Identification of a series of C25-C40 acyclic isoprenoid hydrocarbons in crude oils

The identification of acyclic isoprenoid hydrocarbons in organic extracts of geological samples and particularly in petroleum deserves a great interest from the biological origin of the sedimentary organic matter and the understanding of geochemical processes.     

Synthesis of enantiomerically enriched allenes by (-)-sparteine-mediated lithiation of alkynyl carbamates

[reaction: see text]. The alpha-deprotonation of alkynyl carbamates 3 with the chiral base (-)-sparteine (4)/n-butyllithium, transmetalation with ClTi(O(i)()Pr)3, and subsequent substitution with an aldehyde results in the formation of enantioenriched 4-hydroxyallenyl carbamates 11. Stereoselection is determined by dynamic resolution of the lithium/(-)-sparteine complexes by selective crystallization.     

Über die Polymerisation des Phosphornitrilchlorids II

Zusammenfassung Die Polymerisation des Phosphornitrilchlorids in Substanz erweist sich als thermisch gestartete Radikalpolymerisation, die mit gleicher Geschwindigkeit und gleicher Temperaturabhängigkeit wie die durch Sauerstoff aktivierte Polymerisation in Lösung verläuft. Schon geringer Lösungsmittelzusatz bringt die thermische Polymerisation zum Erliegen. Ein Reaktionsschema mit Start-Kette-Abbruch wird diskutiert, das sowohl die Substanz- wie die Lösungspolymerisation wiedergibt. Der seinerzeit beschriebene Einfluß von Sauerstoff auf den Ablauf der Polymerisation erfährt dadurch eine wesentliche Korrektur.Die Depolymerisation von polymerem Phosphornitrilchlorid wird von 350 bis 600° C verfolgt und als gegenläufige Reaktionsfolge zur Polymerisation gefunden. Für das aus Polymerisation und Depolymerisation resultierende Gleichgewicht werden Druck- und Temperaturabhängigkeit festgestellt.Mit 8 Abbildungen.Herrn Prof. Dr.A. Klemenc zu seinem 70. Geburtstage gewidmet.Als I soll die ArbeitPatat-Kollinsky ¹ Über die Polymerisation des Phosphornitrilchlorids¹ gelten, die im folgenden Text auch mit (I) bezeichnet wird.— Eine Literaturzusammenstellung Phosphornitrilchlorid findet sich in der Monographie vonL. F. Audrieth, R. Steinmann undA. O. F. Toy, Chem. Rev.32, 109 (1943).     

Degradation of ²-O-4 lignin model and related compounds by the ascomyceteChrysonilia sitophila (TFB 27441 strain)

Growth of the ascomyceteChrysonilia sitophila during degradation of lignin model dimers and monomers was compared to a glucose control. An inhibition of growth by Cα-carbonyl monomers and stimulation by β-O-4 lignin model and vanillyl alcohol were observed. A comparison of the degradation by this ascomycete with the basidiomycetePhanerochaete chrysosoporium showed similarities in relation to the type of degradation caused.     

Doppler-free laserspectroscopic investigations of hyperfine structure in the atomic cobalt spectrum

Performing Doppler-free laserspectroscopic investigations in the red wavelength region (640–670 nm) we were able to determine 10A-factors and 9B-factors of atomic cobalt levels. Now precise values of 18A-factors and 16B-factors of levels belonging to the configurations (3d+4s)⁹ are known. Fitting of the one-electron radial parameters to introduce agreement between experimental and theoretical hfs constants allows the prediction of hfs constants of not yet investigated fine structure levels. Values of the electric quadrupole moment of the Co⁵⁹ nucleus are determined in two electron configurations. The resulting mean value of the spectroscopic quadrupole moment isQ=0.35(3) barn.     

Mechanisms for the solvolytic decompositions of nucleoside analogues—I: Acidic hydrolysis of 2-substituted 1-(1-ethoxyethyl)benzimidazoles

A few 2-substituted 1-(1-ethoxyethyl)benzimidazoles have been prepared and the rate constants for their hydrolysis measured at various temperatures and oxonium ion concentrations. The formal kinetics followed and the effect of varying the 2-substitution on the hydrolysis rate suggest that the acid-catalyzed cleavage of these compounds involves a rapid initial protonation of the benzimidazole ring and a subsequent rate-limiting heterolysis of the protonated substrate to form a free nitrogen base and an ocarbenium ion derived from the ethoxyethyl group. The values obtained for the entropy of activation are consistent with the assumed unimolecular nature of the rate-limiting step. The effects of 2-substituents on the acidities of the protonated substrates and their heterolysis rates have been compared. The latter partial reaction has been suggested to be the subject of steric acceleration.     

L X-ray production cross sections, average L shell fluorescence yield and intensity ratios in heavy elements

L X-ray fluorescence cross sections, and intensity ratios were measured for elements in the 70￡Z￡92 atomic range at the excitation energy 59.5 keV using a Si(Li) detector. Furthermore, L X-ray fluorescence cross sections and intensity ratios were calculated for elements in the same range. The average L shell fluorescence yields were derived using experimental L X-ray fluorescence cross sections and theoretical photoionization cross sections. The obtained results were compared with other experimental and theoretical values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermische Zersetzung von CuInSe2, LiInSe2 und LiInTe2

The thermal decompositions of CuInSe₂, LiInSe₂ and LiInTe₂ in vacuum at high temperatures were studied by using TG/DTG coupled with mass spectrometry. For CuInSe₂, two steps were found to be significant. Up to 1000 °C Se₂ and In₂Se evaporate, followed later by Cu₂Se. The Li-containing compounds show similar behaviour. However, Li⁺ was already detected during the first step. Obviously, Li₂Se dissociates more readily than Cu₂Se. No Cu⁺ species were detected up to the complete evaporation of CuInSe₂.     

Oxepinamides A-C and fumiquinazolines H--I: bioactive metabolites from a marine isolate of a fungus of the genus Acremonium

Three new oxepin-containing natural products (1-3) and two new fumiquinazoline metabolites (4-5) have been isolated from organic extracts of the culture broth and mycelia of an Acremonium sp., a fungus obtained from the surface of the Caribbean tunicate Ecteinascidia turbinata. The structures of the five compounds were determined through extensive analysis of 1D- and 2D-NMR data, and mass spectrometry. Compound 1 exhibited good anti-inflammatory activity in a topical RTX-induced mouse ear edema assay. Compounds 4 and 5 exhibited weak antifungal activity toward Candida albicans in a broth microdilution assay.     

Analytical potential from ab initio calculations for the Fe+-H2O and Feo-H2O systems

Analytical intermolecular potentials for the Fe⁺?H₂O and Fe^o?H₂O systems have been determined from ab initio calculations. Interaction energies for a lot of points along the two potential energy surfaces were calculated using Huzinga's MINI ?2 basis set. The results obtained were fitted to an analytical function containing 11 adjustable parameters that we have already used with success for the Fe²⁺?H₂O system. The goodness of the generated intermolecular potentials is discussed.