Silicon in Biological Systems

Summary

This meeting has been concerned with biological aspects of silicon chemistry. We have drawn a clear distinction between the in vivo chemistry evolved by biological systems themselves and the possible chemistry which man’s ingenuity might use in drugs etc. based on silicon. The parallel chemistry of phosphate makes the importance of this division clear. Biological systems themselves use phosphorus in one oxidation state only (phosphate) and most known biological phosphorus reactions are based on condensation between its hydroxyl groups and those of other compounds R-OH.

$$ {\rm{P}}\,{\rm{ - }}\,{\rm{OH}}\,{\rm{ + }}\,{\rm{R}}\,{\rm{ - }}\,{\rm{OH}} \to \,{\rm{R - }}\,{\rm{O}}\,{\rm{ - }}\,{\rm{P}}\,{\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{\rm{O}} $$

These include R-GH of phosphate, sugar and serine. A biological function of P-X bonds where X is an element other than oxygen rarely occurs. By way of contrast man-made compounds which contain P-X bonds of many kinds can be made and employed as potent biological reagents, for example P-F bonds are part of nerve gases, P-C bonds occur in herbicides. I shall assume that biological systems themselves handle silicon much as phosphorus, i.e. as Si-O units only, but that there is a whole potential world of drug and herbicide etc. chemistry which can be based on Si-X bonds where again X is not oxygen. In the first part of this summary I shall restrict myself to remarks about aqueous Si-O chemistry of possible relevance to those compounds which I take to occur in biology.