Non-covalent DNA binding and cytotoxicity of certain mixed-ligand ruthenium(II) complexes of 2,2'-dipyridylamine and diimines

A series of mixed ligand ruthenium(II) complexes [Ru(Hdpa)2(diimine)](ClO4)2, 1-5 where Hdpa is 2,2'-dipyridylamine and diimine is 1,10-phenanthroline (phen) and a modified/extended 1,10-phenanthroline such as, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), 5-methyldipyrido[3,2-d:2',3'-f]quinoxaline (mdpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been isolated and characterized by analytical and spectral methods. The complex [Ru(Hdpa)2(phen)](PF6)2 1 has been structurally characterized and the coordination geometry around Ru(II) in it is described as distorted octahedral. 1H NMR spectral data reveal that 1-5 should have a C2 symmetry lying on the diimine plane due to the rapid flapping of the coordinated Hdpa ligands. The interaction of the complexes with calf thymus (CT) DNA has been explored by using absorption and emission spectral and viscometry and electrochemical techniques and the mode of DNA binding of the complexes has been proposed. The DNA binding affinity of the complexes decreases with decrease in number of planar aromatic rings in the co-ligand supporting the intercalation of the diimine co-ligands in between the DNA base pairs. Circular dichroic spectral studies reveal that the complexes 3-5 exhibit induced circular dichroism upon binding to CT DNA. Interestingly, upon interaction with CT DNA all the complexes show an increase in anodic current in the cyclic voltammograms suggesting that they are involved in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 5 alters the DNA superhelicity upon binding with supercoiled pBR322 DNA, which is consistent with its higher DNA binding affinity. Further, the cytotoxicities of the complexes against human cervical epidermoid carcinoma cell line (ME180) have been examined. Interestingly, 5 exhibits a cytotoxicity against ME180 higher than other complexes with potency approximately 8 times more than cisplatin for 24 h incubation but 4 times lower than cisplatin for 48 h incubation.     

Potassium Ion Induced Changes of Crystal Structure and Fluorescence of a Crown Ether

Luminescence properties and the x-ray structures of the fluorescent crown ether, 16-anthracen-ylmethyl-1,4,7,10,13-pentaoxa-16-aza-cyclooctadecane (CEA) and its complex with potassium hexafluorophosphate (CEAK) have been obtained. In the solid state CEAK gives a structured blue emission and CEA gives a broad structureless green emission. The differences in luminescence behavior are explained on the basis of crystal packing. X-ray analysis shows that every two adjacent anthracene moieties in CEA form a sandwich-like anti-parallel dimer; the green-structureless emission then arises from the π-π stack of the aromatic rings. In CEAK, disruption of the π-π stacking structure forces a large separation between the anthracene rings, which yields an anthracene monomer emission. Luminescence lifetime data support the assignments.     

Ternary dinuclear copper(II) complexes of a hydroxybenzamide ligand with diimine coligands: the 5,6-dmp ligand enhances DNA binding and cleavage and induces apoptosis

The dinuclear copper(II) complexes [Cu(2)(LH)(2)(diimine)(2)(ClO(4))(2)](ClO(4))(2) (1-4), where LH = 2-hydroxy-N-[2-(methylamino)ethyl]benzamide and diimine = 2,2'-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp; 3), and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq; 4), have been isolated and characterized. The X-ray crystal structure of complex 1 contains two copper(II) centers bridged by the phenolate moiety of the amide ligand. All of the complexes display a ligand-field band (630-655 nm) and the PhO(-)-to-Cu(II) ligand-to-metal charge-transfer band (405-420 nm) in solution. Absorption and emission spectral studies and viscosity measurements indicate that complex 4 interacts with calf thymus DNA more strongly than all of the other complexes through strong partial intercalation of the extended planar ring (dpq) with a DNA base stack. Interestingly, 3 exhibits a DNA binding affinity higher than 2, suggesting the involvement in hydrophobic interaction of coordinated 5,6-dmp with the DNA surface. In contrast to the increase in relative viscosities of DNA bound to 2-4, a decrease in viscosity of DNA bound to 1 is observed, indicating a shortening of the DNA chain length through formation of kinks or bends. All of the complexes exhibit an ability to cleave DNA (pUC19 DNA) in a 5% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an oxidant at 100 μM complex concentration, which varies as 4 > 2 > 1 > 3. The order of DNA the cleavage ability at 30 μM concentration in the presence ascorbic acid is 4 > 2 > 1 > 3, and, interestingly, 4 alone shows an ability to convert supercoiled DNA into nicked-coiled DNA even at 6 μM concentration, beyond which complete degradation is observed and the pathway of oxidative DNA cleavage involves hydroxyl radicals. In the presence of distamycin, all of the complexes, except 3, show decreased DNA cleavage activity, suggesting that the complexes prefer to bind in the DNA minor groove. All of the complexes exhibit prominent DNA cleavage even at very low concentrations (nM) in the presence of H(2)O(2) as an activator, with the order of cleavage efficiency being 3 > 2 > 4 > 1. Studies on the anticancer activity toward HEp-2 human larynx cell lines reveal that the ability of the complexes to kill the cancer cell lines varies as 3 > 4 > 2 > 1. Also, interestingly, the IC(50) value of 3 is lower than that of cisplatin, suggesting that the hydrophobicity of methyl groups on the 5 and 6 positions of the complex enhances the anticancer activity. The mode of cell death effected by the complex has been explored by using various biochemical techniques like comet assay, mitochondrial membrane potency, and Western blotting. The complex has been found to induce nuclear condensation and fragmentation in cell lines. Also, it triggers activation of caspases by releasing cytochrome c from mitochondria to cytosol, suggesting that it induces apoptosis in cells via the mitochondrial pathway.     

