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991.
A simple procedure for the large scale preparations of regio-specifically 2-alkylated-3-deuteriated-1-aminocyclopropane-1-carboxylic acids from 1 -deuterio-1,2-dibromoalkanes is described. 相似文献
992.
Xiaoyan Xia Bernard S. Crimmins Philip K. Hopke James J. Pagano Michael S. Milligan Thomas M. Holsen 《Analytical and bioanalytical chemistry》2009,395(2):457-463
Toxaphene is considered to be a problematic organochlorine pollutant because of its bioaccumulation potential and persistence
in aquatic environments. In this study, whole lake trout and walleye composites were used to evaluate two analytical techniques
for total toxaphene and selected congener analysis. The efficacy of using gas chromatography electron ionization tandem mass
spectrometry (GC-EI/MS/MS) and electron capture negative ionization mass spectrometry (GC-ECNI-MS) were compared. Although
the sensitivity using GC-ECNI-MS was approximately five times greater than GC-EI/MS/MS, the latter provided more consistent
inter-Parlar relative response factors (RRF). When using technical calibration mixtures, these results suggest a more accurate
total toxaphene measurement was obtained using the GC-EI/MS/MS method. Total toxaphene concentrations in lake trout composites
from both methods were highly correlated (R
2 = 0.985) with the MS/MS concentrations approximately half of those determined by ECNI, suggesting systematic high bias in
toxaphene concentrations when measured using GC-ECNI. 相似文献
993.
Reactions of 5-phenylthieno[3,2-b]pyran-7-one, 2-phenylbenzo[b]-thieno[3,2-b]pyran-4-one and the corresponding thiones with sodium ethylate, guanidines, hydrazines and amines are described and compared to those observed with benzopyranones. 相似文献
994.
Quantum mechanical calculations using the PCILO method have been performed on the tripeptide model CH3CO-X-Y-NHCH3. Competition between C5, C7, C10 rings and open structures has been investigated through mapping of the whole {φ, Ψ} conformational space and energy minimization.
From these results, it appears that the C10 ring simulating the folding named U-turn, involving a hydrogen bond between the i...i + 3 residues, is the most probable structure although not the most stable in energy. The results are used for predicting
the frequency of U-turns in proteins, α-chymotrypsin is given as an example. 相似文献
995.
Bernard Gordon Robert J. Kumpf Paul C. Painter 《Journal of polymer science. Part A, Polymer chemistry》1988,26(7):1689-1696
m-phenyl benzoate end-capped pre-polybenzoxazole oligomer and a 3,4-diaminobenzene endcapped pre-polybenzimidazole were synthesized. These functionalized oligomers were then condensed to give a polybenzoxazole-polybenzimidazole segmented block copolymer. The functionalized oligomers were characterized by proton NMR, diffuse reflectance FTIR, and thermal gravimetric analysis. The final block copolymer was characterized by diffuse reflectance FTIR and thermal gravimetric analysis. 相似文献
996.
The paper deals with a diagnostic method that allows to detect engineknock. The developed algorithm differentiates three kinds of engine cycles:absence of knock, increasing knock and heavy knock. The decision is takenfrom a block vibration signal. The diagnostic method is based on patternrecognition. Three models of different data shapes provided from theaccelerometer are elaborated. This is done using a time-scale analysis toolcalled a wavelet network. It allows to extract relevant features from thesignal. The aim of the method is then to partition the feature space intoclasses representing the knock states. Experimental results are reported. 相似文献
997.
By condensation of the chlorides of the three 9-oxo-fluorene-2-, -3-, and -4-carboxylic acids with 4-bromo-1,2-xylene on one side, and of the chlorides of o-bromobenzoic acid, 2-bromo-4-methyl-benzoic acid and 2-bromo-4,5-dimethyl-benzoic acid with fluorene, 2-methylfluorene and 3-methylfluorene on the other side, followed by direct or indirect cyclisation and by final reduction, several new methyl derivatives of the indenofluorenes I, II and IV are synthesized. 相似文献
998.
Standard enthalpies of formation of alkaline earth salts M(NH2RCOO) of several amino acids are determined by calorimetry.The thermochemical radii, the standard enthalpies of formation and the protonic affinities of ions (NH2RCOO?) in the gaseous state are calculated.In the case of unbranched carbon chain amino acids, the thermochemical radii are an approximately linear function of protonic affinities of their conjugate bases. 相似文献
999.
Bernard Béguin Edouard Garbowski Stefan Dietrich Peter Michel Primet 《Reaction Kinetics and Catalysis Letters》1996,59(2):253-262
Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl2O4>CuO–Pd/MgAl2O4>Pd–CuO/MgAl2O4>CuO/MgAl2O4. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium. 相似文献
1000.
Mark L. Spell Kristina Deveaux Caitlin G. Bresnahan Bradley L. Bernard William Sheffield Revati Kumar Prof. Dr. Justin R. Ragains 《Angewandte Chemie (International ed. in English)》2016,55(22):6515-6519
Visible‐light irradiation of 4‐p‐methoxyphenyl‐3‐butenylthioglucoside donors in the presence of Umemoto's reagent and alcohol acceptors serves as a mild approach to O‐glycosylation. Visible‐light photocatalysts are not required for activation, and alkyl‐ and arylthioglycosides not bearing the p‐methoxystyrene are inert to these conditions. Experimental and computational evidence for an intervening electron donor–acceptor complex, which is necessary for reactivity, is provided. Yields with primary, secondary, and tertiary alcohol acceptors range from moderate to high. Complete β‐selectivity can be attained through neighboring‐group participation. 相似文献