Determination of ergosterol in Fusarium-infected wheat by liquid chromatography-atmospheric pressure photoionization mass spectrometry

A rapid liquid chromatography-atmospheric pressure photoionization mass spectrometry (LC-APPI-MS) method was developed for the determination of ergosterol in wheat grains. The effects of the dopants acetone, toluene and anisole on the ionization efficiency were studied. To identify the predominant ions, APPI-MS-MS studies were performed. Different LC and MS parameters were optimized to obtain maximum sensitivity. The effects of the mobile phase composition and of the flow rate were investigated. Additionally, the effects of the nebulizer gas pressure, the drying gas flow, the vaporizer temperature, the fragmentor voltage and the capillary voltage on the ionization efficiency were evaluated. The calibration curve exhibited good linearity and reproducibility. The detection limit (S/N=3) was 0.15 ng on column, which allows the determination of ergosterol in wheat at a concentration as low as 0.12 microg/g. Twenty wheat varieties artificially infected with Fusarium graminearum were investigated by this method.     

Structural and spectroscopic properties of the peroxodiferric intermediate of Ricinus communis soluble Δ9 desaturase

Large-scale quantum and molecular mechanical methods (QM/MM) and QM calculations were carried out on the soluble Δ(9) desaturase (Δ(9)D) to investigate various structural models of the spectroscopically defined peroxodiferric (P) intermediate. This allowed us to formulate a consistent mechanistic picture for the initial stages of the reaction mechanism of Δ(9)D, an important diferrous nonheme iron enzyme that cleaves the C-H bonds in alkane chains resulting in the highly specific insertion of double bonds. The methods (density functional theory (DFT), time-dependent DFT (TD-DFT), QM(DFT)/MM, and TD-DFT with electrostatic embedding) were benchmarked by demonstrating that the known spectroscopic effects and structural perturbation caused by substrate binding to diferrous Δ(9)D can be qualitatively reproduced. We show that structural models whose spectroscopic (absorption, circular dichroism (CD), vibrational and M?ssbauer) characteristics correlate best with experimental data for the P intermediate correspond to the μ-1,2-O(2)(2-) binding mode. Coordination of Glu196 to one of the iron centers (Fe(B)) is demonstrated to be flexible, with the monodentate binding providing better agreement with spectroscopic data, and the bidentate structure being slightly favored energetically (1-10 kJ mol(-1)). Further possible structures, containing an additional proton or water molecule are also evaluated in connection with the possible activation of the P intermediate. Specifically, we suggest that protonation of the peroxide moiety, possibly preceded by water binding in the Fe(A) coordination sphere, could be responsible for the conversion of the P intermediate in Δ(9)D into a form capable of hydrogen abstraction. Finally, results are compared with recent findings on the related ribonucleotide reductase and toluene/methane monooxygenase enzymes.     

Highly efficient thermal cyclization reactions of alkylidene esters in continuous flow to give aromatic/heteroaromatic derivatives

Intramolecular thermal cyclization and benzannulation reactions of the Gould–Jacobs and Conrad–Limpach types were performed in a designed continuous flow reactor system at temperatures in the range of 300–360 °C and under high pressure conditions (100–160 bar) with very short residence times (0.45–4.5 min) in tetrahydrofuran as a low-boiling point solvent. Substituted heteroaromatic compounds including pyridopyrimidinones and hydroxyquinolines were synthesized in moderate to high yields. Application of the reaction conditions also allows the synthesis of naphthol and biphenyl derivatives. The procedure involves an easy work-up and the non-batchwise preparative synthesis method is suitable for automation.     

The s-monotone index selection rules for pivot algorithms of linear programming

In this paper we introduce the concept of s-monotone index selection rule for linear programming problems. We show that several known anti-cycling pivot rules like the minimal index, Last-In–First-Out and the most-often-selected-variable pivot rules are s-monotone index selection rules. Furthermore, we show a possible way to define new s-monotone pivot rules. We prove that several known algorithms like the primal (dual) simplex, MBU-simplex algorithms and criss-cross algorithm with s-monotone pivot rules are finite methods.     

Turán type inequalities for Krätzel functions

Complete monotonicity, Laguerre and Turán type inequalities are established for the so-called Krätzel function $Z_{\rho }^{\nu }$, defined by$Z_{\rho }^{\nu }(u)=\underset{0}{\overset{\infty }{\int }}{t}^{\nu ?1}{e}^{?t^{\rho }?\frac{u}{t}}\mathrm{d}t,$ where $u>0$ and $\rho ,\nu \in \mathbb{R}$. Moreover, we prove the complete monotonicity of a determinant function of which entries involve the Krätzel function.     

Separation of Poly(propylene) Samples According to Tacticity Using a Hypercarb Column

Summary: Samples of polypropylene having different stereoregularities, i.e., differing in the isotactic or syndiotactic stereosequence distribution, were separated by means of high-temperature gradient adsorption liquid chromatography. The porous graphite was used as stationary phase in the column packing (Hypercarb®). Predominantly isotactic samples eluted in 1-decanol, while predominantly syndiotactic samples eluted in a binary gradient composed of 1-decanol and 1,2,4-trichlorobenzene. Their elution volumes increased with the average content of the syndiotactic units (racemo dyads mole fraction as determined with the NMR spectroscopy) in the samples. Thus these chromatographic separations represent a new method for the analysis and characterization of stereoregular polyolefins. It requires substantially less time and solvents than the commonly used methods.     

Spanning 2-strong tournaments in 3-strong semicomplete digraphs

We prove that every 3-strong semicomplete digraph on at least 5 vertices contains a spanning 2-strong tournament. Our proof is constructive and implies a polynomial algorithm for finding a spanning 2-strong tournament in a given 3-strong semicomplete digraph. We also show that there are infinitely many (2k−2)-strong semicomplete digraphs which contain no spanning k-strong tournament and conjecture that every(2k−1)-strong semicomplete digraph which is not the complete digraph on 2k vertices contains a spanning k-strong tournament.     

Precise formulae for Bravo coefficients

Daley et al. assessed the BRAVO (balancing reduces asymptotic variance of outputs) effect of a finite-buffer Markovian many-server system in terms of an asymptotic variance ratio. The expressions given for the ratio in just the two cases considered both appear incorrect. Here, we derive the correct expressions.