Influence of substitution of oxygen by sulfur on maltol properties

摘要

Replacing oxygen by sulfur in a maltol molecule generates a family of new very interesting ligands: thiohydroxypyrones. In this work, theoretical calculations have been performed for all possible maltol derivatives created by consecutive substitutions of oxygen atoms by sulfur. The study is focused on molecular properties of thioligands, which are important for the formation of their metal complexes, and potentially useful in medicinal and environmental chemistry. Energetic, tautomeric, aromatic, and charge distribution data are reported and the results are compared with maltol properties. It is shown that, similar to maltol, the most stable tautomer for all thio derivatives, is the one with the keto-enol group. The protonation in cations occurs always on the heteroatom of the (thio)ketone group. The study has been carried out with the aid of some aromaticity indices, such as HOMA, NICS, and ASE. Aromaticity is studied in the heterocyclic pyran ring and in the XCCX part (where X - oxygen or sulfur). All calculations were performed at the B1LYP/6-311++G(d,p) level of theory. We conclude that the aromaticity order determined previously for maltol (cation > neutral molecule > anion) is also preserved for thiohydroxopyrones. The results of the population analysis indicate that upon protonation, a large portion of additional positive charge delocalizes on the entire molecule, whereas upon deprotonation, negative charge accumulates mainly on the heteroatoms of the XCCX group.