Copper catechol complexes

Van den Berg, C.M.G., 1984. Determination of the complexing capacity and conditional stability constants of complexes of copper (II) with natural organic ligands in seawater by CSV of copper-catechol complex ions. Mar. Chem., 15 1-18. 

Van den Berg, C. M. G. (1984) Determination of the Complexing Capacity and Conditional Stability Constants of Complexes of Copper(II) with Natural Organic Ligands in Seawater by Cathodic Stripping Voltammetry of Copper-Catechol Complex Ions, Mar. Chem. 15, 1-18. 

Copper complexation was evaluated by ligand exchange with catechol and cathodic stripping voltammetry of the copper-catechol complexes (28, 29). Titration curves with Cu were obtained by spiking aliquots of lake-water samples with different Cu concentrations. The free [Cu2 ] concentration was calculated from the concentration of copper-catechol complexes formed in equilibrium with free catechol. 

The structural characterization of a series of copper-catecholate complexes, including model structures for catechol oxidase, which have not been known before, and the investigation of a catechol oxidase mechanism (192, 213). 

Model studies and much of the developmental research on synthetic catechol oxidation systems has been concentrated on iron and copper catecholate complexes. 

The development of catalysts for the efficient oxidation of catechol and its derivatives in water is topic of ongoing work in this laboratory. Towards this end, polyethylene glycol side-chains were incorporated in a pentadentate salen ligand to enhance the water solubility of the complexes derived thereof. A dinuclear copper(II) complex is found to catalyze the oxidation of 3,5-di-tert.-butylcatechol into 3,5-di-tert-butyl-o-benzoquinone more than twice as fast in aqueous organic solution as in purely organic solvents (ly,at/knon= 140,000). Preliminary data are discussed. 

Krebs and co-workers synthesized a series of dinuclear copper(II) complexes as models for catechol oxidase 91 (365) (distorted SP Cu-Cu 2.902 A), (366) (distorted five-coordinate geometry Cu-Cu 3.002A), (367) (distorted SP Cu-Cu 2.995 A), (368) (distorted five-coordinate geometry Cu-Cu 2.938 A), and (369) (distorted SP Cu-Cu 2.874 A). These complexes were characterized by spectroscopic and electrochemical methods. From kinetic analysis, a catalytic order for catecholase activity (aerial oxidation of 3,5 -di - ter t-buty lcatec h o 1) was obtained.326... 

There has been enormous activity in the field of copper(I)-dioxygen chemistry in the last 25 years, with our information coming from both biochemical-biophysical studies and to a very important extent from coordination chemistry. This has resulted in the structural and spectroscopic characterization of a large number of copper dioxygen complexes, some of which are represented in Figure 14.2. The complex F, first characterized in a synthetic system was subsequently established to be present in oxy-haemocyanin, and is found in derivatives of tyrosinase and catechol oxidase, implying its involvement in aromatic hydroxylations in both enzymes and chemical systems. 

Adamic and Bartak [6] used high pressure aqueous size exclusion chromatography with reverse pulse amperometric detection to separate copper(II) complexes of poly(amino carboxylic acids), catechol and fulvic acids. The commercially available size exclusion chromatography columns were tested. Columns were eluted with copper(II) complexes of poly(aminocarboxylic acids), citric acids, catechol and water derived fulvic acid. The eluent contained copper(II) to prevent dissociation of the labile metal complexes. Reverse pulse electrochemical measurements were made to minimise oxygen interferences at the detector. Resolution of a mixture of DTP A, EDTA and NTA copper complexes was approximately the same on one size exclusion chromatography column as on Sephadex... 

A number of copper) I) and copper) 11) complexes with [22]py4pz and [22]pr4pz have been isolated and structurally characterized [47—49]. Their structural and catalytic properties, as well as studies on the mechanism of the catalytic oxidation of catechol performed by some of these compounds, are discussed below. 

In conclusion, the mechanism of catechol oxidation by the model compounds is very intricate, which obviously explains often contradictory literature reports on the catalytic behavior of copper(II) complexes. However, despite being sometimes controversial, studies on model compounds offer stimulating results, which improve our knowledge of the structure-activity relationships in natural systems. There is little doubt that the combination of distinct but complementary disci-... 

Further ternary complexes, e.g. [Cu(L-aspartateXL-ornithine)], have been studied spectrophotometrically. A range of spectral techniques have been used to look at the copper(ii) complex of DL-3,4-dihydroxyphenylalanine (dl-DOPA) and copper(ii)-amino-acid-catechol, e.g. (142), systems. 2f-Ray absorption edge spectrometry... 

Various kinetic experiments and product analyses indicate that the catechol oxidation catalyzed by the bispidine-copper(ll) complexes proceeds via the mechanism shown in Scheme 19. There is one quinone product per cycle and dioxygen is reduced to hydrogen peroxide. Interestingly, all individual steps (1 2 3 1) are relatively fast... 

Copper(I) complexes supported by certain capping ligands react with molecular oxygen in a 2 1 ratio to afford dinuclear copper dioxygen (CU2/O2) complexes. Such complexes can be regarded as structural and functional models of the reactive intermediates of tyrosinase and catechol oxidase. Numerous review articles on the subject have been published so far. ... 

As compared to the oxygenation reaction of phenols to catechols (phenolase reaction), dehydrogenation of catechols to the corresponding o-quinones (catecholase reaction) proceeds more readily. Thus, the catalytic activity of several tyrosinase and catechol oxidase models have been examined using 2,4-di-tert-butylcatechol (DTBC) as a substrate.Direct reactions between the (/r-77 77 -peroxo)dicopper(II) complexes and DTBC also have been studied at a low tempera-and a semiquinone-copper(II) complex has been isolated and structurally characterized... 

The initial step in the catechol oxidation is fast, basically for the high reactivity of the copper(II) complex toward DTBCH2. Since quinone formation occurs after a pre-equilibrium binding of the substrate, the reaction... 

The spectroscopic features of the DTBC complex with [Cu2(L55)], which has been detected at low temperature, suggests that catecholate binds as bridging ligand to the dicopper(II) complex in a r r fashion, as proposed for nitrocatecholate-copper(II) complexes (38). In the complex formulated as [CU2/DTBC] in reaction 17 the catechol is supposed to bind to the dicopper(I) complex in a symmetric r r bridging mode (757). A kinetic treatment of the two steps of the catalytic reaction yielded the parameters kj, Kj)j, and Kj)2 The activation and thermodynamic parameters were obtained from the temperature dependence of kj, and Kd2- The constants... 

In the present paper we would like to present the results of synthetic experiments on semiquinone and catechol complexes of copper, with characterization that may provide insights on the extent to which redox activity at both the metal and the quinone ligand contributes to the synthetic course of oxidation reactions with dioxygen. 

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