Cu active site

Figure 17.3 Anatomy of a redox enzyme representation of the X-ray crystallographic structure of Trametes versicolor laccase III (PDB file IKYA) [Bertrand et al., 2002]. The protein is represented in green lines and the Cu atoms are shown as gold spheres. Sugar moieties attached to the surface of the protein are shown in red. A molecule of 2,5-xyhdine that co-crystallized with the protein (shown in stick form in elemental colors) is thought to occupy the broad-specificity hydrophobic binding pocket where organic substrates ate oxidized by the enzyme. Electrons from substrate oxidation are passed to the mononuclear blue Cu center and then to the trinuclear Cu active site where O2 is reduced to H2O. (See color insert.)...

Figure 5. The Cu active site of plastocyanin PCu(I) at pH values > 7 (left) and...

Because of its distorted tetrahedral shape, and the long Cu-S(Met) bond, the type 1 Cu active site has proved difficult to model in low complexes. The unusual EPR spectra with characteristically small hyperfine splitting constants are a consequence of the asymmetry of the copper environment. 

Fig. 17. Showing the coordination of the Cu active site of plastocyanin by Cys 84, and the bonding of the latter to Ty r 83 which is a part of the remote site. The aromatic ting of the latter is solvent exposed...

Figure 12 Vibrational enhancement selectivity available from resonance Raman spectroscopy. The UV-visible spectrum of a P. aeruginosa azurinis shown together with two different Raman spectra (frozen solution at 77 K) that derive from laser excitation within the S(Cys) — Cu(II) charge-transfer absorption band at 625run (647.1 nm) and away from the absorption (488.Onm). Excitation within resonance leads to dramatically increased Raman scattering from the Cu active site, whereas off-resonance excitation produces a spectrum dominated by bands of nonchromophoric ice...

Another interesting bio-mimic revolves around the nature of the dinuclear (Cu-Cu) active site of the Cytochrome C enzyme. Recent reports have shown that it is possible to fully synthesize stable analogs of these active sites with enough stability to survive ex vivo. Researchers at MIT have synthesized a variety of xanthene or dibenzofuran-stabilized pac nzan-type dinuclear porphyrin moieties which show promise for ORR applications. Specifically, a dicobalt bisporphyrin showed ORR activity with 80% selectivity for 4e ORR at +0.70 V vs. RHE. ° Although the material exhibits a 20% peroxide yield, that it is now possible to begin the development of a trae ex vivo bio-mimic is an important first step. Further, accompanying DFT calculations... 

Bond Distances and Angles for the Cu Active Site of Poplar Plastocyanin"... 

A final point concerns the variability in number of amino acids separating the residues coordinating the Cu active site, and the possible controlling influence this might have. Available information is summarized in Table VI. In the case of azurin and pseudoazurin, there is the additional influence of the peptide C=0 on coordination at the Cu. All of the blue copper proteins have similar features, with coordination of the copper to one His from the first part of the sequence, and three other residues from the latter part. At present there appears to be no... 

A solid-state promotion of CuH-ZSM-5 zeolite by cobalt ions results in the over-additive increase of the catalyst activity in C2Hg total oxidation, and leads to the rise of the thermostability of the bi-cationic catalyst. The insertion of cobalt cations into zeolitic channels with stabilization of Cu " active sites is assumed. 

From the above studies it is concluded that, especially in low Cu content catalysts, an intimate contact between Cu and ZnO stabilizes the Cu" active sites with some special structural contributions in the activated state. 

Although structurally related to the Mo hydroxylases, the active structure of the molybdenum containing CODH enzyme is unique among pyranopterin Mo enzymes in that it possesses a heterobimetallic Mo/Cu active site. " In the oxidized resting state, the Mo ion is in the Mo(vi) state while the Cu is reduced in the Cu(i) state. This is interesting since this leads to an oxidized active site that possesses metal centers that differ by five units in oxidation state and by ten d-electrons. However, only the Mo ion is believed to be redox active in the catalytic sequence. The Mo and Cu ions are covalently... 

Collman, J.P., R. Schwenninger, M. Rapta, M. Broring, and L. Fu (1999). New 1,4,7-triazacyclononane-based functional analogues of the Fe/Cu active site of C5 tochrome c oxidase Structure spectroscopy and electrocatal54ic reduction of oxygen. Chem. Commun., 137-138. 

Copper (I) complexes exhibit catalytic activity for the four-electron (4-e) reduction of O2 to water. Natural occurring enzymes like Cu-containing fungal laccase reduce O2 directly to water very efficiently at very positive potentials, not far from the thermodynamic standard potential of the O2/H2O couple. These enzymes involve a trinuclear Cu active site [149-153]. For this reason some authors have investigated the catalytic activity of Cu(I) complexes for ORR, in particular Cu phenanthrolines confined on graphite or glassy carbon surfaces [154-169], with the aim of achieving the total reduction of O2 via the transfer of four-electrons. 

For example, copper(l) 1,10-phenanthroline, Cu(phenP), reduces O2 almost entirely via the transfer of four electrons and four protons to give water [156, 157, 170]. This is quite interesting since, similarly to what is observed with Fe phthalocyanines [99,171], the four-electron reduction of O2 is promoted by singlesite catalysts. The O2 molecule cannot interact simultaneously with two Cu active sites. If this were the case, the order of the reaction in surface concentration would equal to two. Anson et al. [156,157,170] checked this and found that the reaction is first order in Cu coverage, suggesting of a mononuclear Cu site as the active... 

In living cells, various oxidoreductases play an important role in maintaining the metabolism of living systems. So far, peroxidase containing Fe-active site, laccase containing Cu-active site, tyrosinase (polyphenol oxidase, Cu-active site), bilirubin oxidase (Cu-active site), etc, have been reported to act as catalyst for oxidative polymerization of phenol and aniline derivatives and for polymer modification via oxidative coupling. 

Recently we have considered some in silica models of the Cu active site of PHM (Figure 5.6) and addressed the question of the kinetics of the spincrossing reaction within these complexes.We have previously shown that these complexes are decent minimal models of the enzymatic cupric superoxide adducts.In the enzyme the coordination sphere of the Cum active site is... 

Fig. 9.2 (a) Mononuclear Mo active site, (b) Dinuclear Mo-Cu active site... 

Local environment of in zeolite SSZ-13, the proposed acid site for the NH3-SCR reaction. The distance between the Cu ion and the oxygen s marked with an asterisk is 1.93 A [36]. Reprinted from Deka U, Lezcano-Gonzalez , Weckhuysen BM, Beale AM. Local environment and nature of Cu active sites in zeolite-based catalysts for the selective catalytic reduction ofNO. ACS CataL 2013 3 413-427. Copyright 2013,... 

Deka U, Lezcano-Gonzalez I, Weckhuysen BM, Beale AM. Local environment and nature of Cu active sites in zeolite-based catalysts for the selective catalytic reduction of NO. ACS Catal 2013 3 413-27. 

---