Synthesis, structure and properties of unsymmetrical μ-alkoxo-dicopper(II) complexes: biological relevance to phosphodiester and DNA cleavage and cytotoxic activity

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.

Copper(II) complexes of a furan-containing aroylhydrazonic ligand: syntheses, structural studies, solution chemistry and interaction with HSA

Copper(II) complexes have become a potential alternative to the use of platinum drugs in cancer therapy due to their multi-target mode of action. In this context, we report the syntheses of new mononuclear and dinuclear coordination compounds of this element, 1 and 2, derived from the ligand 5-methylsalicylaldehyde 2-furoyl hydrazone (H2L). All three compounds were structurally and spectroscopically characterized, both in the solid state and in solution. In 1, Cu is coordinated by three donor-atoms from the hydrazonic ligand and one chloride ion. H2L is deprotonated at the phenol oxygen. The dinuclear complex 2 is, on the other hand, a dimeric form of 1 in which the chloride ions of a pair of mononuclear units are lost and phenoxo bridges take their places, double-connecting the metal centres and resulting in a single species with the ligand fully deprotonated. The compounds were fairly stable in aqueous medium at room temperature. An experimental-theoretical combined approach demonstrated that all of them are able to bind human serum albumin (HSA), although at different sites and with diverse stoichiometries and affinities (as concluded by the calculated binding energies). In view of this, and due to the well-known antiproliferative activity of hydrazone-containing copper complexes, we consider the compounds presented in here promising, and believe that they deserve more profound studies regarding the assessment of their potential against tumour cell lines.

Synthesis, characterization and computational investigation of the phosphatase activity of a dinuclear Zinc(II) complex containing a new heptadentate asymmetric ligand

We report the synthesis of a new asymmetric heptadentate ligand based on the 1,3-diaminopropan-2-ol backbone. The ligand 3-[[3-(bis-pyridin-2-ylmethyl-amino)-2-hydroxy-propyl]-(2-carbamoyl-ethyl)-amino]-propionamide (HL1) contains two amide and two pyridine groups attached to the 1,3-diaminopropan-2-ol core. Reaction between HL1 and Zn(ClO₄)₂.6H₂O resulted in the formation of the dinuclear [Zn₂(L1)(μ-OAc)](ClO₄)₂ complex, characterized by single crystal X-ray diffraction, ¹H, ¹³C and ¹⁵N NMR, ESI-(+)-MS, CHN elemental analysis as well as infrared spectroscopy. The phosphatase activity of the complex was studied in the pH range 6-11 employing pyridinium bis(2,4-dinitrophenyl)phosphate (py(BDNPP)) as substrate. The complex exhibited activity dependent on the pH, presenting an asymmetric bell shape profile with the highest activity at pH 9; at high pH ligand exchange is rate-limiting. The hydrolysis of BDNPP^- at pH 9 displayed behavior characteristic of Michaelis-Menten kinetics, with k_cat = 5.06 × 10^-3 min^-1 and K_m = 5.7 ± 1.0 mM. DFT calculations map out plausible reaction pathways and identify a terminal, Zn(II)-bound hydroxide as likely nucleophile.

Biomimetics for purple acid phosphatases: A historical perspective

Biomimetics hold potential for varied applications in biotechnology and medicine but have also attracted particular interest as benchmarks for the functional study of their more complex biological counterparts, e.g. metalloenzymes. While many of the synthetic systems adequately mimic some structural and functional aspects of their biological counterparts the catalytic efficiencies displayed are mostly far inferior due to the smaller size and the associated lower complexity. Nonetheless they play an important role in bioinorganic chemistry. Numerous examples of biologically inspired and informed artificial catalysts have been reported, designed to mimic a plethora of chemical transformations, and relevant examples are highlighted in reviews and scientific reports. Herein, we discuss biomimetics of the metallohydrolase purple acid phosphatase (PAP), examples of which have been used to showcase synergistic research advances for both the biological and synthetic systems. In particular, we focus on the seminal contribution of our colleague Prof. Ademir Neves, and his group, pioneers in the design and optimization of suitable ligands that mimic the active site of PAP.

