Construction of multiporphyrin arrays using ruthenium and rhodium coordination to phosphines

The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by (1)H NMR and (31)P NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller and larger arrays.     

On Mercury(I) Oxo Compounds — Quasi‐Relativistic Computational and Experimental Studies

About 60 molecular species composed of up to 10 mercury atoms and of oxygen atoms and/or of some other elements or groups (such as halogen, OH₂, OH, H, alkali, NO₃) have been investigated quantum chemically. Different density functional approaches and the ab initio SCF‐MP2 method were applied, comparing different basis sets and different atomic core sizes. It is important not to treat the Hg 5s, p, d as inactive core shells, and to use sufficiently many polarization functions. The shape of the 〉O‐Hg‐Hg‐O〈 units is not favorable concerning the formation of lattices composed of Hg^I, O and OH only. Despite its bulkiness, the OHgHgO units can easily come into contact with each other and then disproportionate. This is prevented in the so‐called ternary M‐Hg^I oxides by the embedded oxometallate (oxoacidic) anions. Furthermore, the Hg^I and Hg^II oxide bond energies are less favorable towards the stability of Hg^I oxo compounds, as compared to Hg halidic or oxoacidic compounds. Both points are not promising concerning the search for Hg^I oxides/hydroxides, although the preparation of such compounds, including spacer groups, by topochemical reactions can still not be excluded. So far, experimental efforts towards the synthesis of such a new class of compounds have only demonstrated that Hg^II is strictly preferred over Hg^I in the formation of solids of binary Hg‐O or ternary A‐Hg‐O composition (A = electropositive metal such as alkali, in contrast to M = transition or semi‐metal). This is so even if compounds containing ‘electron rich Hg^δ— atoms’ (i.e. A‐Hg amalgams) are oxidized under mild conditions.     

Development of a robust technique for sampling volatile metal(loid)s in wetlands

The formation of volatile organic and inorganic metals and metalloids in aquatic environments is a known, but not very intensively investigated, process. Several techniques have been developed over the past 10 years to determine these trace components. These techniques are of limited use in wetland environments, where samples have to be taken from the soil-water interface, and require an immediate sample analysis due to thermodynamic instabilities of the volatile metal(loid)s. This paper presents an innovative sampling technique for total concentrations of volatile metal(loid)s in wetlands, based on an in situ gas-water separation via a porous PTFE membrane and stabilising the volatile metal(loid)s in a liquid sorbent (NaOCl solution). Samples may thus be collected even at remote sites, where longer storage times have to be accounted for. The sampling system was tested by means of a laboratory facility simulating the generation of arsine and dimethyl arsine under abiotic conditions as well as under field conditions. Results for sampling efficiency, reproducibility, and long-term storage are presented. Application of the sampling system in the field is shown.     

Eine neue Mikro- und Ultramikro-Bestimmung von Sauerstoff in organischen Verbindungen mit Hilfe eines W?rmeleitf?higkeitsdetektors

Zusammenfassung Zur Bestimmung des Sauerstoffs wird die organische Probe in Helium-Atmosphäre gecrackt; die sauerstoffhaltigen Crackprodukte werden über Kohle zu Kohlenmonoxid konvertiert. Um das Kohlenmonoxid von den übrigen Crackprodukten, wie H₂, N₂ und CH₄ abzutrennen, wird es zu Kohlendioxid oxydiert und danach an einem Molekularsieb bei 20° C durch Adsorption zurückgehalten; H₂, N₂ und CH₄ werden aus der Apparatur gespült. Sobald in der Probeleitung reines Spülgas auftritt, wird das adsorbierte Kohlendioxid durch Erhitzen desorbiert und im Detektor gemessen.

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Summary For the determination of oxygen the organic sample is cracked in helium atmosphere. Cracking products, containing oxygen, are converted to carbon monoxide by coal. For separation from the remaining cracking products (H₂, N₂, CH₄) carbon monoxide is oxidized and then adsorbed on molecular sieve 5A at 20°C; H₂, N₂ and CH₄ are flushed out. As soon as pure carrier gas flows through the sample pipe, carbon dioxide is desorbed by heating the molecular sieve and flushed to the detector.

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Es ist uns eine angenehme Pflicht, der Shell Austria AG., Wien, insbesondere Herrn Direktor Dipl.-Ing. R. Wallner, für die Gewährung eines Forschungsstipendiums an den einen von uns (E. W.) ergebenst zu danken.     

On the critical difference of almost bipartite graphs

Journal of Algebraic Combinatorics - A set $$S\subseteq V$$ is independent in a graph $$G=\left( V,E\right) $$ if no two vertices from S are adjacent. The independence number $$\alpha (G)$$ is the...     

Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

New improvements in oligonucleotide synthesis by use of the p-nitrophenylethyl phosphate blocking group and its deprotection by DBU or DBN

Phosphate protection in the phosphotriester approach is improved by the new, versatile p-nitrophenylethyl group due to its stability in the condensation step and its clean removal by DBU and DBN respectively.