A Trinuclear Copper(II) Complex of 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine Shows Prominent DNA Cleavage Activity

Theoretical studies on binding modes of copper-based nucleases with DNA

In the present work, molecular simulations were performed for the purpose of predicting the binding modes of four types of copper nucleases (a total 33 compounds) with DNA. Our docking results accurately predicted the groove binding and electrostatic interaction for some copper nucleases with B-DNA. The intercalation modes were also reproduced by "gap DNA". The obtained results demonstrated that the ligand size, length, functional groups and chelate ring size bound to the copper center could influence the binding affinities of copper nucleases. The binding affinities obtained from the docking calculations herein also replicated results found using MM-PBSA approach. The predicted DNA binding modes of copper nucleases with DNA will ultimately help us to better understand the interaction of copper compounds with DNA.

DNA interaction, SOD, peroxidase and nuclease activity studies of iron complex having ligand with carboxamido nitrogen donors

Complex (Et3HN)[Fe(III)(bpb)Cl2], 1 {where H2bpb: N,N'-(1,2-phenylene)bis(pyridine-2-carboxamide)} was synthesized and characterized by reported procedure (Yang et al., 1991). Complex 1 was found to be effective in superoxide scavenging activity and an IC50 value of 4.1 μM was obtained in xanthine-xanthine oxidase nitro blue tetrazolium assay. Peroxidase-like activity of this complex was determined by the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). DNA interaction studies of complex 1 showed binding of DNA through external or groove binding. Complex 1 exhibited chemical nuclease activity in the presence of hydrogen peroxide and cleaved supercoiled pBR322 DNA to its linear and nicked circular form at physiological pH. Mechanistic studies indicated possible role of hydroxyl radical (·OH) species in DNA cleavage activity via hydroperoxo intermediate: [Fe(III)OOH(-)](2+)→[Fe(IV)O](2+)+(·)OH.

Copper(II) Complexes with N,O-Donor Ligands and Ofloxacin Drug as Antibacterial, DNA Interacting, Cytotoxic and SOD Mimic Agent

ABSTRACT

The N,O-donor bidentate ligands (L (1) -L (7) ) derived from the reaction between chalcones and pyridinium salt of 2-acetyl furan were synthesized and characterized by IR and NMR spectroscopic techniques. Their complexes [1-7] of Cu(II) were synthesized and characterized by elemental analysis, magnetic measurements, TG analyses, IR and mass spectroscopy. Synthesized complexes were carried out for their biological elucidation using different biological experiments like minimum inhibitory concentration, DNA binding and cleavage study, cytotoxicity, and antiradical activity. Efficient cleavage of pUC19 DNA was observed for all the test complexes than the reference drug.

GRAPHICAL ABSTRACT

Increase in DNA chain length and hence the relative viscosity as the complexes binds to DNA via intercalative mode and involves a strong stacking interaction between an aromatic chromophore and the DNA base pair.

CO₂ fixation by dicopper(II) complexes in hypodentate framework of N₈O₂

A new ligand with N8O2 donors containing three potential metal-binding sites (H₂L) and its tricopper(II) complex 1 are synthesized. The tricopper species is found to be formed from a hypodentate dicopper(II) complex 2 in basic solutions. Complex 2 may be isolated from the reaction of H₂L with a copper source under acidic conditions. Complex 2 can undergo CO2-abstraction to yield an octacopper(II) complex 3. The single crystal structures of complexes 2 and 3 are characterized by X-ray crystallography.

