Magnetic solid-phase extraction of Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.     

Determination of chlorophenols in environmental water samples using directly suspended droplet liquid-liquid-liquid phase microextraction prior to high-performance liquid chromatography

A new sample preparation method named directly suspended droplet liquid-liquid-liquid phase microextraction was used in this research for determination of three chlorophenols in environmental water samples. The analytes (2-chlorophenol, 3-chlorophenol and 4-chlorophenol) were extracted from 4.5?mL acidic donor phase, (pH 2, P1) into an organic phase, 350?µL?of benzene/1-octanol (90?:?10 v/v, P2) and then were back-extracted into a 7?µL droplet of an basic (pH 13) aqueous solution (acceptor phase, P3). In this method, contrary to the ordinary single drop liquid-phase microextraction technique, an aqueous large droplet is freely suspended on the surface of the organic solvent, without using a microsyringe as supporting device. This aqueous microdroplet is delivered at the top-centre position of an immiscible organic solvent which is laid over the aqueous donor sample solution while the solution is being agitated. Then, the acceptor phase containing chlorophenols was withdrawn back into a HPLC microsyringe and neutralised by adding of 7?µL HCl 0.1?M. The total amount was eventually injected into the HPLC system with UV detection at 225?nm for further analysis. Parameters such as the organic solvent, phases volumes, extraction and back-extraction times, stirring rate and pH values were optimised. The calibration graphs are linear in the range of 10–2000?µg?L^?1 with r?≥?0.9973. The enrichment factors were ranged from 115 to 170, and the limit of detection (LOD, n?=?7) varied from 5 to 10?µg?L^?1. The relative standard deviations (RSDs, n?=?5) were found 6.8 to 7.4 at S/N?=?3. All experiments were carried out at room temperature, (22?±?0.5°C).     

Determination of 61 organic pollutants in drinking water by solid phase extraction followed by liquid and gas chromatography coupled to tandem mass spectrometry: an analytical strategy for a routine laboratory

A method for determination of 61 organic pollutants (polycyclic aromatic hydrocarbons and organochlorine, organophosphorous and organonitrogen pesticides) is proposed. It is based on solid phase extraction (SPE) and subsequent analysis of the extract by liquid and gas chromatography coupled to tandem mass spectrometry. Method validation yielded to the following values: limits of quantification, from 0.005 to 0.020?µg?L^?1; trueness, 95% to 113% and reproducibility (as percent relative standard deviation), 2% to 15%. Additionally, the method performed well in various proficiency tests.     

A Fully Integrated Continuous‐Flow System for Asymmetric Catalysis: Enantioselective Hydrogenation with Supported Ionic Liquid Phase Catalysts Using Supercritical CO2 as the Mobile Phase

A continuous‐flow process based on a chiral transition‐metal complex in a supported ionic liquid phase (SILP) with supercritical carbon dioxide (scCO₂) as the mobile phase is presented for asymmetric catalytic transformations of low‐volatility organic substrates at mild reaction temperatures. Enantioselectivity of >99 % ee and quantitative conversion were achieved in the hydrogenation of dimethylitaconate for up to 30 h, reaching turnover numbers beyond 100 000 for the chiral QUINAPHOS–rhodium complex. By using an automated high‐pressure continuous‐flow setup, the product was isolated in analytically pure form without the use of any organic co‐solvent and with no detectable catalyst leaching. Phase‐behaviour studies and high‐pressure NMR spectroscopy assisted the localisation of optimum process parameters by quantification of substrate partitioning between the IL and scCO₂. Fundamental insight into the molecular interactions of the metal complex, ionic liquid and the surface of the support in working SILP catalyst materials was gained by means of systematic variations, spectroscopic studies and labelling experiments. In concert, the obtained results provided a rationale for avoiding progressive long‐term deactivation. The optimised system reached stable selectivities and productivities that correspond to 0.7 kg L ^?1 h^?1 space–time yield and at least 100 kg product per gram of rhodium, thus making such processes attractive for larger‐scale application.     

