New perspectives on thiamine catalysis: from enzymic to biomimetic catalysis.

This paper is a brief review of the detailed mechanism of action of thiamine enzymes, based on metal complexes of bivalent transition and post-transition metals of model compounds, thiamine derivatives, synthesized and characterized with spectroscopic techniques and X-ray crystal structure determinations. It is proposed that the enzymatic reaction is initiated with a V conformation of thiamine pyrophosphate, imposed by the enzymic environment. Thiamine pyrophosphate is linked with the proteinic substrate through its pyrophosphate oxygens. In the course of the reaction, the formation of the "active aldehyde" intermediate imposes the S conformation to thiamine, while a bivalent metal ion may be linked through the N1' site of the molecule, at this stage. Finally, the immobilization of thiamine and derivatives on silica has a dramatic effect on the decarboxylation of pyruvic acid, reducing the time of its conversion to acetaldehyde from 330 minutes for the homogeneous system to less than 5 minutes in the heterogenous system.