Catecholase Activity of a Copper(II) Complex with a Macrocyclic Ligand: Unraveling Catalytic Mechanisms

Abstract

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1 4,7 .1 11,14 . 1 17,20 ]triacontane-5,7(28), 11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tertbutylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and ditert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu II and the Cu I complexes are also reported.

Tuning the coordination properties of multi-histidine peptides by using a tripodal scaffold: solution chemical study and catechol oxidase mimicking

“…S11, S12), which is in agreement with many other catecholase model systems. [69][70][71][72] According to the MichaelisMenten model, the observed pseudo-second order reaction rate constant (k', slope of the lines in Figure S11) Figure S11), which confirms the validity of our kinetic data. pH-dependent absorption spectra of Cu(II)-L 1 -H 2 4NC ternary systems were followed at different complex-to-H 2 4NC ratios ( Fig.…”

“…Catechol oxidases are type 3 copper enzymes, 66,67 therefore mostly dinuclear complexes were used for the biomimetic studies. [68][69][70][71][72][73][74] Nevertheless, several mononuclear [75][76][77] or trinuclear 78 complexes were also reported to possess important catecholase-like activity. To screen the enzyme mimetic properties of our oligonuclear copper(II) complexes, their catecholase activity was investigated by using the widely studied 3,5-di-tert-butylcatechol (H 2 DTBC) as model substrate.…”

Structural and spectroscopic studies of a model for catechol oxidase

“…Design and study of model complexes for catechol oxidase and other type 3 copper centers has been an area of much interest [6][7][8][9][10] and various nitrogen-containing binucleating ligands have been used to generate dicopper complexes [6,[15][16][17][18]. 2,6-Bis[bis(pyridin-2-ylmethylamino)methyl]-4-methylphenol (H-BPMP), employed previously to model catechol oxidase [19,20], provides a nitrogen-rich coordination set similar to that of the enzyme (three nitrogen donors) and has previously furnished both trigonal bipyramidal and square pyramidal geometries.…”

Synthesis, structural characterization and catalytic activities of dicopper(II) complexes derived from tridentate pyrazole‐based N2O ligands

“…3, the band at 400 nm increased in intensity with the reaction time at room temperature, indicative of the formation of 3,5-DTBQ and the successive increment of its concentration. Simultaneously the band at 625 nm decreased in intensity with time, indicating that the Cu 21 In all investigations, it was found that the catalytic reaction was finished after 1 h, indicative of the much lower activity of our employed dicopper complexes on comparison with the reported dicopper complexes earlier, 6,20 their catalytic oxidation being generally finished within a few minutes at low catechol to complexes ratios. The reason for this observation can be tentatively ascribed to the stereo effects of the ligands we employed in this work, and our initial investigations on the catalytic activity of the complex [Cu 2 (pmpzpo) 2 ]Br 2 ·CH 3 OH, with more bulky substituents at the 3-position of the pyrazolyl rings, strengthened this assumption.…”