UV-visible Absorption Titration Research Articles

Synthesis, DNA binding of bis-naphthyl ferrocene derivatives and the application as new electroactive indicators for DNA biosensor

A series of bis-naphthyl ferrocene derivatives were synthesized and characterized. Based on the results obtained from UV–visible absorption titration and ethidium bromide (EB) displacement experiments, it was observed that the synthesized compounds exhibited a strong binding ability to dsDNA. In comparison to the viscosity curve of EB, the tested compounds demonstrated a bisintercalation binding mode when interacting with CT-DNA. Differential pulse voltammetry (DPV) was employed to assess the binding specificity of these indicators towards ssDNA and dsDNA. All tested indicators displayed more pronounced signal differences before and after hybridization between probe nucleic acids and target nucleic acids compared to Methylene Blue (MB). Among the evaluated compounds, compound 3j containing an ether chain showed superior performance as an indicator, making it suitable for constructing DNA-based biosensors. Under optimized conditions including probe ssDNA concentration and indicator concentration, this biosensor exhibited good sensitivity, reproducibility, stability, and selectivity. The limit of detection was calculated as 4.53 × 10−11 mol/L. Furthermore, when utilizing 3j as the indicator in serum samples, the biosensor achieved satisfactory recovery rates for detecting the BRCA1 gene.

ÜÇ YENİ BİS(AÇİLHİDRAZON) MONONÜKLEER GEÇIŞ METALI KOMPLEKSİ: SENTEZ, KARAKTERİZASYON VE DNA ETKİLEŞİM ÇALIŞMALARI

In recent years, studies on the design and synthesis of artificial nucleases with biological, structural and coordination properties have been increasing. With this study, mononuclear complex compounds were obtained with Cu(II), Ni(II) and Zn(II) transition metal ion salts of bis(acylhydrazone) ligand, which has the potential to show biological activity and has revolving atoms such as N and O in its structure. The characteristic structures of the obtained complex compounds were elucidated using various techniques such as FTIR, UV-Visible, 1H-NMR, TGA, elemental analysis and magnetic susceptibility. The DNA-binding activities of potential artificial metallonucleases, whose structures were elucidated, were investigated using the UV-visible absorption titration method. Additionally, their DNA-cleavge activities were analyzed using the agarose gel electrophoresis method. The DNA binding mode and cleavage mechanisms were determined as part of this study.. In line with the results obtained, it was determined that the binding mode between DNA and the complexes is a noncovalent interaction. It has been demonstrated that the compounds cleavage DNA both oxidatively and hydrolytically. It has been revealed that the radicals involved in DNA cleavage activity are H2O2, superoxide and hydroxyl radicals. It was revealed that the compound with the highest cleavage and bonding interaction was the Cu(II) complex, followed by Ni(II) and Zn(II) complexes.

Biomolecular interactions of 1,3-bis(2-arylimino)isoindolate-based palladium(II) complexes: Substitution kinetics, DNA/protein-binding, and molecular docking approaches

A series of 1,3-bis(2-arylimino)isoindoline Pd(II) complexes core viz.; Chlorido(1,3-bis(2-pyridylimino)isoindoline)palladium(II), Pd1, Chlorido(1,3-bis(4-methyl-2-pyridylimino)isoindoline)palladium(II), Pd2, Chlorido(1,3-bis(2-pyridylimino)benz(f)isoindoline)palladium(II), Pd3 and Chlorido(1,3-Bis(1-isoquinolylimino)isoindoline)palladium(II), Pd4 were synthesized, appropriately characterized and the crystal structure of Pd2 elucidated. The kinetics and mechanism of the substitution of the chloride ligand with thiourea ligands, Tu, Dmtu and Tmtu, from the complexes were investigated under pseudo-first-order conditions. The analyses were performed using stopped-flow analyzer or UV–visible spectrophotometer. The reactions proceeded through two consecutive steps for most complexes with exception of Pd4 showing only a single step. The substitution rates followed the order: Pd1>Pd2>Pd3>Pd4 due to varying degrees of steric influences and σ-/π-donations caused by the methylation and benzannulation on the cis-/trans-positions of the pyridyl rings of the BPI. The quenching of the fluorescence of CT-DNA/EB by the Pd(II) complexes suggests static quenching mechanism. The simulated docking of the complexes onto CT-DNA suggests they bind mainly in the minor grooves of DNA. The UV–Visible absorption titrations and quenching of tryptophan (Trp) fluorescence of BSA by the complexes depict reasonable interactions which occur mainly in the hydrophobic domains of the former. The order of strength of the interaction of the complexes with DNA or BSA is consistent with the rates of substitution kinetics.

