Oxidation states copper

Loss of copper. Solutions and crystals of ceruloplasmin that have been allowed to stand for several weeks partially lose their blue color and this may indicate changes in copper oxidation state and/or loss of copper. A series of experiments are required to determine whether any copper loss is site preferential and how this is affected by anionic inhibitors. 

The Franck-Condon principle states that there must be no movement of nuclei during an electronic transition therefore, the geometry of the species before and after electron transfer must be unchanged. Consequently, the active site geometry of a redox metalloenzyme must approach that of the appropriate transition state for the electronic transfer. Every known copper enzyme has multiple possible copper oxidation states at its active site, and these are necessary for the enzyme s function. 

This oxygen variation and the Cu oxidation states play a very important role in the superconducting behavior of this compound. For example, the oxygen content (or x vacancy), the copper oxidation states, and the onset temperatures for superconductivity are listed below for different compositions. 

How can it arise that we seem unable to differentiate between the compositions, say, Bi2Sr2CaCu208 33 and BijSrj gyCa-Cu2Og (i.e. for a formal copper oxidation state of +2.33) Under... 

Nd2-xCexCu04, 112,427-45 band structure schematic, 717 cerium oxidation state, 431 comparison with La2CuO>4 systems, 320 composition range, 437 copper oxidation state, 427,442 crystal chemistry, 428-31 crystal growth, 244,436-7,442-4... 

Scheme 10.24 Helix formation as a function of copper oxidation state.

Degradation of PEEK in the presence of copper appears to be catalyzed by Cu(II) or the reduction of Cu(II) to Cu(I). Metallic copper does not catalyze the decomposition of PEEK. On metallic copper, the PEEK remains intact to at least 350°C. Cu(I) does not show a strong interaction with PEEK. PEEK loss from the Cu(I) surface, possibly due to desorption, is apparent below 300 C. Up to 250°C, Cu(II) retains the PEEK in a manner similar to the metallic copper. However, there is a marked loss of PEEK on Cu(II) near 250 C and a reduction in the copper oxidation state. These two observations suggest that chemical reaction is occurring. 

Kinetics studies have shown that the rates of the electron-transfer steps are faster than the encounter rate between 02 and the enzyme. The encounter rate is independent of the copper oxidation state. Km for -02 is high (—B.SmM), which means that, under nearly all conditions, superoxide dismutase turnover is far from saturated. 

One high-temperature superconductor has the general formula YBa2Cu3Ox. The copper is a mixture of Cu(II) and Cu(III) oxidation states. This mixture of oxidation states appears vital for high-temperature superconductivity to occur. A simple method for determining the average copper oxidation state has been reported [D. C. Harris, M. E. Hillis, and T. A. Hewston, ]. Chem. Educ. 64, 847(1987)]. The described analysis takes place in two steps ... 

Metastable species derived from (L)Cu(02), where L- = 2,4-di-te/V-butyl-phenolate linked to l,4-di-z, so-propyl-l,4,7-triazacyclononane, show multiple vCuO bands in the wavenumber range 500-550 cm-1.389 The resonance Raman spectrum of [Cu2(p-0)2(flf4-Me2-etpy)2]2+ has a vCu-O-Cu band at 579 cm-1 (551 cm-1 for lsO).390 Selective catalytic reduction of NO by NH3/02 on copper-faujasite catalysts gave rise to IR bands showing changes in copper oxidation states (using the vas[Cu-0-Cu]+ band near 900 cm-1).391... 

Hole-based superconductors have an average copper oxidation state of approximately 2.2. The holes are normally introduced by oxygen vacancies in the apical oxygens of the copper-oxygen layers. 

Q Calculate the average copper oxidation state in the compounds YBa,Cu30g and YBa2Cu30y and hence predict whether they could be hole-based superconductors. 

Tp CuL complexes catalyze both reactions shown in Scheme 17. The aziridination reaction with such catalysts was discovered using Tp CulCjH ) and Phi=NTs as the nitrene source (Scheme 18). The influence of the hapticity of the Tp ligand and the oxidation state of the copper center were later studied demonstrating that tricoordination of the ligand and +1 as the copper oxidation state were the best choices. The use of the fluorinated version of the above catalyst, that is Tp< u(C2H ) also proved effective. Moreover, the already mentioned Tp Cu(NCMe) complex induced the aziridination reaction not only with the frequently employed olefins (styrene, 1-hexene, cyclooctene) but also with aaylates and using a stoichiometric mixture of olefin and PhI=NTs. ... 

Table 2. Electron configuration and magnetic properties of the three oxidation states of copper. Cu2+ contains an unpaired electron and is therefore EPR-active. Cu+ and Cu3+ are EPR-inactive. These features are utilized in spectroscopic experiments studying copper oxidation states in electron-transfer reactions. When two Cu2+-centers are in close proximity to each other, antiferromagnetic coupling of the two unpaired electrons renders both copper centers EPR-inactive...

Figure 35. Frontier MOs (obtained from TDDFT involved in the photoelectronic Bergman cyclization of copper metalloenediynes. The metal frontier orbitals (yellow) are highlighted along with the pyridine it and it sets for a respective copper oxidation states.

The structures of Cu2Zn2SOD complexes with small inorganic anions have been determined at different copper oxidation states. 

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