Analysis of cyanoacrylate ultraviolet absorbers using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry: influence of fragmentor voltage and solvent on ionization and fragmentation behaviors

Ionization efficiencies and fragmentation patterns of cyanoacrylate ultraviolet (UV) absorbers, Uvinul 3035 and Uvinul 3039, were studied using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS). Solvent effect on the ionization efficiencies was investigated using methanol, ethanol, acetone, and chloroform. The fragmentation patterns were also investigated by varying the fragmentor voltage. Solvated ions, the [M+H + solvent](+) of methanol, ethanol, and acetone were detected, but the [M+H + chloroform](+) ion was not observed. For Uvinul 3039 in chloroform, the [M+CHCl(2)](+) ion was detected instead of the solvated ion. Relative abundance of the solvated ion was decreased by increasing the fragmentor voltage. Fragment ions of m/z 250, 232, and 204 were detected and their abundance increased with an increase in the fragmentor voltage. The m/z 250 ion can be accounted for by a McLafferty rearrangement. The fragment ions of m/z 232 and 204 were formed not only by subsequent fragmentations of the m/z 250 ion, but also by ion-molecule reactions of solvent ion and neutral analyte.     

Cu-facilitated C-O bond formation using N-hydroxyphthalimide: efficient and selective functionalization of benzyl and allylic C-H bonds

A highly efficient protocol for the benzyl or allylic C-H functionalization of simple hydrocarbons has been developed using stoichiometric amounts of N-hydroxyphthalimide and PhI(OAc)2 in the presence of CuCl catalyst. The reaction was revealed to proceed via a radical pathway, in which phthalimide N-oxyl (PINO) radical plays a dual role, serving as a catalytic hydrogen abstractor from hydrocarbons as well as a stoichiometric reagent to couple with the resultant alkyl radicals.     

Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates

An efficient direct one-pot glycosylation method with anomeric hydroxy sugars as glycosyl donors employing phthalic anhydride and triflic anhydride as activating agents has been developed. Thus, highly stereoselective beta-mannopyranosylations were achieved by the reaction of 2,3-di-O-benzyl-4,6-O-benzylidene-D-mannopyranose (2) with phthalic anhydride in the presence of DBU at room temperature followed by sequential addition of DTBMP and Tf2O and glycosyl acceptors to the reaction mixture at -78 degrees C in one-pot. Stereoselective alpha-glucopyranosylations with 2,3-di-O-benzyl-4,6-O-benzylidene-D-glucopyranose (25) and other glycosylations with glucopyranoses and mannopyranoses having tetra-O-benzyl- and tetra-O-benzoyl protecting groups were also possible by utilizing the present one-pot glycosylation protocol. The possible mechanism for the beta-mannosylation with 2 was proposed based on the NMR study, in which alpha-mannosyl phthalate 55alpha and alpha-mannosyl triflate 59 were detected as intermediates. The versatility and efficiency of the present glycosylation methodology, especially those of the beta-mannopyranosylation protocol, were readily demonstrated by the efficient synthesis of protected beta-(1-->4)-D-mannotriose 62 and beta-(1-->4)-D-mannotetraose 67 with perfect beta-stereoselectivity.     

Carbon supported CdSe nanocrystals

Insights to the mechanism of CdSe nanoparticle attachment to carbon nanotubes following the hot injection method are discussed. It was observed that the presence of water improves the nanotube coverage while Cl containing media are responsible for the shape transformation of the nanoparticles and further attachment to the carbon lattice. The experiments also show that the mechanism taking place involves the right balance of several factors, namely, low passivated nanoparticle surface, particles with well-defined crystallographic facets, and interaction with an organics-free sp2 carbon lattice. Furthermore, this procedure can be extended to cover graphene by quantum dots.     

Dopamine detection based on its quenching effect on the anodic electrochemiluminescence of CdSe quantum dots

Anodic electrochemiluminescence (ECL) of CdSe quantum dots (QDs) in a neutral system was for the first time observed at a relatively low potential by using sulfite as a co-reactant to produce the ECL emission at an indium tin oxide (ITO) electrode, which could be used for the sensitive detection of ECL quenchers using dopamine (DA) as a model molecule.     

