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71.
The generation of subnanosecond pulses by the combined effects of stimulated Brillouin scattering (SBS) and laser-induced breakdown has been investigated by obtaining simultaneous streak photographs of the spark, the backscattered and the transmitted pulses. The results demonstrate that the output from an excimer pumped dye laser can yield subnanosecond pulses with a duration of 20ps. The pulse shortening effect results from the nonlinear reflection properties of the Brillouin mirror and the strong absorption of visible radiation by the laser-breakdown plasma. 相似文献
72.
A new assay method has been developed for the quantitation of promethazine (PMZ) with a sensitivity and reproducibility as good as any previously reported method. This method is also capable of quantitatively determining three metabolites of PMZ (monodemethylated, sulphoxidated, and monodemethylated sulphoxidated PMZ), which has not been previously described. The method uses high-performance liquid chromatography with amperometric and UV detection simultaneously and requires only one extraction step from serum with chloroform. The method uses trifluoperazine as the internal standard. The limit of detection level for PMZ is 1.0 ng/ml when a 0.2-mL specimen of plasma is assayed. A validation study is also conducted for evaluating the recovery, precision, linearity of response, sensitivity, and selectivity of the method. 相似文献
73.
Vincent J. Smith Diana Bogdan Mircea Bogdan Susan A. Bourne Sorin I. Fărcaş 《Supramolecular chemistry》2013,25(3):172-177
An inclusion complex formation between α- and β-cyclodextrin and four phenylurea analogues, namely metobromuron, monolinuron, monuron and fenuron, is reported. Complex formation was established using solution 1H NMR spectroscopy. Complex stoichiometries were determined by the method of continuous variation using the chemically induced shifts of both the host and guest protons. An analysis of the spectroscopic data revealed the stoichiometry as 1:1 in all cases while a further analysis of the same data yielded values for the association constant K ranging from 208 to 2749 M? 1. From the observed chemical shifts it was deduced that in all cases, only the guest aromatic ring enters the host cavities, the substituted urea moiety protruding from the secondary rim in the case of α-cyclodextrin, but from the primary rim in the case of β-cyclodextrin. 相似文献
74.
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
75.
Susan A Bourne Xavier Y Mbianda Agnes M Modro Tom A Modro Luigi R Nassimbeni Petrus H Vanrooyen 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):693-696
A series of non-cyclic, cyclic and bicyclic phosphotriamidates has been sythesized and their structure, NMR spectroscopic characteristics and their chemical reactivity are discussed. 相似文献
76.
77.
Hall JF Han X Poliakoff M Bourne RA George MW 《Chemical communications (Cambridge, England)》2012,48(25):3073-3075
Using a continuous fluorous biphasic separation, a photo-oxidation catalyst can be recycled, with increased productivity and a ×20 fold decrease in the amount of catalyst required. 相似文献
78.
Dyanne L. Cruickshank Mircea Bogdan Sorin I. Fărcas Susan A. Bourne 《Supramolecular chemistry》2013,25(6):406-414
The formation of inclusion complexes between the native cyclodextrins (CDs) and the urea herbicide cycluron has been investigated both in solution and in the solid state. Single-crystal X-ray structures of both the uncomplexed guest and the β-CD·cycluron complex were determined while powder X-ray diffraction was used to confirm complexation between γ-CD and cycluron in the solid state. Solution-state complexation between the herbicide and α-, β- and γ-CD was established using 1H NMR spectroscopy and isothermal titration calorimetry (ITC). From the 1H NMR spectroscopic studies 1:1 complex stoichiometry was indicated in all cases and association constant values (K) were determined as 228, 3254 and 155 for the complexes α-CD·cycluron, β-CD·cycluron and γ-CD·cycluron, respectively. Assigning a 1:1 host–guest ratio, the ITC technique produced K values of the same order as those determined using the spectroscopic method. The thermodynamic parameters ΔH, ΔS and ΔG obtained using ITC provide insights into the driving forces involved during complex formation. 相似文献
79.
Adam D. Clayton Edward O. Pyzer-Knapp Mark Purdie Martin F. Jones Alexandre Barthelme John Pavey Nikil Kapur Thomas W. Chamberlain A. John Blacker Richard A. Bourne 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202214511
The optimization of multistep chemical syntheses is critical for the rapid development of new pharmaceuticals. However, concatenating individually optimized reactions can lead to inefficient multistep syntheses, owing to chemical interdependencies between the steps. Herein, we develop an automated continuous flow platform for the simultaneous optimization of telescoped reactions. Our approach is applied to a Heck cyclization-deprotection reaction sequence, used in the synthesis of a precursor for 1-methyltetrahydroisoquinoline C5 functionalization. A simple method for multipoint sampling with a single online HPLC instrument was designed, enabling accurate quantification of each reaction, and an in-depth understanding of the reaction pathways. Notably, integration of Bayesian optimization techniques identified an 81 % overall yield in just 14 h, and revealed a favorable competing pathway for formation of the desired product. 相似文献
80.