Systematical investigation of binding interaction between novel ruthenium(II) arene complex with curcumin analogs and ctDNA

In this study, the interaction between a novel ruthenium(II) arene complex with curcumin analogs and calf thymus DNA (ctDNA) was investigated systematically by viscosity measurement, the DNA melting approach, multispectroscopic techniques and electrochemical methods. The absorption spectra of the ctDNA–drug complex showed a slight red shift and a weak hypochromic effect. The relative viscosity and melting temperature of ctDNA increased on addition of the drug. The evidence obtained from fluorescence competitive experiments indicated that the binding mode of the drug with ctDNA was intercalative. Using acridine orange (AO) as a fluorescence probe, the drug statically quenched the fluorescence of the ctDNA–AO complex, and hydrogen bonding and van der Waals interactions played vital roles in the binding interaction between the drug and ctDNA. The influences of ionic strength, chemical denaturants and pH on the binding interaction were also investigated. Circular dichroism and Fourier transform infrared spectra suggested that this drug might bond with the G–C base pairs of ctDNA and the right‐handed B‐form helicity of ctDNA remained after drug binding. The intercalative binding between the drug and ctDNA was further investigated using electrochemical techniques. All these results suggested that the biological activity of ctDNA was affected by ruthenium(II) arene complex with curcumin analogs. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel mitochondrion-targeting copper(II) complex induces HK2 malfunction and inhibits glycolysis via Drp1-mediating mitophagy in HCC

[Cu(ttpy-tpp)Br₂]Br (abbreviated as CTB) is a novel mitochondrion-targeting copper(II) complex synthesized by our research group, which contains tri-phenyl-phosphonium (TPP) groups as its lipophilic property. In this study, we explored how CTB affects mitochondrial functions and exerts its anti-tumour activity. Multiple functional and molecular analyses including Seahorse XF Bioanalyzer Platform, Western blot, immunofluorescence analysis, co-immunoprecipitation and transmission electron microscopy were used to elucidate the underlying mechanisms. Human hepatoma cells were subcutaneously injected into right armpit of male nude mice for evaluating the effects of CTB in vivo. We discovered that CTB inhibited aerobic glycolysis and cell acidification by impairing the activity of HK2 in hepatoma cells, accompanied by dissociation of HK2 from mitochondria. The modification of HK2 not only led to the complete dissipation of mitochondrial membrane potential (MMP) but also promoted the opening of mitochondrial permeability transition pore (mPTP), contributing to the activation of mitophagy. In addition, CTB co-ordinately promoted dynamin-related protein 1 (Drp1) recruitment in mitochondria to induce mitochondrial fission. Our findings established a previously unrecognized role for copper complex in aerobic glycolysis of tumour cells, revealing the interaction between mitochondrial HK2-mediated mitophagy and Drp1-regulated mitochondrial fission.     

Structure and magnetic properties of polynuclear chloro- and hydroxo-bridged copper(II) complexes formed by a tetramacrocyclic derivative of 1,4,7-triazacyclononane

Two new copper(II) complexes of the ligand 1,2,4,5-tetrakis(1,4,7-triazacyclononan-1-ylmethyl)benzene (L^dur) have been synthesized and characterized by single crystal X-ray studies. The first, [Cu₄L^dur(μ₂-OH)₄]Cl₂(PF₆)₂ · 8H₂O (1), was isolated from a solution of L^dur and Cu²⁺ at pH 9. Under acidic conditions (pH 3), a polymeric complex, {[Cu₄L^dur(μ₂-Cl)₆](PF₆)₂ · 10H₂O}_n (2), crystallized from solution. In both complexes, each of the four triazacyclononane (tacn) rings of the L^dur ligand facially coordinate to separate metal centres. Pairs of Cu(II) centres are then doubly-bridged by hydroxo groups in 1, leading to tetranuclear complex cation units featuring pairs of isolated copper(II) dimers with Cu₂(μ₂-OH)₂ cores folded at the O?O lines. Two forms of the tetranuclear units, featuring slightly different Cu₂(μ₂-OH)₂ core geometries, are present in equal amounts within the crystal lattice. In complex 2, chloro bridging ligands link pairs of Cu(II) centres from neighbouring tetranuclear units, forming a 1D helical polymeric structure. Variable-temperature magnetic susceptibility measurements suggest that the hydroxo-bridged copper(II) centres within one of the tetranuclear units in 1 are weakly antiferromagnetically coupled (J = −27 cm⁻¹), whilst those in the other interact ferromagnetically (J = +19 cm⁻¹). Similar measurements indicate weak ferromagnetic coupling (J = +16 cm⁻¹) for the chloro-bridged copper(II) centres in 2.     