In vitro and in vivo antitumoral activity of a ternary copper (II) complex

Recently, a high number of copper derivatives has been evaluated as DNA-targeting metallodrugs, due to the lower toxicity and its potential to cleave DNA. Several strategies have been testing to develop metal compounds effective against tumour cells. In this work, the ternary copper (doxycycline)-(1,10-phenanthroline) complex [Cu(dox)(phen)]²⁺ was especially designed as an antitumoral drug, previously showing high cytotoxicity and DNA cleavage activity. We aimed to further investigate the in vitro cytotoxic activity in both tumoral and non-tumoral cells, in vitro genotoxic potential, and in vivo antitumor activity using BALB/C mouse injected with sarcoma S180 and Ehrlich cell lines. Our results indicated that this compound exhibits a moderate genotoxic potential, with selective growth inhibition of tumor cells, especially the murine melanoma B16F10. Its main mechanism of action seems to be through ROS generation. We have further shown a significant reduction of the implanted tumor size in the animal model, suggesting that this compound has great antitumoral potential against many tumor types. [Cu(dox)(phen)]²⁺ is selectively cytotoxic for melanoma B16F10 and showed high chemotherapeutic potential in vivo against implanted sarcoma S180 and Ehrlich ascites tumours.

Molecular enneanuclear CuII phosphates containing planar hexanuclear and trinuclear sub-units: syntheses, structures, and magnetism

Highly symmetric enneanuclear copper(ii) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(ii) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(i)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(ii) centres are bridged by a μ3-OH. Each pair of Cu(ii) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(ii) motifs where the two Cu(ii) centres are bridged by an -OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(ii) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.

Mechanism of Intramolecular Nucleophilic Substitution in the Catalytic Hydrolysis of Bis(4-Nitrophenyl) Phosphate Ester in a Metallomicelle

A macrocyclic Schiff base ligand and the corresponding Cu(II) and Ni(II) complexes were synthesized and characterized. The catalytic ability of metallomicelles, made from these complexes and micelles, as mimic hydrolytic metalloenzymes, was investigated in the catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP). The rate of the BNPP catalytic reaction in the metallomicelles is ca 2.0 × 106-fold faster than that of the spontaneous hydrolysis of BNPP in aqueous solution under the same conditions. The analysis of absorption spectra of the hydrolytic reaction systems indicates that key intermediates, comprising BNPP and the Ni(II) or Cu(II) complexes, have been formed and the catalytic hydrolysis of BNPP is an intramolecular nucleophilic substitution reaction. Based on the analysis of the absorption spectrum, a mechanism for the catalytic hydrolysis of BNPP has been proposed and a kinetic mathematical model has been established.

Mechanism and Kinetics of Hydrolysis of Carboxylic Esters Catalysed by Metallomicelles Comprising a Macrocyclic Metal Complex and a Surfactant

Two nickel(II) and copper(II) macrocyclic complexes were synthesised and characterised, and metallomicelles comprising the complex and a surfactant, as a mimic hydrolytic metalloenzyme, were used in the catalytic hydrolysis of a carboxylic ester, p-nitrophenyl picolinate (PNPP). Analysis of absorption spectra of the hydrolytic reaction systems indicates that a key intermediate, comprising PNPP and the nickel(II) or copper(II) complexes, is formed in the reaction. Based on these spectral observations, a mechanism of PNPP catalytic hydrolysis has been proposed; a kinetic mathematical model, applied to calculation of the associated kinetic parameters has been established. The effects of acidity, the structure effect of the complexes and of the presence of micelles on the rate of the hydrolysis are also discussed.

Mapping the working route of phosphate monoester hydrolysis catalyzed by copper based models with special emphasis on the role of oxoanions by experimental and theoretical studies

The mechanistic pathway of phosphate-ester bond hydrolysis with special emphasis on the role of oxoanions was explored by experimental and theoretical study.

Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies

Three, PO₄ ^3-/HPO₄ ^2- and AsO₄ ^3--incorporated, new tetranuclear complexes of copper(II) and zinc(II) ions have been synthesized and fully characterized. In methanol-water, reactions of H₃cpdp (H₃cpdp = N,N'-Bis[2-carboxybenzomethyl]-N,N'-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II) chloride in the presence of either NaOH/Na₂HPO₄·2H₂O or KOH/Na₂HAsO₄·7H₂O lead to the isolation of the tetranuclear complexes Na₃[Cu₄(cpdp)₂(μ₄-PO₄)](OH)₂·14H₂O (1) and K₂[Cu₄(cpdp)₂(μ₄-AsO₄)](OH)·16²/₃H₂O (2), respectively. Similarly, the reaction of H₃cpdp with zinc(II) chloride in the presence of NaOH/Na₂HPO₄·2H₂O yields a tetranuclear complex, Na(H₃O)₂[Zn₄(cpdp)₂(μ₄-HPO₄)]Cl₃·12¹/₂H₂O (3). All complexes are characterized by single-crystal X-ray diffraction and other analytical techniques, such as Fourier transform infrared and UV-vis spectroscopy, thermogravimetric and electrochemical studies. The solid-state molecular framework of each complex contains two monocationic [M₂(cpdp)]⁺ (M = Cu, Zn) units, which are exclusively coordinated to either phosphate/hydrogen phosphate or arsenate groups in a unique mode. All three complexes exhibit a μ₄:η¹:η¹:η¹:η¹ bridging mode of the PO₄ ^3-/HPO₄ ^2-/AsO₄ ^3- groups, with each bridging among four metal ions. The thermal properties of all three complexes have been investigated by thermogravimetric analysis. Low-temperature magnetic studies of complexes 1 and 2 disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxide and phosphate/arsenate bridges. Electrochemical studies of complexes 1 and 2 in dimethylformamide using cyclic voltammetry reveal the presence of a fairly assessable one-electron metal-based irreversible reduction and one quasireversible oxidation couple.