Synthesis, crystal structure, DNA binding, molecular docking, DFT, Hirshfeld surface analysis, and cytotoxicity of copper (II) complex with malonamide and 2,9-dimethyl-1,10-phenanthroline

A new copper (II) complex, [Cu(dmp)(malon)(H2O)](NO3)2 where malon = malonamide and dmp = 2,9-dimethyl-1,10-phenanthroline, has been synthesized and characterized by elemental analysis, FT-IR, UV–Visible and single crystal XRD techniques. The complex was crystallized in a monoclinic system with space group P21/n. Single-crystal XRD studies have established that the copper (II) complex cation has a distorted square-pyramidal geometry, with Jahn-teller distortion occurring in the CuN2O3 core. The DFT/UB3LYP/LANL2DZ level of theory was used to optimize the structure of the present complex. The essential interactions within the crystal structure that lead to molecular packing were identified using Hirshfeld surface analysis. UV–Visible absorption titration, fluorescence, cyclic voltammetry, and viscometric titration studies were used to study the interactions of the present complex with calf thymus DNA (CT-DNA) and propose a partial intercalation binding mechanism. The complex demonstrated strong cytotoxic effects against the human hepatocellular carcinoma cell line (HepG2), and it was discovered to have effective antibacterial and antifungal properties. The efficient binding of the copper (II) complex was observed from molecular docking analysis.

DNA binding and cleavage studies of novel Betti base substituted quaternary Cu(II) and Zn(II) phthalocyanines

Betti base substituted zinc and copper phthalocyanines (ZnBBPc and CuBBPc) and their quaternized derivatives qZnBBPc and qCuBBPc were synthesized and characterized for the first time. The photophysical quantum yield (ΦF) and singlet oxygen quantum yield (ΦΔ) of ZnBBPc and qZnBBPc were measured using comparative and 1,3-diphenylisobenzofuran (DPBF) absorption titration methods respectively. The DNA binding activities of qZnBBPc and qCuBBPc against Calf-Thymus DNA (CT-DNA) were investigated using UV–visible absorption titrations, fluorescent displacement assays with classical intercalator ethidium bromide (EB) and minor groove binder Hoechst dye (HD), as well as by carrying out viscosity measurements in Tris-NaCl buffer (pH 7.4). The results indicated that qCuBBPc and qZnBBPc phthalocyanines showed strong affinities for CT-DNA through intercalation with binding constants (Kb) of the order of 105 M−1. The cleavage activities of compounds on supercoiled pBR322 plasmid DNA were determined by agarose gel electrophoresis in the presence and absence of light and additives. The compound qCuBBPc showed hydroxyl radical mediated oxidative cleavage, while the complex qZnBBPc exhibited singlet oxygen mediated photocleavage.

Synthesis and spectroscopic studies of diaza-8-crown-4-dinitrophenyl ethers

ABSTRACT The macrocycles 3,7-bis(3-nitrophenyl)-1,5,3,7-dioxadiazocane 1 and 3,7-bis(4-nitrophenyl)-1,5,3,7-dioxadiazocane 2 were synthesised by a one-pot reaction with substituted nitroanilines and formaldehyde under acidic conditions. The same reaction with 2-nitroaniline yielded N, N’-(oxybis(methylene))bis(2-nitroaniline) 3 rather than 3,7-bis(2-nitrophenyl)-1,5,3,7-dioxadiazocane 4. The yellow powders 1–3 were characterised by 1H/13C/15N NMR, FTIR and HRMS. The photophysical properties were studied by UV-visible absorption and steady-state fluorescence spectroscopy. Acid dissociation constants were determined by UV-visible absorption titrations in 1:1 (v/v) acetonitrile/water to be 0.80 and 3.1 for the meta- and para-substituted compounds 1 and 2, respectively. Compounds 1 and 2 were discovered to fluoresce in the solid-state, yellow and green, respectively, but not in solution. Density functional theory (DFT) calculations for 1–4 provide insight into the frontier molecular orbital energy levels. These compounds represent a new class of fluorescent heterocyclic building blocks for organic and supramolecular applications.

