THEORETICAL-STUDY OF THE ELECTROSTATIC AND STERIC EFFECTS ON THE SPECTROSCOPIC CHARACTERISTICS IF THE METAL-LIGAND UNIT OF HEME-PROTEINS .3. VIBRATIONAL PROPERTIES OF FE(III)CN-

The vibronic theory of chemical activation and quantum chemical calcul ations are applied to calculate the stretching vibrational frequency o f cyanide, coordinated by the complex of ferric porphyrin with imidazo le. The results show that the frequency of the stretching vibration of the cyanide strongly depends on its coordination geometry and is hard ly affected by the electrostatic perturbations of reasonable magnitude . The comparison of these results with the experimental data on the cy anide complexes of different heme proteins and their models allows to elucidate the cyanide coordination geometry. The combined infrared and resonance Raman scattering experimental investigation of the cyanide and carbonyl complexes with the same heme protein is proposed to disti nguish between the steric and electrostatic contributions to the heme- protein interaction. (C) 1997 Elsevier Science B.V.