number of hydrogen bonds in water becomes less.This study clarifies the changes in the hydrogen bonding network structure and the strength of intermolecular interactions in the water-in-salt-organic solvent ternary system,which is of great significance for the design of anti-freezing batteries with high conductivity and low temperature performance.（3）The effects of 2 nm and 5 nm silicon quantum dots on hydrogen bonding structure in water under low temperature and dynamic high-pressure conditions are analyzed by spontaneous and stimulated Raman spectroscopy.First,the characteristic peaks of water are analyzed by temperature-variable Raman spectroscopy,and it is found that silicon quantum dots increase the phase transition temperature（liquid water-ice Ih）of water,which is due to the strong hydrogen bonding interaction between water molecules and silanol groups on the surface of silicon quantum dots.Then,using stimulated Raman spectroscopy to measure pure water and silicon quantum dot solutions under dynamic high-pressure conditions.It is found that water molecules are adsorbed on silicon surface through electron transfer and form strong hydrogen bonds,leading to the occurrence of stimulated Raman peak assigned to strong hydrogen bonds in silicon quantum dot solutions.And due to the surface effect,the enhancement effect of 2 nm silicon quantum dots on hydrogen bonding is stronger than that of 5 nm silicon quantum dots.In backward stimulated Raman scattering,the hole-electron pairs interact with the pump light,leading to the formation of a large excess of electrons in 2 nm silicon quantum dot aqueous solution,causing a strong electrostatic field(>MV cm^-1).Additionally,the excess electrons couple with water molecules,thereby enhancing the hydrogen bond structure and Raman scattering cross section of water molecules.As a result,a low-frequency lattice vibration peak(313 cm^-1)is found in backward stimulated Raman scattering of 2 nm silicon quantum,indicating the generation of the ice VIII-like structure in solution.This study enriches the microscopic mechanism of the interaction between water and nanoscale materials.