Metallohydrolase biomimetics with catalytic and structural flexibility

The phosphatase activity of zinc complexes containing six- and seven-dentate ligands was evaluated through kinetic and³¹P NMR studies.

A dinuclear zinc(II) complex of a new unsymmetric ligand with an N(5)O(2) donor set: a structural and functional model for the active site of zinc phosphoesterases

The dinuclear complex [Zn(2)(DPCPMP)(pivalate)](ClO4), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate (BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; they reveals that the dinuclear zinc(II) complexes, [Zn(2)(DPCPMP)](2+) and [Zn(2)(DPCPMP)(OH)](+) predominate the solution above pH4. The relatively high pK(a) of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand=0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters ΔH(‡)=95.6kJmol(-1), ΔS(‡)=-44.8Jmol(-1)K(-1), and ΔG(‡)=108.0 kJmol(-1). The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn(2)(DPCPMP)(μ-OH)](+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFT). Calculations show that the reaction goes through one concerted step (S(N)2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; the leaving group dissociates simultaneously in an overall inner sphere type activation. The calculated free energy barrier is in good agreement with the experimentally determined activation parameters.

Iron(iii) complexes of multidentate pyridinyl ligands: synthesis, characterization and catalysis of the direct hydroxylation of benzene

Correlation between the electrochemistry and catalytic performance of multidentate pyridinyl iron complexes in the hydroxylation of benzene suggests that more electron-donating ligands are beneficial for catalysis.

Studies of DNA-Binding and DNA-Cutting Mechanism of an Azamacrocyclic Cerium Complex with Carboxyl Branch

An azamacrocyclic compound with a carboxyl branch, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane- N/-acetic acid (L), and its cerium complex were synthesised and characterised. The mode of combination of the cerium complex with DNA was investigated by fluorescence and UV-Vis absorption spectroscopy. The cutting function of the cerium complex towards supercoiled DNA was studied by the gel electrophoresis method. The results show that metal complex can bind to the phosphate group of DNA double helix and promote the hydrolysis of the phosphodiester bond of supercoiled DNA (Form I); under certain conditions, supercoiled form DNA (Form I) was transformed into the nicked form DNA (Form II) under the strong cutting effect of the macrocyclic cerium complex; the cutting is completed by a hydrolysis mechanism.

DNA binding, DNA cleavage and cytotoxicity studies of a new water soluble copper(II) complex: the effect of ligand shape on the mode of binding

The interaction of native calf thymus DNA (CT-DNA) with [Cu(ph(2)phen)(phen-dione)Cl]Cl was studied at physiological pH by spectrophotometric, spectrofluorometric, circular dichroism, and viscometric techniques. Considerable hypochromicity and red shift are observed in the UV absorption band of the Cu complex. Binding constants (K(b)) of DNA with the complex were calculated at different temperatures. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van't Hoff equation, which indicated that reaction is predominantly enthalpically driven. All these results indicate that Cu(II) complex interacts with CT-DNA via intercalative mode. Also, this new complex induced cleavage in pUC18 plasmid DNA as indicated in gel electrophoresis and showed excellent antitumor activity against K562 (human chronic myeloid leukemia) and human T lymphocyte carcinoma-Jurkat cell lines.

2-{[{2-Hy-droxy-3-[2-methyl-5-(propan-2-yl)phen-oxy]prop-yl}(pyridin-2-ylmeth-yl)amino]-meth-yl}phenol

In the title racemic compound, C(26)H(32)N(2)O(3), an intra-molecular O-H⋯N hydrogen bond is formed between the phenolic OH group and the tertiary amine N atom. Another O-H⋯N hydrogen bond that is formed between the OH group and the pyridine N atom links the mol-ecules into a polymeric chain extending along the a axis. The structure is further stabilized by intramolecular and intermolecular C-H⋯O interactions.

