Modeling of stability and properties of anionic and cationic tautomers of the 3-hydroxypyridin-4-one system

Abstract

DFT, MP2, CBS-APNO, G4 and CCSD(T) calculations were performed for anionic and cationic tautomers of 3-hydroxypyridin-4-one molecule, a parent molecular system for the family of hydroxypyridinones that are known in coordination chemistry as efficient metal ions chelators. Performed calculations show that the 3-hydroxypyridin-4-one’s anion exists in the structure with one hydroxyl group (in the meta position to the nitrogen atom in the ring) and protonated nitrogen atom. Such a “protection” of the OCCO by protonation of one oxygen atom should weaken potentially strong metal ion binding properties of studied system. In the case of 3-hydroxypyridin-4-one’s cation, the most stable is the structure in which all hetero atoms, two oxygens and the nitrogen atoms, are protonated. Properties of anionic and cationic tautomers were studied using several aromaticity indices (HOMA, NICS, PDI, Iring, MCI KMCI) and population analyses (AIM, NBO and GAPT methods). The AIM methodology was also used for determination of hydrogen bond properties and integration of atomic energies. Results served by these methods were used to explain the energetical orders of anionic and cationic tautomers. Changes in atomic charges upon protonation and deprotonation are also discussed.