FeIIIFeIII and FeIIFeIII Complexes as Synthetic Analogues for the Oxidized and Reduced Forms of Purple Acid Phosphatases
journal contributionposted on 10.04.1996, 00:00 by Ademir Neves, Marcos A. de Brito, Ivo Vencato, Valderes Drago, Klaus Griesar, Wolfgang Haase
Novel FeIIIFeIII and FeIIFeIII complexes [Fe2(BBPMP)(μ-OAc)(μ-X)]n (1, X = OAc-, n = 1+; 2, X = OH-, n = 1+; 3, X = OAc-, n = 0; 4, X = OH-, n = 0), where BBPMP3- is the anion of 2,6-bis[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methylphenol, and OAc- is acetate, were prepared in order to provide models for the active site of purple acid phosphatases (PAPs). Complex 1 was obtained by the reaction of H3BBPMP with Fe(ClO4)2·6H2O in methanol and sodium acetate trihydrate under ambient conditions, while complex 3 was synthesized as described for 1, under an argon atmosphere with low levels of dioxygen. 2 was isolated from 1 in acetonitrile by a substitution of the bridging acetate group by hydroxide, while 4 was generated in solution during a spectropotentiostatic experiment on 2, under argon. Complex 1, [FeIII2(BBPMP)(μ-OAc)2]ClO4·H2O, has been characterized by X-ray crystallography. Crystal data: monoclinic, space group P21/n, a = 14.863(5) Å, b = 12.315(3) Å, c = 20.872(8) Å, β = 90.83(3)°, Z = 4. IR, Mössbauer, magnetic, electronic absorption, and electrochemical properties of 1−3 have been investigated, and some of these properties represent a contribution to the understanding of the dinuclear iron center of PAPs. Complexes 2, [FeIII2(BBPMP)(μ-OAc)(μ-OH)]ClO4 (λmax = 568 nm/ε = 4760 M-1 cm-1), and 4 [FeIIFeIII(BBPMP)(μ-OAc)(μ-OH)] (λmax = 516 nm/ε = 4560 M-1 cm-1), constitute good synthetic analogues for the chromophoric site for the oxidized and reduced forms, respectively, of the enzyme.