Die Glykoside der Samen von Dregea volubilis (L.) BENTH. ex HOOK. 2. Mitt. Isolierung weiterer Drevogenine Glykoside und Aglykone, 277. Mitteilung

A total of fifteen substances were identified through thin-layer chromatography, after mild acid hydrolysis of the chloroform extract from the seeds of Dregea volubilis (L.) BENTH . ex HOOK . Of these fifteen substances, eight (B, D, P, O; U, V, H and T) were isolated in crystalline form. Two of these were identical with the known genins drevogenin B (B) and drevogenin D (D). Drevogenin P (P) and the unknown substance O (probably a genin) were isolated for the first time. U proved to be identical with D -cymarose, V with the biose U1 obtained from Asclepias lilacina, and H with (+)-methyl-pachybioside. T was not investigated (probably a sugar derivative).     

A continuous hydride-generation system for direct current plasma atomic-emission spectrometry (DCP-AES) Determination of arsenic and selenium

A continuously operating hydride-generation system has been developed for determination of volatile hydride-forming elements such as arsenic and selenium by d.c. plasma atomic-emission spectrometry. Arsenic and selenium are converted into their hydrides by reduction with sodium borohydride. The hydrides evolved are stripped from the liquid phase in a gas/liquid separator and are continuously fed into the d.c. plasma by a small argon stream. Under optimized operating conditions the detection limits (3s) obtained for arsenic and selenium are 0.3 and 0.5, mug/l., respectively. The precision at the 5 mu/l. level is better than 4% r.s.d. The measurement time, including sample introduction and three replicate measurements with 5-sec integration per sample is about 1 min. The effects of well known interferents such as copper and nickel have been investigated. For minimizing their interference continuous addition of 1, 10-phenanthroline as masking agent has been found useful. The method has been tested by its use for analysing NBS standard reference materials.     

Synthesis,characterization, and application of silver nanoparticle‐thiophenol nanocomposite film on the glassy carbon surface

In this study, 4‐thiophenol modified glassy carbon electrode was prepared by the reduction of 4‐diazothiophenol tetrafluoroborate salt. Silver nanoparticles were attached to the thiophenol modified surface to prepare a thiophenol‐silver nanoparticle composite film. 4‐Aminothiopenol molecules were deposited by self‐assembling technique to form multi‐layered nanofilms of TP/SNP/PhNH₂ on glassy carbon substrate. These surfaces were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, X‐ray photoelectron spectroscopy, reflectance‐absorption infrared spectroscopy, and ellipsometry at each multilayer film growth process. Atomic force microscopic images of GC/TP/SNP/PhNH₂ surfaces were also acquired. The characterization methods show that the amine group containing surface permits the subsequent modification by a variety of coupling reactions for the immobilization of more complex systems. An application of the electrode modification for the determination of uric acid with a significantly lower detection limit is described. Copyright © 2013 John Wiley & Sons, Ltd.     

Aromatic allylation via diazotization: metal-free C-C bond formation

A new method for the synthesis of allyl aromatic compounds not involving any metal-containing reagent or catalyst has been developed. Arylamines substituted with a large number of different substituents were converted via diazotizative deamination with tert-butyl nitrite in allyl bromide and acetonitrile to the corresponding allyl aromatic compounds. The allylation reaction was found to be suitable for larger scale synthesis due to short reaction times, a nonextractive workup, and robustness toward moisture, air, and type of solvent.     

Analyzing the quality of the first order diffracted laser beam emerging from an acousto-optic modulator

The quality of the first-order diffracted laser beam that emerges from an acousto-optic light modulator has been studied, while changing the diameter and the convergence of the incident beam.     

Co-crystal Structure of 11-Hydroxy-2,3,9-trimethoxy-6<Emphasis Type="Italic">H</Emphasis>-chromeno[3,4-<Emphasis Type="Italic">b</Emphasis>]chromen-12-one and 11-Hydroxy-2,3,9-trimethoxy-chromeno[3,4-<Emphasis Type="Italic">b</Emphasis>]chromene-6,12-dione

Abstract  

A 1:1 co-crystal structure of 11-hydroxy-2,3,9-trimethoxy-6H-chromeno[3,4-b]chromen-12-one and 11-hydroxy-2,3,9-trimethoxy-chromeno[3,4-b]chromene-6,12-dione (stemonone) was crystallized from the reaction mixture of 6-deoxyclitoriacetal and methanesulfonyl chloride, and its structure was characterized by X-ray diffraction. This co-crystal crystallizes in a triclinic crystal system, space group P(−1) with unit cell parameters of a = 8.1317(3) Å, b = 9.8224(4) Å, c = 10.7268(3) Å, α = 78.116(1)°, β = 77.463(1)°, γ = 77.140(1)°, Z = 2 and V = 804.11(3) Å³. The crystal structure was solved by direct methods and refined by full-matrix least-squares on F ² to final values of R ₁ = 0.0501 and wR ₂ = 0.1520.     

Solutions for the storage and handling of SPINE standard pucks

Currently there is no rack system for the long‐term storage of SPINE pucks in spite of their commercial availability and heavy usage at the ESRF. The only way to store pucks is in transport dewar canisters which presents a number of limitations and drawbacks. Here a simple affordable rack for storing SPINE pucks is described, which we believe is accessible to not only synchrotrons but also both academic and industrial research laboratories.     

Stress relaxation,creep, and internal stresses in high density polyethylene filled with calcium carbonate

The effect of filling high density polyethylene (HDPE) with calcium carbonate (up to 50% by weight) on the stress relaxation and the creep in uniaxial extension at room temperature was investigated. The addition of CaCO₃ was found to have a strong influence on the flow behaviour of HDPE. In particular, it was observed that the internal stress level, calculated from relaxation data, increased markedly with the filler content. The reduction in creep rate of the filled samples suggested that the CaCO₃-particles induce a change in the structure of the HDPE-interphase close to the filler surface. This was supported by dynamic mechanical measurements performed at low temperatures on swollen HDPE-CaCO₃ samples.     

Electron image series reconstruction of twin interfaces in InP superlattice nanowires

The twin interface structure in twinning superlattice InP nanowires with zincblende structure has been investigated using electron exit wavefunction restoration from focal series images recorded on an aberration-corrected transmission electron microscope. By comparing the exit wavefunction phase with simulations from model structures, it was possible to determine the twin structure to be the ortho type with preserved In-P bonding order across the interface. The bending of the thin nanowires away from the intended 110 axis could be estimated locally from the calculated diffraction pattern, and this parameter was successfully taken into account in the simulations.     

q-Binomials and related symmetric unimodal polynomials

The q-binomial coefficients were conjectured to be unimodal as early as the 1850's but it remained unproven until Sylvester's 1878 proof using invariant theory. In 1982, Proctor gave an ‘elementary’ proof using linear algebra. Finally, in 1989, Kathy O'Hara provided a combinatorial proof of the unimodality of the q-binomial coefficients. Very soon thereafter, Doron Zeilberger translated the argument into an elegant recurrence. We introduce several perturbations to the recurrence to create a larger family of unimodal polynomials. We analyse how these perturbations affect the final polynomial and analyse some specific cases.