Electrospray ionization mass spectrometry fingerprinting of whisky: immediate proof of origin and authenticity

Authentic samples of whisky produced in Scotland and USA and counterfeit whisky samples commercialized in Brazil have been directly submitted to electrospray ionization mass spectrometry (ESI-MS) analysis in both the negative and positive ion modes to assess the potential of this technique for simple and rapid quality control and proof of authenticity of whisky samples. ESI in the negative ion mode yields the most characteristic whisky fingerprinting mass spectra in just a few seconds by direct infusion of the samples, detecting the most polar or acidic components of each sample in their deprotonated anionic forms. No pre-treatment of the sample, such as extraction or derivatization or even dilution, is required. The analysis of the ESI(-)-MS data both by simple visual inspection but more particularly by chemometric data treatment enables separation of the whisky samples into three unequivocally distinct groups: Scotch, American and counterfeit whisky, whereas single malt and blended Scotch whiskies are also distinguished to some extent. As indicated by ESI-MS/MS analysis, the diagnostic anions are simple sugars, disaccharides and phenolic compounds. Direct infusion ESI-MS therefore provides immediate chemical fingerprinting of whisky samples for type, origin and quality control, as demonstrated herein for American, Scottish and counterfeit samples, whereas ESI-MS/MS analysis of diagnostic ions adds a second dimension of fingerprinting characterization when improved selectivity is desired.     

Stereospecific total synthesis of (±)-strempeliopine

The 18-methylene-1,2-dehydroaspidospermidine (III) was stereospecifically transformed into the schizozygane alkaloid strempeliopine (II) in 16,6 % overall yield.     

Procedure for background estimation in energy-dispersive X-ray fluorescence spectra

A method for semi-automatic background estimation in energy-dispersive x-ray fluorescence spectra is outlined. Two cubic splines were investigated and the spline called the Butland interpolant was chosen for further investigation. Prior to the calculation of the spline, peak regions are set up, and suitable knots are defined outside the peak regions. To set up the peak regions, an automatic peak-search routine and a calibration equation are used. For a given peak, the latter relates the full width at half maximum (FWHM) to the peak centre. In turn, the size of the peak regions are defined by the FWHM multiplied by a constant given by the user. The method was tested on several types of spectra. It was found that the optimal size of the peak region decreased with increasing peak density. Reproducibility tests showed that the standard deviation of the summation of counts within a peak region and after background subtraction was less than would be expected from the counting statistics.     

Reduction of chromium in ethylene polymerisation using bis(imido)chromium(VI) catalyst precursors

Hybrid density functional calculations on [Cr(NR)2C3H7(C2H4)]+ (R = H, tBu) have revealed a facile reductive elimination reaction involving beta-hydrogen transfer from the alkyl chain, suggesting that the active species in ethylene polymerisation with bis(imido)chromium(VI) precursors contains a reduced chromium atom.     

Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes

The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed.     

1H detection in MAS solid-state NMR spectroscopy of biomacromolecules employing pulsed field gradients for residual solvent suppression

In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state.     

Diffusion of reagents in macrobeads

A simple and effective method of measuring diffusion rates of various acylating reagents in macro beads (in this work diameters greater than 570 microm) of amino-functionalized resins is presented. The extent of diffusion at various points of time was determined by treating beads with a staining reagent ("chloranil", 2,3,5,6-tetrachloro-1,4-benzoquinone) that colored the regions of the beads that had not yet been permeated by reagent (the central part of the beads). The volume of unstained resin (permeated part) was compared with the volume of the stained part, and diffusion rate constants were calculated. Factors influencing diffusion such as reagent concentration, solvent, temperature, resin type, and mechanical effects were investigated. The results showed that diffusion was promoted by increased temperature, good swelling of the resin, small reagents, and high concentrations but not by sonication or mechanical agitation.     

Photoelectron spectra of uranium(V) in mixed oxides showing characteristic satellite signals

Whereas uranyl compounds at most show electron transfer satellites at 3 eV higher I in the U4f region, mixed oxides containing uranium(V) show a characteristic satellite at 7.9 eV higher I. Uranium-cerium blue and certain U(IV) compounds are also discussed.     

Rapid prototyping of polymer microsystems via excimer laser ablation of polymeric moulds

This study presents a novel method for rapid prototyping of polymer microsystems. The method is based on excimer laser ablation of a thermally and mechanically stable polymer, such as PEEK (poly-ether-ether-ketone). A negative of the desired microsystem is laser machined in PEEK, which can then be used directly for hot embossing or injection moulding of a series of prototypes. This approach is very rapid and considerably cheaper than more traditional approaches to toolmaking, while still performing well in terms of reproduction of tool dimensions. The reduction in time and cost for a master tool using this method opens up new possibilities for testing small series in the R&D phase of a microsystem. Finally, two particular applications of the technique are presented.     

Spectrophotometric and direct-reading methods for the analysis of gas phase peroxyacetic acid

A new method for the determination of peroxyacetic acid (PAA) in gas phase samples is described. It is based on the oxidation of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate) by PAA with formation of a radical cation which is characterized by four strong absorption maxima between 405 nm and 810 nm. These allow for sensitive spectrophotometric determination of the peracid. The selectivity of the method towards hydrogen peroxide is strongly dependent on the sampling method used. Impinger sampling and sampling based on the use of coated solid sorbents (test tubes) was performed. Limits of detection are 10(-8) mol, limits of quantification are 5 x 10(-8) mol, the linear range consists of 1.5 concentration decades in both cases. Using ABTS-coated test tubes above 1 x 10(-7) mol, direct reading of the results is possible and may be used as rapid screening method for the PAA concentration.