Synthesis of monobutyrylglycerol by transesterification with soluble and immobilized lipases

Transesterification between ethyl butyrate and glycerol using very different lipase preparations (native, modified, and immobilized) in a two-phase system—no extra solvent added—has been investigated. Optimal conversion was obtained with the presence of 5% water in the reaction mixture. Only monobutyrin was produced in all conditions tested. The best enzyme preparations were nativeCandida cylindracea lipase,Mucor miehei lipase immobilized on a phenol-formaldehyde exchange resin (Lipozyme?), andC. cylindracea lipase immobilized on Celite.     

Laser-induced breakdown spectroscopy of silicate, vanadate and sulfide rocks

Laser-induced breakdown spectroscopy (LIBS) in air at atmospheric pressure has been used to study four geological samples belonging to different structural families. Atomic emission spectra of vanadinite, pyrite, garnet and a type of quartz (compostela's quartz) are shown. The 532 nm line of a Nd:YAG laser at an irradiance of 18 x 10(11) W cm(-2) was used. The precise focus of the beam allowed microanalysis of a 0.02 mm(2) surface area working in single-laser shot mode. The use of an intensified gateable charge-coupled-device (CCD) detector permitted time-resolved studies. The spectral lines have been assigned to transitions in the neutral charge state of the corresponding atom of the material under investigation. The behavior of different transitions with time delay are shown. In experiments, minor components contained in several minerals have been detected. This fact has been used to demonstrate the applicability of the technique to characterize and identify similar minerals.     

Enantioselective synthesis of imperanene, a platelet aggregation inhibitor

Both enantiomers of imperanene, a platelet aggregation inhibitor, have been synthesized in 82-90% ee. The key step of establishing the chiral center was achieved through stereoselective alkylation with benzyl chloromethyl ether using Enders' RAMP/SAMP chiral auxiliary method. The natural product was determined to be the (S)-enantiomer through comparison of optical rotation data. Reaction: see text.     

The phenylation of acyltetracarbonylferrates

Diaryliodonium salts react with lithium acyltetracarbonylferrates to give aryl ketones and iodides in high yield, provided the THF medium contains a large proportion of pentane.     

Zum mechanismus des strahlenchemischen abbaus von polytetrafluorethylen

The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N₂, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides.     

7-Deazaadenosine: Oligoribonucleotide building block synthesis and autocatalytic hydrolysis of base-modified hammerhead ribozymes

A 7-deazaadenosine ( = tubercidin; c⁷A; 1 ) building block for solid-phase oligoribonucleotide synthesis was prepared. The amino group of 1 was protected with the (dimethylamino)methylidene residue (→ 3 ), and the monomethoxytrityl group was introduced at OH? C(5′) (→ 4 ). Protection of OH? C(2′) was carried out by silylation, showing that use of the (i-Pr)₃Si group resulted in high 2′-O-selectivity (→ 5b , 80%). Reaction of 5b with PCl₃ afforded the phosphonate 7 which was used in solid-phase oligoribonucleotide synthesis. The autocatalytic hydrolysis of hammerhead ribozymes using pG-G-G-A-G-U-C-A-G-U-C-C-C-U-U-C-G-G-G-G-A-C-U-C-U-G-A-A-G-A-G-G-C-G-C as substrate strand (S) and modified G-C-G-C-C-G-A-A-A-C-U-C-C-C as enzyme strand (E) was studied. When c⁷A replaced A¹³ or A¹⁴, a small decrease of catalytic activity was observed, while modification in position A¹⁵ enhanced the autocatalytic hydrolysis. The results demonstrate, that the atom N(7) of adenosine in any of these positions is not crucial for ribozyme action.     

Rapid and sensitive determination of urinary 2,5-hexanedione by reversed-phase high-performance liquid chromatography.

A rapid and sensitive method for the determination of 2,5-hexanedione (HD) (the principal metabolite of n-hexane) in urine samples by reversed-phase high-performance liquid chromatography (HPLC) is described. The sample preparation procedure was based on solid-liquid extraction after acid hydrolysis; it was optimized to enable accurate HD determination in less than 30 min. Analysis of spiked real samples showed a recovery of more than 85% at the 0.1-ppm level, with a relative standard deviation of 5% and a detection limit as low as 0.01 ppm. Intra-assay and inter-assay coefficients of variation at the 0.5-ppm level were 4 and 5%, respectively. The chromatographic peak assigned to HD was identified by collecting the HPLC eluate at the retention time of HD and analysing it using Fourier transform infrared spectrometry coupled with high-resolution gas chromatography. Urine samples of unexposed and exposed subjects were analysed following the proposed analytical procedure. HPLC and high-resolution gas chromatographic analyses were also compared on these samples. A correlation factor of 0.992 was obtained, which showed a good agreement between the two sets of data.     

