DNA Binding Ability Of Complexes Research Articles

Synthesis, spectroscopic characterization, DNA binding and DFT/PCM calculations of new Hydrogen-bonded charge transfer complex between 4-dimethylaminopyridine and Chloranilic acid

A charge transfer hydrogen bonded complex between the electron donor 4-dimethylaminopyridine (4-DMAP) and the electron acceptor Chloranilic acid (CLA) has been synthesized. The complex was studied experimentally and theoretically. A chemical reaction developed due to strong H-bonding, followed by proton transfer from the CLA to the 4-DMAP in acetonitrile medium (ACN). The straight line approach was employed to verify the 1:1 M ratio of the synthesised CT complex. The Benesi-Hildebrand equation was employed to compute the association constant (KCT), molar absorptivity (εCT), and other physical parameters. The synthesized complex was characterized spectroscopically. The presence of proton and charge transfers in the resultant complex was supported by 1H NMR, FT-IR and SEM-EDX investigations. The complex DNA binding ability of complex was investigated using electron absorption spectroscopy to reveal that the CT complex binding mechanism is intercalative and the intrinsic binding constant (Kb) value is 6.7 × 104 M−1. Theoretical calculations using DFT at the basis set CAM-B3LYP/6–31 G (d, p) were used to validate the experimental outcomes. The Mullikan atomic charges, geometrical parameters, and molecular electrostatic potential maps (MEPs) were computed and interpreted in conformity with the experimental results. In addition to e-transfer, the presence of an H-bond influences complex stability. There is good agreement between experimental results and DFT calculations.

Novel Cu(II) and Ni(II) complexes of nicotinamide based Mannich base: Synthesis, characterization, DFT calculation, DNA binding, molecular docking, antioxidant, antimicrobial activities

Nicotinamide incorporating Mannich base ligand (L), Cu(II) and Ni (II) complexes of [CuLCl2].2H2O (1) and [NiLCl2].2H2O (2) were synthesized and characterized by elemental analysis, FT-IR, UV–Visible, ESR and mass spectrometric methods. The square planar geometry of the complexes (1 and 2) were confirmed from analytical and diverse spectroscopic methods. Cyclic votammetric behaviors of complexes (1 and 2) were studied. The optimized geometry of L, complexes (1 and 2) were obtained by Density Functional Theory (DFT) calculations. DNA binding ability of complexes (1 and 2) were studied by electronic absorption and fluorescence techniques. Both the spectroscopic results show that complex 1 (9.64 × 104 M−1) has good binding affinity than complex 2 (6.07 × 104 M−1). The interaction of complexes (1 and 2) with CT-DNA was explored by Molecular docking analysis revealed that an efficient interaction of complexes (1 and 2) with the DNA. The results indicate that prepared complexes (1 and 2) have better binding ability with DNA double helix. Antioxidant activities of complexes (1 and 2) have studied by DPPH method and results suggest that prepared complexes (1 and 2) have better radical scavenging ability. Antimicrobial activities of ligand (L) and complexes (1 and 2) were tested against selected bacterial and fungal pathogens results shows that prepared compounds have higher antimicrobial activity against E. coli and A. niger antimicrobial species than others.

New heteroleptic Zn(II) complexes of thiosemicarbazone and diimine Co-Ligands: Structural analysis and their biological impacts

A thiosemicarbazone ligand HL appended new Zn(II) complexes [Zn(L)(bpy)] (1) and [Zn(L)(phen)] (2) (where, HL = {2-(3-bromo-5-chloro-2-hydroxybenzylidene)-N-phenylhydrazinecarbothioamide}, bpy = 2, 2′-bipyridine and phen = 1, 10-phenanthroline) have been synthesized and well characterized using conventional spectroscopic techniques viz.,1H NMR, FTIR and UV–Vis spectra. The crystal structures of complexes 1 and 2 have been determined by single crystal X-ray diffraction studies. Both the complex 1 (τ = 0.5) and 2 (τ = 0.37) possesses square based pyramidally distorted trigonal bipyramidal geometry. The ground state electronic structures of complexes 1 and 2 were investigated by DFT/B3LYP theoretical analysis using 6-311G (d,p) and LANL2DZ basis set level. The superior DNA binding ability of complex 2 has been evaluated using absorption and fluorescence spectral titration studies. Antimicrobial evaluation reveals that complex 2 endowed better screening than HL and complex 1 against both bacterial as well as fungal species. Consequently, complex 2 possesses highest antibacterial screening against Staphylococcus aureus (MIC = 3.0 ± 0.23 mM) and antifungal screening against Candida albicans (MIC = 6.0 ± 0.11 mM). Furthermore, the anticancer activity of the ligand HL, complexes 1 and 2 have been examined against the MCF-7 cell line (Human breast cancer cell line) using MTT assay. It is remarkable that complex 2 (12 ± 0.67 μM) show highest anticancer activity than HL (25.0 ± 0.91 μM) and complex 1 (15 ± 0.88 μM) due to the presence of phen ligand moiety.

