Liquid transport in a multi-layer froth

When a gas is sparged into an aqueous solution of surfactant in a column, a froth layer is formed above the layer of liquid. If water is injected into the rising column of froth at a particular position, two distinct layers are formed in the froth: a wet layer below the injection plane, and a dry layer above it. In this study, a phase coexistence analysis was performed on the three-layer system. Predictions from the governing drift-flux equation were compared, using two different representations of the drainage terms, which had one and two adjustable parameters, respectively. The analysis was used to predict liquid fractions and superficial liquid velocities for the wet and dry froth zones. These were compared to experimental measurements performed with a laboratory froth column. Both versions of the analysis were in good agreement with experiment. That with the single-parameter drainage term (derived from the Richardson-Zaki equation) was marginally superior. Theoretical predictions of the liquid fraction and overflow rate from the dry froth layer are supported by the data. Considerable convective motions were observed in the wet froth layer, driven by differences in density between the entering wash liquid and the surrounding froth.     

The total synthesis of neoamphimedine

Neoamphimedine, a pyridoacridine alkaloid from Xestospongia sp., is a potent antitumor agent both in vitro and in vivo. Neoamphimedine can efficiently induce topoisomerase II mediated catenation of plasmid DNA in vitro and is the only member of more than one hundred pyridoacridines thus far to have this mechanism of action. Herein we report the first total synthesis of neoamphimedine.     

Araiosamines A-D: tris-bromoindole cyclic guanidine alkaloids from the marine sponge Clathria (Thalysias) araiosa

Four new tris-bromoindole cyclic guanidine alkaloids, araiosamines A-D, were isolated from the methanol extract of a marine sponge, Clathria (Thalysias) araiosa, collected from Vanuatu. Their carbon skeletons delineate a new class of indole alkaloids apparently derived from a linear polymerization process involving a carbon-carbon bond formation. Comparison of the structures including the relative configurations suggests a common intermediate containing a dihydroaminopyrimidine moiety capable of undergoing various modalities of conjugate addition to yield unprecedented ring systems.     

Force-detected ESR Measurements in a Terahertz Range up to 0.5 THz and Application to Hemin

We report a novel force-detected high-frequency electron spin resonance (HFESR) technique using a microcantilever in the terahertz region. In this technique, we attach a tiny sample on the microcantilever end and the ESR signal is detected as the cantilever bending. The bending is sensitively detected by fiber-optic Fabry–Perot interferometry. We applied this technique to a tiny amount (~16 ng) of metalloporphyrin, a model substance of hemoproteins, and successfully observed ESR signals at multiple frequencies up to 0.5 THz. This result indicates that the sample volume needed in multi-frequency HFESR can be greatly reduced by several orders of magnitude, and our novel technique would be a promising tool for HFESR studies of metalloproteins in the future.     

Diels-Alder Approach to Highly Functionalized Tertiary α-Hydroxy Ketones: A Novel Route to the Hexahydrobenzofuran Portion of the Avermectins and Milbemycins

A highly regio- and stereoselective Diels-Alder reaction between dienophiles of type I and dienes of type II (Scheme 1) gives rise to Diels-Alder adducts of type III . Upon treatment with BF₃.Et₂O, these adducts are smoothly converted into the corresponding enones (Scheme 6). Under mild acidic conditions, enone (±)- 33 gave bicyclic diketone (±)- 34 via an intramolecular Michael-type addition. Diketone (±)- 34 has the correct relative configuration and a suitable ketone function at C(6) for further conversion into the hexahydrobenzofuran portion of the avermectins and milbemycins.     

