Biophysical,spectroscopic vis-à-vis biochemical investigation on DNA–metalloprotein interaction: a model study involving cobalt(II)-glutathione complex

Abstract  The interaction of cobalt(II)-glutathione (CoGSH) with deoxyribonucleic acid (DNA) has been studied by UV–vis, fluorescence, circular dichroism (CD), thin-film infrared (IR), and viscometric techniques. From the UV-spectroscopic method, binding constant (K _b) was determined and was found to be 2.3 × 10⁶ M⁻¹. In fluorimetric analysis, the quenching of fluorescence intensity of DNA bound to ethidium bromide (EB) was investigated. The Stern–Volmer quenching constant (K _sv) was also estimated from this study and was found to be 2.8 × 10⁶ M⁻¹at 37 °C. The solution CD spectra of DNA and DNA–CoGSH indicate that in each case, DNA exists in the ‘B’ conformation and suggested an intercalative binding mode. Thin-film IR data also reveal that DNA attains the ‘B’ family of conformations after interaction with CoGSH complex. The increase in DNA viscosity in the presence of CoGSH complexes is attributed to the lengthening of DNA helix due to intercalation. Graphical Abstract  The spectrophotometric, CD, thin film IR, viscometric and fluorimetric studies on the interaction of CoGSH with DNA indicated an intercalative binding mode with the retention of ‘B’ conformation of DNA.      

Simple and sensitive fluorometric sensing of malachite green with native double-stranded calf thymus DNA as sensing material

A novel fluorometric sensing of malachite green is proposed in this paper. The native double-stranded calf thymus DNA was used as sensing material. In the presence of native double-stranded calf thymus DNA, malachite green could interact with the DNA, which resulted in a strong fluorescence emission. The fluorescent intensity was linear with malachite green concentration in the range of 4.0 × 10⁻¹⁰ − 1.8 × 10⁻⁷ g ml⁻¹ and the limit of detection was 2.0 × 10⁻¹⁰ g ml⁻¹. Before fluorescence measurement, the only required operation is the mixing of two solutions. So, this method is rather simple and rapid. The method is very safe for the analyst. Furthermore, the mechanism for fluorescence enhancing of native double-stranded calf thymus DNA on MG was proposed based on a series of experiments. The results suggest that the interaction between MG and calf thymus DNA is intercalation in nature.     

Applying Cu(II) complexes assisted by water-soluble porphyrin to DNA binding and selective anticancer activities

Cancer is one of the killers endangering human health and its treatment has always been a focus of the medical community. For anticancer drugs, water-soluble porphyrin and Schiff bases have always been of interest. We report here three Cu(II)-based complexes functionalized by water-soluble cationic porphyrin and hydrazine Schiff base, which were prepared and evaluated for their biological activity. The three Cu(II) complexes all exhibited potent binding affinity to calf thymus DNA, the strongest interaction being between CuP2 and DNA. We studied the cytotoxicity of the complexes and ligands against different types of cancer cells (A549, H-1975, HepG2 and T47D), results showing the ligands are less cytotoxic; therefore, the anticancer activity of the complexes is improved by complexation. Furthermore, the cytotoxicity of ligands and complexes was also evaluated against the normal cell line Hs 578Bst, complexes showing more negligible cytotoxicity than ligand. Moreover, the cellular uptake of these Cu(II) complexes was investigated using the extraction method and results suggested that CuP2 exhibits the best cellular uptake towards H-1975 cells. Interestingly, fluorescence microscopy experiments and flow cytometric analysis (cell cycle) were used to further investigate the potent anticancer activities.     

