Quantitative energy-dispersive electron probe X-ray microanalysis for single-particle analysis and its application for characterizing atmospheric aerosol particles

An energy-dispersive electron probe X-ray microanalysis (ED-EPMA) technique using an energy-dispersive X-ray detector with an ultra-thin window, designated as low-Z particle EPMA, has been developed. The low-Z particle EPMA allows the quantitative determination of concentrations of low-Z elements such as C, N and O, as well as higher-Z elements that can be analysed by conventional ED-EPMA. The quantitative determination of low-Z elements (using full Monte Carlo simulations, from the electron impact to the X-ray detection) in individual particles has improved the applicability of single-particle analysis, especially in atmospheric environmental aerosol research; many environmentally important atmospheric particles, e.g. sulphates, nitrates, ammonium and carbonaceous particles, contain low-Z elements. To demonstrate its practical applicability, the application of the low-Z particle EPMA for the characterization of Asian Dust, urban and subway aerosol particles is shown herein. In addition, it is demonstrated that the Monte Carlo calculation can also be applied in a quantitative single-particle analysis using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectrometry (EDX), showing that the technique is useful and reliable for the characterization of submicron aerosol particles.     

Chlorpromazine binding to Na+, K+-ATPase and photolabeling: involvement of the ouabain site monitored by fluorescence

This work reports the results of ultraviolet irradiation on the interaction of the phototoxic antipsychotic drug chlorpromazine (CPZ) with the sodium pump Na+, K+-ATPase. The study was performed by monitoring the fluorescence modifications of CPZ itself and of the specific probe anthroylouabain (AO). CPZ association with Na+, K+-ATPase was found to modify the kinetics of CPZ-photodegradation. It was demonstrated that UV irradiation produces a stable fluorescent photoproduct of CPZ covalently bound to Na+, K+-ATPase. The fluorescent probe AO, which specifically binds to the extracellular ouabain site of the pump, was used to localize the CPZ binding site. UV-irradiation of AO-labeled Na+, K+-ATPase treated with CPZ at concentration about 20 microM produced dose-dependent modifications of the AO fluorescence, e.g. increased quantum yield and blue shift. The results demonstrated that CPZ binds near the ouabain site. The photo-induced reaction of CPZ with AO-labeled Na+, K+-ATPase protected the ouabain site from the aqueous environment. It was also found that UV irradiation of CPZ-treated enzyme obstructs the binding of AO, which suggested occlusion of the ouabain site. This effect can be evaluated for a potential use of CPZ in photochemotherapy.     

Fluorescence Studies of gold(III)-Norfloxacin Complexes in Aqueous Solutions

Formation of gold(III) complexes with the synthetic antibiotic norfloxacin (NF) was investigated in aqueous solution at pH 4.0, 7.5 and 10.6, with the ligand in cationic, zwitterionic and anionic forms, respectively. UV-Visible spectroscopy, steady state and time-resolved fluorometry were used to characterize the complexes. Binding sites, association constants and fluorescence lifetimes of the complexes were obtained. Au³⁺ binding to zwitterionic NF produced a fluorescence decrease and a small red shift. Fluorescence changes as a function of Au³⁺ concentration were fitted using a one-site binding model and the association constant was obtained, K_b^zw = 1.7 ×10⁵  \textM¹ K_b^{{zw}} = {1}.{7} \times {1}{0^{{5}}}\;{{\text{M}}^{{1}}} . The association of Au³⁺ with cationic NF was much weaker, the obtained binding constant being K_b^cat = 2.4 ×10³  \textM¹ K_b^{{cat}} = {2}.{4} \times {1}{0^{{3}}}\;{{\text{M}}^{{1}}} . The Au³⁺ binding site for these species involves the carboxyl group, in agreement with a much stronger association of the cation with the carboxylate anion than with the neutral acid. Association of Au³⁺ with nonfluorescent anionic NF presented a clear evidence of two binding sites. The highest affinity site is the unprotonated piperazinyl group with K_b^pip \geqslant 5 ×10⁷  \textM ^{- 1} K_b^{{pip}} \geqslant {5} \times {1}{0^{{7}}}\;{{\text{M}}^{{ - {1}}}} , and the low affinity site includes the carboxylate anion. The results point out to important pH dependent differences in complex formation between transition metal ions and fluoroquinolones, leading to different binding sites and association constants that change by several orders of magnitude.     

