Elucidation of the Hydration Mechanism of Hydrophobic Groups in Organic Compounds as a Clue to Investigate Water Structures in Living Bodies

• Project/Area Number: 13640504
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Physical chemistry
• Research Institution: Fukui University
• Principal Investigator: MIZUNO Kazuko Center for Instrumental Analysis, Assistant professor, 機器分析センター, 助教授 (10126641)
• Project Period (FY): 2001 – 2002
• Project Status: Completed (Fiscal Year 2002)
• Budget Amount: ¥3,500,000 (Direct Cost: ¥3,500,000); Fiscal Year 2002: ¥900,000 (Direct Cost: ¥900,000); Fiscal Year 2001: ¥2,600,000 (Direct Cost: ¥2,600,000)
• Keywords: external double reference method / temperature dependence of chemical shift / hydration of CH / Hydration mechanism / Blue-shifting hydrogen bond / bi-functional hydrogen bond / CH・・・O / 1,4-dioxane / ab initio M.O.法 / ケミカルシフトの温度依存性 / 外部複基準法 / 疎水性基の水和メカニズム / CH…O水素結合 / blue-shifting水素結合 / ケミカルシフトの濃度依存性 / C-H伸縮振動バンド

Research Abstract

1. Presentation of "The External Double Reference Method" to measure chemical shifts on a unified scale
All the chemical shifts were measured by the external reference method using a capillary tube with a bulb at the bottom for a reference substance, and corrected in terms of the difference in bulk volume magnetic susceptibilities between the sample and a reference solution obtained in situ at every temperature. In the present work for the first time, we took the temperature dependence of the chemical shift and the bulk volume magnetic susceptibility of the reference solution into consideration to study temperature dependence of chemical sifts. We call the method the external double reference method.
2. The denial of "The iceberg structure model" on the basis of some experimental proofs
^1H-NMR and IR studies were carried out for 1,4-dioxane/H_2O, 1,3-dioxane/H_2O and 4-methyl-1,3-dioxane/H_2O mixtures over the whole concentration range at temperatures of 1, 25, and 50℃. ^1H NMR spectra w ere also acquired for mixtures. It was found that an anomalous polarization of the water molecules, which had been observed in the dimethylsulfoxide/H_2O and acetone/H_2O mixtures, did not occur in the three different aqueous dioxane mixtures, in which ΔH and ΔS for mixing are negative in water-rich region and so-called hydrophobic hydration occurs. Thus, we have concluded that the hydrophobic moiety in an organic solute itself does not play a role to cause anomalously high polarization of the water molecules. We have also concluded that the hydrogen-bonding basicity of the polar group is an important factor for the anomalous polarization of the water in the water-rich region.
3. A new mechanism for the hydration of CH groups in organic compounds with polar groups
It was found that the frequencies of IR C-H stretching vibration modes of 1,4-dioxane increase and the absorption intensities of the modes decrease with increasing water concentration. Since these spectroscopic features correspond well to the formation of the blue-shifting C-H・・・OH_2 hydrogen bonds obtained from ab initio calculations for complexations in gas phases, we can categorize the solvation of the C-H groups in the dioxanes in aqueous solutions as blue-shifting C-H・・・O hydrogen bonding. Thus we propose for the first time that the hydration of CH groups in organic solutes having a polar group is due to the formation of blueshifting C-H・・・OH_2 hydrogen bonds. We propose the formation of a bi-functionally hydrogen-bonded hydration complex in which each water molecule plays a role as both a proton donor in the conventional O-H・・・X(O, N, ..) hydrogen bonding and an proton acceptor in the blue-shifting C-H・・・O hydrogen bonding simultaneously, X・・・H-O(H)・・・H-C.

Research Products

• [Publications] Mizuno, K., Imafuji, S., Fujiwara, T., Ohta, T., Tamiya, Y.: "Hydration of the CH Groups in 1,4-Dioxane Probed by NMR and IR : Contribution of Blue-shifting CH…OH_2 Hydrogen Bonds"J. Phys. Chem. B. 107. 3972-3978 (2003)
  • Description: 「研究成果報告書概要(和文)」より
• [Publications] Kazuko Mizuno, Shingo Imafuji, Teruko Fujiwara, Tomoko Ohta, and Yuka Tamiya: "Hydration of the CH Groups in 1,4-Dioxane Probed by NMR and IR : Contribution of Blue-shifting CH・・・OH_2 Hydrogen Bonds"J. Phys. Chem. B. 107(16). 3972-3978 (2003)
  • Description: 「研究成果報告書概要(欧文)」より
• [Publications] Mizuno, K., Imafuji, S., Fujiwara, T., Ohta, T., Tamiya, Y.: "Hydration of the CH Groups in 1,4-Dioxane Probed by NMR and IR : Contribution of Blue-shifting CH…OH_2 Hydrogen Bonds"J.Phys.Chem.B. 107・18. (2003)