Magnetic Anisotropy of Small Ir<Subscript>n</Subscript> Clusters (n = 2–5)

We employ a noncollinear implementation of density functional theory (DFT) including spin–orbit coupling (SOC) interaction to calculate the magnetic properties of Ir_n (n = 2–5) clusters. The impact of the magnetic anisotropy on the geometric structures and magnetic properties has been analyzed. SOC leads to formation of large orbital moment and a mixing of different spin states, but does not affect the relative stability of different structural isomers for a given cluster. In order to measure the SOC effect, we further define the spin–orbit energy (E_so) and compute the exact values. Magnetic anisotropy energies (MAEs) obtained from DFT calculations are further supported by the results of torque approach. We find that MAEs of Ir₂ and Ir₃ in ground state configurations are 40.6 and 28.5 meV respectively, while the MAE decreases to 9 meV for Ir₄. For Ir₅, MAE for its ground state structure increases to 38.3 meV.     

A novel detector using a fluorescent sensor array and discrimination of pesticides

A novel, simple, and rapid detector using a fluorescent sensor array for discrimination and quantification of different concentrations (ppb level) of pesticides was proposed in this paper. Employing porphyrin, porphyrin derivatives, and chemically responsive dyes as the sensing elements, the developed sensor array based on a cross-responsive mechanism showed a unique pattern of fluorescence changes upon the reaction that lasted just 10 min. The eigenvalues from raw fluorescence spectra were analyzed via a pattern recognition algorithm, including hierarchical cluster analysis (HCA), principal component analysis (PCA), and back-propagation neural network (BPNN). The results showed that HCA, which were used to assess the feasibility and effectiveness of discrimination of the fluorescent sensor array, revealed a distinct separation between different pesticides. PCA and BPNN were used for automatically predicting the concentration of pesticides, and the recovery was 91.29–109.81 % while the lowest relative standard deviation was up to 3.12 %. It indicates a detector based on the fluorescent sensor array is a rapid and feasible sensing platform for the discrimination and quantitative analysis of pesticides, and also shows the possibilities in the related fields of pesticides identification and detection.     

Synthesis and Chromatographic Evaluation of Perfluorooctyl Stationary Phase for Separation of Basic Compounds

Fluorinated stationary phases provide unique separation effect on basic compounds, due to the fluorine atoms, and pentafluorophenyl stationary phases (PFPs) are the most widely used. Considering that some fluoroalkyls have higher fluorine contents than PFPs do, it is speculated that fluoroalkyl stationary phases should have potential new applications. Herein, we synthesized a silica-based stationary phase bonding perfluoroctyl (FC8) proved by characterization through elemental analysis and solid-state ¹³C cross-polarization/magic-anglespinning nuclear magnetic resonance. The chromatographic behavior of the stationary phase was evaluated with test compounds. In addition, to further study the applicability of FC8 materials, Corydalis decumbens (Thunb.) Pers. fraction, considered as a challenging medicine on reversed-phase chromatography columns, was chosen as a test sample. Results demonstrated that the FC8 stationary phase had better and more satisfactory separation performance than the PFP stationary phase on basic compounds.

     

Synthesis and controlled hydrolysis of organolanthanide complexes with mono- and dianionic benzimidazole-2-thiolate ligands

Treatment of Cp(3)Er with one equivalent of benzimidazole-2-thiol (H(2)Bzimt) in THF affords the monoanionic HBzimt(-) complex Cp(2)Er(η(2)-HBzimt)(THF)(2) (1). Reaction of Cp(3)Yb with two equivalents of H(2)Bzimt gives complex CpYb(η(2)-HBzimt)(2)(THF) (2) at room temperature. Treatment of Cp(3)Ln with three equivalents of H(2)Bzimt in reflux THF affords the homoleptic Ln(η(2)-HBzimt)(3)(THF)(2) (Ln = Er (3), Y (4)). Cp(3)Ln reacts with 0.5 equivalents of H(2)Bzimt to afford the dianionic Bzimt(2-) complexes [(Cp(2)Ln)(THF)](2)(μ-Bzimt) (Ln = Yb (5), Er (6), Dy (7), Y (8)) in good yields, in which the Bzimt(2-) ligand bridges the two metals in an μ-η(2):η(2) coordination mode. Interestingly, controlled hydrolysis of complexes Cp(2)Ln(η(2)-HBzimt)(THF)(2), CpLn(η(2)-HBzimt)(2)(THF) and [(Cp(2)Ln)(THF)](2)(μ-Bzimt) produces the same tetranuclear complexes [CpLn(μ(3)-OH)(μ-η(1):η(2)-HBzimt)](4) (Ln = Yb (9), Er (10), Y (11)), indicating that the hydrolysis selectivity greatly depends on the number of coordinated cyclopentadienyl groups. All complexes were characterized by elemental analysis, spectroscopic properties and X-ray single crystal diffraction analysis.     