Fast Reductive Amination by Transfer Hydrogenation “on Water”

Reductive amination of various ketones and aldehydes by transfer hydrogenation under aqueous conditions has been developed, by using cyclometallated iridium complexes as catalysts and formate as hydrogen source. The pH value of the solution is shown to be critical for a high catalytic chemoselectivity and activity, with the best pH value being 4.8. In comparison with that in organic solvents, the reductive amination in an aqueous phase is faster, and the molar ratio of the substrate to the catalyst (S/C) can be set as high as 1×10⁵, the highest S/C value ever reported in reductive amination reactions. The catalyst is easy to access and the reaction is operationally simple, allowing a wide range of ketones and aldehydes to react with various amines in high yields. The protocol provides a practical and environmental friendly new method for the synthesis of amine compounds.     

The Aqueous Ca2+ System,in Comparison with Zn2+, Fe3 +, and Al3 +: An Ab Initio Molecular Dynamics Study

Herein, we report on the structure and dynamics of the aqueous Ca²⁺ system studied by using ab initio molecular dynamics (AIMD) simulations. Our detailed study revealed the formation of well‐formed hydration shells with characteristics that were significantly different to those of bulk water. To facilitate a robust comparison with state‐of‐the‐art X‐ray absorption fine structure (XAFS) data, we employ a 1st principles MD‐XAFS procedure and directly compare simulated and experimental XAFS spectra. A comparison of the data for the aqueous Ca²⁺ system with those of the recently reported Zn²⁺, Fe³⁺, and Al³⁺ species showed that many of their structural characteristics correlated well with charge density on the cation. Some very important exceptions were found, which indicated a strong sensitivity of the solvent structure towards the cation′s valence electronic structure. Average dipole moments for the 2nd shell of all cations were suppressed relative to bulk water.     

Bioconjugatable Azo‐Based Dark‐Quencher Dyes: Synthesis and Application to Protease‐Activatable Far‐Red Fluorescent Probes

We describe the efficient synthesis and one‐step derivatization of novel, nonfluorescent azo dyes based on the Black Hole Quencher‐3 (BHQ‐3) scaffold. These dyes were equipped with various reactive and/or bioconjugatable groups (azido, α‐iodoacetyl, ketone, terminal alkyne, vicinal diol). The azido derivative was found to be highly reactive in the context of copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reactions and allowed easy synthetic access to the first water‐soluble (sulfonated derivative) and aldehyde‐modified BHQ‐3 dyes, the direct preparation of which failed by means of conventional azo‐coupling reactions. The aldehyde‐ and α‐iodoacetyl‐containing fluorescence quenchers were readily conjugated to aminooxy‐ and cysteine‐containing peptides by the formation of a stable oxime or thioether linkage, respectively. Further fluorescent labeling of the resultant peptide conjugates with red‐ or far‐red‐emitting rhodamine or cyanine dyes through sequential and/or one‐pot bioconjugations, led to novel Förster resonance energy transfer (FRET) based probes suitable for the in vivo detection and imaging of urokinase plasminogen activator, a key protease in cancer invasion and metastasis.     

A Combined Kinetic and Thermodynamic Approach for the Interpretation of Continuous‐Flow Heterogeneous Catalytic Processes

The heterogeneous proline‐catalyzed aldol reaction was investigated under continuous‐flow conditions by means of a packed‐bed microreactor. Reaction‐progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate‐determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow‐injection analysis.     

径向电场对纳米管中水分子通量的影响

水分子在纳米通道中的运动对于生命活动、纳米器件的设计等都有着重要的意义. 现在已经证实, 在(6,6)的碳纳米管中, 水分子会以单分子水链的形式协同通过碳纳米管. 但是如何控制水分子的流量仍然是一个困难的课题. 本文研究了在径向电场作用下, 碳纳米管中水分子通量的变化趋势和碳纳米管的开关行为.发现在碳纳米管两端存在200 MPa的压力差时, 电场强度从1 V·nm^-1增加到3 V·nm^-1, 水分子通量线性减小. 当径向电场强度增加到3 V·nm^-1时, 碳纳米管处于关闭状态, 水分子无法通过碳纳米管. 进一步, 我们发现水偶极与碳纳米管管轴夹角的平均值的概率分布和翻转频率都与水分子在纳米管中的个数有很大关系.