Quality evaluation of Rhizoma Belamcandae (Belamcanda chinensis (L.) DC.) by using high-performance liquid chromatography coupled with diode array detector and mass spectrometry

A high-performance liquid chromatography coupled with diode array detector and mass spectrometry (HPLC-DAD-MS) method was developed to evaluate the quality of Rhizoma Belamcandae (Belamcanda chinensis (L.) DC.) through establishing chromatographic fingerprint and simultaneous determination of seven phenolic compounds. The analysis was achieved on an Alltima C(18) analytical column (250 mm x 4.6 mm i.d. 5 microm) using linear gradient elution of acetonitrile-0.1% trifluoroacetic acid. The correlation coefficients of similarity were determined from the HPLC fingerprints, and they shared a close similarity. By using an online APCI-MS/MS, twenty phenols were identified. In addition, seven of these phenols including mangiferin, 7-O-methylmangiferin, tectoridin, resveratrol, tectorigenin, irigenin and irisflorentin were quantified by the validated HPLC-DAD method. These phenols are considered to be major constituents in Rhizoma Belamcandae, and are generally regarded as the index for quality assessment of this herb. This developed method by having a combination of chromatographic fingerprint and quantification analysis could be applied to the quality control of Rhizoma Belamcandae.     

Speciation of selenomethionine and selenocystine using online micro-column containing Cu(II) loaded nanometer-sized Al2O3 coupled with ICP-MS detection

A flow injection online speciation procedure by using micro-column packed with Cu(II) loaded nanometer-sized Al₂O₃ coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the separation and determination of selenomethionine (SeMet) and selenocystine (SeCys₂) has been developed. The main factors affecting the separation and preconcentration of SeMet and SeCys₂ including pH value, sample flow rate, eluent concentration, eluent volume and flow rate, and interfering ions have been investigated. It was found that SeCys₂ could be selectively retained by micro-column packed with Cu(II) loaded nanometer-sized Al₂O₃ at pH 4.0, and the retained SeCys₂ could be eluted by 1.0 mol L⁻¹ HNO₃, while SeMet was not retained and passed through the micro-column directly at this pH. Both SeMet and SeCys₂ could be quantitatively adsorbed by the micro-column at pH 9.0, and the retained SeMet and SeCys₂ could be easily eluted with 1.0 mol L⁻¹ HNO₃. The content of SeMet was obtained by subtracting the SeCys₂ from the total content of seleno amino acids. With the enrichment factor of 7.8 and 7.7, the limits of detection (LODs) for SeMet and SeCys₂ were found to be 24 pg Se mL⁻¹ and 21 pg Se mL⁻¹, respectively. The relative standard deviations (RSDs) for SeCys₂ and SeMet with seven replicate determinations of 1.0 ng mL⁻¹ SeMet and SeCys₂, were 2.1% and 1.6%, respectively, the sampling frequency of 8 h⁻¹ was obtained. The proposed method was applied to the speciation of SeMet and SeCys₂ in selenized yeast, human urine and serum with satisfactory results.     

Electrochemistry and Voltammetric Determination of Adenosine with N‐Hexylpyridinium Hexafluorophosphate Modified Electrode

An ionic liquid N‐hexylpyridinium hexafluorophosphate (HPPF₆) modified carbon paste electrode was fabricated for the sensitive voltammetric determination of adenosine in this paper. Carbon ionic liquid electrode (CILE) was prepared by mixing graphite powder and HPPF₆ together and the CILE was characterized by scanning electron microscopy (SEM) and electrochemical methods. The electrochemical behaviors of adenosine on the CILE were studied carefully. Compared with the traditional carbon paste electrode (CPE), a small negative shift of the oxidation peak potential appeared with greatly increase of the oxidation peak current, which indicated the presence of ionic liquid in the carbon paste not only as the binder but also as the modifier and promoter. Under the optimal conditions the oxidation peak current increased with the adenosine concentration in the range from 1.0×10^?6 mol/L to 1.4×10^?4 mol/L with the detection limit of 9.1×10^?7 mol/L (S/N=3) by differential pulse voltammetry. The proposed method was applied to the human urine samples detection with satisfactory results.     

