Origin of the blueshift of water molecules at interfaces of hydrophilic cyclic compounds

Title: Origin of blue shift of water molecules at interfaces of hydrophilic cyclic compounds
Authors: Katsufumi Tomobe, Eiji Yamamoto, Dusan Kojić, Yohei Sato, Masato Yasui and Kenji Yasuoka
Journal: Science Advances, 3, e1701400 (2017)
DOI: 10.1126/sciadv.1701400

Abstract:
Water molecules at interfaces of materials exhibit enigmatic properties. A variety of spectroscopic studies have observed a high-frequency motion in these water molecules, represented by a blueshift, at both hydrophobic and hydrophilic interfaces. However, the molecular mechanism behind this blueshift has remained unclear. Using Raman spectroscopy and ab initio molecular dynamics simulations, we reveal the molecular mechanism of the blueshift of water molecules around six monosaccharide isomers. In the first hydration shell, we found weak hydrogen-bonded water molecules that cannot have a stable tetrahedral water network. In the water molecules, the vibrational state of the OH bond oriented toward the bulk solvent strongly contributes to the observed blueshift. Our work suggests that the blueshift in various solutions originates from the vibrational motions of these observed water molecules.