Dinuclear zinc(II)-iron(III) and iron(II)-iron(III) complexes as models for purple acid phosphatases

The heterodinuclear (ZnFeIII)-Fe-II complex 1 and the isostructural Fe-II F e-III complex 2 with the dinucleating ligand from 2,6-bis [{bis(2-pyridylme thyl)amino}methyl]-4-methoxyphenol (HBPMOP, 3) were prepared and characteri zed by X-ray crystallography. Solution studies (UV/Vis spectroscopy; electr ochemistry) 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 oxidation state in purple acid phosphatases. The cleavage accelera tion of the activated phosphodiester 2-hydroxypropyl p-nitrophenyl phosphat e (HPNP) was investigated in acetonitrile/water (1:1) in the presence of co mplexes of the ligand BPMOP and its methyl analogue BPMP with regards to it s dependence on the pH value. At the optimum pH value (8.5 +/- 0.2), the (Z nFeIII)-Fe-II complex from BPMOP shows a 2-fold higher rate acceleration co mpared with that of the complex containing BPMP. The diiron complex from BP MOP is 4-fold more reactive than the homologous complex from BPMP. The hete rodinuclear (ZnFeIII)-Fe-II catalysts are at least 10-fold more reactive th an the homonuclear (FeFeIII)-Fe-II catalysts.