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91.
Antonella Leggio 《Tetrahedron》2007,63(34):8164-8173
A highly efficient and practical synthesis of peptides in solution phase has been developed. The procedure is based on the use of p-nitrobenzenesulfonyl (nosyl) group for the protection of the amino function of α-amino acids. Every step of the procedure, protection of the amino function by the nosyl group, formation of the peptide bond, and removal of the sulfonamide group, is characterized by high yields and excellent purity of the final products. The described strategy allows the preparation of short peptide sequences keeping the chiral integrity of amino acid precursors. Compatibility of nosyl group with the side-chain protecting groups used in Fmoc-based strategy is demonstrated. The method here presented is an alternative strategy that could provide advantages for future peptide synthesis. 相似文献
92.
Cadmium colloids have been prepared by Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming, stable liquid colloids are formed with particle size ranging between 25–100 Å. Zeta potentials were calculated according to the conversion of Hunter and the Hückel equation, for ethanol and dimethyl sulphoxide. UV/VIS measurement of most of the black colloids showed absorption band around 280 nm. For comparison, we prepared CdS colloid with size 400–625 Å. The colloids are stable to oxidation in air and/or oxygen bubbling. The synthesis of colloids and films from Cd with acetone, 2-butanone, ethanol, 2-propanol, 2-methoxyethanol, DMF and DMSO is reported. Transmission Electron Microscopy (TEM) allows us to determine particle size. 相似文献
93.
Rodríguez-Cea A de la Campa MR Sanz-Medel A 《Analytical and bioanalytical chemistry》2005,381(2):388-393
Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with -naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4±0.1 nmol mL–1 P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE–FPLC, with UV detection, or coupled to ICP–MS with an octapole reaction system, ICP–(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP–(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins. 相似文献
94.
A one-step solid-phase extraction procedure, based on a new silica gel adsorbent modified with cholesterol groups, has been
investigated for measurement of cotinine in urine. Cotinine is the main metabolite of nicotine in the human body and is analyzed
as a biomarker for assessment of direct or passive exposure to tobacco smoke. New cholesterol-modified adsorbents have been
obtained by chemical modification of silica gel of different porosity with cholesterol ligands. Although recovery by this
extraction procedure were optimum over a relatively broad range of sample pH (3.1–8.0), analytical conditions such as sample
loading, washing and elution conditions, concentration of cotinine to be extracted, and the type of adsorbent used for extraction
were found to affect the efficiency of the procedure and had to be controlled for optimum recovery. When these conditions
were controlled, recovery of cotinine from spiked human urine was reproducible and depended on compound ionization. Quantitative
analysis of cotinine was performed by reversed-phase high-performance liquid chromatography with UV detection.
Presented at: Conference of the Hyphenation of Liquid Chromatography–Nuclear Magnetic Resonance Spectroscopy, Liquid Chromatography–Mass
Spectrometry and Related Topics, Tuebingen, Germany, March 25–29, 2006. 相似文献
95.
Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes,
both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model
developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for
neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the
other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water
mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity
and basicity, dipolarity/polarizability…).
This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various
journals. 相似文献
96.
D. Levy F. Del Monte X. Quintana J.M. Otón 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1063-1066
Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass
dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals;
no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative
study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid
crystal microdroplets is presented. 相似文献
97.
T. Kowalska 《Chromatographia》1991,31(3-4):119-122
Summary Intermolecular interactions between the solute and the moieties constituting the mobile phase significantly contribute to the overall retention pattern of a given solute in a given chromatographic system. In this paper retention of solute is discussed in the case of the B+AB1+AB2 type mobile phase, which, in a quasithermodynamic way, can be divided into seven individual moieties. One evaluates the influence of each moiety on solute retention, and refers these regularities to the polarity of the solutes. 相似文献
98.
Interaction between octahedrally coordinated Nd3+ and Yd3+ in Cs2NaNd0,4Yb0,6Cl6 reduces the Nd3+ luminescence lifetime by roughly two orders of magnitude with respect to that found in Cs2NaNdCl6– · – Analysis of low temperature absorption and emission spectra reveals that the nonradiative Nd3+–Yb3+ energy transfer has to be assisted by lattice phonon emission, nevertheless the rate of the transfer is high in the 4–300 K temperature region and attains 5.8×105s-1 at room temperature. A phase transition of Cs2NaNd0,4Yb0,6Cl6 between 12 and 13 K is evidenced by abrupt change of both the spectra and lifetimes of Yb3+. Reduction of Yb3+ lifetime from 5.3 ms to 150 μs is at the transition from low symmetry phase to high symmetry phase is supposed to be associated with a three ion interaction which occurs in ordered lattice and disappears in low temperature disordered structure. 相似文献
99.
A sensitive and selective method using liquid chromatography with electrospray ionization mass spectrometric detection was
developed for the quantification of bilobalide and ginkgolides in canine plasma. The analytes were extracted with diethyl
ether-dichloromethane-isopropanol (6:3:1, v/v) after spiking the samples with daidzein (internal standard). The lower limit
of quantification (LLOQ) of the method was 2.5 μg L−1 for ginkgolide B and 10.0 μg L−1 for bilabolide, ginkgolide A and ginkgolide C. The accuracy of the method was within 15% of the actual values over a wide
range of plasma concentrations. The intra-day and inter-day precision was better than 15% (R.S.D.). Finally, the LC-ESI-MS
method was successfully applied to study the pharmacokinetics of ginkgolides and bilabolide after administration of Ginkgo biloba extracts to dogs. 相似文献
100.
Matthew T. AllinghamAndrew Howard-Jones Patrick J. MurphyPeter W.R. Caulkett 《Tetrahedron letters》2003,44(48):8677-8680
The preparation of the tetracyclic C2-symmetric guanidinium salts 5 and 11-13 is reported together with their application to enantioselective transformations. 相似文献