Separation and determination of nitroaniline isomers by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid-sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10⁻⁹ mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory.     

反胶束体系中脂肪酶催化合成异丁酸异戊酯

报道了在CTAB/正己烷和AOT/正己烷反胶束体系中,CCL脂肪酶催化合成异丁酸异戊酯的新方法.考察了水含量w₀、底物与酶的比例、缓冲溶液pH值以及温度等因素对脂肪酶催化酯合成反应的影响.研究结果表明,两种反胶束体系均为合成异丁酸异戊酯提供了较为合适的微环境,所选定的脂肪酶在CTAB和AOT反胶束中的活性分别是有机溶剂中反应活性的6倍和4倍.     

Reactivity of tetracyanoquinodimethane with cobalt(II) chloride and bis(diphylphospino)methane in air

The reactions of CoCl₂·6H₂O, dppm (bis(diphenylphosphino)methane) and TCNQ (7,7,8,8-tetracyanoquinodimethane), with different ratios of the components, provided three new compounds, [Co(dppmdo)₃][TCNQ]₂1 (dppmdo = P,P′-dioxo-bis(diphenylphosphinyl)methane), [Co(dppmdo)₃][(μ-TCNQ)-CoCl₃] 2, and [Co(dppmdo)₃][(μ-DCBE)-CoCl₃] 3 (DCBE = p-dicyanomethyl-benzoic ethyl ester). These products were characterized by IR, UV–Vis and UV–Vis-NIR spectra, X-ray crystallography, magnetic susceptibility measurements and cyclic voltammograms. 1 and 2 reveal low-energy transitions in the near-infrared region, which can be attributed to intra-ligand transitions involving radical anions (TCNQ/TCNQ⁻). It is interesting to note that, except for the redox potentials which are anodically shifted, indicating that it is easier to reduce TCNQ in 1 and 2 than the free TCNQ molecule, the electrochemistry of compounds 1 and 2 resemble that of the independent organic acceptor TCNQ. The magnetic properties suggest that an amount of electron transfer has occurred from the Co^II complex, [Co(dppmdo)₃]²⁺, to the TCNQ⁻ anions in 1; an amount of electron transfer also has occurred from the Co^II cation to the TCNQ⁻ anion via a cyanide-bridge in 2; there is a mixture of spin transition of Co^II ions and antiferromagnetic coupling between Co^II ions in 3.     

Selective solid-phase extraction of dibutyl phthalate from soybean milk using molecular imprinted polymers

An analysis method is reported for dibutyl phthalate and related compounds with high selectivity and sensitivity by using the selective molecularly imprinted solid-phase extraction (MISPE) technique. In this report, dibutyl phthalate (DBP) is employed as the template molecule, and the molecularly imprinted polymers (MIPs) are synthesized through the bulk polymerization of methacrylic acid (MAA). The Scatchard plot suggests that the template-polymer system has two-site binding behavior with the dissociation constants of 0.5187 and 0.01898 mmol L⁻¹, respectively. The rebinding test, based on the MISPE column technique, shows the recoveries of soybean milk samples spiked with 5 phthalates are in the range of 75.8-107.5% with the relative standard deviations of 1.80-10.08%, indicating the feasibility of the prepared MIPs for phthalates extraction. Finally, the method is used to analyze the trace level of phthalates in commercial soybean milk.     

Preparation and evaluation of molecularly imprinted solid-phase micro-extraction fibers for selective extraction of phthalates in an aqueous sample

A novel molecularly imprinted polymer (MIP) that was applied to a solid-phase micro-extraction (SPME) device, which could be coupled directly to gas chromatograph and mass spectrometer (GC/MS), was prepared using dibutyl phthalate (DBP) as the template molecule. The characteristics and application of this fiber were investigated. Electron microscope images indicated that the MIP-coated solid-phase micro-extraction (MI-SPME) fibers were homogeneous and porous. The extraction yield of DBP with the MI-SPME fibers was higher than that of the non-imprinted polymer (NIP)-coated SPME (NI-SPME) fibers. The MI-SPME fibers had a higher selectivity to other phthalates that had similar structures as DBP. A method was developed for the determination of phthalates using MI-SPME fibers coupled with GC/MS. The extraction conditions were optimized. Detection limits for the phthalate samples were within the range of 2.17-20.84 ng L⁻¹. The method was applied to five kinds of phthalates dissolved in spiked aqueous samples and resulted in recoveries of up to 94.54-105.34%, respectively. Thus, the MI-SPME fibers are suitable for the extraction of trace phthalates in complicated samples.     

