Micera, Giovanni and Pecoraro, Vincent L. and Garribba, Eugenio (2009) Assessing the dependence of 51V Az value on the aromatic ring orientation of VIVO2+ pyridine complexes. Inorganic Chemistry, Vol. 48 (13), p. 5790-5796. eISSN 1520-510X. Article.
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Characterization of VIV biomolecules relies strongly on electron paramagnetic resonance (EPR) spectroscopy, particularly the application of the additivity relationship of Az values. It has been shown experimentally that the Az values of VIVO2+ imidazole species have a critical angular dependence. Density-functional theory (DFT) calculations elucidate the dependence of 51V Az value on the orientation of the aromatic ring in VIVO2+ pyridine complexes, following closely the functional dependence observed for VIVO2+ imidazole species, [Az(pyr) = 42.23 + 1.80 × sin(2θ − 90)], with Az measured in 104 cm−1. A DFT re-examination of VIVO2+ imidazole complexes gives an equation very similar [Az(imid) = 42.35 + 2.34 × sin(2θ − 90)] to that experimentally found. These results generalize the application of the additivity relationship for VIVO2+ complexes containing aromatic nitrogen ligands such as pyridine or imidazole. The increase of the absolute value of Az, |Az|, when the dihedral angle θ between the V═O and Npyr−C or Nimid−C bonds varies from a parallel to a perpendicular orientation is due to an increase of the d vanadium orbital contribution and to a decrease of the π aromatic system participation in the singly occupied molecular orbital.
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