Synthesis, characterization and biological evaluation of novel benzimidazole derivatives

In search of achieving less toxic and more potent chemotherapeutics, three novel heterocyclic benzimidazole derivatives: 2-(1H-benzo[d]imidazol-2-yl)-4-chlorophenol (BM1), 4-chloro-2-(6-methyl-1H-benzo[d]imidazol-2-yl)phenol (BM2) and 4-chloro-2-(6-nitro-1H-benzo[d]imidazol-2-yl)phenol (BM3) with DNA-targeting properties, were synthesized and fully characterized by important physicochemical techniques. The DNA binding properties of the compounds were investigated by UV–Visible absorption titrations and thermal denaturation experiments. These molecules exhibited a good binding propensity to fish sperm DNA (FS-DNA), as evident from the high binding constants (Kb) values: 1.9 × 105, 1.39 × 105 and 1.8 × 104 M‒1 for BM1, BM2 and BM3, respectively. Thermal melting studies of DNA further validated the absorption titration results and best interaction was manifested by BM1 with ΔTm = 4.96 °C. The experimental DNA binding results were further validated theoretically by molecular docking study. It was confirmed that the molecules (BM1–BM3) bind to DNA via an intercalative and groove binding mode. The investigations showed a correlation between binding constants and energies obtained experimentally and through molecular docking, indicating a binding preference of benzimidazole derivatives with the minor groove of DNA. BM1 was the preferential candidate for DNA binding because of its flat structure, π–π interactions and less steric hindrance. To complement the DNA interaction, antimicrobial assays (antibacterial & antifungal) were performed. It was observed that compound BM2 showed promising activity against all bacterial strains (Micrococcus luteus, Staphylococcus aureus, Enterobacter aerogenes and Escherichia coli) and fungi (Aspergillus flavus, Aspergillus fumigatus and Fusarium solani), while rest of the compounds were active against selective strains. The MIC values of BM2 were found to be in the range of 12.5 ± 2.2–25 ± 1.5 µg/mL. Thus, the compound BM2 was found to be the effective DNA binding antimicrobial agent. Furthermore, the preliminary cytotoxic properties of synthesized compounds were evaluated by brine shrimps lethality assay to check their nontoxic nature towards healthy normal cells.Communicated by Ramaswamy H. Sarma

Fluorescence and Absorption Titrations of Bio-relevant Imidazole Based Organometallic Pd(II) Complexes with DNA: Synthesis, Characterization, DNA Interaction, Antimicrobial, Cytotoxic and Molecular Docking Studies

Organometallic Pd(II) complexes(4a–4f) of type Na[Pd(3n)Cl2]; where 3n = imidazole ligands (3a–3f), were synthesized. The complexes have been characterized by elemental analysis, thermogravimetric analysis, conductance measurement, mass spectrometry, UV–visible absorption spectroscopy, IR, 1H NMR, 13C APT NMR and Energy-dispersive X-ray spectroscopy. The compounds were screened for various biological activities such as nucleolytic, DNA binding, bacteriostatic (MIC) and cytotoxicity. DNA binding aptitude has been studied by UV–visible absorption titration, fluorescence spectroscopy, molecular modelling and viscosity measurement, which suggests Pd(II) complexes as DNA intercalating agents. Gibb’s free energy, enthalpy and entropy change parameters were evaluated for DNA–complex interaction by UV–visible absorption titration at different temperature, in which negative value of all the thermodynamic parameters suggests that the ligand–DNA complex is stabilized by hydrogen bonding and van der Waals forces. The gel electrophoresis of pUC19 DNA in presence of Pd(II) complexes showed the conversion of supercoiled DNA into open circular and linear form of DNA. Compounds were screened against different pathogens for evaluating their bacteriostatic activity in terms of MIC. In vitro cytotoxicity on Artemia cysts and in vivo cytotoxicity on S. pombe cells propose potent cytotoxic nature of Pd(II) complexes.

