Coordination modes of bridge carboxylates in dinuclear manganese compounds determine their catalase-like activities.
ABSTRACT To explore the role of bridge carboxylate coordination modes on the catalase-like activities of dinuclear manganese compounds, [Mn(II)2(bpmapa)2(H2O)2](ClO4)2 (1), [Mn(II)2(pbpmapa)2(H2O)2](ClO4)2 (2), and [Mn(II)2(bpmaa)2(H2O)3](ClO4)2 (3) (bpmapa = [bis(2-pyridylmethyl)amino]propionic acid, pbpmapa = alpha-phenyl-beta-[bis(2-pyridylmethyl)amino]propionic acid, and bpmaa = [bis(2-pyridylmethyl)amino]acetic acid), in which Mn(II)-Mn(II) centers have a similar coordination sphere but different carboxylate-Mn bridging modes have been synthesized and structurally characterized by single X-ray diffraction, UV-visible, IR, and EPR spectroscopies, and their catalase-like activities were investigated. Studies of their catalytic activities and the influence of the nitrogenous bases on their catalytic activities indicated that the carboxylate-Mn coordination mode was crucial in H2O2 deprotonation, and eventually in H2O2 disproportionation. Compound 1 with a bidentate carboxylate bridge showed higher catalase-like activity than 2 and 3, in which the carboxylate groups have a monodentate bridging mode. The deprotonation ability of the carboxylate anion was determined by the O-C-O angle and the distance between the weakly bound oxygen of the bridging carboxylate to the manganese ion. The smaller the angle, and the shorter the distance, the stronger the basicity that the carboxylate anion exhibits. The bidentate mu-1,1 bridging coordination mode functionally mimicked the glutamate residues at the manganese catalase active site. Our results suggested that increasing the basicity of the bridging carboxylate ligand of the catalase model compounds will increase their deprotonation ability and lead to more active catalase mimics.
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ABSTRACT: This work describes a novel method of urinary oxalate determination based on a catalase model compound MnL(H2O)2(ClO4)2 (L = bis(2-pyridylmethyl)amino)propionic acid). Urinary oxalate is first decomposed by the oxalate oxidase into carbon dioxide and hydrogen peroxide. The later is then disproportionated into water and oxygen by the catalase model compound forming a color compound, which can be spectrophotometrically monitored. The oxalate concentration of the sample is quantified according to the UV-vis absorbance of the formed color compound. This model compound method maintains the specificity and sensitivity of the conventional enzymatic assay. It has several advantages over the traditional enzymatic method, including low cost, simplicity, large linear range, and adjustable assay time. The model compound method showed a very good linearity in the range of 0.002–20 mmol L−1 oxalate, with a detection limit of 2 μmol L−1 oxalate. The mean urinary oxalate determined by this method was 28.6 μg mL−1, standard deviation (SD) was 1.07 μg mL−1, and variation coefficient (CV) is less than 4%. The results are consistent with that acquired from the enzymatic and HPLC methods. The model compound method also showed that the model compounds of the corresponding enzymes can be an alternative to the enzymes, thus the cost of the methods or assays using the enzymes can be greatly decreased.Analytical methods 01/2010; 2(3). · 1.86 Impact Factor