Thesis presented October 05, 2007

Abstract:
This PhD work is divided into two parts and aims at modeling some spectroscopic quantities (Mössbauer, EPR and magnetism) measured in iron containing bioinorganic systems with Density Functional Theory (DFT). The first part of this work deals with the theoretical calculation of two Mössbauer parameters: the isomeric shift Δ and the quadrupole splitting ΔEQ. First, correlations between calculations and experimental data have been established for simple iron complexes. Second, we have been interested in the investigation of a biological system, catalase, an iron containing heme, and we have tried to characterize its various forms. The second part of this work was devoted to rationalizing the variations of two parameters: the EPR g-average value, gav (= (∑gi)/3), and the effective exchange coupling constant Jeff. We have considered a set of [2Fe-2S] clusters in biological systems (ferredoxins, Rieske proteins, xanthine oxydases, etc). We have modeled these quantities with a phenomenological model involving the competition between two antagonist terms: the double exchange term B which reflects electronic delocalization between the iron sites and the trapping term ΔE which preferentially localizes the reducing electron on one iron site. We have been able to express analytically gav et Jeff as a function of the ratio ΔE/B allowing us to explain the source of the observed variations.

Keywords:
Density Functional Theory, Electron Paramagnetic Resonance spectroscopy, Mössbauer spectroscopy, Iron-sulfur cluster, Super exchange mechanism, Vibronic coupling, Broken symetry

On-line thesis.