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Molecular basis of water activity in glycerol-water mixtures

グリセロールと水の混合物の水分活性の分子的基礎

中川 洋; 大山 泰史*

Nakagawa, Hiroshi; Oyama, Taiji*

水分活性は同じ温度の純水とサンプルの水蒸気圧の比で定義された熱力学量である。この値は微生物の増殖挙動、酵素活性、食品の保存性の信頼できる指標になることが知られている。しかし、水分活性の分子基盤は関連する分野で議論になっている。グリセロールと水の混合物は、その割合を変えることで水分活性を制御できる。本研究では、水分活性の分子基盤を、水分収着等温線を軸に示差走査熱分析法,赤外分光法,非干渉性中性子準弾性散乱法で調べた。その結果、水分子の拡散ダイナミクスが水素結合の分子振動と相関があることを見つけた。さらに重要なことに、グリセロール水溶液の水分活性は、溶液中の水の水素結合ネットワークと水のダイナミクスで説明できること見出した。

Water activity is thermodynamic value defined as the ratio of the equilibrated vapor pressure of the sample to the vapor pressure of pure water at the same temperature. It is known that this value is a reliable indication of the microbial growth, enzymatic activity, and preservation and quality of foods. However, a molecular basis of water activity is still under debate in the related multiple area. Glycerol-water mixtures can provide the variation of water activities by controlling the ratio of glycerol and water. In this study, molecular basis of water activity was examined by using differential scanning calorimetry, attenuated total reflection Fourier-transform infrared spectroscopy and incoherent quasi-elastic neutron scattering based on isotherm sorption curve of glycerol-water mixtures. We found that diffusive dynamics of water is correlated with hydrogen bond related local vibrational dynamics in the glycerol-water mixtures. More importantly, water activity of glycerol-water mixtures can be explained by the hydrogen boding network and molecular dynamics of water in the solutions.

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