Thermal behavior, structure, dynamic properties of aqueous glycine solutions confined in mesoporous silica MCM-41 investigated by x-ray diffraction and quasi-elastic neutron scattering.
J Chem Phys
; 149(12): 124502, 2018 Sep 28.
Article
em En
| MEDLINE
| ID: mdl-30278668
ABSTRACT
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.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
J Chem Phys
Ano de publicação:
2018
Tipo de documento:
Article
País de afiliação:
Japão