Silicon-29 NMR evidence of alkoxy substituted aqueous silicate anions

Abstract

Silicon-29 NMR provides the first direct evidence for the presence of stable alkoxy substituted silicate anions in aqueous alkaline silicate solutions to which aliphatic mono-or poly-hydroxy alcohols have been added.

Sensitivity considerations in polarization transfer and filtering using dipole–dipole couplings: Implications for biomineral systems

“…This 2D 29 Si{ 1 H} HETCOR spectrum measured for the diatoms in Fig. 8 is similar to that acquired from powdered siliceous spicules from a species of sponge [53], which also showed predominant and indefinite interactions between the 29 Si atoms in the biogenic silica framework and most likely hydroxyl protons associated with silanol moieties.…”

“…Under both alkaline and acidic conditions, silicon alkoxides are known to undergo hydrolysis reactions in aqueous solutions [88]. However, solution-state NMR measurements have shown that it is possible to form stable Si-O-C bonds in an aqueous environment using tetraalkylammonium species, which may stabilize Si-O-C moieties [53]. Low frustule surface areas ($10 m 2 /g, from N 2 adsorption measurements), a disordered glass-like silica substrate, complicated distributions of organic components, and exceedingly complex biogenic assembly processes contribute to the challenges inherent in characterizing and understanding biosilica materials and biomineral systems in general.…”

Silicon‐29 NMR study of the formation of monomethoxysilicic acid in methanolic alkaline silicate solutions

“…We have not pinpointed in any of our spectra signals other than Q om that could be assigned to the esterification of condensed silicate species. However, Kinrade et al 12 identified a number of such compounds in silicate solutions containing tetrabutylammonium hydroxide and different alcohols.…”

“…We noticed a similar situation, but in markedly more favourable circumstances, in spectra that we obtained for other purposes, and decided to investigate further. Whilst this study was in progress, a short communication appeared 12 reporting the existence of CH 3 OSi(OH) 3 and a range of other alkylated species in silicate solutions containing tetrabutylammonium hydroxide. However, the authors 12 did not examine the dependence of the concentrations on the various factors involved.…”

“…Whilst this study was in progress, a short communication appeared 12 reporting the existence of CH 3 OSi(OH) 3 and a range of other alkylated species in silicate solutions containing tetrabutylammonium hydroxide. However, the authors 12 did not examine the dependence of the concentrations on the various factors involved. Here we report quantitatively the effects of dilution and of the concentrations of methanol and tetraethylammonium hydroxide on the concentration ratio of methoxysilicic acid to orthosilicic acid.…”