Methode zur Sofortbestimmung von 113Sn im Eluat von 113Sn/113m In-Generatoren

Es wird eine radiometrische Untersuchungsmethode zur Bestimmung der ¹¹³Sn-Kontamination im Eluat von Sn/In-Generatoren vorgeslellt. Dubei wird das ¹¹³Sn über Membranfilter abgetrennt. Die Berechnung der ¹¹³Sn-Konzentration erfolgt aus den in 2 Kanälen gemessenen Impulsraten von ¹¹³Sn und ^113m ln. Die Untersuchung dauert ca. 5 min.     

Molecular ordering in microconfined liquid crystals: An infrared linear dichroism study

Abstract

The molecular arrangement of 5CB confined within the cylindrical pores of Anopore membranes was characterized by means of the IR-order parameter obtained from linear dichroism measurements of selected IR absorption bands. The treatment of the experimental data includes a local field correction extended to the twisted nematic configuration, yielding order parameters increased by about 30% in comparison with the uncorrected data. The nematic director of 5CB aligns along the pore axes, whereas in lecithin coated Anopore channels, the local nematic director is oriented approximately radially due to the perpendicular anchoring of the 5CB molecules at the pore wall. Doping of 5CB with the chiral agent CB15 yields local nematic directors tilted with respect to the pore axes. The average tilt angle increases up to about 40° at a fraction of CB15, x _cb15 = 0.25 (w/w). These results are discussed in terms of the conical helicoidal and alternatively the radially twisted axial arrangement of the LC molecules within submicrometer cylindrical cavities.     

Hydrogen-induced changes of the structural and magnetic properties of cerium/iron multilayers

Multilayers of Ce and Fe show a low Curie temperature and saturation magnetization below a critical thickness of the individual Fe layers where amorphous growth occurs. We have studied on a series of such multilayers with different modulation lengths prepared by ion-beam sputtering the impact of hydrogen absorption on their magnetic properties. Hydrogenation was performed during film growth either reactively by introducing hydrogen gas into the UHV chamber or by irradiation with a beam of low-energy hydrogen ions. Hydrogen is absorbed only in the Ce layers, with a concentration near CeH₂. For suitable modulation lengths, the Curie temperature and saturation magnetization are considerably enhanced with respect to the non-hydrided multilayers. This is correlated with the changes in structure and the quality of the interfaces induced by hydrogenation: the irradiation process itself reduces the critical thickness for amorphous growth of Fe, and the chemical interaction of hydrogen causes a considerable sharpening of the interfaces.     

Quantum and semiclassical dynamics of differential optical collisions

We apply quantum and semiclassical theories to differential optical collisions Na(3²S_1/2) + Kr + Na(3²P_1/2,3/2) + Kr. Our results provide a basis to analyze recent experiments in which for the first time optical collisions were investigated with angular resolution under crossed-beam conditions. A characteristic feature of the differential cross sections is the pronounced oscillatory structure due to interferences of different Condon paths. These Stueckelberg oscillations form an extremely sensitive probe of the collisional dynamics and of the molecular interactions. We demonstrate perspectives to determine geometric properties of the collision complex by excitation with polarized light. By final state analysis nonadiabatic (spin-orbit, rotational) interactions can be studied with complete control of the path. In summary it is shown that the method of differential detection of optical collisions opens a variety of new accesses to atomic and molecular subcollisions. Received: 30 July 1997 / Received in final form: 5 November 1997 / Accepted: 8 January 1998     

Hydrolysis of γ-[1-methyl-5-bis(β-chloroethyl) amino-2-benzimidazolyl]butyric acid. Studied by 1H NMR

High resolution ¹H NMR is applied to the study of hydrolysis and equilibria in the complex system of γ-[1-methyl-5-bis(β-chloroethyl)amino-2-benzimidazolyl]butyric acid and D₂O. Kinetic data for the individual hydrolytic steps are obtained for the first time. The hydrolytic reactions are pseudo first order. The differences in the activation energies of the two hydrolysis steps are accounted for by different intermediates. Furthermore, equilibrium constants for the deuteration of the N mustard group in the individual products are quantitatively estimated. They show an increase of the basicity of N mustard with hydrolysis. The applicability of the ¹H NMR method is restricted to a pD range of 0.5–4.     

Synthesis of biologically active peptide nucleic acid-peptide conjugates by sortase-mediated ligation

Sortase A is a transpeptidase that cleaves at a pentapeptide-motif and subsequently transfers the acyl component to a nucleophile containing N-terminal oligoglycines. We investigate the reaction conditions of the sortase-mediated ligation and demonstrate a useful application by the synthesis of a peptide nucleic acid-cell-penetrating peptide chimera, the reaction equilibrium of which can be shifted in favor of the product by dialyzing out the low molecular weight byproduct. The synthesized conjugate exhibits dose-dependent antisense activity.     

Structure characterisation of urinary metabolites of the cannabimimetic JWH-018 using chemically synthesised reference material for the support of LC-MS/MS-based drug testing

As recently reported, the synthetic cannabinoid JWH-018 is the subject of extensive phase I and II metabolic reactions in vivo. Since these studies were based on LC-MS/MS and/or GC-MS identification and characterisation of analytes, the explicit structural assignment of the metabolites was only of preliminary nature, if possible at all. Here, we report the chemical synthesis of five potential in vivo metabolites of JWH-018 derivatives featuring an alkylcarboxy (M1), a terminal alkylhydroxy (M2), a 5-indolehydroxy (M3), an N-dealkylated 5-indolehydroxy (M4) and a 2′-naphthylhydroxy (5) analogue, respectively, and their characterisation by nuclear magnetic resonance spectroscopy. The collision-induced dissociation (CID) patterns of the protonated compounds were studied by high-resolution/high-accuracy tandem mass spectrometry (MS ⁿ ) applying an LTQ Orbitrap with direct infusion and electrospray ionisation of target analytes. An unusual dissociation behaviour including a reversible ion–molecule reaction between a naphthalene cation (m/z 127) and water in the gas phase of the MS was shown to be responsible for nominal neutral losses of 10 u in the course of the CID pathway. LC-MS/MS-supported comparison of synthesised reference standards with an authentic urine sample using an API 4000 QTrap mass spectrometer identified the synthetic JWH-018 analogues M1–M4 as true in vivo metabolites, presuming a chromatographic separation of potentially present regioisomeric analogues. Existing doping control methods were expanded and validated according to international guidelines in order to allow for the detection of the carboxy and the alkylhydroxy metabolites, respectively, as urinary markers for the illegal intake of the synthetic cannabinoid JWH-018. Both metabolites were quantified in authentic doping control urine samples that had been suspicious of JWH-018 abuse after routine screening procedures, and a stable isotope-labelled ¹³C₈-¹⁵N-carboxy metabolite was synthesised for future analytical applications.     

Synthese des dehydroheliotridins und des 3-oxo-dehydroheliotridins

By application of perester oxydation of bicyclic pyrrol derivatives dehydroheliotridine as well as the corresponding 3-oxo derivative were synthesized, both being basic compounds of several products.