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991.
K. Dadachova K. La Riviere P. Anderson 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(3):935-938
Two improved processes of99Mo production have been developed on laboratory scale. The first one allows to purify Mo of natural isotopic composition from tungsten impurities from 64 to <10 ppm by using preferential adsorption of tungsten on hydrated tin(IV) oxide (SnO2 nH2O) before irradiation in a nuclear reactor. The second process deals with the separation of pure fission product99Mo from235U irradiated in a reactor. Two versions of separation process for production of fission99Mo have been developed. Both versions start with the dissolution of235U oxide target in nitric acid and are based on sequential use of alumina and anion exchange resin AG® 1-X8 columns. The yield of99Mo in both versions is 80–89%. 相似文献
992.
James A. Bresson Gordon A. Anderson James E. Bruce Richard D. Smith 《Journal of the American Society for Mass Spectrometry》1998,9(8):799-804
The simultaneous high resolution and accurate mass measurements possible with Fourier transform ion cyclotron resonance mass spectrometry coupled with the gentle ionization of electrospray hold attractions for protein, peptide, and oligonucleotide characterization, including multistage-mass spectrometry measurements for assignment of fragment masses and greater confidence in structural measurements. The detection of cyclotron motion over extended periods of time (in some cases for several minutes) allows higher resolution and mass accuracy. Generally, signal duration has been considered to be limited primarily by background pressure, with ion-neutral collisions leading to the reduction and dephasing of cyclotron motion, causing signal loss. However, recent theoretical work has shown that the ion cloud stability that is a prerequisite for high performance measurements is highly dependent on the electric field generated by the ion cloud, thus giving rise to a minimum number of charges or ions required for extended time-domain signals. The effects of ion population on ion cloud stability and signal duration, and the subsequent effects on resolution and measured isotopic abundances are reported. Individual time-domain signals for bovine insulin isotopic peaks were extracted to allow a comparison of the damping rates for each of these ion clouds and the measured time-domain amplitude maxima are shown to provide a better match with the theoretically predicted isotopic abundances for insulin. These results show that different damping rates of ions of very similar mass, but different ion cloud population sizes, can have dramatic effects on the observed isotopic patterns. Additionally, more accurate, high resolution spectra can be produced by correcting for the effects of the different damping rates that are observed for different ion population sizes. 相似文献
993.
Frankie P. Anderson John F. Gallagher Peter T. M. Kenny Clodagh Ryan David Savage 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):m13-m15
The title compounds, [Fe(C5H5)(C14H13O2)] and [Fe(C5H5)(C15H15O2)], respectively, contain the ferrocenyl η5(C5H4) and phenylene –C6H4– rings in a nearly coplanar arrangement, with interplanar angles of 6.88 (12) and 10.5 (2)°, respectively. Molecules of the ethyl ester form dimers through η5(C5H5)C—H⋯O=C hydrogen bonds, with graph set R(20), and, together with Csp3—H⋯π(C5H5) interactions, generate a one‐dimensional column (irregular ladder). Molecules of the isopropyl ester aggregate through η5(C5H5)C—H⋯π(C6H4) interactions. 相似文献
994.
995.
Malcolm J. Arendse Gordon K. Anderson Nigam P. Rath 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(3):237-239
In [Pt(dppe)(NO3)2], where dppe is ethylene-1,2-bis(diphenylphosphine) (C26H24P2), the Pt atom is coordinated by the two P atoms and by two O atoms of the two nitrate ions. The molecule has a distorted square-planar geometry, with one of the nitrate groups directed on each side of the plane. The cation in cis-[Pt(dppmO-O,P)2](NO3)2·2H2O, where dppmO is bis(diphenylphosphinomethyl)diphenylphosphine oxide (C25H22OP2), comprises two five-membered chelate rings, each dppmO ligand being coordinated to platinum through one P atom and the O atom. The larger P—Pt—P angle of 102.25 (4)° is due to steric interactions between the two phenyl groups on each P atom. 相似文献
996.
Perinchery Narayan Marcus W Hedgcock Charles Anderson 《Magnetic resonance imaging》1993,11(8):XXXVII-XXXVIII
997.