Theoretical study on the DNA interaction properties of copper(II) complexes

Theoretical studies on DNA-cleavage and DNA-binding properties of a series of Cu(II) complexes [Cu(bimda)(diimine)] 1–5 have been carried out by density functional theory (DFT). The optimized structures of Cu(II) complexes were docked into parallel, antiparallel and mixed G-quadruplexes, with which the binding energies of complexes 1–5 were obtained. The cytotoxicities of these complexes can be predicted preliminarily by the binding energies. To explore the energy changes of Cu(II) complexes in duplex DNA, the optimized structures of these complexes were docked into the duplex DNA, and the obtained docking models were further optimized using QM/MM method. The DNA-cleavage abilities of complexes 1–5 can be predicted accurately and explained reasonably by the computed intra-molecular reorganization energies of these complexes. This work reported here has implications for the understanding of the interaction Cu(II) complexes with the DNA, which might be helpful for the future directing the design of novel anticancer Cu(II) complexes.     

Synthesis,characterization, and DNA binding of two copper(II) complexes as DNA fluorescent probes

[Cu(DAPT)₂Cl]Cl·H₂O and [Cu(DBM)(DAPT)Cl] [DAPT = 2,4-diamine-6-(pyrazin-2-yl)-1,3,5-triazine] were synthesized and characterized by IR and UV spectroscopy, elemental analysis, TG–DTA, molar conductivity, and LC–MS. The interaction with calf thymus DNA (ct-DNA) of the two complexes has been studied using UV spectra, fluorescent spectra, cyclic voltammetry, and viscosity measurements. The complexes interact with ct-DNA through classical intercalation. Fluorescence intensity changes of 1 and 2 in the absence and presence of ct-DNA have been investigated for quantitative determination of ct-DNA with the limit of detection of 3.8 and 7.7 ng mL^?1, respectively. From the result, the two complexes are potentially sensitive DNA fluorescent probes.     

Synthesis and antitumor activity of DNA binding cationic porphyrin-platinum(II) complexes

A new series of DNA binding 5,10,15-tri(N-methyl-4-pyridiniumyl)porphyrin (TrisMPyP)-platinum(II) conjugates was synthesized, in which different spacer ligands were used for appropriate coordination to platinum(II) complexes. Compound 9b exhibited in vivo antitumor activity (T/C%, 294) superior to cisplatin (T/C%, 184) against the leukemia L1210 cell line.     

二(2-苯并咪唑亚甲基)胺合钴（II）配合物与DNA作用方式的研究

本文合成并表征了二(2-苯并咪唑亚甲基)胺合钴（II）配合物。利用荧光、透析、粘度、凝胶电泳等手段，研究了其与DNA的结合机制。在20 ℃，5 mmol/L Tris-HCl (pH 7.1)和50 mmol/L NaCl缓冲溶液中，结合常数为1.96×10⁴ mol/L。应用多电解质理论对实验数据进行定量分析，结果表明该配合物与DNA主要是静电作用。粘度实验表明配合物与DNA作用时，并没有明显地改变DNA溶液的粘度，说明配合物并非以插入方式，而是以一种较微弱方式与DNA结合。同时，凝胶电泳实验证明，该配合物只能以静电作用与DNA结合，并不能产生切割作用。所有以上实验结果说明，该配合物主要是通过正负电荷间的静电作用与DNA结合。     

Phosphoester binding,DNA binding,DNA cleavage and in vitro cytotoxicity studies of simple heteroleptic copper(II) complexes with bidentate ligands

