Infinite enantiomeric resolution of basic compounds using highly sulfated cyclodextrin as chiral selector in capillary electrophoresis

Four chiral basic analytes, namely methadone, fluoxetine, venlafaxine, and tramadol, were selected as model compounds for investigating their stereoselective separation with highly sulfated gamma-cyclodextrin (HS gamma-CD) by capillary electrophoresis (CE)-UV and CE-mass spectrometry (MS). At high concentration of chiral selector, the preferentially bonded enantiomer migrated faster in the anodic mode to the detector and high resolutions were obtained for all analytes. In the cathodic mode, at lower highly sulphated cyclodextrin (HS-CD) concentration, basic compounds could be detected, with the weakly bonded enantiomer migrating first (enantiomeric migration order inversion). It was also then possible, at intermediate HS-CD concentration, that only one enantiomer migrated to the detector as cation while the other enantiomer complexed with the CD was negatively charged and presented an opposite mobility. The latter never reached the detector achieving a perfect enantiomeric selectivity. Infinite chiral resolutions were thus achieved by CE-UV as well as by CE-electrospray ionisation (ESI)-MS where concentrations of HS-CD were adapted according to the negative contribution of the nebulization gas pressure of the interface.     

A new test for uranyl ions based on its redox properties

Summary A new test for uranyl ions is proposed. The solution is reduced with liquid zinc amalgam or metallic aluminium. A drop of the reduced solution is treated with excess of ferric iron, and the ferrous ions produced are detected with 1,10-phenanthroline. The test can be improved if the reduced solution is treated with thorium nitrate and ammonium fluoride. The precipitate, with which the uranium is co-precipitated, is centrifuged, washed and treated with ferric iron and 1,10-phenanthroline as before. The sensitivity ispD=4.7, and few ions interfere. Only MoO₄ ^–2, VO₃ ^–, Ti⁺⁺⁺⁺ and WO₄ ^–2 in a 101 proportion reduce the sensitivity topD=3.0.

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Zusammenfassung Es wird eine neue Nachweisreaktion für Uranylionen vorgeschlagen. Diese werden mit flüssigem Zinkamalgam oder mit metallischem Aluminium reduziert. Ein Tropfen der reduzierten Lösung wird mit Eisen(III)ionen versetzt, die dadurch zu Eisen(II)ionen reduziert werden. Das zweiwertige Eisen wird dann mit o-Phenanthrolin nachgewiesen. Der Nachweis kann verbessert werden, wenn man die reduzierte Lösung mit Thoriumnitrat und Ammoniumfluorid versetzt. Der Niederschlag, der das mitgefällte Uran enthält, wird zentrifugiert, gewaschen und mit Eisen(III)ionen und o-Phenanthrolin behandelt. Die EmpfindlichkeitpD beträgt 4,7. Die meisten lonen stören nicht. Nur MoO₄ ^–– VO₃ ^–, Ti⁺⁺⁺⁺ und WO₄ ^–– vermindern bei zehnfachem Überschuß die Empfindlichkeit aufpD = 3,0.

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Résumé On propose une nouvelle réaction pour les ions uranyles. La solution est réduite par l'amalgame de zinc liquide ou par l'aluminium métallique. On traite une goutte de solution réduite par un excès de sel ferrique et les ions ferreux produits sont détectés par la 1,10-phénanthroline. L'essai est amélioré en traitant la solution réduite par le nitrate de thorium et le fluorure d'ammonium. On centrifuge le précipité, lave et traite avec les ions ferriques et la 1,10-phénanthroline comme ci-dessus. La sensibilité estpD = 4,7; peu d'ions interfèrent. Seuls MoO₄ ^–2, VO₃ ^–, Ti⁺⁺⁺⁺ et WO₄ ^–2 dans la proportion 101 réduisent la sensibilité àpD = 3,0.

     

Spectrofluorimetric method for the simultaneous determination of zinc and cadmium

The simultaneous determination of zinc and cadmium using derivative synchronous and multiwavelength synchronous spectrofluorimetry is described. Effects of experimental variables on the fluorescence intensities and on the spectral resolution of the fluorescent chelates of these metals with 8-(p-toluenesulfonamido)-quinoline (TSQ) in a sodium lauryl sulfate micellar medium have been studied. Mixtures containing 10–200 g L^–1 Zn and 15–250 g L^–1 Cd have been analyzed with good results. The proposed method has been applied to a biological sample.     

Gas cluster growth by solute diffusion in porous media. Experiments and automaton simulation on pore network

The study presented in this paper deals with the liquid–gas phase change by pressure decline of supersaturated CO₂ solutions in 2D porous media. The growth of the gas phase is studied experimentally and numerically as a function of supersaturation, wettability and gravity. Experiments are performed on a transparent etched network (micromodel) and simulations with a specific numerical automaton.In the experiments, the nucleation process, i.e. the occurrence of the gas bubbles, as well as the growth of these bubbles are visualised and analysed by means of a micro video camera and an image processing apparatus. The observations confirm the heterogeneous nature of nucleation and the disordered growth pattern of the gas phase. The analysis of the growth rate of a single gas cluster shows that this phenomenon is different from the compact growth of an isolated single bubble in the bulk. As previously predicted, the bubble growth by mass transfer and volume expansion in porous media is characterised by a pattern of the invasion percolation type under normal laboratory conditions.Numerical simulations of the growth pattern and the growth rate of a single gas cluster are performed with a numerical automaton. Based on a pore network modelling technique and a set of hypotheses derived from the observations, this automaton is first validated by comparing the numerical results with the experiments. Then, the automaton is used to conduct a sensitivity study. In particular, the influences of the Jakob number, pressure decline rate, Bond number, wettability and characteristics of the microstructure are investigated.     

