A new ruthenium-catalyzed hydrogen-transfer reaction: transformation of 3-benzyl but-1-ynyl ethers into 1,3-dienes and benzaldehyde

We report a ruthenium-catalyzed reaction for various 3-benzyl but-1-ynyl ethers with suitable functionalities. Treatment of these substrates with TpRu(PPh3)(CH3CN)2PF6 (8.0 mol %) catalyst in 1,2-dichloroethane (80 degrees C, 12 h) afforded functionalized 1,3-dienes and benzyl aldehyde in good yields. This process is considered to be a tandem dealkoxylation and transfer hydrogenation. Deuterium-labeling experiments reveal that the migration of different hydrogen atoms proceeds regiospecifically. A plausible mechanism is proposed on the basis of the results of isotope experiment.     

Drag on two nonuniformly structured flocs moving along the axis of a cylindrical tube

The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc. The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing that deviation.     

Synthesis of symmetrical 1,5-bis-thio-substituted anthraquinones for cytotoxicity in cultured tumor cells and lipid peroxidation

The synthesis of a series of anthraquinone moieties bearing symmetrical sulfur-linked substituents in the 1 and 5 positions is described. These compounds were evaluated for their ability to inhibit the growth of suspended rat glioma C6 cells and human hepatoma G2 cells, respectively. In addition, the redox property of the compounds was determined based on the inhibition of lipid peroxidation in model membranes. Compounds 2a and 2h in this series compared favorably and exhibited the most potent cytotoxicity (0.02, 0.05 microM) against C6 cells in the XTT colorimetric assay. As far as redox properties are concerned, all bis-thio-anthraquinones show potential lipid peroxidation in model membranes very close to that of mitoxantrone (MX), and 2a, 2d, 2e, 2i, 2j, and 2k have more potential than that of MX. The lack of cytotoxicity of compound 2i cannot be related to lipid peroxidation, but the steric and electronic properties of the side-chain substituent maybe impair effective recognition of the cleavable complex. In contrast to MX, 2a and 2h are cytotoxic in rat glioma C6 cells and do not enhance lipid peroxidation in model membranes.     

Synthesis, stereochemistry confirmation and biological activity evaluation of a constituent from Isodon excisus

A synthesis and stereochemistry confirmation of a constituent recently isolated from the whole plant Isodon excisus is reported. An enantioselective catalytic boron-mediated reduction of an α-bromoketone was utilized in the key synthetic transformation. The methodology described herein was also used for the synthesis of the natural product's enantiomer and several derivatives. In addition, the compounds were evaluated for inhibitory activity in a caspase induction assay. The natural product was found to be devoid of activity, but several derivatives had moderate inhibitory activity (EC₅₀<1 μM).     

The 1,3-Dipolar Cycloadditions of 3-Arylsydnone-4-Carbonitrile Oxides with Alkenes

3-Arylsydnone-4-carbonitrile oxides may undergo 1,3-dipolar cycloadditions with alkenes to produce the corresponding 3-aryl-4-(5-substituted-isoxazolin-3-yl)sydnones. The direct reaction of 3-arylsydone-4-carbohydroximic acid chlorides with alkenes may also give the same products, and with higher yield.     

Synthesis and Structure of MnCl2(HDpyF) (HDpyF = N,N′‐di(2‐pyridyl)formamidine): New Crystallographic Disorder and Bonding Mode of the HDpyF Ligand

The reaction of N,N′‐di(2‐pyridyl)formamidine (HDpyF) with MnCl₂‐4H₂O afforded the complex MnCl₂(HDpyF), which was characterized by X‐ray crystallography. The HDpyF ligand chelates to the Mn(II) center through the first and the third nitrogen atoms to form a six‐membered ring, leaving the second and the fourth nitrogen atoms uncoordinated. The HDpyF ligand is crystallographically disordered such that two different molecules can be solved. The neutral HDpyF ligand adopts the new s‐cis‐syn‐s‐trans conformation.     

