1,721,259 research outputs found
Investigation of how the chemical and physical properties of thermally evaporated SnS vary with source and substrate temperatures
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Enantioselective Total Synthesis and Structure Determination of the Antiherpetic Anthrapyran Antibiotic AH‐1763 IIa.
No full textTotal synthesis of the proposed structure of the anthrapyran metabolite delta-indomycinone
No full textThe first total synthesis of the proposed structure of delta-indomycinone has been accomplished. The key steps involve the Diels-Alder reaction of a bromonaphthoquinone (6) and 1-methoxy-3-methyl-1-trimethylsiloxy- 1,3-butadiene (7) to access the anthraquinone skeleton, representing a common building block of other naturally occurring anthraquinone antibiotics, regioselective bromination of anthraquinone (14) and a highly diastereoselective alkylation of enantiomerically pure dioxotanone 8. The reported synthetic approach has the advantage of high yields, excellent selectivity and a remarkable general applicability for the total synthesis of other anthrapyran natural products. ne spectroscopic data obtained for the synthetic compounds 2 and 36 are not in agreement with those reported for the natural product, and therefore revision of the assigned structure is required
Enantioselective total synthesis and structure determination of the antiherpetic anthrapyran antibiotic AH-1763 IIa
No full textFirst enantioselective total synthesis and structure determination of the anthrapyran metabolite gamma-indomycinone
No full textThe first total synthesis of (R)-gamma-indomycinone has been achieved which allowed the determination of the configuration of the stereogenic center of natural gamma-indomycinone as (S). The approach stands out for its generality and efficiency
Deposition and Characterisation of SnS Thin Films for Application in Photovoltaic Solar Cell Devices
No full textThin films of SnS have been deposited onto heated glass substrates using the thermal evaporation method and the chemical and physical properties of the layers determined and correlated to the deposition conditions and to post-deposition heat treatments. In particular scanning electron microscopy, energy dispersive X-ray analysis, X-ray di.ractrometry and Raman studies were used to determine the material properties, transmittance and reflectance spectroscopy to determine the optical constants and 4-probe and van der Pauw measurements to determine the electrical properties. The results indicate that for a wide range of deposition conditions it is possible to produce high quality layers of SnS that are free from pin-holes and cracks, that are made of densely packed grains, and that adhere strongly to the substrate. For substrate temperatures between 280°C to 360°C it is possible to produce single phase SnS layers. The energy bandgap of these layers was in the range 1.3eV to 1.35eV, was direct, and had an optical absorption coefficient α > 105 cm-1 for photons with energies greater than the energy bandgap. The electrical properties indicate that all the layers are p-conductivity type with resistivities in the range 40Ωcm to 100Ωcm. Solar cell devices were fabricated in the superstrate and substrate configurations using n-type cadmium sulphide (CdS) and zinc indium diselenide (ZIS) buffer layers to partner the p-type SnS. The devices were investigated by measuring the I-V characteristics in the dark, to determine the predominant conduction mechanisms, the I-V characteristics under illumination to determine the open-circuit voltage V, the short circuit current density Jsc, the fill factor FF and solar conversion efficiency of the devices, C-V studies to determine the doping profile in the SnS and the built-in voltage at the junction and spectral response measurements to determine the minority carrier diffusion length in the p-SnS. Devices made with CdS as the n-type partner had a high density of interface states (1.36 x 1011 F C-1cm-2) with low photovoltaic parameters and a negative
band offset of -0.36 eV obtained (as measured using x-ray photoelectron spectroscopy). The best devices made were substrate configuration solar cells in which the back contact on glass was molybdenum and the bu.er layer was ZIS. These devices have Voc = 472 mV, Jsc = 16.1 mA/cm2 , FF = 0.38 and a solar conversion efficiency of 2.9%. This is a world record efficiency for SnS-based solar cells at the time of submission of this PhD thesis
ChemInform Abstract: Isolation, Enantioselective Total Synthesis and Structure Determination of the Anthrapyran Metabolite SS 43405‐e.
No full textIsolation, Enantioselective Total Synthesis and Structure Determination of the Anthrapyran Metabolite SS 43405‐e
No full textThe first enantioselective total synthesis of the anthrapyran metabolite SS 43405-e, isolated from a marine-derived streptomycete, is described, which also allows the determination of the so far unknown absolute (R) configuration of the natural product. For the synthesis the bromoanthracene derivative 3 is lithiated and coupled with the enantiopure aldehyde (S)-4 to give 9, which is oxidatively transformed into the corresponding anthraquinone 10 and further into the ketone 2. The final step is the cyclization of 2 under acidic conditions to give the desired antibiotic (S)-1. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007
Novel strategies for the synthesis of anthrapyran antibiotics: discovery of a new antitumor agent and total synthesis of (S)-espicufolin
No full textTwo high-yielding strategies for the synthesis of 4H-anthra[1,2-b]pyran antibiotics have been developed giving access to novel antitumor agent 24 (ED50 1.5 mu M) and to (S)-espicufolin (3). A key step for the assembly of the tetracyclic 4H-anthra[1,2-b]pyran-4,7,12-trione skeleton is the nucleophilic addition of an aryl lithium species onto an aldehyde which allows the introduction of either an ynone or 1,3-diketo side chain, serving as precursors for an acid-catalysed cyclisation
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