Theoretical investigation on conformational preferences and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane

A new family of dialphosphacyclohexane is introduced which has three nucleophilic centers. The conformational stabilities and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane were investigated computationally by DFT calculations and NBO analyses at B3LYP/6-31+G(d,p). Relative energy trend in 1,3-diphosphinane and 1,3-dimethyl-1,3-diphosphinane conformations explored from steric and hyperconjugative point of view. The stability trend of 2-lithio derivatives based on calculated relative energies in 1,3-diphosphinane is 1d > 1f > 1b > 1a > 1c > 1e and for 1,3-dimethyl-1,3-diphosphinane derivatives is 2f > 2d > 2b > 2a > 2c > 2e. Calculated NBO atomic charges indicate that high positive charge at lithium and small C–Li Wiberg bond indexes in these derivatives are demonstrators of ionic nature of the C–Li bonds. Stereoelectronic interactions, polarizability of phosphorus, and chelate formation between each of phosphorous and lithium are determining factors in stability trend observed in these derivatives. Ease of lithiation in bis(dimethylphosphino)methane, 1,3-diphosphinane, and 1,3-dimethyl-1,3-diphosphinane derivatives was estimated and compared by isodesmic reaction.     

A New Kinetic‐Mechanistic Approach to Elucidate Formaldehyde Electrooxidation on Copper Electrode

Electrocatalytic oxidation of formaldehyde was investigated on copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of formaldehyde the peak current increase of the oxidation of Cu(III) is followed by a decrease in the corresponding cathodic current. A new mechanism based on the electrochemical generation of Cu(III) active sites and their subsequent consumption by the formaldehyde in question was also investigated.     

Systematic study of the fluorescence decays of amino‐coumarin dyes in polymer matrices

We measured the fluorescence decays of seven different amino‐coumarin dyes in polymer films of poly(methyl methacrylate) (PMMA), poly(styrene) (PS), and ethylene‐butene rubber (EBR); as well as in the small molecule analogs ethyl acetate and toluene. Many of the dye‐solvent and dye‐polymer combinations exhibited single exponential decays with lifetimes ranging from 2.3 to 3.9 ns. Small deviations from single exponential behavior occurred for most of the dyes in EBR. Significant deviations from single exponential behavior occurred for 7‐(diethylamino)‐2‐oxo‐2H‐1‐benzopyran‐3‐carboxylic acid (coumarin‐3) in ethyl acetate and in all polymer matrices and 2,3,6,7‐tetrahydro‐11‐oxo‐1H,5H,11H‐[1]benzopyrano[6,7,8‐ij]quinolizin‐10‐carboxylic acid (coumarin‐343) in all of the polymer matrices. Time‐resolved fluorescence spectra indicated the presence of two different excited states for coumarin‐3 and coumarin‐343 in PMMA; these spectra were qualitatively different from the time‐resolved spectra of coumarin‐3 in ethyl acetate. We rationalize these results in terms of the chemical functionalities of the various dyes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2333–2343, 2007     

Synthesis,characterization, and applications of novel Co(II)-pyridoxal phosphate-Schiff base/SBA-15 as a nanocatalyst for the green synthesis of benzothiazole heterocycles

Mesoporous heterogeneous santa barbara amorphous (SBA)-15-supported cobalt complex, as a novel nanocatalyst containing N–O chelating Schiff-base ligand was successfully synthesized by the reaction of SBA-15 and Cobalt(II)-Schiff-base complex. The Co(II)-Schiff base complex also was prepared for the first time, by the reaction of pyridoxal 5′-phosphate or PLP (biological active form of vitamin B6), 3-(aminopropyl)-triethoxysilane in methanol that complexation with CoCl₂. The subsequent grafting of entitled complex to SBA-15 afforded Co(II)-PLP-Schiff base/SBA-15 mesoporous catalyst. Characterization of the product was carried out with powder X-ray diffraction, Brunauer–Emmett–Teller nitrogen adsorption–desorption, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, atomic absorption spectroscopy, and inductively coupled plasma, Fourier-transform infrared spectroscopy. The results revealed the retention of the textural properties and hexagonally uniform structures of SBA-15 during the grafting procedure. This nanocatalyst was applied successfully for one-pot synthesis of various benzothiazole heterocycles under green conditions. This catalyst is an active, reusable, and stable nanomaterial with no leaching of metal ions to the reaction medium. It was used for the synthesis of desired benzothiazole heterocycles by the cyclo-condensation of aryl-aldehydes with 2-aminothiophenol with good to excellent yields and under green conditions.     

