The application of vinylogous iminium salt derivatives to efficient formal syntheses of the marine alkaloids lamellarin G trimethyl ether and ningalin B

Studies directed at the synthesis of lamellarin G trimethyl ether and ningalin B via vinylogous iminium salt derivatives are described. The successful strategy relies on the formation of a 2,4-disubstituted pyrrole or a 1,2,3,4-tetrasubstituted pyrrole from a vinylogous iminium salt or vinylogous iminium salt derivative. Subsequent transformations of these highly substituted pyrroles lead to efficient and regiocontrolled formal syntheses of the respective pyrrole containing natural products.     

Design and testing of a small-scale sublimation apparatus

In many areas of scientific research and development, for example in the pharmaceutical industry, it is important to prepare and to characterize crystals of pure organic compounds which are thermodynamically stable. The formation of crystals from the gas phase is technically less straightforward than crystallisation from solution, but sublimation techniques can have several important features. In the present paper we report the design and testing of a novel apparatus for small scale sublimation and fractional deposition of crystals. The instrument has been developed with special reference to the needs in the pharmaceutical industry. A few mg of the samples are enclosed, under reduced pressure, in thin-walled glass tubes, along which a well defined temperature gradient can be formed. During an experiment the substance will sublime from the hot end of the glass tube and crystals will be deposited along the temperature gradient. The applicability of the instrument has been verified by experiments with several test compounds. Results from experiments with carbamazepine, are reported in some detail. Carbamazepine single crystals of high quality were obtained and the transition temperature between the triclinic (Form I) and the monoclinic (Form III) crystal modifications agreed with literature values.     

Chemical studies on an endemic Philippine plant: sulfated glucoside and seco-A-ring triterpenoids from Dillenia philippinensis

The leaves of the endemic Philippine plant, Dillenia philippinensis yielded 11 compounds including one new sulfated glucoside and a new seco-A-ring oleanane-type triterpenoid. The molecular structures of these compounds were elucidated by means of NMR, MS and other spectroscopic techniques, as well as by comparison with literature data. Anti-Leishmania activity and cytotoxic activity against A549 human lung adenocarcinoma cells were also examined.     

Use of Styrene as Sole Carbon Source by the Fungus Exophiala oligosperma: Optimization and Modeling of Biodegradation, Pathway Elucidation, and Cell Membrane Composition

Biodegradation of styrene by Exophiala sp. was tested at different initial concentrations (19.3?C170.6?mg?l^?1), pH (2.8?C8.7), and temperatures (19.8?C45.1?°C), for 120?h according to a 2³ full-factorial central composite design. The specific growth rate (SGR, per hour) and specific styrene utilization rate (SUR, milligrams of styrene per milligram of biomass per hour) values were used as the response variables for optimization purposes. The interactions between concentration and temperature (P?=?0.022), and pH and temperature (P?=?0.010) for SGR, and interactions between concentration and temperature (P?=?0.012) for SUR were found to be statistically significant. The optimal values for achieving high SGR (0.15?h^?1) and SUR (0.3622?mg styrene mg^?1 biomass h^?1) were calculated from the regression model equation. Those values are C _o ?=?89.1?mg?l^?1, pH?=?5.4, and T?=?31.5?°C for SGR and C _o ?=?69.2?mg?l^?1, pH?=?5.5, and T?=?32.4?°C for SUR. It was also observed that the Exophiala strain degrades styrene via phenylacetic acid, involving initial oxidation of the vinyl side chain. Besides, in the presence of styrene, changes in the fatty acids profile were also observed. It is hypothesized that an increasing amount of linoleic acid (18:2) may be involved in the protection of the fungus against toxic substrate.     

N-H stretching modes of adenosine monomer in solution studied by ultrafast nonlinear infrared spectroscopy and ab initio calculations

The N-H stretching vibrations of adenine, one of the building blocks of DNA, are studied by combining infrared absorption and nonlinear two-dimensional infrared spectroscopy with ab initio calculations. We determine diagonal and off-diagonal anharmonicities of N-H stretching vibrations in chemically modified adenosine monomer dissolved in chloroform. For the single-quantum excitation manifold, the normal mode picture with symmetric and asymmetric NH(2) stretching vibrations is fully appropriate. For the two-quantum excitation manifold, however, the interplay between intermode coupling and frequency shifts due to a large diagonal anharmonicity leads to a situation where strong mixing does not occur. We compare our findings with previously reported values obtained on overtone spectroscopy of coupled hydrogen stretching oscillators.     

