Potential inhibitors of DNA topoisomerase II: ruthenium(II) poly-pyridyl and pyridyl-azine complexes

In search of new DNA probes a series of new mono and binuclear cationic complexes [RuH(CO)(PPh₃)₂(L)]⁺ and [RuH(CO)(PPh₃)₂(-μ-L)RuH(CO)(PPh₃)₂]²⁺ [L=pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)aldimine (pbp) and p-biphenylene-bis(picoline)aldimine (bbp)] have been synthesized. The reaction products were characterized by microanalyses, spectral (IR, UV-Vis, NMR and ESMS and FAB-MS) and electrochemical studies. Structure of the representative mononuclear complex [RuH(CO)(PPh₃)₂(paa)]BF₄ was crystallographically determined. The crystal packing in the complex [RuH(CO)(PPh₃)₂(paa)]BF₄ is stabilized by intermolecular π-π stacking resulting into a spiral network. Topoisomerase II inhibitory activity of the complexes and a few other related complexes [RuH(CO)(PPh₃)₂(L)]⁺ {L=2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and 2,3-bis(2-pyridyl)-pyrazine (bppz)} have been examined against filarial parasite Setaria cervi. Absorption titration experiments provided good support for DNA interaction and binding constants have also been calculated which were found in the range 1.2 × 10³-4.01 × 10⁴ M⁻¹.     

Snthesis and x-ray structure of an isomeric cyclophosphazene complex containing antimony(III)

The monosilylated acyclic phosphazene ligand Me₃SiNP(NMe₂)₂NP(NMe₂)₂ NH₂ (3) has been synthesized and characterized. The reaction of 3 with antimony triacetate, Sb(OOCMe₃), in refluxing toluene forms a cyclic phosphazene derivative, [N{P(NMe₂)₂NH}₂Sb(OOCMe)₂ (4), which is characterized by elemental analyses, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis. Complex 4 crystallizes in the form of a cis and trans isomeric chain in the solid state.     

Synergistic extraction and separation studies of uranium(VI)

A method is described for the extractive separation and spectrophotometric determination of uranium(VI) from an aqueous solution of pH 5.0–7.0 using benzoylacetone (bzac) and pyridine (py) dissolved in toluene as extractants. The extracted species are UO₂(bzac(₂·2py. The method provides separation of uranium(VI) from lanthanum(III), samarium(III), neodymium(III), cerium(III) and thorium(IV). The method is precise, accurate, fast and selective.     

Studies on differential sensing of dopamine at the surface of chemically sensitized ormosil-modified electrodes

We report herein the preparation of few chemically sensitized organically modified sol–gel glass (ormosil) films and sensing of dopamine at the surface of the modified electrodes derived from these films. The chemical sensitization in ormosil-modified electrodes is introduced by incorporating: (a) potassium ferricyanide and (b) either Nafion, or dibenzo-18-crown-6 or in situ generated Prussian blue from potassium ferricyanide. Electrochemical sensing of dopamine on the surfaces of these modified electrodes have been investigated and found that: (i) the presence of dibenzo-18-crown-6 facilitate the magnitude of dopamine sensing, (ii) conversion of potassium ferricyanide into Prussian blue also enhances the magnitude of dopamine sensing as compared to that of control and Nafion sensitized modified electrodes, (iii) both dibenzo-18-crown-6 and Nafion sensitized ormosil-modified electrodes are found selective to dopamine in the presence of ascorbic acid present under physiological concentration range. These finding again directed our attention to investigate the sensing of dopamine: (a) on dibenzo-18-crown-6 incorporated within Prussian blue sensitized modified electrode and (b) in the presence of varying concentrations of dibenzo-18-crown-6 in the Prussian blue modified electrodes. The investigations made on these lines again suggested the following: (1) increase in dibenzo-18-crown-6 concentrations in the modified electrode increases the magnitude of dopamine sensing upto an optimum concentration of macrocycle; (2) the detection limit of dopamine sensing goes down to 30 nM as compared to that of dibenzo-18-crown-6 incorporated with potassium ferricyanide which was found to the order of 100 nM. Investigations of the interference of ascorbic acid revealed that the presence of dibenzo-18-crown-6 introduces selectivity in dopamine sensing in the presence such common interfering analyte like ascorbic acid.     

Spectral and theoretical studies of N-p-(ethylbenzene)thiobenzohydroxamic acid metal chelates

The preparation of N-p-(ethylbenzene)thiobenzohydroxamic acid chelates with several metal ions and their spectral properties are described in this paper. This is followed by a theoretical study of metal complexes of some thiohydroxamic acids, as well as the prepared chelates. The electronic properties of the metal complexes are discussed. The experimental and theoretical electronic spectra are also compared. A possible reason for the smaller pKa values of thiohydroxamic acid complexes than those of the corresponding hydroxamic acids is given.     