Synthesis, characterization, antibacterial activity, SOD mimic and interaction with DNA of drug based copper(II) complexes

Novel metal complexes of the second-generation quinolone antibacterial agent enrofloxacin with copper(II) and neutral bidentate ligands have been prepared and characterized with elemental analysis reflectance, IR and mass spectroscopy. Complexes have been screened for their in-vitro antibacterial activity against two Gram(+ve) Staphylococcus aureus, Bacillus subtilis, and three Gram((-ve)) Serratia marcescens, Escherichia coli and Pseudomonas aeruginosa organisms using the double dilution technique. The binding of this complex with CT-DNA has been investigated by absorption titration, salt effect and viscosity measurements. Binding constant is ranging from 1.3×10(4)-3.7×10(4). The cleavage ability of complexes has been assessed by gel electrophoresis using pUC19 DNA. The catalytic activity of the copper(II) complexes towards the superoxide anion (O2.-) dismutation was assayed by their ability to inhibit the reduction of nitroblue tetrazolium (NBT).

Expedient synthesis of a modular phosphate affinity reagent

Isolation and identification of phosphorylated macromolecules is essential for the deconvolution of most biological regulatory networks. Koike and co-workers recently reported the application of a dinuclear zinc-(pyridylmethyl)amine complex to phosphate-specific affinity purifications and gave it the shorthand name "phos-tag". This complex is valuable for studying phosphorylation because it binds selectively to phosphate dianion in the presence of acidic functional groups at physiological pH, and because the binding is largely independent of molecular context. These properties of phos-tag recommend it for applications in phosphoproteomics, metabolomics, and nucleic acid biology. The catch has been that the molecule is difficult to make and prohibitively expensive to buy. Here, we describe an efficient and inexpensive synthesis of a phos-tag derivative with a versatile alkyne handle. The alkyne handle allows for attachment of phos-tag to alkyl azides via the copper(I)-catalyzed azide-alkyne cycloaddition reaction ("click chemistry"). We characterize the phosphate binding behavior of the new phos-tag derivative in a variety of experimental assays, including its conjugation to a fluorescent reporter, to acrylamide gels, and to sepharose chromatography resin. The synthesis we report should enable a broader use of phos-tag for phosphate-related biochemistry, as both an analytical and a preparative reagent.

Mixed-ligand copper(II) maltolate complexes: synthesis, characterization, DNA binding and cleavage, and cytotoxicity

The mixed-ligand complexes [Cu(L)(maltol)] where L = 2,2'-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), 1,10-phenanthroline-5,6-dione (phendione; 3), dipyrido[3,2-a:2',3'-c]phenazine (dppz; 4), and 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]-phenanthroline-6,13-dione (bipyridylglycoluril; bpg; 5) have been synthesized and characterized by structural, analytical, and spectral methods. The single-crystal X-ray structures of 1, 2, and 5 exhibit a distorted square-pyramidal structure, with the polypyridyl ligands and maltol occupying equatorial positions and either a water or nitrate anion at the axial position. The N,N-dimethylformamide glass as well as the single-crystal electron paramagnetic resonance of the complexes confirms the distorted square-pyramidal structure. The DNA binding investigated using different techniques (absorption titration, viscosity, thermal melting, and fluorescence quenching) indicates the partial intercalation of the planar polypyridyl ligands into DNA. The complexes cleave plasmid pBR322 DNA by a hydrolytic mechanism. The kinetic aspects of DNA cleavage under pseudo-Michaelis-Menten and true Michaelis-Menten conditions as well as the phosphodiesterase activity using model 4-nitrophenylphosphate are also detailed. The cytotoxicity of the complexes against HeLa (cervical) cancer cell lines shows that synergy between the metal and ligands results in a significant enhancement in the cell death with IC(50) of approximately 150-270 microg mL(-1).

Kinetic Study on P-Nitrophenyl Picolinate Hydrolysis Promoted by the Complex Bis(O,O'-Di(2-Benzyl)Dithiophosphato)Nickel(Ii)

The complex Ni[S2P(OCH2Ph)2]2 (MR) was synthesised and characterised by elemental analysis, IR spectroscopy and 1H NMR spectroscopy. The hydrolysis of p-nitrophenyl picolinate (PNPP) as promoted by this complex was investigated by the UV-vis method, the results showing that MR acts as a very efficient catalyst. The specific absorption spectra of the hydrolytic reaction systems indicated that the key intermediate, made up of PNPP and MR was formed during reaction. Based on these spectra, a mechanism for the catalytic hydrolysis of PNPP has been proposed and a kinetic mathematical model established.