Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear FeIIIMII center (MII = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a variety of ...phosphoric acid esters. The dinuclear complex (H2O)FeIII(μ-OH)ZnII(L-H)(ClO4)2 (2) with the ligand 2-N-bis(2-pyridylmethyl)aminomethyl-4-methyl-6-N′-(2-pyridylmethyl)(2-hydroxybenzyl) aminomethylphenol (H2 L-H) has recently been prepared and is found to closely mimic the coordination environment of the FeIIIZnII active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the FeIII center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted FeIIIN2O4 octahedron with a dominant tetragonal compression aligned along the μ-OH−Fe−Ophenolate direction. To probe the role of the Fe−Ophenolate bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (−CH3, −H, −Br, −NO2) in the 5-position. The effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic structural information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order −NO2 ←Br ←H ←CH3 when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k cat/k 0) is plotted against the Hammett parameter σ. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing −NO2 and electron-donating −CH3 groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups.
The fuel cell is a continuously operating, low environmental impact, highly energy-efficient electrochemical device that has been cited as a clean energy source to replace fossil fuels. However, ...noble metals, such as platinum, are used as electrocatalysts to improve reaction kinetics, which raises the cost of this renewable energy source. This work aimed to evaluate a graphite paste electrode, modified with a copper(II) coordination compound containing N,O-donor groups, as an electrocatalyst in oxygen reduction reactions (ORR) and its catalase-like activity. Through electrochemical analyses, such as cyclic voltammetry and chronoamperometry, the modified electrode activity was investigated at different pH values and scan rates. Catalase activity was also investigated at different pH values in order to establish which would be the most active. The modified electrode proved to be a promising electrocatalyst in ORR in alkaline medium, and the copper(II) complex actively degraded hydrogen peroxide under alkaline conditions, which can help to increase the lifetime of the fuel cell device.
Graphical Abstract
Copper(II) complex with electrocatalytic activity in the ORR and catalase-like
Developing new non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is an essential challenge in electrochemical device research. Among these, we highlight the metal Schiff-base ...complexes, which can be used as modified carbon paste electrodes (CPE). Herein, we present a facile one-pot method for preparing a new family of cobalt(II) complexes with Schiffbase ligands obtained from glycine and para-substituted aldehydes. Complexes were characterized by different techniques, and the effects of para-substituents on the electronic properties of the complexes were confirmed by ultraviolet-visible spectroscopy and cyclic voltammetry (CV). The CV was also used to evaluate the ORR behavior of metal complex-modified CPE in an alkaline medium. The three complex-modified CPE were found to be highly effective for ORR, and the electron-withdrawing character of para-substituent affects the electrochemical reactivity. Density functional theory (DFT) calculations were used to complement the study and correlate the electrochemical activity, the redox potentials, and the Hammett parameter (σp) with the singly occupied molecular orbital (SOMO) energy of the complexes. DFT data were also able to shed light on the likely ORR mechanism. In summary, electronic tuning of the ligand affects the electronic properties of the metal center and allows for systematic oxygen reduction-catalytic control.
Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear Fe(III)M(II) center (M(II) = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a ...variety of phosphoric acid esters. The dinuclear complex (H(2)O)Fe(III)(μ-OH)Zn(II)(L-H)(ClO(4))(2) (2) with the ligand 2-N-bis(2-pyridylmethyl)aminomethyl-4-methyl-6-N'-(2-pyridylmethyl)(2-hydroxybenzyl) aminomethylphenol (H(2)L-H) has recently been prepared and is found to closely mimic the coordination environment of the Fe(III)Zn(II) active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the Fe(III) center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted Fe(III)N(2)O(4) octahedron with a dominant tetragonal compression aligned along the μ-OH-Fe-O(phenolate) direction. To probe the role of the Fe-O(phenolate) bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (-CH(3), -H, -Br, -NO(2)) in the 5-position. The effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic structural information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order -NO(2) ←Br ←H ←CH(3) when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k(cat)/k(0)) is plotted against the Hammett parameter σ. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing -NO(2) and electron-donating -CH(3) groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups.
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)2ClO4 (1) and GaIIICoII(BPBPMP)(μ-OAc)2ClO4 (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)2ClO4 (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 (Å) 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+ (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 k H/k D 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.
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