Adsorptive Voltammetric Behaviors of Resveratrol at Graphite Electrode and its Determination in Tablet Dosage Form

The adsorptive voltammetric behavior of resveratrol was studied at a graphite electrode in B‐R buffer (pH = 6.0) solution using adsorptive cyclic voltammetric technique. The oxidation of resveratrol is an irreversible adsorption controlled process. The oxidation mechanism was proposed and discussed in this work. The dependence of the current on pH and the concentration and nature of buffer were investigated to optimize the experimental conditions for the determination of resveratrol. It was found that in the range of 8.0 × 10^?9 ～ 2.0 × 10^?6 mol/L, the currents measured by differential pulse voltammetries presented a good linear property as a function of the concentrations of resveratrol. In addition, validation parameters, such as reproducibility, sensitivity and recovery were evaluated as well. The proposed method was also successfully applied for the determination of resveratrol in Chinese patent medicine with good results.     

Determination of Polybrominated Diphenyl Ethers in Coastal and River Sediments by Pressurized Liquid Extraction Coupled with Gas Chromatography‐Mass Spectrometry

This study presents a time‐ and solvent‐saving method, pressurized liquid extraction (PLE), to extract polybrominated diphenyl ethers (PBDEs) in sediment samples. The effects of various operating parameters (i.e., extraction solution, temperature, pressure, static/dynamic extraction times) for the quantitative extraction of PBDEs by home‐made PLE were systematically investigated and optimized. The analytes were then identified and quantitated by gas chromatography‐mass spectrometry (GC‐MS) in selected ion monitoring (SIM) mode. The 16 PBDE congeners (from tri‐ to deca‐BDE) can be completely extracted by dichloromethane: n‐hexane (3/2, v/v) at 100 °C and 100 atm combined with 15 min static and then 15 min dynamic extraction steps. Recovery of PBDEs in spiked sediment samples ranged from 52 to 104% with 2‐16% RSD, except for BDE‐206. Limits of quantitation (LOQ) were established between 4 and 400 pg/g (dry weight) in 10 g of sediment sample. The extraction efficiency of the PLE was also compared with the traditional Soxhlet extraction method. The total contents of PBDEs ranged from 8.0 to 37.9 ng/g (dry weight) in various river and coastal sediment samples in Taiwan. Deca‐BDE (BDE‐209) was the major PBDE detected in these sediment samples.     

A new dihydroisocoumarin from the strain Aspergillus sp. CMM, an endophytic fungus of Cephalotaxus mannii

From the branch tissue of Cephalotaxus mannii, the endophytic fungal strain CMM was isolated and determined to belong to the genus Aspergillus according to its internal transcribed spacer (ITS) sequence of rDNA (ITS1-5.8S-ITS2). From the extracts of the fermentation broth of CMM, a new compound, namely 5-O-α-D-glucopyranosyl-5-hydroxymellein (1), was isolated, together with a known compound 4-hydroxymellein (2). Their structures were elucidated on the basis of 1D and 2D NMR data. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 461–462, September-October, 2008.     

聚苯乙烯负载聚酰胺-胺型螯合树脂对Hg2+的吸附分离性能

以聚苯乙烯负载聚酰胺-胺型螯合树脂为吸附剂,确定了金属离子溶液的pH值及流速;洗脱液的流速.浓度及酸度等最佳柱实验条件,测定了以Na 、Mg2 、Ca2 、Ba2 、Ni2 、Cd2 ,Pb2 、Cu2 、Zn2 等金属离子作为干扰离子时谊吸附荆对Hg2 的回收率.实验结果表明,该树脂对Hg2 具有较高的吸附选择性,从二元金属离子混合液中对Hg2 的回收率达到85.3%以上.     

Visible-Light-Driven Three-Component Reaction of Unactivated Alkenes Enables Access to Monofluoro γ-Amino Acids

A strategy for the synthesis of diverse protected α-monofluoro-γ-amino acid derivatives has been developed. This reaction assembles a simple enamide, quinoxalin-2(1H)-one, and diethyl 2-bromo-2-fluoromalonate through a three-component reaction driven by visible light. The advantages of this protocol include the simplicity of its operation, mild conditions, high functional group tolerance, and applicability to a wide variety of substrates. The synthesis of this fluorine-containing amino acid derivative has significant value for potential applications in medicinal chemistry and chemical biology.