Free Radical Formation from Excited States of Aliphatic Carboxylic Acids and esters in solution as studied by electron spin resonance

During UV.-irradiation of aliphatic carboxylic acids and esters in aqueous and nonaqueous solutions various alkyl and acyl type radicals derived from parent compounds and solvents have been observed by ESR.-spectroscopy. The structures of the radicals point to α-cleavage, β-dehalogenation and photoreduction as major photolytic processes of carboxylic acids and esters. The relative contributions of these processes to the overall photodecompositions depend on the carboxyl substituents, on solvent and temperature. Similarities of carboxyl and carbonyl group photochemistry are discussed.     

Mikromethoden zur Gemäldeuntersuchung

Zusammenfassung Als wesentlichstes Ergebnis der vorliegenden Arbeit ist das in der Tabelle 2 angeführte Trennschema zu nennen, welches gestattet, die zwanzig in der Maltechnik wichtigsten und häufigsten Elemente ineinem Analysengang nachzuweisen. Hierbei wurden, wenn nicht durch Literaturhinweise gekennzeichnet, andere Nachweisreaktionen angeführt, dieFeiglschen Tüpfelreaktionen in weitestem Maße herangezogen und so ein weiterer Beweis erbracht, daß es sehr wohl möglich ist, ganze Trennungsgänge im Mikromaßstab, rascher und einfacher als dies in der Makroanalyse der Fall ist, durchzuführen. Zur weiteren Herabsetzung der Empfindlichkeitsgrenzen wurden die vonG. Skalos angegebenen Akroreaktionen herangezogen. Wo eine Filtration notwendig war, wurde diese nach demGorbachschen Verfahren durchgeführt. Weiters wird, um die Auffindung der charakteristischen Ionen zu erleichtern, eine tabellarische Übersicht über die mögliche chemische Zusammensetzung der Farben verbunden mit chronologischen Daten gebracht.Der Verfasser dankt seinem Lehrer, akademischem Maler Prof.Heinrich Prohaska, für die außerordentliche Förderung und Unterstützung, sowie Herrn Dekan Prof. Dr.G. Jantsch und Prof. Dr.G. Gorbach für die Ermöglichung der Arbeit.

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Summary The essential result of this study is the separation scheme given in Table 2, which permits the detection, in a single analytical procedure, of the twenty most important and most frequent elements used by artists. When not indicated by literature references, other detection reactions were mentioned, theFeigl spot reactions were drawn on to the fullest extent. Thus a further proof was given that it is entirely possible to accomplish entire separation procedures on a micro-scale more rapidly and simpler than by macroanalytical methods. The acro-reactions given byG. Skalos were employed to lower the sensitivity limits still more. When a filtration was necessary, theGorbach procedure was used. A tabular review of the possible chemical composition of the pigments together with chronological data is also given to facilitate the discovery of the characteristic ions.

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Résumé Le point le plus saillant et important de ce travail est le schéma de séparation du Tableau 2, dans lequel les vingt éléments les plus fréquents et les plus importants des peintures sont décelables dans une seule analyse. De nouvelles réactions ont été employées lorsque la littérature n'en mentionnait pas; le plus souvent les réactions sur gouttes à la manière deFeigl ont servi. Ceci démontre que des marches de séparation analytiques à l'échelle microchimique plus rapides et plus simples qu'en macroanalyse sont toujours possibles. Les limites de sensibilité ont été fixées grace l'Akroreaction deG. Skalos. On se sert de la méthode deGorbach pour les filtrations nécessaires. Pour faciliter la détection des ions caractéristiques, il est donné un tableau synoptique de la composition chimique des couleurs en relation avec les données chronologiques.

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The kinetics of thiyl radical-induced reactions of monounsaturated fatty acid esters

The time-dependent isomerizations and thiol additions of several Z- and E-monounsaturated fatty acid methyl esters catalyzed by alkanethiyl radicals during gamma-radiolysis of tert-butyl alcohol solutions are analyzed on the basis of the radiation chemical yield of radicals and established rate data. This provides room-temperature rate constants for the reversible thiyl addition. Within experimental errors, they do not depend on the double bond position in the alkyl chains. Particularly noteworthy is the very fast beta-elimination of thiyl radicals from alkyl radicals which carry a second beta-substituent. It is supported by additional evidence obtained with a radical clock methodology, and the large preference of fragmentation to the E-isomers is attributed to different barriers for the formation of the E- and Z-transition states from the equilibrium radical structure.     

Essential methodological improvements in the oxygen isotope ratio analysis of N‐containing organic compounds

The quantitative conversion of organically bound oxygen into CO, a prerequisite for the ¹⁸O/¹⁶O analysis of organic compounds, is generally performed by high‐temperature conversion in the presence of carbon at ～1450°C. Since this high‐temperature procedure demands complicated and expensive equipment, a lower temperature method that could be utilized on standard elemental analyzers was evaluated. By substituting glassy carbon with carbon black, the conversion temperature could be reduced to 1170°C. However, regardless of the temperature, N‐containing compounds yielded incorrect results, despite quantitative conversion of the bound oxygen into CO. We believe that the problems were partially caused by interfering gases produced by a secondary decomposition of N‐ and C‐containing polymers formed during the decomposition of the analyte. In order to overcome the interference, we replaced the gas chromatographic (GC) separation of CO and N₂ by reversible CO adsorption, yielding the possibility of collecting and purifying the CO more efficiently. After CO collection, the interfering gases were vented by means of a specific stream diverter, thus preventing them from entering the trap and the mass spectrometer. Simultaneously, a make‐up He flow was used to purge the gas‐specific trap before the desorption of the CO and its subsequent mass spectrometric analysis. Furthermore, the formation of interfering gases was reduced by the use of polyethylene as an additive for analytes with a N:O ratio greater than 1. These methodological modifications to the thermal conversion of N‐containing analytes, depending on their structure or O:N ratio, led to satisfactory results and showed that it was possible to optimize the conditions for their individual oxygen isotope ratio analysis, even at 1170°C. With these methodological modifications, correct and precise δ¹⁸O results were obtained on N‐containing analytes even at 1170°C. Differences from the expected standard values were below ±1‰ with standard deviations of the analysis <0.2‰. Copyright © 2010 John Wiley & Sons, Ltd.     

A new route to antimony telluride nanoplates from a single-source precursor

Aerosol-assisted chemical vapor deposition (AACVD) of Sb[(TePiPr2)2N]3 results in pure hexagonal Sb2Te3 nanoplates between 375 and 475 degrees C on glass substrates, with a potential for enhanced thermoelectric properties for novel nanodevices.     

Structures and conformational dynamics of gold(I) halide complexes of resorcinarene tetraphosphinite ligands

Gold(I) halide derivatives of several tetrakis(diphenylphosphinite) tetraester resorcinarene compounds have been prepared. The complexes are shown to exist in boat conformations, and two different boat conformations were characterized by X-ray structure determinations; the structural characterization of both boat conformations of the same parent resorcinarene is unprecedented. Intramolecular Au.Au interactions were observed in the solid state for both boat conformers and could cause twisting of the resorcinarene skeleton. Several of the complexes exist in solution as an equilibrium mixture of the two different boat conformers, and the equilibrium and dynamics of exchange were studied by variable-temperature NMR.     

Ring-opening polymerization of gold macrocycles and self-assembly of a coordination polymer through hydrogen-bonding

The equilibrium between digold and tetragold rings and a ring-opened oligomer and polymer is established by NMR and ESI-MS studies in solution and by structure determinations in the solid state; the polymer containing amide-derivatized ligands undergoes self-assembly through hydrogen bonding to give an ordered network.