Adsorption behavior of Pb(II) on montmorillonite

The present work investigated the adsorption and desorption behaviors of Pb(II) on montmorillonite. The adsorption experiments were carried out using batch process. The results show that the adsorption is dependent on the pH value of the medium, and the uptake of Pb(II) increases with the pH increasing in the pH range of 2.0–10.0. The adsorption kinetics is in better agreement with pseudo-second order kinetics, and the adsorption data is a good fit with Langmuir isotherm. The presence of EDTA may result in a decrease of the amount of Pb(II) adsorbed. The presence of electrolyte and EDTA may enhance the desorption of Pb(II) ions adsorbed. The adsorption mechanism of Pb(II) on montmorillonite may be explained in two aspects: the chemical binding between Pb(II) ions and surface hydroxyl groups; and the electrostatic binding between Pb(II) ions and the permanent negatively charged sites of montmorillonite.     

Multi-residue determination of seven quinolones antibiotics in gilthead seabream using liquid chromatography-tandem mass spectrometry

A sensitive and selective confirmatory analytical method for the multi-residue determination of seven quinolones (ciprofloxacin, enrofloxacin, sarafloxacin, danofloxacin, oxolinic acid, nalidixic acid and flumequine) in gilthead seabream (Sparus aurata) was developed. The sample pre-treatment involves extraction with 0.1M NaOH and purification by solid-phase extraction (SPE) on Waters Oasis HLB cartridges followed by the determination of all compounds in a single LC-electrospray ionization MS/MS run. Separation was achieved on a Perfectsil ODS-2, 5mum, 250mmx4mm, analytical column (MZ Analysentechnik) by gradient elution using a mixture of 0.2% (v/v) formic acid, methanol and acetonitrile within 30min. Multiple reaction monitoring (MRM) was used for selective detection of each quinolone. Accuracy was evaluated through recovery studies at three different fortification levels. The mean recoveries are between 90 and 132% for the selected levels with RSD values lower than 20%. The method presents satisfactory results for linearity, precision and limits of quantification. The latter are much lower than the maximum residue limits (MRLs) established by the European Union for quinolones in fish tissues (6-8mug/kg).     

Synthesis of Cu(II) and Mn(III) Complexes Involving Derivatives of Pyridine

Two complexes with derivatives of pyridine as ligands were synthesized and characterized. From the reaction of 2-pyridinecarboxaldehyde oxime with Cu(OAc)₂ · H₂O afforded the complex C₂₀H₃₀N₆O₁₂Cu₃ (I), and the use of 3-hydroxy-2-pyridinecarboxylic acid with anhydrous MnCl₂ · 4H₂O led to the formation of another complex C₁₂H₁₄N₂OCl₂Mn (II). They were characterized by X-ray diffraction (CIF files CCDC nos. 568718 (I) and 1568880 (II)), NMR, IR and elemental analysis. For I: terigonal, space group R\(\bar 3\)/H, a = 42.548(3), c = 10.2774(9) Å, V = 16113(2) ų, Z = 18, ρ_calcd = 1.367 Mg/m³, the final R factor was R₁ = 0.0945, 6662 for reflections were observed with I > 2σ(I), wR = 0.162 for all data. For II: triclinic, Pī, a = 5.6174(9), b = 7.7259(13), c = 9.7160(16) Å, α = 70.444(3)°, β = 88.009(3)°, γ = 89.818(3)°, V = 397.09(11) ų, Z = 1, ρ_calcd = 1.840 Mg/m³, the final R factor was R₁ = 0.0281, 4280 for reflections were observed with I > 2σ(I), wR = 0.0775 for all data.     

Seasonal variations in metabolite profiling of the fruits of Ligustrum lucidum Ait

The metabolite profiling of fruits of the herb Ligustrum lucidum Ait collected during different months has been performed using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC/QTOFMS) and multivariate statistical analysis techniques. The markers such as oleuropein acid, neonuezhenide, specnuezhenide, oleuropein and ligustrosidic acid accountable for such variations were identified through the loadings plot of principal component analysis (PCA), and the tentative identification of the markers is completed by comparing the mass spectra and retention times with those of reference compounds and/or tentatively assigned by matching empirical molecular formulae and MS/MS data with those of the known compounds published. Furthermore, one of the chemical markers, such as specnuezhenide, which is water-soluble, biologically active and also the predominant compound in this crude drug, was quantified by ultra-performance liquid chromatography coupled with a tunable UV detector (UPLC-TUV). The developed UPLC method provides good linearity (r(2)=0.9991), repeatability (RSD=2.96%), intra- and inter-day precisions (RSD=0.21%, 0.96%), with accuracies of 99.18-100.26% and a recovery of specnuezhenide of 97.57%. The fruits of L. lucidum Ait collected from August to December were tested. The results clearly show that the fruits of L. lucidum Ait harvested in October have the highest yields of specnuezhenide. It is also noted that the variations of content of specnuezhenide obtained by both methods have a strong correlation. This suggests that the newly proposed strategy is a reliable and simple method for the rapid discrimination of subtle variations, within the same plant species or strains, due to different seasonal collection times.     

Communication: state-to-state differential cross sections for H2O(B̃) photodissociation

Quantum state-to-state differential cross sections, along with the absorption spectrum and product internal state distributions, have been calculated for the photodissociation of H(2)O in its B band on a new set of ab initio potential energy surfaces in a diabatic representation. The theoretical attributes are in good agreement with the recent experimental data, shedding light on the non-adiabatic dissociation dynamics.     

Accessing the long-lived near-IR-emissive triplet excited state in naphthalenediimide with light-harvesting diimine platinum(II) bisacetylide complex and its application for upconversion

Room temperature near-IR phosphorescence of naphthalenediimide (NDI) was observed with N^N Pt(II) bisacetylide complex (Pt-NDI) in which the NDI was connected to Pt(II) center via acetylide. Pt-NDI shows intense absorption of visible light and long-lived NDI-localized excited state ((3)IL) (τ(T) = 22.3 μs). Pt-NDI was used as a triplet sensitizer for upconversion.     

Development of a Biomimetic Enzyme‐linked Immunosorbent Assay Method for the Determination of Methimazole in Urine Sample

A fast and direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method was developed for the determination of methimazole (MMZ) in urine sample based on a molecularly imprinted film as an artificial antibody. This is the first example to monitor methimazole with a direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method. The imprinted film was directly synthesized on the well surface of MaxiSorp polystyrene 96‐well plate and characterized. The results showed that it exhibited an antibody‐like binding ability, rapid adsorption speed, high stability, which was particularly advantageous and suitable for BELISA development. The BELISA method established in this paper had a higher selectivity for MMZ than for the structurally related compounds and the IC₅₀ (calculated as the concentration giving 50% inhibition of color development) and the detection limit values under optimized experimental conditions were 70 ± 4 μg L^‐1 and 0.9 ± 0.04 μg L^‐1, respectively. The method was applied to the determination of MMZ in spiked urine sample with excellent recoveries ranging from 90% to 95%, and the imprinted film was able to be reused for 20 times without loss of sensitivity. The results obtained by BELISA correlated well with that obtained by the high performance liquid chromatography (HPLC) method.     

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ～10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.     

On-resin peptide ligation via C-terminus benzyl ester

Here, we reported a new approach of on-resin peptide ligation using C-terminal benzyl ester as the stabilized precursor of thioester, which enables both N-terminal elongation and C-terminal peptide ligation on a Rink Amide resin.