The use of supercritical fluid extraction for the determination of 4-deoxynivalenol in grains: The effect of the sample clean-up and analytical methods on quantitative results

Summary Deoxynivalenol (DON) is one of the trichothecene mycotoxins produced byFusarium molds in grains. Polar cosolvents in supercritical carbon dioxide (SC-CO₂) are needed to extract and isolate the polar DON moiety. This unfortunately results in the extraction of many interfering compounds from the grains into the extracts obtained by supercritical fluid extraction (SFE). Analysis of DON by high performance liquid chromatography (HPLC) using ultraviolet detection (UV) does not provide a specific detection method, although specific detection of DON can be enhanced by using purification steps after SFE. Alternatively, combining SFE with an immunoaffinity method can improve detection specificity and sample cleanup. In this study, SFE was employed to determine DON in grains and cereal products. The effectiveness of the SFE method was compared with two different solvent extraction methods. The extracted DON was quantitatively determined by HPLC-UV using external standardization or competitive enzymelinked immunosorbent assay (ELISA). In some cases, extracts were purified prior to quantitative analysis of the DON by using solvent partitioning, and/or solid phase extraction, or immunoaffinity columns. Therefore, this paper describes the analysis of DON in cereals using different extraction, cleanup and analysis methods. Names are necessary to report factually on available data: however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the products to the exclusion of others that may also be suitable.     

Surface-tension-driven flow in a slender cone

After a droplet has broken away from a slender thread or jetof liquid, the tip of the thread or jet recoils rapidly. Atthe moment of break-off, the tip of the thread/jet is observedto have the shape of a cone close to the bifurcation point.In this paper, we study the evolution of an ideal fluid whichis initially conical, where the only force acting on the fluidis due to surface tension. We find an asymptotic solution tothe problem in terms of the aspect ratio of the cone which isassumed to be small. Using a similarity transformation, whichis valid for small times after the bifurcation, we identifya rapidly oscillating non-linear wave which propagates awayfrom the tip, as observed in experiments.     

On the basis‐set dependence of local and integrated electron density properties: Application of a new computer program for quantum‐chemical density analysis

A new computer program for post‐processing analysis of quantum‐chemical electron densities is described. The code can work with Slater‐ and Gaussian‐type basis functions of arbitrary angular momentum. It has been applied to explore the basis‐set dependence of the electron density and its Laplacian in terms of local and integrated topological properties. Our analysis, including Gaussian/Slater basis sets up to sextuple/quadruple‐zeta order, shows that these properties considerably depend on the choice of type and number of primitives utilized in the wavefunction expansion. Basis sets with high angular momentum (l = 5 or l = 6) are necessary to achieve convergence for local properties of the density and the Laplacian. In agreement with previous studies, atomic charges defined within Bader's Quantum Theory of Atoms in Molecules appear to be much more basis‐set dependent than the Hirshfeld's stockholder charges. The former ones converge only at the quadruple‐zeta/higher level with Gaussian/Slater functions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Effects of excitation energy on the autodetachment lifetimes of small iodide-doped ROH clusters (R═H-, CH3-, CH3CH(2)-)

The effect of excitation energy on the lifetimes of the charge-transfer-to-solvent (CTTS) states of small (4 ≤ n ≤ 10) iodide-doped water and alcohol clusters was explored using femtosecond time-resolved photoelectron imaging. Excitation of the CTTS state at wavelengths ranging from 272 to 238 nm leads to the formation of the I···(ROH)(n)(-) (R═H-, CH(3)-, and CH(3)CH(2)-) species, which can be thought of as a vibrationally excited bare solvent cluster anion perturbed by an iodine atom. Autodetachment lifetimes for alcohol-containing clusters range from 1 to 71 ps, while water clusters survive for hundreds of ps in this size range. Autodetachment lifetimes were observed to decrease significantly with increasing excitation energy for a particular number and type of solvent molecules. The application of Klots' model for thermionic emission from clusters to I(-)(H(2)O)(5) and I(-)(CH(3)OH)(7) qualitatively reproduces experimental trends and reveals a high sensitivity to energy parametrization while remaining relatively insensitive to the number of vibrational modes. Experimental and computational results therefore suggest that the rate of electron emission is primarily determined by the energetics of the cluster system rather than by details of molecular structure.     

