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21.
Wu R Marta RA Martens JK Eldridge KR McMahon TB 《Journal of the American Society for Mass Spectrometry》2011,22(9):1651-1659
The structure of the proton-bound lysine dimer has been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy
and electronic structure calculations. The structures of different possible isomers of the proton-bound lysine dimer have
been optimized at the B3LYP/6-31 + G(d) level of theory and IR spectra calculated using the same computational method. Based
on relative Gibbs free energies (298 K) calculated at the MP2/aug-cc-pVTZ//B3LYP/6-31 + G(d) level of theory, LL-CS01, and
followed closely (1.1 kJ mol–1) by LL-CS02 are the most stable non-zwitterionic isomers. At the MP2/aug-cc-pVTZ//6-31 + G(d) and MP2/aug-cc-pVTZ//6-31 + (d,p)
levels of theory, isomer LL-CS02 is favored by 3.0 and 2.3 kJ mol–1, respectively. The relative Gibbs free energies calculated by the aforementioned levels of theory for LL-CS01 and LL-CS02
are very close and strongly suggest that diagnostic vibrational signatures found in the IRMPD spectrum of the proton-bound
dimer of lysine can be attributed to the existence of both isomers. LL-ZW01 is the most stable zwitterionic isomer, in which
the zwitterionic structure of the neutral lysine is well stabilized by the protonated lysine moiety via a very strong intermolecular
hydrogen bond. At the MP2/aug-cc-pVTZ//B3LYP/6-31 + G(d), MP2/aug-cc-pVTZ//6-31 + G(d) and MP2/aug-cc-pVTZ//6-31 + G(d,p)
levels of theory, the most stable zwitterionic isomer (LL-ZW01) is less favored than LL-CS01 by 7.3, 4.1 and 2.3 kJ mol–1, respectively. The experimental IRMPD spectrum also confirms that the proton-bound dimer of lysine largely exists as charge-solvated
isomers. Investigation of zwitterionic and charge-solvated species of amino acids in the gas phase will aid in a further understanding
of structure, property, and function of biological molecules. 相似文献
22.
D'Autry W Wolfs K Hoogmartens J Adams E Van Schepdael A 《Journal of chromatography. A》2011,1218(26):4034-4038
Gas chromatography-mass spectrometry is a well established analytical technique. However, mass spectrometers with electron ionization sources may suffer from signal drifts, hereby negatively influencing quantitative performance. To demonstrate this phenomenon for a real application, a static headspace-gas chromatography method in combination with electron ionization-quadrupole mass spectrometry was optimized for the determination of residual dichloromethane in coronary stent coatings. Validating the method, the quantitative performance of an original stainless steel ion source was compared to that of a modified ion source. Ion source modification included the application of a gold coating on the repeller and exit plate. Several validation aspects such as limit of detection, limit of quantification, linearity and precision were evaluated using both ion sources. It was found that, as expected, the stainless steel ion source suffered from signal drift. As a consequence, non-linearity and high RSD values for repeated analyses were obtained. An additional experiment was performed to check whether an internal standard compound would lead to better results. It was found that the signal drift patterns of the analyte and internal standard were different, consequently leading to high RSD values for the response factor. With the modified ion source however, a more stable signal was observed resulting in acceptable linearity and precision. Moreover, it was also found that sensitivity improved compared to the stainless steel ion source. Finally, the optimized method with the modified ion source was applied to determine residual dichloromethane in the coating of coronary stents. The solvent was detected but found to be below the limit of quantification. 相似文献
23.
24.
V. P. Belousov I. M. Belousova A. S. Grenishin O. B. Danilov V. M. Kiselev A. V. Kris’ko A. A. Mak T. D. Murav’eva V. N. Sosnov 《Optics and Spectroscopy》2003,95(6):830-832
The possibility of lasing in the fullerene-oxygen-iodine system with optical excitation of fullerene is studied. Laser radiation with an energy of 25 mJ and a pulse duration of 5–10 ms is obtained. 相似文献
25.
Yury G. Galyametdinov Larisa V. Malykhina Wolfgang Haase Kris Driesen Koen Binnemans 《Liquid crystals》2002,29(12):1581-1584
Lewis-base adducts of tris( β-diketonato)lanthanide(III) complexes were prepared, where the β-diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β-diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature. 相似文献
26.
Recently, the PVLAS Collaboration reported an anomalously large rotation of the polarization of light in the presence of a magnetic field in vacuum. As a possible explanation, they consider the existence of a light spin-zero particle coupled to two photons. We propose here a method of independently testing this result using a high-energy photon regeneration experiment (the x-ray analogue of "invisible light shining through walls") using the synchrotron x rays from a free-electron laser. With such an experiment the region of parameter space implied by PVLAS could be probed in a matter of minutes. 相似文献
27.
Edder C Armstrong PB Prado KB Fréchet JM 《Chemical communications (Cambridge, England)》2006,(18):1965-1967
We report the design, synthesis and characterization of new benzothiadiazole- and pyrrole-based copolymers whose solubility and bandgap drastically change after thermal treatment of their thin films. 相似文献
28.
We introduce methods for visualization of data structured along trees, especially hierarchically structured collections of time series. To this end, we identify questions that often emerge when working with hierarchical data and provide an R package to simplify their investigation. Our key contribution is the adaptation of the visualization principles of focus-plus-context and linking to the study of tree-structured data. Our motivating application is to the analysis of bacterial time series, where an evolutionary tree relating bacteria is available a priori. However, we have identified common problem types where, if a tree is not directly available, it can be constructed from data and then studied using our techniques. We perform detailed case studies to describe the alternative use cases, interpretations, and utility of the proposed visualization methods. 相似文献
29.
Adissu Alemayehu Asfaw Juan Aspromonte Kris Wolfs Ann Van Schepdael Erwin Adams 《Journal of separation science》2019,42(1):214-225
Sample preparation and introduction techniques are very critical steps in gas chromatography analysis and particularly in the analysis of volatiles in solid samples. In these cases, they can be divided into two main categories: direct and indirect approaches, based on how the solid sample is treated, i.e. with and without dissolution (or extraction) of analytes from the solid sample. To enable routine application, coupling with sample preparation techniques (especially solid or solvent‐based microextractions) is needed to achieve automation. Here, an overview of the most common sample introduction techniques for gas chromatography with their advantages and drawbacks is presented and discussed, including references to relevant examples. So, this review can serve as guidance for new users. 相似文献
30.
De Gussem K Vandenabeele P Verbeken A Moens L 《Analytical and bioanalytical chemistry》2007,387(8):2823-2832
Confocal Raman spectroscopy is a non-destructive analytical method which is useful to obtain detailed information about the
molecular composition of biological samples. Its high spatial resolution was used to collect spectra of single basidiospores
of macrofungi of the genera Collybia, Gymnopus, Laccaria, Lactarius, Mycena and Russula. These spectra can be divided into three major taxon-related groups, with general compositional differences, such as the
relative amount of lipids compared to proteins. In this study, collapsing of thin-walled spores during storage was often observed,
a phenomenon which has been given little attention in the literature. The Raman spectra are treated with different chemometric
preprocessing techniques, including Savitsky–Golay, standard normal variate (SNV) preprocessing and extended multiplicative
scatter correction (EMSC). By using linear discriminant analysis, approximately 90% of the spectra can be assigned to the
correct genus, but identification on the species level was not possible. 相似文献