A large scale enzyme screen in the search for new methods of silicon-oxygen bond formation

Biotransformations make use of biological systems to catalyze or promote specific chemical reactions. Transformations that utilize enzymes as “greener” and milder catalysts compared to traditional reaction conditions are of particular interest. Recently, organosilicon compounds have begun to be explored as non-natural enzymatic substrates for biotransformations. The aims of this study were to screen readily available (approximately eighty) enzymes for their ability to catalyze in vitro siloxane bond formation under mild reaction conditions using a model monoalkoxysilane as the substrate and to make a preliminary evaluation of potential factors that might lead to activity or inactivity of a particular enzyme. Several new hydrolase enzymes were observed to catalyze the formation of the condensation product when compared to peptide controls, or buffer solutions at the same pH, as judged from quantitative analyses by gas chromatography. Aspergillus ficuum phytase, Aspergillus niger phytase, chicken egg white lysozyme, porcine gastric mucosa pepsin, and Rhizopus oryzae lipase all catalyzed the condensation of silanols in aqueous media. Factors involved in determining the activity of an enzyme towards silanol condensation appear to include: the presence of imidazole and hydroxyl functions in the active site; solvent; the presence of water; the surface properties of the enzyme; possible covalent inhibition; and steric factors in the substrate.