A PROMISING DNA GROOVE BINDER AND PHOTOCLEAVER BASED ON A DINUCLEAR RUTHENIUM(II) COMPLEX

A dinuclear ruthenium complex [Ru2(bpy)4(bip-phenol)](ClO4)4 {bpy = 2,2′-bipyridine, bip-phenol = 2,4-bis(1 H -imidazo[4,5- f ][1,10]phenanthrolin-2-yl) phenol} has been synthesized and characterized. The calf thymus (ct) DNA binding properties of the complex are investigated by means of DNA viscosity and optical spectroscopic techniques of UV-visible absorption and emission spectral titrations, steady-state emission quenching with ferrocyanide, ethidium bromide competitive binding, DNA thermal denaturation and reverse salt effect, together with molecular simulation technology. The results suggest that the complex is a promising DNA groove binder with a large DNA binding constant on 106 M−1 order of magnitude. The fluorescence of the complex manifests by 6.3-fold upon binding saturately to DNA. The complex is also demonstrated to be an efficient photocleaver of pBR 322 DNA.

Synthesis, characterization, and antitumor activity of three ternary dinuclear copper (II) complexes with a reduced Schiff base ligand and diimine coligands in vitro and in vivo

Three ternary copper (II) complexes containing 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), with the formulation [Cu2(NCL)2(H4PASP)]·4.5H2O (1–3) (where NCL=the diimine coligand, H4PASP=N,N′-(p-xylylene)di-2-aminosuccinic acid), were isolated and characterized. The binding of these complexes with calf thymus DNA was studied using UV–visible absorption titration, emission, and circular dichroism spectroscopy, among other methods. The changes in physicochemical properties that occurred upon binding of these complexes with DNA indicate that binding occurs primarily through intercalative interactions. Human tumor cell lines HeLa, PC3, and HepG2 were treated with the copper(II) complexes in vitro and cell survival rate was assessed by 3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay and crystal violet survival assay. Flow cytometry was performed on treated cells labeled with AnnexinV/Propidium Iodide staining to determine rates of apoptosis. Western blot was performed to determine the expression levels of the apoptotic markers p53, Bax, and Bcl-2. The complexes reduced cell viability and induced apoptosis in cells of human tumor cell lines in a dose-dependent manner. In addition, using a nude mouse xenograft model, we found that the three ternary copper (II) complexes inhibited human tumor cell growth in vivo. In conclusion, these novel synthetic copper complexes have profound antitumor effects on human tumor cells and are promising therapeutic agents for human tumors.

Polyethyleneimine anchored copper(II) complexes: Synthesis, characterization, in vitro DNA binding studies and cytotoxicity studies

The water soluble polyethyleneimine–copper(II) complexes, [Cu(phen)(L-tyr)BPEI]ClO4 (where phen=1,10-phenanthroline, L-tyr=L-tyrosine and BPEI=branched polyethyleneimine) with various degree of copper(II) complex units in the polymer chain were synthesized and characterized by elemental analysis and electronic, FT-IR, EPR spectroscopic techniques. The binding of these complexes with CT-DNA was studied using UV–visible absorption titration, thermal denaturation, emission, circular dichroism spectroscopy and cyclic voltammetric methods. The changes observed in the physicochemcial properties indicated that the binding between the polymer–copper complexes and DNA was mostly through electrostatic mode of binding. Among these complexes, the polymer–copper(II) complex with the highest degrees of copper(II) complex units (higher degrees of coordination) showed higher binding constant than those with lower copper(II) complex units (lower degrees of coordination) complexes. The complex with the highest number of metal centre bound strongly due to the cooperative binding effect. Therefore, anticancer study was carried out using this complex. The cytotoxic activity for this complex on MCF-7 breast cancer cell line was determined adopting MTT assay, acridine orange/ethidium bromide (AO/EB) staining and comet assay techniques, which revealed that the cells were committed to specific mode of cell death either apoptosis or necrosis.

The capture and stabilization of curcumin using hydrophobically modified polyacrylate aggregates and hydrogels.

