BIO-RELATED COPPER-MEDIATED OXIDATIVE PROCESSES

Time-Dependent Self-Assembly of Copper(II) Coordination Polymers and Tetranuclear Rings: Catalysts for Oxidative Functionalization of Saturated Hydrocarbons

This study describes a time-dependent self-assembly generation of new copper(II) coordination compounds from an aqueous-medium reaction mixture composed of copper(II) nitrate, H₃bes biobuffer (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), ammonium hydroxide, and benzenecarboxylic acid, namely, 4-methoxybenzoic (Hfmba) or 4-chlorobenzoic (Hfcba) acid. Two products were isolated from each reaction, namely, 1D coordination polymers [Cu₃(μ₃-OH)₂(μ-fmba)₂(fmba)₂(H₂O)₂]_n (1) or [Cu₂(μ-OH)₂(μ-fcba)₂]_n (2) and discrete tetracopper(II) rings [Cu₄(μ-Hbes)₃(μ-H₂bes)(μ-fmba)]·2H₂O (3) or [Cu₄(μ-Hbes)₃(μ-H₂bes)(μ-fcba)]·4H₂O (4), respectively. These four compounds were obtained as microcrystalline air-stable solids and characterized by standard methods, including the single-crystal X-ray diffraction. The structures of 1 and 2 feature distinct types of metal-organic chains driven by the μ₃- or μ-OH^- ligands along with the μ-benzenecarboxylate linkers. The structures of 3 and 4 disclose the chairlike Cu₄ rings assembled from four μ-bridging and chelating aminoalcoholate ligands along with μ-benzenecarboxylate moieties playing a core-stabilizing role. Catalytic activity of 1-4 was investigated in two model reactions, namely, (a) the mild oxidation of saturated hydrocarbons with hydrogen peroxide to form alcohols and ketones and (b) the mild carboxylation of alkanes with carbon monoxide, water, and peroxodisulfate to generate carboxylic acids. Cyclohexane and propane were used as model cyclic and gaseous alkanes, while the substrate scope also included cyclopentane, cycloheptane, and cyclooctane. Different reaction parameters were investigated, including an effect of the acid cocatalyst and various selectivity parameters. The obtained total product yields (up to 34% based on C₃H₈ or up to 47% based on C₆H₁₂) in the carboxylation of propane and cyclohexane are remarkable taking into account an inertness of these saturated hydrocarbons and low reaction temperatures (50-60 °C). Apart from notable catalytic activity, this study showcases a novel time-dependent synthetic strategy for the self-assembly of two different Cu(II) compounds from the same reaction mixture.

Novel sampangine derivatives as potent inhibitors of Cu2+-mediated amyloid-β protein aggregation, oxidative stress and inflammation

A series of 11-substituted sampangine derivatives have been designed, synthesized, and tested for their ability to inhibit cholinesterase. Their chelating ability and selectivity for Cu²⁺ over other biologically relevant metal ions were demonstrated by isothermal titration calorimetry. Their blood-brain barrier permeability was also tested by parallel artificial membrane permeation assay. Among the synthesized derivatives, compound 11 with the strong anti-acetylcholinesterase activity, high blood-brain barrier penetration ability and high binding affinity to Cu²⁺ was selected for further research. Western blotting analysis, transmission electron microscopy, DCFH-DA assay and paralysis experiment indicated that compound 11 suppressed the formation of Cu²⁺-Aβ complexes, alleviated the Cu²⁺ induced neurotoxicity and inhibited the production of ROS catalyzed by Cu²⁺ in Aβ42 transgenic C. elegans. Moreover, compound 11 also inhibited the expressions of proinflammatory cytokines, such as NO, TNF-α, IL-6 and IL-1β, induced by Cu²⁺ + Aβ_1-42 in BV2 microglial cells. In general, this work provided new insights into the design and development of potent metal-chelating agents for AD treatment.

Mild C-H functionalization of alkanes catalyzed by bioinspired copper(ii) cores

Three new copper(ii) coordination compounds formulated as [Cu(H_1.5bdea)₂](hba)·2H₂O (1), [Cu₂(μ-Hbdea)₂(aca)₂]·4H₂O (2), and [Cu₂(μ-Hbdea)₂(μ-bdca)]_n (3) were generated by aqueous medium self-assembly synthesis from Cu(NO₃)₂, N-butyldiethanolamine (H₂bdea) as a main N,O-chelating building block and different carboxylic acids [4-hydroxybenzoic (Hhba), 9-anthracenecarboxylic (Haca), or 4,4'-biphenyldicarboxylic (H₂bdca) acid] as supporting carboxylate ligands. The structures of products range from discrete mono- (1) or dicopper(ii) (2) cores to a 1D coordination polymer (3), and widen a family of copper(ii) coordination compounds derived from H₂bdea. The obtained compounds were applied as bioinspired homogeneous catalysts for the mild C-H functionalization of saturated hydrocarbons (cyclic and linear C₅-C₈ alkanes). Two model catalytic reactions were explored, namely the oxidation of hydrocarbons with H₂O₂ to a mixture of alcohols and ketones, and the carboxylation of alkanes with CO/S₂O₈^2- to carboxylic acids. Both processes proceed under mild conditions with a high efficiency and the effects of different parameters (e.g., reaction time and presence of acid promoter, amount of catalyst and solvent composition, substrate scope and selectivity features) were studied and discussed in detail. In particular, an interesting promoting effect of water was unveiled in the oxidation of cyclohexane that is especially remarkable in the reaction catalyzed by 3, thus allowing a potential use of diluted, in situ generated solutions of hydrogen peroxide. Moreover, the obtained values of product yields (up to 41% based on alkane substrate) are very high when dealing with the C-H functionalization of saturated hydrocarbons and the mild conditions of these catalytic reactions (50-60 °C, H₂O/CH₃CN medium). This study thus contributes to an important field of alkane functionalization and provides a notable example of new Cu-based catalytic systems that can be easily generated by self-assembly from simple and low-cost chemicals.