DNA binding affinity of a macrocyclic copper(II) complex: Spectroscopic and molecular docking studies

The interaction of a novel macrocyclic copper(II) complex, ([CuL(ClO₄)₂] that L is 1,3,6,10,12,15-hexaazatricyclo[13.3.1.1^6,10]eicosane) with calf thymus DNA (ct-DNA) was investigated by various physicochemical techniques and molecular docking at simulated physiological conditions (pH = 7.4). The absorption spectra of the Cu(II) complex with ct-DNA showed a marked hyperchroism with 10 nm blue shift. The intrinsic binding constant (K_b) was determined as 1.25 × 10⁴ M^?1, which is more in keeping with the groove binding with DNA. Furthermore, competitive fluorimetric studies with Hoechst33258 have shown that Cu(II) complex exhibits the ability to displace the ct-DNA-bound Hoechst33258 indicating that it binds to ct-DNA in strong competition with Hoechst33258 for the groove binding. Also, no change in the relative viscosity of ct-DNA and fluorescence intensity of ct-DNA-MB complex in the present of Cu(II) complex is another evidence to groove binding. The thermodynamic parameters are calculated by van't Hoff equation, which demonstrated that hydrogen bonds and van der Waals interactions played major roles in the binding reaction. The experimental results were in agreement with the results obtained via molecular docking study.     

A new tetranuclear copper(II) complex with oximate bridges: Structure, magnetic properties and DFT study

A new tetranuclear complex, [Cu₄L₄](ClO₄)₄·2H₂O (1), has been synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligand (2E,3E)-3-(2-aminopropylimino) butan-2-one oxime (HL). Single-crystal X-ray diffraction studies reveal that complex 1 consists of a Cu₄(NO)₄ core where the four copper(II) centers having square pyramidal environment are arranged in a distorted tetrahedral geometry. They are linked together by a rare bridging mode (μ₃-η¹,η²,η¹) of oximato ligands. Analysis of magnetic susceptibility data indicates moderate antiferromagnetic (J₁ = −48 cm⁻¹, J₂ = −40 cm⁻¹ and J₃ = −52 cm⁻¹) exchange interaction through σ-superexchange pathways (in-plane bridging) of the oxime group. Theoretical calculations based on DFT technique have been used to obtain the energy states of different spin configurations and estimate the coupling constants and to understand the exact magnetic exchange pathways.     

Dose‐dependent actions of curcumin in experimentally induced myocardial necrosis: a biochemical,histopathological, and electron microscopic evidence

