Acetylation of Cellulose Nanowhiskers with Vinyl Acetate under Moderate Conditions

A novel and straightforward method for the surface acetylation of cellulose nanowhiskers by transesterification of vinyl acetate is proposed. The reaction of vinyl acetate with the hydroxyl groups of cellulose nanowhiskers obtained from cotton linters was examined with potassium carbonate as catalyst. Results indicate that during the first stage of the reaction, only the surface of the nanowhiskers was modified, while their dimensions and crystallinity remained unchanged. With increasing reaction time, diffusion mechanisms controlled the rate, leading to nanowhiskers with higher levels of acetylation, smaller dimensions, and lower crystallinity. In THF, a solvent of low polarity, the suspensions from modified nanowhiskers showed improved stability with increased acetylation.

     

The Central Atom Size Effect on the Structure of Group 14 Tetratolyls

Size matters! The structure and dynamics of the tetratolyl Group 14 elements, which were probed by using high‐resolution inelastic neutron scattering spectra, show a remarkable dependence on the size of the central atom. The para‐methyl groups at the periphery of the molecules constitute the frontier intermolecular interactions of increasingly larger tetrahedra, which becomes critical at the molecular radius of the Si and Ge analogues (see picture).

     

A comparison of monocyclic and bicyclic phospholanes as acyl-transfer catalysts

The synthesis and evaluation of chiral phosphines 11, 15a, 19a, 24a, and 28a as nucleophilic catalysts for anhydride activation and kinetic resolution of alcohols is described. The relative reactivity follows the order 11a > 11b > 15a > 1 in the monocyclic series, and 24a > 19a > 28ain the bicyclic series, with an overall rate advantage of ca. 2 orders of magnitude for the bicyclic phospholanes over the monocyclic analogues. The increased reactivity of the bicyclic phospholanes for the acylation of alcohols is attributed to conformational effects and ground-state destabilization in a highly associative mechanism. Kinetic resolution data demonstrate promising enantioselectivities for 24a.     

Investigating magnetically aligned phospholipid bilayers with EPR spectroscopy at 94 GHz

In this paper, we report our initial results on studying magnetically aligned phospholipid bilayers (bicelles) at high magnetic fields (approximately 3.4 T) with electron paramagnetic resonance (EPR) spectroscopy at 95 GHz (W-band). In order to characterize this system for W-band EPR studies, we have utilized the nitroxide spin probe 3beta-doxyl-5alpha-cholestane to demonstrate the effects of macroscopic bilayer alignment. At W-band due to the increase in magnetic field strength (when compared to X-band studies at 9.5 GHz) (S. M. Garber et al., J. Am. Chem. Soc. 121, 3240-3241 (1999)), we were able to examine magnetically aligned phospholipid bilayers at two orientations with the bilayer normal oriented either perpendicular or parallel (upon addition of YbCl3) with respect to the direction of the static magnetic field. Additionally, at a magnetic field of 3.4 T (g=2 resonance at W-band), we were able to study the parallel alignment with a lower concentration of Yb3+, thereby eliminating the possible unwanted effects associated with lanthanide-protein interactions and paramagnetic shifts and/or line broadening induced by the lanthanide ions. The development of this new spin label alignment technique will open up a whole new area of investigation for phospholipid bilayer systems and membrane protein EPR studies at high magnetic fields.     

Zur Analytik mikrobiocider Isothiazolone

Zusammenfassung Zur Isolierung von 2-Methyl-isothiazol-3-on und 5-Chlor-2-methyl-isothiazol-3-on bzw. 2-n-Octylisothiazol-3-on aus den entsprechenden handelsüblichen Formulierungen wie Kathon CG bzw. Kathon 893 wird eine einfache, rasch durchzuführende Methode beschrieben. Die Methode basiert auf Fraktionierung durch Anwendung der Flash-Chromatographie — einer optimierten Variante der Niederdruck-Säulen-Chromatographie.Die erhaltenen Fraktionen wurden mit Hilfe von Dünnschicht-Chromatographie und Hochleistungs-Flüssigkeits-Chromatographie auf ihre Identität und Reinheit untersucht. Anschließend wurden die Gehalte mit einer im Halbmikromaßstab ausgeführten maßanalytischen Absolutmethode bestimmt. Diese Lösungen können als Eichbzw. Kalibrierungsstandards für Quantifizierungszwecke verwendet werden.

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Analysis of microbiocidal isothiazolonesIV. Separation of commercial formulations by flash chromatography and determination of the content by an iodometric absolute method

Summary A method is described for the separation of 2-methyl-isothiazol-3-one and 5-chloro-2-methyl-isothiazol-3-one resp. 2-n-octyl-isothiazol-3-one from corresponding commercial formulations as Kathon CG resp. Kathon 893. This simple and fast method is based on fractionation by flash chromatography — an optimized version of low-pressure column chromatography.The fractions received were analyzed by thin-layer chromatography and high-performance liquid chromatography regarding their identity and purity. The isothiazolone contents were determined by an iodometric absolute method. These solutions can be used as calibration standards for quantification.

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Teil III: Fresenius Z Anal Chem (1985) 322:465     

Beta-delayed proton emitter kr

The nucleide ⁷³Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10⁻³ proton/decay. The protons populate the ground state and also the first excited 2⁺ state at 866 keV in ⁷²Se with a relative intensity of (35±9) %. The value of Q_EC−B_p, where B_p is the proton separation energy for the nucleus ⁷³Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay.     

Identification of threo-ig-fluoro.9,10-Dihydroxystearic acid:a novel cofluorinated fatty acid from dichapetalum toxicarium seeds.

A novel co-fluorinated fatty acid has been isolated from seeds of Dichapetalum toxicarium and identified as threo-18-fluoro-9,10-dihydroxystearic acid (1).     

Comments on "Speech Understanding and Aging"

The hypothesis advanced by the CHABA Working Group on Speech Understanding and Aging [J. Acoust. Soc. Am. 83, 859-895 (1986)] that the systematic decline in speech understanding with age might be explained by concomitant decline in extra-auditory cognitive factors was tested by examining speech audiometric findings in patients with dementia. The fact that performance was consistent with normal central auditory function in 12 of 23 such patients, in spite of deficits in immediate memory for spoken material, tolerance of distraction, mental tracking and sequencing, cognitive flexibility, and set shifting argues against the hypothesis that speech understanding deficits in the elderly can be explained as the simple consequence of cognitive decline.