Abstract

Two mononuclear heteroleptic copper complexes, [Cu(±trans-dach)(bpy)](ClO₄)₂ 1a and [Cu(±trans-dach)(phen)](ClO₄)₂ 2a [dach?=?1,2-diaminocyclohexane, bpy?=?2,2′-bipyridine and phen?=?1,10-phenanthroline], were synthesized and analyzed by CHN analysis, electronic absorption, FT-IR spectroscopy, EPR, and SXRD. The molecular structures of 1a and 2a showed octahedral geometry around Cu(II). Both complexes interacted with phosphoesters and DNA. Their binding affinities with diphenylphosphate, di n-butylphosphate, trimethylphosphate, and triphenylphosphate were studied by UV–vis spectroscopy. For understanding the stereochemical role of dach ligand toward DNA interaction, enantiopure DACH complexes [Cu(R,R-trans-dach(bpy)](ClO₄)₂ 1b, [Cu(S,S-trans-dach)(bpy)](ClO₄)₂ 1c, [Cu(cis-dach)(bpy)](ClO₄)₂ 1d, [Cu(R,R-trans-dach)(phen)](ClO₄)₂ 2b, [Cu(S,S-trans-dach)(phen)](ClO₄)₂ 2c, and [Cu(cis-dach)(phen)](ClO₄)₂ 2d were synthesized and analyzed. All complexes interacted with calf thymus-DNA (CT-DNA) as studied by UV–vis spectroscopy. The nature of binding to CT-DNA was groove/electrostatic as supported by circular dichroism, cyclic voltammetry, and docking studies. Complexes were able to cleave plasmid DNA at 12.5 µM (1a–d) and 6 µM (2a–d), where 2d showed 64% Form II and 36% Form III. The in vitro cytotoxic studies of two different cancer cell lines showed inhibition with low IC₅₀ value in comparison to reference control (cisplatin). These complexes are efficient in inducing apoptosis in cancer cells, making them viable for potent anticancer activity.     

A comparative study on the interaction with calf thymus DNA of a Ni(II) complex of the anticancer drug adriamycin and a Ni(II) complex of sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulphonate

The anthracycline drug adriamycin and its metal complexes are efficient in treating several forms of human cancers with recognized antineoplastic activity attributed to strong interactions with DNA within the target cells. The hydroxy-9,10-anthraquinone unit present in the molecule controls and regulates drug action. Metal ions when linked to adriamycin help to reduce the generation of radicals responsible for toxic side effects. A complex of adriamycin with Ni(II) was prepared and its physicochemical characteristics and DNA-binding ability were compared to a Ni(II) complex of sodium-1,4-dihydroxy-9,10-anthraquinone-2-sulphonate (NaLH₂), an analog of adriamycin. Interactions with calf thymus DNA of both complexes were studied by UV-Vis and fluorescence spectroscopy. Binding parameters determined for both complexes agree with each other. Binding of the Ni(II)-adriamycin complex to DNA was five to eight times stronger than for the Ni(II) complex of the hydroxy-9,10-anthraquinone analog, Na₂[Ni(NaLH)₂Cl₂]?·?2H₂O, i.e., Ni(NaLH)₂. The difference in binding was attributed to the presence of sugar units in adriamycin and to its absence in NaLH₂. Although the Ni(II) complex of the hydroxy-9,10-anthraquinone analog of adriamycin [Ni(NaLH)₂] was slightly weaker in binding DNA than the drug and its Ni(II) complex, a much lower cost of the former justifies its consideration as a substitute for the anthracycline drugs that are now in use.     

Synthesis,spectroscopic, thermal properties,Calf thymus DNA binding and quantum chemical studies of M(II) complexes

A new series of transition metal complexes of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) were prepared from the ligand of 5‐(4‐benzenesulfonic acid azo)‐2‐thioxo‐4‐thiazolidinone (H₂L). The M(II) complexes were structurally elucidated by elemental analysis, infrared spectra, spectral studies, thermal analysis, magnetic measurements and X‐ray diffraction analysis. Elemental analysis and IR result suggested the ligand was bonded to the metal ions in monobasic/neutral bidentate through the nitrogen atom of the hydrazone group and oxygen atom of carbonyl group. The bond length, bond angle, HOMO, LUMO and quantum chemical parameters were calculated to confirm the geometry of the ligand and the M(II) complexes. In vitro antimicrobial behavior of ligand (H₂L) and its M(II) complexes (1‐5) was screened with targeted bacterial and fungal strains. Spectroscopic (UV‐vis) technique was employed in order to study the binding mode and binding strength of the ligand (H₂L) and its M(II) complexes to Calf thymus DNA (CT‐DNA). Intercalation is the most possible mode of interaction of the ligand (H₂L) and its M(II) complexes with CT‐DNA and the determined binding constants. Molecular docking was used to predict the binding between the starts (4‐aminobenzenesulfonic acid (start 1) and 2‐thioxo‐4‐thiazolidinone (start 2)) and tautomers (A‐C) of ligand (H₂L) with the receptors of prostate cancer mutant (PDB code: 2Q7K) and breast cancer mutant (PDB code: 3HB5).     

