Influence of organic solvents on interfacial water at surfaces of silica gel and partially silylated fumed silica

The effects of organic solvents (dimethylsulfoxide-d6 (DMSO-d6), chloroform-d, acetone-d6, and acetonitrile-d3) on the properties of interfacial water at surfaces of silica gel Si-40 and partially silylated fumed silica A-380 were studied by means of the 1H NMR spectroscopy with freezing-out of adsorbed water at 180 < T < 273 K. The results of the 1H NMR investigations were also analysed on the basis of the structural characteristics of silicas and quantum chemical calculations of the chemical shifts dH and solvent effects. DMSO-d6 and acetonitrile-d3 are poorly miscible with water in silica gel pores in contrast to the bulk liquids. DMSO-d6 and chloroform-d affect the structure of the interfacial water weaker than acetone-d6 and acetonitrile-d3 at amounts of liquids greater than the pore volume. Acetone-d6 and acetonitrile-d3 can displace water from pores under this condition. The chemical shift of protons in water adsorbed on silica gel is 3.5–6.5 ppm, which corresponds to the formation of two to four hydrogen bonds per molecule. Water adsorbed on partially silylated fumed silica has two 1H NMR signals at 5 and 1.1–1.7 ppm related to different structures (droplets and small clusters) of the interfacial water. # 2004 Elsevier B.V. All rights reserved.