Syntheses, structures, physical properties, and theoretical studies of CeMxOS (M = Cu, Ag; x approximately 0.8) and CeAgOS

Black single crystals of the two nonstoichiometric cerium coinage-metal oxysulfide compounds CeCu(x)OS and CeAg(x)OS (x approximately 0.8) have been prepared by the reactions of Ce2S3 and CuO or Ag2O at 1223 or 1173 K, respectively. A black powder sample of CeAgOS has been prepared by the stoichiometric reaction of Ce2S3, CeO2, Ag2S, and Ag at 1073 K. These isostructural materials crystallize in the ZrSiCuAs structure type with two formula units in the tetragonal space group P4/nmm. Refined crystal structure results and chemical analyses provide evidence that the previously known anomalously small unit-cell volume of LnCuOS for Ln = Ce (Ln = rare-earth metal) is the result of Cu vacancies and the concomitant presence of both Ce3+ and Ce4+. Both CeCu(0.8)OS and CeAgOS are paramagnetic with mu(eff) values of 2.13(6) and 2.10(1) mu(B), respectively. CeCu(0.8)OS is a p-type semiconductor with a thermal activation energy Ea = 0.22 eV, sigma(electrical) = 9.8(1) 10(-3) S/cm at 298 K, and an optical band gap Eg < 0.73 eV. CeAgOS has conductivity sigma(conductivity) = 0.16(4) S/cm and an optical band gap Eg = 0.71 eV at 298 K. Theoretical calculations with an on-site Coulomb repulsion parameter indicate that the Ce 4f states are fully spin-polarized and are not localized in CeCuOS, CeCu(0.75)OS, or CeAgOS. Calculated band gaps for CeCu(0.75)OS and CeAgOS are 0.6 and 0.8 eV, respectively.     

Charge transport and optical properties of MOCVD-derived highly transparent and conductive Mg- and Sn-doped In2O3 thin films

Mg- and Sn-doped In2O3 (MgIn(x)Sn(y)O(z), 6.0 < x < 16.0; 3.0 < y < 8.0) thin films were grown by low-pressure metal-organic chemical vapor deposition using the volatile metal-organic precursors tris(2,2,6,6-tetramethyl-3,5-heptanedionato)indium(III) [In(dpm)3], bis(2,4-pentanedionato)tin(II) [Sn(acac)2], and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(N,N,N',N'-tetramethylethylenediamine)magnesium(II) [Mg(dpm)2(TMEDA)]. Films in this compositional range retain the cubic In2O3 bixbyite crystal structure. The highest conductivity is found to be approximately 1000 S/cm for an as-grown film with a nominal composition MgIn14.3Sn6.93O(z). Annealing of such films in a vacuum raises the conductivity to approximately 2000 S/cm. The optical transmission window of the present films is significantly wider than that of typical indium tin oxide (ITO) films from 300 to 3300 nm, and the transmittance is also greater than or comparable to that of commercial ITO films.     

Sebastianines A and B,novel biologically active pyridoacridine alkaloids from the Brazilian ascidian Cystodytes dellechiajei

Fractionation of the crude methanol extract of the ascidian Cystodytes dellechiajei collected in Brazil yielded two novel alkaloids, sebastianine A (1) and sebastianine B (2). The structures of both 1 and 2 were established by analysis of spectroscopic data, indicating an unprecedented ring system for both compounds, comprising a pyridoacridine system fused with a pyrrole unit in sebastianine A (1) and a pyridoacridine system fused with a pyrrolidine system condensed with alpha-hydroxyisovaleric acid in sebastianine B (2). Both alkaloids displayed a cytotoxic profile against a panel of HCT-116 colon carcinoma cells indicative of a p53 dependent mechanism.     

Investigation of Inhomogeneites in Epitaxial AlxGa1−xN Layers Grown on Sapphire

 Procedures for the preparation of bevels and the determination of their geometrical parameters have been developed. Using these procedures study of compositional and optical spatially resolved inhomogeneities of Al_xGa_1−xN layers grown on (0001) sapphire have been studied by EPMA and cathodolu-minescence. It has been found that the nonuniform distribution in depth of Al in epitaxial layers grown under constant conditions is connected with presence of stresses in the layer.