Carbon-13 nuclear magnetic resonance examination of benzonorbornene derivatives. Assignment of site of aromatic ring substitution in benzonorbornen-2-ones

¹³C nuclear magnetic resonance spectra were collected for a series of 5- and 6-monoaromatic ring-substituted benzonorbornadienes and 5-, 6-, 7-, and 8-monosubstituted benzonorbornen-2-ones. ¹³C chemical shifts values were found to be useful in the differentiation of the four monosubstituted aromatic ring isomers of benzonorbornen-2-one (1). We found that the ¹³C NMR spectrum of a substituted benzonorbornen-2-one (A) could be predicted with good accuracy (R² for each aromatic carbon ≥ 0.925) from a knowledge of the ¹³C NMR spectrum of 1 and the appropriately substituted benzene. The substituents studied were NO₂, NH₂, I, CF₃, CN, OCH₃, and H. Correlation analysis showed that the carbonyl in A was effectively insulated from the ring π-system.     

Contributions to the investigation of inorganic non-stoichiometric compounds. XXXI. A New NbOx Phase with ß-ZrNb24O62 structure

Chemical transport reactions with HgCl₂ as transport agent were used to prepare crystals (l = 1–2 mm) of the phases Nb₂₂O₅₄, Nb₄₇O₁₁₆, Nb₂₅O₆₂ and Nb₅₃O₁₃₂. Due to the high temperature applied (T ≈ 1250 to 1280°C) a new NbO_x phase was formed. Without a transport agent the temperature had to be even higher (≈ 1350°C). The complicated block structure of the new phase corresponding to the ideal composition Nb₂₅O₆₂ was revealed by HRTEM. The structure visible by this method remained unchanged on oxidation to Nb₂O₅.     

Investigation of chemical looping combustion of natural gas at 1 MWth scale

Chemical looping combustion (CLC) is an advanced oxyfuel process that enables CO₂ capture with low efficiency penalty. CLC of gaseous fuels has successfully been demonstrated in several pilots up to 150 kW_th. Numerous oxygen carriers have been tested regarding fuel conversion performance and lifetime. This work is a scale-up study of gaseous fuel CLC to MW_th scale. A Ca-Mn-based oxygen carrier has been developed and manufactured in ton-scale prior to the present test. Investigations were conducted in a 1 MW_th CLC unit that was adapted to utilize natural gas as fuel. Stable CLC conditions were reached during tests with Ca-Mn-based material, and the transition to operation with ilmenite was studied. The fuel conversion was in the range of 80%. During operation, 99% of the unburned methane was converted in the post oxidation chamber. The solids circulation rate and the lifetime of solids were determined by means of solids samples from the process, which were investigated in terms of attrition and degree of oxidation. The solids circulation rate was 17 tons h^?1  MW^?1 which is higher than in former tests but lower compared to other units. The most important limiting factors of the fuel conversion are the low solids inventory of the fuel reactor and the oxygen carrier to fuel ratio that corresponds to the solids circulation.     

Query generation to search for inhibitors of enzymatic reactions

A method for the generation of intermediates of enzyme-catalyzed reactions is presented. These intermediates can be used as three-dimensional structural queries for searching for inhibitors of enzymatic reactions. The intermediates can be considered as being structurally quite close to transition-state analogues. For this application, a database containing detailed chemical information on metabolic reactions is used. The likely three-dimensional structure of the intermediates of enzyme-catalyzed reactions can be generated from the information in the database. For three reactions catalyzed by the enzymes AMP deaminase (EC code 3.5.4.6), triose phosphate isomerase (EC code 5.3.1.1), and arginase II (EC code 3.5.3.1), we show how a 3D model of these intermediates can be superimposed onto known inhibitors of these enzymes by a program that uses a genetic algorithm. For this, we test different methods for the superimposition using information on the enzymatic binding site, using information on physicochemical properties calculated from the molecular structure, or without having any information in the superimposition process. We show that these inhibitors are most similar to the corresponding intermediates regarding the 3D structure.     

Noncovalent self-assembly of bicyclo[4.2.2]diketopiperazines: influence of saturation in the bridging carbacyclic ring

[structure: see text] We have prepared 7,9-diazabicyclo[4.2.2]dec-3-ene-8,10-dione (3) and 7,9-diazabicyclo[4.2.2]decane-8,10-dione (4), which differ by virtue of the degree of unsaturation in the bridging carbacyclic tether on a 2,5-diketopiperazine. Remarkably different self-assembly patterns were observed in the solid state for the two compounds, attributed to subtle variations in the conformational constraints imposed by the tether.     

Cross-section measurement of charged-pion photoproduction from hydrogen and deuterium

We have measured the differential cross section for the gamman-->pi(-)p and gammap-->pi(+)n reactions at theta(c.m.)=90 degrees in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E(gamma) greater, similar 3.3 GeV exhibit a global scaling behavior for both pi(-) and pi(+) photoproduction, consistent with the constituent counting rule and the existing pi(+) photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi(-) to pi(+) photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.     

Search for the electron-positron decay of an axionlike particle from a 590 MeV proton beam dump

A search was made for the decay of a light neutral particle into ane ⁺ e ^?-pair behind the dump of the PSI (formerly SIN) 590 MeV proton beam. The detector consisted of two counter triggered optical spark chambers mounted two meters apart. A decay signal would have been detected within a cone of about 10° around the direction to the beam dump. For 300 coulomb of protons we found no excess of decay events over the backgroud. Consequently we can exclude the existence of a standard axion forX-parameters between 13.6 and 300, equivalent to masses between 2m _e and 20 MeV. For the decay modea ⁰→e ⁺ e ^? the standard axion model predicts a decay rate Г _ee ≈2×10⁶ m _a ^?1 MeVs^?1 whereas our analysis yields a limit Г _ee <36m _a ^?1 MeVs^?1 with 90% confidence. In the general case, e.g. for an axionlike boson χ⁰ we exclude values for the decay constantf _x <10⁴ GeV with 90% confidence for masses between 2m _e and 20 MeV.