Synthesis,structure, stability and DNA cleavage activities of three Cr(III) complexes with salicylate and ammonium ligands

Complexes [Cr(III)(SA)(en)₂]⁺ (1), [Cr(III)(SA)(DETA)(H₂O)]⁺ (2) and [Cr(III)(SA)(TETA)]⁺ (3) were synthesized (H₂SA = salicylic acid, en = ethylenediamine, DETA = diethylenetriamine, TETA = triethylenetetramine). Kinetics studies show that 2 is the most instable one among these complexes. In addition, only 2 is found to be a very efficient catalyst of the cleavage of PBR322 DNA in the absence of any added cofactor. The degradation rate from supercoiled form to nicked form was 1.05 ± 0.081 h^− 1 (10^− 5 M) at pH 7.4 and 37 °C. Thiobarbituric acid-reactive substances assay shows 2 fail to produce OH causing any degradation of deoxyribose ring even in the presence of ascorbic acid. Ethidium bromide displacement assay suggests that only 2 can kick out EB from the groove of DNA. The interaction with DNA causes a blue shift of the d → d transition spectra of 2.     

Comparison of DNA binding and cleavage abilities between mono- and trinuclear copper(II) complexes of benzimidazole derivatives

Two copper(II) complexes, [CuLCl₂] (1) and [Cu₃L′Cl₆] (2) (L = bis(2-benzimidazolylmethyl)amine, L′ = 2,4,6-tris[bis(2′-benzimidazolylmethyl) amine]-1,3,5-triazine), have been synthesized and characterized. Both complexes bind to DNA and cleave the supercoiled pUC19 plasmid DNA into its nicked and linear forms at micromolar concentrations and physiologically relevant conditions. The DNA cleavage efficacy of 1 is higher than that of 2 though its DNA binding ability is lower than the latter. The cleavage mechanism in the presence of hydrogen peroxide appears to be different for 1 and 2.     

Water soluble copper(II) complex [Cu(dipica)(CH3COO)]ClO4: DNA binding,pH dependent DNA cleavage and cytotoxicity

A mononuclear copper(II) complex [Cu(dipica)(CH₃COO)]ClO₄ (1), where dipica is di-(2-picolyl)amine, has been isolated. The electronic absorption (646 nm) and electron paramagnetic resonance (EPR) spectral parameters (g_||, 2.223; A_||, 187 × 10^− 4 cm^− 1; g_||/A_||, 119 cm) reveal that 1 possesses a near square planar geometry with CuN₃O chromophore. Absorption, circular dichroic and emission spectral measurements and electrochemical measurements clearly demonstrate groove binding of 1 to calf thymus DNA. Notably, 1 exhibits more effective DNA (pUC 19 DNA) cleavage at acidic pH. It shows significant cytotoxicity (IC₅₀, 55 μM) against human cervical carcinoma cells (HeLa) at 48 h incubation time and is non-toxic to healthy cells.     

Bio active mixed ligand complexes of Cu(II), Ni(II) and Zn(II): Synthesis,spectral, XRD,DNA binding and cleavage properties

The paper presents the synthesis of complex combinations of Cu(II), Zn(II) and Ni(II) with Schiff bases obtained by the condensation reaction of diphenylglyoxal with 1-amino-4-nitrobenzene (L¹)/1-amino-4-chlorobenzene (L²)/p-anisidine (L³) as the main ligand and 1,10-phenanthroline as the co-ligand respectively. The characterization of newly formed complexes has been done by spectral and molar conductivity studies. The bioefficacy of the ligands and their complexes have been examined against the growth of bacteria and fungi in vitro to evaluate their antimicrobial potential. The in vitro antibacterial and antifungal assay indicates that these complexes are good antimicrobial agents against various pathogens. X-ray powder diffraction illustrates that the complexes have crystalline nature. The effect of the metal complexes on DNA is carried out by pUC19 DNA agarose gel electrophoresis at 50 V for 2 h. The results indicate that the complexes bind to DNA through intercalation and act as efficient cleaving agents.     

New mechanisms in DNA cleavage by metal complexes

The chemistry of new families of DNA cleavage agents based on oxoruthenium(IV) or diplatinum pyrophosphite complexes is reviewed. The ruthenium complexes derived from Ru(tpy)(bpy)O²⁺ (tpy, 2, 2, 2-terpyridine; bpy, 2, 2-bipyridine) are effective DNA cleavage agents both electrocatalytically or thermally. The stoichiometric reaction quantitatively produces Ru(II), which also binds to DNA covalently in a slow, follow-up reaction. The cleavage by Pt₂(pop)₄ ^4– (pop, P₂O₅H₂) is photoactivated and proceeds via H-atom abstraction by the platinum complex.     