Model Studies of DNA Photorepair: Enthalpy of Cleavage of a Pyrimidine Dimer Measured by Photothermal Beam Deflection Calorimetry

Abstract— The enzyme DNA photolyase mediates the repair of pyrimidine dimers. This repair step, a net retro [²+2] reaction, proceeds through either the cation or anion radical of the pyrimidine dimer. In order to understand how electron transfer makes the repair process possible, its energetics have been examined by photothermal beam deflection calorimetry, fluorescence quenching and quantum yield studies. The enthalpy for the cleavage reaction of cis-syn 1,3-dimethylthymine dimer itself was found to be -19 kcal/mol. In addition, from the redox potentials, the enthalpies for the cleavage reactions of the dimer cation radical and the anion radical were determined to be -19 kcal/mol and -28 kcal/mol, respectively.     

Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface

Silane coupling agents are commonly applied to glass fibers to promote fiber/resin adhesion and enhance durability in composite parts. In this study, a coupling agent multilayer on glass was doped with trace levels of the dimethylaminonitrostilbene (DMANS) fluorophore. The fluorophore was immobilized on the glass surface by tethering the molecule to a triethoxy silane coupling agent, creating the DMANS/silane coupling agent molecule (DMSCA). DMSCA was then diluted with commonly used coupling agents and grafted to a glass microscope coverslip to create a model composite interface. A 53-nm blue shift in fluorescence from the immobilized DMSCA can be followed during cure of an epoxy resin overlayer, giving this technique potential to monitor the properties of the fiber/resin interface during composite processing. Contact angle measurements on these coupling agent layers were similar in the presence or absence of the DMSCA molecule, suggesting that trace levels of the fluorescent probe did not affect the structure of the layer. The immobilized DMSCA molecule behaved similarly to the DMANS precursor in solution. Both showed longer wavelength fluorescence in more polar environments. Copyright 2000 Academic Press.     

Unsymmetrical linear pentanuclear nickel string complexes: [Ni(5)(tpda)(4)(H(2)O)(BF(4))](BF(4))(2) and [Ni(5)(tpda)(4)(SO(3)CF(3))(2)](SO(3)CF(3))

The one-electron oxidized linear pentanuclear nickel complexes [Ni(5)(tpda)(4)(H(2)O)(BF(4))](BF(4))(2) (1) and [Ni(5)(tpda)(4)(SO(3)CF(3))(2)](SO(3)CF(3)) (2) have been synthesized by reacting the neutral compound [Ni(5)(tpda)(4)Cl(2)] with the corresponding silver salts. These compounds have been characterized by various spectroscopic techniques. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 15.3022(1) A, b = 31.0705(3) A, c = 15.8109(2) A, beta = 92.2425(4) degrees, V = 7511.49(13) A(3), Z = 4, and compound 2 crystallizes in the monoclinic space group C2/c with a = 42.1894(7) A, b = 17.0770(3) A, c = 21.2117(4) A, beta = 102.5688(8) degrees, V = 14916.1(5) A(3), Z = 8. X-ray structural studies reveal an unsymmetrical Ni(5) unit for both compounds 1 and 2. Compounds 1 and 2 show stronger Ni-Ni interactions as compared to those of the neutral compounds.     

Catalytic Pyrolysis of Methane

Methane decomposition over metal oxides/SiO₂ surface was investigated. At 1400 K obtained product distribution of this decomposition varied with metal oxide used. The effectiveness of these catalysts has been discussed in terms of activity and C₂ selectivity. ThO₂/SiO₂ was found to be the most effective catalyst for the catalytic decomposition of methane. Positive catalytic effect of ThO₂/SiO₂ on the pyrolysis has also been confirmed at 1073 K. At low reaction conversions, ethane and ethylene are found as major products. Yields of ethylene and other unsaturated products are sensitively inhibited by NO impurities in the methane. A reaction mechanism has been proposed to account observed experimental results.