Hydrophobically modified polyacrylates are shown to suppress the degradation of the medicinal pigment curcumin under physiological conditions. In aqueous solution, the 3% octadecyl randomly substituted polyacrylate, PAAC18, forms micelle-like aggregates at a concentration of <1 wt % and a hydrogel at >1 wt %. Under both conditions, PAAC18 shows a remarkable ability to suppress the degradation of curcumin at pH 7.4 and 37 °C such that its degradation half-life is increased by 1600-2000-fold. The suppression of degradation is attributed to hydrophobic interactions between curcumin and the octadecyl substituents of PAAC18 within the micelle-like aggregates and the hydrogel, as indicated by 2D NOESY (1)H NMR spectroscopy. UV-visible absorption titration results are consistent with the interaction of curcumin with five octadecyl substituents on average, which appears to substantially exclude water and greatly decrease the curcumin degradation rate. Dynamic light scattering and zeta potential measurements show the average hydrodynamic diameters of the PAAC18 aggregates to be 0.86-1.15 μm with a negative surface charge. In contrast to the octadecyl substitution, the 3% dodecyl randomly substituted polyacrylate, PAAC12, shows a negligible effect on slowing the degradation of curcumin, consistent with the dodecyl substituents being insufficiently long to capture curcumin in a adequately hydrophobic environment. These observations indicate the potential for PAAC18 to act as a model drug delivery system.

Experimental and theoretical investigations of the self-association of oxaliplatin.

Self-aggregation in water of anti-cancer agents such as oxaliplatin (1) or its palladium-containing parent (2) is suspected to be the main reason for the exceptional resistance of concentrated infusions of these complexes to hydrolysis; this hypothesis, i.e. the self-association of metal chelates, was investigated in a systematic manner by experimental and theoretical means. (1)H diffusion-ordered NMR spectroscopy (DOSY NMR) and UV-visible absorption titration were inconclusive as to the formation of a dimer of 1 in water or DMSO. Further isothermal titration calorimetry (ITC) methods allowed the accurate determination of the enthalpy of formation of only the homodimer [2]2 and putative heterodimer [1·2] together with an estimation of the formation constants, which indicate that dimer formation is not a spontaneous process in solution, whereas electrospray ESI mass spectroscopy tends to suggest the contrary in the gas phase. A dispersion-corrected DFT method, i.e. DFT-D (BLYP-D3), was used to model the aggregation in solution (COSMO) and to investigate the assisting role of London force in the cohesion of bimolecular aggregates. The concordance of experimental and theoretical thermodynamic parameters was judged reasonably even though the treatment of solvation by conventional continuum models does not account for specific interactions of the solute with molecules of solvent; nonetheless these results outline the importance of dispersion, a.k.a. London force. The role of the latter was further stressed by computing the affinities of 1 and 2 for the lipophilic cavity of cucurbit[7]uril in modeled water (COSMO-RS), which were preliminarily determined experimentally by ITC methods using pure water as solvent. From our investigations carried out in pure water the connection between the notorious chemical stability of “concentrated” infusions of 1 in aqueous media and the formation of oligomers remains unsettled.

Metal–polybenzimidazole complexes as a nonviral gene carrier: Effects of the DNA affinity on gene delivery

The metal complex-based carriers are emerging likely as a new type of gene-delivery systems prone to systematic structural alteration and chemical tailoring. In our work, the DNA affinity of metal complexes with polybenzimidazoles was found to be one of the determinants that can regulate expression of the transgenes. Here, the correlations between the DNA affinity and transfection efficacy were explored by characterizing gene-delivering properties of a series of Co2+- and Ca2+–polybenzimidazole complexes. The binding equilibrium constants (Kobs) of the divalent metal complexes to DNA, which is considered as a measure of the DNA affinity of metal complexes, were evaluated by isothermal titration calorimetry (ITC) and UV–visible absorption titration. The properties of DNA condensates formed with the metal complexes including sizes, ζ potential and morphology were observed to be altered with Kobs values. The monodispersed spherical condensates were found only for the Ca2+ complexes whose DNA affinity is weaker than that of the Co2+ complexes. However, the cell internalization examination indicated that cell uptake of the DNA condensates is independent of homogeneity in their sizes and morphology. The comparison of transgene expression showed that that the Ca2+ complex-mediated transfection has higher efficiency than the Co2+ complexes under the conditions tested, and the transfection efficacy cannot be correlated with the cell uptake of DNA condensates. Moreover, the Ca2+ complexes and their DNA condensates had lower cytotoxicity than the Co2+ complexes. Thus, the DNA affinity should be one of the factors to be capable of regulating the gene-delivering property of metal complexes.