Stephen G. Anderson Karl W. Sohlberg Stephen L. Howard Anil K. Shukla Jean H. Futrell 《Journal of the American Society for Mass Spectrometry》1991,2(6):506-510
A hemispherical energy analyzer was constructed by using a novel approach to control the fringing electrostatic field. It provides several properties useful in ion spectrometers: namely, rather simple fabrication and compact size, high transmission efficiency at moderate resolution, and the capability to adjust resolution by changing the intersphere potentials. A computer program was developed to evaluate ion trajectories through the hemispherical analyzer. Data obtained from the trajectories were used to predict the characteristics of the analyzer. Experiments performed to determine the kinetic energy dependence of the absolute transmission and the resolution functions are in accord with theoretical calculations. 相似文献
998.
999.
Investigating chemical constraints to the measurement of phosphorus in soils using diffusive gradients in thin films (DGT) and resin methods 总被引:2,自引:0,他引:2
The effect of potential chemical constraints on the performance of two relatively new soil P testing methods, anion exchange membrane (AEM) and diffusive gradients in thin films (DGT), were evaluated. Exposures to ranges of anion (Cl(-), NO(3)(-), SO(4)(2-) and HCO(3)(-)) concentrations relevant to agricultural soils had minimal effect on P recoveries using DGT. It has also been shown previously that DGT P recoveries are unaffected by varying pH (3-9). In contrast, increasing NO(3)(-) and SO(4)(2-) concentrations in solution reduced the recovery of P using the resin method (anion exchange membrane, AEM) by 24% at 50mgL(-1) NO(3)(-) and by 47% at 12mgL(-1) SO(4)(2-) when the P concentration of the test solution was 2mgL(-1). Phosphorus sorption by the resin decreased with increasing Cl(-) concentrations until there was a 100% decrease at 300mgL(-1) Cl(-) when the P concentration of the test solution was 2mgL(-1) and a 92% reduction at 700mgL(-1) Cl(-) when the P concentration of the test solution was 0.2mgL(-1). There was also a small but significant effect of carbonate species on P sorption to the resin at carbonate concentrations that can occur in agricultural soils. Changing the pH of the solution had minimal effects on the resin P measurements in solutions above pH 4, but below pH 4, resin P measurements decreased dramatically. A poor coefficient of determination for the regression fit between DGT and resin measurements on eight agricultural soils suggested that these two methods are measuring different amounts of P for different soils. Resin P measurements increased significantly, but non-uniformly across soils, when the soil:water ratio was decreased but this did not result in an improved relationship with DGT P. There was a minimal effect on measured P using either Cl(-) or HCO(3)(-) as counter ions on the resin. 相似文献
1000.
Corinne Boudon Jean-Paul Gisselbrecht Maurice Gross Lyle Isaacs Harry L. Anderson Rüdiger Faust Franois Diederich 《Helvetica chimica acta》1995,78(5):1334-1344
The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties of covalent fullerene derivatives ( 2 – 11 ) as a function of increasing number of addends is reported. Dialkynylmethanofullerenes 2 – 4 undergo multiple, fullerene-centered reduction steps at slightly more negative potentials than C60 ( 1 ; see Table and Fig. 1). The two C-spheres in the dumbbell-shaped dimeric fullerene derivative 4 show independent, identical redox characteristics. This highlights the insulating character of the sp3-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methano bridge to the fullerene sphere. In the series of mono- through hexakis-adducts 5 – 11 , formed by tether-directed remote functionalization, reductions become increasingly difficult and more irreversible with increasing number of addends (see Table and Fig. 2). Whereas, in 0.1M Bu4NPF6/CH2Cl2, the first reduction of mono-adduct 5 occurs reversibly at ?1.06 V vs. the ferrocene/ferricinium couple (Fc/Fc+), hexakis-adduct 11 is reduced irreversibly only at ? 1.87 V. Hence, with incremental functionalization of the fullerene, the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the relative spatial disposition of the addends on the surface of the fullerene sphere. Observed UV/VIS spectral changes and changes in the chemical reactivity along the series 5 – 11 are in accord with the results of electrochemical measurements. Further, with increasing number of addends, the oxidation of derivatives 5 – 11 becomes more reversible. Whereas oxidations are increasingly facilitated upon going from mono-adduct 5 (+1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same potential (+0.95 to +0.99 V) in the higher adducts 8 – 11 . This indicates that the oxidations occur in these compounds at a common sub-structural element, for which a ‘cubic’ cyclophane is proposed (see Fig. 3). This sub-structure is fully developed in hexakis-adduct 11 . 相似文献