Determination of darusentan enantiomers in rat plasma by enantioselective liquid chromatography with tandem mass spectrometry using cellulose-based chiral stationary phase

A sensitive, specific and rapid liquid chromatography-mass spectrometry (LC-MS/MS) method has been developed and validated for enantioselective determination of darusentan enantiomers, orally active potent endothelin-A receptor antagonist, in rat plasma. The plasma samples were pretreated by protein precipitation with methanol and baseline chromatographic separation was performed on a Chiralcel OD-RH column with a mobile phase consisting of acetonitrile/water/formic acid (50:50:0.1, v/v/v) at a flow rate of 0.5 mL/min. The detection was accomplished by multiple-reaction monitoring (MRM) scanning via electrospray ionization (ESI) source operating in the negative ionization mode. The calibration curve was linear over the investigated concentration from 0.500 to 2500 ng/mL (r≥0.995) for each enantiomer using 50 μL of rat plasma. The lower limit of quantitation (LLOQ) for each enantiomer was 0.500 ng/mL. The intra- and inter-day precisions were not more than 10.2% and the accuracy was within the range from -5.4 to 6.3% for darusentan enantiomers. No chiral inversion was observed during the plasma preparation, storage and analysis. The method proved adequate for enantioselective pharmacokinetic studies of darusentan enantiomers after oral administration of three different doses of racemic darusentan.     

Rapid simultaneous determination of isoflavones in Radix puerariae using high-performance liquid chromatography-triple quadrupole mass spectrometry with novel shell-type column

A high-performance liquid chromatography (HPLC) coupled with triple quadrupole mass spectrometry (MS/MS) method was developed for rapid determination of 13 isoflavones in Radix puerariae. A novel shell-type column, namely Kinetex core-shell C(18) column (50 mm×2.1 mm id, 2.6 μm), and gradient elution were used during the analysis. The chromatographic peaks of 13 investigated compounds were identified by comparing their retention time and MS data with the related reference compounds. Multiple-reaction monitoring (MRM) was employed for the quantitative analysis with negative ionization mode. All calibration curves showed good linearity (r(2)>0.9990) within test ranges. The LOD and LOQ were lower than 0.017 and 0.873 μg/mL on column, respectively. The intra- and inter-day precisions for 13 analytes were <1.17 and 2.17%, respectively, and the recoveries were 93.1-104.4%. The validated method was applied for quantitative analysis of 13 isoflavones in 7 species of Radix puerariae. The result demonstrated that HPLC-MS/MS system with Kinetex column could be a promising analytical tool for the determination of isoflavones in traditional Chinese medicines, which is helpful for comprehensive evaluation of quality of R. puerariae.     

Rapid simultaneous determination of multiple pesticide residues in traditional Chinese medicines using programmed temperature vaporizer injection-fast gas chromatography coupled with mass spectrometry

A fast gas chromatography coupled with mass spectrometry (GC-MS) using large volume injection with programmed temperature vaporizer in solvent vent mode (PTV-LVI-SV) was developed for the trace determination of multiple pesticide residues in traditional Chinese medicines (TCMs). Experimental conditions of PTV-LVI-SV injection were optimized by central composite design. The optimized result was that initial temperature was held at 40°C for 39 s, vent flow rate was set at 45 mL/min and vent pressure was held at 0 psi for 36 s, injection volume was 10 μL. Furthermore, the quick and effective QuEChERS (quick, easy, cheap, effective, rugged and safe) method was performed to extract and purify pesticide residues in TCMs. The prepared samples were analyzed with GC-MS in the selected ion monitoring mode (SIM). The lowest LOD was 4 μg/kg for some pesticides. The recoveries were checked by spiking samples with pesticides at 25, 50 and 250 μg/kg. The average recoveries of most pesticides were from 80 to 118%. The result indicated that QuEChERS and PTV-LVI-SV GC-MS method was a rapid and sensitive analysis technique for the determination of multiple pesticide residues in TCMs.     

Characterizing compact Clifford semigroups that embed into convolution and functor-semigroups

We study algebraic and topological properties of the convolution semigroup of probability measures on a topological groups and show that a compact Clifford topological semigroup S embeds into the convolution semigroup P(G) over some topological group G if and only if S embeds into the semigroup exp(G)\exp(G) of compact subsets of G if and only if S is an inverse semigroup and has zero-dimensional maximal semilattice. We also show that such a Clifford semigroup S embeds into the functor-semigroup F(G) over a suitable compact topological group G for each weakly normal monadic functor F in the category of compacta such that F(G) contains a G-invariant element (which is an analogue of the Haar measure on G).     

