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91.
Huybrechts T Dewulf J Van Craeynest K Van Langenhove H 《Journal of chromatography. A》2001,922(1-2):207-218
A recently developed method for the sampling and analysis of volatile organic compounds in air has been evaluated. The system is based on the enrichment of analytes in tetraethylene glycol dimethyl ether or tetraglyme, a water-soluble organic liquid. The subsequent analysis consists of dispersion of a sample aliquot in water followed by purge-and-trap and gas chromatographic separation. Physico-chemical data were investigated for 10 volatile organic compounds, providing information on the possibilities and limitations of the tetraglyme method. The target analytes included chlorinated alkanes and alkenes, and monocyclic aromatic hydrocarbons. Air/tetraglyme partition coefficients Kat were determined over an environmental relevant temperature range of 2-25 degrees C to evaluate sorption efficiencies and estimate breakthrough volumes at the sampling stage. At 2 degrees C breakthrough volumes (allowing 5% of breakthrough) ranged from 5.8 (1,1-dichloroethane) to 312 l (1,1,2-trichloroethane) for 20 ml of tetraglyme. With regard to the desorption stage, the effect of tetraglyme on the air/water partition of organic compounds was investigated through the measurement of air/tetraglyme-water partition coefficients Kat-w for 2-31% (v/v) tetraglyme in water. Finally a clean-up procedure for tetraglyme was evaluated. Analysis of a blank tetraglyme-water (17:83, v:v) mixture by gas chromatography-flame ionization detection/mass spectrometry showed minor background signals. None of the target compounds were detected. 相似文献
92.
[reaction: see text] Since peroxidase-catalyzed dityrosine formation is inefficient for peptides, we have developed alternative conditions for intermolecular dityrosine formation using the Miyaura-Suzuki reaction. A one-pot reaction is effective for cross-linking short peptides, but longer peptides inhibit the Suzuki step, mandating a traditional two-step procedure using potassium acetate for the Miyaura reaction and potassium carbonate for the Suzuki coupling. These palladium-based methods are complementary to the well-established peroxidase-catalyzed oxidative phenolic coupling of full-length proteins. 相似文献
93.
94.
When a two-phase column consisting of paraffin oil and silicon oil is placed in an otherwise air-filled, horizontal glass capillary, the column starts moving spontaneously. Silicon oil displaces paraffin oil, which in its turn displaces air at atmospheric conditions; a stable film of silicon oil is left at the receding silicon oil/air meniscus. The driving force for the motion is the difference in capillary pressure at the free interfaces. However, the column moves considerably more slowly than predicted by the driving forces; it appears that the forces resisting the motion at the moving liquid/liquid/solid line are much larger than one would expect on the basis of the interfacial tension and the viscosities of the two phase system. Some considerations are made on the relationship of the theory of Fowkes to our system. Also, a method for measuring low interfacial tensions between immiscible liquids is proposed. 相似文献
95.
R. Meij D.J. Stufkens K. Vrieze W. Van Gerresheim C.H. Stam 《Journal of organometallic chemistry》1979,164(3):353-370
Each of the compounds [MCl(Pr3)2(ArylNSO)] (M = RhI, IrI; R = i-Pr, Cy: Aryl = C6H5, 4-MeC6H4, 4-ClC6H4, 2,4,6-Me3C6H2 appears to exist as two isomers both in the solid state and in solution. The molecular and single crystal structure of one of the isomers of [RhCl(P-i-Pr)3)2(4-Me6H4NSO)] shows that the N-sulfinylaniline ligand is in the cis-configuration and coordinated to the rhodium atom via the sulfur-atom. The ligand lies in a plane which includes the rhodium atom and is in agreement with the Rh-S distance of 2.10 Å. IR results of the compounds (solid and solutions), 21P NMR data and 15N NMR of a 15N labelled compound, which yielded a 103Rh15N coupling constant of 15.5 Hz, show that in the second isomer the N-sulfinylaniline ligand is probably bonded to the metal atom via the π-NS bond.The ratio of the metal-π-NS bonded isomer and the metal-S bonded isomer decreases in the order Aryl = 4-ClC6H4 > C6H5 > 4-MeC6H4; R = i-Pr > Cy and M = Rh > Ir. The interconversion of the two isomers is intramolecular and becomes observable on the 31P NMR time scale at about 40° C for M = Rh.In the case of [Ir(P-i-Pr3)2(4-MeC6H4NSO)], cyclometallation of the sul- finylaniline is observed via the ortho-carbon atom, whereas cyclometallation via P-i-Pr3 is observed when the ortho-positions are blocked by methyl groups, e.g. when L = 2,4,6-Me3C6H2NSO. 相似文献
96.
97.
Tran Quang Minh Léon Christiaens Pierre Grandclaudon Alain Lablache-Combier 《Tetrahedron》1977,33(17):2225-2229
Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 ) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans. 相似文献
98.
Li YS Xiao Y Wright PB Tran T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1675-1681
3-(Triethoxysilyl)propionitrile (TESPN) sol-gel has been prepared under different conditions. It was employed for coating the surfaces of quartz and aluminum. Infrared (IR) and Raman spectra of TESPN and TESPN sol-gels have been recorded in the study of the sol-gel process. Transmission and reflection absorption IR (RAIR) spectra of TESPN sol-gel coated quartz and aluminum have also been collected for better understanding the film formation on the substrate surfaces. Spectra collected at different temperatures indicated that the silane film on quartz decomposes at 700 degrees C. Results from thermal gravimetric analysis (TGA) supported this result. Based on the group frequencies and the spectral behavior in different states, some vibrational modes were assigned to the observed bands. The anticorrosion behavior of the sol-gel coated aluminum in comparison with the uncoated metal was evaluated by measuring the potentiodynamic polarization and electrochemical impedance spectra (EIS). 相似文献
99.
The diagnostic value of an interpretation system for vibrational spectra has been investigated in relation to the number of structural units the system can cope with. For five structural units the correlated wavenumber intervals are derived from three infrared and three Raman files by the CRISE program. The interpretative value of each interval in relation to the intensity threshold is discussed. For most intervals a decrease is found on increasing the number of structural units. 相似文献
100.