ISSN:
1573-8779
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Conclusions 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 Mössbauer 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 Mössbauer spectroscopy in fairly great detail. The combined use of the two methods for investigating hemoproteins and model iron porphyrins, viz., Mössbauer 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 Mössbauer results, and on the other hand, the data from Mössbauer 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. The results presented in this review demonstrate the importance and pithiness of the theoretical conceptions and methods which are used in modern quantum chemistry to analyze and interpret data from Mössbauer spectroscopy. Important roles for the qualitative analysis and quantitative comparison with experimental data are played by the following in the theory: the EFG tensor, its principal components and their orientations relative to the molecular system of coordination; the one-electron energy levels and the energies of the terms corresponding to electronic states with different symmetries; the characteristics of the ion-ligand interaction the spin-orbit coupling; the contributions of the one-electron orbitals to the electron density on the57Fe nucleus; the effects of the mutual influence of the valence and core electrons in the molecule. In general quantum-chemical calculations permit a more thorough analysis of the intramolecular interactions responsible for the changes observed in Mössbauer spectra and make it possible to obtain information on the electronic states and oxidation numbers of the Fe ions, on the symmetry of the electronic terms and the configurational features of the states, as well as to draw definite conclusions regarding the confornational states of the ligands and their coordination schemes in many cases.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00751463
Permalink