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991.
David Fuchs Charlotte Gabel-Jensen Henrik Jensen Kasper D. Rand Stig Pedersen-Bjergaard Steen Honoré Hansen Nickolaj Jacob Petersen 《Analytica chimica acta》2016
A fully integrated and automated electromembrane extraction LC-MS (EME-LC-MS) system has been developed and characterized. Hyphenation of a flow–flow EME probe to LC-MS was accomplished by using an in-built 10-port switching valve of the LC-MS system. The 10-port switching valve decoupled the high pressure of the UHPLC-system from the low pressure required for operation of the EME-probe by automated switching between a sample extraction/analysis and a sample load position. In the sample load position the extracted analytes were loaded into a HPLC sample loop. By switching the valve to the sample extraction/analysis position the setup allowed simultaneous analysis of previously loaded analytes while extracting a new sample. Performance of the system was characterized with respect to precision and linearity (RSD < 2.5%, R2: 0.998) and the setup was applied for studying the in-vitro metabolism of methadone by rat liver microsomes. As the metabolic reaction proceeded, methadone and its metabolites were extracted and analyzed in parallel by LC-MS using either isocratic or gradient elution. Compared to a conventional in-vitro metabolism analysis based on protein precipitation followed by LC-MS analysis the fully automated EME-LC-MS system offers a significant time saving and in addition demonstrates increased sensitivity as the analytes were automatically enriched during the extraction process. The experiment revealed 6 to 16 times higher S/N ratios of the EME-LC-MS method compared to protein precipitation followed by LC-MS and thus concomitantly lower LOD and LOQ. The setup integrates a complete analytical workflow of rapid extraction, enrichment, separation and detection of analytes in a fully automated manner. These attributes make the developed system a powerful alternative approach for a wide range of analytical applications. 相似文献
992.
993.
Boyer J Burke DL Butler F Gidal G Abrams GS Amidei D Baden AR Barklow T Boyarski AM Breidenbach M Burchat P Dorfan JM Feldman GJ Gladney L Gold MS Goldhaber G Golding LJ Haggerty J Hanson G Hayes K Herrup D Hollebeek RJ Innes WR Jaros JA Juricic I Kadyk JA Karlen D Klein SR Lankford AJ Larsen RR LeClaire BW Levi ME Lockyer NS Lüth V Matteuzzi C Nelson ME Ong RA Perl ML Richter B Riles K Ross MC Rowson PC Schaad T Schellman H Schmidke WB Sheldon PD Smith JR Trilling GH de la Vaissiere C Wood DR 《Physical review letters》1986,56(3):207-210
994.
Aderholz M Aggarwal MM Akbari H Allport PP Baba PV Badyal SK Barth M Baton JP Bingham HH Brucker EB Burnstein RA Campbell RC Cence R Chatterjee TK Clayton EF Corrigan G Coutures C De Prospo D Devanand De Wolf E Faulkner PJ Fretter WB Gupta VK Guy J Hanlon J Harigel G Harris F Jabiol MA Jacques P Jain V Jones GT Jones MD Jones RW Kafka T Kalelkar M Kasper P Kaul GL Kaur M Kohli JM Koller EL Krawiec RJ Lauko M Lys J Mann WA Marage P Milburn RH Miller DB Mittra IS Mobayyen MM Moreels J 《Physical review letters》1989,63(21):2349-2352
995.
Difference between Extra‐ and Intracellular T1 Values of Carboxylic Acids Affects the Quantitative Analysis of Cellular Kinetics by Hyperpolarized NMR
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Dr. Magnus Karlsson Dr. Pernille Rose Jensen Prof. Jan Henrik Ardenkjær‐Larsen Dr. Mathilde H. Lerche 《Angewandte Chemie (International ed. in English)》2016,55(43):13567-13570
Incomplete knowledge of the longitudinal relaxation time constant (T1) leads to incorrect assumptions in quantitative kinetic models of cellular systems, studied by hyperpolarized real‐time NMR. Using an assay that measures the intracellular signal of small carboxylic acids in living cells, the intracellular T1 of the carboxylic acid moiety of acetate, keto‐isocaproate, pyruvate, and butyrate was determined. The intracellular T1 is shown to be up to four‐fold shorter than the extracellular T1. Such a large difference in T1 values between the inside and the outside of the cell has significant influence on the quantification of intracellular metabolic activity. It is expected that the significantly shorter T1 value of the carboxylic moieties inside cells is a result of macromolecular crowding. An artificial cytosol has been prepared and applied to predict the T1 of other carboxylic acids. We demonstrate the value of this prediction tool. 相似文献
996.
