New unsymmetric dinuclear CuIICuII complexes and their relevance to copper(II) containing metalloenzymes and DNA cleavage

The influence of thioether-substituted ligands in dicopper(II) complexes: Enhancing oxidation and biological activities

This paper describes the synthesis, structural analysis, as well as the magnetic and spectroscopic characterizations of three new dicopper(II) complexes with dinucleating phenol-based ligands containing different thioether donor substituents: aromatic (1), aliphatic (2) or thiophene (3). Temperature-dependent magnetometry reveals the presence of antiferromagnetic coupling for 1 and 3 (J = -2.27 cm-1 and -5.01 cm-1, respectively, H = -2JS1S2) and ferromagnetic coupling for 2 (J = 5.72 cm-1). Broken symmetry DFT calculations attribute this behavior to a major contribution from the dz2 orbitals for 1 and 3, and from the dx2-y2 orbitals for 2, along with the p orbitals of the oxygens. The bioinspired catalytic activities of these complexes related to catechol oxidase were studied using 3,5-di-tert-butylcatechol as substrate. The order of catalytic rates for the substrate oxidation follows the trend 1 > 2 > 3 with kcat of (90.79 ± 2.90) × 10-3 for 1, (64.21 ± 0.99) × 10-3 for 2 and (14.20 ± 0.32) × 10-3 s-1 for 3. The complexes also cleave DNA through an oxidative mechanism with minor-groove preference, as indicated by experimental and molecular docking assays. Antimicrobial potential of these highly active complexes has shown that 3 inhibits both Staphylococcus aureus bacterium and Epidermophyton floccosum fungus. Notably, the complexes were found to be nontoxic to normal cells but exhibited cytotoxicity against epidermoid carcinoma cells, surpassing the activity of the metallodrug cisplatin. This research shows the multifaceted properties of these complexes, making them promising candidates for various applications in catalysis, nucleic acids research, and antimicrobial activities.

Catechol oxidation promoted by bridging phenoxo moieties in a bis(μ-phenoxo)-bridged dicopper(ii) complex

A dinuclear copper(ii) complex [Cu₂(papy)₂(CH₃OH)₂] has been synthesized by reaction of one equiv. of Cu(OAc)₂·2H₂O with one equiv. of the tetradentate tripodal ligand H₂papy [N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] and has been characterized by various spectroscopic techniques and its solid state structure has been confirmed by X-ray crystal structure analysis. The single-crystal structure of the complex reveals that the two copper centers are hexa-coordinated and bridged by two O-atoms of the phenoxo moieties. The variable temperature magnetic susceptibility measurement of the complex reveals weak ferromagnetic interactions among the Cu(ii) ions with a J value of 1.1 cm⁻¹. The catecholase activity of the complex has been investigated spectrophotometrically using 3,5-di-tert-butyl catechol as a model substrate in methanol solvent under aerobic conditions. The Michaelis–Menten kinetic treatment has been applied using different excess substrate concentrations. The parameters obtained from the catecholase activity by the complex are K_M 2.97 × 10⁻⁴ M, V_max 2 × 10⁻⁴ M s⁻¹, and k_cat 7.2 × 10³ h⁻¹. A reaction mechanism has been proposed based on experimental findings and theoretical calculations. The catechol substrate binds to dicopper(ii) centers and subsequently two electrons are transferred to the metal centers from the substrate. The bridging phenoxo moieties participate as a Brønsted base by accepting protons from catechol during the catalytic cycle and thereby facilitating the catechol oxidation process.

A bis(μ-phenoxo)-bridged dicopper(ii) complex capable of oxidizing catechol with the highest efficiency amongst any bis(μ-phenoxo)-bridged dicopper(ii) complexes is reported.

Targeting an Artificial Metal Nuclease to DNA by a Simple Chemical Modification and Its Drastic Effect on Catalysis

A novel metal complex was synthesized containing a purine derived ligand in order to increase its binding to DNA. We observed a huge increase in nuclease activity and, quite interestingly, an improvement on DNA sequence selectivity. A potential site of specific cleavage in the presence of a reductant in the reaction medium is suggested. We were able to synthesize a novel metal nuclease with improved activity on DNA, and with sequence specificity when exposed to a coreactant, this opens up new possibilities to create site specific and redox status modulated artificial nucleases.

