Near-infrared spectroscopic study of molecular interaction in ethanol-water mixtures

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2019-11, Vol.222, p.117183, Article 117183
• Main Authors: Dong, Qin, Yu, Chen, Li, Lian, Nie, Lei, Li, Danyang, Zang, Hengchang
• Format: Article
• Language: English
• Subjects: Aquaphotomics; Hydrogen bonds; Hydrophobic hydration; Molecular interaction; Near infrared spectroscopy
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2019.117183

Given the importance of ethanol-water mixtures in many chemical and biological processes, the molecular interaction in ethanol-water binary system was studied using near-infrared (NIR) spectroscopy. Excess spectra (in form of excess absorption coefficient) and Gaussian fitting were applied to analyze low concentration ethanol-water mixtures, ranging from 0 to 10% (v/v). With the knowledge of aquaphotomics, six kinds of water species were identified for 0–10% ethanol-water system, and it was indicated that water can be a sensitive probe for analyzing the structural changes and the interactions in the solutions. The excess spectra and two-dimensional (2D) correlation spectroscopy were introduced for high concentration mixtures (10–100%) analysis and found that the intermolecular hydrogen bonding strength between ethanol and water reaches to the maximum at 40% ethanol concentration which may be related to some abnormal properties of alcoholic solutions reported previously. In 40–100% mixtures, ethanol molecules tend to initiate the self-association which leads to the weakening of the interaction between ethanol and water. This paper not only deepens the understanding of the structure and dynamics of alcoholic solution, but also opens a new perspective in molecular interaction analysis in aqueous system by understanding the roles of water. [Display omitted] •Excess spectra were used to explain hydrogen bonding changes in ethanol-water mixtures.•Water was proved to be a probe sensing for the molecular interactions.•The maximum hydrogen bonding strength was found in 40% ethanol-water mixture.•Hydrogen bonding changes may explain the abnormal properties and protein precipitation.