Orientation of the axial ligands and magnetic properties of the hemes in the cytochrome c7 family from Geobacter sulfurreducens determined by paramagnetic NMR

Geobacter sulfurreducens is a sediment bacterium that contains a large number of multiheme cytochromes. The family of five c(7) triheme periplasmic cytochromes from Geobacter sulfurreducens shows structural diversity of the heme core. Structural characterization of the relative orientation of the axial ligands of these proteins by (13)C-paramagnetic NMR was carried out. The structures in solution were compared with those obtained by X-ray crystallography. For some hemes significant differences exist between the two methods such that orientation of the magnetic axes obtained from NMR data and the orientation taken from the X-ray coordinates differ. The results allowed the orientation of the magnetic axes to be defined confidently with respect to the heme frame in solution, a necessary step for the use of paramagnetic constraints to improve the complete solution structure of these proteins.     

Factorization of linear elliptic boundary value problems in non-cylindrical domains

We present a method of factorization for linear elliptic boundary value problems considered in non-cylindrical domains. We associate a control problem to the boundary value problem which regularizes it. The technique of change of variables is used to study this problem.     

Non-pixeled amorphous silicon-based image sensors

Large area hydrogenated amorphous silicon p–i–n structures with low conductivity doped layers were proposed as single element monochrome image sensors. The investigation of the sensor output under different scanner wavelengths and varying electrical bias reveals that the response can be tuned to a certain wavelength, thus enabling color separation. The measurement technique is described in detail and two methods for color separation are proposed. The sensor output characteristics are evaluated under different bias voltages and wavelengths. The color separation mechanism can be explained by the variation of the band bending with light wavelength.The operation of the sensor is exemplified under illumination with a polychromatic image and using one of the proposed detection methods.     

A factorization method for elliptic problems in a circular domain

We present a method to factorize a second order elliptic boundary value problem in a circular domain, in a system of uncoupled first order initial value problems. We use a space invariant embedding technique along the radius of the circle, in a decreasing way. This technique is inspired in the temporal invariant embedding used by J.-L. Lions for the control of parabolic systems. The singularity at the origin for the initial value problems is studied. A formal calculation for more general star-shaped domains is presented. To cite this article: J. Henry et al., C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Two-layer exchange flows over a dune: effect of large-scale bottom roughness

Graphical Abstract  

     

2-Pyridinoformamide-derived thiosemicarbazones and their iron(III) complexes: Potential antineoplastic activity

The iron(III) complexes [Fe(2Am4DH)₂]Cl (1), [Fe(2Am4Me)₂]Cl (2) and [Fe(2Am4Et)₂]Cl (3) with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me) and N(4)-ethyl (H2Am4Et) derivatives were obtained and characterized by means microanalyses, infrared and EPR spectra. The electrochemical behavior of the complexes was investigated. The thiosemicarbazones and complexes (1) and (2) presented toxicity against Artemia salina at low concentrations. Since this bioassay has a good correlation with cytotoxic activity in human solid tumors, the studied compounds present potential pharmacological applications.     

钨离子团簇与N_2分子的反应性

利用激光蒸发团簇源产生Wn 团簇束 ,团簇束通过一个充有N2 气体分子的低压反应池 ,利用飞行时间质谱探测反应产物 ,在类单次碰撞条件下研究了W 10 -W 50 和N2 分子的反应性 ,在室温条件下测量了N2 分子与W n 团簇反应的反应几率。团簇尺寸在 10～ 2 6原子的团簇与N2 分子的反应几率与团簇尺寸有很强的相关性 ,对n =16,2 2 ,2 3的团簇具有比较高的反应性。W n 与N2 分子的反应性与Wn 与N2 分子的反应性显示出相似的规律性。