Cupric complex

Samples are hydrolyzed with hydrochloric acid and stannous chloride solution at elevated temperature, and the evolved carbon disulfide is drawn with an air steam through two gas washing tubes in series containing lead acetate and sodium hydroxide solutions and an absorption tube containing an ethanolic solution of cupric acetate and diethanolamine. Lead acetate and sodium hydroxide remove hydrogen sulfide and other impurities. In the absorption tube, the carbon disulfide forms two cupric complexes of Af,Af-bis(2-hydroxyethyl)dithiocarbamic acid with molecular ratios Cu CS2 of 1 1 and 1 2. These complexes are measured simultaneously by spectrophotometry at 453 nm. 

The NO reduction of the Cu(II) complex Cu(dmp)2(H20)2+ (dmp = 2,9-dimethyl-l,10-phenanthroline) to give Cu(dmp)2 plus nitrite ion (Eq. (20)) has been studied in aqueous solution and various mixed solvents (42a). The reduction potential for Cu(dmp)2(H20)2+ (0.58 V vs. NHE in water) (48) is substantially more positive than those for most cupric complexes owing to steric repulsion between the 2,9-methyl substituents that provide a bias toward the tetrahedral coordination of Cu(I). The less crowded bis(l,10-phenanthroline) complex Cu(phen)2(H20)2+ is a weaker oxidant (0.18 V) (48). 

Theory Gravimetric analysis of proguanil hydrochloride involves the precipitation of the proguanil-cupric complex that results on the addition of ammoniacal cupric chloride solution to a solution of proguanil hydrochloride. The reaction can be expressed by the following equation ... 

Figure 5 shows that at very high chloride activities the cuprous complex, CUCI32-, becomes very dominant, being oxidised to cupric complexes only above pE = 10. This information is of value because methods of stabilising particular valence states such as Cu offer means of separating metals that would be difficult to separate in their normal valence states. 

From the given experimental results it is inferred that the reduction of the iodobenzoate-cupric complex produces a system of unstable configuration, which decomposes by atom transfer before it has a chance to readjust to the stable iodo-benzoate-cuprous complex... 

In general, the effects of complexing on the reactivities of the mercuric (Korinek and Halpern, 26) and silver (Webster and Halpern, 12) ions are susceptible to similar interpretations, although it should be noted that the order of activity of the various complexes differs for the three metals. Thus, the chloride and acetate complexes of the mercuric ion (which are much more stable than the corresponding cupric complexes) are less reactive than the aquo complex, while the relatively unstable sulfate complex is more reactive. In the case of silver, the acetate and ethylenediamine complexes are more reactive than the uncomplexed ion, while the very stable cyanide complex is inactive. 

In the absence of an adequate knowledge of the chemical nature of hydrogenase, it is not possible to interpret its properties in detail. In a number of important respects, however, its catalytic behavior resembles that of some of the homogeneous catalysts that have been studied. Among these, the cupric complexes probably come closest to serving as models for this enzyme. 

In the preceding discussion the reaction has been represented as involving undissociated Cu(OAc)2 molecules rather than simple cupric ions or other cupric complexes. This appears to be consistent with the kinetic results taken in conjunction with independent measurements of the dissociation constants of cupric acetate. These measurements indicate that in solutions of the composition used in these experiments, cupric acetate is predominantly undissociated. The degree of dissociation to CuOAc+ ranges from about 10% at the highest NaOAc (used as a buffer) concen-... 

Halpern and his associates have recently extended their studies of the activation of hydrogen by aqueous solutions of cupric, mercuric, mercurous, and silver salts. The catalytic activities of a series of cupric complexes decrease in the following order butyrate, propionate > acetate > sulfate > chloride > water (perchlorate solution) > glycine,... 

Fig. 2. Representative crystal structures of thiolate cupric complexes. Reprinted with permission from Refs. 53-59.

After comparing spectra it was determined that the species which tends to decrease in absorbance during the reaction was the cupric tartrate complex found in the biuret reagent. Its absorbance is significant even down to wavelengths of slightly below 530 nm. The complications caused by the absorbance of the cupric complex at 550 nm appear to be a substantial cause of the unusual rate curve observed in the early part of the reaction. 

These simulation programs, based on a perturbation approach, have been used to estimate the metal-metal distance for a number of dipolar-coupled ( 2 J < 30 cm-1) cupric complexes (Boyd, P. D. W. et al. J. Chem. Soc. Dalton, 1549 (1973)) and show good agreement when compared with x-ray crystallographic results... 

A general method for synthesizing starch-metal complexes with Ba, Ca, Sr, Be, Mg, Zn, Al, Fe, and Cu is given by a 1926 British patent,522 wherein alkali starches were treated with one or more metal salts. The cupric complex was reported to have disinfecting properties. 

Gerega K. and Kozlowski H., Cupric complexes with 3,4-dihydroxybenzoic acid. Inorg. Chim. Acta 138(1987) pp.31-34. 

This is an area which has received almost no systematic study, in spite of occasional reports indicating that metals can have substantial effects. We may mention the general spectral intensification shown when conal-bumin binds two moles of Fe (Warner and Weber, 1953), which may be explained in part by the broad-band ultraviolet absorptivity of ferric ion with various ligands (Buck et al., 1954). We have already noted (Fig. 4) the substantial spectral effects of cadmium and zinc binding by thionein (Kagi and Vallee, 1961). The strong absorptivity of the cupric complexes of amino acids around 2300 A (Spies, 1952) is also pertinent here. 

Copper-proteins are wide-spread in both animals and plants and have been related to many metabolic processes, as oxygen transport, electron transfer and hydroxylation Copper-containing sites are usually classified in three different types " the type 1, or blue center is characterized by a combination of properties that has not yet been reproduced in model complexes (an intense absorption band at 600 nm, a very small copper hyperfine coupling constant A and a high positive redox potential for the Cu(II)/ Cu(I) couple) the type 2, or non-blue center has properties comparable to those of low molecular weight cupric complexes the type 3 consists of an antiferromagnetically coupled copper(II) pair. 

The main factor which allows observation of the NMR signals is the rather small magnitude of hyperfine couplings involved. Small A values will not greatly affect the transverse relaxation time T2 of the proton [equation (18)] and thus the NMR bandwidth will not be greatly increased. Byers and Williams (56) have studied some dimeric cupric complexes which are models for copper dimer units in proteins. Interest was particularly centred around the possibility that, if appreciable copper(ii) interactions occur, a mechanism for mutual fast relaxation is provided which in turn may lead to much narrower linewidths and measurable paramagnetic shifts. The systems are illustrated in [6]. 

Taylor, M. R., Gabe, E. J., Glusker, J. P., Minkin, J. A., and Patterson, A. L. The crystal structures of compounds with antitumor activity. 2-Keto-3-ethoxybutyraldehyde bis(thiosemicarbazone) and its cupric complex. J. Amer. Chem. Soc. 88, 1845-1846 (1966). 

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