Thermodynamics and kinetics of methylglyoxal dimer formation: a computational study.

Density functional theory (B3LYP//6-311+G*) calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to study the hydration of methylglyoxal and the subsequent formation of dimeric species in solution. Our calculations show that, unlike glyoxal, fully hydrated species are not thermodynamically favored over their less hydrated counterparts, nor are dioxolane ring species the thermodynamic sink, which is in agreement with experimental data. Instead, we find that aldol condensations are the most favored oligomerization reactions for methylglyoxal. These results differ from those of glyoxal, which, lacking the methyl group, cannot access the enol structure leading to aldol condensation. For methylglyoxal, the product from nucleophilic attack at the aldehyde rather than the ketone was favored. Our results help explain some of the observed differences between methylglyoxal and glyoxal, in particular the different array of oligomers formed.