Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Photoproteins as luminescent labels in binding assays

Certain marine organisms produce calcium-activated photoproteins that allow them to emit light for a variety of purposes, such as defense, feeding, breeding, etc. Even though there are many bioluminescent organisms in nature, only a few photoproteins have been isolated and characterized. The mechanism of emission of light in the blue region is the result of an internal chemical reaction. Because there is no need for excitation through external irradiation for the emission of bioluminescence, the signal produced has virtually no background. This allows for the detection of the proteins at extremely low levels, making these photoproteins attractive labels for analytical applications. In that regard, the use of certain photoproteins, namely, aequorin, obelin, and the green fluorescent protein as labels in the design and development of binding assays for biomolecules has been reviewed. In addition, a related fluorescent photoprotein, the green fluorescent protein (GFP), has been recently employed in bioanalysis. The use of GFP in binding assays is also discussed in this review.     

Fluoridolyse von Cyclophosphazenen und linearen Polyphosphazenen

Fluoridolysis of Cyclophosphazenes and Lineary Polyphosphazenes The fluorination of nongeminal trans P₃N₃Cl₄(NEt₂)₂ and nongeminal trans P₃N₃Cl₃(NEt₂)₃ with the fluorination agent Et₃N · 0,6 HF ( B ) occurs under retention of configuration yielding P₃N₃Cl₂F₂(NEt₂)₂ and P₃N₃F₄(NEt₂)₂ or P₃N₃F₃(NEt₂)₃, respectively. P₃N₃Cl₆ is nearly quantitatively converted into P₃N₃F₆. Poly(dichlorophosphazene) reacts to a poly(difluorophosphazene), (PNF₂)_n, distinguished by a moderate solubility in THF.     

Use of long-chain alkylamines for preconcentration and determination of traces of molybdenum, tungsten and rhenium by atomic-absorption spectroscopy-II: molybdenum in soils, sediments and natural waters

Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range.     

The determination of sulphur in copper,nickel and aluminium alloys by proton activation analysis

The ³⁴S(p, n)^34mCl reaction induced by 13-MeV protons is used for the determination of sulphur in copper, nickel and aluminium alloys. The ^34mCl is separated by repeated precipitation as silver chloride. The results obtained were 3.08 ± 0.47, 1.47 ± 0.17 and <1μg g^-1 for copper, nickel and aluminium alloys, respectively.     

A comparison of SCF-Xα and extended Hückel methods for metal clusters

A comparison of some results from Xα-scattered wave (Xα-SW) and extended Hückel (EH) calculations for metal clusters is given. It is found that small clusters of atoms (≈ 13 atoms) using the Xα-SW method reproduce many of the features of the electronic structure of the bulk metals, whereas this is not the case for the same clusters using the EH method. A more systematic approach to EH parametrizations is suggested in order to make this method a more viable approach to treating metal clusters.     

π-Electron hyperconjugation in organic molecules and ions

The extent of energetic stabilization by alkyl groups with -electron systems via hyperconjugation is investigated theoretically by MINDO molecular orbital calculations. In neutral hydrocarbons, this stabilization represents about 4 % of the effective C-C bond energy, and is additive in the number of alkyl groups present. Calculations for conjugated, polar, and ionic molecules are also discussed.

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Zusammenfassung Das Ausma\ der energetischen Stabilisierung von -Elektronen-Systemen mit Alkylgruppen durch Hyperkonjugation wird theoretisch durch MINDO-MO-Berechnungen untersucht. In neutralen Kohlenwasserstoffen betrÄgt diese Stabilisierung etwa 4% der effektiven C-C Bindungsenergie und ist additiv entsprechend der Zahl der vorhandenen Alkylgruppen. Berechnungen für konjugierte, polare und ionische Moleküle werden ebenfalls diskutiert.

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Résumé La méthode des orbitales moléculaires MINDO est utilisée pour calculer le degré de stabilisation par hyperconjugaison entre des groupements alkyles et des systèmes d'électrons . Dans des hydrocarbures neutres cette stabilisation représente environ 4% de l'énergie effective de la liason C-C; elle est additive par rapport au nombre de groupements alkyles. On discute aussi des calculs effectués pour des molécules conjuguées polaires ou ioniques.

     

Zur Kenntnis des Phosphatstoffwechsels der Hefe

Scheinbare Divergenzen zwischen den seinerzeit aufgestellten Phosphatbilanzen in Säureextrakten aus phosphatangereicherter und-verarmter Hefe und den in der letzten Mitteilung dieser Reihe erhobenen Befunden über den Gehalt an freien Nucleotiden in demselben Material, veranlaßten eine genauere Überprüfung der Frage, inwieweit die Extraktionsmethoden die Ergebnisse der Nucleotidbestimmung und der Phosphatbilanzen beeinflussen. Es zeigte sich, daß bei Bestimmung der freien Nucleotide, trotz Verwendung verschiedener Extraktionsmittel, sowohl qualitativ als auch quantitativ weitgehend entsprechende Ergebnisse erhalten wurden.Die Resultate können wieder in dem Sinne erklärt werden, daß während der Phosphatanreicherung eine Synthese von Nucleinsäure auf Kosten der freien Nucleotide erfolgt.Gleichzeitig durchgeführte Phosphatbilanzen in den Säureextrakten aus phosphat-verarmter und-angereicherter Hefe ergaben je nach den Extraktionsbedingungen starke, zur Zeit noch schwer deutbare Konzentrationsunterschiede in den einzelnen Phosphatfraktionen.

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Glass open-tubular capillary columns with chemically bonded methyl-phenyl siloxane stationary phases of tailor made polarity

Summary The previously described method yielding apolar, chemically bonded methyl polysiloxane glass capillary columns was extended to the production of capillary systems of controlled polarity. The approach involved prior synthesis of a reactive methyl-phenyl polysiloxane polymer by copolymerisation of a mixture of dimethyl and diphenyl chlorosilanes. The polymer was then chemically bonded to the capillary glass surface to yield remarkably stable, high resolution analytical systems which were shown to be particularly well suited to the separation of biochemical mixtures at the subnanogram level. The principle of copolymerisation of differently substituted silanes confers to the method a considerable flexibility which could be used to devise polar capillary systems tailor made for a given analytical problem.