Mechanism of DNA cleavage due to green cobalt(III)-bleomycin hydroperoxide irradiated by visible light

The origin of the DNA cleavage reaction due to green cobalt(III)-bleomycin hydroperoxide irradiated by light (366 nm) was developed; the importance of the activation of the peroxide ion by transferring an electron from the occupied orbital to the σ^*-orbital of the peroxide ion was pointed out.     

Phosphate diester hydrolysis promoted by new Cu(II) alkoxide complexes

Three Cu(II) complexes of N3 donor pyridyl-amine ligands, bis-(2-pyridin-2-yl-ethyl)-amine (L¹), which does not have an alcohol pendant, and 2-[bis-(2-pyridin-2-yl-ethyl)-amino]-ethanol (L²) and 3-[bis-(2-pyridin-2-yl-ethyl)-amino]-propan-1-ol (L³), both containing alcohol pendants, have been synthesized and structurally characterized. The reactivities of CuL¹ (1), CuL² (2), and CuL³ (3) for promoting the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) have been investigated, showing that 3 is much more active (observed second order rate constant k = 6.1 × 10⁻¹ M⁻¹ s⁻¹ at pH 8.4, 50 °C) than 1 (k = 9.4 × 10⁻³ M⁻¹ s⁻¹ at pH 8.4, 50 °C) or 3 (observed second order rate constant k = 5.2 × 10⁻³ M⁻¹ s⁻¹ at pH 8.4, 50 °C) at promoting the hydrolysis of BNPP. The much higher reactivity of 3 compared to 2 and 1 may be explained by the higher flexibility of the alkoxide tether in 3, which may allow the nucleophilic alkoxide O-atom in 3 better access to attack a metal-bound BNPP substrate, whereas 2, which has a shorter alkoxide tether, may resort to hydrolyzing the BNPP substrate with a metal-bound hydroxide instead of utilizing its alkoxide moiety because of constraints in the ligand tether. The similar reactivities of 1 and 2 suggest that this is a possible scenario. Another possible explanation for the difference in reactivity between 3 and 2 may be attributed to the alcohol pendant in 3 being better oriented to serve as a proton acceptor from a Cu(II)-bound aqua ligand, which would facilitate its deprotonation and the subsequent nucleophilic attack of the Cu(II)-hydroxide moiety towards the substrate. The reactivities of 2 and 3 towards hydrolyzing BNPP are also compared with that of their Zn(II) analogues, showing that the Cu(II) complexes of the same ligand sets are more hydrolytically active than the corresponding Zn(II) complexes. Single crystal X-ray structures of 1, 2, and 3 are also reported, which show that complexes 2 and 3 form dimers with bridging alkoxide ligands in the solid state, while 1 forms a dimer with bridging chloride ligands in the solid state.     

Studies on interaction of Cr(III) polypyridyl complexes with DNA

Two chromium(III) complexes containing derivatives of 1,10-phenanthroline were synthesized and characterized using different spectroscopic methods. The interaction of the synthesized complexes with DNA was performed. From the absorption titration data, the binding constant for the complexes [Cr(imiphen)₂Cl₂]⁺ (1) and [Cr(furphen)₂Cl₂]⁺ (2) with DNA were found to be 5.69 ± 0.3 × 10⁴ M^− 1 for 1 and 3.7 ± 0.2 × 10⁴ M^− 1 for 2, respectively. The viscosity studies show that both the complexes bind to DNA in a partial intercalative mode. The results of competitive binding assay reveal that both complexes displace EB from DNA marginally. Gel electrophoresis data show that both the complexes 1 and 2 requires co-reagent to induce DNA cleavage but complex 2 exhibit better nuclease activity compared to complex 1. The results from this study describe the role of ligand structure in the binding and cleavage of DNA as furan based ligand exhibit better cleaving ability compared to imidazole moiety.     

Gallium(III) and indium(III) complexes of cross-bridged tetraamine ligands

Gallium(III) and indium(III) complexes of cross-bridged cyclam and cyclen tetraaza macrocyclic ligands have been prepared and structurally characterized. In the crystalline state, both the GaCl₃ (cross-bridged cyclam) and InBr₃ (cross-bridged cyclen) complexes feature hexacoordinate cations in cis-folded tetradentate ligand clefts with ancillary cis-dihalides. These represent the first well-characterized gallium and indium halide complexes of tetraazamacrocycles.     

