Behaviour of selenium and tellurium species and their determination by ion chromatography

Summary An ion chromatographic method has been developed for the separation of Te (IV) and Se(IV) in hydrochloric acid mobile phases; the method has been used to determine tellurium in a high-purity non-stoichiometric semiconducting ZnCdTe-based material. Different cation-exchange columns (IonPac CS2, CS3, CS10), a mixed bed ion-exchange column (IonPac CS5), a multi-mode cation-exchange column (OmniPac PCX-500), anion-exchange columns (IonPac AS4, AS4A, AS5, AS5A, AS10, AS11) and a multi-mode anion-exchange column (OmniPac PAX-500) were evaluated for ion chromatographic separation of Se and Te and to study the chemical forms in which the analytes were eluted. The chromatographic data obtained enabled the calculation of both the sign and the chaarge of the eluting species.     

Ion chromatography with inductively coupled plasma mass spectrometry,a powerful analytical tool for complex matrices estimation of Pt and Pd in environmental samples

A new method for palladium and platinum direct determination in environmental samples is proposed by coupling ion chromatography with quadrupole inductively coupled plasma MS. In order to optimise Pd and Pt separation and to minimise interference from matrix in real samples, several anionic and cationic stationary phases have been compared at different mobile phase compositions. In particular, the effect of acidity and of the addition of oxalic acid to the eluent on separation and detection performance has been studied, and the anion-exchange column AG11 turned out to be more suitable. After chromatographic and mass spectrometer parameter optimisation, several potential interferences and the main quality parameters of the method, according to the Eurachem-CITAC recommendations, were evaluated: the detection limit for Pt was 5 ng l(-1) while the value for Pd was 230 ng l(-1). The method was successfully employed in the determination of platinum group elements in urban road dust and atmospheric particulates and the complete absence of matrix spectral interferences was demonstrated.     

Mechanochemical and solution reactions between AgCH3COO and [H2NC6H10NH2] yield three isomers of the coordination network {Ag[H2NC6H10NH2]+}infinity

Solid-state co-grinding of silver acetate and solid trans-1,4-diaminocyclohexane, [H2NC6H10NH2] yields two isomeric coordination networks depending on the crystallization conditions; a third isomeric form is obtained when the same reaction is carried out in solution.     

The role of the peripheral anionic site and cation-pi interactions in the ligand penetration of the human AChE gorge

We study the ligand (tetramethylammonium) recognition by the peripheral anionic site and its penetration of the human AChE gorge by using atomistic molecular dynamics simulations and our recently developed metadynamics method. The role of both the peripheral anionic site and the formation of cation-pi interactions in the ligand entrance are clearly shown. In particular, a simulation with the W286A mutant shows the fundamental role of this residue in anchoring the ligand at the peripheral anionic site of the enzyme and in positioning it prior to the gorge entrance. Once the ligand is properly oriented, the formation of specific and synchronized cation-pi interactions with W86, F295, and Y341 enables the gorge penetration. Eventually, the ligand is stabilized in a free energy basin by means of cation-pi interactions with W86.     

Ionization of aqueous dimethylbenzoic acids: Conductance and thermodynamics

Precise conductance measurements are reported for four xylic acids, 2,3-2,5-2,6 and 3,5-dimethylbenzoics. Limiting molar conductances Λ_O and pK _a obtained from a Fuoss type analysis, are reported for each of these acids at five degree intervals covering the range from 0° to 100°C. The Λ_O values for each acid are described by a polynomial in the Celsius temperature. The pK _a were smoothed as a function of the Kelvin temperature T with an equation of the form: $$pK_{\text{a}} = A{\text{ }} + {\text{ }}B/T{\text{ }} + {\text{ }}C{\text{ }}logT{\text{ }} + {\text{ }}DT$$ where the term linear in T was required only for the 2,3-acid. Standard enthalpy, entropy, and heat capacity changes were calculated by suitable differentiation of this equation. Walden products were calculated for the four anions at each of the temperatures and are compared with earlier data for the toluate and the benzoate ions. Those acids with ortho groups undergo a large decrease in enthalpy on ionization and are substantially more acidic than benzoic acid. These effects are especially large for 2,6-dimethylbenzoic acid. A methyl group in the meta position lowers acidity slightly both in m-toluic and in 2,5-dimethylbenzoic acid. However, 2,3-dimethylbenzoic acid is more acidic than o-toluic.