Design and synthesis of new models for diiron biosites.

In order to mimic dinuclear active sites of some non-heme diiron proteins, ten new polydentate and potentially dinucleating ligands have been synthesized. Each ligand contains a carboxylate moiety designed to bridge two metal atoms. These central carboxylate moieties are derived from substituted benzoic acids that in turn are linked to terminal nitrogen or oxygen donors by spacers so that framework-type polydentate ligands similar to the polypeptide frames in diiron metallobiosites are formed. Reaction of these ligands with Fe(ClO4)3 x 9H2O leads to ferric mu-oxo-mu-carboxylato iron complexes of the general formulas [Fe2O(L)2(H2O)2](ClO4)2 and [Fe2O(L)(BzO)](ClO4)2 (L = ligand), containing one or two immobilized bridging carboxylates, respectively. While X-ray crystallography shows that some of these complexes are dimers or network polymers in the solid state, electrospray ionization mass spectrometry (ESMS) and spectroscopic data (UV-Vis, NMR, Móssbauer) indicate that they dissociate to monomeric Fe2O units in dilute CH3CN solutions.

The mechanism of methane and dioxygen activation in the catalytic cycle of methane monooxygenase.

The binuclear structure of the active center of methane monooxygenase plays a determining role in dioxygen activation and in selectivity and specificity of alkane oxidation with this enzyme. A new mechanism is suggested for binding and activation of O2, which involves side-on binding of O2-(2) to iron atoms followed by its conversion to the bis-mu-oxo complex considered as an alternative of ferryl in CH4 activation. This mechanism results in the sequence of the cleavage of the O-O bond of peroxide O/O2-instead of the opposite sequence O2-/O, which takes place in the case of heme monooxygenase cytochrome P-450. Therefore, in this case there is no necessity of the charge relay system [N.B. Gerber and S.G. Sligar, J. Am. Chem. Soc. 114 (1992) 8742] for the transformation of O2 to an active intermediate. The experiment for checking this hypothesis is suggested.