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101.
X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
102.
Bacteria have evolved pathways to metabolize phosphonates as a nutrient source for phosphorus. In Sinorhizobium meliloti 1021, 2-aminoethylphosphonate is catabolized to phosphonoacetate, which is converted to acetate and inorganic phosphate by phosphonoacetate hydrolase (PhnA). Here we present detailed biochemical and structural characterization of PhnA that provides insights into the mechanism of C-P bond cleavage. The 1.35?? resolution crystal structure reveals a catalytic core similar to those of alkaline phosphatases and nucleotide pyrophosphatases but with notable differences, such as a longer metal-metal distance. Detailed structure-guided analysis of active site residues and four additional cocrystal structures with phosphonoacetate substrate, acetate, phosphonoformate inhibitor, and a covalently bound transition state mimic provide insight into active site features that may facilitate cleavage of the C-P bond. These studies expand upon the array of reactions that can be catalyzed by enzymes of the alkaline phosphatase superfamily. 相似文献
103.
Aguilar-Arevalo AA Bazarko AO Brice SJ Brown BC Bugel L Cao J Coney L Conrad JM Cox DC Curioni A Djurcic Z Finley DA Fleming BT Ford R Garcia FG Garvey GT Green C Green JA Hart TL Hawker E Imlay R Johnson RA Kasper P Katori T Kobilarcik T Kourbanis I Koutsoliotas S Laird EM Link JM Liu Y Liu Y Louis WC Mahn KB Marsh W Martin PS McGregor G Metcalf W Meyers PD Mills F Mills GB Monroe J Moore CD Nelson RH Nienaber P Ouedraogo S Patterson RB Perevalov D Polly CC Prebys E Raaf JL Ray H Roe BP 《Physical review letters》2007,98(23):231801
The MiniBooNE Collaboration reports first results of a search for nu e appearance in a nu mu beam. With two largely independent analyses, we observe no significant excess of events above the background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model. 相似文献
104.
3-Keto-4-diazo-5-α-dihydrosteroids are prepared using the Hendrickson diazo transfer reaction on the corresponding β-diketones, which are available from 3-ketoΔ-4-steroids Li/NH3 reduction and acylation of the kinetic enolate. 相似文献
105.
D. Peterson T. Böhringer P. Franzini K. Han S.W. Herb G. Mageras E. Rice J.K. Yoh G. Giannini J. Lee-Franzini R.D. Schamberger M. Sivertz L.J. Spencer P.M. Tuts R. Imlay G. Levman W. Metcalf V. Sreedhar H. Vogel 《Physics letters. [Part B]》1982,114(4):277-281
We have studied the topologies of hadronic events in e+e- annihilation data taken in the region of the upsilon resonances with the non-magnetic CUSB detectors at CESR. Using a thrust-like variable we compare the decay of ?, ?′ and ?Prime; find for ?″ a significant excess of high thrust events, which we interpret as evidence for electric dipole transitions. 相似文献
106.
J. V. Allaby U. Amaldi G. Barbiellini M. Baubillier F. Bergsma A. Capone W. Flegel F. Grancagnolo L. Lanceri M. Metcalf C. Nieuwenhuis R. Pain J. Panman R. Plunckett K. Winter I. Abt J. Aspiazu A. Bungener F. W. Büsser P. D. Gall T. Hebbeker F. Niebergall P. Schütt P. Stähelin P. Gorbunov E. Grigoriev V. Khovansky A. Rosanov A. Baroncelli L. Barone B. Borgia C. Bosio M. Diemoz C. Dionisi U. Dore F. Ferroni E. Longo P. F. Loverre L. Luminari P. Monacelli S. Morganti F. de Notaristefani C. Santoni L. Tortora V. Valente CHARM Collaboration 《Zeitschrift fur Physik C Particles and Fields》1987,36(4):611-628
The cross-section ratio of neutral-current and charged-current semileptonic interactions of muon-neutrinos on isoscalar nuclei has been measured with the result:R v =0.3093±0.0031 for hadronic energy larger than 4 GeV. From this ratio we determined the electroweak mixing angle sin2 θ W , wherem c is the charm-quark mass in GeV/c2. Comparison with direct measurements ofm w andm z determines the radiative shift of the intermediate boson mass Δr=0.077±0.025(exp.)±0.038(syst.), in agreement with the prediction. Assuming the validity of the electroweak standard theory we determined ?=0.990?0.013(m c ?1.5)±0.009(exp.)±0.003(theor.). 相似文献
107.
M Muhlbauer J C Metcalf J T Robertson G Fridland D M Desiderio 《Biomedical chromatography : BMC》1986,1(4):155-158
Endogenous opioid receptoractive peptides in the cerebrospinal fluid (CSF) of human controls and in those patients diagnosed as having senile dementia of the Alzheimer's type (SDAT) are measured with a radioreceptorassay following HPLC separation. [3H]Etorphine is the ligand used to detect in the HPLC fractions the presence of those endogenous peptides that preferentially interact with several opioid receptors. The RRA uses a receptor-rich P2 fraction extracted from a canine limbic system. The total opioid peptide content found in the HPLC fractions 6-20 (to avoid salts in fractions 1-5) of SDAT CSF (383 +/- 187 pmol ME-equivalents per ml CSF) is significantly higher than the corresponding total from patients with no known neurological disorders (89.1 +/- 46.3 pmol ME-equivalents per ml). 相似文献
108.
Semak V Metcalf TA Endoma-Arias MA Mach P Hudlicky T 《Organic & biomolecular chemistry》2012,10(22):4407-4416
A series of ortho-, meta-, and para- halogen-substituted methyl benzoate esters was subjected to enzymatic dihydroxylation via the whole-cell fermentation with E. coli JM109 (pDTG601A). Only ortho-substituted benzoates were metabolized. Methyl 2-fluorobenzoate yielded one diol regioselectively whereas methyl 2-chloro-, methyl 2-bromo- and methyl 2-iodobenzoates each yielded a mixture of regioisomers. Absolute stereochemistry was determined for all new metabolites. Computational analysis of these results and a possible rationale for the regioselectivity of the enzymatic dihydroxylation is advanced. 相似文献
109.
110.
Mo SK Denlinger JD Kim HD Park JH Allen JW Sekiyama A Yamasaki A Kadono K Suga S Saitoh Y Muro T Metcalf P Keller G Held K Eyert V Anisimov VI Vollhardt D 《Physical review letters》2003,90(18):186403
We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory. 相似文献