Efficient synthesis of substituted 1‐dimethylamino or 1‐methylthio but‐3‐enylidene‐bis‐phosphonates,via the [2,3]‐sigmatropic rearrangement of related transient ammonium or sulfonium ylides

New variously substituted 1‐dimethylamino or 1‐methylthio but‐3‐enylidene‐bis‐phosphonates have been prepared from readily availableα‐dimethylamino or α‐methylthio methylene‐bis‐phosphonates by postulated [2,3]‐Wittig rearrangements of the corresponding N‐ or S‐allylic intermediate ylides. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 281–289, 1999     

K2ReH9, eine Neubestimmung der Struktur

K₂ReH₉, a Redetermination of the Structure The crystal structure of K₂ReH₉ was redetermined on a single crystal via neutron diffraction (four circle diffractometer TAS2, 364 symmetrically independent reflections). The atomic arrangement determined by Abrahams et al. in 1964 could be confirmed in its essentials (Space group P62m, Z = 3). Nevertheless the structural parameters, which are much more precise now, yield positions of the hydrogen atoms showing that the co-ordination polyhedra of the two crystallographically independent [ReH₉^2–] – units are identical within the accuracy of the measurement. The results confirm the formula K₂ReH₉, an average structure with lower hydrogen content and statistically occupied hydrogen positions can be ruled out.     

Utility of membrane preconcentration-capillary electrophoresis-mass spectrometry in overcoming limited sample loading for analysis of biologically derived drug metabolites, peptides, and proteins

The limited loading of capillary electrophoresis (CE) leads to relatively poor concentration limits of detection. In this work a unique method for analyte preconcentration with capillary electrophoresis-mass spectrometry (CE-MS) is described. A cartridge containing an impregnated membrane is installed at the inlet of the CE capillary, and we term this approach membrane preconcentration capillary electrophoresis-mass spectrometry (mPC-CE-MS). The analysis of in vivo derived metabolites, peptides, and proteins is described showing the wide applicability of the technology in the analysis of numerous compound classes ranging in molecular weight from 200–60,000 u. In particular, we describe the direct mPC-CE-MS analysis of urine obtained from a patient receiving the neuroleptic drug haloperidol. Three metabolites were found in the urine, and two of them are implicated in the Parkinsonian-like side effects caused by taking this drug. The technique is also applied to the analysis of major histocompatibility complex class I peptides obtained from EG-7 cells. Furthermore, the clinical potential of this approach is described by the direct analysis of urine from a patient suffering from multiple myeloma, as well as aqueous humor derived from a patient undergoing surgery. Finally we show that the use of mPC-ME-MS in conjunction with either analyte stacking (small organic molecules such as metabolites) or moving-boundary transient isotachophoresis (peptides and proteins) after analytes have been eluted from the adsorptive membrane affords optimal performance and no compromise in CE mass spectrometry performance.     

Evaluation of Dead Time Calculation in Reversed-Phase Liquid Chromatography Using a Multiparametric Mathematical Method

In reversed phase liquid chromatography (RP-HPLC), the validity of a multiparametric non-linear least-squares regression iterative method for the determination of the column dead time t_M and the regression parameter (slope b), based on the use of alkan-2-ones, alkyl aryl ketones, and 1-nitroalkanes has been evaluated. The determination of t_M and b has been extensively studied for two mobile phase systems acetonitrile-water and methanol-water on seven octadecyl-C₁₈ and one octyl C₈ analytical columns. The calculated t_M and b values were compared with those obtained by Guardino's and Grobler's methods. The influence exerted thereon by the nature of the homologous series, the mobile phase composition, and the packing materials were investigated.     

NMR relaxivity of coated and non-coated size-sorted maghemite nanoparticles

ABSTRACT

The effect of polymer coating on MNR relaxometry of maghemite nanoparticles has been studied. The samples were carefully sorted by size in order to reach narrow size distribution (<0.2) with size ranging from 4.5 to 12.5?nm. Relaxation dispersion profile as well as studies at a fixed Larmor frequency, were recorded for numerous either uncoated or polymer coated samples. The NMR relaxivities r₁ and r₂ increase with nanoparticle diameter. We have analysed the role of polydispersity for nanoparticles with the same mean size on the dispersion curves. We have compared the role of coating on nanoparticles NMR relaxivity between bare and poly(sodium acrylate-co-maleate) coated nanoparticles. We have investigated the influence of nanoparticle size on the T₁ and T₂ activation energy Ea. While Ea decreases with nanoparticle diameter when determined from T₁, it increases from T₂ determination. The influence is more important for small particles (<9?nm) than for big particles (>9?nm). Moreover, the PAAMA coating changes the energy Ea obtained from T₂: Ea becomes independent of the nanoparticle diameter. These results highlight the need of a complete characterisation of the role of the coating on the relaxation of magnetic particles.     

Direct Numerical Simulations of Hotspot-induced Ignition in Homogeneous Hydrogen-air Pre-mixtures and Ignition Spot Tracking

A systematic study relying on Direct Numerical Simulations (DNS) of premixed hydrogen-air mixtures has been performed to investigate the hotspot ignition characteristics and ignition probability under turbulent conditions. An ignition diagram is first obtained under laminar conditions by a parametric study. The impact of turbulence intensity on ignition delays and ignition probability is then quantified in a statistically-significant manner by repeating a large number of independent DNS realizations. By tracking in a Lagrangian frame the ignition spot, the balance between heat diffusion and heat of chemical reaction is observed as function of time. The evolution of each chemical species and radicals at the ignition spot is checked and the mechanism leading to ignition or misfire are analyzed. It is observed that successful ignition is mostly connected to a sufficient build-up of a HO₂ pool, ultimately initiating production of OH. Turbulence always delays ignition, and ignition probability goes to zero at sufficiently high turbulence intensity when keeping temperature and size of the initial hotspot constant.     

Neutron depolarization study on the magnetic correlation length of nickel ferrite with different packing densities

The magnetic correlation length of a mixed nickel ferrite powder was studied by a newly commissioned depolarized neutron beamline at the W3 port of Tsing Hua Open Pool Reactor (THOR). In this work, Ni ferrite powder samples with different packing densities were studied. The magnetic correlation lengths of the sample were observed to be 2 μm at virgin state and about 3.1 μm at remanent state from the packing density of 20–60%. This magnetic domain size is smaller than particle size. No significant change of domain size at this packing density implies the domain wall motion is hindered by the porosity effectively up to at least 60% of packing density.     

Filamentation “remote” sensing of chemical and biological agents/pollutants using only one femtosecond laser source

All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the “remote” sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.