Application of external micro-spectrophotometric detection to improve sensitivity on microchips

The goal of this work was to increase the sensitivity of a UV–Vis spectrophotometer by decreasing the background noise and lengthening the optical path. A microphotometer has been modified to precisely select very small parts of a microfluidic channel pattern of a chip and to measure light absorbance on a magnified area of the selected part of the channel. The viability of combining a projection microscope and a spectrophotometer for external absorbance measurements on disposable PDMS chips was studied. Besides the external direct detection above a microfluidic channel, the optical pathlength was lengthened by detecting in the region of the perpendicular exit port. Increasing the cross-sectional area of the zone of irradiation improved the signal-to-noise ratio and the limits of detection (LOD).     

Preparation,homogeneity and stability studies of a candidate LRM for Se speciation

A laboratory reference material (LRM) was prepared from Brazil nuts (Bertholletia excelsa) for quality control (QC) purposes of selenium speciation. The preparation of this LRM led through the usual operation steps applied during routine reference material production from biota samples-preparation of the raw material, homogenisation, storage design, checking of homogeneity, microbiological status and possible irradiation effects, and monitoring the species stability vs time at different storage temperatures. The selenium speciation studies to check species stability were carried out on a HPLC-UV-HG-AFS measurement set-up. Special attention was paid to the correct identification of selenium species by applying independent HPLC separation techniques (ion-pairing and anion-exchange chromatography). The concentration of selenomethionine (SeMet) and total Se content were quantified (79.9 microg g(-1) (calculated as Se) and 82.9 microg g(-1), respectively). The homogeneity and stability of this candidate reference material passed the relevant tests recommended by Bureau Communautaire de Référence (BCR).     

Detection and characterization of twenty‐eight isomers of fumonisin B1 (FB1) mycotoxin in a solid rice culture infected with Fusarium verticillioides by reversed‐phase high‐performance liquid chromatography/electrospray ionization time‐of‐flight and ion trap mass spectrometry

Fumonisin mycotoxins which are hazardous to humans and animals were produced in a Fusarium verticillioides‐infected solid rice culture. To decrease the possibility of the formation of artifacts, the fumonisins were analysed by reversed‐phase high‐performance liquid chromatography/electrospray ionization time‐of‐flight (RP‐HPLC/ESI‐TOFMS) and ion trap mass spectrometry (RP‐HPLC/ESI‐ITMS) immediately after the extraction of the culture material, without any further sample clean‐up. The fumonisin isomers were separated by using a flat gradient on a special, high‐coverage C₁₈, narrow‐bore HPLC column (YMC‐Pack J'sphere ODS H80) suggested for the separation of structural isomers by the manufacturer. Exact mass measurements (TOFMS) of the protonated molecules and extraction of the ion chromatogram corresponding to the empirical formula (C₃₄H₅₉NO₁₅) of FB₁ toxins led to the identification of 29 peaks and shoulders, including those of FB₁. The FB₁ toxin and 28 of its isomers were also detected by ITMS after separation with RP‐HPLC. The characteristic m/z values of the product ions, including the backbones obtained by ITMS², undoubtedly indicated the structures of the FB₁ isomers for 28 peaks and shoulders. In the MS² spectra of the protonated molecules of the FB₁ isomers, with some exceptions, 15 characteristic product ions including the hydrocarbon backbone at m/z 299 were observed. The abundance ratio of the cation at m/z 299 ranged up to 5.8%. The relative quantities of the isomers found in the sample extract were expressed as percentages of the FB₁ content (0.001–0.579%). The total amount of the 28 FB₁ isomers was 2.803% of the quantity of FB₁ that is important from the aspect of food and feed safety. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural analysis and biomedical potential of novel salicyloyloxy estrane derivatives synthesized by microwave irradiation

New estrane salicyloyloxy or D-homo derivatives were synthesized under microwave (MW) or conventional heating from estrane precursors and methyl salicylate. The MW technique provides advantages regarding product yield and reaction time, and represents a more environmentally friendly approach than conventional heating. Considering the biomedical potential of estrane compounds, we evaluated the antioxidant activity and cytotoxicity of synthesized estrane derivatives in a series of in vitro tests, as well as their 3β-hydroxysteroid dehydrogenase/Δ⁵ → Δ⁴ isomerase (3βHSD) and 17β-hydroxysteroid dehydrogenase types 1, 2 and 3 (17βHSD1, 17βHSD2 and 17βHSD3) inhibition potentials. In DPPH tests, 3-methoxyestra-1,3,5(10)-trien-17β-yl salicylate displayed antioxidant potential, while all compounds exhibited OH radical neutralization activity. 3-Oxoestr-4-en-17β-yl salicylate showed strong cytotoxicity against MDA-MB-231 breast cancer cells, while 17-oxoestra-1,3,5(10)-trien-3-yl salicylate, estra-1,3,5(10)-triene-3,17β-diyl 3-benzoate 17-salicylate and 3-benzyloxy-17-salicyloyloxy-16,17-secoestra-1,3,5(10)-triene-16-nitrile showed the strongest inhibition of PC-3 prostate cancer cell growth. 3-Hydroxyestra-1,3,5(10)-trien-17β-yl salicylate was the best inhibitor of 17βHSD2, suggesting potential use in treating pathological conditions associated with estrogen depletion. For 3-methoxyestra-1,3,5(10)-trien-17β-yl salicylate and 3-oxoestr-4-en-17β-yl salicylate, X-ray crystal structure analysis and molecular energy optimization were performed to define their conformations and energy minima. Very good overlap in the region of the steroidal nucleus was observed for the molecular structures of each analyzed molecule in the crystalline state and after energy optimization, while conformer analysis indicates conformational flexibility in the form of rotation around the C17···O2 bond. Structural geometry analysis for these compounds shows that the region of ring A in steroids, and especially the C3 atom functional group, is important structural features concerning antiproliferative activity against MDA-MB-231 cells.

     

Study on the reactivity of In2O3 in mixtures with ammonium-zeolites

In ground mixtures of In₂O₃ and NH₄Y, incorporation of In⁺ cations into the zeolitic phase occurs upon thermal treatment by partial reductive solid-state ion exchange associated with oxidation of ammonium ions or released ammonia to N₂ and NH₂OH. Cationic InO⁺ species, created in zeolites by reductive solid-state ion exchange of In₂O₃/NH₄-zeolite mixtures in hydrogen atmosphere and subsequent oxidation of the In⁺ lattice cations by oxygen, do not undergo autoreduction up to 970 K. Reductive solid-state ion exchange easily proceeds in carbon monoxide atmosphere at temperatures between 620 and 770 K. The significance of these observations for the use of indium-containing zeolites as catalysts is discussed.