Total Syntheses of 11-Acetoxy-4-deoxyasbestinin D, 4-Deoxyasbestinin C,Asbestinin-10, -20, -21 and -23

Six members of the asbestinin family of marine diterpene natural products have been synthesized in an efficient and stereoselective manner from a single oxa-bridged intermediate. Five of these natural products have not been synthesized previously and the structures of four of them have been confirmed as those proposed originally or following revisions to the original structures. The fifth natural product—asbestinin-21—has been shown to be a diastereomer of the compound that had been proposed previously.     

Effect of MWCNT content on thermal and shape memory properties of epoxy nanocomposites as material for morphing wing skin

Journal of Thermal Analysis and Calorimetry - In the present study, a shape memory epoxy polymer (SMEP) system was prepared from commercially available EPON 826 and NGDE, and then, 0.5%, 1.0% and...     

Spectrofluorimetric Determination Of Indium with 1,2,4-Trihydroxyanthraquinone

A new method for the spectrofluorimetric determination of indium by formation of a fluorescent 1:1 complex with 1,2,4-trihydroxyanthraquinone is proposed. The complex is formed in a mixed, 60:40 v/v acetone-water medium at pH 3.8 provided by an acetic acid-sodium acetate buffer. The calibration graph is linear between 10 and 600 ng/ml. The effect of potential interferents on the determination was assessed and the proposed method was applied to the determination of indium in synthetic samples.     

Photopyroelectric spectroscopy of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> - ZnO ceramics

Photopyroelectric spectroscopy is used to study the band-gap energy of the ceramic (ZnO + xSb₂O₃), x = 0.1 - 1.5 mol% and the ceramic (ZnO + 0.4 mol%  Bi₂O₃ + xSb₂O₃), x = 0 - 1.5 mol% sintered at isothermal temperature, 1280 °C, for 1 and 2 hours. The wavelength of incident light, modulated at 9 Hz, is kept in the visible range and the photopyroelectric spectrum with reference to doping level is discussed. The band-gap energy is reduced from 3.2 eV, for pure ZnO, to 2.86, 2.83 eV for the samples without Bi₂O₃at 0.1 mol% of Sb₂O₃ for 1 and 2 hours of sintering time, respectively. It is reduced to 2.83, 2.80 eV for the samples with Bi₂O₃ at 0 mol% of Sb₂O₃ for 1 and 2 hours of sintering time, respectively. The steepness factor σ_A which characterizes the slop of exponential optical absorption is discussed with reference to the doping level. The phase constitution is determined by XRD analysis; microstructure and compositional analysis of the selected areas are analyzed using SEM and EDX.     

Novel bis-betaines and betaines within [1(4)]meta-heterophane frameworks

After prior selection of betaine building blocks for the construction of quadrupolar heterophane frameworks, a convergent "3+1" synthetic strategy is reported for the synthesis of the title macrocycles composed of heterocyclic betaine subunit(s). These typify the first example of simple cyclophanes constructed out of both highly pi-excessive and highly pi-deficient heteroaromatic moieties linked in a 1,3-alternating fashion. The chemical reactivity of the quadrupolar heterophanes 1a and 1c toward electrophiles under neutral conditions corroborated their bis-betaine structure. The structural features of the bis-betaines 1, betaines 2 x PF6 and 5 x X, and the corresponding dicationic [1(4)]heterophanes 3 x 2X and 4 x 2Cl were studied by 1H and 13C NMR spectroscopy and electrospray ionization mass spectrometry, and confirmed by single-crystal X-ray diffraction analysis of macrocycles 1a and 2a x PF6.     

A diversity-oriented strategy for the construction of tetrasubstituted pyrroles via coupled domino processes

A new microwave-assisted rearrangement of 1,3-oxazolidines scaffolds is the basis for a new, metal-free, direct, and modular construction of tetrasubstituted pyrroles from terminal-conjugated alkynes, aldehydes, and primary amines. This new reaction manifold entails two linked domino processes in a one-pot manner with both atom- and bond-efficiency and under very simple and environment-friendly experimental conditions.     

Elysiapyrones from Elysia diomedea. Do such metabolites evidence an enzymatically assisted electrocyclization cascade for the biosynthesis of their bicyclo[4.2.0]octane core?

[structure: see text] Biogenetically interesting polypropionate-derived metabolites 1 and 2, featuring an unprecedented skeleton, have been isolated from the sea slug Elysia diomedea. Their enantiomeric character indicates that the current spontaneous electrocyclization cascade biogenetic hypothesis for the bicyclo[4.2.0]octane core must be enzymatically aided. These compounds are isomeric with the 15-nor-9,10-deoxytridachione/15-norphotodeoxytridachione pair of metabolites and encourage speculation about their biosynthetic relationship.     

Phoebegrandine C, a novel proaporphine-tryptamine dimer, from Phoebe grandis (Nees) Merr

A novel proaporphine-tryptamine dimer alkaloid, named phoebegrandine C 1, was isolated from the leaves of Phoebe grandis (Nees) Merr. Its structural elucidation was carried out using spectroscopic techniques, notably 2D NMR.     

Development of an optical refractometer by analysis of one-dimensional photonic bandgap structures with defects

A theoretical analysis of an optical fiber photonic-bandgap-based refractometer is presented. The design is based on a quarter-wave reflector with one defect. By modifying both the real and the imaginary parts of the index of refraction of the defects we begin to change either the frequency or the amplitude of the localized optical mode. So we could fabricate a specific optical fiber refractometer by combining all the variables: index of refractive index of the defects and the rest of layers, thickness of the defect, number of layers, etc. to yield a large set of design possibilities, for example, detecting wider or thinner ranges of refractive indices, or controlling the detection accuracy. Some rules for the practical implementation of the refractometer are given.