Theoretical and X-Ray Evidence of Electrostatic Phosphonium anti and gauche Effects.

Sulphur, not phosphorus, is the only known third-row element capable of experiencing an electrostatic gauche effect with fluorine. Some six-membered rings containing an endocyclic phosphorus atom and a ß-fluorine substituent that can interconvert to axial (gauche relative to phosphorus) and equatorial positions were then analysed. While phosphines do not establish an electrostatic attraction between fluorine and phosphorus, some oxidised forms exhibit surprising stability for the sterically disfavoured axial orientation. Because the nature of this behaviour was not obvious, since an intramolecular hydrogen bond can appear, a phosphonium derivative was further studied and its axial conformation was found to be highly stable. A preference for the gauche arrangement appears even for the acyclic and sterically hindered (2-fluoroethyl)triphenylphosphonium cation. On the other hand, (ethane-1,2-diyl)bis(phosphonium) cations are exclusively in anti conformation due to an (+/+)-electrostatic repulsion between the positively charged phosphonium groups.

A validated 1H NMR method for quantitative analysis of α-bisabolol in essential oils of Eremanthus erythropappus.

α-Bisabolol is a natural terpene produced by Eremanthus erythropappus and is widely used in cosmetics and pharmaceuticals due to its anti-inflammatory, antibacterial and antimycotic properties. Due to these applications, a control of composition and authenticity of commercial oils rich in this terpene is required, resulting in a demand for new methodologies for quality control. In this work a rapid and efficient method for quantification of α-bisabolol in the essential oil of E. erythropappus (candeia) using 1H NMR was developed, validated and compared to gas chromatography (GC) method. The quantification of α-bisabolol by 1H NMR was successfully achieved for most of the essential oil samples of E. erythropappus evaluated, except for those with a more complex composition. To circumvent this limitation a 2D NMR COSY contour map was used. This method proved to be a fast and efficient alternative, providing results with standard deviations SD<0.3%. All evaluated parameters (selectivity, linearity, accuracy/precision, repeatability, robustness and stability of analyte and internal standard in solution) gave satisfactory results. Using the 1H NMR signals at 5.36 and 5.13ppm, the limit of detection (LOD) and limit of quantification (LOQ) were 0.26 and 2.59mg, respectively. The results obtained by the 1H NMR method presented SD=0.59%, smaller than the value found for GC (SD=1.18%). Tukey tests have shown that the results obtained by 1H NMR and COSY methodology are similar to the obtained by the traditional GC-FID technique using external and internal standardization and normalization with 95% confidence.

Unusual 2(1H)-pyrazinones isolated from a culture of a Brazilian marine-derived Streptomyces sp.

Four new secondary metabolites, giovaninones A-D (1-4), were isolated from an ethyl acetate extract of a culture of a marine-derived Streptomyces strain designated SS99BA-2. Chemical analysis was completely conducted in a coupled automated LC-SPE system with the use of a cryogenic NMR probehead and HRMS. The application of this system to identify, purify and elucidate all the structures is described.

Use of diffusion-ordered NMR spectroscopy and HPLC-UV-SPE-NMR to identify undeclared synthetic drugs in medicines illegally sold as phytotherapies.

The informal (and/or illegal) e-commerce of pharmaceutical formulations causes problems that governmental health agencies find hard to control, one of which concerns formulas sold as natural products. The purpose of this work was to explore the advantages and limitations of DOSY and HPLC-UV-SPE-NMR. These techniques were used to identify the components of a formula illegally marketed in Brazil as an herbal medicine possessing anti-inflammatory and analgesic properties. DOSY was able to detect the major components present at higher concentrations. Complete characterization was achieved using HPLC-UV-SPE-NMR, and 1D and 2D NMR analyses enabled the identification of known synthetic drugs. These were ranitidine and a mixture of orphenadrine citrate, piroxicam, and dexamethasone, which are co-formulated in a remedy called Rheumazim that is used to relieve severe pain, but it is prohibited in Brazil because of a lack of sufficient pharmacokinetic and pharmacodynamic information.

Average shear rate in three pneumatic bioreactors.

A method proposed in recent literature was applied to evaluate the average shear rate (γav) in three pneumatic bioreactors of 5-dm3 working volume: bubble column, split airlift, and concentric-tube airlift. The volumetric oxygen transfer coefficient (k(L) a) is the appropriate characteristic parameter to assess the average shear rate (γav) in this methodology. Correlations for γav as a function of superficial gas velocity in the riser region (U(GR)) and rheological fluid properties (consistency index, K, and flow index, n) were obtained for each model of pneumatic bioreactor studied. The γav values estimated by the proposed methodology lay within the range of values calculated by classical correlations. The proposed correlations were utilized to predict the γav during the Streptomyces clavuligerus cultivations carried out at the same specific air flow rate (3.5 vvm) in the different types of pneumatic bioreactors. The lowest values of γav related to the highest values of consistency index (K) were found for the bubble column bioreactor, and the highest values of γav related to the lowest values of K were found for the concentric-tube airlift bioreactor. Intermediate values were found for the split airlift bioreactor. The results showed that high γav values affect the structural health of the mycelia by the rupture of the hipha.