Unsymmetrical Fe(III)Co(II) and Ga(III)Co(II) complexes as chemical hydrolases: biomimetic models for purple acid phosphatases (PAPs)

• Published in: Inorganic chemistry Vol. 48; no. 16; pp. 7905 - 7921
• Main Authors: Xavier, Fernando R, Neves, Ademir, Casellato, Annelise, Peralta, Rosely A, Bortoluzzi, Adailton J, Szpoganicz, Bruno, Severino, Patricia C, Terenzi, Hernán, Tomkowicz, Zbigniew, Ostrovsky, Sergei, Haase, Wolfgang, Ozarowski, Andrew, Krzystek, Jerzy, Telser, Joshua, Schenk, Gerhard, Gahan, Lawrence R
• Format: Journal Article
• Language: English
• Published: United States 17-08-2009
• Subjects: Absorption; Acid Phosphatase - chemistry; Acid Phosphatase - metabolism; Animals; Biocatalysis; Biomimetics; Cattle; Circular Dichroism; Cobalt - chemistry; DNA - metabolism; Electrochemistry; Electron Spin Resonance Spectroscopy; Ferric Compounds - chemistry; Ferric Compounds - metabolism; Gallium - chemistry; Glycoproteins - chemistry; Glycoproteins - metabolism; Hydrolysis; Kinetics; Magnetics; Potentiometry; Titrimetry
• ISSN: 1520-510X
• DOI: 10.1021/ic900831q

The design and development of suitable biomimetic catalytic systems capable of mimicking the functional properties of enzymes continues to be a challenge for bioinorganic chemists. In this study, we report on the synthesis, X-ray structures, and physicochemical characterization of the novel isostructural [Fe(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (1) and [Ga(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (2) complexes with the unsymmetrical dinucleating ligand H(2)BPBPMP (2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol). The previously reported complex [Fe(III)Zn(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (3) was investigated here by electron paramagnetic resonance for comparison with such studies on 1 and 2. A magneto-structural correlation between the exchange parameter J (cm(-1)) and the average bond lengh d (A) of the [Fe(III)-O-M(II)] structural unit for 1 and for related isostructural Fe(III)M(II) complexes using the correlation J = -10(7) exp(-6.8d) reveals that this parameter is the major factor that determines the degree of antiferromagnetic coupling in the series [(BPBPMP)Fe(III)(mu-OAc)(2)M(II)](+) (M(II) = Mn, Fe, Co, Ni) of complexes. Potentiometric and spectrophotometric titrations along with electronic absorption studies show that, in aqueous solution, complexes 1 and 2 generate the [(HO)M(III)(mu-OH)Co(II)(H(2)O)] complex as the catalytically active species in diester hydrolysis reactions. Kinetic studies on the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate by 1 and 2 show Michaelis-Menten behavior, with 2 being 35% more active than 1. In combination with k(H)/k(D) isotope effects, the kinetic studies suggest a mechanism in which a terminal M(III)-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst. In addition, the complexes show maximum catalytic activity in DNA hydrolysis near physiological pH. The modest reactivity difference between 1 and 2 is consistent with the slightly increased nucleophilic character of the Ga(III)-OH terminal group in comparison to Fe(III)-OH in the dinuclear M(III)Co(II) species.