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81.
Ahmed SN Anthony AE Beier EW Bellerive A Biller SD Boger J Boulay MG Bowler MG Bowles TJ Brice SJ Bullard TV Chan YD Chen M Chen X Cleveland BT Cox GA Dai X Dalnoki-Veress F Doe PJ Dosanjh RS Doucas G Dragowsky MR Duba CA Duncan FA Dunford M Dunmore JA Earle ED Elliott SR Evans HC Ewan GT Farine J Fergani H Fleurot F Formaggio JA Fowler MM Frame K Frati W Fulsom BG Gagnon N Graham K Grant DR Hahn RL Hall JC Hallin AL Hallman ED Hamer AS Handler WB Hargrove CK Harvey PJ Hazama R Heeger KM 《Physical review letters》2004,92(10):102004
Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to "invisible" modes, such as n-->3nu. The analysis was based on a search for gamma rays from the deexcitation of the residual nucleus that would result from the disappearance of either a proton or neutron from 16O. A limit of tau(inv)>2 x 10(29) yr is obtained at 90% confidence for either neutron- or proton-decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton-decay modes and 400 times more stringent than similar neutron modes. 相似文献
82.
Hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (4) incorporates a disc-shaped hexaphenylbenzene core and six peripheral diaminotriazine groups that can engage in hydrogen bonding according to established motifs. Under all conditions examined, compound 4 crystallizes as planned to give closely related noninterpenetrated three-dimensional networks built from sheets in which each molecule has six hydrogen-bonded neighbors. In the structure of compound 4, the number of hydrogen bonds per molecule and the percentage of volume accessible to guests approach the highest values so far observed in molecular networks. Analogue 5 (which has the same hexaphenylbenzene core but only four diaminotriazine groups at the 1,2,4,5-positions) and analogue 7 (in which the two unsubstituted phenyl groups of compound 5 are replaced by methyl groups) crystallize according to a closely similar pattern. Analogues with flatter pentaphenylbenzene or tetraphenylbenzene cores crystallize differently, underscoring the importance of maintaining a consistent molecular shape in attempts to engineer crystals with predetermined properties. 相似文献
83.
We developed and validated a novel on-line preconcentration liquid chromatography-tandem mass spectrometry method for the determination of anti-infectives in wastewaters. The presented method preconcentrates 1 mL of sample in a load column using a switching-valve technique. The method was optimized with respect to sample load flow rate, volume of the load column wash and organic solvent content of the load column wash. The sample is cleaned using a 30% organic solvent washing step and then gradually eluted to an analytical column for separation. To compensate for matrix effects, quantitation was performed using standard additions. Confirmation of the presence of the detected compounds was done using a second selective reaction monitoring transition. Method intra-day precision was less than 9% and inter-day precision %R.S.D. varied between 2.5 and 23%. Limits of detection for the selected anti-infective compounds ranged from 13 to 61 ng L−1. All the target anti-infectives were found in the city of Montréal WWTP effluent in concentrations ranging from 71 to 289 ng L−1. This automated method eases the rapid quantitation of those trace contaminants using small sample volumes. 相似文献
84.
85.
Andr B. Charette Alexandre Gagnon Francine Blanger‐Garipy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):538-540
The title compound, [Mg2Br2(C14H14NO)2(C4H8O)4]·2C7H8, has been crystallized as a C2‐symmetric dimer and the Mg atom has a distorted octahedral geometry. The metal is chelated by the N atom of the ketiminate and the O atom of the ether moiety, giving a rigid structure. 相似文献
86.
Yannic J. Gagnon Justin C. Burton Connie B. Roth 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):244-257
Employing a quartz crystal microbalance (QCM) as a MHz-viscoelastic sensor requires extracting information from higher harmonics beyond the Sauerbrey limit, which can be problematic for rubbery polymer films that are highly dissipative because of the onset of anharmonic side bands and film resonance. Data analysis for QCM can frequently obscure the underlying physics or involve approximations that tend to break down at higher harmonics. In this study, modern computational tools are leveraged to solve a continuum physics model for the QCM's acoustic shear wave propagation through a polymer film with zero approximations, retaining the physical intuition of how the experimental signal connects to the shear modulus of the material. The resulting set of three coupled equations are solved numerically to fit experimental data for the resonance frequency Δfn and dissipation ΔΓn shifts as a function of harmonic number n, over an extended harmonic range approaching film resonance. This allows the frequency-dependent modulus of polymer films at MHz frequencies, modeled as linear on a log–log scale, to be determined for rubbery polybutadiene (PB) and polydimethylsiloxane (PDMS) films, showing excellent agreement with time–temperature shifted rheometry data from the literature. 相似文献
87.
