The preparation of new chiral diphenyl-substituted macrocyclic polyether-diester compounds and their enantiomeric recognition of chiral organic ammonium salts

A series of chiral diphenyl-substituted macrocyclic polyether-diester ligands have been prepared from the chiral diphenyl-substituted tetraethylene glycol. Enantiomeric recogntion by the chiral diphenyl-substituted pyridino-diester-18-crown-6 compound ( 7 ) was studied by temperature dependent ¹H NMR spectroscopy in deuteriodichloromethane. This ligand exhibited chiral recognition when complexed with the hydrogen per-chlorate salts of (R)- and (S)-α-(1-naphthyl)ethylamine and (R)- and (S)-methyl phenylalaninate.     

Assessing induced folding of an intrinsically disordered protein by site-directed spin-labeling electron paramagnetic resonance spectroscopy

We used site-directed spin-labeling electron paramagnetic resonance (EPR) spectroscopy to study the induced folding of the intrinsically disordered C-terminal domain of measles virus nucleoprotein (N(TAIL)). Four single-site N(TAIL) mutants (S407C, S488C, L496C, and V517C), located in three conserved regions, were prepared and labeled with a nitroxide paramagnetic probe. We could monitor the gain of rigidity that N(TAIL) undergoes in the presence of either the secondary structure stabilizer 2,2,2-trifluoroethanol (TFE) or one of its physiological partners, namely, the C-terminal domain (XD) of the viral phosphoprotein. The mobility of the spin label grafted at positions 488, 496, and 517 was significantly reduced upon addition of XD, contrary to that of the spin label bound to position 407, which was unaffected. Furthermore, the EPR spectra of spin-labeled S488C and L496C bound to XD in the presence of 30% sucrose are indicative of the formation of an alpha-helix in the proximity of the spin labels. Such an alpha-helix had been already identified by previous biochemical and structural studies. Using TFE we unveiled a previously undetected structural propensity within the N-terminal region of N(TAIL) and showed that its C-terminal region "resists" gaining structure even at high TFE concentrations. Finally, we for the first time showed the reversibility of the induced folding process that N(TAIL) undergoes in the presence of XD. These results highlight the suitability of site-directed spin-labeling EPR spectroscopy to identify protein regions involved in binding and folding events, while providing insights at the residue level.     

Separation of arsenic anions by capillary zone electrophoresis with UV detection

Summary Capillary zone electrophoresis (CZE) in capillary silica columns has been used for the separation of arsenite (AsO ₂ ^– ), arsenate (AsO ₄ ^3– ), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The separation of these ionic species has been achieved using a capillary silica column (72 cm×50 m i.d.) with an acidic phosphate buffer and with an on-column UV detection (190 nm). Optimization of experimental parameters (pH, temperature, voltage) were studied. The selectivity of the separation can be improved by working in the pH-range of 4.5–6.5. For analytical inorganic separations of UV-absorbing anions, capillary zone electrophoresis has advantages because of the relatively simple equipment, the short analysis time (15 min), the high efficiency and the low mass detection limit (40 pg for arsenate).     

Chemotaxonomic features associated with flavonoids of cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) in relation to hops (Humulus lupulus L.)

The major flavonoids present in the leaves and flowers of the cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) cultivars Felina and Futura are orientin (1), vitexin (2), luteolin-7-O-beta-D-glucuronide (3), and apigenin-7-O-beta-D-glucuronide (4), while prenylated flavonoids, to which the potent estrogenicity of hops (Humilus lupulus L.) is associated, are absent. The different composition of flavonoids has chemotaxonomic value.     

Fragmentation of doubly charged argon clusters

Fragmentation of doubly charged argon clusters is reported. Neutral argon clusters are excited with monochromatized synchrotron radiation in the energy regime of the argonL ₃/L ₂ absorption edges (240–260 eV) leading predominantly to cluster dication formation. All charged particles are detected in a photoelectron-photoion-photoion-concidence (PEPIPICO) experiment. Symmetric and asymmetric charge separation reactions (Coulomb explosion) are identified for clusters below the critical size of stable dication formation. The peak shapes of the coincidence signals are investigated as a function of neutral cluster size. Characteristic changes in peak shape are observed which are used to derive fragmentation mechanisms involving sequential evaporation of neutrals before and after charge separation. The spectra indicate in accordance with low kinetic energy releases occurring in charge separation of large dissociative cluster dications (Ar _n ²⁺ , withn>50) that due to large charge separation distances the momenta of both singly charged fragments are not any more directed into opposite direction, as it is typical for Coulomb explosion. The results are compared to collision induced fragmentation of mass selected argon cluster dications as well as photon stimulated desorption spectra of condensed argon.     

Enantioselective separations by capillary GC on derivatized cyclodextrins. Part 2: Determination of enantiomeric excess of some racemic 2,3-isopropylidene-1,2,3-cyclohexanetriol derivatives on permethyl α-, β-, and γ-cyclodextrins

Capillary GC on permethyl α-, β-, and γ-cyclodextrins has been applied to separate and quantify the enantiomers of some 2,3-iso-propylidene-1,2,3-cyclohexanetriol derivatives. Quantitative CGC data are compared to those obtained with chiral shift ¹H NMR.     

Retention of β blockers on native titania stationary phase

In recent years, metal oxides such as titania have been commercially available as chromatographic beds that can potentially be used to achieve novel separations of polar compounds. For example β blockers, which are more often encountered in environmental sciences, have a wide range of polarity, and their basic character leads to difficult sample treatment and separation on conventional silica‐based sorbents. The contribution of titania to the selective analysis of nine β blockers was evaluated in terms of retention mechanisms observed in hydrophilic interaction LC using acetonitrile/water mobile phases with various additives. The mobile phase additives enabled to control the β blocker charge as well as the titania surface charge. Depending on their respective ionic state, various retention mechanisms were identified at low water contents (<40%), including mainly adsorption mixed with hydrophilic interaction LC partition, ion exchange and ion exclusion. An unexpected retention was also observed for high water content and high pH, changing the selectivity of the support.