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91.
The biosynthesis of adenosylcobalamin (vitamin B12) 总被引:9,自引:0,他引:9
92.
Cattaneo H Laurila T Hernberg R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(14):1093-3275
A vertical-cavity surface-emitting laser (VCSEL) was used to study the absorption spectrum of water vapor in the 940nm region. Measurements were performed in ambient air at room temperature and in a hydrogen-oxygen flame over the temperature range of 1500-1800K. Several rotational absorption lines within the 2v1 + v3 vibrational band were measured. The absorption spectra were well resolved, which demonstrates the feasibility of VCSEL-based spectroscopic measurements of water vapor at room and high-temperature in this spectral region. The results were in good agreement with the values obtained from the HITRAN-96 database. 相似文献
93.
The synthesis of a new tailor-made derivatization agent for the selective determination of (di)isocyanates is presented. Starting from cyanuric chloride, the reagent 4-methoxy-6-(4-methoxy-1-naphthyl)-1,3,5-triazine-2-(1-piperazine)(MMNTP) is synthesized by subsequent substitution of the three chlorine atoms. This new derivatization agent and the five urea derivatives of phenylisocyanate (PI), hexamethylene-diisocyanate (HDI), toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI) and methylenebisphenyl-4,4-diisocyanate (MDI) show good spectroscopic properties with small compound-to-compound variabilities (RSD([epsilon])= 5.3 %, RSD(relative fluorescence)= 9.4 %). Therefore, using UV detection, a single calibration is needed for the quantification of all diisocyanates and isocyanates respectively. For separation and analysis a HPLC method with a RP column and a binary gradient is presented. All derivatives are separated and show low limits of detection. In addition to the good spectroscopic properties and low limits of detection, good reactivity for the derivatizations at room temperature is observed. The aromatic diisocyanates can be measured immediately whereas aliphatic diisocyanates need 2 h incubation. These advantages make MMNTP a powerful and versatile derivatization agent for (di)isocyanates which is demonstrated by a real sample with solid phase sampling, where the reagent is coated on a sorbent. 相似文献
94.
Integrated platform for detection of DNA sequence variants using capillary array electrophoresis 总被引:8,自引:0,他引:8
We have developed a highly versatile platform that performs temperature gradient capillary electrophoresis (TGCE) for mutation/single-nucleotide polymorphism (SNP) detection, sequencing and mutation/SNP genotyping for identification of sequence variants on an automated 24-, 96- or 192-capillary array instrument. In the first mode, multiple DNA samples consisting of homoduplexes and heteroduplexes are separated by CE, during which a temperature gradient is applied that covers all possible temperatures of 50% melting equilibrium (Tms) for the samples. The differences in Tms result in separation of homoduplexes from heteroduplexes, thereby identifying the presence of DNA variants. The sequencing mode is then used to determine the exact location of the mutation/SNPs in the DNA variants. The first two modes allow the rapid identification of variants from the screening of a large number of samples. Only the variants need to be sequenced. The third mode utilizes multiplexed single-base extensions (SBEs) to survey mutations and SNPs at the known sites of DNA sequence. The TGCE approach combined with sequencing and SBE is fast and cost-effective for high-throughput mutation/SNP detection. 相似文献
95.
A liquid chromatography (LC) method is described for the determination of oxytetracycline (OTC) in farmed Atlantic salmon muscle tissue. The method involves homogenization of salmon tissue, extraction of OTC into Mcllvaine-EDTA buffer, acid precipitation of proteins, cleanup through tandem solid-phase extraction cartridges (Strata-X and aminopropyl), elution with mobile phase containing slightly alkaline buffer and Mg2+, and LC separation with metal-chelate induced fluorescence detection. Salmon tissue was fortified with 0.10, 0.25, 0.50, 0.75, and 1.0 microg/g (ppm) oxytetracycline. Average absolute recoveries were 84, 76, 70, 76, and 85%, respectively, with relative standard deviation (RSD) values all less than 9%. The interassay average recovery was 78%, with a 4.2% RSD. Determination was based on a standard graph using peak areas with standard solutions equivalent to 0.0625, 0.125, 0.25, 0.50, and 1.0 ppm in tissue. A set of 5 matrix controls (unfortified salmon tissue) were also analyzed, in which no OTC was detected. The lowest standard was used as the limit of quantitation. 相似文献
96.
Lauterwasser F Nieger M Mansikkamäki H Nättinen K Bräse S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(15):4509-4525
A set of 20 novel [2.2]paracyclophane ketimines with planar and central chirality has been synthesized from enantiomerically pure and racemic 5-acyl-4-hydroxy[2.2]paracyclophane and alpha-branched chiral amines. Their X-ray structures were determined to elucidate the three-dimensional structures and the absolute configuration. The ketimines were used as catalysts in the asymmetric 1,2-addition reactions of diethylzinc with substituted benzaldehydes to furnish chiral alcohols in up to 95 % ee. 相似文献
97.
Joseph Dommen Martin Forster Heidi Ruprecht Alfred Bauder Hans-Heinrich Günthard 《Helvetica chimica acta》1982,65(2):504-520
Investigation of the formation of complex reaction products in the gas-phase system O3/NO2/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified; N2O5, HNO3, HNO4, CH3NO2, CH3ONO, CH3COONO2 and CH3COO2NO2 (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N2O5, HNO3. CH3COONO, CH3COONO2 required for reference purposes are presented. It is shown that PAN-formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NOx-containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies. 相似文献
98.
Jerry P. Jasinski Heidi E. Exel Alfonso Castiñeiras Elena Bermejo Heloisa Beraldo Douglas X. West 《Journal of chemical crystallography》2003,33(1):11-18
The crystal and molecular structure of copper(II) complexes of benzil bis(3-piperidylthiosemicarbazone), [Cu(Bnzpip)] and 1-phenylpropane-1,2-dione bis(3-piperidylthiosemicarbazone), [Cu(Pmpip)] have been determined. [Cu(Bnzpip)] is monoclinic, space group P21/n with a = 13.9375(10) Å, b = 11.6621(4) Å, c = 16.4710(10) Å, = 100.667(2)°, and V = 2630.9(3) Å3 with Z = 4, for d
calc = 1.399 g/cm3. [Cu(Pmpip)] is also monoclinic, space group P21/n with a = 11.292(6) Å, b = 10.219(5) Å, c = 20.292(6) Å, = 101.50(3)°, and V = 2295(2) Å3 with Z = 4, for d
calc = 1.525 g/cm3. Both complexes involve N2S2 coordination, are relatively planar except for the phenyl rings and have similar bond distances and angles to copper(II) complexes of other 3-piperidylthiosemicarbazones. 相似文献
99.
Gel points in random polymerizations of the general type ΣiRA + ΣjRB in which A-groups react with A- and B-groups, and B-groups react only with A-groups are considered. (The symbols Σi and Σi signify that the A- and B-bearing reactants RA and RB can be mixtures of monomers of different functionalities, denoted generally as fai and fbj.) The usual case of A-groups reacting only with B-groups is a special case of the present theory. The effects of chemical kinetics, the competitive reaction of A- and B-groups, are separated from the generalized statistical condition for gelation. The former are used to define reaction curves and the latter, gelation curves. Both types of curve are represented as pa as a function of pb. For a given polymerization, gelation occurs when the reaction curve and the gelation curve intersect. When A-groups react only with B-groups, the gel points are those for the usual type of ΣiRA + ΣjRB polymerization, and, in the limit of A-groups only reacting with A-groups, the gel points are those for ΣiRA self polymerizations. 相似文献
100.