Synthesis,structure elucidation,DNA binding and molecular docking studies of novel copper(II) complexes of two 1,3,4-thiadiazolethiosemicarbazone derivatives

Four novel Cu(II) chelates were synthesized by reacting hydrated CuCl₂ and Cu(CH₃COO)₂ with two derivatives of 1,3,4-thiadiazolethiosemicarbazone. The structures and geometries of the synthesized complexes were deduced applying the alternative analytical and spectral tools confirming the complexes to have the formulae [(LH)Cu(Cl)]•0.5H₂O, [(LH)Cu(OAc)(H₂O)₂]•0.5H₂O, [(LCl)Cu(Cl)(H₂O)₂]•H₂O and [(LCl)Cu(OAc)]; where LH and LCl are phenyl and p-chlorophenyl derivatives of 1,3,4-thiadiazolethiosemicarbazone ligands, respectively (deprotonated form). IR spectral data confirmed the coordination of the ligands to the copper center as monobasic tridentate in the thiol form. Thermal analysis, UV–Vis spectra and magnetic moment assured the geometry around the copper center to be square planar, trigonal bipyramid and octahedral which have been confirmed by the computational studies. The two ligand derivatives and their copper complexes were applied to evaluate their binding modes with SS-DNA via UV–Vis spectral titration and viscosity measurements. The DNA-binding constant (k_b) values of the investigated derivatives were calculated and compared with ethidium bromide in order to assess their mode of binding with DNA. Moreover, docking study of these complexes was carried out to recognize the drug–DNA interactions and to calculate their binding energies.     

Coordination behavior of 3,4-bis(2-pyridylmethylthio)toluene with copper(II) ions: Synthesis,structural characterization and reactivity,and DNA binding study of the dinuclear copper(II) complex

On reaction of different copper(II) salts with 3,4-bis(2-pyridylmethylthio)toluene (L) having neutral tetradentate NSSN donor set in different chemical environments, two mononuclear copper(II), one dinuclear copper(I) and one dinuclear copper(II) complexes, formulated as [Cu^II(L)(H₂O)₂](NO₃)₂ (1), [Cu^II(pic)₂] (2), [Cu^I₂(L)₂](ClO₄)₂ (3) and [Cu^II₂(L)₂Cl₂](ClO₄)₂ (4), respectively, were isolated in pure form [where pic = picolinate]. All the complexes were characterized by physicochemical and spectroscopic methods. The product of the reactions are dependent on the counter anion of copper(II) salts used as reactant and on the reaction medium. Complexes 1 and 4 were obtained with nitrate and perchlorate copper(II) salts, respectively. On the other hand, C–S bond cleavage was observed in the reaction of L with copper(II) chloride to form in situ picolinic acid and complex 2. Dinuclear complexes 3 and 4 were separated out when copper(II) perchlorate was allowed to react with L in methanol and in acetonitrile, respectively, under aerobic condition. The X-ray diffraction analysis of the dinuclear complex 3 shows a highly distorted tetrahedral geometry about each copper ion. Complex 4 is converted to 3 in acetonitrile in presence of catechol. The spectral study of complex 4 with calf thymus DNA is indicative of a groove binding mode interaction.     