Theoretical study of spin–orbit coupling and kinetics in spin-forbidden reaction between Ta(NH2)3 and N2O

The activation mechanism of the nitrous oxide (N₂O) with the Ta(NH₂)₃ complex on the singlet and triplet potential energy surfaces has been investigated using the hybrid exchange correlation functional B3LYP. The minimum energy crossing point (MECP) is located by using the methods of Harvey et al. The rate-determining step of the N–O activation reaction is the intersystem crossing from ¹ 2 to ³ 2. The reacting system will change its spin multiplicities from the singlet state to the triplet state near MECP-1, which takes place with a spin crossing barrier of 32.5 kcal mol^?1, and then move on the triplet potential energy surface as the reaction proceeds. Analysis of spin–orbit coupling (SOC) using localized orbitals shows that MECP-1 will produce the significant SOC matrix element, the value of SOC is 272.46 cm^?1, due to the electron shift between two perpendicular π orbitals with the same rotation direction and the contribution from heavy atom Ta. The rate coefficients are calculated using Non-adiabatic Rice-Ramsperger-Kassel-Marcus (RRKM). Results indicate that the coefficients, k(E), are exceedingly high, k(E) > 10¹² s^?1, for energies above the intersystem crossing barrier (32.5 kcal mol^?1); however, in the lower temperature range of 200–600 K, the intersystem crossing is very slow, k(T) < 10^?6 s^?1.     

Free radical scavenging activity and characterization of sesquiterpenoids in four species of Curcuma using a TLC bioautography assay and GC-MS analysis

The sesquiterpenoids are one of major groups of antioxidants in Curcuma besides curcuminoids. However, the real substances contributing to the antioxidant activity are still unknown. In this paper, the antioxidant activity of sesquiterpenoids in four species and two essential oils from Curcuma genus was determined and compared based on TLC separation and DPPH bioautography assay. Their antioxidant capacities were quantitatively evaluated using densitometry with detection at 530 nm (λ(reference )= 800 nm) using vitamin C as reference. The results showed that Curcuma longa rhizomes had the highest antioxidant capacity while C. phaeocaulis presented the lowest one among the four species of Curcuma. Moreover, essential oil of C. wenyujin showed higher antioxidant potential than that of C. longa. The main TLC bands with antioxidant activity of the four species of Curcuma were collected and characterized using GC-MS, and thus curzerene, furanodiene, α-turmerone, β-turmerone and β-sesquiphellandrene were determined as major sesquiterpenoids with antioxidant activity in Curcuma.     

Two 3-D supramolecular architecture based on the linkages of Co(II) complexes and lattice water molecules

Two new 3-D supramolecular compounds [Co(phen)(tdc)(H₂O)₃]·5H₂O (1) and [Co(phen)(Htdc)(H₂O)₃]·(Htdc)·2H₂O (2, phen = 1,10-phenanthroline, H₂tdc = thiophene-2,5-dicarboxylate) have been hydrothermally synthesized and structurally characterized. In 1, the neutral [Co(phen)(tdc)(H₂O)₃] complexes behave as pillars to join the water layers to make an overall 3-D supramolecular architecture by H-bond interactions. In 2, similar 2-D water layer is not observed, which could be due to one uncoordinated Htdc ligand instead of three lattice water molecules of 1. The thermal stabilities of 1 and 2 were investigated by thermogravimetric measurements.     

Structural,electronic and magnetic properties of cementite-type Fe3X (X = B,C, N) by first-principles calculations

Using first-principles technique, the crystal structure of cementite-type Fe₃N is predicted. The average magnetic moment (Ms) of cementite-type Fe₃N is also predicted as 1.4929 μ_B/atom. The Ms of Fe₃N is bigger than that of Fe₃C, but smaller than that of Fe₃B. Fe Ms between two different Fe sites in Fe₃N are different (2.0541 and 2.0139 μ_B), which indicates that Fe Ms are sensitive to the local short-range order in the cementite-type crystal. The Ms of B, C and N are ?0.3525, ?0.2474 and ?0.1102 μ_B/atom in Fe₃X (X = B, C, N), respectively. The chemical bonds of Fe₃X (X = B, C, N) take on metallicity, covalence, and ionicity. The ionicity of Fe₃X (X = B, C, N) strengthens and the covalence of Fe–X weakens, going from Fe₃B, Fe₃C to Fe₃N.     

Suppressed molecular orientation in nylon 6/clay nanocomposite at large strain: Role of microvoiding

A micro‐FTIR measurement has been conducted to explore the molecular orientation of amorphous phase in the nylon 6/clay nanocomposite at large strain. Our results indicate that the molecular orientation in such a nanocomposite during stretching is lower than that observed for the pure nylon 6 counterpart, which is further evidenced by the true stress‐strain dependence. The relaxation of the molecular network, resulted from the destruction of γ‐crystals in part and mostly from microvoding (demonstrated by volume dilatation and 2D‐SAXS measurements), should be responsible for the suppressed molecular orientation in the nylon 6/clay nanocomposite. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 514–519, 2010