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  • Electronic Resource  (9)
  • 1995-1999  (9)
  • Analytical Chemistry and Spectroscopy  (6)
  • Capillary electrophoresis  (3)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1546-1551 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The analysis of matrix-assisted laser desorption ionization post-source decay (MALDI-PSD) mass spectra of peptides by using the cross-correlation method for database searching is illustrated. MALDI-PSD mass spectra are shown to contain sufficient fragmentation information to uniquely identify the correct amino acid sequence from large protein databases (∼160000 entries). A search employing the MALDI-PSD mass spectrum of a phosphorylated peptide that correctly identifies the amino acid sequence and the site of phosphorylation is also illustrated.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Steric and substituent effects can play large roles in influencing the outcomes of organic reactions. In this work, the use of ion-molecule reactions of dibenzo-16-crown-5 compounds (lariat ethers) by tandem mass spectrometry to probe the influence of the pendant groups on the selectivity of their gas-phase reactions was evaluated. Lariat ethers are macrocyclic ethers with pendant substituents that have been developed as new types of hosts for molecular recognition. Dimethyl ether (DME) was the reactant chosen because of its well characterized reactivity with various organic substrates possessing different functional groups. Only those dibenzo-16-crown-5 compounds with no or at most one substituent at the center carbon of the three-carbon bridge form the diagnostic [M + 13]+ product ion through a methylene substitution process. Dibenzo-16-crown-5 compounds with geminal substituents on the center carbon of the three-carbon bridge form the [M + 45]+ ion, but not the characteristic [M + 13]+ ion. Causative factors may be steric blocking of the reaction pathway by the geminal groups or a requirement for the presence of at least one hydrogen on the center carbon of the three-center bridge for formation of the [M + 13]+ ion. CAD, deuterium labelling, molecular orbital calculations and comparisons with model compounds provide additional information about the reaction pathways.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A hydride Meisenheimer complex of 2,4,6-trinitrotoluene (TNT) (TNTH-) was synthesized using tetramethylammonium octahydroborate. TNT and TNTH- (as the tetramethylammonium salt) were analyzed by direct exposure probe mass spectrometry using electron impact (EI), chemical ionization (CI) and negative-ion chemical ionization (NCI). For further identification, the ions of the mass spectra were investigated using tandem mass spectrometry with collision-induced dissociation (CID). Although the EI mass spectra of both compounds were similar, the CID mass spectra of the ions at m/z 227 (M+ of TNT) of the two compounds showed large differences in daughter ion abundances. A major difference between the two compounds also appeared in their CI methane mass spectra. Two abundant ions, at m/z 183 and 198, appeared only in the CI mass spectrum of TNNH-. CID parent ion scans showed that the origin of these two ions was not the m/z 227 ion. We suggest that these ions are formed by chemical reactions of the complex on the surface of the heated probe tip, followed by ionization. These reactions, probably a reduction process forming m/z 198 and hydrolysis forming m/z 183, occur preferentially in TNTH-, the already reduced form of TNT. Formation of the ions at m/z 183 and 198 was also observed in the liquid chromatography particle beam CI mass spectrum of TNTH-.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 3 (1997), S. 421-433 
    ISSN: 1075-4261
    Keywords: plant photoreceptor ; photoisomerization mechanism ; excited state lifetime ; fluorescence quantum yield ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Time-resolved absorption spectra of Pr phytochrome were obtained using a regeneratively amplified femtosecond titanium : sapphire laser system. The early time transient absorption spectra are comprised of prompt Pr photobleaching, stimulated emission, and excited-state absorption features that decay with a 24 ps time constant that matches the ground state appearance time of the primary photoproduct. Based on the 5 ns radiative lifetime calculated from the absorption and spontaneous emission spectra and the fluorescence quantum yield of 5.5 (± 0.5) × 10-3, we calculate an excited-state lifetime of 28 ps that agrees well with the directly determined lifetime. The transient absorption spectra are consistent with a primary photochemical reaction quantum yield of 0.15, and the absorption spectrum of the primary photoproduct closely resembles that of the low-temperature trapped intermediate, lumi-R. We conclude that the primary photoisomerization, which is believed to be a Z,syn → E,syn isomerization of the C15=C16 chromophore bond, occurs in 24 ps. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 421-433, 1997
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 29-32 