Comparisons of spectral characteristics of wind noise between omnidirectional and directional microphones

Wind noise reduction is a topic of ongoing research and development for hearing aids and cochlear implants. The purposes of this study were to examine spectral characteristics of wind noise generated by directional (DIR) and omnidirectional (OMNI) microphones on different styles of hearing aids and to derive wind noise reduction strategies. Three digital hearing aids (BTE, ITE, and ITC) were fitted to Knowles Electronic Manikin for Acoustic Research. They were programmed to have linear amplification and matching frequency responses between the DIR and OMNI modes. Flow noise recordings were made from 0° to 360° azimuths at flow velocities of 4.5, 9.0, and 13.5 m/s in a quiet wind tunnel. Noise levels were analyzed in one-third octave bands from 100 to 8000 Hz. Comparison of wind noise revealed that DIR generally produced higher noise levels than OMNI for all hearing aids, but it could result in lower levels than OMNI at some frequencies and head angles. Wind noise reduction algorithms can be designed to detect noise levels of DIR and OMNI outputs in each frequency channel, remove the constraint to switch to OMNI in low-frequency channel(s) only, and adopt the microphone mode with lower noise levels to take advantage of the microphone differences.     

Ethane cation decomposition characterization by EBMI spectroscopy: gas-phase dissociative recombination as a source of secondary products

The decomposition products of the d(6) -ethane cation following charge-transfer ionization with Ar(+) , under conditions of varying ionization electron current, have been isolated in solid argon matrices at 18?K and examined using Fourier transform infrared spectroscopy. Gas samples containing 1?:?1600 d(6) -ethane?:?Ar were subjected to electron bombardment by using either a high (pin) or a low (plate) ionization density anode configuration with ionization currents between 20 and 150?μA. Under high ionization density conditions, the observed major products were d(4) -ethene (C(2) D(4) ) and d(2) -acetylene (C(2) D(2) ), with smaller yields of C(2) D(5) , C(2) D(3) , and C(2) D. The yield of each dehydrogenation product was enhanced with increased current. Analogous experiments employing the low ionization density plate anode resulted in reduced C(2) D(6) destruction and the formation of only C(2) D(4) and C(2) D(2) . The results suggest the onset of dissociative recombination processes under high ion density conditions. In this context, the results can be interpreted as a dissociative recombination of primary ion products, which gives rise to further dehydrogenation, and appearance of additional neutral radical products.     

The sphericity of the diverse 10-vertex polyhedra found in bare post-transition metal clusters: germanium clusters with interstitial magnesium atoms as model systems

Theoretical studies show that pendant dimethylamino groups can play a significant role in the chemistry of unsaturated binuclear dimethylaminoborole iron carbonyls. For [C₄H₄BN(CH₃)₂]₂Fe₂(CO)₅, the lowest energy structures have single CO bridges and Fe?CFe single bonds of lengths ~2.8 ?. The lowest energy [C₄H₄BN(CH₃)₂]₂Fe₂(CO) _n (n?=?4, 3) structures have two bridging CO groups with Fe=Fe double bonds of lengths ~2.5 ? for n?=?4 and three bridging CO groups with Fe??Fe triple bonds of lengths ~2.2 ? for n?=?3. These structures are similar to structures previously found for the corresponding methylborole derivatives (C₄H₄BCH₃)Fe₂(CO) _n . However, slightly higher energy [C₄H₄BN(CH₃)₂]₂Fe₂(CO) _n (n?=?4, 3) structures are found in which dimethylaminoborole is a six-electron donor bridging ligand using electron pairs from the nitrogen atom as well as from the two C=C double bonds. For the more highly unsaturated [C₄H₄BN(CH₃)₂]₂Fe₂(CO) _n (n?=?2, 1), low energy singlet (n?=?2) and triplet (n?=?1) perpendicular structures are also found with similar bridging six-electron donor dimethylaminoborole ligands. In addition, highly unsaturated [C₄H₄BN(CH₃)₂]₂Fe₂(CO) _n (n?=?3, 2, 1) structures are found with agostic hydrogen atoms bridging an iron?Ccarbon bond.     

Bond length and bond multiplicity: sigma-bond prevents short pi-bonds

Analysis of model compounds such as Fe2(CO)6, C2 and HBBH shows that pi-bonds left to themselves are shorter than sigma-bonds; in many ways sigma-bonds prevent pi-bonds from adopting their optimal shorter distances.     

Oblate deltahedra in dimetallaboranes: geometry and chemical bonding

A new series of nonspherical and very oblate deltahedra, conveniently called the oblatocloso deltahedra, is found in dimetallaboranes among which the dirhenaboranes Cp2Re2B(n-2)H(n-2) (8 相似文献