1,2,3-Thiadiazole derivatives with a nearly linear N-S…O grouping. X-ray crystal structure analysis of four methylated products of 4-phenyl-1,2,3-thiadiazole-5-carbaldoxime

The title oxime 6 was methylated under different conditions and yielded four monomethylated products 7-10 and two bismethylated products 11 and 12 which were easily distinguished by their ¹³C nmr spectra. In view of the potential thiapentalene character of 8, 9, 10 and 11 , their X-ray crystal structures were determined. The structural properties of the nitroso compound 9 are in accordance with a thiapentalene structure, whereas those of the other compounds deviate in the order 10 < 11 < < 8 .     

Influence of benzo-bridging on the stability of 6aλ4-thia-1,2,5,6-tetraazapentalenic systems

Methylation of the phenylhydrazone derived from 8-oxo-8H-indeno[1,2-d]-1,2,3-thiadiazole 5 with Meerwein's reagent furnishes the two methylated products 7 and 8. Single crystal X-ray analyses of these compounds reveal no significant S…NPh interaction, thus excluding a thiapentalene structure.     

In-beam spectroscopy of 253, 254No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei ^{253, 254}No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyv?skyl?. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of ²⁵³No are discussed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rdh@ns.ph.liv.ac.uk RID="b" ID="b"Present address: GANIL, F-14021 Caen, France. RID="c" ID="c"Permanent address: IReS Strasbourg, IN2P3-CNRS, F-67037-Strasbourg, France. RID="d" ID="d"Present address: CEA/DIF DCRE/SDE/LDN F-91680 Bruyeres-le-Chatel. RID="e" ID="e"Present address: Daresbury Laboratory, Daresbury WA4 4AD, UK. RID="f" ID="f"Permanent address: IPN Lyon, IN2P3-CNRS, F-69037 Lyon, France.     

Lifetimes of high-spin yrast states in 154Er

Lifetimes for high-spin levels (between about 10 and 30 ?) in ¹⁵⁴Er have been measured by the recoil-distance method. Non-collective, moderately collective and collective E2 transitions from states with lifetimes between at most 10 and 400 ps have been found. All available data on this nucleus are discussed within the framework of the oblate coupling scheme with the addition of collective degrees of freedom.     

Mechanism and kinetics of the catalytic CO-H2 reaction: An approach by chemical transients and surface relaxation spectroscopy

The aim of this paper is to demonstrate the importance of providing time-resolved information in catalysis research. Two truly in situ methods will be presented and compared for their merits and drawbacks: chemical transient kinetics (CTK) and pulsed field desorption mass spectrometry (PFDMS). The presentation will be given by way of example choosing the syngas (CO/H2) reaction over cobalt-based catalysts as a catalytic process. Despite numerous efforts in the past, the mechanism of this reaction is still under debate. In CTK the reaction is studied on a metal-supported catalyst under flow conditions in a pressure range extending from atmospheric pressure down to 100 Pa. Sudden changes in the partial pressures of the reactants then allow following the relaxation to either steady-state conditions ("transients") or cleanoff ("back transients"). In PFDMS short field pulses of several volts per nanometer are applied to a model catalyst which resembles a single metal particle grain (a "tip"). These pulses intervene during the ongoing reaction under flow conditions at pressures ranging from 10(-1) to 10(-5) Pa and cause field desorption of adsorbed species. This method is particularly suited to detect reaction intermediates in a time-dependent manner since the repetition frequency of the pulses can be systematically varied. It is shown that both methods lead to complementary results. While CTK allows conclusions on the mechanism of CO hydrogenation by following the time-dependent formation of hydrocarbon species, PFDMS provides insight into the initial steps leading to adsorbed CxHy species. A quantitative assessment of the CTK data allows the demonstration that the catalyst under working conditions is in an oxidized rather than metallic state. The initial steps to oxidation are also traced by PFDMS. Most importantly, however, CTK results allow formulation of a reaction mechanism that is common for both hydrocarbon and oxygenate formation and is based on the occurrence of a formate-type species as the most abundant surface intermediate.     

Investigation of uremic analytes in hemodialysate and their structural elucidation from accurate mass maps generated by a multi‐dimensional liquid chromatography/mass spectrometry approach

Historically, structural elucidation of unknown analytes by mass spectrometry alone has involved tandem mass spectrometry experiments using electron ionization. Most target molecules for bioanalysis in the metabolome are unsuitable for detection by this previous methodology. Recent publications have used high‐resolution accurate mass analysis using an LTQ‐Orbitrap with the more modern approach of electrospray ionization to identify new metabolites of known metabolic pathways. We have investigated the use of this methodology to build accurate mass fragmentation maps for the structural elucidation of unknown compounds. This has included the development and validation of a novel multi‐dimensional LC/MS/MS methodology to identify known uremic analytes in a clinical hemodialysate sample. Good inter‐ and intra‐day reproducibility of both chromatographic stages with a high degree of mass accuracy and precision was achieved with the multi‐dimensional liquid chromatography/tandem mass spectrometry (LC/MS/MS) system. Fragmentation maps were generated most successfully using collision‐induced dissociation (CID) as, unlike high‐energy CID (HCD), ions formed by this technique could be fragmented further. Structural elucidation is more challenging for large analytes >270 Da and distinguishing between isomers where their initial fragmentation pattern is insufficiently different. For small molecules (<200 Da), where fragmentation data may be obtained without loss of signal intensity, complete structures can be proposed from just the accurate mass fragmentation data. This methodology has led to the discovery of a selection of known uremic analytes and two completely novel moieties with chemical structural assignments made. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantum imaging with incoherent photons

We propose a technique to obtain subwavelength resolution in quantum imaging with potentially 100% contrast using incoherent light. Our method requires neither path-entangled number states nor multiphoton absorption. The scheme makes use of N photons spontaneously emitted by N atoms and registered by N detectors. It is shown that for coincident detection at particular detector positions a resolution of lambda/N can be achieved.     

Generation of symmetric Dicke states of remote qubits with linear optics

We propose a method for generating all symmetric Dicke states, either in the long-lived internal levels of N massive particles or in the polarization degrees of freedom of photonic qubits, using linear optical tools only. By means of a suitable multiphoton detection technique, erasing Welcher-Weg information, our proposed scheme allows the generation and measurement of an important class of entangled multiqubit states.     

On a multistage discrete stochastic optimization problem with stochastic constraints and nested sampling

Mathematical Programming -