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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 1148-1154 
    ISSN: 0749-1581
    Keywords: Self-diffusion ; Pulsed gradient ; Complexation phenomena ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 133Cs NMR self-diffusion measurements were performed by means of the pulsed gradient spin-echo method (PGSE) to evaluate the complex formation constants of Cs and 18-crown-6 and those of Cs and some ethylene glycols in D2O. The calculated complex formation constants were checked as far as possible by using similar calculations based on relaxation data. Chemical shift measurements do not allow the evaluation of complex formation constants in these systems. A cross-check was introduced to verify the calculations based on the diffusion data. Similar investigations were performed on Na, K, Cs complexes and N-phenylaza-15-crown-5 in methanol. In this case, analysis of the diffusion data and as the relaxation rate and chemical shift data led to complex formation constants for 1:1 complexes, which is in contrast to a previous report suggesting the formation of 2:1 complexes.
    Additional Material: 9 Ill.
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  • 2
    ISSN: 0749-1581
    Keywords: [Lys8]-vasopressin homologues ; NMR assignments in peptides ; Conformational analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assignment of proton NMR signals and the conformational analysis of N-(Gly)-[Lys8]-vasopressin and N-(Gly—Gly—Gly)—[Lys8]-vasopressin in dimethyl sulfoxide solution by means of one- and two-dimensional NMR techniques are presented. Dihedral angles obtained from 3J (HN—C—α-H) vicinal couplings, intramolecular distances estimated from nuclear Overhauser enhancements (NOEs) and two-dimensional experiments in the rotating frame (ROESY), as well as temperature dependences of the amide protons, suggest a more or less rigid ring conformation with an inverse γ-turn for both cyclic peptides.
    Additional Material: 3 Ill.
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  • 3
    ISSN: 0749-1581
    Keywords: Vasopressins ; Peptide dynamics in solution ; NMR relaxation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamic behaviour of [Lys8]-vasopressin derivatives, especially of N-Gly-Gly-Gly-[Lys8]-vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from 13C spin-lattice relaxation times, T1, spin-spin relaxation times, T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co-workers and the ‘model-free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108-109 s-1, we observe a faster mobility of the order of 109-1010 s-1 in addition to slow dynamic contributions. The latter can be associated by means of T1, measurements with a motion involving the S—S linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from 13C relaxation were corroborated by 15N T1 measurements, performed at the 15N natural abundance level by an INEPT-reverse INEPT method, and by 15N NOE investigations.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: This work is concerned with the relationship between chemical shifts (δ) of protons and their charge densities (q). It can be shown that the relation δH = a + bqH + cqC (qC = charge density at the corresponding C-atom) fits best for a prediction of δ-values from calculated charge densities. The smallest standard error for the prediction of δ-values is obtained if the charge densities are calculated by the CNDO- or INDO-method.
    Notes: Es ist gezeigt worden, daß von den in dieser Arbeit untersuchten Beziehungen zwischen den chemischen Verschiebungen δ von Protonen und deren Ladungsdichten q die Beziehung δH = a + bqH + cqC (qC ist die Ladungsdichte des mit dem Proton in Bindung stehenden C-Atoms) für eine Voraussage der δ-Werte aus gerechneten Ladungsdichtewerten am geeignetsten ist. Der Standardfehler der Voraussage der δ-Werte wird dabei am kleinsten, wenn die in die Beziehung einzusetzenden Ladungsdichtewerte nach der CNDO- oder INDO-Methode berechnet werden.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: An attempt was made to predict the chemical shifts of 1H, 13C and 19F atoms based on SCF LCGO MO calculations. The expectation value 〈1/R〉 as a measure for the diamagnetism was calculated exactly, the paramagnetism approximated by 〈1/R3〉 and values of the charge density bond order matrix. The influence of the neighbouring atoms was calculated point by point by the electron-density p(r) estimated by a spherical screening function. The terms permit one to calculate the 1H and 13C chemical shifts in fluoroacetylene, fluoroethylene and fluoroethane by a linear relationship with a standard deviation of 0.39 ppm for 1H and 1.6 ppm for 13C. The 19F chemical shifts were calculated directly by assuming σdia: σpara = 1:10.
    Notes: Die Vorhersage der chemischen Verschiebung für 1H, 13C und 19F Atome wird auf der Basis von SCF-LCGO-MO-rechnungen versucht. Der 〈1/R〉 Erwartungswert als Maß für den Diamagnetismus wird exakt berechnet, der Paramagnetismus durch 〈1/R3〉 sowie Werte der Ladungsbindungsordnung angenähert. Der Einfluß der Nachbaratome wird über die Elektronendichte p(r) auf einem kugelförmigen Raster ermittelt. Die Terme ermöglichen in Form eines linear funktionalen Ansatzes die Berechnung von 1H und 13C Verschiebungen an Fluoracetylen, Fluoräthylen und Fluoräthan wobei die Regressionsrechnung für 1H einen Standardfehler von 0,39 ppm und für 13C einen Standardfehler von 1,6 ppm ergibt. Die 19F Verschiebungen werden direkt durch Festlegung des σdia:σpara Verhältnisses berechnet.
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 11 (1978), S. 453-456 
    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 existence of radical pairs during the photolysis and the thermolysis of substituted benzenediazonium tetrafluoroborates and hydroquinone in acetonitrile is shown by means of CIDNP. The reaction is assumed to occur via a one-electron-step to form first a radical pair consisting of phenyldiazene and p-benzosemiquinone. This radical pair is able to lose nitrogen either by photolysis or thermolysis and can lead either to a disproportionation or to various recombinations.
    Notes: Mit Hilfe des CIDNP-Effekts wird die Existenz von Radikalpaaren bei der Photolyse und Thermolyse von substituierten Phenyldiazoniumtetrafluoroboraten und Hydrochinon in Azetonitril aufgezeigt. Die Reaktion wird als Einelektronenübergang unter Ausbildung von Phenyldiazen und p-Benzosemichinon formuliert. Dieses Radikalpaar verliert, entweder durch Photolyse oder Thermolyse, Stickstoff und kann eine Disproportionierung oder verschiedene Rekombinationen eingehen.
    Additional Material: 2 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. S3 
    ISSN: 0749-1581
    Keywords: Transient NOE experiments ; Synchronous nutation experiments ; NAD stack interactions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cross-relaxation interactions between the nicotinamide moiety and the adenine moiety of NAD in D2O solution were unambiguously revealed by steady-state NOE experiments, transient NOE experiments and synchronous nutation experiments. The experimental results, which allow a concise description in terms of auto-relaxation and cross-relaxation, are interpreted as the result of a stacking interaction. Studies of 13C relaxation and investigations on ternary mixtures with 6-methylpurine give evidence for an inter- rather than intra-molecular stack interaction, at least in the NMR concentration range.
    Additional Material: 5 Ill.
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  • 8
    ISSN: 0749-1581
    Keywords: 1H NMR ; Structure determination ; MD calculation ; Vasopressin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of N-(Gly-Gly-Gly)-Lys-vasopressin (TGVP) in aqueous solution was determined by 1H NMR spectroscopy. The structural data were compared with those obtained in DMSO. Refinement of the structure derived from NMR data and a description of the conformational dynamics were accomplished by molecular dynamics simulations in aqueous solution.
    Additional Material: 6 Ill.
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