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Unsymmetrical FeIIICoII and GaIIICoII Complexes as Chemical Hydrolases: Biomimetic Models for Purple Acid Phosphatases (PAPs)

Xavier, Fernando R. and Neves, Ademir and Casellato, Annelise and Peralta, Rosaly A. and Bortoluzzi, Adailton J. and Szpoganicz, Bruno and Severino, Patricia C. and Terenzi, Hernan and Tomkowicz, Zbigniew and Haase, Wolfgang and Ozarowski, Andrew and Krzystek, Jerzy and Telser, Joshua and Schenk, Gerhard and Gahan, Lawrence R. (2009) Unsymmetrical FeIIICoII and GaIIICoII Complexes as Chemical Hydrolases: Biomimetic Models for Purple Acid Phosphatases (PAPs). Inorganic Chemistry, 48. pp. 7905-7091. ISSN 0020-1669

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Abstract

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 [FeIIICoII(BPBPMP)(μ-OAc)2]ClO4 (1) and [GaIIICoII(BPBPMP)(μ-OAc)2]ClO4 (2) complexes with the unsymmetrical dinucleating ligand H2BPBPMP (2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol). The previously reported complex [FeIIIZnII(BPBPMP)(μ-OAc)2]ClO4 (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 [FeIII-O-MII] structural unit for 1 and for related isostructural FeIIIMII complexes using the correlation J = -107 exp(-6.8d) reveals that this parameter is the major factor that determines the degree of antiferromagnetic coupling in the series [(BPBPMP)FeIII(μ-OAc)2MII]þ (MII = 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)MIII(μ-OH)CoII(H2O)] 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 kH/kD isotope effects, the kinetic studies suggest a mechanism in which a terminal MIII-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 GaIII-OH terminal group in comparison to FeIII-OH in the dinuclear MIIICoII species.

Item Type: Article
Additional Information: The definitive version of this article is available in Inorganic Chemistry, 2009, 48, 7905–7921 DOI: 10.1021/ic900831q . © 2009 American Chemical Society
Keywords: Unsymmetrical FeIIICoII; GaIIICoII Complexes; Chemical Hydrolases; Biomimetic Models; Purple Acid Phosphatases; PAPs;
Subjects: Science & Engineering > Chemistry
Item ID: 3727
Depositing User: Gary Schenk
Date Deposited: 06 Jun 2012 07:40
Journal or Publication Title: Inorganic Chemistry
Publisher: American Chemical Society
Refereed: Yes
URI:

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