Accurate localization and relative quantification of arginine methylation using nanoflow liquid chromatography coupled to electron transfer dissociation and drbitrap mass spectrometry

Protein arginine (Arg) methylation serves an important functional role in eucaryotic cells, and typically occurs in domains consisting of multiple Arg in close proximity. Localization of methylarginine (MA) within Arg-rich domains poses a challenge for mass spectrometry (MS)-based methods; the peptides are highly charged under electrospray ionization (ESI), which limits the number of sequence-informative products produced by collision induced dissociation (CID), and loss of the labile methylation moieties during CID precludes effective fragmentation of the peptide backbone. Here the fragmentation behavior of Arg-rich peptides was investigated comprehensively using electron-transfer dissociation (ETD) and CID for both methylated and unmodified glycine-/Arg-rich peptides (GAR), derived from residues 679–695 of human nucleolin, which contains methylation motifs that are widely-represented in biological systems. ETD produced abundant information for sequencing and MA localization, whereas CID failed to provide credible identification for any available charge state (z=2–4). Nevertheless, CID produced characteristic neutral losses that can be employed to distinguish among different types of MA, as suggested by previous works and confirmed here with product ion scans of high accuracy/resolution by an LTQ/Orbitrap. To analyze MA-peptides in relatively complex mixtures, a method was developed that employs nano-LC coupled to alternating CID/ETD for peptide sequencing and MA localization/characterization, and an Orbitrap for accurate precursor measurement and relative quantification of MA-peptide stoichiometries. As proof of concept, GAR-peptides methylated in vitro by protein arginine N-methyltransferases PRMT1 and PRMT7 were analyzed. It was observed that PRMT1 generated a number of monomethylated (MMA) and asymmetric-dimethylated peptides, while PRMT7 produced predominantly MMA peptides and some symmetric-dimethylated peptides. This approach and the results may advance understanding of the actions of PRMTs and the functional significance of Arg methylation patterns.     

Cd2Ge2O6 nanowires grown by a simple hydrothermal route

Cd₂Ge₂O₆ nanowires have been synthesized by a simple hydrothermal route in the absence of any surfactants. The diameter and length of the Cd₂Ge₂O₆ nanowires with flat tips are 30‐300 nm and several dozens of micrometers, respectivley. X‐ray diffraction and high‐resolution transmission electron microscopy results show that the nanowires are composed of monoclinic Cd₂Ge₂O₆ phase. The growth condition dependence results show that the formation of the Cd₂Ge₂O₆ nanowires undergoes three morphological changes from spherical particles to nanorods, and finally to nanowires. The photoluminescence spectrum of the Cd₂Ge₂O₆ nanowires exhibits three fluorescence emission peaks centered at 422 nm, 490 nm and 528 nm showing the potential application for optical devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical behavior in a stage-structured differential-algebraic prey-predator model with discrete time delay and harvesting

A differential-algebraic model system which considers a prey-predator system with stage structure for prey and harvest effort on predator is proposed. By using the differential-algebraic system theory and bifurcation theory, dynamic behavior of the proposed model system with and without discrete time delay is investigated. Local stability analysis of the model system without discrete time delay reveals that there is a phenomenon of singularity induced bifurcation due to variation of the economic interest of harvesting, and a state feedback controller is designed to stabilize the proposed model system at the interior equilibrium; Furthermore, local stability of the model system with discrete time delay is studied. It reveals that the discrete time delay has a destabilizing effect in the population dynamics, and a phenomenon of Hopf bifurcation occurs as the discrete time delay increases through a certain threshold. Finally, numerical simulations are carried out to show the consistency with theoretical analysis obtained in this paper.     

The approximation of a Crank–Nicolson scheme for the stochastic Navier–Stokes equations

In this paper we prove the convergence of stochastic Navier–Stokes equations driven by white noise. A linearized version of the implicit Crank–Nicolson scheme is considered for the approximation of the solutions to the N–S equations. The noise is defined as the distributional derivative of a Wiener process and approximated by using the generalized _L2$L_2$-projection operator. Optimal strong convergence error estimates in the _L2$L_2$ norm are obtained.     

Insurance claims modulated by a hidden Brownian marked point process

Aimed at better modeling insurance claims in an economic environment driven by business cycles, a new Markov-modulated Poisson process model is proposed, and an algorithm is derived to estimate the hidden Markov process by using the observed information. Our method differs from existing ones in the following ways: the new hidden process can model more efficiently the cyclic state of the economic environment; our theory is based on a variation of the law of large numbers and is easy to understand; the Fourier expansion-based parameter estimation algorithm is flexible and can be more easily implemented than other algorithms. Simulation results not only demonstrate the practicality of our model and algorithm, but also show the efficiency and robustness of the estimation algorithm.     

On equivalence and explicit solutions of a class of matrix equations

It is shown in this paper that three types of matrix equations AX−XF=BY,AX−EXF=BY and which have wide applications in control systems theory, are equivalent to the matrix equation with their coefficient matrices satisfying some relations. Based on right coprime factorization to , explicit solutions to the equation are proposed and thus explicit solutions to the former three types of matrix equations can be immediately established. With the special structure of the proposed solutions, necessary conditions to the nonsingularity of matrix X are also obtained. The proposed solutions give an ultimate and unified formula for the explicit solutions to these four types of linear matrix equations.