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Structural and Functional Investigations on Diiron Complexes: Catalase‐Like Activity and Mechanistic Studies on the Formation of (μ‐Peroxo)diiron(III) Adducts
Author(s) -
Than Roberto,
Schrodt Antje,
Westerheide Lars,
van Eldik Rudi,
Krebs Bernt
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199909)1999:9<1537::aid-ejic1537>3.0.co;2-c
Subject(s) - chemistry , adduct , hydrogen peroxide , ligand (biochemistry) , molecule , reaction rate constant , stoichiometry , solvent , hydrogen bond , medicinal chemistry , crystallography , inorganic chemistry , kinetics , stereochemistry , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The new diiron complex [Fe 2 (tbpo){O 2 As(CH 3 ) 2 }(CH 3 O)(CH 3 OH)](ClO 4 ) 3 · 5 CH 3 OH · 2 H 2 O ( 1 ) containing a (μ‐alkoxo)(μ‐dimethylarsinato)diiron(III) core was synthesized using the heptadentate ligand N , N , N′ , N′ ‐Tetrakis(2‐benzimidazolylmethyl)‐1,3‐diamino‐2‐propanol (Htbpo). The complex was characterized structurally by X‐ray crystallography. 1 reproduces the coordination mode and the stoichiometry of the proposed purple acid phosphatase‐arsenate inhibitor complex. More importantly, 1 is a good functional model for the activation of small molecules, since the solvent molecule in the coordination sphere of each iron ion can be substituted very easily by a small substrate molecule. This is confirmed by the comparatively high pH‐dependent catalase‐like activity of 1 . In order to study the influence of the cacodylate bridge on the formation of the metastable adduct with hydrogen peroxide, the analogous hydroxo‐bridged complex [Fe 2 (tbpo)(OH)(NO 3 ) 2 ](NO 3 ) 2 · CH 3 OH · 2 H 2 O ( 2 ) was employed. The reactions of 1 and 2 with H 2 O 2 were studied as a function of [H 2 O 2 ], pH, temperature, and pressure, and the kinetic results including the activation parameters are reported. In the case of compound 2 the reaction proceeds in one step, and the observed first order rate constant, k obs , shows a linear dependence on the hydrogen peroxide concentration with a zero intercept. For complex 1 the kinetic traces could be fitted to two exponential functions. One of the observed pseudo‐first‐order rate constants, k obs1 , exhibits a linear dependence on the hydrogen peroxide concentration with a zero intercept, whereas the other rate constant, k obs2, was independent of the hydrogen peroxide concentration. A mechanistic interpretation is presented.