Influence of substitution of oxygen by sulfur on maltol properties

Abstract

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/6-311RRG(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.

Is Vanadate Reduced by Thiols under Biological Conditions? Changing the Redox Potential of V(V)/V(IV) by Complexation in Aqueous Solution

“…A range of vanadium-sulfur complexes and their chemistries have demonstrated that vanadium-sulfur complexes have interest as models for nitrogenase chemistry,2 as the vanadium binding proteins,3,4 as anti-amoebic agents,5–7 as anti-diabetic agents,8 and as catalysts 9,10. The literature provides many examples that rapid reduction of vanadium(V) compounds takes place in the presence of biological thiols such as glutathione, cysteine, 2-mercaptoethanol and dithiothreitol (DTT) under physiological conditions 11–17.…”

Molecular properties of selenomaltols: new interesting ligands for bioactive metal complexes

“…The results of these calculations are collected in Table . The examination of these data clearly shows that the previously established order of aromaticity for maltol, other hydroxypyrones and maltol thio derivatives also remains in the present seleno compounds. The aromaticity order of hydroxypyrones and their derivatives starts with the anionic form that is non‐aromatic or sometimes slightly anti‐aromatic (depending on the aromaticity index and the position(s) and number(s) of oxygen atoms that are replaced by selenium).…”

“…However, unlike B3LYP, B1LYP has only one parameter that is additionally not fitted, but it is rooted in the theory. The B1LYP functional was used in our previous investigation on thiohydroxypyrones . Thus, the results collected in the previous calculations and in this study can be compared.…”

“…For cations, the structures with two hydroxyl groups in the para and meta positions to the heteroatom in the ring are the most stable ones. These keto‐enol structures have been determined to be the lowest energetic ones in our previous studies on hydroxypyrones and their thio derivatives . Thus, we assume that the same tautomers are the most stable structures for the selenomaltol derivatives.…”

“…The present study is a continuation of research on the aromatic properties of hydroxypyrones and its thio derivatives . Maltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one, Fig.…”