Department of Chemistry, Faculty of Science, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180, Japan.
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), 162-1 Shirakata, Tokai 319-1106, Japan.
J Chem Phys. 2018 Sep 28;149(12):124502. doi: 10.1063/1.5039892.
Differential scanning calorimetry, X-ray diffraction, and quasi-elastic neutron scattering (QENS) measurements of aqueous glycine solutions confined in mesoporous silica (MCM-41) were performed at different glycine concentrations, pH, and loading ratio (=mass of glycine solution/mass of dry MCM-41) in the temperature range from 305 to 180 K to discuss the confinement effect on the thermal behavior, the structure, and the dynamic properties of the solutions. The freezing points of the confined glycine solutions decreased, compared with those of the bulk solutions. The corresponding exothermic peak due to ice formation became broader with an increase in the glycine concentration. By subtracting X-ray diffraction patterns of dry MCM-41 from those of glycine solution-loaded MCM-41, information about the structure of the confined glycine solutions was obtained. The radial distribution functions of the confined glycine solutions showed that the peaks assigned to the interaction between glycine molecules and the surface silanol (Si-OH) groups of MCM-41 at pH = 5 were observed, in contrast to the case at pH = 2. The QENS data on H/D substituted aqueous glycine solutions gave the translational diffusion coefficients and the residence time of glycine and water molecules confined in MCM-41 individually. The activation energy of the diffusion coefficient of a glycine molecule at pH = 5 was larger than that at pH = 2. These results imply that glycine molecules locate near the pore surface of MCM-41 due to the formation of hydrogen bonding between glycine molecules and the silanol group of the MCM-41 wall at pH = 5.
采用差示扫描量热法、X 射线衍射和准弹性中子散射（QENS）技术，在不同甘氨酸浓度、pH 值和负载比（甘氨酸溶液质量/干燥 MCM-41 质量）下，对介孔二氧化硅（MCM-41）中受限水合甘氨酸溶液进行了测量，温度范围为 305 至 180 K，以讨论受限效应对溶液热行为、结构和动力学性质的影响。与本体溶液相比，受限甘氨酸溶液的冰点降低。随着甘氨酸浓度的增加，冰形成的放热峰变得更宽。通过从负载甘氨酸溶液的 MCM-41 的 X 射线衍射图案中减去干燥 MCM-41 的 X 射线衍射图案，获得了受限甘氨酸溶液结构的信息。受限甘氨酸溶液的径向分布函数表明，在 pH = 5 时观察到了归因于甘氨酸分子与 MCM-41 表面硅醇（Si-OH）基团之间相互作用的峰，而在 pH = 2 时则没有。氘代水合甘氨酸溶液的 QENS 数据给出了甘氨酸和水分子在 MCM-41 中受限的平移扩散系数和停留时间。在 pH = 5 时，甘氨酸分子的扩散系数的活化能大于在 pH = 2 时的活化能。这些结果表明，由于甘氨酸分子与 MCM-41 壁的硅醇基团之间形成氢键，甘氨酸分子在 pH = 5 时位于 MCM-41 孔表面附近。
