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41.
Karyne M. Rogers Kerry Somerton Pamela Rogers Julie Cox 《Rapid communications in mass spectrometry : RCM》2010,24(16):2370-2374
Carbon isotope analyses (δ13C) of some New Zealand Manuka honeys show that they often fail the internationally recognised Association of Official Analytical Chemists sugar test (AOAC method 998.12) which detects added C4 sugar, although these honeys are from unadulterated sources. Failure of these high value products is detrimental to the New Zealand honey industry, not only in lost export revenue, but also in brand and market reputation damage. The standard AOAC test compares the carbon isotope value of the whole honey and corresponding protein isolated from the same honey. Differences between whole honey and protein δ13C values should not be greater than +1.0‰, as it indicates the possibility of adulteration with syrups or sugars from C4 plants such as high fructose corn syrup or cane sugar. We have determined that during the standard AOAC method, pollen and other insoluble components are isolated with the flocculated protein. These non‐protein components have isotope values which are considerably different from those of the pure protein, and can shift the apparent δ13C value of protein further away from the δ13C value of the whole honey, giving a false positive result for added C4 sugar. To eliminate a false positive C4 sugar test for Manuka honey, prior removal of pollen and other insoluble material from the honey is necessary to ensure that only the pure protein is isolated. This will enable a true comparison between whole honey and protein δ13C isotopes. Furthermore, we strongly suggest this modification to the AOAC method be universally adopted for all honey C4 sugar tests. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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A new phase transition is observed experimentally in a dry granular gas subject to vertical vibration between two horizontal plates. Molecular dynamics simulations of this system allow us to investigate the observed phase separation in detail. We find a high-density, low temperature liquid, coexisting with a low-density, high temperature gas moving coherently. The importance of the coherent motion for phase separation is investigated using frequency modulation. 相似文献
45.
Ecevit Bilgili Juan Yepes Luke Stephenson Kerry Johanson Brian Scarlett 《Particle & Particle Systems Characterization》2004,21(4):293-302
In the mechanical characterization of powders using the direct shear testers such as the Jenike shear cell, the existence of a uniform or well‐defined stress field in a powder specimen is assumed. This assumption has not been subjected to any serious scrutiny in the literature. In this study, the normal stress variation in a silica powder was locally determined by locating a pressure‐sensitive TekScan pad at the bottom section of a Jenike shear cell. A computer simulation of the consolidation and pre‐shearing stages of the Jenike test procedure was performed using the Discrete Element Method (DEM). The paper presents both experimental and computational evidence for the existence of a complex stress field in the powder specimen, thus clearly invalidating the long‐standing stress homogeneity assumption in the direct shear testing of powders. The implications of the stress inhomogeneity in terms of the accuracy of the material properties extracted from the Jenike test are also presented. 相似文献
46.
Summary Non-destructive epithermal neutron activation analysis in conjunction with Compton suppression has been applied to determine arsenic in seven biological standard reference materials from the National Institute of Standards and Technology. The accuracy is in excellent agreement with all the certified values and compilation results. For four of the materials detection limits between 1–4 ng/g were easily achieved while for three others they ranged from 18–50 ng/g. Overall analytical precision typically varied between 2–4% for five of the reference materials while for two other it was between 12–16%. These methods clearly demonstrate that through a judicious approach of anti-coincidence techniques, nanogram quantities of arsenic can be reliably determined without the need for labor intensive chemical separations. 相似文献
47.
Hassell KM LeBlanc Y McLuckey SA 《Rapid communications in mass spectrometry : RCM》2011,25(4):476-482
A novel charge inversion process that involves the removal of an excess cation from an analyte ion and the transfer of an anion to the neutral analyte in a single ion/ion encounter is described. Polyamidoamine (PAMAM) half-generation dendrimer anions that contain small anions, such as the chloride ion, were used as charge inversion reagents. Several competing processes can occur that include removal of the cation to neutralize the analyte, the removal of the excess cation and an additional proton to yield the deprotonated molecule, or removal of the excess cation and transfer of a small anion to the analyte. For the latter process to dominate, several requirements for both the reagent anion and the analyte cation must be met. The reagent anion must form multiply charged anions and must be able to incorporate one or more small anions for transfer. The analyte must have no strongly acidic sites as well as a relatively high affinity for small anion attachment. The PAMAM dendrimer anions must meet the conditions for the reagent anions and the cations of the corticosteroids meet the conditions for the analyte. The estrogenic steroid estrone, on the other hand, does not meet the requirements and, as a result, is largely neutralized when reacted with the reagent anions. This reaction, therefore, is highly selective and might serve as a useful reaction for the screening of appropriate analytes. 相似文献
48.
Taylor BL Swift EC Waetzig JD Jarvo ER 《Journal of the American Chemical Society》2011,133(3):389-391
Secondary benzylic ethers undergo stereospecific substitution reactions with Grignard reagents in the presence of nickel catalysts. Reactions proceed with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols. 相似文献
49.
Ding F Lee KJ Vahedi-Faridi A Huang T Xu XH 《Analytical and bioanalytical chemistry》2011,400(1):223-235
We have designed and constructed fusion genes of C-terminal (Ct) or N-terminal (Nt) bmrA with EGFP vectors and successfully expressed them in ΔBmrA (BmrA deletion strain of Bacillus subtilis), generating two new strains of B. subtilis (Ct-BmrA-EGFP and Nt-BmrA-EGFP). The fusion genes were characterized using gel electrophoresis and DNA sequencing. Their
expression in live cells was determined by measuring the fluorescence of EGFP in single live cells using fluorescence microscopy
and spectroscopy. The efflux function of the new strains was studied by measuring their accumulation kinetics of intracellular
Hoechst dye molecules (a pump substrate) using fluorescence spectroscopy, which were compared with wild-type (WT-BmrA) and
ΔBmrA strains. Both new strains show lower accumulation rates than ΔBmrA, and their efflux kinetics are inhibited by a pump
inhibitor (orthovanadate). The results suggest that both strains extrude the dye molecules and the fusion proteins retain
the efflux function of BmrA (ATP-binding cassette, ABC, transporter). Notably, Nt-BmrA-EGFP strain shows lower accumulation
rates (higher efflux rates) than Ct-BmrA-EGFP. Modeled structures of the fusion proteins illustrate a highly flexible linker
region connecting EGFP with BmrA, suggesting a minimal obstruction of EGFP to the BmrA. A closer distance of two C termini
(∼14 ?) than two N termini (47.9 ?) of the “closed” BmrA dimer depicts the larger steric effect of C-terminal fusion. This
study also shows that glucose affects the fluorescence study of efflux function of BmrA, suggesting that efflux kinetics of
ABC membrane transporters in live cells must be characterized in the absence of glucose. 相似文献
50.
Salandria KJ Arico JW Calhoun AK McLaughlin LW 《Journal of the American Chemical Society》2011,133(6):1766-1768
We describe here the synthesis and properties of A-T rich DNA containing covalently bound water mimics located in the DNA minor groove. 相似文献