Selective oxidation of alcohols with hydrogen peroxide catalyzed by hexadentate binding 8-quinolinolato manganese(III) complexes

A series of hexadentate 8-quinolinolato manganese(III) complexes were synthesized and proven to own a distorted octahedral geometry via elemental analysis, solid UV–vis spectroscopy and Hartree–Fock/3-21G+ calculation. These Mn(III) complexes were found to be more efficient than their corresponding tetradentate 8-quinolinolato manganese(II) and salen-Mn^IIIOAc for the oxidation of alcohols in acetone medium, being due to their special hexadentate binding structures that could open an axial MnO bond to form the more active pentadentate structures in the presence of aqueous hydrogen peroxide, as supported by UV–vis spectra. The halogen substituents in ligand's aryl ring could significantly enhance the catalytic activities and 5-chloro-7-iodo-8-quinolinolato manganese(III) gave the highest turnover number (TON). A reasonable mechanism for the present catalytic system was proposed.     

SOD mimic activity,DNA binding and in-vitro antibacterial studies of drug based copper(II) complexes

Square pyramidal complexes [Cu^II(PFL)(bpa)Cl]?5H₂O (1) and [Cu^II(LFL)(bpa)Cl]?5H₂O (2) have been synthesized and characterized. Compounds were checked for their in-vitro antimicrobial activity against two Gram^(+ ve) and three Gram^(–ve) bacterial species. Intrinsic binding constant (K_b) of complexes with CT DNA were determined using absorption titration. Viscosity measurement suggests that complexes bind with CT DNA through partial nonclassical intercalative mode. Superoxide dismutase (SOD) like activity of the complexes was also compared with previously reported compounds.     

Screening of ATP hydrolysis by Zr(IV) and Eu(III) complexes

The dephosphorylation of adenosine triphosphate (ATP) by various zirconium (IV) and europium (III) complexes is described. Release of phosphate was followed by an automated, robotics-based colorimetric assay which is compatible with the presence of these high-valent metal ions.     

Antioxidation and DNA binding properties of binuclear Nd(III) complexes with Schiff-base ligands derived from 8-hydroxyquinoline-2-carboxyaldehyde and four aroylhydrazides

Nd(III) and four Schiff-base ligands can form binuclear nine-coordination [NdL^1–4(NO₃)(DMF)₂]₂ complexes with 1:1 metal-to-ligand stoichiometry at Nd(III) center. All the ligands and Nd(III) complexes may be used as potential anticancer drugs, binding to Calf thymus DNA through intercalations with the binding constants at the order of magnitude 10⁵–10⁶ M⁻¹. In addition, Nd(III) complexes present stronger affinities to DNA than ligands. All the ligands and Nd(III) complexes have strong scavenging effects for hydroxyl radicals and superoxide radicals.     

Oxidation of cyclohexane promoted by [Fe(III)(Salen)Cl] and [Mn(III)(Salen)Cl]

Salen complexes of iron(III) and manganese(III) were synthesized and employed as catalysts in the oxidation of cyclohexane, using hydrogen peroxide and tert–butylhydroperoxide. The reactions were carried out in acetonitrile at room temperature. The catalysts were characterized by infrared and Mössbauer spectroscopy, elemental analysis, conductivity and cyclic voltammetry. Conversions up to 10.2% (4.2% and 6.0% yields for cyclohexanol and cyclohexanone, respectively) were obtained for the system [Fe(III)(Salen)Cl]/tBuOOH.     

Evaluation of the antioxidant,DNA interaction and tumor cell cytotoxicity activities of Copper(II) complexes with Paeonol Schiff-base

Herein, we report for the first time on the preparation of four Paeonol Schiff-base ligands: 1,2-Bis(2-hydroxy-4-methoxy-α-methylbenzylideneimino) ethane (H₂L¹), 2-hydroxy-4-methoxy-α-methylbenzylidene (benzoyl) hydrazone (HL²), 2-hydroxy-4-methoxyacetophenone-ethanolamine Schiff-base (HL³), and 2-hydroxy-4-methoxyacetophenone(2′-hydroxybenzoyl) hydrazone (H₂L⁴), and their Cu(II) complexes, of which the structure of C₁₁N₂O₆H₁₄Cu(CuL^3.NO₃) was confirmed by X-ray diffraction. Antioxidant activities of four Cu(II) complexes were studied by the standard non-enzymatic NBT method and Fenton system, used to produce superoxide anion radicals and hydroxyl radicals, respectively. The results show these Cu(II) complexes have excellent antioxidant activities. DNA-binding and in vitro cytotoxicity experiments were utilized to further investigate the biological activities of C₁₁N₂O₆H₁₄Cu(CuL^3.NO₃). These results support C₁₁N₂O₆H₁₄Cu as a potential candidate for biological use because it shows not only high antioxidant and moderate DNA-binding activities, but also good tumor cell cytotoxicity activities in human cell lines carcinomas Hep-2 (larynx), for the range of concentrations tested.     

