Copper redox behavior

To provide a model for nitrite reductases72 Karlin and co-workers characterized a nitrite-bound complex (226) (r = 0.05)214 In an endeavor to model nitrite reductase activity, Tanaka and co-workers prepared a few mononuclear complexes (227) (r = 0.74)215 (228) (r = 0.82),216 (229) (r = 0.97),217 (230) (r = 0.16),217 (231) (r = 0.07),217 and (232) (r = 0.43 and r = 0.53)217 and studied the electrochemical reduction of N02A As a part of their activity on modeling heme-copper terminal oxidases, Holm and co-workers prepared complex (233) (r = 0.96).218 Using a sterically hindered tris(pyridylmethyl)amine, Canary et al. prepared a complex (234) (r=1.00), studied its redox behavior, and discussed various factors that may contribute to the difference (higher potential for the new complex) in the redox potential of a Cu Cu1 couple between substituted and unsubstituted ligands.2 9... 

M. M. Gunter, T. Ressler, R. E. lentoft, and B. Bems, Redox behavior of copper oxide catalysts in the steam reforming of methanol studied by in situ X-ray diffraction and absorption spectroscopy, J. Catal. 203, 133-149 (2001). 

Extensive analysis of the EPR and redox behavior of this unusual copper protein led to the hypothesis that the protein might contain a Cu(A) site similar to that in cytochrome oxidase (Riester et ai, 1989) and that the unusual seven-line EPR is due to the Cu(A)-type site. An alternative interpretation of this EPR is based on electron spin-echo spectroscopy as well, and that is that the seven-line EPR is due to a half-met Cu—Cu pair and to unusual type I sites (Jin et ai, 1989). Three sets of spin-echo peaks can be attributed to nitrogens on imidazole ligands to a CuA-type site and to another imidazole on the half-met site. The electron spin-echo spectra of cytochrome oxidase are similar, although there is not enough copper in cytochrome oxidase for a half-met site. Conceivably, the property of delocalization of the paramagnetic electron could be effected by the proposed bridging between Cub and heme as (nomenclature summarized by Capaldi, 1990), which are proposed to be 3-4 A apart. 

The current chapter focuses on the electrochemistry of the ionic forms of copper in solution, starting with the potentials of various copper species. This includes the effect of coordination geometry, donor atoms, and solvent upon the electrochemical potentials of copper redox couples, specifically Cu(II/I). This is followed by a discussion of the various types of coupled chemical reactions that may contribute to the observed Cu(II/I) electrochemical behavior and the characteristics that may be used to distinguish the presence of each of these mechanisms. The chapter concludes with brief discussions of the electrochemical properties of copper proteins, unidentate and binuclear complexes. 

The specific phenomenon in this copper-induced reaction is the configuration of the reduced complex which facilitates the oxidation of Cu(I) to Cu(III). The effect of configuration on the redox behavior of a ligand may be important in interpreting metal-induced enzymatic redox reactions. 

Gunter et al. (2001) XAS Cu/ZnO Phase stability of copper and role of strain, redox behavior + + + Methanol steam reforming... 

Copper (III)-Peptide Complexes. Molecular oxygen reacts with Cu(II)tetraglycine (G4) in neutral solution to produce a yellow species with an intense absorption band at 362 nm. As the oxygen in the solution is consumed, the amount of the yellow species decays (Figure 6). The uv-visible spectrum, molar absorptivity, dissociation kinetics in acid and in base, and the redox behavior of this yellow species are similar to those of Cunl(H.3G4)", which is generated by IrCl62 or by electrolytic oxidation of the corresponding Cu(II) complex. The peptide products after... 

Cytochromes/( J from Latin frons for leaf) and were discovered almost half a century ago hy Hill and Scarisbrick and by Hill, respectively. In fact, the redox behavior of these chloroplast c)do-chromes led Robin Hill and Fay Bendall to formulate the so-called Z-scheme for oxygenic photosynthesis. In 1972, Nelson and Neumann" isolated a partially purified complex from a digitonin-fraction-ated PS-I particle obtained from lettuce chloroplasts. The complex was found to contain Cyt/, Cyt and non-heme iron, which led the authors to note its similarity to the Cyt-bci complex (i.e., complex III) of mitochondria. In 1975 Sugahara, Shaw and this author isolated a complex from spinach TSF-I particles and by investigation of its spectroscopic and EPR properties, showed that it also contained Cyt/, Cyt b and nonheme iron, consistent with its being a bjcomplex. The fraction also displayed a distinct EPR signal characteristic of a copper protein, apparently due to plastocyanin co-precipitated during fractionation. 

The redox behavior of nucleic acids, especially at mercury and carbon electrodes, has been studied for decades, and a variety of quantitative methods exist [117-120, and references therein]. Recently, under-ivatized nucleic acids in solution have been selectively quantitated by ac voltammetry at copper electrodes [121], while DNA bound to gold electrode surfaces via gold-thiol chemisorption has been quantitated by chronocoulometry using charge-compensating redox markers [122]. Derivative square wave voltammetry has been used to examine chemically induced DNA damage following reaction with styrene oxide [123]. 

Type II copper sites, with one copper(II) ion in a practically square planar environment, possess no distinctive spectroscopic properties,which are comparable to those of "normal" copper compounds. They also "show considerable variability in redox behavior" [6]. 

The important properties of metal oxides that are of certain interest in different fields of applied science and technology are connected with magnetic, electrical, dielectric, optical, acid-base, and redox behavior. In particular, transition metal oxides with redox properties are of interest for applications in catalysis [1]. Metal oxides and in particular transition metal oxides can possess more than one stable oxidation state making them possible to catalyze reactions which necessitate electron exchanges between reactant(s) and surface active sites (e.g., oxidation, dehydrogenation, etc.). Conversely, other kinds of metal oxides are known to be almost complete irreducible. Oxides of copper, nickel, cobalt, molybdenum, are only few examples of reducible... 

Esemann and Forster [104] employed far-infrared and X-ray absorption spectroscopy, assisted by computer modeling, to study copper exchange into ZSM-5 by solid-state reaction, the siting of the introduced cations, NO adsorption and decomposition on and redox behavior of the obtained Cu-ZSM-5. Forster and Hatje [105] applied EXAFS techniques to study the incorporation of Cu+ as well as of Zn " and Ni + (vide infra) into Y-type zeolite. The oxidation state of introduced Cu" remained unchanged upon SSIE The determined Cu+-oxygen distances were too small as to suggest a coordination to the oxygen... 

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