Hydrogen-bonded structure of hydrated water in polyvinyl pyrrolidone aqueous solution investigated by X-ray absorption and emission spectroscopy

• Published in: Journal of molecular liquids 2024-06, Vol.403, p.124822, Article 124822
• Main Authors: Ozaki, Koichi, Nakada, Masaru, Kunisu, Masahiro, Yahiro, Jumpei, Yamazoe, Kosuke, Cui, Yitao, Miyawaki, Jun, Harada, Yoshihisa
• Format: Article
• Language: English
• Subjects: Hydrogen-bonded structure; Intermediate water; Non-freezing water; Polyvinylpyrrolidone; X-ray absorption spectroscopy; X-ray emission spectroscopy
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2024.124822

•The O 1s XAS and XES measurements of PVP aqueous solutions were performed under ambient pressure.•The XES spectra of water molecules interacting with PVP were extracted.•The non-freezing water in PVP aqueous solutions has a highly distorted hydrogen-bonded structure.•The intermediate water has a characteristic shape of the 1b1 peak with an indistinct gap between the 1b1′ and 1b1″. Polyvinylpyrrolidone (PVP) is a hydrophilic polymer that is widely used in various biomedical applications owing to its excellent biocompatibility. It has been suggested that water-polymer interactions play a key role in controlling biocompatibility, although the molecular-level consequences of these interactions remain unknown. In this study, the hydrogen-bonded structures of water molecules hydrating PVP were investigated using X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). XAS spectral profiles revealed that the CO bonds in highly concentrated PVP aqueous solutions have at least two states: one where hydrogen bonds are formed with water molecules and the other where they are not. In the XES profile of water extracted from a solution with a stoichiometric ratio of nw = 1.0, increased hydrogen bonding and hydrogen bond distortion were identified from the enhancement of 1b1′ and 3a1 peaks, respectively. Because it is difficult for water molecules to form strong hydrogen-bonded structures in tetrahedral coordination at nw = 1.0, these findings suggest that the presence of strong hydrogen bonds between the CO sites and water prevents the formation of tetrahedrally coordinated hydrogen-bonded structures among water molecules.