Synthesis and structural studies of some copper-benzoate complexes

The reaction of CuCl2·2H2O with 3,5-diisopropylpyrazole (PziPr2H) in the presence of sodium parafluorobenzoate (Na-p-FBz) resulted in the formation of an oxo-chloro-bridged tetranuclear complex [Cu4(PziPr2H)4(μ-O)(μ-Cl)6] 1, whereas the reaction of Cu(NO3)2·3H2O with PziPr2H in the presence of different benzoates gave [Cu(PziPr2H)2(μ-OCH3)]2(NO3)2 2, [Cu(PziPr2H)3(NO3)(p-ClBz)]·CH3CN 3, [Cu(p-CH3Bz)2(PziPr2H)]2·2CH3CN 4, [Cu(p-OCH3Bz)2(CH3CN)]2·4CH3CN 5 and [Cu(p-CNBz)(CH3CN)]2 6. Single-crystal X-ray diffraction studies confirmed these formulations. DNA binding studies for these complexes were performed by means of UV-visible absorption titration and viscosity measurements. Gel electrophoresis studies showed that hydroxyl radicals are involved in DNA cleavage in the presence of the complexes.

Synthesis and Binding Properties of Arylethyne-Linked Porphyrin-Zinc Complexes for Organic Electronics Applications

Conjugated meso-alkynyl 5,15-dimesitylporphyrin metal complexes have been synthesized by Sonogashira coupling reaction in good yields. Alkynyl groups were chosen as a link at the meso positions in order to extend the pi-conjugated length of porphyrin rings. These synthesized porphyrin derivatives were characterized by 1H NMR spectroscopy and MALDI-TOF mass spectrometry. Moreover, UV-visible spectroscopy and fluorescence spectroscopy were also used to investigate their photophysical properties. It has been demonstrated that central metal ions as well as meso substituents on porphyrin rings affected the electronic absorption and emission spectra of the compounds. Spectroscopic results revealed that alkyne-linked porphyrin metal complexes showed higher pi-conjugation compared with porphyrin building blocks resulting in red shifts in both absorption and emission spectra. Coordination properties of synthesized porphyrins were preliminarily investigated by UV-visible absorption and fluorescence emission spectroscopic titration with pyridine as axial ligand. The formation of porphyrin-pyridine complexes resulted in significant red shifts in absorption spectra and decrease of fluorescence intensity in emission spectra. Moreover, the 1H NMR titration experiments suggested that central metal ions play an important role to coordinate with pyridine and the coordination of porphyrin zinc(II) complex with pyridine occur in a 1:1 ratio. From these spectroscopic results, alkyne-linked porphyrin metal complexes offer potential applications as materials for optical organic nanosensors.

PH luminescence switch, DNA binding and photocleavage, and cytotoxicity of a dinuclear ruthenium complex

The ground- and excited-state acid-base properties of [Ru2(bpy)4(H2bipt)]Cl4 1 {bpy = 2,2'-bipyridine, H2bipt = 2,5-bis[1,10]phenanthrolin[4,5-f]-imidazol-2-yl)thiophene} are investigated by emission and UV-visible absorption spectrophotometric pH titrations. The DNA binding properties of 1 are studied by means of DNA viscosity and optical spectroscopic techniques of UV-visible absorption and emission spectral titrations, steady-state emission quenching with ferrocyanide, ethidium bromide competitive binding, and DNA thermal denaturation as well as density functional theoretical calculations. The DNA photocleavage and singlet oxygen generation properties as well as in vitro anticancer activities against five cancer cell lines are studied as well. The results demonstrated that pH-induced luminescence switching, DNA binding, and anticancer properties of 1 are much improved with respect to those of the mononuclear analog [Ru(bpy)2(Htip)]Cl2 {Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}.

