Copper peroxide

Abstract: The direct discharge of copper containing wastewater into the water body not only causes serious harm to the ecological environment, but also results in copper resource wastage. A green approach was successfully developed to prepare CuO nanosheets (NSs) from simulated Cu(II) waste effluents by alkaline H2O2 reaction. The FTIR, EXAFS and XPS results revealed that peroxide group exists on the surface of the as-prepared CuO nanosheets, and the formation mechanism of copper peroxide has been proposed. Assisted by visible light irradiation, the CuO NS as a recyclable Fenton-like catalyst achieved complete degradation of phenol within 40 min. Moreover, the copper ions leached during the Fenton-like process were recycled via alkaline H2O2 reaction and their concentration in the solution reduced to below 1 mg L−1, therefore realizing a copper life cycle and Fenton-like degradation of organic pollutants.

Abstract: Bis(pyrazolyl)methane ligands are excellent components of model complexes used to investigate the activity of the enzyme tyrosinase. Combining the N donors 3-tert-butylpyrazole and 1-methylimidazole results in a ligand that is capable of stabilising a (μ-η(2) :η(2) )-dicopper(II) core that resembles the active centre of tyrosinase. UV/Vis spectroscopy shows blueshifted UV bands in comparison to other known peroxo complexes, due to donor competition from different ligand substituents. This effect was investigated with the help of theoretical calculations, including DFT and natural transition orbital analysis. The peroxo complex acts as a catalyst capable of hydroxylating a variety of phenols by using oxygen. Catalytic conversion with the non-biological phenolic substrate 8-hydroxyquinoline resulted in remarkable turnover numbers. In stoichiometric reactions, substrate-binding kinetics was observed and the intrinsic hydroxylation constant, kox , was determined for five phenolates. It was found to be the fastest hydroxylation model system determined so far, reaching almost biological activity. Furthermore, Hammett analysis proved the electrophilic character of the reaction. This sheds light on the subtle role of donor strength and its influence on hydroxylation activity.

Abstract: Tyrosinase model systems pinpoint pathways to translating Nature's synthetic abilities for useful synthetic catalysts. Mostly, they use N-donor ligands which mimic the histidine residues coordinating the two copper centres. Copper complexes with bis(pyrazolyl) methanes with pyridinyl or imidazolyl moieties are already reported as excellent tyrosinase models. Substitution of the pyridinyl donor results in the new ligand HC(3-tBuPz)(2)(4-CO2MePy) which stabilises a room-temperature stable mu-eta(2):eta(2)-peroxide dicopper(II) species upon oxygenation. It reveals highly efficient catalytic activity as it hydroxylates 8-hydroxyquinoline in high yields (TONs of up to 20) and much faster than all other model systems (max. conversion within 7.5 min). Stoichiometric reactions with para-substituted sodium phenolates show saturation kinetics which are nearly linear for electron-rich substrates. The resulting Hammett correlation proves the electrophilic aromatic substitution mechanism. Furthermore, density functional theory (DFT) calculations elucidate the influence of the substituent at the pyridinyl donor: the carboxymethyl group adjusts the basicity and nucleophilicity without additional steric demand. This substitution opens up new pathways in reactivity tuning.