Predicting 51V nuclear magnetic resonance observables in molecular crystals

Solid-state nuclear magnetic resonance (NMR) spectroscopy and quantum chemical density functional theory (DFT) calculations are widely used to characterize vanadium centers in biological and pharmaceutically relevant compounds. Several techniques have been recently developed to improve the accuracy of predicted NMR parameters obtained from DFT. Fragment-based and planewave-corrected methods employing hybrid density functionals are particularly effective tools for solid-state applications. A recent benchmark study involving molecular crystal compounds found that fragment-based NMR calculations using hybrid density functionals improve the accuracy of predicted 51V chemical shieldings by 20% relative to traditional planewave methods. This work extends the previous study, including a careful analysis of 51V chemical shift anisotropy, electric field gradient calculations, and a more extensive test set. The accuracy of planewave-corrected techniques and recently developed fragment-based methods using electrostatic embedding based on the polarized continuum model (PCM) are found to be highly competitive with previous methods. Planewave-corrected methods achieve a 34% improvement in the errors of predicted 51V chemical shieldings relative to planewave. Additionally, planewave-corrected and fragment-based calculations were performed using PCM embedding, improving the accuracy of predicted 51V chemical shielding (CS) tensor principal values by 30% andC q values by 15% relative to traditional planewave methods. The performance of these methods is further examined using a redox-active oxovandium complex and a common 51V NMR reference compound.

Accurate fragment-based 51-V chemical shift predictions in molecular crystals

Nuclear magnetic resonance (NMR) spectroscopy plays a crucial role in determining molecular structure for complex biological and pharmaceutical compounds. NMR investigations are increasingly reliant on computation for mapping spectral features to chemical structures. Here we benchmark the accuracy of fragment-based ⁵¹V chemical shielding tensor calculations using a training set comprised of 10 biologically and pharmaceutically relevant oxovanadium complexes. Using our self-consistent reproduction of the Madelung potential (SCRMP) electrostatic embedding model, we demonstrate comparable performance between fragment methods and computationally demanding cluster-based techniques. Specifically, fragment methods employing hybrid density functionals are capable of reproducing the experimental ⁵¹V isotropic chemical shifts with a training set rms error of ~9 ​ppm, representing a 20% improvement over traditional plane wave techniques. We provide training set-derived linear regression models for mapping the absolute shieldings obtained from computation to the experimentally determined chemical shifts using four common density functionals; PBE0, B3LYP, PBE, and BLYP. Finally, we establish the utility of fragment methods and the reported regression parameters examining four oxovanadium structures excluded from the training set including the tetracoordinate oxovanadium silicate [Formula: see text] , VO¹⁵NGlySalbz which contains redox-active ligands, and the solid-state form of the common ⁵¹V NMR reference compound VOCl₃.

51V magic angle spinning NMR spectroscopy and quantum chemical calculations in vanadium bio-inorganic systems: current perspective

In recent years, 51V magic angle spinning (MAS) NMR spectroscopy has been widely used to characterize vanadium centers in biology, biomimetic complexes, and inorganic compounds of medicinal and industrial relevance. It has been demonstrated that 51V NMR parameters are sensitive probes of the coordination geometry and chemical environment of the metal center, beyond the first coordination sphere. To establish the relationships between NMR parameters and structure of the vanadium centers, over the past decade a large series of coordination complexes have been analyzed by MAS NMR spectroscopy. It has been demonstrated that the interpretation of the NMR parameters requires the use of theoretical methods, such as density functional (DFT) theory, whereby the experimental NMR observables are linked to the electronic and structural properties of a molecule. DFT calculations have been successfully employed to not only predict NMR parameters but to also yield valuable information regarding the structure and function of various vanadium compounds. In this report, we review the current state of the field, and present a survey of bioinorganic vanadium complexes as well as vanadium-dependent haloperoxidases analyzed using 51V MAS NMR spectroscopy and DFT calculations, to illustrate the rich information content available from such a combined approach.

H+-Assisted fluorescent differentiation of Cu+ and Cu2+: effect of Al3+-induced acidity on chemical sensing and generation of two novel and independent logic gating pathways

A novel logic gate containing protecting groups interacts with various species (acetonitrile) with fluorescence responses relating to ligand non innocence.

Effect of Ancillary Ligand on Electronic Structure as Probed by 51V Solid-State NMR Spectroscopy for Vanadium-o-Dioxolene Complexes

A series of vanadium(V) complexes with o-dioxolene (catecholato) ligands and an ancillary ligand, (N-(salicylideneaminato)ethylenediamine) (hensal), were investigated using ⁵¹V solid-state magic angle spinning NMR spectroscopy (⁵¹V MAS NMR) to assess the local environment of the vanadium(V). The solid-state ⁵¹V NMR parameters of vanadium(V) complexes with a related potentially tetradentate ancillary ligand (N-salicylidene-N'-(2-hydroxyethyl)ethylenediamine) (h₂shed) were previously shown to be associated with the size of the HOMO-LUMO gap in the complex, and as such provide insights on the interaction between metal ion and ligand (P. B. Chatterjee, et al., Inorg. Chem 50 (2011) 9794). Our results show that the modification of the ancillary ligand does not impact the observed trend between complexes ranging from catechols with electron rich to electron poor substituents. However, the ancillary ligand does impact the size of the HOMO-LUMO separation in the parent complex and thus the solid-state vanadium NMR chemical shift of the unsubstituted vanadium complex. For these complexes significant changes observed in the isotropic shifts and more modest changes detected in the C_Q reflect the electronic changes in the complex as the catechol is varied. However, no obvious trend was observed in the chemical shift anisotropies (δ_σ and η_σ) with the variation in the catechol. The electronic changes in the coordination environment of the vanadium can be described using solid-state ⁵¹V NMR spectroscopy.