Copper oxidative addition model

Oxidative Addition Model of Oxygen Binding to Iron and Copper Proteins... 

The oxidative addition model for reversible O2 binding by metal proteins is also reasonable for hemocyanin. Hemocyanin is a copper protein which binds one O2 molecule for every two copper atoms. The deoxy Cu(I) form has no appreciable absorption in the visible region. When oxygenated, the protein is blue and exhibits a rich visible spectrum, wiA bands at 700 (c 75), 570 (c 500), 440 (c 65), and 347 nm (c 8900) (53). The pattern of bands around 570 nm leaves little doubt that oxyhemocyanin contains Cu(II) (53). The enhanced LF band intensities further suggest a dimeric Cu(II) complex. For comparison. 

The complexes [Cu(NHC)(MeCN)][BF ], NHC = IPr, SIPr, IMes, catalyse the diboration of styrene with (Bcat) in high conversions (5 mol%, THF, rt or reflux). The (BcaO /styrene ratio has also an important effect on chemoselectivity (mono-versus di-substituted borylated species). Use of equimolecular ratios or excess of BCcat) results in the diborylated product, while higher alkene B(cat)j ratios lead selectively to mono-borylated species. Alkynes (phenylacetylene, diphenylacety-lene) are converted selectively (90-95%) to the c/x-di-borylated products under the same conditions. The mechanism of the reaction possibly involves a-bond metathetical reactions, but no oxidative addition at the copper. This mechanistic model was supported by DFT calculations [68]. 

An exploratory study was carried out with respect to the performance of a copper fuel additive in combination with monolithic wall flow filters for the removal of soot firom diesel exhaust gas. Cordierite filters, copper coated cordierite filters, and silicon carbide filters were studied. Model experiments have been performed to investigate the influence of contact between soot and catalyst on the oxidation rate. 

The selectivity of the aldol addition can be rationalized in terms of a Zimmer -man-Traxler transition-state model with TS-2-50 having the lowest energy and leading to dr-values of >95 5 for 2-51 and 2-52 [18]. The chiral copper complex, responsible for the enantioselective 1,4-addition of the dialkyl zinc derivative in the first anionic transformation, seems to have no influence on the aldol addition. To facilitate the ee-determination of the domino Michael/aldol products and to show that 2-51 and 2-52 are l -epimers, the mixture of the two compounds was oxidized to the corresponding diketones 2-53. 

Copper enzymes are involved in reactions with a large number of other, mostly inorganic substrates. In addition to its role in oxygen and superoxide activation described above, copper is also involved in enzymes that activate methane, nitrite and nitrous oxide. The structure of particulate methane mono-oxygenase from the methanotrophic bacteria Methylococcus capsulatus has been determined at a resolution of 2.8 A. It is a trimer with an a3P33 polypeptide arrangement. Two metal centres, modelled as mononuclear and dinuclear copper, are located in the soluble part of each P-subunit, which resembles CcOx subunit II. A third metal centre, occupied by Zn in the crystal, is located within the membrane. 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

For consistency with the experimental data, an equivalent site model requires that the absorption characteristics of each of the two type 3 copper ions be independent of their state of coupling. For a nonequivalent site model one has to assume that the absorption at 330 nm is entirely caused by the Cu(II) ion with the higher redox potential, so that the observed equilibrium can be assigned to the oxidation-reduction of this site. In both cases we take into account that the addition of four oxidizing equivalents restore the original absorption of the enzyme, and we assume... 

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