Biopolym. Cell. 2007; 23(6):519-528.
Molecular Biophysics
Investigation of infrared spectrum of Fe(II) porphin in different spin states by quantum chemical density functional theory
1Minaev B. F., 1Minaev A. B., 2Hovorun D. N.
  1. B. Khmelnyckyy Cherkasy National University
    81, Shevchenko Blvd., Cherkassy, Ukraine, 18031
  2. Institute of Molecular Biology and Genetics, NAS of Ukraine
    150, Akademika Zabolotnoho Str., Kyiv, Ukraine, 03680


The infrared (IR) absorption spectra of the Fe(II) porphin molecule (Fe(II)P) are calculated by the quantum-chemical method of density functional theory (DFT) for the singlet, triplet, and quintet spin states. The UB3LYP functional with the 6-311G basis set is used in geometry optimization and IR calculations. The quintet state 5B2g of the D2h symmetry is found to be the ground state. Though the close-lying triplet 3A2g and high-energy singlet 1A1g states belong to the D4h symmetry, the IR spectra have been analyzed in terms of the lower symmetry D2h point group. All IR active vibrations are tabulated and discussed. The low-frequency modes with large out-of-plane displacements of Fe(II) ion have different IR intensities, normal vibrations, and frequency shifts in the quintet state in respect to the singlet and triplet states.
Keywords: Fe(II) porphin, singlet, triplet, quintet, spin states, density functional theory, IR absorption spectrum, low-frequency modes


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