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471.
Three long and 1 short reversed-phase C18 columns were compared for separation of deoxynivalenol (DON) in extracts of naturally contaminated wheat samples using liquid chromatography with ultraviolet detection and liquid chromatography/mass spectrometry (LC/MS). Among the 3 long columns used, a Symmetry C18 column with an isocratic solvent mixture of water-acetonitrile-methanol (90 + 5 + 5, v/v/v) gave the best separation for DON without interferences from other compounds in the wheat extracts. The Symmetry short (75 mm) column was comparable with the long column (250 mm) in resolving DON but significantly reduced retention time (i.e., 5.8 versus 16.3 min). Increasing the column temperature from 25 to 45 degrees C resulted in a further reduction in retention time. Identity of DON in the wheat extracts and standard solutions was confirmed by LC/MS in the positive ion mode, whereby DON appeared with an (M+1)+ ion at a mass-to-charge ratio of 297 plus fragment ions associated with loss of water and/or a 30 atomic mass unit (amu) CH2O fragment. The Symmetry short column was also capable of separating a mixture of the mycotoxins DON, 15-acetyl-DON, nivalenol, and zearalenone by use of a combination of an isocratic and gradient solvent system. The overall method showed high precision, exhibiting a relative standard deviation of 4.8%, limit of detection of 50 ng/g, and limit of quantitation of 165 ng/g. It was significantly correlated with enzyme-linked immunosorbent assay analysis, indicating its appropriateness for safety and quality assurance of wheat and related grains. 相似文献
472.
Transition metal complexes bonded to silica via silanes with β-diketonate groups can be used as packings for complexation gas chromatography or as immobilized homogenous metal complex
catalysts. On basis of elemental analysis and the determination of surface area, possible structures of the complexes formed
on the silica surface have been proposed. The possibility of using the immobilized complexes as catalysts has been indicated.
Especially nickel complexes were taken into consideration. These immobilized complexes were used previously as packings for
complexation gas chromatography. 相似文献
473.
Galetskiy D Susnea I Reiser V Adamska I Przybylski M 《Journal of the American Society for Mass Spectrometry》2008,19(7):1004-1013
Structure and dynamics of membrane-bound light-harvesting pigment-protein complexes (LHCs), which collect and transmit light energy for photosynthesis and thereby play an essential role in the regulation of photosynthesis and photoprotection, were identified and characterized using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). LHCs from photosystem II (LHCII) were isolated from the thylakoid membrane of Arabidopsis thaliana leaves after light stress treatment using sucrose density gradient centrifugation, and separated by gel-filtration into LHCII subcomplexes. Using reversed-phase high-performance liquid chromatography and two-dimensional (2D) gel electrophoresis, the LHCII proteins, Lhcb1-6 and fibrillins, were efficiently separated and identified by FTICR-MS. Some of the LHCII subcomplexes were shown to migrate from photosystem II to photosystem I as a result of short-term adaptation to changes in light intensity. In the mobile LHCII subcomplexes, decreased levels of fibrillins and a modified composition of LHCII protein isoforms were identified compared to the tightly bound LHCII subcomplexes. In addition, FTICR-MS analysis revealed several oxidative modifications of LHCII proteins. A number of protein spots in 2D gels were found to contain a mixture of proteins, illustrating the feasibility of high-resolution mass spectrometry to identify proteins that remain unseparated in 2D gels even upon extended pH gradients. 相似文献
474.
475.
Langer J Dabkowska I Zhang Y Illenberger E 《Physical chemistry chemical physics : PCCP》2008,10(11):1523-1531
Electron attachment to pentafluorobenzonitrile (C(6)F(5)CN) and pentafluoronitrobenzene (C(6)F(5)NO(2)) is studied in the energy range 0-16 eV by means of a crossed electron-molecular beam experiment with mass spectrometric detection of the anions. We find that pentafluoronitrobenzene exclusively generates fragment anions via dissociative electron attachment (DEA), while pentafluorobenzonitrile forms a long lived parent anion within a narrow energy range close to 0 eV and additionally undergoes DEA at higher energies. This is in contrast to the behaviour of the non-fluorinated analogues as in nitrobenzene the non-decomposed anion is formed while in benzonitrile only DEA is observed. The associated reactions involve simple bond cleavages but also complex unimolecular decompositions associated with structural and electronic rearrangement also resulting in the deterioration of the cyclic structure. 相似文献
476.
Haranczyk M Lupica G Dabkowska I Gutowski M 《The journal of physical chemistry. B》2008,112(7):2198-2206
Changes of electrostatic potential around the DNA molecule resulting from chemical modifications of nucleotides may play a role in enzymatic recognition of damaged sites. Effects of chemical modifications of nucleotides on the structure of DNA have been characterized through electronic structure computations. Quantum mechanical structural optimizations of fragments of five pairs of nucleotides with thymine or thymine glycol were performed at the density functional level of theory with a B3LYP exchange-correlation functional and 6-31G(d,p) basis sets. The electrostatic potential (EP) around DNA fragments was projected on a cylindrical surface around the double helix. The 2D maps of EP of intact and damaged DNA fragments were compared using image analysis methods to identify and measure modifications of the EP that result from the occurrence of thymine glycol. It was found that distortions of phosphate groups and displacements of the accompanying countercations by up to approximately 0.5 angstroms along the axis of DNA are clearly reflected in the EP maps. Modifications of the EP in the major groove of DNA near the damaged site are also reported. 相似文献
477.
Figueira-Duarte TM Lloveras V Vidal-Gancedo J Gégout A Delavaux-Nicot B Welter R Veciana J Rovira C Nierengarten JF 《Chemical communications (Cambridge, England)》2007,(42):4345-4347
The strength of the electronic interactions between the two redox moieties in fullerene-substituted mixed-valence bis(ferrocenylethynyl)ethene derivatives is modulated by the through-space intramolecular electronic interactions of C(60) with the bridging conjugated system. 相似文献
478.
Nastasi F Puntoriero F Campagna S Schergna S Maggini M Cardinali F Delavaux-Nicot B Nierengarten JF 《Chemical communications (Cambridge, England)》2007,(34):3556-3558
The first system containing a luminescent Ir(m) cyclometallated species and a functionalized C60 unit has been prepared; triplet-triplet energy transfer from the Ir-based MLCT state to the C60 triplet state occurs, leading to phosphorescence (lifetime, 4.8 ms) of the derivatized-C60 at 77 K. 相似文献
479.
480.
Andrzej Wawer Iwona Wawer Boguslawa Piekarska-Bartoszewicz Andrzej Temeriusz 《光谱学快报》2013,46(6):1079-1090
Abstract The acidic properties of ureido NH protons in two new derivatives of methyl 3,4,6-triacetyl-2-deoxy-β-D-glucopyranoside and i-butylamine (1) and L-leucine (2) were studied by 1H NMR. Stronger influence of polar aprotic solvents, more effective interaction with nitroxyl radical and faster H/D exchange indicate that N1'-H proton which is proximate to the glucopyranose ring is more acidic than N3'-H one in both ureido sugars, this conclusion was supported by semi-empirical AM1 calculation. Hydrogen to deuterium exchange rates are 1.2 x 10?2 to 5.5x 10?3 M?1 min?l. Significantly slower exchange of N3'-H proton standing by Leu residue in 2 can be explained by the existence of internal H-bonds. 相似文献