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31.
Frabetti PL Cheung HW Cumalat JP Dallapiccola C Ginkel JF Greene SV Johns WE Nehring MS Butler JN Cihangir S Gaines I Garren L Garbincius PH Gourlay SA Harding DJ Kasper P Kreymer A Lebrun P Shukla S Bianco S Fabbri FL Sarwar S Zallo A Culbertson R Gardner RW Greene R Wiss J Alimonti G Bellini G Caccianiga B Cinquini L Di Corato M Giammarchi M Inzani P Leveraro F Malvezzi S Menasce D Meroni E Moroni L Pedrini D Perasso L Sala A Sala S Toretta D Vittone M Buchholz D Claes D Gobbi B O'Reilly B 《Physical review letters》1993,70(12):1755-1758
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G. Kennedy 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(2):239-245
A method has been developed for the correction of counting losses in NAA for the case of a mixture of short-lived radionuclides. It is applicable to systems with Ge detectors and Wilkinson or successive approximation ADC's and will correct losses from pulse pileup and ADC dead time up to 90%. The losses are modeled as a constant plus time-dependent terms expressed as a fourth order polynomial function of the count rates of the short-lived radionuclides. The correction factors are calculated iteratively using the peak areas of the short-lived radionuclides in the spectrum and the average losses as given by the difference between the live time and true time clocks of the MCA. To calibrate the system a measurement is performed for each short-lived nuclide. In a test where the dead time varied from 70% at the start of the measurement to 13% at the end, the measured activities were corrected with an accuracy of 1%. 相似文献
35.
Despite the popularity of boron and silicon allylation reagents in stereocontrolled synthesis, they suffer from a number of inherent limitations that have slowed down their development as synthetic tools for nucleophilic additions to carbonyl compounds and imine derivatives. These limitations are the low reactivity and diastereoselectivity of allyl trialkylsilane reagents, and the lack of catalytic systems for the activation and substoichiometric control of enantioselectivity in the additions of allyl boron reagents. To develop more efficient and general methods for the control of absolute stereochemistry in the resulting homoallylic alcohols, new approaches aimed at solving the problem of activation of allylic boron and silicon reagents are needed. This Minireview describes a number of recent approaches that have been devised to address this problem. 相似文献
36.
Argouarch G Stones G Gibson CL Kennedy AR Sherrington DC 《Organic & biomolecular chemistry》2003,1(24):4408-4417
Three chiral 2,6-disubstituted tri-N-methyl azamacrocycles have been prepared by modular methods. These macrocycles were accessed from three chiral 1,4,7-triazaheptanes intermediates that were prepared by two independent routes. The first of these routes involved the benzylamine opening of chiral tosyl aziridines followed by debenzylation but was problematic on solubility grounds. A second, more effective, route was developed which avoided debenzylation by using ammonia in the nucleophilic opening of chiral tosyl aziridines. 相似文献
37.
M. OKeeffe A. Conneely K. M. Cooper D. G. Kennedy L. Kovacsics Andrea Fodor P. P. J. Mulder J. A. van Rhijn G. Trigueros 《Analytica chimica acta》2004,520(1-2):125-131
Use of nitrofuran drugs in food-producing animals has been prohibited within the EU because they may represent a public health risk. Monitoring compliance with the ban has focused on the detection of protein-bound nitrofuran metabolites which, in contrast to the parent compounds, are stable and persist in animal tissues. As part of the “FoodBRAND” project, an extensive survey of pork was undertaken across 15 European countries. Samples (n = 1500) purchased at retail outlets were analysed for the nitrofuran metabolites AOZ, AMOZ, AHD and SEM using LC–MS/MS determination of nitrobenzaldehyde derivatives. Limits of quantification for the method were 0.1 μg/kg (AOZ, AMOZ), 0.2 μg/kg (SEM) and 0.5 μg/kg (AHD). Of the 1500 samples tested, measurable residues of nitrofuran metabolites were confirmed in 12 samples (0.8% incidence overall) of which 10 samples were purchased in Portugal (AOZ, 0.3 μg/kg; AMOZ, 0.2–0.6 μg/kg) and one sample each in Italy (AMOZ, 1.0 μg/kg) and Greece (AOZ, 3.0 μg/kg). 相似文献
38.
