Solvation, interaction and dynamics of xenon atoms in HPLC column materials studied by variable-temperature dependent 129Xe, 1H–129Xe cross-polarization, and two-dimensional exchange NMR experiments
Department of Chemistry and Biochemistry, California State University, 5151 State University Drive, Los Angeles, CA 90032, USA Microporous and Mesoporous Materials
(Impact Factor: 3.45).
10/2003; 64(1-3):155-163. DOI: 10.1016/S1387-1811(03)00463-3
Xenon NMR is a useful method for probing structure and dynamics of micro-porous materials due to the sensitivity of xenon’s chemical shifts to its local interactions, and the diffusion property of xenon atoms. Here, we report a study of solvation, interaction and diffusion of xenon atoms inside the HPLC column materials, Zorbax SB-C18 and XDB-C18 which were made of siloxane surface coatings of porous silica, by variable-temperature dependent (VT) 129Xe, 1H–129Xe cross-polarization (CP), and two-dimensional exchange (2D EXSY) NMR experiments. The VT NMR experiment showed the solvation and dynamics of xenon atoms in the column materials. The CP experiment at low temperature provided evidence for probing the direct interaction of xenon atoms with the hydrocarbon chains of the stationary phase, and helped for assigning the 129Xe peaks in the VT NMR spectra. The 2D EXSY NMR experimental result showed the diffusion of xenon atoms within the accessible spaces in the column materials. Combined with our previous study, a full picture of xenon’s behavior inside the column materials has been described. This study provides a basic understanding of xenon NMR of the column materials, which enables us to conduct further investigation of retention mechanisms of column materials in terms of molecular interaction and diffusion by xenon NMR method.
Available from: Jiang-Hai Wang
- "The retention characteristics of free and esterified ergosterols on six reversed-phase columns are shown in Table 1. The results show that the best peak shapes for these analytes in GSL were obtained using the ZORBAX Eclipse XDB-C18 column because there were less surface defects for the XDB-C18 materials (Chagolla et al. 2003 "
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ABSTRACT: The fruiting bodies, spores, and lipid from the spores of Ganoderma lucidum have been widely used for medicinal purpose in China. Ergosterol content may be a suitable marker for evaluating the quality of ganoderma spore and ganoderma spore lipid (GSL) products. A gradient reversed-phase high-performance liquid chromatography method was developed for the simultaneous determination of free and esterified ergosterols in G. lucidum. The contents of free and esterified ergosterols in the different parts (the stipe, pileus, tubes, and spores) of G. lucidum and GSL were determined. The results showed that total ergosterol levels in the stipe, pileus, tubes, and spores of G. lucidum were between 0.8 and 1.6 mg/g. The relative abundances of free to esterified ergosterol were different in the different parts of G. lucidum. The spores and the tubes, the hymenophore tissue that contains the spore-producing cells, have a considerably higher percentage of ergosteryl esters (41.9 and 39.7% of total ergosterol) in comparison with the pileus and stipe tissues (3.6 and 6.2%).
Applied Microbiology and Biotechnology 12/2007; 77(1):159-65. DOI:10.1007/s00253-007-1147-x · 3.34 Impact Factor
Available from: E. R. Deazevedo
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ABSTRACT: Paper based on a presentation at the 14 th International Symposium "Spectroscopy in Theory and Practice", Nova Gorica, Slovenia, 2005. Solid Polymer Electrolytes are obtained by dissolving an alkali metal salt inside poly(ethylene oxide) based materials. The properties of these materials are strongly related to the behavior of the different active species : solvent (polymer), cation, and anion. In this paper, we compare various NMR techniques capable of deciphering different aspects of these new materials : the structure and dynamics of the polymer, the cations and anions as well as the supramolecular interactions between these different species. These data are very useful for understanding the conductivity mechanisms inside various families of PEO-based materials (nanocomposites, block oligomers and copolymers, and liquid crystals) developed by our group.
Acta Chimica Slovenica 01/2005; 52(4). · 0.69 Impact Factor
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ABSTRACT: VT (129)Xe NMR was applied to probe the interactions of solvents having different polarity indices with the stationary phase of a RP-C18 HPLC column material. It was observed that the highly polar ethylene glycol molecules do not mix with the alkyl chains of the RP-C18 stationary phase and the solvent is unable to enter the pores and the spaces between the particles. Three phases in this sample are defined as stationary/xenon phase, xenon gas phase (in the pores and the spaces between the particles) and ethylene glycol/xenon phase. In contrast to ethylene glycol, the nonpolar solvent cyclohexane was observed to be well mixed with the RP-C18 stationary phase. The capillary rise effect allows the solvent to enter the pores and the spaces between the particles. Two phases in this sample are defined as stationary/cyclohexane/xenon phase and cyclohexane/xenon phases. The properties of ethyl acetate are between those of ethylene glycol and cyclohexane. The (129)Xe NMR results show that the rational reversed phases should be conditioned from highly solvating to more polar solvents to remove the trapped air. The (129)Xe NMR results also show that pure stationary phase exists only when a highly polar solvent is used in reversed-phase chromatography. For a solvent with lower polarity, a stationary/solvent phase actually forms. This, together with the mobile phase, determines the selective factor for separating mixtures.
Journal of Chromatography A 08/2006; 1121(1):23-31. DOI:10.1016/j.chroma.2006.03.117 · 4.17 Impact Factor
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