Asymmetric total synthesis of nigerone

[reaction: see text] An enantioselective synthesis of the chiral bisnaphthopyrone natural product nigerone is reported. The key step was an eight-step isomerization process to form the final natural product. The isomerization precursor was constructed via asymmetric oxidative biaryl coupling of an advanced intermediate with a 1,5-diaza-cis-decalin copper catalyst.     

Electrical and material properties of hydrothermally grown single crystal (111) UO<Subscript>2</Subscript>

The semiconductor and optical properties of UO₂ are investigated. The very long drift carrier lifetimes, obtained from current–voltage I(V) and capacitance–voltage C(V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO₂ is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations.     

Mass and magnetic moment of Σ− by the exotic atom method

The energies and lineshapes of five circular transitions (n = 15 → n = 14 through n = 11 → = 10) of the Σ^?Pb atom were measured wit of the transitions 15 → 14 through 12 → 11 were determined; these energies were compared with energies calculated from quantum electrodynamics, and the mass of Σ^? was adjusted to achieve a best fit. The result was m_Σ^? = 1197.24 ±0.15 MeV. The lineshape of the 12→11 transition, which is broadened by the fine structure, has been analyzed to extract the magnetic moment of Σ^?. The result was μ_Σ^? = ?1.40_?0.28^+0.41or 0.651_?0.40^+0.28 nuclear magnetons. Comparisons with SU (3) predictions are made.     

Ringschlussreaktionen an Pleiocarpa-Alkaloiden

Alkaloids with the pleiocarpin skeleton have been found to undergo ring closure on pyrolysis to give heptacyclic compounds with the kopsan (XI) carbon skeleton. Kopsinic acid (V), the main example, gave kopsanone (XIII). The structure XIII for kopsanone has been established by physical and chemical methods, degradation to the methine base XVII and reduction to kopsan (XI). A mechanism to explain these cyclizations is discussed.     

Laser Doppler spectroscopy of atomic hydrogen in the photodissociation of HI

Laser induced fluorescence Doppler spectroscopy has been applied for the first time to atomic hydrogen using tunable VUV light at the Lyman-α line. The dissociation of HI at 266 nm into H+I(P _1/2) and H+I(P _3/2) has been investigated. The recoil energy, angular distribution and branching ratio of the H atom have been measured, serving to test and study the feasibility and applicability of the technique.     

E2 dynamic mixing in p̄ and k− atoms of 238U

The energies of the lower atomic transitions of the p and the K^? atoms of ²³⁸U have been measured. The measured values are significantly higher than the energies calculated from the electromagnetic interactions with the ground state of the ²³⁸U nucleus. It is shown that the dynamic mixing of the first excited quadrupole state can explain such shifts.     

Evaluation of high-performance liquid chromatography column retentivity using macromolecular probes I

The application of macromolecular probes is proposed for evaluation of HPLC column retentivity. The idea is tested with a set of different commercial silica C₁₈ reversed-phases. For comparison, porous glass C₁₈ and polystyrene/divinylbenzene column packings are also included. Polar, mainly silanophilic interactions are evaluated. The retention volumes of a series of narrow molar mass distribution polystyrenes (PS) and poly(methyl methacrylate)s (PMMA) in toluene eluent are compared. Toluene is a weak mobile phase concerning silica gel surface and it promotes adsorption of PMMA on silanols, while PS is not adsorbed from toluene. Simultaneously, toluene is a thermodynamically good solvent for both polymers so that extensive partition in favour of stationary phase is not probable. Differences in retention behaviour of PS and PMMA indicate presence of abundant free silanols on the surface of some reversed-phases. These silanols are accessible even for large macromolecules of PMMA. Pore diameter and pore volume of the column packing can be semiquantitatively evaluated from the elution data of PS in toluene in the course of retentivity tests.     

Novel bioactive breviane spiroditerpenoids from Penicillium brevicompactum Dierckx

The structures of four new, naturally occurring bioactive spiroditerpenoids, (+)-breviones B, C, D, and E, potential allelopathic agents, have been determined from extracts of semisolid fermented Penicillium brevicompactum Dierckx. The structures display the novel breviane spiroditerpenoid skeleton. Structure elucidation was performed by chemical transformations and by homo- and heteronuclear 2D-NMR spectral data. On the basis of combined studies of the theoretical conformations and NOEDIFF data, their relative stereochemistry is proposed. A mixed biogenesis for this novel family of spiroditerpenoids is tendered. The levels of activity shown by breviones B, C, and E in the etiolated wheat coleoptiles bioassay, especially breviones E (100% inhibition) and C (80% inhibition) both at 10(-4) M, suggest them as lead compounds for new agrochemicals.     

EPR studies of free-radical reactions of carboxyfullerenes

Carboxyfullerene is a class of water-soluble buckminsterfullerene with three malonic acids. Electron paramagnetic resonance (EPR) experiments are performed to examine the capacity of carboxyfullerenes to scavenge reactive oxygen species, methyl radicals and peroxyl radicals. Three types of reactions are reported: (1) reactions of^⋅OH and^⋅O ₂ ⁻ with carboxyfullerenes with 5,5-dimethyl-1-pyrroline N-oxide as the trapping agent, (2) reaction of^⋅CH₃ with scavenging agents, and (3) reactions of lipid alkyl/peroxyl radicals with carboxyfullerenes. The study enables one to evaluate the efficacy of carboxyfullerene as a free-radical scavenger and an antioxidatant.