Synthesis, characterization, DNA binding, cleavage activity and cytotoxicity of copper(II) complexes

Three new mononuclear copper(II) complexes, [Cu(L2)](2+) (1), [Cu(acac)(L)](+) (2), and [Cu(acac-Cl)(L)](+) (3) (L = 2-(4-pyridine)oxazo[4,5-f]1,10-phenanthroline (4-PDOP); acac = acetylacetone; acac-Cl = 3-chloroacetylacetone), have been synthesized and characterized by elemental analysis, high resolution mass spectrometry (Q-TOF), and IR spectroscopy. Two of the complexes were structurally characterized by single-crystal X-ray diffraction techniques. Their interactions with DNA were studied by UV-vis absorption and emission spectra, viscosity, thermal melting, DNA unwinding assay and CD spectroscopy. The nucleolytic cleavage activity of the compounds was carried out on double stranded pBR322 circular plasmid DNA by using a gel electrophoresis experiment in the presence and absence of an oxidant (H2O2). Active oxygen intermediates such as hydroxyl radicals and hydrogen peroxide generated in the presence of L and complexes 1-3 may act as active species for the DNA scission. The cytotoxicity of the complexes against HepG2 cancer cells was also studied.

DNA binding, cytotoxicity and apoptosis induction activity of a mixed-ligand copper(II) complex with taurine Schiff base and imidazole

A novel binuclear copper(II) complex (complex 1) with taurine Schiff base and imidazole has been synthesized and structurally characterized by single crystal X-ray diffraction, elemental analysis, ESI-MS spectrometry, UV-vis and IR spectroscopy. Single-crystal analysis revealed that 1 displays the sulfonate-bridged dinuclear copper(II) centers. Both copper atoms are five-coordinated and exhibit slightly distorted square pyramidal geometries. Each of copper atom is surrounded by three oxygen atoms and one nitrogen atom from different taurine Schiff base ligands, and one nitrogen atom from one imidazole ligand. The interaction between 1 and calf thymus DNA (CT-DNA) was investigated by UV-vis, fluorescence, circular dichroism (CD) spectra and agarose gel electrophoresis. The experimental results indicated that 1 could bind to CT-DNA via an intercalative mode and show efficient cleavage activity. In addition, 1 showed an antitumor effect on cell cycle and apoptosis. Flow cytometric analysis revealed that MGC-803 cells were arrested in the S phase after treatment with 1. Fluorescence microscopic observation indicated that 1 could induce apoptosis of MGC-803 cells.

Efficient hydrolytic cleavage of plasmid DNA by chloro-cobalt(II) complexes based on sterically hindered pyridyl tripod tetraamine ligands: synthesis, crystal structure and DNA cleavage

Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.

Self-assembled Cu(ii) and Ni(ii) metallamacrocycles formed from 3,3,3′,3′-tetrabenzyl-1,1′-aroylbis(thiourea) ligands: DNA and protein binding studies, and cytotoxicity of trinuclear complexes

The synthesis and characterization of metallamacrocyclic square planar Ni(ii) and Cu(ii) complexes and the interaction of cytotoxic trinuclear complexes with CT DNA and BSA protein are described.

Carbohydrate linked organotin(IV) complexes as human topoisomerase Iα inhibitor and their antiproliferative effects against the human carcinoma cell line

Dimethyltin(IV) complexes with ethanolamine (1) and biologically significant N-glycosides (2 and 3) were designed and synthesized. The structural elucidation of complexes 1-3 was done using elemental and spectroscopic methods; in addition, complex 1 was studied by single crystal X-ray diffraction studies. The in vitro DNA binding profile of complexes 2 and 3 was carried out by employing different biophysical methods to ascertain the feasibility of glycosylated complexes. Further, the cleaving ability of 2 and 3 was investigated by the agarose gel electrophoretic mobility assay with supercoiled pBR322 DNA, and demonstrated significantly good nuclease activity. Furthermore, both the complexes exhibited significant inhibitory effects on the catalytic activity of human Topo I at lower concentration than standard drugs. Computer-aided molecular docking techniques were used to ascertain the mode and mechanism of action towards the molecular target DNA and Topo I. The cytotoxicity of 2 and 3 against human hepatoma cancer cells (Huh7) was evaluated, which revealed significant regression in cancerous cells as compared with the standard drug. The antiproliferative activities of 2 and 3 were tested against human hepatoma cancer cells (Huh7), and results showed significantly good activity. Additionally, to validate the remarkable antiproliferative activity of complexes 2 and 3, specific regulatory gene expression (MMP-2 and TGF-β) was obtained by real time PCR.