Effect of Mg doping level on the antibacterial activity of (Mg + F)-doped ZnO nanopowders synthesized using a soft chemical route

ZnO nanopowders simultaneously doped with fluorine (20 at.%) and magnesium (4, 8, 12 and 16 at.%) (ZnO:F:Mg) have been synthesized using an inexpensive simple soft chemical route for the first time. The effect of Mg doping level on certain physical properties and antibacterial activities of ZnO:F:Mg nanopowders has been investigated and reported. XRD studies showed that the products have the hexagonal wurtzite structure of ZnO. Fourier transform infrared spectra authenticate the presence of MgO stretching vibration, which is responsible for the increased antibacterial activity of the synthesized samples. The antibacterial activity of ZnO:F:Mg nanopowders was found to be enhanced with increase in Mg doping level as it causes a reduction in the grain size.     

Distribution of hexavalent Cr species across the clay mineral surface-water interface

The adsorption isotherms of Cr(VI) on kaolinite, montmorillonite, and alumina were adequately treated with Langmuir model showing behavior characteristic of single-layer adsorption. The efficiency of the adsorbents in removing Cr(VI) from water follows the order alumina > kaolinite > montmorillonite > silica. Speciation studies indicate that hydrogen chromate ions were the major adsorbed species and simultaneous adsorption of dichromate ion occurred at concentrations greater than approximately 10(-3) mol L(-1). It is most probable that the mechanism of adsorption of the hydrogen chromate ion at the surface of alumina is predominantly electrostatic adsorption, with outer sphere complex formation.     

Resolving the emission times of solute and solvent four-wave mixing signals by spectral interferometry

Electric field-resolved transient grating measurements are used to distinguish the four-wave mixing signal emission from a resonant solute and a non-resonant solvent. The two components of the solution (i.e., solute and solvent) emit signal fields at different times with respect to the arrival of the probe pulse to the sample. This gives rise to a recurrence in the temporal profile of the total signal field. We show that the origin of this interference is the difference in relaxation time scales of the holographic gratings associated with the solute and solvent. The grating of the resonant solute relaxes on the time scale of a few picoseconds due to depopulation of its excited electronic state, whereas the electronic polarizability response of the solvent relaxes on the femtosecond time scale. This separability of responses is a general phenomenon that is particularly useful for studying weakly absorbing solute dynamics in polarizable solvents.     

Simultaneous determination of eight biologically active thiol compounds using gradient elution-liquid chromatography with Coul-Array detection

The most active form of sulfur in biomolecules is the thiol group, present in a number of biologically active compounds. Here we present a comprehensive study of thiol analysis using flow injection analysis/HPLC with electrochemical detection. The effect of different potentials of working electrodes, of organic solvent contents in the mobile phase, and of isocratic and gradient elution on simultaneous determination of thiol compounds (cysteine, cystine, N-acetylcysteine, homocysteine, reduced and oxidised glutathione, desglycinephytochelatin, and phytochelatins) are described and discussed. These thiol compounds were well separated and detected under optimised HPLC-electrochemical detection conditions (mobile phase: 80 mM trifluoroacetic acid and methanol with a gradient profile starting at 97:3 (TFA:methanol), kept constant for the first 8 min, then decreasing to 85:15 during one minute, kept constant for 8 min, and finally increasing linearly up to 97:3 from 17 to 18 min; the flow rate was 0.8 mL/min, column and detector temperature 25 degrees C, and the electrode potential 900 mV). We were able to determine tens of femtomoles (3 S/N) of the thiols per injection (5 microL), except for phytochelatin5 whose detection limit was 2.1 pmole. This technique was consequently used for simultaneous determination of compounds of interest in biological samples (maize tissue and human blood serum).