Center problem and bifurcation behavior for a class of quasi analytic systems

Results about the study of nonanalytic systems’ center-focus and bifurcations of limit cycles are hardly seen in published references up till now. In this paper, we investigated the problems of determining center or focus and bifurcations for a class of planar quasi cubic analytic systems. The recursive formula to figure out generalized focal values is given, ulteriorly the conditions for four limit cycles from the origin or the point at infinity are obtained and center problems are considered. What is worth pointing out is that we offer a kind of interesting phenomenon that the exponent parameter λ control the non-analyticity of studied system (3.8) in this paper. In terms of nonanalytic differential systems, our work is new.     

Error rates in classification of multivariate Gaussian random field observation

We consider the problem of supervised classifying the multivariate Gaussian random field (GRF) single observation into one of two populations in case of given training sample. The populations are specified by different regression mean models and by common factorized covariance function. For completely specified populations, we derive a formula for Bayes error rate. In the case of unknown regression parameters and feature covariance matrix, the plug-in Bayes discriminant function based on ML estimators of parameters is used for classification. We derive the actual error rate and the asymptotic expansion of the expected error rate associated with plug-in Bayes discriminant function. These results are multivariate generalizations of previous ones. Numerical analysis of the derived formulas is implemented for the bivariate GRF observations at locations belonging to the two-dimensional lattice with unit spacing.     

A bargaining game model for measuring performance of two-stage network structures

Data envelopment analysis (DEA) is a method for measuring the efficiency of peer decision making units (DMUs), where the internal structures of DMUs are treated as a black-box. Recently DEA has been extended to examine the efficiency of DMUs that have two-stage network structures or processes, where all the outputs from the first stage are intermediate measures that make up the inputs to the second stage. The resulting two-stage DEA model not only provides an overall efficiency score for the entire process, but also yields an efficiency score for each of the individual stages. The current paper develops a Nash bargaining game model to measure the performance of DMUs that have a two-stage structure. Under Nash bargaining theory, the two stages are viewed as players and the DEA efficiency model is a cooperative game model. It is shown that when only one intermediate measure exists between the two stages, our newly developed Nash bargaining game approach yields the same results as applying the standard DEA approach to each stage separately. Two real world data sets are used to demonstrate our bargaining game model.     

The Spectrum of Tetrahedral Quadruple Systems

An ordered analogue of quadruple systems is tetrahedral quadruple systems. A tetrahedral quadruple system of order v and index λ, TQS(v, λ), is a pair (S, T){(S, \mathcal{T})} where S is a finite set of v elements and T{\mathcal{T}} is a family of oriented tetrahedrons of elements of S called blocks, such that every directed 3-cycle on S is contained in exactly λ blocks of T{\mathcal{T}} . When λ = 1, the spectrum problem of TQS(v, 1) has been completely determined. It is proved that a TQS(v, λ) exists if and only if λ(v − 1)(v − 2) ≡ 0 (mod 3), λv(v − 1)(v − 2) ≡ 0 (mod 4) and v ≥ 4.     

交叉货币百慕大式互换期权的定价

本文首先研究了涉及两种货币市场的Hull-White随机利率模型.以此为基础,本文给出了交叉货币百慕大式互换期权的定价公式.由于无法得到显式定价公式,我们使用了Least Squared Monte-Carlo(LSM)算法来确定期权的最优执行时刻.最后本文给出了数值计算方面的结果.     

A diruthenium catalyst for selective, intramolecular allylic C-H amination: reaction development and mechanistic insight gained through experiment and theory

The mixed-valent paddlewheel complex tetrakis(2-oxypyridinato)diruthenium(II,III) chloride, [Ru(2)(hp)(4)Cl], catalyzes intramolecular allylic C-H amination with bis(homoallylic) sulfamate esters. These results stand in marked contrast to reactions performed with dirhodium catalysts, which favor aziridine products. The following discussion constitutes the first report of C-H amination using complexes such as [Ru(2)(hp)(4)Cl] and related diruthenium adducts. Computational and experimental studies implicate a mechanism for [Ru(2)(hp)(4)Cl]-promoted C-H amination involving hydrogen-atom abstraction/radical recombination and the intermediacy of a discrete, albeit short-lived, diradical species. The collective data offer a coherent model for understanding the preference of this catalyst to oxidize allylic (and benzylic) C-H bonds.