Copper(II) complexes of aminocarbohydrate beta-ketoenaminic ligands: efficient catalysts in catechol oxidation

One-pot synthesized copper-imidazole-2-carboxaldehyde complex material with oxidase-like activity for the colorimetric detection of glutathione and ascorbic acid

Due to the copper (Cu) active sites, its complexes with oxidase-like activity have superior catalytic properties, which can catalyze a series of specific substrates like 3,3',5,5'-tetramethylbenzidine (TMB), producing colorimetric reactions for the detection of different reducing small-molecule compounds. Attribute to the competitive coordination effects between water molecules and central Cu ions, most of the Cu complexes can hardly be used in the pure aqueous reaction system. In this study, a Cu-based material (Cu-imidazole-2-carboxaldehyde, Cu-ICA) was prepared using copper ions and ICA through a one-step process in the water solution. After the morphology of the material being characterized, the mimetic enzyme behavior of the Cu-ICA was demonstrated through the TMB oxidation. Compared to the other reported oxidase-like mimics, Cu-ICA has better aqueous stability and oxidase-like activity, and shows a higher vmax. Furthermore, basing on the oxidase-like activity of Cu-ICA, a colorimetric method was developed for the ascorbic acid and glutathione detections with linear ranges of 0.5-5 μM and 0.5-4 μM, and limit of detection of 0.1304 μM and 0.097 μM, respectively. Owing to its excellent aqueous stability and oxidase-like activity, Cu-ICA has bright application prospects in the analysis of reducing small-molecule compounds.

Novel {Cu4} and {Cu4Cd6} clusters derived from flexible aminoalcohols: synthesis, characterization, crystal structures, and evaluation of anticancer properties

Two new copper clusters, {Cu₄} and {Cu₄Cd₆}, with polydentate aminoalcohol ligands, diethanol propanolamine (H₃L¹) and bis-tris{2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol} (H₆L²), have been synthesized under mild conditions and characterized thoroughly by single-crystal X-ray diffraction (XRD), infrared spectroscopy, elemental analysis, powder XRD, magnetic and DFT studies, and absorption and fluorescence spectroscopy. The cluster {Cu₄} exhibits a rare tetranuclear copper cubane core whereas {Cu₄Cd₆} forms an unusual heterometallic cage owing to the introduction of the second metal Cd into the ligand. A hexapodal ligand (H₆L²) with N and O donor atoms was chosen deliberately for the construction of a high-nuclearity cluster, i.e., {Cu₄Cd₆}. Interestingly, both the clusters displayed significant cytotoxicity towards human cervical (HeLa) and lung (A549) cancer cells as evident from the shallow IC₅₀ values [15.6 ± 0.8 μM (HeLa), 18.5 ± 1.9 μM (A549) for {Cu₄}, and 11.1 ± 1.5 μM (HeLa), 10.2 ± 1.3 μM (A549) for {Cu₄Cd₆}] obtained after a 24 h incubation. However, moderate toxicity was observed toward immortalized lung epithelial normal cells (HPL1D) with IC₅₀ values of 32.4 ± 1.2 μM for {Cu₄} and 27.6 ± 1.7 μM for {Cu₄Cd₆}. A cellular apoptotic study using HeLa cells revealed that the {Cu₄} cluster triggered apoptosis at both the early and late phases while the {Cu₄Cd₆} cluster facilitate apoptosis mainly at the late apoptotic stage. A standard 2',7'-dichlorodihydrofluorescein-diacetate (DCFH-DA) test affirms that both the clusters enhanced ROS production inside the cancer cells, responsible for promoting cell apoptosis. The decanuclear {Cu₄Cd₆} clusters demonstrated better anticancer activity compared to the tetranuclear {Cu₄} clusters, indicating the role of high nuclearity and additional Cd metal in the enhanced intracellular production of ROS.

Effect of structural variation on enzymatic activity in tetranuclear (Cu4) clusters with defective cubane core

The stimulus to the modeling of enzyme functioning sites comes from their potential to give insight into the natural enzyme's mechanistic pathways, ascertain the role of that different metal ion in the active site and construct better catalysts motivated by nature. The presence of metal ion leads to the activation of molecular oxygen in the metalloenzymes. The metalloenzymes such as the catechol oxidase (CO) enzyme that oxidizes the catechol to corresponding quinones which eventually protect damage tissues from plant and pathogen. Thus, the design and characterization of catalysts used as selectively and efficiently oxidation reactions have grown to be unique challenges for modern inorganic chemists. In this work, two novel tetranuclear complexes (1 and 2) have been synthesized in excellent yield. The complexes were characterized using various spectroscopic techniques such as FTIR, UV-Visible and PXRD pattern. The structure of 1 and 2 was elucidated by SC-XRD (single crystal X-ray diffraction) analysis. The magnetic study reveals the presence of the antiferromagnetic nature of 1 and 2. Both 1 and 2 shows a very good catecholase-like activity by oxidizing the catechol to analogous quinone in methanolic solution. Thus, a structure-activity relationship can further help us design other substituted tetranuclear complexes with enhanced catecholase like activity.Communicated by Ramaswamy H. Sarma.

