Inspired by Nature, biocatalysis and biotechnology have quickly become burgeoning fields in silicon chemistry. From cell cultures to isolated enzymes researchers are exploring the use of biological systems to affect chemical transformations at or near silicon atoms. This review will examine the history of biotechnology as it pertains to organosilicon compounds (i.e., compounds with one or more Si-C bonds) and provide some insights into future directions for the field.

Certain proteolytic enzymes are capable of mediating the processing of tri- and tetra-alkoxysilanes to form monolithic silica via the sol-gel process, or silsesquioxane sol-gels under green, solvent-free conditions.

More and more enzymes are being explored as alternatives to conventional catalysts in chemical reactions. To utilize these biocatalysts to their fullest, it is incumbent on researchers to gain a complete understanding of the reaction conditions that particular enzymes will tolerate. To this end siloxane-containing polyesters and polyamides have been produced via N435-mediated catalysis at temperatures well above the normal denaturation temperature for free CalB. Low molecular weight disiloxane-based acceptors release the enzyme from its acylated state with equal proficiency while longer chain siloxanes favours polyester synthesis. The thermal tolerance of the enzyme catalyst is increased using longer chain diesters and generally more hydrophobic substrates.

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Alternative gene splicing is pervasive in metazoa, particularly in humans, where the majority of genes generate splice variant transcripts. Characterizing the biological significance of alternative transcripts is methodologically difficult since it is impractical to assess thousands of splice variants as to whether they actually encode proteins, whether these proteins are functional, or whether transcripts have a function independent of protein synthesis. Consequently, to elucidate the functional significance of splice variants and to investigate mechanisms underlying the fidelity of mRNA splicing, we used an indirect approach based on analyzing the evolutionary conservation of splice variants among species. Using DNA polymerase b as an indicator locus, we cloned and characterized the types and frequencies of transcripts generated in primary cell lines of five primate species. Overall, we found that in addition to the canonical DNA polymerase b transcript, there were 25 alternative transcripts generated, most containing premature terminating codons. We used a statistical method borrowed from community ecology to show that there is significant diversity and little conservation in alternative splicing patterns among species, despite high sequence similarity in the underlying genomic (exonic) sequences. However, the frequency of alternative splicing at this locus correlates well with life history parameters such as the maximal longevity of each species, indicating that the alternative splicing of unproductive splice variants may have adaptive significance, even if the specific RNA transcripts themselves have no function. These results demonstrate the validity of the phylogenetic conservation approach in elucidating the biological significance of alternative splicing.

The immobilized lipase B from Candida antarctica (CALB) was used to synthesize silicone polyesters. CALB routinely generated between 74-95% polytransesterification depending on the monomers that were used. Low molecular weight diols resulted in the highest rates of esterification. Rate constants were determined for the CALB catalyzed polytransesterifications at various reaction temperatures. The temperature dependence of the CALB-mediated polytransesterifications was examined. A lipase from C. rugosa was only successful in performing esterifications using carboxy-modified silicones that possessed alkyl chains greater than three methylene units between the carbonyl and the dimethylsiloxy groups. The proteases alpha-chymotrypsin and papain were not suitable enzymes for catalyzing any polytransesterification reactions.

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In an initial report we demonstrated that some serine proteases were suitable candidates for the hydrolysis and condensation of tetraethoxysilane and phenyltrimethoxysilane under solvent-free conditions. Using trypsin as a model enzyme, we have demonstrated the generality of this method by expanding the number of available silicon-based substrates that can be processed by the enzyme, as well as including pepsin to demonstrate that this phenomenon is not exclusive to a single family of enzymes. A series of time course 29 Si NMR experiments using D 2 O revealed that the rate of hydrolysis of phenyltrimethoxysilane could be enhanced by a factor of 11-155 times over enzyme-free controls when either trypsin or pepsin were used as catalysts. The following trend was observed when comparing the hydrolysis/condensation rates of a number of different organotrimethoxysilanes: methyltrimethoxysilane>allytrime-thoxysilane>ethyltrimethoxysilane>phenyltrimethoxysilane.