Theoretical study of the stability and NMR spectroscopic properties of vanadium(V) complexes

Abstract

Several vanadium(V) complexes have been investigated as possible antidiabetic and anticancer therapeutic agents. Among these, vanadium(V) complexes linked to tridentate ONO Schiff bases stand out for their potential in the treatment for cancer. However, further studies are necessary in order to learn about their specific action at the cellular level. We investigate structural and spectroscopic properties of these particular complexes, which are formed by a Schiff base linked to a [VO2]+ ion that contains different functional groups. Molecular structure optimizations of these vanadium-containing complexes were performed by the ONIOM (QM1:QM2) method, where the high layer (complexes) were described by density functional theory methods whereas the low layer (eight water molecules) were described by the HF approach. Various solvation models were utilized; however, the introduction of both implicit (using a solvation model based on density, SMD) and explicit (eight water molecules) solvation improves the stability of the systems. Interestingly, we found that the location of the explicit water molecules in the different octahydrated vanadium complexes was conserved surrounding the oxo-vanadate moiety. A detailed analysis of the chemical shift (δ) values for 1H, 13C and 51V is presented based on the ONIOM optimized geometries using the gauge-independent atomic orbital methodology. For obtaining accurately chemical shifts, the complete basis set using the correlation-consistent Dunning basis sets from double-ξ to quadruple-ξ and the Ahlrichs basis set were utilized. The results from the methodology presented here are consistent with those reported experimentally for 1H. Again, the inclusion of explicit water molecules in the inner solvation shell during the calculation of the chemical shifts was crucial. The analysis of solvation energies also indicates the relevance of including explicit water molecules as the main stabilization factor suggesting the central role of intermolecular interaction in the stability of the metallic complexes. From this analysis, a possible vanadium complex candidate for further evaluation in the cellular environment is suggested. This work not only provides evidence of a suitable methodology for studying the structural and spectroscopic properties of vanadium complexes but also highlights the relevance of explicitly including water molecules in their inner shell.