Amycomycins C and D,new angucyclines from Kitasatospora sp.

Two new angucycline compounds containing O-glycosylated 6-deoxy-α-l-talose were isolated from Kitasatospora sp. The compounds were elucidated based on spectroscopic methods including UV, HR-ESIMS, and NMR. A feeding experiment using alizarin led to the conversion of alizarin to a monoglycosylated product with high efficiency, which allows isolation of the sugar after hydrolysis and determination of the absolute configuration of the sugar.     

Experimental Investigation of Particle Collection on Single Fibres of Different Configurations

This presentation is part of a fundamental investigation into the influence of structural characteristics on particle collection in fibrous filters. The collection on single fibres has been experimentally determined, whereby different fibre configurations were set. For this purpose, particle fluxes upstream and downstream of the fibres were measured simultaneously using an optical particle counter which operates with two purely optically delineated measuring volumes and two detectors. The experimental results are compared with published values.     

Zur Chemie des Bis(methylsulfonyl)-amins (Dimesylamins). IV. Synthese von N-Alkyldimesylaminen mit Tetra-n-butylammonium-dimesylaminid

Investigations on Bis(methylsulfonyl)-amine (Dimesylamine). IV. Synthesis of N-Alkyl-dimesylamines with Tetra-n-butylammonium Dimesylaminide Primary and secondary alkyl iodides, diiodomethane, and α,ω-diiodoalkanes I[CH₂]_nI with n > 2 react with [(C₄H₉)₄N]N(SO₂Me)₂ in boiling CHCl₃ to form the corresponding dimesylamino alkanes. By this procedure, the new compounds 3 — 9 , 11 , 13 and 14 were prepared. Addition of bromine to the allyl compound 9 affords 10 . Alkyl chlorides and bromides do not react under these conditions. Cyclohexyl and tert.-butyl iodide eliminate olefins. ICH₂CH₂I is decomposed, forming I₂. 1,2-Bis(dimesylamino)-ethane ( 12 ), however, is prepared from ICH₂CH₂I and (MeSO₂)₂NCl. The kinetics of the alkaline hydrolysis of MeN(SO₂Me)₂ ( 1 ) is investigated.     

Formation and characterization of 1-substituted 1,2-dithiolanyl radicals by laser flash photolysis

Photolyses of 1-alkylthio-3-propanethiols, 1,3-propanedtthiol and 1-phenylthio-3-propanethiol in acetonitrtle, 2-propanol or aqueous mixtures of these solvents lead to five membered cyclic sulfuranyl radicals of the type \(\left[ {R - \overline {S - S - CH_2 - CH_2 - C} H_2 } \right]\) which exhibit characteristic uv/vis absorption spectra. These 1-substituted 1,2-dithiolanyl radicals are formed by intramolecular cyclization of the primarily formed thiyl radicals generaeed by S-H- bond cleavage in the excited starting material. The wavelength of the absorption maximum observed for these transients depends on the natuee of the substituntt R on the sulfur atom (R=H, alkyl, aryl).     

Up to fourth virial coefficients from simple and efficient internal-coordinate sampling: application to neon

A simple and efficient internal-coordinate importance sampling protocol for the Monte Carlo computation of (up to fourth-order) virial coefficients ?B(n) of atomic systems is proposed. The key feature is a multivariate sampling distribution that mimics the product structure of the dominating pairwise-additive parts of the ?B(n). This scheme is shown to be competitive over routine numerical methods and, as a proof of principle, applied to neon: The second, third, and fourth virial coefficients of neon as well as equation-of-state data are computed from ab initio two- and three-body potentials; four-body contributions are found to be insignificant. Kirkwood-Wigner quantum corrections to first order are found to be crucial to the observed agreement with recent ab initio and experimental reference data sets but are likely inadequate at very low temperatures.     

Sensitivity of the thermal and acoustic virial coefficients of argon to the argon interaction potential

Second, third, and fourth thermal and acoustic virial coefficients between 100 and 1000 K are computed for different argon interaction models derived from combinations of accurate two- and three-body potentials. Differences between the various interaction models tested mirror the presumed order in the accuracy of these models, but are not well captured at the level of the lowest-order contributions in the virial expansion: While the second- and third-order virial coefficients are found to be rather insensitive to small variations in the two- and three-body potentials, more pronounced differences in higher-order coefficients are currently of limited use in assessing the accuracy of the interaction potential due to difficulties in the unambiguous experimental determination of these higher-order coefficients. In contrast, pressure-volume and speed-of-sound data - both of which are experimentally known to highest accuracies - are found to be insensitive to small variations in the interaction model. All but the least accurate models reproduce experimental pressure-volume and speed-of-sound data near-quantitatively in regions where the (fourth-order) virial expansions apply. All quantities considered are found to be completely unaffected by a non-vanishing quadruple-dipole four-body potential.