The synthesis and characterisation of two cobalt(II) complexes, [CoIILBr-acrCl2] (1a) and [CoIILH-acrCl2] (1b), with acridine head-units resulting from an unexpected ligand rearrangement from a diphenylamine head-unit, and the intended cobalt(II) complex, CoIILBr-dpa(Cl)(H2O) (2), are reported. Single crystals of the two dark green acridine-based cobalt(II) complexes, 1a and 1b, form in a one-pot reaction of cobalt(II) chloride, the chosen diphenylamine-2,2′-dicarboxaldehyde (Ia 4,4-′dibromo- or Ib unsubstituted), triethylamine and two equivalents of 2,4-dimethylaniline in acetonitrile, in 23% yield. In contrast, the intended diphenylamine-based complex was isolated in two steps: first isolation of the Schiff base ligand, then complexation with cobalt(II) chloride and deprotonation with potassium tert-butoxide, in methanol/dichloromethane, giving 2 as a bright yellow solid in 67% yield. All three complexes feature cobalt(II) centres, with N2Cl2 approximately tetrahedral coordination for 1a and 1b confirmed by single crystal structure determinations. It is proposed that after one imine ‘arm’ forms, cobalt(II) coordination facilitates the other aldehyde undergoing an intramolecular cyclisation to form the new heterocyclic acridine head-unit. The structures of both of the resulting acridine-based complexes, 1a and 1b, and that of the originally intended Schiff base ligand, HLBr-dpa, were confirmed by single-crystal X-ray diffraction. These are the first examples of complexes of an acridine ligand of this type. 相似文献
997.
Online coupling of capillary electrophoresis (CE) to electrospray ionization mass spectrometry (MS) has shown considerable potential, however, technical challenges have limited its use. In this study, we have developed a simple and sensitive sheathless CE-MS interface based on the novel concept of forming a sub-micrometer fracture directly in the capillary. The simple interface design allowed the generation of a stable ESI spray capable of ionization at low nanoliter flow-rates (45–90 nL/min) for high sensitivity MS analysis of challenging samples like those containing proteins and peptides. By analysis of a model peptide (leucine enkephalin), a limit of detection (LOD) of 0.045 pmol/μL (corresponding to 67 attomol in a sample volume of ∼15 nL) was obtained. The merit of the CE-MS approach was demonstrated by analysis of bovine serum albumin (BSA) tryptic peptides. A well-resolved separation profile was achieved and comparable sequence coverage was obtained by the CE-MS method (73%) compared to a representative UPLC-MS method (77%). The CE-MS interface was subsequently used to analyse a more complex sample of pharmaceutically relevant human proteins including insulin, tissue factor and α-synuclein. Efficient separation and protein ESI mass spectra of adequate quality could be achieved using only a small amount of sample (30 fmol). In addition, analysis of ubiquitin samples under both native and denatured conditions, indicate that the CE-MS setup can facilitate native MS applications to probe the conformational properties of proteins. Thus, the described CE-MS setup should be useful for a wide range of high-sensitivity applications in protein research. 相似文献
998.
Anion-exchange chromatography of the rare earth (Sm, Nd, Pr, Ce) ions in methanol-nitric acid-water media is performed using
high-pressure liquid chromatography. The separation method is especially designed for determination of148Nd in the nuclear fuel cycle in order to find precise burn-up values. The high-pressure liquid chromatography method presented
here is very fast, gives high resolutions, and enables collection of selected fractions containing nmoles of rare earth by
UV monitoring at 280 nm of the eluate. 相似文献
999.
The influence of a preceding electrode process in the analytical use of a.c., differential pulse and other polarographic methods is discussed. Coupled chemical reactions, such as found with the Cr(III)/Fe(III) system, cause considerable interference in all the techniques examined, interference is readily recognized by a shift in peak potential and a change in the wave shape on addition of increasing concentrations of the more positively reduced species. With other systems, a depolarizer more negatively reduced than another can be determined over a wide range of conditions with three-electrode instrumentation. IR-drop problems with two-electrode systems place considerable restrictions on their use. With Zn/Cu and Cd/Cu and other systems, reliable determinations were possible only when the concentration of the more positively reduced species was less than 10?2 M. 相似文献
1000.
The absolute configuration of molecules containing two chromophores of the type -NH-CC-CO bridged by -?-?- have been studied in solution by UV absorption and circular dichroism. The spectra have been simulated by means of component curves shaped as skew gaussians. The data have been interpreted by means of exciton theory for coupled chromophores to give information about the relative orientation of the chromophores. The result is compared with the result of an X-ray structure determination of N,N'-bis(4-oxo-2-penten-2-yl)-R-1,2-diaminopropane. 相似文献