Curcumin, an active component of turmeric, is a well‐known antioxidant due to its reactive oxygen species (ROS) scavenging property. However, some in vitro studies have suggested that curcumin induces generation of ROS at higher doses and thus exerts pro‐oxidant effect. We demonstrate, for the first time, the dose‐dependent effects of curcumin in isoprenaline‐induced model of myocardial necrosis in rats. The animals were assigned to control, isoprenaline and three curcumin treatment groups. Curcumin (100, 200, and 400 mg/kg) and vehicle (dimethyl sulfoxide) were administrated orally for 15 days and isoprenaline (85 mg/kg, s.c.) was given to curcumin treated and isoprenaline group on 13th and 14th day, respectively. Thereafter, on 15th day, the animals were sacrificed for biochemical analysis along with histopathological and ultrastructural examination. There was an increase in glutathione, superoxide dismutase (SOD), creatine kinase‐MB (CK‐MB) and lactate dehydrogenase (LDH) levels, decrease in thiobarbituric acid reactive substances (TBARS), and preservation of myocardial architecture in the curcumin (100 and 200 mg/kg) treated groups. However, at 400 mg/kg dose there was ineffectual protection against isoprenaline‐induced myocardial damage. Instead, there was significant lipid peroxidation as evident by increased levels of TBARS (93.87 ± 9.93, p < 0.0001) and decrease in CK‐MB (206.32 ± 13.54, p < 0.0001) and LDH (134.26 ± 9.13, p < 0.01) as compared to the two lower doses. Hence, it can be concluded that curcumin augments endogenous antioxidant system at lower doses but mediates ROS induction at higher concentration leading to myocardial damage. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic investigation into the interaction of a diazacyclam‐based macrocyclic copper(ii) complex with bovine serum albumin

Cyclam‐based ligands and their complexes are known to show antitumor activity. This study was undertaken to examine the interaction of a diazacyclam‐based macrocyclic copper(II) complex with bovine serum albumin (BSA) under physiological conditions. The interactions of different metal‐based drugs with blood proteins, especially those with serum albumin, may affect the concentration and deactivation of metal drugs, and thereby influence their availability and toxicity during chemotherapy. In this vein, several spectral methods including UV–vis absorption, fluorescence and circular dichroism (CD) spectroscopy techniques were used. Spectroscopic analysis of the fluorescence quenching confirmed that the Cu(II) complex quenched BSA fluorescence intensity by a dynamic mechanism. In order to further determine the quenching mechanism, an analysis of Stern–Volmer plots at various concentrations of BSA was carried out. It was found that the K_SV value increased with the BSA concentration. It was suggested that the fluorescence quenching process was a dynamic quenching rather than a static quenching mechanism. Based on Förster's theory, the average binding distance between the Cu(II) complex and BSA (r) was found to be 4.98 nm; as the binding distance was less than 8 nm, energy transfer from BSA to the Cu(II) complex had a high possibility of occurrence. Thermodynamic parameters (positive ΔH and ΔS values) and measurement of competitive fluorescence with 1‐anilinonaphthalene‐8‐sulphonic acid (1,8‐ANS) indicated that hydrophobic interaction plays a major role in the Cu(II) complex interaction with BSA. A Job's plot of the results confirmed that there was one binding site in BSA for the Cu(II) complex (1:1 stoichiometry). The site marker competitive experiment confirmed that the Cu(II) complex was located in site I (subdomain IIA) of BSA. Finally, CD data indicated that interaction of the Cu(II) complex with BSA caused a small increase in the α‐helical content. Copyright © 2016 John Wiley & Sons, Ltd.     

DNA binding and oxidative DNA damage induced by a quercetin copper(II) complex: potential mechanism of its antitumor properties

The interaction of a quercetin copper(II) complex with DNA was investigated using UV–vis spectra, fluorescence measurement, viscosity measurement, agarose gel electrophoresis, and thiobarbituric acid reactive substances assay. The results indicate that the quercetin copper(II) complex can promote the cleavage of plasmid DNA, producing single and double DNA strand breaks, and intercalate into the stacked base pairs of DNA. Moreover, the complex can induce oxidative DNA damage involving generation of reactive oxygen species such as H₂O₂ and Cu(I)OOH. In addition, the cytotoxicity experiments carried out with A549 cells confirmed its apoptosis-inducing activity. And we also demonstrate that the levels of survivin protein expression in A549 cells decreased, and that relative activity of caspase-3 increased significantly after treatment with the complex. So our results suggest that the antitumor mechanism of the quercetin copper(II) complex involves not only its oxidative DNA damage with generation of reactive oxygen species but also its specific interaction with DNA. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Unprecedented formation of binuclear copper(II) complex with a perylene derived ligand by the oxidative reaction