A potentiometric study on the complex equilibria between nickel(II) and 2-mercapto-2-phenylacetic acid

Complex formation between nickel(II) and 2-mercapto-2-phenylacetic acid (H₂MPA) has been studied at 25°C and 1 mol dm^?3 ClO₄^? in     

Analysis of trace levels of sulfonamides in surface water and soil samples by liquid chromatography-fluorescence

Methods are reported for determining six sulfonamides used as veterinary drugs in water and soil samples. Analytes are isolated from water samples by solid-phase extraction on HBL cartridges and pre-concentration factors of up to 250 were obtained. Soil samples are treated using microwave-assisted extraction of analytes with acetonitrile and further clean up by solid-phase extraction. Determination is carried out by high-performance liquid chromatography using fluorimetric detection with precolumn derivatization with fluorescamine. The separation of the derivatized sulfonamides is performed on an octadecyl column using binary gradient elution with acetate buffer/acetonitrile mixtures. For water analysis, the detection limits of the whole process are in the low nanogram per liter level and recovery rates range from 70 to 104%, with standard deviations 2-11%. For soil analysis, extraction efficiency is evaluated using three soil samples with different physicochemical characteristics. Recovery rates range from 60 to 98% and detection limits are between 1 and 6ngg(-1).     

SYNTHESIS,CHARACTERIZATION, AND SURFACE ACTIVITY OF SURFACTANTS DERIVED FROM NONYLPHENOL,ETHYLENE OXIDE AND CARBON DIOXIDE

The synthesis of the nonylphenol poly(ethylene carbonate) surfactants derived from nonylphenol (NP), carbon dioxide and ethylene oxide (EO) were carried out with high yields in the presence of alkali metal salts (K₂CO₃, Na₂CO₃, K₂SnO₃ and zinc glutamate) as base catalysts. The synthesis reactions were carried out in a stainless-steel reactor in the temperature range of 150-200°C under an initial pressure of 800 psi, with an initial molar ratio of CO2/EO = 0·21, catalyst concentration of 1 × 10³ M for a 24 h-period. The surfactants were characterized by FT-IR and by H-NMR. The percentages of carbon dioxide incorporation were between 7 and 16% indicating that the activation of CO₂ is a rather difficult process under the catalytic conditions used L175-200 °C and 800 psi of final pressure)

It was found that the most probable mechanism for the synthesis of the surfactants occurs in two steps. The first reaction involves the role of the base as a catalyst for the formation of the cyclic ethylene carbonate from CO₂ and ethylene oxide. The next step is the reaction of the nonylphenol in the presence of cyclic ethylene carbonate and ethylene oxide to generate the surface active compounds. This mechanism indicates that for each mol of carbon dioxide incorporated, one mol of EO has to be added.

The CMC values of the surfactants decrease (from 200 to 100 mM) with the increase in the molar ratio CO₂/EO (from 0·08 to 0·3) which can be attributted to a decrease in the hydrophilic character of the surfactant heads due to the addition of carbonate groups(-O-C(=0)-0-) to the ethoxylated chains (between I to 3 moles).     

The Mechanism of Stereospecific C?H Oxidation by Fe(Pytacn) Complexes: Bioinspired Non‐Heme Iron Catalysts Containing cis‐Labile Exchangeable Sites

A detailed mechanistic study of the hydroxylation of alkane C? H bonds using H₂O₂ by a family of mononuclear non heme iron catalysts with the formula [Fe^II(CF₃SO₃)₂(L)] is described, in which L is a tetradentate ligand containing a triazacyclononane tripod and a pyridine ring bearing different substituents at the α and γ positions, which tune the electronic or steric properties of the corresponding iron complexes. Two inequivalent cis‐labile exchangeable sites, occupied by triflate ions, complete the octahedral iron coordination sphere. The C? H hydroxylation mediated by this family of complexes takes place with retention of configuration. Oxygen atoms from water are incorporated into hydroxylated products and the extent of this incorporation depends in a systematic manner on the nature of the catalyst, and the substrate. Mechanistic probes and isotopic analyses, in combination with detailed density functional theory (DFT) calculations, provide strong evidence that C? H hydroxylation is performed by highly electrophilic [Fe^V(O)(OH)L] species through a concerted asynchronous mechanism, involving homolytic breakage of the C? H bond, followed by rebound of the hydroxyl ligand. The [Fe^V(O)(OH)L] species can exist in two tautomeric forms, differing in the position of oxo and hydroxide ligands. Isotopic‐labeling analysis shows that the relative reactivities of the two tautomeric forms are sensitively affected by the α substituent of the pyridine, and this reactivity behavior is rationalized by computational methods.