Spectroscopy Of Supramolecular Clusters In Ethanol-Water Solution And Different Chinese Liquor

Water is an indispensable substance to sustain human life and survival.Despite its seemingly simple molecular structure,it is a very complex system.Ethanol is not only an important fuel in industry and daily life but also a commonly used organic raw material and solvent in laboratory.Ethanol molecule is a typical organic molecule containing hydrophobic and hydrophilic groups.Compared with the ideal solution,the mixed solution of water and ethanol exhibits significant deviations in various thermodynamic properties and parameters,such as self-diffusion coefficient,shear viscosity,excess volume,excess enthalpy,compressibility,and acoustic attenuation coefficient.Besides,we use 75%(v/v)ethanol sterilization in daily life.The main reason is that the bactericidal effect of ethanol solution at 75%has been proved to be the best.The real reason behind these anomalous properties and the generally accepted wisdom has to do with the hydrogen bond supramolecular network formed by water and ethanol and its induced local properties or global structure.Therefore,understanding the microscopic behavior and molecular interaction of ethanol-water solution in depth will be of great scientific significance to reveal the structure of the aqueous solution and explore its role in a variety of chemical and biological systems.More than 98% of Chinese liquor is composed of organic compounds such as ethanol-water solutions and less than 2%of the remaining trace ingredients which are composed of ester,phenolic,aldehydes,additives and other organic compounds.Different types of baijiu vary greatly in taste.Even the same type of baijiu of the same brand,taste of different degrees is also very different.Also,the taste of old spirits also changes with time compared with the new spirits.The change of chemical composition and the reduction of pungent odor played a leading role,but the optimal deconstruction of ethanol-water clusters was also considered to be important.Therefore,the study of supramolecular clusters formed by ethanol and water in liquor may play a very important role in monitoring the production quality of liquor and the improvement of its taste.In the first part of this paper,we investigated the differences of the supramolecular clusters formed in ethanol-water solutions measured over different concentrations of ethanol and different incubation times.The emission spectra and vibration spectra of different concentrations of ethanol were obtained by fluorescence spectra,Raman spectra,and its two-dimensional correlation spectra analysis.Different emission spectra positions correspond to different supramolecular clusters.The Raman shift of the vibration spectrum of the hydroxyl group can provide information about the hydrogen bond between ethanol and water.Among them,the correlation results indicate that at a low concentration range of 10-45%,the dominated cluster is(H₂O)_m(Et OH)corresponding to an emission peak at 373 nm,and the hydrogen bond formed between ethanol and water gradually strengthened.The fluorescence peak located at 373 nm was preferred to the fluorescence peak at 308 nm.In the medium concentration range of50?75%,ethanol began to self-association.The fluorescence peak located at 330 nm was preferred to the fluorescence peak at 308 nm.The cluster formed in this range is(H₂O)_m(Et OH)_n whose emission peak is located at 330 nm.In addition,the cluster is also the most stable than other clusters.At a high concentration range of 80-100%,the main cluster is(H₂O)(Et OH)_n corresponding to an emission peak at 308 nm.In this concentration range,the hydrogen bond formed between ethanol and water molecules is gradually weakened,and alcohol molecules preferentially self-association.The fluorescence peak located at 308 nm was preferred to the fluorescence peak at 373 nm.At this point,the(H₂O)_m cluster disintegrates,and the supramolecular cluster formed is dominated by(H₂O)(Et OH)_n corresponding to an emission peak at 308 nm.Therefore,the combination of multiple spectroscopic studies provides a new method for distinguishing different supramolecular clusters and their structures in ethanol-water mixtures.In the second part of this paper,the essence of supramolecular clusters and their intrinsic structural differences in three kinds of Fenjiu are studied by two-dimensional correlation fluorescence and Raman spectra.The effects of dilution,incubation time,and p H on the supramolecular clusters formed by three kinds of Fenjiu were studied.The results showed that the fluorescence spectrum of Fenjiu(a)was simple,and the peak position of Fenjiu(a)did not change significantly with the increase of incubation time.Moreover,after incubation at low p H for 12 hours,the position of the fluorescence spectrum of Fenjiu(a)did not change significantly(the emission peak located at 330nm),which indicated that the supramolecular clusters formed in Fenjiu(a)were dominated by(H₂O)_m(Et OH)_n.For Fenjiu(b)and Fenjiu(c),the main emission peak of the fluorescence spectrum is located at 310 nm which corresponding to the main supramolecular cluster is(H₂O)(Et OH)_n.Among them,the emission peak of the fluorescence spectrum of Fenjiu(b)was a significant difference with continuous dilution,and it was affected by p H greatly.The emission peak position of the fluorescence spectrum of Fenjiu(c)did not change significantly with continuous dilution,but it was affected by p H greatly.Based on 2DCOS of Raman,strong hydrogen bonds are mainly formed in Fenjiu(a)and Fenjiu(c),while weak hydrogen bonds are mainly formed in Fenjiu(b).To sum up,it is concluded that Fenjiu(a)is superior to Fenjiu(c)and superior to Fenjiu(b).Therefore,the fluorescence spectra,Raman spectra,and their two-dimensional correlation analysis may provide some quantitative indicators for the identification of different quality Fenjiu and other clear flavor liquors.