CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Antifungal Activity of Isolated Compounds from the Leaves of Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal against Fusarium Pathogens

Crop diseases caused by Fusarium pathogens, among other microorganisms, threaten crop production in both commercial and smallholder farming. There are increasing concerns about the use of conventional synthetic fungicides due to fungal resistance and the associated negative effects of these chemicals on human health, livestock and the environment. This leads to the search for alternative fungicides from nature, especially from plants. The objectives of this study were to characterize isolated compounds from Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal leaf extracts, evaluate their antifungal activity against Fusarium pathogens, their phytotoxicity on maize seed germination and their cytotoxicity effect on Raw 264.7 macrophage cells. The investigation led to the isolation of antifungal compounds characterized as 5-hydroxy-7,4′-dimethoxyflavone, maslinic acid (21-hydroxy-3-oxo-olean-12-en-28-oic acid) and withaferin A (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide). The structural elucidation of the isolated compounds was established using nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS) and, in comparison, with the available published data. These compounds showed good antifungal activity with minimum inhibitory concentrations (MIC) less than 1.0 mg/mL against one or more of the tested Fusarium pathogens (F. oxysporum, F. verticilloides, F. subglutinans, F. proliferatum, F. solani, F. graminearum, F. chlamydosporum and F. semitectum). The findings from this study indicate that medicinal plants are a good source of natural antifungals. Furthermore, the isolated antifungal compounds did not show any phytotoxic effects on maize seed germination. The toxicity of the compounds A (5-hydroxy-7,4′-dimethoxyflavone) and AI (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide) was dose-dependent, while compound B (21-hydroxy-3-oxo-olean-12-en-28-oic acid) showed no toxicity effect against Raw 264.7 macrophage cells.     

The Fourier transform infrared spectrum of the boron trifluoride–nitrous oxide complex

The Fourier transform infrared spectra of boron trifluoride and nitrous oxide, co-deposited in nitrogen and argon matrices at cryogenic temperatures, have been recorded. Concentration and temperature cycling experiments have established the existence of a 1:1 molecular complex, the spectrum of which is consistent with a structure similar to that of BF₃.N₂O in the gas phase. The structure derived from the infrared spectrum is also consistent with the results of a series of ab initio molecular orbital calculations reported by us recently. The experimental wavenumbers and complex-monomer wavenumber shifts compare reasonably well, by and large, with those predicted by the ab initio calculations.     

The vibrational spectra of the boron halides and their molecular complexes, part 5 An ab initio study of the infrared spectrum of the boron trifluoride-carbon dioxide complex

The optimized structures, interaction energies, Mulliken charges and vibrational spectra of three conformers of a 1:1 complex between boron trifluoride and carbon dioxide have been determined by means of ab initio calculations at the second-order level of M?ller-Plesset perturbation theory, using the 6-31G* basis set. All three structures feature a B⋯O electron donor-acceptor interaction. One of the structures, in which the carbon dioxide axis eclipses one of the BF bonds, was found to be a genuine minimum, one (the corresponding staggered form) a first-order saddle point and the third (a linearly bonded B⋯OCO species) a second-order transition state. The computed infrared spectrum of the preferred conformer has been used to predict the appearance of the spectrum of boron trifluoride and carbon dioxide co-deposited in cryogenic matrices, which will be reported in a forthcoming publication. Received: 18 November 1996 / Accepted: 11 March 1997     

Magnesiation of N-Heterocycles Using i-PrMgCl · LiCl and Catalytic Diisopropylamine

The direct magnesiation of various N-heterocyclic compounds with i-PrMgCl · LiCl and catalytic diisopropylamine allows for preparation of 2-substituted pyrroles, imidazole, indoles, and benzimidazoles, in moderate to good yields. The magnesiated substrates canreadily undergo a Kumada-type coupling with iodo-aryls in the presence of catalytic Pd(PPh₃)₄.