Chunli Xu

Simultaneous determination of three organophosphorus pesticides residues in vegetables using continuous-flow chemiluminescence with artificial neural network calibration

In this article, a continuous-flow chemiluminescence (CL) system with artificial neural network calibration is proposed for simultaneous determination of three organophosphorus pesiticides residues. This method is based on the fact that organophosphorus pesticides can be decomposed into orthophosphate with potassium peroxodisulphate as oxidant under ultraviolet radiation and that the decomposing kinetic characteristics of the organophosphorus pesticides with different molecular structure are significantly different. The produced orthophosphate can react with molybdate and vanadate to form the vanadomolybdophosphoric heteropoly acid, which can oxidize luminol to produce intense CL emission. The CL intensity of the solution was measured and recorded every 2s in the range of 0-250s. The obtained data were processed chemometrically by use of a three-layered feed-forward artificial neural network trained by back-propagation learning algorithm, in which input node, hidden node and output nodes were 65, 21 and 3, respectively. The proposed multi-residue analysis method was successfully applied to the simultaneous determination of the three organophosphorus pesticides residue in some vegetables samples.

Visual chiral recognition of tryptophan enantiomers using unmodified gold nanoparticles as colorimetric probes.

A simple protocol to distinguish enantiomers is extremely intriguing and useful. In this study, we propose a low-cost, facile, sensitive method for visual chiral recognition of enantimers. It is based on the inherent chirality of gold nanoparticles (AuNPs), and the unmodified AuNPs are used as chiral selector for D- and L-Tryptophan (Trp). In the presence of D-Trp, an appreciable red-to-blue color change of AuNPs solution can be observed, whereas no color change is found in the presence of L-Trp. The method can be used to detect D-Trp in the range of 0.2-10 μM, and the limit of detection is 0.1 μM. The chiral assay described in this work is easily readout with the naked eye or using a UV-vis spectrometer. Furthermore, the AuNPs can selectively adsorb D-Trp, and simple centrifugation can allow the precipitation of D-Trp with AuNPs and leave a net excess of the other enantiomer in solution, thus resulting in enantioseparation. In this method, AuNPs do not need any labeling or modifying with chiral molecules. The method is more attractive because of its high sensitivity, low cost, ready availability and simple manipulation.

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis.

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn(2+) which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO(4)(-) passes through the mini-column to be waste, then the concentrated Mn(2+) is eluted reversely and measured by the luminol-H(2)O(2) CL system. The calibration graph is linear in the range of 4-4000 mg l(-1) and the detection limit is 2 mg l(-1). A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h(-1). The relative standard deviation was 4.4% for 10 mg l(-1) COD (n=11), 4.8% for 100 mg l(-1) COD (n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.

Chemiluminescence flow-through sensor for ofloxacin using solid-phase PbO2 as an oxidant

A novel chemiluminscence (CL) flow-through sensor for ofloxacin is described. It was based on the sensitizing effect of ofloxacin on the CL oxidation of sulfite by PbO(2) in H(2)SO(4) media. By a very simply means, the solid-phase PbO(2) was immobilized inside of the CL flow cell as CL oxidant. The column of solid PbO(2) could be reused about 400 times during a period of 50 h. The calibration graph is linear in the range 0.2-10 mug ml(-1) with a detection limit of 7.8x10(-8) g ml(-1) (S/N=3). This method has been successfully applied to determine ofloxacin in pharmaceutical preparation.

β-Cyclodextrin-modified silver nanoparticles as colorimetric probes for the direct visual enantioselective recognition of aromatic α-amino acids

Efficient enantiomer discrimination by a convenient method remains a challenge in biochemical and pharmaceutical fields. Herein we have modified silver nanoparticles (AgNPs) with β-cyclodextrin (β-CD) to obtain a probe for the chiral recognition of aromatic α-amino acids. This assay relies on the distance-dependent optical properties of AgNPs and the difference in inclusion binding strength between the aromatic amino acid enantiomers and the β-CD host. The response of β-CD functionalized-AgNPs to certain chiral aromatic amino acid enantiomers namely D- and L-phenylalanine (Phe), D- and L-tryptophan (Trp), and D- and L-tyrosine (Tyr) in phosphate buffer solutions was studied in detail. In the presence of D-Phe (or L-Trp or L-Tyr), an appreciable yellow-to-red color change of the AgNP solution can be observed, whereas no color change is found in the presence of L-Phe (or D-Trp or D-Tyr). This method can be used to quantitatively determine the percentage of D-Phe in a mixture of D- and L-Phe. The chiral assay described in this work is easily readout with the naked eye or using a cheap UV-vis spectrometer. This method excels by its simplicity, low cost, and good availability of materials.

Self-assembly of L-cysteine–gold nanoparticles as chiral probes for visual recognition of 3,4-dihydroxyphenylalanine enantiomers

A simple protocol to distinguish enantiomers is extremely intriguing and useful. Herein, we report on a method for the visual recognition of 3,4-dihydroxyphenylalanine (Dopa) enantiomers. It is based on the chirality of L-cysteine-capped gold nanoparticles (L-Cys-capped AuNPs) that can be used as a chiral selector for L- and D- forms of Dopa. On addition of L-Dopa to a solution of the L-Cys-capped AuNPs, a color change from red to blue can be seen, while no color change is found on addition of D-Dopa. The chiral recognition can be achieved by eye and simple spectrophotometry. Notably, this method does not require complicated chiral modification. The method excels through its low-cost, good availability of materials, and its simplicity.

Cu–Ag/hydrotalcite catalysts for dehydrogenative cross-coupling of primary and secondary benzylic alcohols

The development of new and inexpensive heterogeneous catalysts for direct C–C cross-coupling of primary and secondary alcohols is a challenging goal and has great importance in academic and industrial sectors. In this work Cu–Ag/hydrotalcite (Cu–Ag/HT) catalysts were prepared and tested for their impact on this cross-coupling. The effect of supports, including MgO, γ-Al2O3 and HT with different Mg:Al molar ratios, was investigated. It was found that the acidic or basic properties of the supports affected product selectivity. The roles of Cu and Ag sites in the cross-coupling were also investigated with the prepared Cu–Ag/HT catalyst demonstrating high activity and selectivity for the reaction. The yield-to-target product of β-phenylpropiophenone reached 99% after 1 h under optimum reaction conditions. The stability in air and reusability studies show that Cu–Ag/HT can be stored for 6 days and can be used five times without apparent deactivation, respectively.

Ag–Cu nanoparticles as efficient catalysts for transesterification of β-keto esters under acid/base-free conditions

Transesterification of β-keto esters and alcohols are traditionally catalyzed by acid or basic catalysts. However, these traditional catalysts do not always meet the requirements of modern synthetic chemistry which need to be highly efficient, selective, and environmentally friendly. In this work, Ag–Cu metal sites were first introduced as transesterification catalysts. The effect of the support, Ag : Cu molar ratio, and reaction conditions were investigated. The Ag–Cu metal sites were proved to be active in the β-ketoester transesterification with various alcohols, having yields comparable to the conventional acid- or base-catalysts.