Dinuclear Zinc(II)-Iron(III) and Iron(II)-Iron(III) Complexes as Models for Purple Acid Phosphatases

摘要

The heterodinuclear Zn~(II)Fe~(III) complex 1 and the isostructural Fe~(II)Fe~(III) complex 2 with the dinucleating ligand from 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methoxyphenol (HBPMOP, 3) were prepared and characterized by X-ray crystallography. Solution studies (UV/Vis spectroscoy; electrochemistry) are described. A pH-induced change in the coordination spheres of the metal centers is seen. These complexes serve as models for the mixed-valence oxidationstate inpurple acid phosphatases. The cleavage acceleration of the activated phosphodiester 2-hydoxypropyl p-nitrophenyl phosphate (HPNP) was investigated inacetonitrile/water (1:1) in the presence of complexes of the ligand BPMOP and its methyl analogue BPMP with regards to its dependence on the pH value. At the optimum pH value (8.5 +- 0.2), the Zn~(II)Fe~(III) complex fromBPMOP shows a 2-fold higher rate acceleration compared with that of the complex containing BPMP. The diiron complex from BPMOP is 4-fold more reactive than the homologous complex from BPMP. The heterodinuclear Zn~(II)Fe~(III) catalysts are at least 10-fold more reactive than the homonuclear Fe~(II)Fe~(III) catalysts.