Unconstrained Polarization (Chebyshev) Problems: Basic Properties and Riesz Kernel Asymptotics

Potential Analysis - We introduce and study the unconstrained polarization (or Chebyshev) problem which requires to find an N-point configuration that maximizes the minimum value of its potential...     

Simultaneous Determination of Isoquinoline Alkaloids in Medicinal Asiatic Plants by Ultrasound-Assisted Extraction and High-Performance Liquid Chromatography – Mass Spectrometry with Principal Component Analysis

Isoquinoline alkaloids (papaverine, noscapine, berberine, emetine, and quinine) were determined in medicinal plants and herbs used in Traditional Chinese Medicine and Ayurveda by liquid chromatography with tandem mass spectrometry detection (LC-MS/MS). The analyzed alkaloids were separated at gradient conditions using methanol and 2% acetic acid within 12?min. The validated method was successfully applied for 17 herbal samples: Ashwagandha, Astragalus membranaceus, Emblica officinalis, Mucuna pruriens, Pueraria lobata, Ocimum sanctum, Rehmannia glutinosa, Schisandra sinensis, Terminalia arjuna, Terminalia chebula, and dietary supplements. The highest concentration of studied alkaloids was observed for berberine in Puearia lobata (6.68?±?0.62?mg 100?g^?1 d.m.), while the lowest value was obtained for noscapine in a dietary supplement containing Terminalia arjuna (0.09?±?0.01?mg 100?g^?1 d.m.). Principal component analysis, cluster analysis, and one-way ANOVA tests were also performed. The results indicate the need to control plant materials and dietary supplements in terms of the content of alkaloids and toxic components.     

Mixture Design PARAFAC HPLC-DAD Metabolomic Fingerprints of Fractionated Organic and Basic Extracts from <Emphasis Type="Italic">Erythrina speciosa</Emphasis> Andrews Leaves

HPLC-DAD analysis of statistical mixture design extracts of Erythrina speciosa Andrews leaves provided chromatographic and UV–visible profiles of their basic and organic fractions that were treated with the PARAFAC multivariate method. The design extracts provided greater varieties and amounts of metabolites than could be obtained by classical extraction methods. Fractionation provided more diverse fingerprint information than obtained previously from only the crude extract. The two largest chromatographic peaks, one with a 4.8 min elution time having an intense spectral band at 235 nm and the other a 5.8 min peak with an intense 238 nm band for the basic fraction were obtained with the ternary 1:1:1 ethanol–dichloromethane–hexane mixture. These can be assigned to diene-type and lactonic alkaloids. Peaks with the same retention times are also found in the organic fraction but are extracted with different mixtures and have distinct spectral behavior in the 235 nm region, probably being aromatic alkaloids. The above strategy permits a more unambiguous assignment of metabolic groups to specific chromatographic peaks. This can be expected to provide higher quality chromatographic fingerprints for natural products’ chemistry.     

Crystal and molecular structure ofo-aminobenzoato (o-(p-dimethylaminobenzalidine)benzoato)(o-ammoniobenzoate)dimethyltin(IV), an example of a mixed carboxylate complex of tin

The structure of the title compound, [Me₂Sn(O₂CC₆H₄NH₂-o)(O₂CC₆H₄(N=C(H)C₆H₄NMe₂-p)-o)(^–O₂CC₆H₄NH₃-o)], has been determined at room temperature. The structure features a distorted trigonal bipyramidal coordination geometry for Sn, defined by three O atoms derived from chemically different, monodentate carboxylate ligands and two methyl groups. Crystals are monoclinic, space groupP2₁/n witha=14.718(5),b=10.981(4),c=20.321(3) Å, =110.74(2)°,Z=4; refinement on 2480 reflections gaveR=0.046.     

Separating versus strictly separating vectors

Let be a linear manifold of Banach space operators which is closed in the strong operator topology. Existence of a disjoint pair of separating vectors does not guarantee reflexivity of , but must be reflexive if one of these vectors is strictly separating. must also be reflexive if all non--zero linear combinations of some independent pair of vectors strictly separate .

     

Characterization and Reactivity of the [N,N-Dimethyl(thioformamidyl)]-9-fluorenyl Cation(1)

The 9-[N,N-dimethyl(thioformamidyl)]-9-fluorenyl cation was generated under stable ion conditions and characterized by UV/visible and NMR spectroscopy and methanol trapping reactions. The same cation was generated by laser excitation of the appropriate chloride precursor in 2,2,2-trifluoroethanol, and rate constants for nucleophilic quenching by alcohols and several anions were measured. The quenching data for this and other 9-fluorenyl cations demonstrate that the reactivity decreases for 9-substituents in the order H > carbomethoxy > N,N-dimethyl(thioformamidyl), demonstrating that the thioamidyl group imparts substantial kinetic stabilization to an adjacent cationic center. Both steric and electronic factors are suggested to be important in determining this reactivity order.     

The Briggs-Rauscher oscillatory reactions catalyzed by nickel macrocyclic complexes

The investigation of Briggs-Rauscher reactions (BRR) with nickel complexes have shown that the range of the standard redox potentials of BRR catalysts is at least 0.7–1.7 V. An inner-sphere interaction of metal ions with hydrogen peroxide is a prerequisite of the oscillatory behavior. The unique catalytic properties of the nickel compounds are probably due to their lower redox potential.     

Julia sets for the gamma recursion in nonlinear psychophysics

Julia sets for the map za(z–ie)(1–z)(z+ie) are illustrated for some attractors of interest. This work extends previous analyses of the cubic complex polynomial and considers dynamics in regions which may be associated with the modelling of the results of overload in sensory inputs.Work supported by grant No. A7881403 (1988) from the Australian Research Council.     

Solvothermal synthesis of nanocrystalline copper nitride from an energetically unstable copper azide precursor

Nonaqueous solvothermal chemical reactions have found extensive utility in the growth of inorganic non-oxide materials. This report describes the successful use of organic solvothermal environments to synthesize energetically unstable copper azide precursors that are then decomposed in situ to crystalline metastable copper nitride at temperatures below 200 degrees C. A comparison of Cu3N products formed from nonpolar (toluene) and coordinating (THF) solvents is described. The cubic Cu3N products are nanocrystalline with aggregated particle-like extended structures and were characterized by X-ray diffraction, electron microscopy, IR spectroscopy, and mass spectrometry. The thermal stability and composition of Cu3N was examined by thermogravimetric analysis and bulk elemental analysis. The particle surfaces contain bound residual solvent species that can be removed by heating. The poorly coordinating solvent, toluene, lead to a more crystalline product containing less residual organic content. Benchtop reactions were performed to follow the temporal formation and decomposition of metal azide intermediates. These studies provided more detailed information on the progression of metal azide to metal nitride materials in a solvothermal environment.