Electronic structure of iron porphyrins and hemoproteins and parameters of their Mössbauer spectra

The biochemical properties of hemoproteins are determined to a considerable extent by the electronic structure of the Fe ions of the heme groups, their oxidation numbers, and their spin states. In both hemoproteins and the model iron porphyrins these characteristics have a significant influence on the electron-nuclear interactions which determine the features of the57Fe Mossbauer spectra. A methodology which makes it possible to understand and interpret and sometimes to predict the experimental results on the basis of quantum-chemically calculated one-electron energies and wave functions has been developed for Mossbauer spectroscopy in fairly great detail. The combined use of the two methods for investigating hemoproteins and model iron porphyrins, viz., Mossbauer spectroscopy and quantum chemistry, makes it possible to more profoundly and completely answer questions regarding the relationship between the electronic, coordination, spin, and stereochemical properties of these compounds. On the one hand, quantum-chemical calculations can serve as an investigative tool and a methodological basis for interpreting Mossbauer results, and on the other hand, the data from Mossbauer spectroscopy can serve as a criterion of the correctness of the description of the real electronic structure by quantum-chemical methods and a criterion for selecting reliable structural representations.