Analytical Sciences

Thermal Behavior and Structure of Low-temperature Water Confined in Sephadex G15 Gel by Differential Scanning Calorimetry and X-ray Diffraction Method

Kanae ITO,* Koji YOSHIDA,* Kikujiro UJIMOTO,* and Toshio YAMAGUCHI*,**

*Department of Chemistry, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180, Japan
**Advanced Materials Institute, Fukuoka University, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180, Japan

The thermal behavior and structure of water confined in Sephadex G15 gel were investigated over a temperature range of 298 – 173 K at hydration levels, h (= mass of water/mass of dry G15 gel), of 0.24 – 1.38 by differential scanning calorimetry (DSC) and an X-ray diffraction (XRD) method, respectively. The ice-melting peaks on the DSC curves were deconvoluted to estimate the amounts of three states of water in G15 with h: free water, freezable bound water, and unfrozen water. The X-ray radial distribution functions of unfrozen water at h = 0.24 revealed that the hydrogen-bonded structure of water is largely distorted, due to hydrogen bonding with the surface hydroxyl groups of gel substrates, compared with those of freezable bound water at h = 0.47 and bulk water. A plausible separation mechanism of solutes in gel chromatography was considered from a structural point of view of confined water.

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