A Mo-based MOF is an efficient electrocatalyst for the N2 reduction reaction with a low overpotential of 0.18 V.

(51)V NMR chemical shifts calculated from QM/MM-optimized (QM=quantum mechanical; MM=molecular mechanical) models of vanadium-dependent chloroperoxidase (VCPO) are presented. An extensive number of protonation states for the vanadium cofactor (active site of the protein) and a number of probable positional isomers for each of the protonation states are considered. The size of the QM region is increased incrementally to observe the convergence behavior of the (51)V NMR chemical shifts. A total of 40 models are assessed by comparison to experimental solid-state (51)V NMR results recently reported in the literature. Isotropic chemical shifts are found to be a poor indicator of the protonation state; however, anisotropic chemical shifts and the nuclear quadrupole tensors appear to be sensitive to changes in the proton environment of the vanadium nuclei. This detailed investigation of the (51)V NMR chemical shifts computed from QM/MM models provides further evidence that the ground state is either a triply protonated (one axial water and one equatorial hydroxyl group) or a doubly protonated vanadate moiety in VCPO. Particular attention is given to the electrostatic and geometric effects of the protein environment. This is the first study to compute anisotropic NMR chemical shifts from QM/MM models of an active metalloprotein for direct comparison with solid-state MAS NMR data. This theoretical approach enhances the potential use of experimental solid-state NMR spectroscopy for the structural determination of metalloproteins.

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51V NMR chemical shifts have been computed at the GIAO-B3LYP level for non-oxo vanadium(V) complexes related to oxidized amavadin, [Delta-VV{(S,S)-hidpa}2]- (H3hidpa = 2,2'-hydroxyiminodipropionic acid). According to model calculations, the unusual deshielding of the 51V resonance is due to a combination of conventional substituent effects (e.g., oxo vs dihydroxo or alkoxy vs carboxylato ligands), rather than to a non-innocent nature of the hidpa ligand. For selected diastereomeric vanadium hidpa complexes, Born-Oppenheimer molecular dynamics simulations have been carried out to rationalize the observed differentiation of 51V NMR chemical shifts. Strongly deshielded 51V complexes that contain catecholate ligands do show significant disagreement between density functional theory (DFT)-computed chemical shifts and experiment. The possible cause for this deviation is indicated to result from ligand-to-metal charge transfer which can give rise to some open-shell character and temperature-dependent paramagnetic contributions. Electron-withdrawing groups at the catechol moiety tend to increase the corresponding transition energy, thereby reducing these contributions and limiting the non-innocence to the closed-shell ground-state wavefunction.