A new perylene-pendent tridentate ligand, N-(3-perylenylmethyl)-N,N-bis(2-pyridylmethyl)amine (perbpa) 1 and its Cu(II) complex, [Cu(perbpa)Cl₂] (2) were prepared and structurally characterized by the X-ray diffraction method. In the packing structure of ligand 1, perylene groups were aggregated to form a π-π stacked layer of dimerized pelylene moieties similar to the packing of pristine perylene. This result suggests both that the π-π interactions among the perylene moieties predominate for the arrangement of perbpa molecules in the crystal and that this ligand is a good candidate for constructing electron conducting path. A complex 2 was prepared from the ligand 1 and a copper(II) chloride dehydrate. Complex 2 had a mononuclear and 5-coordinate distorted square pyramidal structure with a perbpa and two coordinated chloride ions. The chemical oxidation of 2 by iodine resulted in the unprecedented binuclear Cu(II) species, [Cu₂(μ-Cl)₂(perbpa)₂](I₃)₂, 3·(I₃)₂. An X-ray crystal structure analysis of 3·(I₃)₂ revealed the binuclear structure bridged by the chloride ions. A temperature dependent magnetic susceptibility measurement of 3 showed a weak ferromagnetic exchange interaction with S = 1 ground state, g = 2.12 and J = +1.17 cm⁻¹, based on H = −2JS₁ · S₂. The UV-Vis absorption and the EPR spectra of 3 showed that the perylene groups are not oxidized. These results indicate a couple of Cu(II) constructed S = 1 ground state with intermolecular ferromagnetic interaction. The electrochemical study suggested that the crystallization of 3·(I₃)₂ was initiated by the oxidation of the N,N-bis-(2-pyridylmethyl)amino (bpa) groups of 2 by I₂.     

An oxamato bridged trinuclear copper(II) complex: Synthesis, crystal structure, reactivity, DNA binding study and magnetic properties

A linear tri-nuclear oxamato bridged copper(II) complex [Cu₃(pba)(dpa)₂(H₂O)(ClO₄)](ClO₄)·H₂O (1) (pbaH₄ = 1,3-propanediylbis(oxamic acid), dpa = 2,2′-dipyridylamine) was isolated from the reaction mixture of Na₂[Cu(pba)]·3H₂O, copper perchlorate hexahydrate and dipyridylamine in methanol. On reaction with dpa or DMF in basic medium (KOH) at ambient temperature complex 1 changed to dinuclear oxalate bridged copper(II) derivatives, [Cu₂(μ-C₂O₄)(dpa)₄](ClO₄)₂ (2) and [Cu₂(μ-C₂O₄)(dpa)₂(DMF)₂](ClO₄)₂ (3), respectively. The complexes 1, 2 and 3 have been characterized by physicochemical and spectroscopic tools, and also by the X-ray single crystal analysis. The hydrolysis of 1 in basic medium and thermo-gravimetric analysis has been studied. Absorption and emission spectral studies showed that complex 1 interacts with calf thymus-DNA (CT-DNA) with a binding constant (K_b) of 4.01 × 10⁴ M⁻¹ and linear Stern-Volmer quenching constant (K_sv) of 6.9 × 10⁴. A strong anti-ferromagnetic interaction with a coupling constant J_CuCu of 320.0 ± 0.3 cm⁻¹ was observed from the study of magnetic behavior of complex 1 in the temperature range of 2-300 K. Electrochemical equivalency of three copper(II) ions in 1 was identified by getting only one quasi reversible cyclic voltammogram.     