Cetylpyridinium chloride micelles as a selective fluorescence quenching solvent media for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons

Fluorescence behavior of 41 polycyclic aromatic hydrocarbons (PAHs) dissolved in aqueous micellar cetyltrimethylammonium chloride (CTAC) solvent media and in five different cetyltrimethylammonium chloride + cetylpyridinium chloride (CPC) surfactant mixtures is reported. Experimental fluorescence measurements reveal that CPC is a selective fluorescence quenching agent for alternant PAHs. The cetylpyridinium ion effectively quenched emission intensities of the 21 alternant PAHs studied. Emission intensities of nonalternant PAHs, with a few noted exceptions, were unaffected by the presence of CPC in the mixed cationic surfactant micelles.     

Conjugate polymer-based membranes for gas separation applications: current status and future prospects

Conjugate polymers provide the possibility of exploiting both the chemical and physical attributes of the polymers for membrane-based gas separation. The presence of delocalized π electrons provides high chain stiffness with low packing density, thus making the membrane a rigid structure that favors facilitated transport. Historically, the polymeric membranes were constrained by the tradeoff relationship between gas permeability and gas selectivity. So, different methods were investigated to prepare the membranes that can overcome the limitation. In recent years, electroconductive polymeric membranes have gained attention with their enhanced transportation properties combining the separation behavior depending on both molecular size discrimination as well as the facilitated transport. They offer better selectivity toward polar gases such as CO₂ because of the increased solubility. This review is aimed to provide a literature survey on gas separation using conjugate polymers such as polyaniline, polypyrrole, and some derivatives of polythiophenes. It contains various methods used by different researchers to enhance the gas separation properties of the membranes with improved mechanical and thermal stability such as changing the morphology and membrane preparation methods. In addition, it provides the pros and cons of various factors affecting the conjugate polymer membrane performance. The major challenges and future work that can be done in improving the transportation properties through the membrane to achieve viable membranes are also discussed so that they can be used for commercial and practical applications in the future.     

Self-assembled Gemini surfactant film-mediated dispersion stability

The force-distance curves of 12-2-12 and 12-4-12 Gemini quaternary ammonium bromide surfactants on mica and silica surfaces obtained by atomic force microscopy (AFM) were correlated with the structure of the adsorption layer. The critical micelle concentration was measured in the presence or absence of electrolyte. The electrolyte effect (the decrease of CMC) is significantly more pronounced for Gemini than for single-chain surfactants. The maximum compressive force, F(max), of the adsorbed surfactant aggregates was determined. On the mica surface in the presence of 0.1 M NaCl, the Gemini micelles and strong repulsive barrier appear at surfactant concentrations 0.02-0.05 mM, which is significantly lower than that for the single C(12)TAB (5-10 mM). This difference between single and Gemini surfactants can be explained by a stronger adsorption energy of Gemini surfactants. The low concentration of Gemini at which this surfactant forms the strong micellar layer on the solid/solution interface proves that Gemini aggregates (micelles) potentially act as dispersing agent in processes such as chemical mechanical polishing or collector in flotation. The AFM force-distance results obtained for the Gemini surfactants were used along with turbidity measurements to determine how adsorption of Gemini surfactants affects dispersion stability. It has been shown that Gemini (or two-chain) surfactants are more effective dispersing agents, and that in the presence of electrolyte, the silica dispersion stability at pH 4.0 can also be achieved at very low surfactant concentrations ( approximately 0.02 mM).     

Benzofurano derivatives of coumarins as possible antifertility agents

Synthesis and medicinal importance of 4-methyl-6-nitro-8,9,10,11-tetrahydro-2H-benzofuro[2,3-b]-1-benzo-pyran-2-one (I), 4-ethyl-11-nitro-6,7,8,9-tetrahydro-2H-benzofuro[3,2-g]-1-benzopyran-2-one (II), and 6,7-di-hydro-4,13-dimethylbis-1-benzopyrano[6,7-d:7′,6′-d']-2H,11H-benzo[1,2-b:3,4-b']difuran-2,11-dione (III) is presented. The structures of these compounds were confirmed by elemental analysis and spectral studies.     

2′,3′‐Dehydrosalannol

The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)‐8‐(3‐furyl)‐2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c‐dodeca­hydro‐3‐hydroxy‐2a,5a,6a,7‐tetra­methyl‐5‐(3‐methylbut‐2‐enoyl­oxy)‐2H,3H‐cyclo­penta­[4′,5′]­furo­[2′,3′:6,5]benzo[cd]­isobenzo­furan‐6‐acetate, C₃₂H₄₂O₈, was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been found to possess antifeedant activity against Spodptera litura. The conformations of the functional groups are similar to those of 3‐des­acetyl­salannin, which was isolated from neem kernels. The mol­ecules are linked into chains by intermolecular O—H?O hydrogen bonds.