Hydrogen-Bonded Complexes of Silica with Organic Compounds

TLDR: In the case of polysilicic acid, the formation of SiO-H-C hydrogen bonds is promoted by the presence of salt and by lower temperature, but becomes weaker above 60°C as mentioned in this paper, due to steric hindrance by nearby counter cations.

Abstract: At ordinary temperature in water solution, labile bonds are formed between the neutral oxygen or nitrogen atoms of alcohols, ketones, ethers, amides and the hydrogen atoms of silanol groups, SiOH. The resulting Si-O-H-C hydrogen bonds are formed both in the case of the SiOH groups of polysilicic acid and with those on the surface of silica particles but apparently not with those of monosilicic acid, Si(OH)4, which is a weaker acid. Hydrogen bond formation is promoted by the presence of salt and by lower temperature, but becomes weaker above 60°C. Hydrogen bonds do not form near negatively charged −SiO− sites which increasingly populate the silica surface above pH 7. This is probably due to steric hindrance by nearby counter cations. The complexes are much more stable when many hydrogen bonds can be formed in parallel; for example, between a long polyethylene oxide molecule and the surface of a particle of colloidal silica. Phase separation occurs when a hydrophobic complex is formed and separates as a coacervate. Precipitation occurs when silica particles act as crosslinks between polymer molecules. Denaturation of protein occurs when the affinity of amide and basic nitrogen groups for the silica surface distorts the natural molecular conformation. In addition to H-bonding, certain compounds form chelate type bonds which are probably involved in the metabolism of silicon.