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  • Computational Chemistry and Molecular Modeling  (3)
  • Polarography  (3)
  • Wiley-Blackwell  (6)
  • Public Library of Science (PLoS)
  • Springer Nature
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  • Wiley-Blackwell  (6)
  • Public Library of Science (PLoS)
  • Springer Nature
Years
  • 1
    Electronic Resource
    Electronic Resource
    Kinematic distribution function to calculate rotational populations of photofragments from photodissociation of triatomic molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 359-370 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400835
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  • 2
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part I: Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56-61] MT I (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 663-669 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Methallothioneins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain a better understanding of the electrochemical behavior of the Metallothionein (MT), the peptidic fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I (FT) compound constitutive of the proteic structure has been studied. The elucidation of the electrochemical mechanism at the electrode could be reached from comparison with other mechanisms proposed for similar molecules. This study stems from a more complete work. Under our experimental conditions, with a low concentration of the substance (〈 5 × 10-5 M) and the use of a dropping mercury electrode, a diffusion controlled mechanism is suggested for the electrochemical behavior of FT. In this case the mercury electrode itself is involved in the charge transfer step and the polarographic response is attributed to the oxidation of the mercury electrode in the presence of the chelating agent FT. This hypothesis was supported by the lack of modification of the electrocapillary curves in the presence of low concentration of FT in relation to those obtained with the supporting electrolyte alone and by the linear relationship between the polarographic intensity and the concentration at a low concentration of FT. The influence of the pH of the solution on the behavior of FT was investigated using DC and DPP methods. The variation of i1, ip and Ep with pH was determined. From these results the apparent acid-base dissociation constant of the FT was evaluated, corresponding to the dissociation of protons from the thiol groups. Likewise the apparent stability constants of the Hg-FT were estimated as a function of the pH. It was assumed that the main complex of Hg-FT possessed a stoichiometry of 1 : 1 but it is probable that two or more different complexes coexisted.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070713
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  • 3
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part III: Metallothionein (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 674-680 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Metallothionein ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical behavior of Cd-Zn Thionein from rabbit liver and horse kidney with respect to pH of the solution at the dropping mercury electrode was studied, using differential pulse polarography (DPP). At pH 7.5 three well defined peaks were observed at a potential different from the potentials corresponding to pure Cd2+ and Zn2+. Two different electrochemical systems are involved: the oxidation of the mercury electrode in the presence of thiol groups contained in the metallothionein and the reduction of either free (pH 〈 4) or complexed (pH 〉 6) metal ions. The apparent acid-base dissociation constant of metallothionein was estimated. The apparent stability constants of the complexes CdT, ZnT and HgT were estimated at different pH values. Cadmium forms at least two complexes with thionein exhibiting different stabilities and probably different structures. Modifications in the polarograms with the addition of Cd, Zn and the peptidic fragment [56-61] MT I, a molecule intrinsic to the metallothionein structure, were studied. A diagram showing the oxido-reduction potentials corresponding to twelve diflerent electrochemical species is given. DPP allows one to distinguish the chemical forms of compounds (speciation).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070715
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  • 4
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part II: Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56-61] MT I in the presence of cadmium and/or zinc (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 670-673 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Metallothioneins ; related molecules ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An electrochemical study, using differential pulse polarography (DPP), of a peptide Lys-Cys-Thr-Cys-Cys-Ala Thionein Fragment [56-61] MT I (FT) was performed in order to compare the behavior of metallothioneins and that of this less complex molecule, intrinsic to the metallothionein structure. The influence of different parameters, such as the solution pH and the concentration of metal elements, cadmium and zinc was investigated. Two different electrochemical systems were distinguished: in the first one, the mercury electrode itself is involved in the charge transfer steps; in this case, peaks are attributed to the oxidation of the mercury electrode in the presence of the peptide acting as a chelating agent. The second electrochemical system corresponds to the reduction of metal cations, cadmium and zinc, at a dropping mercury electrode either as free ions or complexed by the peptide. The apparent stability constants for complexes of FT with cadmium, zinc and mercury were estimated. The order of affinity is: K′HgFT ≫ K′CdFT 〉 K′ZnFT. The DPP response can be used for elucidation of the chemical forms of compounds (speciation).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070714
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical calculations of β-lactam antibiotics. III. AM1, MNDO, and MINDO/3 calculations of hydrolysis of β-lactam compound (azetidin-2-one ring) (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 681-692 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Semiempirical AM1, MINDO/3, and MNDO methods have been used in the study of the alkaline hydrolysis of β-lactam antibiotics through a base-catalyzed, acyl-cleavage, bimolecular mechanism. In this work, the hydroxyl ion has been chosen as nucleophilic agent and the azetidin-2-one ring like a model of β-lactam antibiotic. The MINDO/3 method does not predict correctly the energies of small rings. This, together with the fact that, like MNDO, it cannot detect the occurrence of hydrogen bonds, gives rise to uncertain estimates of energy barriers. The AM1 method can be considered the most suitable for studying the hydrolysis of β-lactam compounds.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130603
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical calculations of β-lactam antibiotics. V. AM1 calculations of hydrolysis of cephalothin in gaseous phase and influence of the solvent (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 1545-1552 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A comprehensive study on the gas-phase alkaline hydrolysis of cephalosporins by using the semiempirical AM1 method was carried out. Cephalothin was the model compound used on account of the presence of a good leaving group at C(3′). According to the results obtained, the hydrolysis process takes place via a twostep reaction mechanism that involves the formation of an intermediate with a fully open β-lactam ring that still preserves the acetate group. Likewise, the exo methylene end product is chiefly formed by nucleophilic attack on the β-lactam carbonyl group of cephalosporins containing a good leaving group at C(3′). On the other hand, the alternative mechanism involving hydrolysis of the ester function in the side chain at 3′ and subsequent hydrolysis of the resulting β-lactam yieds essentially the corresponding enamine. The presence of a first solvation layer consisting of five water molecules showed that, even though some potential barriers are slightly increased, the mechanism involved is identical to that of the gas-phase hydrolysis of this antibiotic. © John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540141217
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