DFT Calculation of the Structure of the Coordination Unit of Chlrophyll-Containing Proteins

In a DFT/B3LYP study (6-31G(d) basis set), the structure, IR spectra, and thermodynamic parameters of Mg-porphin-imidazole and Mg-khlorin-imidazole complexes, serving as models of the coordination unit of chlorophyll in proteins, have been calculated. When an axial ligand is added, the Mg atom goes out of the plane of the tetrapyrrole macrocycle, the deviation being 0.34 Å. The frequency of the out-of-plane vibrations of Mg in the complexes increased by 50 cm⁻¹, and the frequencies of the two in-plane vibrations decreased by 25 cm^{− 1}–30 cm⁻¹. IR vibrational spectra have been simulated.Original Russian Text Copyright © 2004 by M. D. Elkin, O. D. Ziganshina, K. V. Berezin, and V. V. Nechaev__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1132–1135, November–December, 2004.