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931.
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933.
934.
Wald RM 《Physical review D: Particles and fields》1993,48(8):R3427-R3431
935.
Qualitative screening procedures have been developed for the rapid detection and identification of the hydrolysis products of chemical warfare agents in aqueous samples and extracts, using liquid chromatography-mass spectrometry with positive and negative atmospheric pressure chemical ionisation (APCI). Previously reported screening procedures, which used positive APCI or electrospray ionisation (ESI), were modified by using LC conditions that allowed acquisition of positive and negative ion mass spectra. APCI was generally found to be more robust than ESI, probably due to variable adduct ion formation with ESI, depending on the condition of the sample and the system. Negative APCI provided selective detection of acidic analytes and allowed facile differentiation of alkyl alkylphosphonic acids from isomeric dialkyl alkylphosphonates. The combination of positive and negative APCI, using a C18 column and water-methanol mobile phase modified with ammonium formate, provides a rapid screening procedure for chemical warfare agent degradation products, with limits of detectability in the range 10-100 ng/ml. In the case of proficiency test samples, where analyte concentrations are in the range 1-10 ppm, introduction of the sample by infusion may provide an even faster preliminary screening procedure. 相似文献
936.
Davis CJ Lewis PT Billodeaux DR Fronczek FR Escobedo JO Strongin RM 《Organic letters》2001,3(16):2443-2445
[structure: see text] An X-ray crystallographic study of unique hydrogen-bonded supramolecular solid-state networks comprised of a tetraarylboronic acid resorcinarene is described. When 1 is recrystallized from 9:1 MeOH:EtOH, partial esterification takes place to give compound 2, the corresponding half methyl ester, which forms an infinite two-dimensional array. Each molecule participates in 12 hydrogen bonds with other macrocycles. These hydrogen bonds are both B-OH- - - OH (phenolic) and OH (phenolic)- - -OH (phenolic). 相似文献
937.
938.
Hybrid peptide-polyketides are a class of medically and biologically important natural products characterized by stereochemical and functional diversity. In their biosynthesis, hybrids are often macrocyclized to achieve rigid structures that populate bioactive conformations. We herein present a chemoenzymatic strategy to access the stereochemical and functional diversity found in macrocyclic hybrid natural products in a manner amenable to efficient library synthesis. Our method makes use of small building blocks in the form of Fmoc-protected epsilon-amino acids containing embedded polyketide functionality. The building block approach allows for combinatorial synthesis of linear molecules that can be activated as soluble thioesters or tethered to a solid-phase resin. We demonstrate that these linear molecules are substrates for macrocyclization by a tolerant catalyst, TycC TE, derived from a nonribosomal peptide synthetase. The method should allow for access to diverse structures with hybrid peptide-polyketide character that can be screened for improved or novel activities. 相似文献
939.
Observation of a neutrino burst in coincidence with supernova 1987A in the Large Magellanic Cloud 总被引:1,自引:0,他引:1
Bionta RM Blewitt G Bratton CB Casper D Ciocio A Claus R Cortez B Crouch M Dye ST Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG LoSecco JM Matthews J Miller R Mudan MS Park HS Price LR Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak LR Svoboda R Thornton G van der Velde JC Wuest C 《Physical review letters》1987,58(14):1494-1496
940.