Hydrolysis of dinucleoside phosphates - mRNA 5' cap analogues - promoted by a binuclear copper(II)-zinc(II) complex

The hydrolysis of a 5' cap analogue, diadenosinyl-5',5'-triphosphate (ApppA), and two dinucleoside monophosphates: adenylyl(3',5')adenosine (ApA) and uridylyl(3',5')uridine (UpU) promoted by an imidazolate-bridged heterobinuclear copper(II)-zinc(II) complex, Cu(II)-diethylenetriamino-micro-imidazolato-Zn(II)- tris(aminoethyl)amine trisperchlorate (denoted as Cu,Zn-complex in the followings) has been investigated. Kinetic measurements were performed in order to explore the effects of pH, the total concentration of the Cu,Zn-complex and temperature on the cleavage rate. The catalytic activity of the Cu,Zn-complex was quantified by pseudo-first-order rate constants obtained in the excess of the cleaving agent. The results show that the Cu,Zn-complex and its deprotonated forms have phosphoesterase activity and with ApppA the metal complex promoted cleavage takes place selectively within the triphosphate bridge.     

A new Schiff base copper (II) complex derived from estrone and d-glucosamine: Synthesis,characterization and its interaction with DNA

A novel copper (II) complex of Schiff base prepared through condensation between 2-formyl-17-deoxyestrone and d-glucosamine was synthesized and characterized. Fluorescence spectroscopy was conducted to assess their binding ability with CT-DNA. The results showed that the copper (II) complex could bind to DNA with a weak intercalative mode. The interaction between the copper (II) complex and DNA was also investigated by gel electrophoresis. Interestingly, we found that the complex could cleave plasmid DNA (pUC19) to nicked and linear forms through an oxidative mechanism without the use of exogenous agents.     

The use of trans-4-cotininecarboxylate to construct a polymeric copper(II) azido complex: Hydro(solvo)thermal synthesis, structure and magnetic properties

A new pyridyl-carboxylate ligand, the anion of trans-4-cotininecarboxylic acid, HL, 1, has been used to prepare a new polymeric copper(II) complex, [CuLN₃]_2n, 2, based on a [CuLN₃]₂ dimeric building block. The single crystal structures of both 1 and 2 have been determined and 1 has been found to be in its zwitterionic configuration. The structure of 2 is a one-dimensional tape-like polymeric structure based on an end-on azido-bridged binuclear [Cu₂N₃]₂ backbone moiety. Magnetic studies reveal that 2 is close to paramagnetic from 2 to 300 K with a Curie constant of 1.094 emu K/mol, a Weiss temperature of 0.73 K and a corresponding μ_eff of 2.09 μ_B. A fit of χ_MT for 2 with S₁ = S₂ = ½, yields g = 2.441(6), J = −0.49(3) cm⁻¹, zJ = −0.38(2) cm⁻¹ and N(α) = 0.00053(12) emu/mol, a fit that indicates the presence of both very weak intramolecular intrachain antiferromagnetic exchange coupling within the one-dimensional tape-like chains and very weak interchain antiferromagnetic exchange coupling between these chains.     

Tautomeric changes in guanfacine and its copper(II) complex as revealed by X-ray crystallography; synthesis and EPR

Obtention and crystal structure of guanfacine (guaH) together with synthesis and crystal structure of its copper complex [Cu^II(gua)₂] · DMF were reported. The free molecule guaH exhibits one tautomeric form (B) in contrast to the form (A) which was reported in the Merck index. In the copper(II) complex, the anionic form gua⁻ exhibits the third tautomeric form (C). This complex is characterized by a CuN₂O₂ coordination. The EPR spectrum is in agreement with a Cu(II) ion in a square planar configuration.     

Binding of copper(II) ions to the polyproline II helices of PEVK modules of the giant elastic protein titin as revealed by ESI-MS, CD, and NMR