Synthesis, pH-induced “on–off–on” luminescence switching, and partially intercalative DNA-binding and DNA photocleavage properties of an β-d-allopyranoside-grafted ruthenium(II) complex

A new ruthenium(II) complex [Ru(Happip)3](ClO4)2 {Happip=2-(4-(β-d-allopyranoside)phenyl)imidazo[4,5-f][1,10]phenanthroline} was synthesized and characterized by elemental analysis, 1H NMR and matrix-assisted laser desorption ionization mass spectrometry. Calf-thymus DNA-binding properties were studied by DNA viscosity measurements and spectroscopic methods of UV-visible (UV-vis) absorption and luminescence titrations, steady-state emission quenching, DNA competitive binding with ethidium bromide and DNA melting experiments, indicating that the complex partially intercalates into the DNA with a large binding constant greater than 106M−1. The pH effects on UV-vis absorption and emission spectra of the complex were studied, demonstrating that the complex acted as an excellent pH-induced “on–off–on” luminescence switch with large on–off intensity ratios of 88 and 50 with one of luminescence on/off switching actions occurring in near-physiological pH region (pKa2=7.33). The DNA photocleaving properties of [Ru(Happip)3]2+ were also studied and compared with those of [Ru(bpy)2(Happip)]2+ and [Ru(bpy)2(Hpip)]2+{bpy=2,2′-bipyridine, Hpip=2-(4-phenyl)imidazo[4,5-f][1,10]phenanthroline}.

Dual Molecular Light Switches for pH and DNA Based on a Novel Ru(II) Complex. A Non-Intercalating Ru(II) Complex for DNA Molecular Light Switch

A new Ru(II) complex of [Ru(phen)(2)(Hcdpq)](ClO(4))(2) {phen = 1,10-phenanthroline, Hcdpq = 2-carboxyldipyrido[3,2-f:2',3'-h]quinoxaline} was synthesized and characterized. The spectrophotometric pH and calf thymus DNA (ct-DNA) titrations showed that the complex acted as a dual molecular light switch for pH and ct-DNA with emission enhancement factors of 17 and 26, respectively. It was shown to be capable of distinguishing ct-DNA from yeast RNA with this binding selectivity being superior to two well-known DNA molecular light switches of [Ru(bpy)(2)(dppz)](2+) {bpy =2,2'-bipyridine, and dppz = dipyrido-[3,2-a:2',3'-c]phenazine}and ethidium bromide. The complex bond to ct-DNA probably in groove mode with a binding constant of (4.67 ± 0.06) × 10(3) M(-1) in 5 mM Tris-HCl, 50 mM NaCl (pH = 7.10) buffer solution, as evidenced by UV-visible absorption and luminescence titrations, the dependence of DNA binding constants on NaCl concentrations, DNA competitive binding with ethidium bromide, and emission lifetime and viscosity measurements. To get insight into the light-switch mechanism, theoretical calculations were also performed by applying density functional theory (DFT) and time-dependent DFT.

Synthesis, crystal structures and DNA-binding properties of two new mononuclear copper(II) complexes

Two mononuclear copper(II) complexes, [Cu(bpy)2(CH3OH)](pic)2 (1) and [Cu(Me2bpy)2(H2O)](pic)2 (2) (bpy = 2,2′-bipyridine; Me2bpy = 4,4′-dimethyl-2,2′-bipyridine; Hpic = 2,4,6-trinitrophenol), were synthesized and characterized by elemental analyses, conductivity measurements, IR, UV–Visible spectroscopy and single crystal X-ray analyses. Both complexes 1 and 2 are mononuclear compounds. The copper atom in complex 1 is in a distorted square pyramidal geometry with a CuN4O chromophore as revealed from the τ value (0.25), while the Cu(II) ion in complex 2 displays a distorted trigonal bipyramidal stereochemistry with τ = 0.72. Hydrogen bonding interactions and π–π stacking interactions link the mononuclear copper complex 1 or 2 into a 1D infinite chain. The interactions of the two mononuclear complexes with herring sperm DNA (HS-DNA) have been studied by UV–visible absorption titration, fluorescence titration and ethidium bromide (EB) displacement experiments. The results suggest that both complexes might bind to DNA by intercalation.