DNA binding of mixed-metal supramolecular Ru, Pt complexes

The mixed-metal supramolecular complexes [(tpy)Ru(PEt₂Ph)(dpp)PtCl₂](PF₆)₂ and [(tpy)Ru(PEt₂Ph)(bpm)PtCl₂](PF₆)₂ are of interest in that they couple light absorbing ruthenium centers to a reactive metal site through a communicative bridge (tpy=2,2^′:6^′,2^′′-terpyridine, BPM=2,2^′-bipyrimidine and DPP=2,3-bis(2-pyridyl)pyrazine). These systems have been studied and shown to avidly bind to DNA, greatly reducing its mobility through an agarose gel.     

New bis-o-iminosemiquinonate aluminium(III) complexes

The first aluminium(III) complexes based on sterically hindered 4,6-di-tert-butyl-N-(2,6-di-iso-propyl-phenyl)-o-iminobenzoquinone (imQ) of general formula imSQ₂AlR (where imSQ — is a radical anion of imQ, R = I (1), NCS (2) and N₃ (3)) were synthesized. Compounds 1–3 demonstrate biradical X-band EPR spectra in frozen toluene matrix. The crystalline samples of 1–3 were characterized using magnetic susceptibility measurements. The antiferromagnetic coupling between spins of o-iminosemiquinonate radicals in 1–3 is predominant and, as the result, the singlet ground state for pentacoordinated biradical compounds is observed. The molecular structures of all the complexes obtained have been established by the single crystal X-ray analysis.     

Electrometric study of La(III), Ce(III), Pr(III) and Sm(III) complexes of n-glycylglycine

Saxena and co-workers have made extensive study on the complexing tendencies of several thiols and some of the aminoacids with various metals[1–4]. This paper reports the determination of composition and stabilities of La(III), Ce(III), Pr(III) and Sm(III) complexes of N-Glycylglycine at 30° C and 40° C by applying potentiometric and conductometric titration techniques and also the values of ΔG, ΔH and ΔS at 30° C accompanying the complexation reactions. There is however, no reference in the literature on the study of the present system.     

Reactions of organic disulfides and gold(i) complexes

Gold-thiolate/disulfide exchange reactions of (p-SC(6)H(4)Cl)(2) with Ph(3)PAu(SC(6)H(4)CH(3)), dppm(AuSC(6)H(4)CH(3))(2), and dppe(AuSC(6)H(4)CH(3)) (2) were investigated. The rate of reactivity of the gold-thiolate complexes with (p-SC(6)H(4)Cl)(2) is: dppm(AuSC(6)H(4)CH(3))(2)> dppe(AuSC(6)H(4)CH(3))(2)>Ph(2)PAu (SC(6)H(4)CH(3)). This order correlates with conductivity measurements and two ionic mechanisms have been evaluated. (1)H NMR experiments demonstrate that in the reaction of dppm(AuSC(6)H(4)CH(3))(2) with (p-SC(6)H(4)Cl)(2), the mixed disulfide, ClC(6)H(4)SSC(6)H(4)CH(3), forms first, followed by the formation of (p-SC(6)H(4)CH(3))(2). The rate law is first order in (pp-SC(6)H (4)Cl)(2) and partial order in dppm(AuSC(6)H(4)CH(3))(2). Results from electrochemical and chemical reactivity studies suggest that free thiolate is not involved in the gold-thiolate/disulfide exchange reaction. A more likely source of ions is the dissociation of a proton from the methylene backbone of the dppm ligand which has been shown to exchange with D(2)O. The implications of this are discussed in terms of a possible mechanism for the gold-thiolate/disulfide exchange reaction.     

Synthesis,isolation and characterization of dinuclear oxidodiiron(III) complexes modified by monodentate pyridines

In the present study, iron complexes modified by differently substituted monodentate pyridine ligands containing a [Fe–O–Fe] unit have been synthesized, isolated and characterized. Noteworthy, the complexes are easily accessible by the reaction of pyridines with iron(II) chloride in the presence of molecular oxygen, which is the source for the oxido bridge as proven by labelling experiments. Interestingly, in dependency of the electronic and steric properties of the applied ligand different geometries have been observed by X-ray diffraction analysis. On one hand with pyridine or 4-dimethylaminopyridine as ligand (L) a L₄ClFe–O–FeCl₃ motif was accessible, while with 4-tert-butylpyridine a L₂Cl₂Fe–O–FeCl₂L₂ motif was realized. With the aid of Mößbauer spectroscopy an oxidation state + III was assigned for all iron centres. Moreover, the complexes were easily converted by addition of silver benzoate to trinuclear complexes with a [Fe₃O] core.