Toluidine blue adsorbed on alcohol dehydrogenase modified glassy carbon electrode for voltammetric determination of ethanol

A novel toluidine blue O (TBO) adsorbed alcohol dehydrogenase (ADH) biocomposite film have been prepared through simple adsorption technique with the help of electrostatic interaction between oppositely charged layers. Nafion (NF) coating was made on top of the biocomposite film modified glassy carbon electrode (GCE) to protect ADH from leaching. The fabricated ADH/TBO/NF biocomposite electrode remains highly stable in the pH range from 4 to 13. More facile electron transfer process occurs at ADH/TBO/NF biocomposite than at TBO/NF film, which is obvious from the six folds increase in k_s value. Maximum surface coverage concentration (Γ) of TBO is noticed at ADH/TBO/NF film, which is 82% higher than at TBO/NF and 15% higher than at ADH/TBO film modified GCEs. Electrochemical impedance spectroscopy studies reveal that ADH has been well immobilized in the biocomposite film. Scanning electron microscopy studies confirm the discriminate surface morphology of various components present in the biocomposite film. Cyclic voltammetry studies validate that ADH/TBO/NF biocomposite film exhibits excellent electrocatalytic activity for ethanol oxidation at low over potential (I_pa = −0.14 V). The same studies show biocomposite film possesses a good sensitivity of 7.91 μA M⁻¹ cm⁻² for ethanol determination. This above sensitivity value is 17.40% higher than the sensitivity obtained for TBO/NF film (6.74 μA M⁻¹ cm⁻²). Further, using differential pulse voltammetry, a sensitivity of 1.70 μA M⁻¹ cm⁻² has been achieved for ADH/TBO/NF biocomposite film.     

Fluorescence decay of indole in water

Summary The time-resolved fluorescence decay of indole in water does not provide evidence for a short-lifetime component (approximation 0.7 ns) as claimed in a recent report by Giorgianniet. al.     

Time resolved area normalized emission spectroscopy (TRANES) of DMABN confirms emission from two states

4-N, N-Dimethylaminobenzonitrile (DMABN) is a simple molecule which is extensively studied to understand the excited state kinetics and the origin of time dependent fluorescence in several organic solvents. We use a recently described method, time resolved area normalized emission spectroscopy (TRANES), for the analysis of wavelength dependent fluorescence of DMABN in acetonitrile and 1,4-dioxane. An isoemissive point was observed in the TRANES spectra, which confirms that there are only two emissive species A* and B*: A → A* ? B*.     

Novel synthesis of cyclobutanone derivatives via dimetalation of iminium ions with the TiCl4-trialkylamine reagent system

Iminium salts are generated in situ, react with TiCl4-trialkylamines, and diaryl ketones to produce 3,3-diaryl-cyclobutanones in moderate to good yields.     

Reversible Photobleaching of Fluorescein Conjugates in Air-Saturated Viscous Solutions: Singlet and Triplet State Quenching by Tryptophan

Abstract— Fluorescence recovery after photobleaching (FRAP) measurements on air-saturated aqueous solutions of fluorescein made viscous with glycerol or sucrose revealed a rapid component of fluorescence recovery with exponential time constants of 30-120 μs at viscosities of 15-300 cP. The rapid recovery process was not related to fluorophore translational diffusion and was insensitive to fluorophore concentration and the additive used to increase solution viscosity. At constant viscosity, the rate of reversible photobleaching recovery increased 2.5-fold in an O₂- vs N₂-saturated solution. The relative efficiency of reversible-to-irreversible photobleaching decreased with increasing photobleaching time and/or beam intensity. Reversible photobleaching was also detected for conjugates of fluorescein with dextrans and proteins in viscous media. In screening triplet state quenchers that might influence the reversible recovery, it was found that tryptophan enhanced the rate of reversible photobleaching recovery (two-fold increase at 8 m M ) and quenched the fluorescein singlet state (Stern-Volmer constant, 12 M ⁻¹). Analysis of fluorescein lifetimes and photobleaching parameters for a series of fluorescein-labeled proteins with different numbers of tryptophans were also carried out. The results provide evidence for an oxygen-dependent, reversible photobleaching mechanism for the fluorescein chromophore involving triplet state relaxation. The identification of reversible fluorescein photobleaching has important implications for FRAP measurements of rapid solute diffusion in biological systems.     

Hydroboration or hydrogenation of alkenes with CoCl2-NaBH4

The CoCl₂-NaBH₄ reagent hydroborates or hydrogenates alkenes under appropriate conditions.     

Kinetics and mechanism of oxidation of excited state Tris-(2,2′-bipyridyl)-ruthenium (II) complex by peroxomonosulfate,peroxodisulfate, and peroxodiphosphate

Excitation of Ru(bipy)₃²⁺ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)₃³⁺. The kinetics of this photochemical oxidation of Ru(bipy)₃²⁺ by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy)₃²⁺] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)₃²⁺ occurred but only when at 1.0 M [H⁺] and > 10^?2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)₃³⁺ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)₃²⁺] on the visible light induced oxidation of Ru(bipy)₃²⁺ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.