[reaction: see text] Irradiation of 2- and 4-xanthone acetic acid in aqueous buffer (pH 7.4) leads to efficient (Phi = 0.67 and 0.64, respectively) photodecarboxylation to give the corresponding methyl products, consistent with an intermediate benzylic carbanion. Fluorescence and laser flash photolysis (LFP) studies suggest singlet state reactivity, which is unusual for aromatic ketones. 3-Xanthone acetic acid is photoinert under the same conditions. The results suggest that the reactive xanthone acetic acids are promising precursors for carbanion-mediated photocages. 相似文献
88.
Elliott Wright Heather Daurie Graham A. Gagnon 《International journal of environmental analytical chemistry》2013,93(13):1302-1316
The goal of this research was to develop a robust method for taste and odour compounds that can be implemented by laboratories with mass spectrometers lacking chemical ionisation capabilities or specialised sample introduction hardware that are commonly used for taste and odour methods. Development, optimisation, and validation of a solid-phase extraction method using liquid injection and gas chromatography – tandem mass spectrometry detection with electron impact ionisation are described. Camphor was used as an internal standard, and through method development and robustness testing it was shown to extract similarly to other taste and odour compounds, making it a cost-effective alternative to deuterated analogs. The instrumental parameters and extraction procedure were fully optimised prior to assessing the method’s linearity, precision, and accuracy. Using a 2000-fold enrichment factor, method recoveries for priority compounds geosmin (GSM) and 2-methylisoborneol (2-MIB) were >90%. Excellent linearity was obtained from the reportable detection limits up to 200 ng L?1 and precision %relative standard deviations were 8.5% and 10.9% for GSM and 2-MIB, respectively. Detection limits of 0.9 and 5.5 ng L?1 for GSM and 2-MIB respectively were deemed fit-for-purpose in comparison to their odour thresholds. Validation data were also obtained for other commonly analysed taste and odour compounds, including 2,4,6-trichloroanisole, 2-isopropyl-3-methoxypyrazine, and 2-isobutyl-3-methoxypyrazine. The validated method was used to screen surface waters in Nova Scotia, Canada for presence of taste and odour compounds, highlighting the presence of GSM on the east coast of Canada. 相似文献
89.
[reaction: see text] Homochiral alpha-amino acids, heterocycles, and carbocycles are efficiently constructed via a short sequence of reactions starting from the chiral auxiliary p-menthane-3-carboxaldehyde. The key feature of the sequence is a highly selective tandem Mitsunobu/3,3-sigmatropic rearrangement of hydrazoic acid that procures enantiomerically enriched allylic azides. The sequence is either terminated by oxidative cleavage to provide amino acids or by ring-closing metathesis to provide heterocycles or carbocycles bearing nitrogen. 相似文献
90.
André Lajeunesse Christian Gagnon 《International journal of environmental analytical chemistry》2013,93(8):565-578
A gas chromatography–tandem mass spectrometry (GC–MS/MS) method has been developed for the determination of selected pharmaceutical residues (carbamazepine, salicylic acid, clofibric acid, ibuprofen, 2-hydroxy-ibuprofen, fenoprofen, naproxen, ketoprofen, diclofenac, and triclosan) in sewage influent and roughly primary-treated effluent. The method involved solid-phase extraction (SPE) with polymeric sorbents, and two SPE cartridges were compared for the extraction and elution of the targeted compounds in complex matrices. A successful chemical derivatization of carbamazepine and acidic compounds using N,O-bis(trimethylsilyl) trifluoroacetamide +10% trimethylchlorosilane is also described. The quantification limits of the analytical procedure ranged from 30 to 60?ng?L?1 for 500?mL of wastewater. The best recovery rates (72–102%) in spiked effluent samples were obtained with Phenomenex Strata-X? cartridges. Detection limits (S/N?=?3) were estimated at between 1 and 18?ng?L?1. The reported GC–MS/MS method significantly reduces the strong matrix effects encountered with more expensive LC-MS/MS techniques. Application of the developed method showed that most selected analytes were detected at concentrations ranging from low µg?L?1 to trace level ng?L?1 in Montreal's wastewater treatment plant effluent and influent, as well as in the receiving waters at more than 8?km downstream of the effluent outfall. The rugged alternative analytical method is suitable for the simultaneous analysis of carbamazepine and pharmaceutical acidic residues in wastewater samples from influents and effluents that have undergone rough primary treatment. 相似文献