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51.
N. I. Foster R. Dannals H. D. Burns N. D. Heindel 《Journal of Radioanalytical and Nuclear Chemistry》1981,65(1-2):95-105
Pyrrolidyl triazenes prepared by interception of the diazonium transient in the Sandmeyer reaction of amines can serve as
useful intermediates in the iodination and radioiodination of aryl rings. Decomposition of such triazenes in the presence
of iodide is acid-catalyzed and is sensitive to choice of solvent, acid, and triazene structure. A condition variation study
by HPLC of four different solvent systems and two non-nucleophilic acids was carried out on the123I iodination of the triazenes of p-nitroaniline, p-anisidine and p-toluidine. This method has proven useful in radiolabeling
of two pharmaceutical analogs which were not amenable to labeling through the classic Sandmeyer method. 相似文献
52.
53.
PMR spectra of several Meisenheimer compounds have been measured in various solvents. Evidence is given that in such products derived from 1,3,5-trinitrobenzene the alkoxy group is readily exchanged in solvolysis by the acetonyl group. Products formed in solution by various concentrations of methoxide on several different polynitroaromatics have also been studied. 相似文献
54.
55.
This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described. 相似文献
56.
Dewald EL Suter LJ Landen OL Holder JP Schein J Lee FD Campbell KM Weber FA Pellinen DG Schneider MB Celeste JR McDonald JW Foster JM Niemann C Mackinnon AJ Glenzer SH Young BK Haynam CA Shaw MJ Turner RE Froula D Kauffman RL Thomas BR Atherton LJ Bonanno RE Dixit SN Eder DC Holtmeier G Kalantar DH Koniges AE Macgowan BJ Manes KR Munro DH Murray JR Parham TG Piston K Van Wonterghem BM Wallace RJ Wegner PJ Whitman PK Hammel BA Moses EI 《Physical review letters》2005,95(21):215004
The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums. 相似文献
57.
We present a Mie theory-based analysis of angularly resolved light scattering from intact cells that involves the product of a particle size distribution rho and the scattering cross section sigma. The analysis shows that the ability to size intracellular organelles depends strongly upon the assumed functional form of the particle size distribution; however, the product sigma rho extracts the dominant light scatterers regardless of this choice. We examine goniometer measurements from our own and another laboratory and find that this analysis reconciles seemingly conflicting results and confirms that mitochondrial-sized organelles dominate scattering from intact cells in the angular range 50 degrees - 90 degrees. 相似文献
58.
Detection of hypophosphite, phosphite, and orthophosphate in natural geothermal water by ion chromatography 总被引:3,自引:0,他引:3
McDowell MM Ivey MM Lee ME Firpo VV Salmassi TM Khachikian CS Foster KL 《Journal of chromatography. A》2004,1039(1-2):105-111
Current doctrine states that phosphorus is incorporated into cells in the pentavalent(V) oxidation state as orthophosphate. However, recent studies show that microorganisms contain enzymes used to metabolize reduced forms of phosphorous, including phosphite(III) and hypophosphite(I), which suggests that there is a natural source for these chemical species. This paper will discuss suppressed conductivity ion chromatography methods developed to detect hypophosphite, phosphite, and orthophosphate in a geothermal water matrix containing fluoride, chloride, bromide, nitrate, hydrogen carbonate and sulfate. All peaks were clearly resolved, and calibrations were linear with estimated 3sigma detection limits of 0.83, 0.39, and 0.35 microM for hypophosphite, phosphite, and orthophosphate, respectively. 相似文献
59.
Lehtinen PO Foster AS Ma Y Krasheninnikov AV Nieminen RM 《Physical review letters》2004,93(18):187202
Recent experiments indicate that proton irradiation triggers ferromagnetism in originally nonmagnetic graphite samples while He ion bombardment has a much smaller effect. To understand the origin of irradiation-induced magnetism, we have performed spin-polarized density functional theory calculations of the magnetic properties of the defects which are most likely to appear under irradiation vacancies and vacancy-hydrogen complexes. Both defects are magnetic, but as for the latter we find that H adsorption on one of the vacancy dangling bonds gives rise to a magnetic moment double that of the naked vacancy. We show that for small irradiation doses vacancy-hydrogen complexes result in a macroscopic magnetic signal which agrees well with the experimental values. 相似文献
60.
We present the results of diffuse reflectance measurements made on the surface of a tissue-simulating phantom containing intact human erythrocytes. These measurements indicate that the absorption spectrum of hemoglobin in its natural environment is significantly different from that measured in homogeneous fluid solution, especially in the spectral regions of highest absorption. We show that this difference can be explained by the pigment packaging theory developed by Duysens [Biochim. Biophys. Acta 19, 1 (1956)] and that the adoption of basis spectra that take this effect into account improves the accuracy of fitting diffuse reflectance spectra. 相似文献