High resolution measurement of the3 P 1–3 P 0 transition isotopic shift between24Mg and26Mg

The isotopic frequency shift for the³ P ₁–³ P ₀ Δm _J =0 fine structure transition in the metastable triplet of²⁴Mg and²⁶Mg is reported. The transitions corresponding to the two even isotopes of Mg (λ?498 µm) are observed in a metastable atomic beam through a two-zones Ramsey interaction technique with a transit time limited full width at half maximum of 1.2 kHz (Q=5×10⁸). The isotopic shift turned out to be 1712.5±0.2 kHz.     

Esters and amides from aziridine 2-carboxylic acid salts

Potassium salts of aziridine-2-carboxylic acid derivatives are efficiently converted into esters of amides by reactions with alkyl halides, alkyl dihalides or by acylation with trimethylacetyl chloride followed by aminolyses.     

Ionenaustausch- und Extraktionsmethoden zur Abtrennung von Uran

Zusammenfassung Im vorliegenden Übersichtsartikel wird auf die wichtigsten Ionenaustausch- und Extraktionsmethoden zur Abtrennung des Urans eingegangen. Unter den Anionenaustauschprozessen, die am häufigsten zur Uranabtrennung verwendet werden, sind jene von größter Bedeutung, bei denen das Uran entweder als anionischer Sulfato- oder Chlorokomplex auf stark basischen Harzen, wie z. B. Dowex 1, adsorbiert wird. Dabei sind jene Methoden für analytische Zwecke besonders geeignet, die auf der Trennung des Urans in salzsauren, gemischt wäßrig-organischen Systemen beruhen. Auch bei den Kationenaustauschmethoden wird eine hohe Selektivität der Trennungen in gemischt wäßrig-organischen Medien, insbesondere in einer salpetersauren Tetrahydrofuranlösung, erreicht. Bei der Besprechung der Extraktionsmethoden wird auf die Extraktion des Urans aus salpetersauren Lösungen mit phosphororganischen Verbindungen näher eingegangen.

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Summary The most important ion exchange and extraction methods for the separation of uranium are discussed in this review article. Among the anion exchange methods, most frequently employed for the separation of uranium, the ones of most importance are those in which the uranium is absorbed either as anionic sulfato- or chloro complex on strongly basic resins, such as Dowex 1. The methods particularly suited for analytical purposes are those based on the separation of the uranium in hydrochloric acid-mixed water-organic systems. Likewise, in the cation exchange methods, a high selectivity of the separations is attained in mixed water-organic media, especially in a nitric acid-tetrahydrofuran solution. The extraction of the uranium from nitric acid solutions by means of phosphorus organic compounds is discussed in more detail in the discussion of the extraction methods.

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Résumé Dans l'article d'ensemble qui est présenté, on s'intéresse aux méthodes les plus importantes d'échange ionique et d'extraction pour la séparation de l'uranium. Parmi les processes d'échange anionique utilisés le plus couramment pour la séparation de l'uranium, les plus importants sont ceux oú l'uranium est absorbé sous forme de complexe anionique chloro ou sulfato sur résines fortement basiques comme par exemple Dowex 1. Dans ce cas, les méthodes répondant à des buts analytiques et reposant sur la séparation de l'uranium dans les systèmes chlorhydriques, aquo-organiques, conviennent particulièrement bien. Pour les méthodes avec échange cationique, on obtient aussi une sélectivité élevée des séparations dans les milieux organiques aqueux en mélanges, en particulier dans une solution nitrique de tétrahydrofurane. Pour décrire les méthodes d'extraction, on considère d'une manière plus approfondie l'extraction de l'uranium en solution nitrique par des composés phosphoro-organiques.

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Herrn Prof. Dr.F. Wessely anläßlich seines 70. Geburtstages am 3. August 1967 herzlichst gewidmet.