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81.
Zhou SN Reiner EJ Marvin CH Helm PA Brindle ID 《Rapid communications in mass spectrometry : RCM》2011,25(3):443-448
Although the two flame retardants 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) and 1,2,5,6-tetrabromocyclooctane (TBCO) have been widely used, a selective instrumental method of analysis for these compounds has not been developed to date. In this study, we demonstrate the feasibility to utilize liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the separation and analysis of α- and β-TBCO and α-, β-, γ-, and δ-TBECH. Acetone was initially used in a tetrahedron solvent system for LC optimization. A simple isocratic elution allowed near-baseline separation of these compounds. Different ionization approaches and mechanisms were investigated. The mass spectrometric transition of [M + O(2)](-) => Br(-) (459.8 => 78.9) was a selective detection method for the target analytes. Good instrument detection limits (5 pg for γ-/δ-TBECH, 125 pg for α-/β-TBECH, and 30 pg for α-/β-TBCO with 2.0 μL injection) were obtained. Excellent linearity up to 50 ng/μL (R(2) >0.999) was also achieved. This method has been applied to environmental samples (surface water) for screening purposes with recoveries ranging from 76-92% (CV%: 5-8%). This method shows significant improvement over previous methods. 相似文献
82.
Asx-Pro-turns have been identified with high frequency in protein structures nucleating type I β-turns. By bridging the amino acid side chain in position i with a nitrogen substituent in position i+2 by ring-closing olefin metathesis (RCM), peptide mimetics of type 1 could be developed. NMR based conformational investigations indicated a stable intramolecular H-bond constraining a U-turn conformation that was predicted to simulate a type I β-turn. 相似文献
83.
Stelling A Salzer R Kirsch M Sobottka SB Geiger K Koch E Schackert G Steiner G 《Analytical and bioanalytical chemistry》2011,400(9):2745-2753
Established methods for characterization of tissue and diagnostics, for example histochemistry, magnetic resonance imaging
(MRI), X-ray tomography, or positron emission tomography (PET), are mostly not suitable for intra-operative use. However,
there is a clear need for an intra-operative diagnostics especially to identify the borderline between normal and tumor tissue.
Currently, vibrational spectroscopy techniques (both Raman and infrared) complement the standard methods for tissue diagnostics.
Vibrational spectroscopy has the potential for intra-operative use, because it can provide a biochemically based profile of
tissue in real time and without requiring additional contrast agents, which may perturb the tissue under investigation. In
addition, no electric potential needs to be applied, and the measurements are not affected by electromagnetic fields. Currently,
promising approaches include Raman fiber techniques and nonlinear Raman spectroscopy. Infrared spectroscopy is also being
used to examine freshly resected tissue ex vivo in the operating theater. The immense volume of information contained in Raman
and infrared spectra requires multivariate analysis to extract relevant information to distinguish different types of tissue.
The promise and limitations of vibrational spectroscopy methods as intra-operative tools are surveyed in this review. 相似文献
84.
85.
Willi Sicking Reiner Sustmann Johann Mulzer Rolf Huisgen 《Helvetica chimica acta》2011,94(8):1389-1405
A computational study on the rearrangement of 2,2‐diphenyl‐1‐[(E)‐2‐phenylethenyl]cyclopropane ( 1 ) is presented, using density functional theory (DFT), (U)B3LYP with the 6‐31G* basis set (DFT1) and (U)M05‐2X with the 6‐311+G** basis set (DFT2). In agreement with a biradical character of the transition structure (TS) or intermediate, the potential‐energy hypersurface is lowered by the influence of three conjugated Ph groups. Surprisingly, two conformations of the geminal diphenyl group (different twist angles) induce two different minimum‐energy pathways for the rearrangement. Independent of the functional used, the first hypersurface harbors true biradical intermediates, whereas the second energy surface is a flat, slightly ascending slope from the starting material to the TS. The functional (U)M05‐2X with the basis set 6‐311+G** provides realistic energies which seem to be close to experiment. The activation energy for racemization of enantiomers of 1 is lower than that of rearrangement by 2.5 kcal mol?1, in agreement with experiment. 相似文献
86.
Faulstich FR Castro HV de Oliveira LF Neumann R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,80(1):102-105
In this investigation, Raman spectroscopy with 1064 and 632.8 nm excitation was used to investigate real mineral samples of bauxite ore from mines of Northern Brazil, together with Raman mapping and X-rays diffraction. The obtained results show clearly that the use of microRaman spectroscopy is a powerful tool for the identification of all the minerals usually found in bauxites: gibbsite, kaolinite, goethite, hematite, anatase and quartz. Bulk samples can also be analysed, and FT-Raman is more adequate due to better signal-to-noise ratio and representativity, although not efficient for kaolinite. The identification of fingerprinting vibrations for all the minerals allows the acquisition of Raman-based chemical maps, potentially powerful tools for process mineralogy applied to bauxite ores. 相似文献
87.
88.
89.
Becker SM Scheuermann M Sepelák V Eichhöfer A Chen D Mönig R Ulrich AS Hahn H Indris S 《Physical chemistry chemical physics : PCCP》2011,13(43):19624-19631
We studied the electrochemical insertion of Li in mechanochemically prepared Zn(2)SnO(4). The mechanism of the electrochemical reaction was investigated by using X-ray diffraction, nuclear magnetic resonance spectroscopy, and M?ssbauer spectroscopy. Changes in the morphology of the Zn(2)SnO(4) particles were studied by in situ scanning electron microscopy. The results were compared with mixtures of SnO(2) + ZnO and with Zn(2)SnO(4) prepared by conventional solid-state synthesis and showed that the mechanochemically prepared Zn(2)SnO(4) exhibits the best cyclic stability of these samples. 相似文献
90.