DNA cleavage behavior of a new p-xylyl spaced bisCu(BPA)Cl2 complex: the steric effect of a bulky p-xylyl-derived spacer

The different DNA cleavage behaviors of 1,3- and 1,4-xylylene spaced bisCu(BPA)Cl2 complexes (BPA, bis(pyridyl-2-methyl)amine) display the positioning effect of xylylene spacers, implying the essential roles of spacers in the related cleavage (Y. Zhao et al., Chem.–Eur. J., 2006, 12, 6621–6629). Herein, a p-xylyl derivative (2,1,3-benzoxadiazole-4,7-dimethylene (BDDM)) was utilized as a bulky spacer to construct a new p-xylyl spaced bisCu(BPA)Cl2 complex 1 to explore the spacer's steric effect on the related DNA cleavage. Agarose gel electrophoresis demonstrated that complex 1 is able to convert the supercoiled plasmid pUC19 DNA into the nicked DNA and linear DNA in the presence of excessive reductant. This DNA cleavage behavior is different from that of simple p-xylylene spaced Cu2(pTPXA)Cl4, which mediates only the nicked DNA and random DNA fragments. The DNA binding ability of complex 1 is higher than that of Cu2(pTPXA)Cl4, while its DNA nicking ability is lower than that of Cu(BPA)Cl2, as well as the dinuclear Cu2(pTPXA)Cl4, which displays a high DNA nicking efficiency due to the internuclear synergy in activating O2 to damage DNA. The linear DNA formation induced by complex 1 is realized via a non-random double-stranded scission process. The temporal profiles of the nicked DNA and linear DNA in the presence of 8 μM complex 1 imply that the two sequential neighboring breaks in the complementary strands lead to the formation of linear DNA. With the DNA cleavage behavior in the presence of different reactive oxygen species (ROS) quenchers, the DNA-bound hydroxyl radical was proposed as the main ROS involved in the cleavage. Structural optimization of this complex disclosed its larger intramolecular Cu–Cu distance than Cu2(pTPXA)Cl4, which may disfavor the internuclear synergic O2 activation. It was also proposed that the bulky BDDM spacer favors the two spaced copper centers function solely to damage in situ the two adjacent deoxyriboses from complementary strands to form the linear DNA, and the specific DNA binding mode of complex 1 due to the BDDM spacer disfavors the DNA-bound ROS to abstract a proton from deoxyribose and results in a lower DNA cleavage efficiency than mononuclear Cu(BPA)Cl2. The non-random linear DNA mediating ability and the decreased DNA cleavage efficiency caused by the bulky internuclear spacer shown in the current study provides a new alternative to regulate the DNA cleavage behavior of polycopper artificial nucleases via spacer modification.

Oxidative DNA Cleavage Promoted by Multinuclear Copper Complexes: Activity Dependence on the Complex Structure

Polynuclear copper complexes with two or three Cu(BPA) (BPA, bis(2-pyridylmethyl)amine) motifs, [Cu2(mTPXA)Cl4]3 H2O (1), [Cu2(pTPXA)Cl4]3 H2O (2), [Cu3(HPTAB)Cl5]Cl3 H2O (3) (mTPXA = N,N,N',N'-tetra-(2-pyridylmethyl)-m-xylylene diamine; pTPXA = N,N, N',N'-tetra-(2-pyridylmethyl)-p-xylylenediamine; HPTAB = N,N,N',N',N'',N''-hexakis(2-pyridylmethyl)-1,3,5-tris-(aminomethyl)benzene) have been synthesized and characterized. The crystal structures of compounds 2 and 3 showed each Cu(BPA) motif had a 4+1 square-pyramidal coordination environment with one chloride occupying the apical position and three N atoms from the same BPA moiety together with another Cl atom forming the basal plane. Fluorescence and circular dichroism (CD) spectroscopy studies indicated that the DNA binding followed an order of 3>2>1 in the compounds. These complexes cleave plasmid pUC19 DNA by using an oxidative mechanism with mercaptopropionic acid (MPA) as the reductant under aerobic conditions. Dinuclear Cu2+ complexes 1 and 2 showed much higher cleavage efficiency than their mononuclear analogue [Cu(bpa)Cl2] at the same [Cu2+] concentration, suggesting a synergistic effect of the Cu2+ centers. Moreover, the meta-dicopper centers in complex 1 facilitated the formation of linear DNA. Interestingly, the additional copper center to the meta-dicopper motif in complex 3 decreased the cleavage efficacy of meta-dicopper motif in complex 1, although it is able to cleave DNA to the linear form at higher [Cu2+] concentrations. Therefore, the higher DNA binding ability of complex 3 did not lead to higher cleavage efficiency. These findings have been correlated to the DNA binding mode and the ability of the Cu2+ complexes to activate oxygen (O2). This work is a good example of the rational design of multinuclear Cu2+ artificial nuclease and the activity of which can be manipulated by the geometry and the number of metal centers.