Blue copper structural analysis

The addition of 2 equivalents of copper ions (Cu(N03)2, Cul, or CuBr) to an aqueous solution of (41) + produced a pale blue solution, from which blue crystals were obtained. An x-ray crystal structure analysis indicated a 2 4 assembly of (41) + and Cu, namely, a 4 4 4 complex of (31)" +, CA -and Cu, as shown in Figure 3.11 and designated 42 (Zn2U)4-(CA ")4-[ l-Cu2(OH)2]2 This structure is stabilized by N -Zn + coordination bonds between Zn + and CA , 7t-7t stacking between bpy units, and hydrogen bonds between two CA - function to stabilize (42) 2-. ... 

The mechanism presented above represents a series of stiuctures based on prior knowledge of the laccase system from the hterature and the XAS/FEFF8 analysis presented in this chapter. It is to some extent still unclear in areas (particularly structures II and V), but the aim was to use in situ XAS to elucidate the mechanism of ORR in laccase as it occurs on a BFC cathode. As a result, the mechanism in Figure 15.20 describes the behavior of laccase under the constraints of the experimental conditions for which the measurements were made. It is important to note that many other mechanisms have been proposed. In Particular, the Solomon and Atanassov research groups have been instmmental in providing important and detailed information on the active sites of a variety of blue copper oxidases [42,45,47-50,62,65,68-73]. 

Fig. 6.7. Copper-based catalysts for methanol synthesis. A novel device for controlled precipitation enabled separation of blue from green products. Structural analysis (top left) revealed that the blue products are disordered nanocrystalline materials furnishing poor catalysts. The green products are mixtures of two phases, malachite (violet) and auricalcite (red). By systematically optimizing the reaction conditions it was possible to prepare phase-pure green products and thereby to improve thesynthesisofthe working catalyst based on pure malachite precursors. In the X-ray diffraction pattern (top right), the features are labeled by the Miller Indices, indicating the diffraction lattice plane of the crystal °29 is the diffraction angle.

There are bi-, tri-, and tetradentate formazan dyes7 but only the tetradentate copper complex formazan dyes have found use as commercial products. The dye Cl Reactive Blue 160, of generic structure (41), is a representative example. Because of the intensity of their colors, the metal complex formazan dyes have also found application in analysis. Thus, the dye (42) detects zinc at a concentration of 1 part in 50 million.31... 

Three dimensional X-ray diffraction analysis has been employed to elucidate the molecular and crystal structure of Copper Phthalocyanine Blue ((3-modifica-tion). In all modifications, the planar and almost square phthalocyanine molecules are arranged like rolls of coins, i.e., in one dimensional stacks. The modifications vary only in terms of how these stacks are arranged relative to each other. One important aspect is the angle between staple axis and molecular plane. The a-phase features an angle of 24.7°, while the stacks in the -modification deviate by as much as 45.8° [13]. 

The other copper-only binuclear centre to be considered is the CuA or purple copper complex. It is part of the terminal oxidase in mitochondrial respiration, cytochrome c oxidase (COX). Its EPR signature, a seven-line spectrum, has since long been known to be different from the classes type 1 to 3 and arises from two copper ions in a 1.5 valence (or mixed valence) state, first proposed from EPR-analysis of a similar center in nitrous oxide (N20) reductase. There is a close correspondence between the blue and purple states of copper since each of the two copper ions in CuA can be considered as being structurally related to the mononuclear blue site coordination. 

The insolubilities of phthalocyanines made their analysis difficult and it took some time before a satisfactory structure was elucidated. Initial work was undertaken by the Linstead group at Imperial College in the 1930s that culminated in a series of six back to back papers published in 1934 [14], It was also Linstead who named the compounds in recognition of their synthesis from phthalic anhydride and similarity to the blue cyanine dyes. Definitive characterization of the nickel, platinum and copper phthalocyanine complexes, together with the metal-free compound, was revealed in 1935 following the publication of their X-ray structures by Robertson [15] the copper and metal-free compounds are illustrated in Fig. 7.5. 

A Messerschmidt, A Rossi, R Ladenstein, R Huber, M Bolognesi, G Gatti, A Marchesini, R Petruzelli, A Finazzi-Agro. X-ray crystal structure of the blue oxidase ascorbate oxidase from zucchini. Analysis of the polypeptide fold and a model of the copper sites and ligands. J Mol Biol 206 513-529, 1989. 

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