Behavior ofZ- andE-s-cis-ferrocenyl-1,3-dienes in cycloaddition and dimerization reactions

Z-3-Ferrocenylmethylene-2-methylenecamphane andE-2-ferrocenylmethylene-3-methylenequinuclidine were synthesized by isomerization of the corresponding isomericE- andZ-1,3-dienes in an acidic medium. The dienes obtained form [4+2]-cycloadditionendo-adducts withN-phenylmaleimide, do not form cyclodimers upon thermal or acid-catalyzed [4+2]-cyclodimerization, and addZ-3-ferrocenylmethylene-1,2,7,7-tetramethylbicyclo[2.2.1]hept-2-ylium andE-2-ferrocenylmethylene-3-methyl-1-azoniabicyclo[2.2.1]oct-3-ylium salts, respectively, at the terminal methylene group to give linear addition products. The latter undergo fragmentation on treatment with HBF₄ to form the corresponding carbocation tetrafluroborates. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1223–1228, June, 1998.     

Novel antihyperglycemic terpenoid-quinones from Pycnanthus angolensis

Two new compounds, pycnanthuquinone A (1) and pycnanthuquinone B (2), were isolated from leaves and stems of the African plant, Pycnanthus angolensis (Welw.) Warb (Myristicaceae), by bioassay-guided fractionation of an ethanolic extract using a diabetic mouse model. Pycnanthuquinones A and B are the first representatives of a novel terpenoid-type quinone skeleton, and both compounds possess significant antihyperglycemic activity.     

Thermodesorption profiles for hydrogen from coked and sulfided Rh/Al2O3 catalysts

Significant amounts of hydrogen can be thermodesorbed at high temperature (300–500°C) from coked Rh/Al₂O₃ catalysts. This hydrogen results from partial decomposition of the coke deposited on the catalyst.

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, Rh/Al₂O₃. , .

     

Optimization and application of SPME for the gas chromatographic determination of endosulfan and its major metabolites in the ng L<Superscript>−1</Superscript> range in aqueous solutions

In the present study an analytical method was optimized for the determination of alpha-endosulfan, beta-endosulfan, endosulfan sulfate, endosulfan ether and endosulfan lactone in small volumes of environmental aqueous samples using solid-phase microextraction (SPME) and gas chromatography-electron capture detection (GC-ECD). A 100 micro m polydimethylsiloxane (PDMS) phase was used for the extraction. The limit of detection (LOD) for the analytes varied between 0.01 and 0.03 micro g L(-1) with a relative standard deviation of 3 to 11%. The influence of the ionic strength on the extraction efficiency was investigated for the individual compounds. alpha-Endosulfan, beta-endosulfan, endosulfan sulfate and endosulfan ether were extracted successfully without salt addition. The extraction efficiency of endosulfan lactone was improved with 30% NaCl content. A general decrease in extraction efficiency for alpha-endosulfan, beta-endosulfan, endosulfan sulfate and endosulfan ether with high NaCl content (20-30%) in the solution was observed due to glass surface adsorption. No effect of dissolved organic material (DOM) on the extraction efficiency was observed. The extraction coefficients changed between Log K=2.17 and 3.33. A sample from the Antarctic region was analyzed using the optimized GC-ECD/SPME method. To confirm the results obtained for the real sample a GC with a mass spectrometer (MS) was used. Endosulfan sulfate, the most toxic metabolite of endosulfan, was found in the sample at a concentration of 0.3 micro g L(-1).     

Observation of Upsilon(3S)-->tau+tau- and tests of lepton universality in Upsilon decays

Using data collected with the CLEO III detector at the CESR e+e- collider, we report on a first observation of the decay Upsilon(3S)-->tau+tau-, and precisely measure the ratio of branching fractions of Upsilon(nS), n=1, 2, 3, to tau+tau- and mu+mu- final states, finding agreement with expectations from lepton universality. We derive absolute branching fractions for these decays, and also set a limit on the influence of a low mass CP-odd Higgs boson in the decay of the Upsilon(1S).     

Precision determination of the D0 mass

A precision measurement of the D0 meson mass has been made using approximately 281 pb(-1) of e+e- annihilation data taken with the CLEO-c detector at the psi(3770) resonance. The exclusive decay D0-->K_{S}phi has been used to obtain M(D0)=1864.847+/-0.150(stat)+/-0.095(syst) MeV. This corresponds to M(D0D*0)=3871.81+/-0.36 MeV, and leads to a well-constrained determination of the binding energy of the proposed D0D*0 molecule X(3872), as Eb=0.6+/-0.6 MeV.     

Coarse-grained molecular dynamics simulation on the placement of nanoparticles within symmetric diblock copolymers under shear flow

We present molecular dynamics simulations coupled with a dissipative particle dynamics thermostat to model and simulate the behavior of symmetric diblock copolymer/nanoparticle systems under simple shear flow. We consider two categories of nanoparticles, one with selective interactions toward one of the blocks of a model diblock copolymer and the other with nonselective interactions with both blocks. For the selective nanoparticles, we consider additional variants by changing the particle diameter and the particle-polymer interaction potential. The aim of our present study is to understand how the nanoparticles disperse in a block copolymer system under shear flow and how the presence of nanoparticles affects the rheology, structure, and flow behavior of block copolymer systems. We keep the volume fraction of nanoparticles low (0.1) to preserve lamellar morphology in the nanocomposite. Our results show that shear can have a pronounced effect on the location of nanoparticles in block copolymers and can therefore be used as another parameter to control nanocomposite self-assembly. In addition, we investigate the effect of nanoparticles on shear-induced lamellar transition from parallel to perpendicular orientation to further elucidate nanocomposite behavior under shear, which is an important tool to induce long-range order in self-assembling materials such as block copolymers.