Synthesis of core‐crosslinked carbosilane block copolymer micelles and their thermal transformation to silicon‐based ceramics nanoparticles

Carbosilane fine particles were synthesized by core‐crosslinking of carbosilane block copolymer micelles and they were pyrolytically transformed into silica nanoparticles. The carbosilane block copolymer, poly(1‐(3‐butenyl)‐1‐methylsilacyclobutane)‐block‐polystyrene, (polyBMSB‐b‐polySt), [(m, n) = (31, 16), (54, 30), and (75, 28)], was synthesized by anionic polymerization of BMSB and St, where m and n represent polymerization degrees of BMSB and St segments, respectively. The block copolymer formed micelles in N,N‐dimethylformamide (DMF). The hydrodynamic diameters (D_h) of the micelles evaluated by dynamic light scattering ranged from 40 to 158 nm depending on the copolymer molecular weight. The core of the micelle was cross‐linked by Pt‐catalyzed hydrosilation with 1,2‐bis(dimethylsilylethane). The D_h of the core‐cross‐linked micelles in THF ranged from 56 to 164 nm. These precursor particles were pyrolyzed at 850 °C under N₂ to give ceramic nanoparticles. The diameters of the spherical ceramic particles estimated by AFM ranged from 25 to 60 nm. X‐ray fluorescence analysis of the ceramic products revealed that it consisted of mainly SiO₂ rather than SiC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3778–3787, 2005     

A stereoselective route towards heliannuol A

Both epimers of Heliannuol A, first heliannane reported in the literature, isolated from Heliannthus annuus, have been prepared individually in a stereoselective route using a ring closing metathesis (RCM) as a key step to obtain the eight-membered ring. Very good overall yield was obtained in both cases.     

Analysis of sodium alkylsulphonates using filament heated in-beam electron impact mass spectrometry

Summary By means of the filament heated in-beam method at 280–450° C, the series of sodium alkylsulphonates (RSO₃Na, where R=C₂H₅ to n-C₁₂H₂₅) give very simple mass spectra: Na⁺, [RSO₃Na₂]⁺, which is the base peak except for R=n-C₄H₉, [(RSO₃)₂Na₃]⁺ and, in most cases, [(RSO₃)₃Na₄]⁺. Fragmentations other than these three or four peaks are observed only in the case of n-heptylsulphonate. The proposed method of analysis for simple alkylsulphonic acids is applicable to ordinary electron-impact mass spectrometers.

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Analyse von Natrium-alkylsulfonaten durch Elektronenstoß-Massenspektrometrie mit Probenerhitzung im Elektronenstrahl

Zusammenfassung Mit Hilfe dieser Methode (280–450° C) erhält man für Natriumalkylsulfonate (RSO₃Na mit R=C₂H₅ bis n-C₁₂H₂₅) sehr einfache Massenspektren: Na⁺, [RSO₃Na₂]⁺ (Basispeak mit Ausnahme von R=n-C₄H₉), [(RSO₃)₂Na₃]⁺ und in den meisten Fällen [(RSO₃)₃Na₄]⁺. Andere Fragmentierungen als diese 3 oder 4 Peaks wurden nur bei n-Heptylsulfonat beobachtet. Dieses Verfahren zur Analyse einfacher Alkylsulfonsäuren ist für übliche Elektronenstoß-Massenspektrometer verwendbar.

     

Synthetic studies on carbapenem antibiotics from penicillins.II. regio- and stereoselective aldol reaction of a chiral azetidinone: a synthesis of optically active 6-epicarpetimycins

Aldol and alkylation reactions of the chiral 4-allylazetidinone 1 gave 3,4-trans-azetidinones as major products, in which 10 was converted in several steps to the optically active 6-epicarpetimycins 2.     

Sacculatal and isosacculatal,two new exceptional diterpenedials from the liverwort, trichocoleopsis sacculata

The stereostructures of the two new exceptional diterpene dialdehydes from the liverwort, Trichocoleopsis sacculata: sacculatal (1), responsible for the characteristic pungent taste, and isosacculatal (2) have been determined by the spectral evidence and by comparison with polygodial (3), isopolygodial (4), and drimanediol (6) of known relative configurations.     

Synthesis of spirocyclic C-arylribosides via cyclotrimerization

[reaction: see text] Spirocyclic C-arylribosides were synthesized from the known gamma-ribonolactone derivative. Lithium acetylide addition followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the ribonolactone to silylated diynes. After desilylation or iodination, subsequent ruthenium-catalyzed cycloaddition of resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylribosides.     

Growth and characterization of GaSb/AlGaSb multi-quantum well structures on Si (0 0 1) substrates

GaSb/AlGaSb multi-quantum well (MQW) structures with an AlSb initiation layer and a relatively thick GaSb buffer layer grown on Si (0 0 1) substrates were prepared by molecular beam epitaxy (MBE). Transmission electron microscopy (TEM) images and high-resolution X-ray diffraction (XRD) patterns indicated definite MQW structures. The photoluminescence (PL) emission around 1.55 μm wavelength was observed for 10.34 nm GaSb/30 nm Al_0.6Ga_0.4Sb MQW structure at room temperature. Dependence of PL emission energy on GaSb well width was well explained by finite square well potential model.     

Molecular structure of carbonyl bromide as studied by gas electron diffraction

The molecular structure of COBr₂ has been determined as follows by an analysis of electron diffraction intensity: r_g(CO) = 1.178 ± 0.009 Å, r_g(C-Br) = 1.923 ± 0.005 Å and θ°_α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed.