Minireview: Advances in Germanium Isotope Analysis by Multiple Collector–Inductively Coupled Plasma–Mass Spectrometry

The advent of multiple collector–inductively coupled plasma–mass spectrometry (MC-ICP-MS) has made the high-precision determination of Ge isotopes possible, which leads to the widespread application of Ge isotopes in earth, ocean, and cosmochemistry fields. This paper reviews the history of Ge isotope analysis, chemical dissolution and purification, and mass spectrometry measurements. Concentrated HNO₃ is sufficient to dissolve nearly all types of samples and HF is also involved for Si-rich samples. Low-temperature ashing prior to dissolution is an alternative way to preconcentrate Ge in organic-rich samples. For different matrices, Ge isotopes can be determined by MC-ICP-MS coupled with a traditional nebulizer system or hydride generation system after two-step separation, one step cation/anion-exchange separation, or Mg/Fe co-precipitation protocols. Ion-exchange column methods are suitable for samples with elevated matrix and Ge content such as sulfides, iron oxides, silicate rocks, and coals, whereas Mg or Fe coprecipitation methods are particularly suitable for all kinds of water. Hydride generation systems are improved over traditional nebulizer system due to the smaller sample quantity and fewer matrix-related interferences. Sample-standard bracketing, double spike, and external Ga isotope normalization are used to mass bias correction and yield consistent results. Analytical methods involving Ge-poor samples and Ge isotope analyses based on different Ge species or specific Ge compound in natural environment will be important prospects in the further study. For further applications of Ge isotopes in mineral deposits such as sulfide and iron oxide deposits, sulfides, and iron oxides reference materials should be developed in the future.     

An efficient stereoselective synthesis of aminocyclohexenes from 7-azanorbornenes via LiAlH4 mediated tandem double bond migration-ring opening sequence

hNav1.7 had received great interest in the past decade owing to its attractive mechanism of actions in pain processing pathway. More recently, we developed a series of efficacious hNav1.7 inhibitors for analgesic, which were characterized with a novel aminocyclohexene as pharmacophore. Herein, we reported our synthetic efforts to construct the unique scaffold, which can be rapidly accessed from readily available 7-azanorbornenes via an unexpected catalyst-free, LiAlH₄ mediated tandem double bond migration-ring opening sequence. A probable mechanism was proposed to illuminate the good regio- and stereoselectivity.     

Phenanthrene derivatives combined charge transport properties and strong solid-state emission

Science China Chemistry - As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and DSPa) were designed and studied. Both materials show...     

Fluorescent Carbon Dots as Cost-Effective and Facile Probes for Caffeic Acid Sensing via a Fluorescence Quenching Process

Caffeic acid (CA), a familiar color stabilizing reagent, has aroused general concern due to its uncontrolled addition, and thus the detection of CA is increasingly important. In our report, the bright carbon dots (CDs) were prepared via hydrothermal treatment with urea and citric acid act as raw material and their characteristics were discussed through X-ray diffraction (XRD), transmission electron microscopy (TEM) and so on. Impressively, the strong emission of the as-prepared CDs (Quantum Yield: 24.3%) decreased sharply upon a full reaction with the added CA. Hence, we first present an improved strategy for determining CA based upon the quenching of the strong emission of CDs. In this strategy, 0.79–100.0 µmol L^??1 caffeic acid could be simply detected, and a detection limit of 0.24 µmol L^??1 was allowed. Additionally, CA in red wine samples can be successfully detected by this method and the exploration of the quenching mechanism of the CA-CDs system was done.     

Palladium-catalyzed cycloaromatization polymerization of enediynes

Bergman cyclization has shown great promise in constructing conjugated polymers.However,the application of this reaction in polymer science is still limited due to the harsh reaction condition and ill-defined structure of the achieved polymers.To this end,the cycloaromatization polymerization of enediynes catalyzed by a series of transition metal catalysts is investigated in this work,by taking advantage of the coordination chemistry of the enediyne with the transition metal complexes.According to the nuclear magnetic resonance (NMR),Fourier transform infrared (FTIR),ultraviolet-visble (UV-Vis) spectroscopies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis,the cycloaromatization polymerization of enediynes proceeds under milder conditions and in a more controlled manner in the presence of palladium(Ⅱ) complexes,giving structurally regulated conjugated polymers in high yields.     

Multiresidue determination of 29 pesticide residues in pepper through a modified QuEChERS method and gas chromatography–mass spectrometry

This study describes the development and use of a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with gas chromatography with mass spectrometry to determine 29 pesticide residues in green, red and dehydrated red peppers. Pesticides were extracted with acetonitrile (1% acetic acid), partitioned with sodium chloride and purified with primary secondary amino and octadecyl silane in acetone. The QuEChERS extraction conditions were optimized, and the matrix effects that might influence recoveries were evaluated and minimized using matrix‐matched calibration curves. Under the optimized conditions, the calibration curves for 29 pesticides showed good linearity in the concentration range of 0.1–10 μg/mL with determination coefficient R² > 0.998. The limits of quantification of the 29 pesticides were 0.006–0.06 mg/kg for green pepper, 0.005–0.039 mg/kg for red pepper and 0.014–0.25 mg/kg for dehydrated red pepper. These values are below the suggested regulatory maximum residue limits. The mean recoveries ranged between 70.1 and 110%, and the relative standard deviations were <13%. The developed method was successfully applied to commercial samples. Some samples were found to contain the 29 pesticides with levels below the legal limits. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis, structure and solution properties of the novel polyampholytes based on cellulose

A novel cellulose-based polyampholyte derivative, carboxylethyl quaternized cellulose (CEQC), was homogeneously synthesized by introducing positively charged quaternary ammonium groups and negatively charged carboxyl groups to the backbone of cellulose. The structure and dilute solution properties of CEQCs were characterized with elemental analysis, FTIR, NMR, viscometer, light scattering and zeta-potential measurement. The nitrogen content and total degree of substituent of acylamino and carboxyl groups increased with an increase of the molar ratio of acrylamide to the anhydroglucose unit of quaternized cellulose (QC). The salt-resistance of CEQC was improved remarkably by introducing opposite charged carboxyl to the QC chains. The intrinsic viscosity of the prepared polyampholytes was found to be very sensitive to the pH of the solutions. CEQC-1, the sample with relative low content of carboxyl groups, behaved as a classical cationic polyelectrolyte. However, CEQC-2 and CEQC-3, the samples with higher content of carboxyl groups, displayed typical polyampholyte behavior, and the isoelectric points (IEP) were determined to be 5.0 and 3.8 respectively. This work provided a facile method for the synthesis of novel cellulose-based polyampholytes with different IEP.