Dipartimento di Chimica, Università di Sassari, Via Vienna 2, I-07100 Sassari, Italy.
Inorg Chem. 2009 Jul 6;48(13):5790-6. doi: 10.1021/ic9001779.
Characterization of V(IV) biomolecules relies strongly on electron paramagnetic resonance (EPR) spectroscopy, particularly the application of the additivity relationship of A(z) values. It has been shown experimentally that the A(z) values of V(IV)O(2+) imidazole species have a critical angular dependence. Density-functional theory (DFT) calculations elucidate the dependence of (51)V A(z) value on the orientation of the aromatic ring in V(IV)O(2+) pyridine complexes, following closely the functional dependence observed for V(IV)O(2+) imidazole species, [A(z)(pyr) = 42.23 + 1.80 x sin(2theta - 90)], with A(z) measured in 10(4) cm(-1). A DFT re-examination of V(IV)O(2+) imidazole complexes gives an equation very similar [A(z)(imid) = 42.35 + 2.34 x sin(2theta - 90)] to that experimentally found. These results generalize the application of the additivity relationship for V(IV)O(2+) complexes containing aromatic nitrogen ligands such as pyridine or imidazole. The increase of the absolute value of A(z), |A(z)|, when the dihedral angle theta between the V=O and N(pyr)-C or N(imid)-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 pi aromatic system participation in the singly occupied molecular orbital.
V(IV)生物分子的特性主要依赖于电子顺磁共振（EPR）光谱，特别是 A(z) 值加和关系的应用。实验表明，V(IV)O(2+)咪唑物种的 A(z) 值具有关键的角度依赖性。密度泛函理论（DFT）计算阐明了 V(IV)O(2+)吡啶配合物中芳香环取向对 (51)V A(z) 值的依赖性，非常接近观察到的 V(IV)O(2+)咪唑物种的函数依赖性，[A(z)(pyr) = 42.23 + 1.80 x sin(2theta - 90)]，其中 A(z) 以 10(4) cm(-1)为单位测量。对 V(IV)O(2+)咪唑配合物的 DFT 重新研究给出了一个非常类似于实验发现的方程[A(z)(imid) = 42.35 + 2.34 x sin(2theta - 90)]。这些结果推广了加和关系在含有芳香氮配体（如吡啶或咪唑）的 V(IV)O(2+)配合物中的应用。当 V=O 和 N(pyr)-C 或 N(imid)-C 键之间的二面角 theta 从平行变为垂直时，A(z)的绝对值 |A(z)| 的增加是由于 d 钒轨道贡献的增加和单占分子轨道中芳香π系统参与的减少。