Self-activating nuclease and anticancer activities of copper(II) complexes with aryl-modified 2,6-di(thiazol-2-yl)pyridine

Three mononuclear copper complexes [Cu(PDTP)Cl2] (PDTP = 4-phenyl-2,6-di(thiazole-2-yl)pyridine, CuPDTP), [Cu(ADTP)Cl2] (ADTP = 4-(anthracen-9-yl)-2,6-di(thiazole-2-yl)pyridine, CuADTP) and [Cu(BFDTP)Cl2] (BFDTP = 4-(benzofuran-2-yl)-2,6-di(thiazole-2-yl)pyridine, CuBFDTP) were synthesized and characterized. The X-ray single crystallography results indicated that the Cu(II) ions showed slightly distorted square pyramid coordination environments, and the ligands deviated from ideal planarity in all three compounds. Based on the DNA binding studies, it was demonstrated that these three complexes exhibited weak DNA binding strengths, which were most likely groove binding modes. CuPDTP, CuADTP and CuBFDTP induced efficient DNA cleavage in the dark without the addition of external catalysts (oxidant or reductant). In contrast, in the presence of reducing or oxidizing agents, the nuclease activities increased more than 10-fold. Mechanistic investigations revealed the participation of reactive oxygen species, which can be trapped by ROS radical scavengers and ROS sensors. In the same experimental conditions, the free ligands and CuCl2 did not display any DNA cleaving activity. This result indicates that the complexes, rather than their components, play a significant role in the nuclease reaction process and that DNA cleavage may be initiated in an oxidative pattern. The proposed mechanism was attributed to the in situ activation of molecular oxygen by the oxidation of the copper complexes. In the MTT cytotoxicity studies, the three Cu(II) complexes exhibited an antitumor activity against the HeLa, BEL-7402 and HepG2 tumor cell lines. The HeLa cells treated with Cu(II) complexes demonstrated marked changes in their nuclear morphology, which were detected by Hoechst 33258 nuclear staining and acridine orange/ethidium bromide (AO/EB) staining assays. Nuclear chromatin cleavage also was observed from alkaline single-cell gel electrophoresis (comet assay).

Improving nuclease activity of copper(II)-terpyridine complex through solubilizing and charge effects of glycine

Copper complexes are potential metallonucleases that may find application in biotechnology and molecular biology. In this study, a ternary copper-terpyridine complex [Cu(ttpy)(Gly)(NO3)](NO3)·H2O (1) (ttpy=4'-p-tolyl-2,2':6,2″-terpyridine) is synthesized and characterized by X-ray crystallography and ESI-MS as an artificial nuclease. Glycine (Gly) is introduced into the complex to enhance the water-solubility and electrostatic affinity for the nucleic acid target. The interaction between complex 1 and DNA has been studied by spectroscopy and gel electrophoresis, using a structural analog [Cu(ttpy)(NO3)2] (2) as the reference. Complex 1 demonstrates an increased DNA binding ability and oxidative cleavage activity towards supercoiled pBR322 DNA as compared with complex 2. The enhanced water-solubility and positive charge of complex 1 may facilitate its access to DNA and formation of hydrogen bonds with the sugar-phosphate backbone. The results indicate that carefully positioned auxiliary groups in a copper complex can significantly affect the substrate binding or activation ability and consequently the nuclease efficiency of the complex.

Infinite copper(II) coordination architectures from a resonative aminotriazine-derived tripodal ligand: synthesis, structures, and magnetic properties