Bould J McInnes YM Carr MJ Kennedy JD 《Chemical communications (Cambridge, England)》2004,(21):2380-2381
[(PMe2Ph)4Pt2B10H10] reversibly takes up atmospheric dioxygen to give the fluxional dioxygen-dimetallaborane complex [(PMe2Ph)4(O2)Pt2B10H10], which has Pt-Pt 2.7143(3), Pt-O 2.141(4) and 2.151(4) and O-O 1.434(6)A. 相似文献
39.
Evert J. Ditzel Xavier L. R. Fontaine Norman N. Greenwood John D. Kennedy Mark Thornton-Pett 《无机化学与普通化学杂志》1992,616(10):79-85
The action of SMe2 on the ten-vertex nido-ruthenaborane [6-(η6-C6Me6)RuB9Hl3] ( 1 ) provides a high-yield route to the unsubstituted isocloso-ruthenaborane [1-(η6-C6Me6)RuB9H9] (2). The benzene analogue [1-(η6-C6Me6)RuB9H9] is prepared similarly. By contrast, reaction of (1) with PhNH2 gives a variety of B-phenylamino isocloso derivatives, including orange crystals of [1-(η6-C6Me6)-2-(PhNH)-isocloso-1-RuB 9 H8] ( 3 ), red-orange [1-(η6-C6Me6)-2,3-(PhNH)2-isocloso-1-RuB9H7] ( 4 ) and dark-red [1-(η6-C6Me6)-5,6,7-(PhNH)3-isocloso-1-RuB9H6] ( 5 ). Detailed 1H and 11B nmr properties of these various compounds are described. The structure of ( 3 ) has been established by a single-crystal X-ray diffraction study of the solvate [1-(η6-C6Me6)-2-(PhNH)-isocloso-1-RuB9H8] · 1/2 CH2Cl2; the crystals were monoclinic, space group C2/c, with a = 1895.1(3), b = 1556.6(3), c = 1716.4(3) pm, β = 104.37(1)° and z = 8. 相似文献
40.
Joseph P. Kennedy Kenneth F. Castner 《Journal of polymer science. Part A, Polymer chemistry》1979,17(7):2039-2054
The reaction between tert-butylchloride (t-BuCl) and dimethylcyclopentadienylaluminum (Me2AlCPD) was studied as a model for initiation by the tert-butyl cation (t-Bu⊕) and termination by cyclopentadienylation by the Me2Al(CPD)Cl? counteranion of isobutylene polymerization. All reaction products formed in this model system have been identified and quantitatively determined. A comprehensive scheme that indicates pathways to these products was developed (scheme III). It is proposed that the predominant product, tert-butylcyclopentadiene (t-BuCPD), arises in the collapse of the t-Bu⊕-Me2Al(CPD)Cl? ion pair, mainly by CPD? transfer to the tert-butyl cation. The minor products are neopentane (t-BuMe) and isobutylene (i-C4H8), which are probably formed, respectively, by Me? transfer to and proton loss from the t-butyl cation. Cyclopentadienylation selectivity increases by lowering the temperature and extrapolation of results suggests 100% cyclopentadienylation at ?55°C. The t-BuCl/Me2AlCPD ratio strongly influences the overall reaction pathway. The reaction is first order in t-BuCl with ΔEa of ca. 7 kcal/mole (1,2-dichloroethane or chlorobenzene solvents, +24 to ?29°C). Indirect evidence indicates that the kinetic product of cyclopentadienylation is 5-t-BuCPD and that this isomer cannot be tert-butylated; that is, the initiation of 5-t-BuCPD polymerization by t-Bu⊕ is sterically unfavorable. Detailed analysis of the chemistry and kinetics of the t-BuCl/Me2AlCPD model system holds important clues to the controlled polymerization of olefins leading to macromolecules with cyclopentadiene (CPD) termini. 相似文献