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; electroosmotic flow ; frit ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation of bubbles in capillary electrochromatography (CEC) is well documented: possible origins include Joule heating and variations in EOF velocity on passing from the stationary phase through the frit and into the open tube. Methods for the prevention of bubble formation are discussed which are confirmed by experimental results. Using frit lengths varying from 1 mm to 6 mm it is shown how frit length is directly related to the likelihood of bubble formation and how this is affected by applied voltage. It is shown that the change in applied voltage across a capillary affects the formation of bubbles and also that rebonding octadecylsilane (ODS) onto the silica frit after formation of the frit can minimize the formation of bubbles and how this effects the chromatography. A method is also described for increasing the robustness of silica capillaries using a column coupler along with modifications made to conventional capillary electrophoresis equipment to cater for CEC.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0173-0835
    Keywords: DNA sequencing ; Capillary electrophoresis ; Confocal fluorescence detection ; Energy transfer primers ; Mitochondrial DNA polymorphisms ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The design, construction and operation of a four-color capillary array electrophoresis scanner are presented. The use of sensitive energy transfer primers facilitates four-color detection of the DNA sequencing fragments following excitation at a single laser wavelength (488 nm). This scanner collects fluorescence data from up to 25 capillaries in parallel. The resulting four-color image files are automatically reduced to four-color line plots, and a base-calling program (Sax) is used to call the sequence. The performance of this system for DNA sequencing is demonstrated by examining twelve different motifs of the hypervariable region I of human mitochondrial (mt) DNA obtained from a Sierra Leone population.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0173-0835
    Keywords: DNA sequencing ; Capillary electrophoresis ; Energy transfer primers ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Capillary electrophoresis DNA sequencing has been accomplished by using four different energy transfer primers and three fluorescence detection channels. Methods have also been developed to deconvolve the three-color data into the four base concentrations. The nonnegative least squares and model selection method resulted in the best accuracy. The three-color data were compared to sequencing data obtained using four detection channels and four energy transfer primers. The average accuracy rates obtained over three 500 base M13mp18 runs using three-color coding were 96% including 18 uncallable compressions and 99.6% if these compressions are excluded. The average accuracy rate obtained using four-color coding was 96.3% including 18 uncallable compressions and 99.9% if these compressions are excluded. Although it is unlikely that three-color schemes will replace four-color sequencing, these methods have exposed basic concepts that will be useful in the development of higher-order multiplex coding methods for DNA analysis.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 501-505 
    ISSN: 0749-1581
    Keywords: NMR ; solid-state NMR ; 13C NMR ; magic angle spinning ; steroids ; fluorinated compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-resolution carbon-13 NMR spectra were obtained for three solid fluorinated steroids. Assignments were carried out using several approaches, including two-dimensional spectra of the compounds in solution. Solid-state and solution-state chemical shifts are compared. Signals from one of the fluorine-containing carbons in each compound show the effect of interplay between shielding, dipolar and indirect scalar (J) coupling tensors. One sample is found to be a mixture of two polymorphic forms.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0173-0835
    Keywords: Cancer diagnosis ; Short tandem repeat ; Capillary electrophoresis ; Energy-transfer primers ; Microsatellites ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The development of sensitive, rapid, and accurate methods and apparatus for high-throughput short tandem repeat (STR) analysis will be critical for the use of microsatellite alteration in cancer screening. Here we show that STR-based bladder cancer diagnosis can be performed using capillary array electrophoresis and two-color labeling with energy-transfer (ET) fluorescent primers. Rapid (≤35 min) separations are achieved on capillary arrays using replaceable separation matrices and the allelic ratios are quantitatively determined with a precision of ± 10%. With this precision, a variation of 20% was considered diagnostically significant. These methods provide a significant improvement in the speed, ease, and precision of STR analyses compared to slab gel electrophoresis.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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