Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 809-814 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The aim of this article was to study the influence of different matrix molecules on the quality of matrix-assisted laser desorption/ionization mass spectra of oligosaccharides. An important criterion was the sample preparation, i.e. the crystallization process leading to the matrix from which the analytes were desorbed and investigated. Quality criteria were, among others, the resulting molecular peak intensity, the mass resolution, and the suppression of unwanted matrix peaks. It was found that a mixture of 2,5-dihydroxy benzoic acid (DHB) and 1-hydroxy isoquinoline (HIC) in a weight ratio of 3:1 was best suited for the analytical investigation of oligosaccharides. In addition, this matrix mixture was found to be quite tolerant against all kinds of buffers, salts, and even additives such as sodium dodecyl sulfate (SDS). Furthermore, we determined the different affinities of the alkaline metals to the carbohydrates and found that cesium and potassium ions ionize oligosaccharides about three times better than sodium ions and therefore have an important influence on the quantum yield.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A Nafion membrane was tested as a new tool for a fast and easy sample pretreatment for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) measurements. This membrane material was used for ion exchange and carbohydrate purification with minimal quantities of sample solution. An ion exchange method for carbohydrates was developed and demonstrated on a Dextran sample. The cations of the original sample were replaced within minutes by potassium or cesium ions. Another feature of this membrane was the fact that proteins and peptides adsorb on the acid surface. This behavior was investigated as a purification step for carbohydrates with high peptide and protein impurity concentrations. It was found that oligosaccharide libraries from rat- and mouse IgG mass spectra can be obtained clearly in the presence of high peptide impurities.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The chemical shifts of aromatic nitriles of the general structure para-Y—C6H4—X—CN with X = O, S, Se and N(CH3) have been investigated by the 13C NMR technique. For cyanates (X = O) the 14N shifts and for Y = F the 19F shifts were likewise measured. The chemical shifts and the corresponding 13C shift increments Δn have been found to correlate with the appropriate substituent constants σR0, σp0 and σI, as well as with the π-electron densities calculated in the PPP approximation.
    Notes: An aromatischen Nitrilverbindungen der allgemeinen Struktur para-Y—C6H4—X—CN mit X = O, S, Se und N(CH3) wurden die 13C-NMR- sowie für X = O die 14N-NMR-und für Y = F die 19F-NMR-chemischen Verschiebungen bestimmt. Die Meßergebnisse wurden in Zusammenhang mit der elektronischen Struktur der Moleküle (Substituentenkonstanten, π-Elektronendichten in PPP-Näherung) diskutiert.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 12 (1979), S. 95-97 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Carbon-13 chemical shifts of several benzimidazole- and benzoxazole derivatives have been measured. The signals of the homonuclear carbon atoms in unsymmetrical benzoheteroazoles can be assigned with the aid of additivity parameters. The structures of compounds obtained from the reaction of benzimidazoline- and benzoxazoline-2-thione with aryl cyanates were elucidated.
    Notes: Für verschiedene Benzimidazol- und Benzoxazolderivate wurden die chemischen Verschiebungen im 13C-NMR-Spektrum bestimmt. Mit Hilfe von Additivitätsparametern lassen sich die 13C-Signale der Benzokohlenstoffatome in unsymmetrischen Benzheteroazolen bestimmen. Die Struktur der Reaktionsprodukte aus Benzimidazolin- und Benzoxazolin-thion-(2) und Arylcyanaten werden abgeleitet.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 21-30 
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR chemical shifts of 74 N-acylated 2-aminobenzimidazoles were determined and assigned. The chemical shifts are discussed as a function of electronic and spatial substituent effects. Line broadening for certain C signals are traced to prototropy at N-1 and N-3, and N-3 and Nexo.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 0749-1581
    Keywords: 4-Methyl catechol ; Autoxidation ; Electron spin resonance spectroscopy ; Nucleophiles ; Semiquinones ; Allergic contact dermatitis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of 4-methylcatechol by dioxygen and the subsequent reactions of the two nucleophiles OH- and MeO- with the oxidation products were studied by electron spin resonance (ESR) spectroscopy. These reactions are models for those of skin proteins with substituted 1,2-dihydroxybenzenes (catechols) which produce the severe allergic contact dermatitis associated with plants such as poison ivy, poison oakd and the Japanese lac tree. The rates of formation of the primary and secondary semiquinone radical anions show a large kinetic deuterium isotope effect (ca 10) at 20°C, which is ascribed to a slow deprotonation of the hydrogen bridged 4-methylcatechol monoanion. There is a marked difference in regioselectivity for OH- and MeO- substitution of the 4-methylcatechol monoanione; OH- reacts exclusively at the 3-position whereas MeO- attacks at the 5-position. This dissimilarity between two normally similar nucleophiles is also ascribed to the occurrence of hydrogen bridging between the substituting OH- at the 3-position and the adjacent quinone oxygen at the 2-position. The expected attack at the more electropositive 5-position occurs with MeO- because no such hydrogen bonding can occur. Disubstitution occurs for OH- but not for MeO-, probably reflecting the greater nucleophilicity of the former.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...