The isolation and structure determination of cryptomisrine,a novel indolo[3,2-b]quinoline dimeric alkaloid from cryptolepis sanguinolenta

The isolation and structure determination of cryptomisrine, a novel indolo[3,2-b]quinoline dimeric alkaloid obtained from extracts of the roots of the Ghanaian medicinal plant Cryptolepis sanguinolenta is reported. The structure determination was made via a consideration of the spectral data, including uv, ir, nmr, and mass spectra. In particular, one-dimensional proton/carbon nmr, one-dimensional nOe difference nmr, and a series of homonuclear (COSY) and inverse-detected heteronuclear two-dimensional (HMQC, HMBC) experiments were utilized, as well as high resolution FABMS. Cryptomisrine is most unusual in that its two monomeric parts apparently exist in such a C₂ symmetric environment that only one set of proton and carbon nmr resonances are observed. Cryptomisrine is the first example of a dimeric indolo-[3,2-b]quinoline alkaloid to have been isolated from nature.     

Promotion by phosphorus compounds of ruthenium-catalyzed methyl formate homologation

Trivalent phosphorus compounds are promoters for methyl formate homologation to ethanol and ethyl formate catalyzed by ruthenium compounds in the presence of iodide at 220°C and 27 MPa of synthesis gas. Under these conditions the phosphines are quaternized, but decomposition of phosphonium salts occurs during the reaction. Promotion is also observed for methyltriphenyl-phosphonium bromide and triphenylphosphine sulfide, but benzyltrimethyl-ammonium bromide, triphenylarsine, and triphenylantimony are not effective. The major ruthenium species present is Ru(CO)₃I₃^- but with triphenylantimony a trimethylantimony complex, Ru(CO)₂(Sb(CH₃)₃)₂I₂, can be isolated in high yield.     

Sequence distribution of partially hydrolyzed poly(vinyl acetate)

Copolymers of vinyl acetate and vinyl alcohol were studied by differential thermal analysis. The melting points of the copolymers are not a simple function of the composition, but depend on the method of preparation of the copolymers. Partial saponification of poly(vinyl acetate) with sodium hydroxide leads to high melting, ordered copolymers, while reacetylation of poly(vinyl alcohol) leads to low melting, random copolymers. Catalytic alcoholysis of PVAc yields copolymers intermediate in melting point and order. The results are treated by assuming that equal melting points indicate similar sequence length distributions of crystallizable units.     

Microchemical characterization of paintings — A case study

Summary The fundamental importance of scientific research for the preservation and restoration of works of art is uncontestable. The methods described in this paper, such as light microscopy, microchemical tests, emission spectroscopy, chromatography, scanning electron analysis, electron microprobe analysis and infrared spectroscopy, are of special significance in this filed. Nevertheless a better understanding of the problems that arise out of new special questions of art history can be obtained only by the right interpretation of the data obtained by scientific methods.

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Mikrochemische Charakterisierung von Gemälden

Zusammenfassung Die grundlegende Bedeutung wissenschaftlicher Forschung für die Erhaltung und Restaurierung von Kunstwerken ist unbestritten. Die hier beschriebenen Methoden (Lichtmikroskopie, mikrochemische Reaktionen, Emissionsspektroskopie, Chromatographie, Rasterelektronen-Analyse und Infrarotspektroskopie) sind hierfür von zunehmender Bedeutung. Sie ermöglichen ein besseres Verständnis neuerer kunsthistorischer Probleme nur durch die richtige Interpretation der Ergebnisse wissenschaftlicher Methoden.

     

Kinetics and mechanism of the acid-catalysed decarboxylation of thecis-α- andcis-β-carbonato(3,6-dimethyl-1,8-diamino-3,6-diazaoctane)-cobalt(III) ions

Summary The acid-catalysed decarboxylation of thecis-- andcis--[CoL(CO₃)]⁺ complexes (L = 3,6-dimethyl-1,8-diamino-3,6-diazaoctane) have been studied over a range of HClO₄ concentrations and the temperatures 25, 35 and 45° at I = 1.0 mol dm^–3 (NaClO₄). The rate expression takes the form k_obs = k₀ + k₁[H⁺] where k_obs is the observed first order rate constant at constant hydrogen ion concentration. The k₀ term makes only a minor contribution to the overall reaction. Both complexes display solvent deuterium isotope effects ofca. 2.6 for the acid-catalysed decarboxylation, consistent with a rapid proton pre-equilibrium mechanism. Activation parameters have been determined and the mechanism of the reaction discussed. The magnitude of the solvent isotope effect is consistent with an A-1 type mechanism involving formation of a 5-coordinate intermediate.     

Synthesis and structural characterisation of [(Ph3P)AuCo(CO)3(PPh3)]

Summary [(Ph₃P)AuCo(CO)₃(PPh₃)] has been synthesised from [(Ph₃P)AuCo(CO)₄], PPh₃v and Me₃NO in acetonitrile. Its molecular structure, determined by single-crystal x-ray crystallography, consists of an almost linear P-Au-Co-P arrangement in which the Co atom is in a slightly distorted trigonalbipyramidal geometry, with the Au and P atoms occupying the apical sites. The Au-Co bond length of 2.450(1) ? is shorter than that reported for [(Ph₃P)AuCo(CO)₄]. The carbonyl ligands are bent towards the Au atom and the mean Au-Co-C angle is 81(1)°.