Synthesis and characterization of FeIII(μ-OH)ZnII complexes: effects of a second coordination sphere and increase in the chelate ring size on the hydrolysis of a phosphate diester and DNA

Effects of a second coordination sphere and of the chelate ring size in Fe^III(μ-OH)Zn^II complexes properties and catalysis.

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).

Characterization and catechole oxidase activity of a family of copper complexes coordinated by tripodal pyrazole-based ligands

A family of tripodal pyrazole-based ligands has been synthesized by a condensation reaction between 1-hydroxypyrazoles and aminoalcohols. The diversity was introduced both on the substituents of the pyrazole ring and on the side chain. The corresponding copper(II) complexes have been prepared by reaction with CuCl(2) in tetrahydrofuran. They have been characterized by EPR, UV spectroscopy and cyclic voltammetry. The absence of the half-field splitting signals in EPR suggests that the complex exists in solution as mononuclear species. The influence of substituents and side chain of the tripodal ligand on the catecholase activity of the complexes was studied. The reaction rate depends on two factors. First, the presence of an oxygen atom in the third position of the side chain should be avoided to keep the effectiveness of the reaction. Second, the electronic and steric effects of substituents on the pyrazole ring strongly affect the catalytic activity of the complex. Thus, best results were obtained with complexes containing unsubstituted pyrazole based-ligands. Kinetic investigations with the best catalyst based on the Michaelis-Menten model show that the catalytic activity of the mononuclear complex is close to that of some dicopper complexes described in literature.

Mononuclear Cu(II)-phenolate bioinspired complex is catalytically promiscuous: phosphodiester and peptide amide bond cleavage

In this work, the cleavage activity of the metal complex [Cu(C(21)H(21)N(3)O(2))(OH(2))(2)](2+) is demonstrated to occur toward double-stranded DNA, in addition to its previously described amide bond cleavage activity, thus suggesting catalytic promiscuity for this complex.

Binuclear copper(II) complexes with N4O3 coordinating heptadentate ligand: synthesis, structure, magnetic properties, density-functional theory study, and catecholase activity

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1).

The first dinuclear copper(ii) and zinc(ii) complexes containing novel Bis-TACN: syntheses, structures, and DNA cleavage activities

Two novel binuclear complexes [Cu(2)(L)].(ClO(4))(2) (1) and [Zn(2)(L)].(ClO(4))(2) (2) were synthesized and crystallographically characterized {L = 1(4),5(4)-dimethyl-1(2),5(2)-dihydroxy-1(1,3),5(1,3)-dibenzene-3(1,4),7(1,4)-di-1,4,7-triazacyclononane}. The cation [Cu(2)(L)](2+) structure of 1 is similar to that of [Zn(2)(L)](2+) of 2. The central ion is bridged by the di-phenoxo of L and lies in a close to perfect square pyramidal geometry. 1 and 2 crystallize in the triclinic space group P1. The two complexes effectively promote the cleavage of plasmid DNA in the presence of activating agents at physiological pH and temperature. The pseudo-Michaelis-Menten kinetic parameters k(cat) = 1.61 h(-1), K(m) = 1.35 x 10(-5) M for complex 1 in the presence of mercaptoethanol; k(cat) = 2.48 h(-1), K(m) = 5.5 x 10(-5)M for complex 2 in the presence of hydrogen peroxide were obtained. The mechanism of plasmid DNA cleavage was studied by adding standard radical scavengers. DNA cleavage reaction by the binuclear Zn(II)/H(2)O(2) system is a hydrolytic mechanism.

Catalytic Promiscuity in Biomimetic Systems: Catecholase-like Activity, Phosphatase-like Activity, and Hydrolytic DNA Cleavage Promoted by a New Dicopper(II) Hydroxo-Bridged Complex

Presented in this Communication are the structure, physicochemical properties, and catalytic promiscuity of a new dinuclear CuII(mu-OH)CuII complex containing a novel N,O-donor symmetric dinucleating ligand.