On the clathratogenic properties of the Ni (NCS)2 (4-Vinylpyridine)4 host

The crystal structure of the non-clathrated -Ni(NCS)₂ (4-Vinylpyridine)₄ complex was solved and refined to R=0.056 (crystal data: a=11.27(3), b=16.86(1), c=32.06(1) Z=8, V=6092 ų;Pbca; d_x=1.30 g. cm^–3). The complex molecule adopts an asymmetric, windmill conformation of the four pyridine ligands. The -phase was used as a solid substrate for clathration of liquid o-, m- and p-xylene, at 25°C. The composition of the products, the enthalpies of clathration and kinetic course of the processes were investigated. The clathration enthalpies, per mole of the host, are equal to 17.07, 14.1 and 21.77 kJ and correspond to the 1.05, 1.11 and 1.30 guest/host molar ratios for, respectively, ortho, meta and para-xylene. The clathration rates follow the order para>ortho>meta. The results are discussed from the structural point of view.     

Measurement of δ13C values of soil amino acids by GC–C–IRMS using trimethylsilylation: a critical assessment

In this study, we evaluated trimethylsilyl (TMS) derivatives as derivatization reagents for the compound-specific stable carbon isotope analysis of soil amino acids by gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS). We used non-proteinogenic amino acids to show that the extraction–derivatization–analysis procedure provides a reliable method to measure δ¹³C values of amino acids extracted from soil. However, we found a number of drawbacks that significantly increase the final total uncertainty. These include the following:

• production of multiple peaks for each amino acid, identified as di-, tri- and tetra-TMS derivatives;

• a number of TMS-carbon (TMS-C) atoms added lower than the stoichiometric one, possibly due to incomplete combustion;

• different TMS-C δ¹³C for di-, tri- and tetra-TMS derivatives.

For soil samples, only four amino acids (leucine, valine, threonine and serine) provide reliable δ¹³C values with a total average uncertainty of 1.3?‰. We conclude that trimethylsilyl derivatives are only suitable for determining the ¹³C incorporation in amino acids within experiments using ¹³C-labelled tracers but cannot be applied for amino acids with natural carbon isotope abundance until the drawbacks described here are overcome and the measured total uncertainty significantly decreased.     

Problems of standard qualities and standards in environmental analysis

Summary Various problems arising with standards in environmental analysis are described and discussed. Every actual analytical result is only meaningful in correlation to the standard qualities of the system in consideration. Need, purpose, evailability and use of standards are discussed and several examples are presented.

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Problematik der Standards und ihrer Qualität in der Analyse von Umweltmaterial

Zusammenfassung Die zahlreichen Probleme, die sich bei der Suche nach Standards für die Analyse von Umweltmaterial ergeben, werden aufgezeigt und diskutiert. Ein analytisches Resultat hat nur Bedeutung, wenn es in Beziehung zu den Standardqualitäten des betreffenden Systems gesehen wird. Notwendigkeit, Zweck, Verfügbarkeit und Anwendung des Standards werden erörtert und mit Beispielen erläutert.

Presented at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria.     

Transient and stationary nutations in chemically induced dynamic nuclear polarization

Transient nutations are observed in nuclear magnetic resonance during continuous generation of magnetization at and near resonance in reactions leading to chemically induced dynamic nuclear polarization. Modulation of the reaction with the nutation frequency leads to stationary nutations. The phase-sensitive detection of the nutation signals is used to discriminate effects of chemically induced polarization from steady state resonance signals. For single line spectra the effects are quantitatively explained by Bloch-type equations containing magnetization production terms. Experimental results obtained during photochemical reactions of di-tert-butyl ketone demonstrate general applications of the method.     

Ring contraction in 2,2,6,6-tetramethylpiperidin-4-one with dichlorocarbene under phase transfer conditions

The preparation of a 5-membered lactam via a postulated dichlorooxirane intermediate is described.     

Education in Analytical Chemistry

Summary After pointing out the necessity of including philosophical aspects in the teaching areas of Analytical Chemistry, proposals are made of new definitions of Analytical Chemistry and considerations are given of samples as representatives of a collective and carriers of information. An idealistic curriculum is presented for discussion.Presented at Euroanalysis III conference, Dublin, August 20–25, 1978