Preparation of β-cyclodextrin covalent organic framework-immobilized poly(glycidyl methacrylate) nanoparticle-coated open tubular capillary electrochromatography column for chiral separation

A new enantioselective open-tubular capillary electrochromatography was developed employing poly(glycidyl methacrylate) nanoparticles/β-cyclodextrin covalent organic frameworks chemically immobilized on the inner wall of the capillary as a stationary phase. A pretreated silica-fused capillary reacted with 3-aminopropyl-trimethoxysilane followed by poly(glycidyl methacrylate) nanoparticles and β-cyclodextrin covalent organic frameworks through a ring-opening reaction. The resulting coating layer on the capillary was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The electroosmotic flow was studied to evaluate the variation of the immobilized columns. The chiral separation performance of the fabricated capillary columns was validated by the analysis of the four racemic proton pump inhibitors including lansoprazole, pantoprazole, tenatoprazole, and omeprazole. The influences of bonding concentration, bonding time, bonding temperature, buffer type and concentration, buffer pH, and applied voltage on the enantioseparation of four proton pump inhibitors were investigated. Good enantioseparation efficiencies were achieved for all enantiomers. In the optimum conditions, the enantiomers of four proton pump inhibitors were fully resolved within 10 min with high resolutions of 9.5–13.9. The column-to-column and inter- to intra-day repeatability of the fabricated capillary columns through relative standard deviation were found better than 9.54%, exhibiting satisfactory stability and repeatability of the fabricated capillary columns.     

Electrochemical determination of nitrite and iodate based on Pt nanoparticles self-assembled on a chitosan modified glassy carbon electrode

A promising electrochemical sensor was fabricated by the self-assembling of Pt nanoparticles (nano-Pts) on a chitosan (CS) modified glassy carbon electrode (GCE). A field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and electrochemical techniques were used for characterization of these composites. It has been found that nano-Pts are inserted into the CS layer uniformly, and have a larger surface area compared to the chitosan modified glassy carbon electrode. Electrocatalytic experiments for the oxidation of nitrite and the reduction of iodate have shown that nano-Pts/CS/GCE can decrease the over-potential and increase the faradic current, which can be used for the sensitive determination of nitrite and iodate. Moreover, the prepared modified electrode exhibits good reproducibility and stability, and it is possible that this novel electrochemical sensor can be applied in the sensing and/or biosensing field.     

Kinetics and mechanism of oxidation of <Emphasis Type="Italic">N</Emphasis>-methylethylamine by bis(hydrogenperiodato)argentate(III) complex anion

Oxidation of N-methylethylamine by bis(hydrogenperiodato)argentate(III) ([Ag(HIO₆)₂]⁵⁻) in alkaline medium results in demethylation, giving rise to formaldehyde and ethylamine as the oxidation products. The oxidation kinetics has been followed spectrophotometrically in the temperature range of 20.0–35.0 °C, and shows an overall second-order character: being first-order with respect to both Ag(III) and N-methylethylamine. The observed second-order rate constants k′ increase with increasing [OH⁻] of the reaction medium, but decrease with increasing the total concentration of periodate. An empirical rate expression for k′ has been derived as: k′ = (k _a + k _b[OH⁻])K ₁/{f([OH⁻])[IO₄ ⁻]_tot + K ₁}, where k _a and k _b are rate parameters, and K ₁ is an equilibrium constant. These parameters have been evaluated at all the temperatures studied, enabling calculation of activation parameters. A reaction mechanism is suggested to involve two pre-equilibria, leading to formation of an intermediate Ag(III) complex, namely [Ag(HIO₆)(OH)(MeNHEt)]²⁻. In the subsequent rate-determining steps, this intermediate undergoes inner-sphere electron transfer from the coordinated amine to the metal center via two distinct routes, one of which is spontaneous while the other is mediated by a hydroxide ion.