Titin, a family of giant elastic proteins, constitutes an elastic sarcomere matrix in striated muscle. In the I-band region of the sarcomere, the titin PEVK segment acts as a molecular spring to generate elasticity as well as sites of adhesion with parallel thin filaments. Previously, we reported that PEVK consists of tandem repeats of 28 residue modules and that the "polyproline II-coil" motif is the fundamental conformational motif of the PEVK module. In order to characterize the factors that may affect and alter the PPII-coil conformational motifs, we have initiated a systematic study of the interaction with divalent cations (Cu2+, Ca2+, Zn2+, and Ni2+) and a conformational profile of PEVK peptides (a representative 28-mer peptide PR: PEPPKEVVPEKKAPVAPPKKPEVPPVKV and its subfragments PR1: kvPEPPKEVVPE, PR2: VPEKKAPVAPPK, PR3: KPEVPPVKV). UV-Vis absorption difference spectra and CD spectra showed that Cu2+ bound to PR1 with high affinity (20 microM), while its binding to PR2 and PR3 as well as the binding of other cations to all four peptides were of lower affinity (>100 microM). Conformational studies by CD revealed that Cu2+ binding to PR1 resulted in a polyproline II to turn transition up to a 1:2 PR1/Cu2+ ratio and a coil to turn transition at higher Cu2+ concentration. ESI-MS provided the stoichiometry of PEVK peptide-Cu2+ complexes at both low and high ion strength, confirming the specific high affinity binding of Cu2+ to PR1 and PR. Furthermore, NMR and ESI-MS/MS fragmentation analysis elucidated the binding sites of the PEVK peptide-Cu2+ complexes at (-2)KVPE2, 8VPE10, 13APV15, and 22EVP24. A potential application of Cu2+ binding in peptide sequencing by mass spectrometry was also revealed. We conclude that Cu2+ binds and bends PEVK peptides to a beta-turn-like structure at specific sites. The specific targeting of Cu2+ towards PPII is likely to be of significant value in elucidating the roles of PPII in titin elasticity as well as in interactions of proline-rich proteins.     

Equilibrium and kinetic studies of ligand BMXD complexation with copper(II) and glycylglycine

Equilibrium studies of BMXD complexation with copper(II) and glycylglycine were performed by potentiometric and UV-visible titration. The equilibrium constants determined by potentiometry for the ternary system are: [LCu₂P³⁺]/[LCu₂⁴⁺][P⁻]=8.11(3), [LCu₂HP⁴⁺]/[LCu₂P³⁺][H⁺]=5.39(2), [LCu₂H₋₁P²⁺][H⁺]/[LCu₂P³⁺]=−6.33(2), [LCu₂(OH)H₋₁P⁺][H⁺]/[LCu₂H₋₁P²⁺]=−8.20(1) and [LCu₂(OH)₂HH₋₁P][H⁺]/[LCu₂(OH)H₋₁P⁻¹]=−10.33(3), which are in good agreement with the values determined by UV-visible titration. The species formed were confirmed by electrospray mass spectrometry. The association constants, determined by kinetic studies, for the association of the second molecule of glycylglycine with the LCu₂P complex, for two ionic media, are 1.29 (KCl) and 1.27 (KNO₃). These are in good agreement with the values determined by thermodynamic measurements 1.41 (KCl) and 1.26 (KNO₃).     

Transition metal complexes of a tridentate ligand bearing two pendant pyridine bases: The X-ray crystal structure of pentacoordinate copper(II) complex

The synthesis of a tridentate ligand, N,N′-bis(2-pyridinyl)-2,6-pyridinedicarboxamide [H₂L] is described together with its manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes which were characterized based on elemental analysis, conductivity measurements, spectral, magnetic and thermal studies. The IR spectral studies of all the complexes exhibit a similar feature about the ligating nature of the ligand to the metal ions and revealed that the ligand has coordinated through the nitrogens of the deprotonated amides and the central pyridine. The two pendant pyridine nitrogens in all the complexes are protonated and involved in hydrogen bonding with the oxygens of amide groups. This observation is confirmed by the single-crystal X-ray crystallographic studies of copper(II) complex. The geometry around the copper atom can be viewed as a distorted trigonal bipyramid with τ = 0.74 [structural parameter, τ = (β − α)/60; where α and β are the two basal angles in a five coordinate complex]. The electrochemical study of the copper(II) complex shows single quasi-reversible redox peak [Cu(II) ↔ Cu(I)]. The EPR spectrum of copper(II) complex exhibits rhombic pattern [g₁ = 2.0276, g₂ = 2.0926 and g₃ = 2.18].