| Vanadium is widely found in nature, occurring at concentrations of up to 100 ppm in the earth's crust, and at 30-50 nM in seawater. Several classes of proteins are known to contain a vanadium cofactor, including vanadium nitrogenases and the vanadium haloperoxidases that are studied in this work. Vanadium is also of interest due to its anti-diabetic and anti-carcinogenic properties. Further study of the electronic properties of vanadium is integral to developing industrial and biomedical applications of vanadium compounds.51V solid-state NMR spectroscopy has proven to be a useful tool for characterization of vanadium compounds. In this study, we look at a group of V(V)O2 dipicolinic acid complexes, which have shown potential as phosphate inhibitors as well as insulin enhancing compounds useful for the treatment of diabetes. We have studied the effect of ligand substitution on the electric field gradient and chemical shift anisotropies of these compounds. The electric field gradient tensor was found to be significantly affected by ligand changes on the dipicolinate ring, with quadrupolar coupling constants ranging from 5.8 to 8.3 MHz, whereas the chemical shift anisotropies varied much less dramatically, from -550 to -600 ppm. Additionally, we address the level of theory required for accurate prediction of NMR parameters using DFT calculations, looking at variation in functional, basis set, and structural model. At a high level of theory, functional and basis set have a minor impact on the accuracy of results, and using original x-ray structures with all counter ions leads to most accurate results. |