Microwave assisted syntheses of 2,5-disubstituted 1,3,4-oxadiazoles

2,5-Disubstituted 1,3,4-oxadiazoles have been synthesized by oxidation of 1-aroyl-2-arylidene hydrazines with potassium permanganate on the surface of a solid mineral support as well as in mixtures of acetone and water under microwave irradiation.     

A Mild and Chemoselective Dithioacetalization of Aldehydes in the Presence of Anhydrous Copper (II) Sulfate

Various aldehydes have been protected with different thiols as dithioacetals with excellent yields using anhydrous copper sulfate as a mild and chemoselective catalyst. The reaction is carried out in a solvent and/or under solvent-free conditions. The transthioacetalization of oxyacetals into dithioacetals was also achieved in an excellent yield.     

Ni/Al LDH纳米粒子改性的陶瓷碳电极对甲醇和乙醇电催化氧化性能(英文)

A Ni/Al layered double hydroxide(LDH) nanoparticle modified carbon ceramic electrode(Ni/Al LDH/NMCC) was fabricated and used for the electrocatalytic oxidation of methanol and ethanol in alkaline media.Cyclic voltammetric(CV) studies showed that it gave a significantly higher activity for methanol and ethanol oxidation and can be used as an electrocatalytic anode for fuel cells.The kinetic parameters of the electron transfer coefficient(α) and number of electrons involved in the rate determining step(nα) for the oxidation of methanol and ethanol were determined using CV.The anodic currents showed a linear dependence on the concentration of methanol and ethanol.     

On the presence of spectral shortcut in the energy budget of an asymmetric jet–wake flow in a forward-curved centrifugal turbomachine as deduced from SPIV measurements

Viscous dissipation and its contribution to turbulent kinetic energy (TKE) budget are investigated in the asymmetric jet–wake flow of a forward-curved centrifugal turbomachine. Single-plane three-dimensional turbulent data are obtained using stereoscopic particle image velocimetry (SPIV). Viscous dissipation is indirectly estimated from subgrid-scale (SGS) dissipation (SGS energy flux) by filtering velocity field using a top-hat filter. The filter scale should be within the inertial sub-range and this is ensured by spectral analysis of the measured field. Reduction of turbulent energy flux for smaller filter scales plus underestimation of viscous dissipation as compared with other TKE terms both suggest the presence of spectral shortcut. This bypass energy transfer (from intermediate scales towards dissipative scales) works in parallel with direct SGS energy transfer and affects the classical energy cascade. Analysis of TKE budget in the rotor exit region shows significant radial/circumferential variations in the contributing terms. These variations are mainly due to jet–wake–volute interactions, circumferential asymmetry of volute area and expansion of flow toward the fan outlet.     

Effect of finite-temperature local field corrections on many-body properties of quantum wires

The effect of low temperature on the many-body properties of an n-type GaAs-based quasi one-dimensional electron gas (quantum wire) has been investigated in the RPA, Hubbard and STLS approximations. Numerical results for the finite-temperature static structure factors, local field corrections, pair correlation functions, plasmon dispersion relations and inverse static dielectric functions of the system have been obtained and compared with the zero-temperature values. As a general result, the behavior of the system at finite-temperature does not change significantly at small values of wave vectors. Also, it has been found out that while applying the temperature dependent Hubbard and STLS to the quantum wire yields different results for local field corrections and pair correlation functions, the increase in temperature within all approximations causes the plasmon modes to shift upward in energy and the sharp peaks in the inverse static dielectric curve to become less pronounced.