Simultaneous measurement of leucine and isoleucine by multivariate image analysis-thin layer chromatography (MIA-TLC)

This paper introduces a new application of multivariate image analysis-thin layer chromatography, as simple and inexpensive method, for semi-separation and simultaneous measurement of two isomeric amino acids leucine (Leu) and isoleucine (Ile). The images recorded by a digital camera were processed by home-made software and were converted to TLC chromatograms. Linear calibration graphs were obtained for individual analytes with detection limits of 0.60 and 0.48 μg for Leu and Ile, respectively. The mobile phase composition was optimized for maximum separation. However, complete separation of the spots of the analytes was not obtained. So, the chromatograms were processed by partial least square regression to resolve the overlapped chromatogram. This offered simultaneous determination of Leu and Ile in their binary mixtures. Suitable models were obtained with root mean square error of prediction of 0.008 and 0.009 μg for Leu and Ile, respectively. The prediction ability of the developed model was assessed by determination of the analytes in diluted serum plasma and the obtained percent of recoveries were in the range of 95–105 %.     

A link between impact sensitivity of energetic compounds and their activation energies of thermal decomposition

A new relationship is introduced between impact sensitivity of energetic compounds and their activation energies of thermal decomposition. In this relationship, the impact sensitivity of an energetic compound with general formula C_aH_bN_cO_d is a function of its activation energy of thermal decomposition as well as the ratio of \( \left( {\frac{{n_{\text{H}} }}{{n_{\text{O}} }}} \right) \) and the contribution of specific molecular structural parameters. The new correlation can help us to elucidate the mechanism of initiation of energetic materials by impact. It can be used to predict the magnitude of impact sensitivity of new energetic materials. The new correlation has the root mean square and the average deviations of 2.22 and 1.79 J, respectively, for 40 energetic compounds with different molecular structures. The proposed new method is also tested for 11 energetic compounds, which have complex molecular structures, e.g., 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane and 1,3,7,9-tetranitrophenoxazine.     

用于光电化学氧化氯酸盐的钒酸铋光电阳极的合成与表征

采用便捷的涉及电沉积和退火过程的两步法在F掺杂的氧化锡基体上制备了高品质的多晶钒酸铋(BiVO4)薄膜,并运用扫描电镜、透射电镜、X射线衍射(XRD)、傅里叶变换红外光谱、紫外-可见光吸收光谱和拉曼光谱表征了所制薄膜的形貌和结构特征.XRD和光学分析结果表明,BiVO4薄膜为纯相的单斜白钨矿晶相结构.将该薄膜通过电化学(EC),光化学(PC)和光电化学(PEC)过程用于水溶液中氯酸离子的多相氧化反应中.采用紫外-可见吸附光谱仪监测氯酸盐浓度的降低.结果发现,在光的照射下采用PEC法时,BiVO4可有效催化氯酸盐的氧化.氯酸盐氧化反应级数为1级,PEC过程的反应速率常数明显高于EC和PC过程的.同时,提出了基于形成了高氯酸离子的催化氧化氯酸盐的反应机理.     

Dry reforming of greenhouse gases CH4/CO2 over MgO-promoted Ni–Co/Al2O3–ZrO2 nanocatalyst: effect of MgO addition via sol–gel method on catalytic properties and hydrogen yield

Sol–gel method was employed to prepare Ni–Co/Al₂O₃–MgO–ZrO₂ nanocatalyst with various loadings of MgO (5, 10 and 25 wt%) for dry reforming of methane. The physiochemical properties of nanocatalysts were characterized by XRD, field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), BET and fourier transform infrared spectroscopy (FTIR) analysis. Evaluation of catalytic performance was conducted in atmospheric pressure, stoichiometric feed ratio, GHSV of 24 l/g_cat h and temperature range from 550 to 850 °C. XRD patterns represented that as MgO content increases, the amorphous behavior slightly intensifies and also dispersion of active phase improves which probably caused by strong metal–support interaction. Furthermore, FESEM analysis confirmed that all of prepared samples are nano scale. EDX results besides verifying the declared claim about the dispersion of samples proved the presence and detected the position of the various elements. In addition, based on the FESEM analysis, narrow particle size distribution, uniform morphology and dispersion without agglomeration were found for Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO. Moreover, smallest average particle size 11.6 nm (close to the critical size for Ni–Co catalyst to avoid carbon formation) was obtained for this nanocatalyst. Also, according to the BET analysis, MgO rich nanocatalyst represented the higher surface area than the other ones. Based on the excellent characterizations, Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO exhibited the best products yield through all of the investigated temperature e.g. H₂ = 96.9 % and CO = 97.1 % at 850 °C. Furthermore, this nanocatalyst demonstrated the stable yield with H₂/CO close to unit during 1,440 min stability test.     

Nuclear Magnetic Resonance Study of the Stoichiometry and Stability of Several Li+‐Crown Ether Complexes in Various Acetonitrile‐Nitrobenzene Mixtures

Lithium‐7 NMR spectrometry was used to study the complexation reaction between lithium ions and several 12‐, 15‐ and 18‐membered crown ethers in a number of binary acetonitrile‐nitrobenzene mixtures. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift‐mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. Among different sized crown ethers used, 15‐crowns were found to form the most stable Li⁺ complexes in the series. The influence of substitution on the macrocyclic rings on the stability of the resulting complexes is discussed.     

Influence of crucible geometry and position on the induction heating process in crystal growth systems

A series of 2D finite element numerical simulations of induction heating process for an oxide Czochralski crystal growth system has been done for different shapes and locations of a metal crucible. Comparison between the computational results shows the importance of crucible shape, geometry and its position with respect to the RF-coil on the electromagnetic field and heat generation distribution in the growth setup.     

Silabenzene through divalent precursors at theoretical levels

Abstract  

Based on geometries and relative energies, three different mechanisms are proposed for the rearrangements of five isomers of silacyclohexadienylidenes to silabenzene at B3LYP and MP2 levels: (1) [1,2]-hydrogen migration through a planar transition state, (2) [1,4]-hydrogen migration through a boat transition state, and (3) zip-zap mechanism, comprised of three successive [1,2]-hydrogen migrations. The above results are compared and contrasted to rearrangements of the corresponding cyclohexadienylidenes to benzene.     

Optimal server scheduling in nonpreemptive finite-population queueing systems

We consider a finite-population queueing system with heterogeneous classes of customers and a single server. For the case of nonpreemptive service, we fully characterize the structure of the server's optimal service policy that minimizes the total average customer waiting costs. We show that the optimal service policy may never serve some classes of customers. For those classes that are served, we show that the optimal service policy is a simple static priority policy. We also derive sufficient conditions that determine the optimal priority sequence.