Copper spectral properties

In contrast to the well-established methods for identifying and quantifying naturally occurring chlorophylls, very few reports concern quantitative analysis of chlorophyllin copper complexes in color additives and in foodstuffs. Analytical methods proposed are based on spectral properties, elemental analysis, chromatographic separation, and molecular structure elucidation or a combination of these procedures. 

Spectral results [180] for copper(II) complexes of 2-acetylpyridine N-dimethylthiosemicarbazone, 9, and 2-acetylpyridine 3-(4-methylpiperidine) thiosemicarbazone, 12, are included in Table 2. While the complexes of 9-H have spectral properties consistent with the other copper(II) complexes of Table 2, those of 12-H, with the exception of [Cu(12-H)F], show considerably higher values of g, and consequently higher values of k. These values indicate that there is little in-plane 7t-bonding, possibly due to the bulkiness of the 4-methylpiperidine group. 

Table 5.2 Spectral Properties of Some Copper Enzymes...

This discussion of copper-containing enzymes has focused on structure and function information for Type I blue copper proteins azurin and plastocyanin, Type III hemocyanin, and Type II superoxide dismutase s structure and mechanism of activity. Information on spectral properties for some metalloproteins and their model compounds has been included in Tables 5.2, 5.3, and 5.7. One model system for Type I copper proteins39 and one for Type II centers40 have been discussed. Many others can be found in the literature. A more complete discussion, including mechanistic detail, about hemocyanin and tyrosinase model systems has been included. Models for the blue copper oxidases laccase and ascorbate oxidases have not been discussed. Students are referred to the references listed in the reference section for discussion of some other model systems. Many more are to be found in literature searches.50... 

Recent work in our laboratories has confirmed the existence of a similar pathway in the oxidation of vindoline in mammals (777). The availability of compounds such as 59 as analytical standards, along with published mass spectral and NMR spectral properties of this compound, served to facilitate identification of metabolites formed in mammalian liver microsome incubations. Two compounds are produced during incubations with mouse liver microsome preparations 17-deacetylvindoline, and the dihydrovindoline ether dimer 59. Both compounds were isolated and completely characterized by spectral comparison to authentic standards. This work emphasizes the prospective value of microbial and enzymatic transformation studies in predicting pathways of metabolism in mammalian systems. This work would also suggest the involvement of cytochrome P-450 enzyme system(s) in the oxidation process. Whether the first steps involve direct introduction of molecular oxygen at position 3 of vindoline or an initial abstraction of electrons, as in Scheme 15, remains unknown. The establishment of a metabolic pathway in mammals, identical to those found in Strep-tomycetes, with copper oxidases and peroxidases again confirms the prospective value of the microbial models of mammalian metabolism concept. 

The blue copper site exhibits unique spectral properties when compared with those of normal copper complexes. These spectral features include an unusually small copper h perfine splitting of the EPR signal in thej, region (A < 70x10 cm as compared to Aj = 150x10 cm for normal tetragonal copper) [Figure 1] and an... 

Among the coordination compounds obtained on the basis of polypyrazolyl-borates, it is worth emphasizing the copper chelates 235 which are still the only biomimetic model of blue copper proteins, reproducing all their physical (UV-and EPR-spectral) properties [441,446-448], Compound 236 [449] is also an example of complexes of this kind of system ... 

Copper(II) sites in proteins can be classified into three types based on their spectral properties. The blue (Type I) copper proteins are characterised by a visible absorption... 

There is some interest in the spectral properties of copper complexes of thieno[2,3-d]-pyrimidines <88ICA165>, and of polymers of thieno[2,3-6]pyrazines <92CC1672, 93SM960). The latter have been investigated as low band-gap polymers. 

Axial Coordination to Copper (II)—Peptide Complexes. Although inplane coordination dominates the thermodynamic, kinetic, and spectral properties of the Cu( II)-peptides, axial coordination also is important. While the carboxylate groups in Cu(H.3G4)2" and Cu(H 2GGhis)"... 

Cytochrome c oxidase is the terminal member of the respiratory chain in all animals and plants, aerobic yeasts, and some bacteria." " This enzyme is always found associated with a membrane the inner mitochondrial membrane in higher organisms or the cell membrane in bacteria. It is a large, complex, multisubunit enzyme whose characterization has been complicated by its size, by the fact that it is membrane-bound, and by the diversity of the four redox metal sites, i.e., two copper ions and two heme iron units, each of which is found in a different type of environment within the protein. Because of the complexity of this system and the absence of detailed structural information, spectroscopic studies of this enzyme and comparisons of spectral properties with 02-binding proteins (see Chapter 4) and with model iron-porphyrin and copper complexes have been invaluable in its characterization. 

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