A DFT study of the 67Zn, 14N and 2H electric field gradient tensors in Zinc(II)-4-MeIm complexes and extrapolation to superoxide dismutase.

A computational investigation was carried out to characterize the (14)N and (2)H electric field gradient, EFG, in four protonated forms of 4-methyl imidazole (4-MeIm) and Histidine. In an attempt to establish metal binding effect in biological systems, we have considered the various forms of zinc (II) complexes of 4-MeIm. The computations were performed at the B3LYP and PW91P86 levels with 6-311++G(d,P) standard basis set. Calculated EFG tensors were used to determine (14)N and (2)H nuclear quadrupole coupling constant, chi and asymmetry parameter, eta. The results show that Zn(2+) has a strong effect on the NQR parameters (chi, eta) of proximal nitrogen in contrast with the remote nitrogen. In addition, EFG tensors at the Zn nuclear site were calculated for Zn-4-MeIm complexes and estimated the chi and eta values of (67)Zn. The influence of the bulk solvent was investigated at the B3LYP/6-311++G(d,p) level using the polarizable continuum model. Finally, we predicted (chi=1.95 MHz, eta=0.84) for proximal nitrogen, (chi=2.38 MHz, eta=0.07) for remote nitrogen and (chi=1.28 MHz, eta=0.22) for Zn in superoxide dismutase.