Aerosol direct fluorination: Direct synthesis of perfluorinated glyme ethers

Aerosol direct fluorination of 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, triethyleneglycol dimethyl ether, and tetraethyleneglycol dimethyl ether produced the perfluorinated analogs in 36%, 22%, 30% and 15% isolated yields based on total input of hydrocarbon into the reactor. High effluent concentrations in excess of 80% were obtained in all cases indicating that low yields are primarily due to mechanical losses, not fragmentation or incomplete reaction. The clean reaction and the ability to produce high molecular weight fluorocarbons by direct fluorination suggests the applicability of aerosol fluorination to the production of fluorinated fluids and oils.     

Investigation of cation environment and framework changes in silicotitanate exchange materials using solid-state Na, Si, and Cs MAS NMR

Crystalline silicotitanate (CST), HNa₃Ti₄Si₂O₁₄·4H₂O and the Nb-substituted CST (Nb-CST), HNa₂Ti₃NbSi₂O₁₄·4H₂O, are highly selective Cs⁺ sorbents, which makes them attractive materials for the selective removal of radioactive species from nuclear waste solutions. The structural basis for the improved Cs⁺ selectivity in the niobium analogs was investigated through a series of solid-state magic angle spinning (MAS) NMR experiments. Changes in the local environment of the Na⁺ and Cs⁺ cations in both CST and Nb-CST materials as a function of weight percent cesium exchange were investigated using ²³Na and ¹³³Cs MAS NMR. Framework changes induced by Cs⁺ loading and hydration state were investigated with ²⁹Si MAS NMR. Multiple Cs⁺ environments were observed in the CST and Nb-CST material. The relative population of these different Cs⁺ environments varies with the extent of Cs⁺ loading. Marked changes in the framework Si environment were noted with the initial incorporation of Cs⁺, however with increased Cs⁺ loading the impact to the Si environment becomes less pronounced. The Cs⁺ environment and Si framework structure were influenced by the Nb-substitution and were greatly affected by the amount of water present in the materials. The increased Cs⁺ selectivity of the Nb-CST materials arises from both the chemistry and geometry of the tunnels and pores.     

Evaluation of different carbon and nitrogen sources in production of rhamnolipids by a strain of Pseudomonas aeruginosa

Culture conditions involving variations in carbon and nitrogen sources and different C:N ratios were examined with the aim of increasing productivity in the process of rhamnolipid synthesis by Pseudomonas aeruginosa. In addition to the differences in productivity, the use of different carbon sources resulted in several proportions related to the types of rhamnolipids synthesized (monorhamnolipids and dirhamnolipids). Furthermore, the variation in nutrients, mainly the nitrogen source, resulted in different amounts of virulence factors, as phenazines and extracellular proteins. The data point out a new concern in the choice of substrate to be used for rhamnolipid production by P. aeruginosa: toxic byproducts.     

Role du methyle 4β dans la formation des oxetanones en serie steroïde. Cas du cycle B.

The formation of oxetanones $\text{5}$ from bromoketonee $\text{2}$ requires the presence of a β-methyl group at C-4. The yield of the reaction $\text{2}$→$\text{5}$ is improved by addition of water to the medium.     

Regio- and stereospecific models for the biosynthesis of the indole alkaloids—III : The Aspidosperma-Iboga-secodine relationship

In vitro transformation of the Aspidosperma alkaloid (?) tabersonine (1) to (±)-pseudocatharanthine (7) via (+) allocatharanthine (6) and dehydrosecodine A (3) is described as a model for the biochemical interconversion of Aspidosperma and Iboga alkaloids. Facile conversion of 1, 2 and 7 in xylene solution to the carbazole (9) suggests the intermediacy of dehydrosecodines (as 8) in these reactions. In methanol solution the racemic salt (12) is formed in 50% yield from catharanthine at 175°. Further pyrolysis of the salt yields the carbazole (9). Reduction of the salt (12) with NaBH₄ affords (±) dihydrosecodine (16) identical with the natural alkaloid from Rhazya stricta.     

Multinuclear NMR investigations of the oxygen, water, and hydroxyl environments in sodium hexaniobate

Solid-state (1)H, (17)O MAS NMR, (1)H-(93)Nb TRAPDOR NMR, and (1)H double quantum 2D MAS NMR experiments were used to characterize the oxygen, water, and hydroxyl environments in the monoprotonated hexaniobate material, Na(7)[HNb(6)O(19)].15H(2)O. These solid-state NMR experiments demonstrate that the proton is located on the bridging oxygen of the [Nb(6)O(19)](8-) cluster. The solid-state NMR results also show that the NbOH protons are spatially isolated from similar protons, but undergo proton exchange with the water species located in the crystal lattice. On the basis of double quantum (1)H MAS NMR measurements, it was determined that the water species in the crystal lattice have restricted motional dynamics. Two-dimensional (1)H-(17)O MAS NMR correlation experiments show that these restricted waters are preferentially associated with the bridging oxygen. Solution (17)O NMR experiments show that the hydroxyl proton is also attached to the bridging oxygen for the compound in solution. In addition, solution (17)O NMR kinetic studies for the hexaniobate allowed the measurement of relative oxygen exchange rates between the bridging, terminal, and hydroxyl oxygen and the oxygen of the solvent as a function of pH and temperature. These NMR experiments are some of the first investigations into the proton location, oxygen and proton exchange processes, and water dynamics for a base stable polyoxoniobate material, and they provide insight into the chemistry and reactivity of these materials.     

High-power blue/UV light-emitting diodes as excitation sources for sensitive detection

With advances in III-V nitride manufacturing processes, high-power light-emitting diode (LED) chips in the blue and UV wavelengths are now commercially available at reasonable cost and can be used as excitation sources in optical sensing. We describe the use of these high-power blue and UV LEDs for sensitive fluorescence detection, including chip-based flow cytometry, capillary electrophoresis (CE), and single-molecule imaging. By using a blue LED with a focusable power of approximately 40 mW as the excitation source for fluorescent beads, we demonstrate a simple chip-based bead sorter capable of enriching the concentration of green fluorescent beads from 63% to 95%. In CE experiments, we show that a mixture of analyte solution containing 30 nM 6-carboxyrhodamine 6G and 10 nM fluorescein can be separated and detected with excellent signal-to-noise ratio (approximately 17 for 10 nM fluorescein) using the collimated emission from a blue LED; the estimated mass detection limit was approximately 200 zmol for fluorescein. We also demonstrated ultrasensitive fluorescence imaging of single rhodamine 123 molecules and individual lambda-DNA molecules. At a small fraction of the cost of an Ar+ laser, high-power blue and UV LEDs are effective alternatives for lasers and arc lamps in fluorescence applications that demand portability, low cost, and convenience.     

Fe Supported Catalysts Prepared by The Sol-Gel Method. Characterization and Evaluation in Phenol Abatement

Iron supported catalysts containing 10 wt% of iron, as oxide, on TiO₂ and Al₂O₃ have been prepared by the sol gel method and the traditional method based of the impregnation of the support with the metal precursor on commercial and sol-gel supports. The samples were characterised by measuring the specific area (S _BET), temperature programmed reduction (TPR), infrared spectroscopy (FTIR), electrophoretic migration (IP), chemical oxygen demand (COD) and X-ray diffraction (XRD). The catalytic activity was measured in a batch reactor using ozone as oxidizing agent. It was found presence of highly dispersed iron oxide in the samples prepared by cogelation, whereas in those prepared by impregnation of the iron precursor, the dispersion was very poor. Catalytic activity indicates that phenol is degraded with a low mineralization to CO_2.