Palladium and platinum complexes of a benzannulated N-heterocyclic plumbylene with an unusual bonding mode

Reaction of the N,N'-diisobutyl-substituted benzannulated N-heterocyclic plumbylene (NHPb) 1 with [Pd(PPh(3))(4)] and [Pt(PPh(3))(4)] gave the complexes [M(NHPb)(PPh(3))(3)] (M = Pd [2], Pt [3]). X-ray diffraction studies of both complexes showed an angle of ~125° between the plumbylene plane and the transition-metal-Pb axis, indicating coordination of the transition metal to the empty π orbital of the plumbylene Pb atom. The experimentally determined metric parameters of complexes [2] and [3] are discussed on the basis of DFT calculations.     

Tunnelling control of chemical reactions--the organic chemist's perspective

Even though quantum mechanical tunnelling has been appearing recurrently mostly in theoretical studies that emphasize its decisive role for many chemical reactions, it still appears suspicious to most organic chemists. Recent experiments in combination with powerful computational approaches, however, have demonstrated that tunnelling must be included to fully understand chemical reactivity. Here we provide an overview of the importance of tunnelling in organic chemical reactions.     

Study of the thermal decomposition of flame-retarded unsaturated polyester resins by thermogravimetric analysis and Py-GC/MS

The thermal degradation behaviours of flame-retarded unsaturated polyester resin formulations containing ammonium polyphosphate (APP), Cloisite 25A nanoclay and zinc based smoke suppressants have been studied using thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases (EGA) and pyrolysis/gas chromatography-mass spectrometry (GC/MS). In TGA-EGA experiments, the mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂) and oxygen (O₂) consumption as measured by an oxygen analyser. The effect of APP, Cloisite 25A and the smoke suppressants on the evolution of CO and CO₂ has been examined. The decomposition behaviour of flame-retarded polyester resins under isothermal pyrolytic conditions was investigated and the evolved gaseous products were collected and qualitatively and semi-quantitatively analysed via GC/MS. The addition of APP does not yield many new gaseous products relative to the unmodified polyester resin neither does the presence of zinc borate (ZB) and zinc stannate (ZS) together with APP. Possible chemical interactions are discussed in an attempt to explain the observed results.     

Formation and crystal structure of an unexpected inclusion complex of a metal-free phthalocyanine and oxalic acid

Treatment of 3-(2,4-dimethyl-3-pentyloxy)phthalonitrile (2) with CeCl3 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n-pentanol gives the corresponding metal-free phthalocyanine 3, which unexpectedly traps the oxalic acid in the crystal lattice forming a 1:1 inclusion complex.     

Pore-scale study of nonaqueous phase liquid dissolution in porous media using laser-induced fluorescence

Little quantitative, experimental pore-scale information exists regarding nonaqueous phase liquid (NAPL) ganglia undergoing dissolution in porous media. By using refractive index matched fluids and porous media, we have been able to nonintrusively visualize NAPL dissolution (at constant capillary numbers) in three dimensions using laser-induced fluorescence. The results provide dynamic, quantitative information regarding ganglia surface area, volume, position, and shape. It appears that ganglia smaller than a few pore volumes are spheroid, whereas larger ganglia exhibit a fractal area to volume scaling. Evidence of ganglia breakup is found for all capillary numbers studied. Mobilization, however, is only important at higher capillary numbers.     

Synthesis of 3,4-dihydrothioxanthene-1,9-dione analogs as potential antimalarial agents

7-Chloro-3-(2,4-dichlorophenyl)-3,4-dihydro-1H-thioxanthene-1,9 (2H)-dione (10), and a variety of analogs and derivatives were prepared as sulfur isosteric analogs of the acridinedione antimalarial agent, floxacrine. The compounds were devoid of antimalarial activity against P. berghei in mice.     

The role of nitric oxide in cancer improved methods for measurement of nitrite and nitrate by high-performance ion chromatography

The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to 100mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl⁻ ions from small sample volumes using Ag⁺ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime.     

Dimethylsilylene transfer from hexamethylsilirane to olefins

The thermolysis of hexamethylsilirane in the presence of cis- and trans-4-octene, cyclooctene, propenyltrimethylsilane and trimethylethylethylene resulted in dimethylsilylene transfer and formation of the respective silacyclopropanes. In contrast, silacyclopentane derivatives were formed when such thermolysis was carried out in the presence of styrene and α-methylstyrene. This is believed to be a result of the interception of the intermediate diradical from hexamethylsilirane ring opening by the styrene.     

Reversible voltammetric response for a molecule containing four non-equivalent redox sites with application to cytochrome c3 of Desulfovibrio vulgaris, strain Miyazaki

The cyclic voltammetric and differential pulse polarographic behavior of cytochrome c₃ of Desulfovibrio vulgaris, strain Miyazaki, has been evaluated in terms of a model employing four reversible redox centers. Both types of experiments can be fit by digital simulations using the four standard potentials: E₁⁰=?0.467, E₂⁰=?0.519, E₃⁰=?0.539 and E₄⁰=?0.580 V vs. SCE. The results are interpreted to mean that the four redox centers are chemically different and only weakly interacting. The relationships between the observed macroscopic standard potentials and the microscopic standard potentials for reduction of individual sites are discussed.