农药异丙威与小牛胸腺DNA的作用研究

在生理酸度条件下,采用紫外光谱和荧光光谱法研究异丙威与小牛胸腺DNA的作用表明:DNA对异丙威的荧光有明显的猝灭作用,属于静态猝灭方式;K4[Fe(CN)6]猝灭试验发现DNA对异丙威有明显的保护作用,离子强度的改变对异丙威和异丙威-DNA体系的荧光均无明显影响;异丙威的加入使DNA的熔点升高,并且异丙威能够竞争置换EB与DNA的结合位点。上述实验也表明,异丙威以嵌插方式作用于DNA的结合位点,有可能通过形成DNA加合物的形式造成DNA损伤,从而最终导致基因突变。     

钌卟啉[Ru(bpy)2(MPyTPP)Cl]+与DNA作用的研究

钌卟啉(ruthenated porphyrin)是通过卟啉环上的配位基团与多吡啶钌配位而得到的一类具有丰富的光谱和化学活性的大分子配合物[1～5]. 目前, 对钌卟啉的研究大都集中在其氧化还原、电化学以及催化氧化反应活性和超分子自组装等方面, 而对钌卟啉生物功能方面的研究则鲜为报道[6].     

Novel hydridotris(pyrazolyl)borate ruthenium(II) complexes containing the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane: Synthesis and evaluation of DNA binding properties

A series of half-sandwich ruthenium(II) complexes containing κ³(N,N,N)-hydridotris(pyrazolyl)borate (κ³(N,N,N)-Tp) and the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane (PTA) [RuX{κ³(N,N,N)-Tp}(PPh₃)_2−n(PTA)_n] (n = 2, X = Cl (1), n = 1, X = Cl (2), I (3), NCS (4), H (5)) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)L][PF₆] (L = NCMe (6), PTA (7)) have been synthesized. Complexes containing 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane(m-PTA) triflate [RuCl{κ³(N,N,N)-Tp}(m-PTA)₂][CF₃SO₃]₂ (8) and [RuX{κ³(N,N,N)-Tp}(PPh₃)(m-PTA)][CF₃SO₃] (X = Cl (9), H (10)) have been obtained by treatment, respectively, of complexes 1, 2 and 5 with methyl triflate. Single crystal X-ray diffraction analysis for complexes 1, 2 and 4 have been carried out. DNA binding properties by using a mobility shift assay and antimicrobial activity of selected complexes have been evaluated.     

DNA binding behaviour of mixed ligand vanadium(V) complex based on novel tridentate hydrazone and benzhydroxamic acid ligand systems

Novel tridentate ONO hydrazone ligand (HL) and the corresponding vanadium(V) complex, [VO(HL)(Benz)], based on the ligand and benzhydroxamic acid, were synthesized and characterized using UV–visible, Fourier transform infrared, NMR and mass spectral studies. In order to assess the binding efficacy of the synthesized complex with DNA, UV absorption spectral titrations, fluorescence displacement assays using ethidium bromide and acridine orange dyes, circular dichroism, viscosity and molecular docking studies were carried out. Based on the results obtained, it is evident that the complex shows significant intercalating ability almost comparable to that of the standard intercalator drug cisplatin. The binding affinity values for the [VO(HL)(Benz)] complex and cisplatin were found to be (3.84 ± 0.08) × 10⁴ M⁻¹ and (4.27 ± 0.012) × 10⁴ M⁻¹. In addition, the cytotoxicity of [VO(HL)(Benz)] was also assessed by MTT assay against the MCF‐7 cell line.     

环斑铂立体异构体与DNA的作用

研究了环斑铂的三种立体异构体（RSRR和SS）与小牛胸腺DNA的作用．用等温滴定量热法（ITC）测得三种化合物与DNA在298．15K时相互作用的摩尔烙变分别为-1．1,－7．2和16KJ·mol－1;差示扫描量热法（DSC）结果证实三种化合物与DNA作用使得其解链温度分别升高3．56,7.66和8．53K;而圆二色性波谱研究（CD）则显示出在室温时三种化合物与DNA间的作用使得其摩尔椭圆度发生了不等的微弱变化;核磁共振波谱法（NMR）结果告诉我们在室温时DNA的加入未使SS-环斑铂1H谱的化学位移及峰型出现明显的改变．综合热力学及波谱实验结果,对环斑钥立体异构体与DNA作用及结合的方式进行了讨论．