Udk 539.19:541.65 Dft Study of the Oxaloacetic Acid Condensation — the First Step of the Citric Acid Cycle

The mechanism of acylation of oxaloacetic acid (OA) with acetyl—CoA was studied at the DFT level using basis functions 6-311G(d,p) and different numbers of diffuse functions. Four mechanisms were considered in this study. It was found that the most probable mechanism, in the approximation of isolated molecules, starts with the enol forms of oxaloacetic acid and acetylcysteamine (final fragment from acetyl—CoA). The mechanisms were commented from the point of view of their thermodynamics. The calculations and UV/VIS spectroscopic analysis of OA showed that the enol form of the compound is available in ethanol, water and diethylether. The higher stability of the OA enol form (as compared to the ketoform) was also reconfirmed by its experimental IR spectrum. Very high energy barrier of the enolization reaction of OA was calculated.