Hydroxyl-radical-initiated oxidation mechanism of bromopropane

Bromopropane has been considered as a replacement for chlorofluorocarbons used as the active component of industrial cleaning solvents, more specifically for HCFC-141b. The proposed mechanism for the atmospheric oxidation of bromopropane is studied via ab initio methodology. Ab initio molecular orbital methods at the CCSD(T)/6-311++G(2df,2p)//MP2/6-31G(d) level of theory have been used to determine the structure and energetics of the 58 species and transition states involved in the atmospheric oxidation of bromopropane. The calculations show that the major oxidation species is bromoacetone. Other brominated species that result from the oxidation are BrCH 2CH 2C(O)H, BrC(O)CH 2CH 3, and BrC(O)H, potential new bromine reservoir species that result from bromopropane in the atmosphere.     

Fluorescent Saxitoxins for Live Cell Imaging of Single Voltage-Gated Sodium Ion Channels beyond the Optical Diffraction Limit

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Highlights? Fluorescent saxitoxins synthesized as imaging agents for sodium ion channels (Na_Vs) ? Electrophysiology and confocal imaging establish potency and selectivity of Na_V probes ? Single-molecule and super-resolution imaging reveal subdiffraction Na_V distributions ? Dynamic motions of Na_Vs measured in specific membrane regions in live cells     

Expanding the substrate scope for C-H amination reactions: oxidative cyclization of urea and guanidine derivatives

[reaction: see text] Oxidative C-H amination of N-trichloroethoxysulfonyl-protected ureas and guanidines is demonstrated to proceed in high yield for tertiary and benzylic-derived substrates. The success of these reactions is predicated on the choice of the electron-withdrawn 2,2,2-trichloroethoxysulfonyl (Tces) protecting group, the commercial catalyst Rh(2)(esp)(2) (1-2 mol %), and toluene as solvent. The frequency with which the heterocyclic imidazolidin-2-ones and 2-aminoimidazolines appear as structural elements in both natural products and therapeutically designed molecules confers these methods with a large number of potential applications.     

Correction of the self-absorption for reversed spectral lines: application to two resonance lines of neutral aluminium

A new method for the correction of reversed spectral lines, in consequence of self-absorption, is proposed in this article. This method was applied to two resonance lines of neutral aluminium (Al I) obtained by a laser pulse on an aluminium solid placed in air. Several spectra of these lines were corrected for various delays after the laser pulse. The evolution of several parameters of these lines was computed as a function of this delay after the correction of self-absorption.     

QWIP detectors and thermal imagers

Standard GaAs/AlGaAs QWIPs (Quantum Well Infrared Photodetector) are now well established for long wave infrared (LWIR) detection. The main advantage of this technology is the duality with the technology of commercial GaAs devices. The realization of large FPAs (up to 640×480) drawing on the standard III–V technological process has already been demonstrated. The second advantage widely claimed for QWIPs is the so-called band-gap engineering, allowing the custom design of the quantum structure to fulfill the requirements of specific applications such as multispectral detection. QWIP technology has been growing up over the last ten years and now reaches an undeniable level of maturity. As with all quantum detectors, the thermal current, particularly in the LWIR range, limits the operating temperature of QWIPs. It is very crucial to achieve an operating temperature as high as possible and at least above 77 K in order to reduce volume and power consumption and to improve the reliability of the detection module. This thermal current offset has three detrimental effects: noise increase, storage capacitor saturation and high sensitivity of FPAs to fluctuations in operating temperature. For LWIR FPAs, large cryocoolers are required, which means volume and power consumption unsuitable for handheld systems. The understanding of detection mechanisms has led us to design and realize high performance ‘standard’ QWIPs working near 77 K. Furthermore, a new in situ skimmed architecture accommodating this offset has already been demonstrated. In this paper we summarize the contribution of THALES Research & Technology to this progress. We present the current status of QWIPs in France, including the latest performances achieved with both standard and skimmed architectures. We illustrate the potential of our QWIPs through features of Thales Optronique's products for third thermal imager generation. To cite this article: E. Costard et al., C. R. Physique 4 (2003).     

NUPACK: Analysis and design of nucleic acid systems

The Nucleic Acid Package (NUPACK) is a growing software suite for the analysis and design of nucleic acid systems. The NUPACK web server ( http://www.nupack.org ) currently enables:

• Analysis: thermodynamic analysis of dilute solutions of interacting nucleic acid strands.
• Design: sequence design for complexes of nucleic acid strands intended to adopt a target secondary structure at equilibrium.
• Utilities: evaluation, display, and annotation of equilibrium properties of a complex of nucleic acid strands.

NUPACK algorithms are formulated in terms of nucleic acid secondary structure. In most cases, pseudoknots are excluded from the structural ensemble. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Growth of ordered silver nanoparticles in silica film mesostructured with a triblock copolymer PEO-PPO-PEO

Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide, (PEO-PPO-PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV-visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8 nm have been obtained by NaBH₄ reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40 nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substrate-film interface is shown by the RBS experiment.