title: Density-functional study on the equilibria in the ThDP activation.
abstract: The equilibria among the various ionization and tautomeric states involved in the activation of ThDP is addressed using high level density functional theory calculations, X3LYP/6-311++G(d,p)//X3LYP(PB)/6-31++G(d,p). This study provides the first theoretically derived thermodynamic data for the internal equilibria in the activation of ThDP. The role of the medium polarity on the geometry and thermodynamics of the diverse equilibria of ThDP is addressed. The media chosen are cyclohexane and water, as paradigms of apolar and polar media. The results suggest that all ionization and tautomeric states are accessible during the catalytic cycle, even in the absence of substrate, being APH(+) the form required to interconvert the AP and IP tautomers; and the generation of the ylide proceeds via the formation of the IP form. Additionally, the calculated ΔG° values allow to calculate all the equilibrium constants, including the pK(C2) for the thiazolium C2 atom whose ionization is believed to initiate the catalytic cycle.
authors.affiliation: Theoretical and Computational Chemistry Group (QTC), Physical Chemistry Department, Facultad de Ciencias Químicas, casilla 160-C, Universidad de Concepción, Concepción, Chile. edelgado@udec.cl
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Delgado
authors.forename: Joel B
authors.initials: JB
authors.lastname: Alderete
authors.forename: Gonzalo A
authors.initials: GA
authors.lastname: Jaña
mesh_terms: D002384:Catalysis; D008956:Models, Chemical; D013816:Thermodynamics; D013835:Thiamine Pyrophosphate / Q000737:chemistry*
chemical_list: D013835:Thiamine Pyrophosphate