Tetracopper(II) Cores Driven by an Unexplored Trifunctional Aminoalcohol Sulfonic Acid for Mild Catalytic C–H Functionalization of Alkanes

Three new tetracopper(II) coordination compounds were easily generated from Cu(NO3)2, a trifunctional aminoalcohol sulfonic acid (H3bes, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid) as a principal building block, and a benzene carboxylic acid as a supporting ligand (i.e., benzoic (Hba), 4-hydroxybenzoic (Hfba), or 3-hydroxybenzoic (Hthba) acid). The obtained microcrystalline products, [Cu4(µ-Hbes)3(µ-H2bes)(µ-L)]·2H2O (L = ba− (1), fhba− (2), and thba− (3)), were fully characterized by FTIR (Fourier-transform infrared spectroscopy), elemental analysis, ESI-MS (Electrospray Ionisation Mass Spectrometry), and single-crystal X-ray diffraction methods. Compounds 1–3 were applied as effective homogeneous catalysts in the oxidative C−H functionalization of alkanes (cycloalkanes and propane). Two different model reactions were explored: (1) mild oxidation of alkanes with hydrogen peroxide to give alcohols and ketones, and (2) mild carboxylation of alkanes with carbon monoxide, water, and potassium peroxodisulfate to give carboxylic acids. For these reactions, effects of different parameters, as well as mechanistic and selectivity characteristics, were studied.

Mixed-ligand aminoalcohol-dicarboxylate copper(II) coordination polymers as catalysts for the oxidative functionalization of cyclic alkanes and alkenes

New copper(II) catalytic systems for the mild oxidative C–H functionalization of cycloalkanes and cycloalkenes were developed, which are based on a series of mixed-ligand aminoalcohol-dicarboxylate coordination polymers, namely [Cu2(μ-dmea)2(μ-nda)(H2O)2]n·2nH2O (1), [Cu2(μ-Hmdea)2(μ-nda)]n·2nH2O (2), and [Cu2(μ-Hbdea)2(μ-nda)]n·2nH2O (3) that bear slightly different dicopper(II) aminoalcoholate cores, as well as on a structurally distinct dicopper(II) [Cu2(H4etda)2(μ-nda)]·nda·4H2O (4) derivative [abbreviations: H2nda, 2,6-naphthalenedicarboxylic acid; Hdmea, N,N′-dimethylethanolamine; H2mdea, N-methyldiethanolamine; H2bdea, N-butyldiethanolamine; H4etda, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine]. Compounds 1–4 act as homogeneous catalysts in the three types of model catalytic reactions that proceed in aqueous acetonitrile medium under mild conditions (50–60°C): (i) the oxidation of cyclohexane by hydrogen peroxide to cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone, (ii) the oxidation of cycloalkenes (cyclohexene, cyclooctene) by hydrogen peroxide to a mixture of different oxidation products, and (iii) the single-pot hydrocarboxylation of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, cyclooctane) by carbon monoxide, water, and a peroxodisulfate oxidant into the corresponding cycloalkanecarboxylic acids. The catalyst and substrate scope as well as some mechanistic features were investigated; the highest catalytic activity of 1–4 was observed in the hydrocarboxylation of cycloalkanes, allowing to achieve up to 50% total product yields (based on substrate).

Self-assembly generation, structural features, and oxidation catalytic properties of new aqua-soluble copper(ii)-aminoalcohol derivatives

Multidentate aminoalcohols were applied as unexplored building blocks to generate two novel Cu(ii) coordination compounds that act as efficient catalysts for the mild and acid-promoter-free oxidation of C₅–C₈ cycloalkanes.

New tricopper(ii) cores self-assembled from aminoalcohol biobuffers and homophthalic acid: synthesis, structural and topological features, magnetic properties and mild catalytic oxidation of cyclic and linear C5–C8 alkanes

Two new compounds with distinct tricopper(ii) cores were synthesised and applied as bio-inspired pre-catalysts for mild oxidation of alkanes.

Copper Catalysts for Aerobic Oxidation of Alcohols

Inspired by reactions catalyzed by galactose oxidase, a copper-containing enzyme, extensive studies were carried out on copper-based catalysts for alcohol oxidation using O2 as the terminal oxidant. Significant advances have been made towards the development of homogeneous and heterogeneous copper catalysts. These advances over the past decades are reviewed.

DFT/TDDFT insights into the chemistry, biochemistry and photophysics of copper coordination compounds

Highlighting the recent progress in DFT/TDDFT application to coordination chemistry of copper.

Highly cytotoxic DNA-interacting copper(ii) coordination compounds

Copper complexes from Schiff-base ligands show high cytotoxicity against diverse cancer cell lines, with IC₅₀ values down to 0.23 μM.