The enzymatic cleavage of Si–O bonds: A kinetic analysis of the biocatalyzed hydrolysis of phenyltrimethoxysilane

Previously we reported the ability of trypsin to mediate the cross-linking of alkoxysily-functionalized silicone polymers. Although enzymes and silicon-containing compounds are not necessarily incompatible species, the exact mechanism of how enzymes process silicon substrates is not fully understood. The focus of this current work was to examine the reaction kinetics associated with the processing of an alkoxysilane substrate by enzymes using 29Si NMR so as to gain a greater insight into the actual reaction mechanism, especially those involving more complex silicone systems. A series of time course 29Si NMR experiments using D2O revealed that the trypsin-mediated hydrolysis of a single alkoxy moiety in water is a pseudo-first order reaction. The relative effect of the enzyme was determined to be β = 3.549 while the relative effect of water was γ = 3.325. Prolonged contact with phenyltrimethoxysilane was not sufficiently deleterious to the enzyme and did not induce the complete and irreversible denaturation of trypsin. Computational evidence suggests that while in the active site of the enzyme, serine addition to silicon to forms a pentacoordinate species and is favoured over histidine addition.