Synthesis and structural characterization of hexa-μ2-chlorido-μ4-oxido-tetra-kis-{[4-(phenyl-ethyn-yl)pyridine-κN]copper(II)} di-chloro-methane monosolvate

In the crystal structure of the title compound, [Cu4Cl6O(C13H9N)4]·CH2Cl2, the core mol-ecular structure consists of a Cu4 tetra-hedron with a central inter-stitial O atom. Each edge of the Cu4 tetra-hedron is bridged by a chlorido ligand. Each copper(II) cation is coordinated to the central O atom, two chlorido ligands and one N atom of the 4-phenyl-ethynyl-pyridine ligand. In the crystal, the mol-ecules are linked by inter-molecular C-H⋯Cl inter-actions. Furthermore, C-H⋯π and π-π inter-actions also connect the mol-ecules, forming a three-dimensional network. Hirshfeld surface analysis indicates that the most important contributions for the packing arrangement are from H⋯H and C⋯H/H⋯C inter-actions.

Tuning the coordination properties of multi-histidine peptides by using a tripodal scaffold: solution chemical study and catechol oxidase mimicking

Histidine-rich tripodal peptides form unique oligonuclear complexes with copper(ii), which exhibit efficient catecholase-like activity.

Hydroxide-bridged dicopper complexes: the influence of secondary coordination sphere on structure and catecholase activity

This work illustrates the syntheses, structures and catecholase activities of dicopper(ii) complexes having a Cu(μ-OH)Cu core encased within a secondary coordination sphere intricately created by appended heterocyclic rings.

Cubane-like tetranuclear Cu(ii) complexes bearing a Cu4O4 core: crystal structure, magnetic properties, DFT calculations and phenoxazinone synthase like activity

Two tetranuclear copper complexes with a Cu₄O₄ cubane core exhibiting phenoxazinone synthase like activity are reported.

Aminoalcohols and benzoates-friends or foes? Tuning nuclearity of Cu(ii) complexes, studies of their structures, magnetism, and catecholase-like activities as well as performing DFT and TDDFT studies

The Cu(ii) complexes of varying nuclearity are synthesized, characterized and assessed for catecholase activities.

Copper(ii) cubanes with a {Cu4O} core and well defined S = 1 ground state

Three copper cubanes with the unusual S = 1 ground state have been characterized and their magnetic properties rationalized as a function of the asymmetry of the {Cu₄O₄} cage and correlated with the Cu–O–Cu bond angles.

Catecholase activity of Mannich-based dinuclear CuII complexes with theoretical modeling: new insight into the solvent role in the catalytic cycle

Catecholase activity has been explored by combined experimental and theoretical approaches using di-copper(ii) complexes of Mannich-base ligands.

The synthesis, characterization and catecholase activity of dinuclear cobalt(ii/iii) complexes of an O-donor rich Schiff base ligand

A dinuclear Co^III complex oxidizes 3,5-di-tert-butylcatechol by binding to two molecules of the substrate simultaneously during oxidation along with the formation of H₂O₂.

Modeling tyrosinase and catecholase activity using new m-Xylyl-based ligands with bidentate alkylamine terminal coordination

Chemical model systems possessing the reactivity aspects of both tyrosinase and catechol oxidase are presented. Using two m-xylyl-based ligands providing bidentate alkylamine terminal coordination, 1,3-bis[(N,N-dimethylaminoethyl)aminomethyl]benzene (L(H,H)) and 1,3-bis[(N,N,N'-trimethylaminoethyl)aminomethyl]benzene (L(Me,Me)), four new dicopper(I) complexes, [Cu(I)(2)(L(H,H))(MeCN)(4)][ClO(4)](2) (1), [Cu(I)(2)(L(H,H))(PPh(3))(2)(MeCN)(2)][ClO(4)](2) (2), [Cu(I)(2)(L(Me,Me))(MeCN)(2)][ClO(4)](2) (3), and [Cu(I)(2)(L(Me,Me))(PPh(3))(2)][ClO(4)](2) (4), have been synthesized and characterized. Complex 2 has been structurally characterized. Reaction of the dicopper(I) complex 3(2+) with dioxygen at 183 K generates putative bis(μ-oxo)dicopper(III) intermediate (absorption spectroscopy). Oxygenation of 1 and 3 brings about m-xylyl-ring hydroxylation (monooxygenase-like activity), with a noticeable color change from pale-yellow to dark green. The presence of phenoxo- and hydroxo-bridges in the end products [Cu(II)(2)(L(H,H)-O)(OH)(MeCN)(2)][ClO(4)](2) (5) and [Cu(II)(2)(L(Me,Me)-O)(OH)(OClO(3))][ClO(4)]·MeCN(6) has been authenticated by structural characterization. Oxygenation of 3 afforded not only the green complex 6 isolation but also a blue complex [Cu(II)(2)(L(Me,Me))(OH)(2)][ClO(4)](2) (7). Variable temperature magnetic susceptibility measurements on 5 and 6 establish that the Cu(II) centers are strongly antiferromagnetically coupled [singlet-triplet energy gap (J) = -528 cm(-1) (5) and -505 cm(-1) (6)]. The abilities of phenoxo- and hydroxo-bridged dicopper(II) complexes 5 and 6, the previously reported complex [Cu(II)(2)(L(1)-O)(OH)(OClO(3))(2)]·1.5H(2)O (8) (L(1)-OH = 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol), and [Cu(II)(2)(L(2)-O)(OH)(OClO(3))()][ClO(4)]() (9) (L(2)-OH = 1,3-[(2-dimethylaminoethyl)iminomethyl][(N,N,N'-trimethyl)aminoethyl]-4-methylphenol) have been examined to catalyze the oxidation of catechol to quinone (catecholase activity of tyrosinase and catechol oxidase-like activity) by employing the model substrate 3,5-di-tert-butylcatechol. Saturation kinetic studies have been performed on these systems to arrive at the following reactivity order [k(cat)/K(M) (catalytic efficiency) × 10(-3) (M(-1) h(-1))]: 470 (6) > 367 (5) > 128 (9) > 90 (8).