The ligand 2,4,6-tris(2-picolylamino)-1,3,5-triazine (o-H3tpat) with essentially resonative structure and two copper(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H2tpat)(H2O)]·MeOH·CH2Cl2 (1) and [Cu2(o-H2tpat)(H2O)(MeOH)(NO3)2](NO3)·3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H3tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H3tpat form I adopts an asymmetric-configured all-amino resonative tautomer with three cis-trans-trans-arranged pyridyl groups, whereas the o-H3tpat form II adopts also an identical resonative structure but where two of the three pyridyl groups are in a cis-manner and the third one is nearly coplanar with the central aminotriazine core. On the other hand, the designed tripodal ligand in both Cu(II)-complexes serves as a monoanion, o-H2tpat(-), which suits a propeller-configured all-imino resonative structure in 1 and a syn-anti-configured amino-imino-imino resonative structure in 2. These observations significantly indicate that the o-H3tpat ligand can self-adjust and interconvert its conformation via a possible structure transformation associated with proton-shift to adapt a change in the crystallization and self-assembly reaction systems. In the magnetic point of view, 1 is treated as repeated chains composed of infinite {Cu6Cl10} units wherein the hexanuclear unit is further decomposed to one {Cu(II)4Cl6} and two magnetically isolated {Cu(II)Cl2} subunits. Antiferromagnetic interactions are found for the Cu4 subunits (g = 2.33, 2J1 = -5.6 cm(-1), 2J2 = -8.6 cm(-1), 2J3 = -4.1 cm(-1), and J4 held to zero). For 2, it is considered as an infinite chain that composes of Cu2 units antiferromagnetically coupled (g = 2.03, 2J1 = -0.2 cm(-1)). The small antiferromagnetic exchange constants in both 1 and 2 suggest that the unpaired spins do not effectively interact through the tripodal o-H2tpat(-) ligands.

Studies on synthesis, characterization, DNA interaction and cytotoxicity of ruthenium(II) Schiff base complexes

The synthesis and characterization of three hexa-coordinated ruthenium(II) Schiff base complexes of the type [RuCl(CO)(B)L] (B=PPh(3)/AsPh(3)/py and L=monobasic tridentate Schiff base ligand derived by the condensation of salicylaldehyde with 4-aminoantipyrine) are reported. IR, electronic, NMR and mass spectral data of the complexes are discussed. An octahedral geometry has been tentatively proposed for all the complexes. DNA binding properties of the ligand and its ruthenium(II) complexes have been investigated by electronic absorption spectroscopy. Two of the complexes were tested for DNA cleavage property. Finally, in vitro study of the cytotoxicity of the ligand and the complex [RuCl(CO)(PPh(3))L] on HeLa were tested. The IC(50) value for the ligand and the complex were 52.3 and 31.6μm respectively.

New heterobimetallic Cu(II)-Sn2(IV) complex as potential topoisomerase I inhibitor: in vitro DNA binding, cleavage and cytotoxicity against human cancer cell lines

The new heterobimetallic Cu(II)-Sn(2)(IV)/Ni(II)-Sn(2)(IV) complexes 1 and 2 bearing bioactive pharmacophore ligand scaffold; 1,10-phenanthroline and ethylenediamine were synthesized and characterized by spectroscopic (IR, UV-vis, NMR, ESI-MS) and analytical methods. The in vitro DNA binding studies of 1 and 2 with CT-DNA were carried out by employing various biophysical methods which reveal strong electrostatic binding via phosphate backbone of DNA helix, in addition to partial intercalation in the minor groove and stabilized by intramolecular hydrogen bonding. To gain further insight into the molecular recognition at the target site, UV-vis titrations of 1 with 5'-GMP was carried out and validated by (1)H and (31)P NMR. Complex 1 cleaved pBR322 DNA via oxidative pathway and exhibited high inhibition activity against Topo-I at 20 μM. Furthermore, the cytotoxicity of 1 was examined on a panel of human tumor cell lines of different histological origins showing promising antitumor activity.

Nuclease activity via self-activation and anticancer activity of a mononuclear copper(II) complex: novel role of the tertiary butyl group in the ligand frame

The copper complex [Cu((t)BuPhimp)(Cl)] (1) derived from tridentate ligand (t)BuPhimpH having N(2)O donors was synthesized, and its molecular structure was determined. A phenoxyl radical complex was generated in solution at room temperature using Ce(IV). The nuclease and anticancer activities of 1 were investigated. The roles of the tert-butyl group and singlet oxygen in the DNA cleavage activity were also discussed.