Chem. J. Chinese Universities ›› 2023, Vol. 44 ›› Issue (6): 20230017.doi: 10.7503/cjcu20230017

• Analytical Chemistry • Previous Articles     Next Articles

Understanding the Water Structures in Deep Eutectic Solvents by Near-infrared Spectroscopy

WANG Yan1,2, CAI Wengsheng1,2, SHAO Xueguang1,2()   

  1. 1.Research Center for Analytical Sciences,College of Chemistry,Tianjin Key Laboratory of Biosensing and Molecular Recognition,State Key Laboratory of Medicinal Chemical Biology,Nankai University,Tianjin 300071,China
    2.Haihe Laboratory of Sustainable Chemical Transformations,Tianjin 300192,China
  • Received:2023-01-13 Online:2023-06-10 Published:2023-03-04
  • Contact: SHAO Xueguang E-mail:xshao@nankai.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(22174075);the Natural Science Foundation of Tianjin, China(20JCYBJC01480);the Foundation Research Funds for the Central Universities, Nankai University, China(63211019);the Program of Haihe Laboratory of Sustainable Chemical Transformations, China(ZYTS202105)

Abstract:

The hydrogen bond network structure of choline chloride/urea deep eutectic solvents(DESs)-water mixtures was studied in the range of 5%—95% water content by near infrared spectroscopy. Through the analysis of the near-infrared spectra after choline chloride and urea mixing, the spectral feature of the interaction between urea —NH group and choline chloride Cl- was found, indicating that the formation of NH···Cl- was the reason for the decrease of DESs melting point. Through the near-infrared spectrum analysis of DESs-water mixtures with different water contents, the spectral information of the interaction between water molecules and between water molecules and the —NH and C=O groups in urea was found. Water mainly exists in three kinds of structures, including the bulk water, the hydrated water with urea C=O and the bridge water connect —NH groups. The bulk water destroyed NH···Cl- in DESs, reducing the stability of the system, while the bridge water between urea —NH molecules and the hydrated water with urea C=O increase the stability of the system. The relative content of the three water structures in DESs is related to the water content. The water content of 40%—80% can not only effectively reduce the viscosity of the system, but also maintain the properties of DESs.

Key words: Near infrared spectroscopy, Deep eutectic solvent, Choline chloride/urea, Water structure

CLC Number: 

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