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  • Digitale Medien  (5)
  • AM1  (1)
  • Antitumor agents  (1)
  • Cobalt(III) complexes  (1)
  • Diol formation / Enolization  (1)
  • Electrostatic potential  (1)
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Materialart
  • Digitale Medien  (5)
Erscheinungszeitraum
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    The Important Role of Active Site Water in the Catalytic Mechanism of Human Carbonic Anhydrase II – A Semiempirical MO Approach to the Hydration of CO2 † (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 355-365 
    Details
    ISSN: 0948-5023
    Schlagwort(e): Keywords Human Carbonic Anhydrase II ; Semiempirical MO Theory ; AM1 ; Enzyme Catalysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The approach of CO2 to a series of active site model complexes of human carbonic anhydrase   II (HCAII) and its catalytic hydration to bicarbonate anion have been investigated using semiempirical MO theory (AM1). The results show that direct nucleophilic attack of zinc-bound hydroxide to the substrate carbon occurs in each model system. Further rearrangement of the bicarbonate complex thus formed via a rotation-like movement of the bicarbonate ligand can only be found in active site model systems that include at least one additional water molecule. Further refinement of the model complex by adding a methanol molecule to mimic Thr-199 makes this process almost activationless. The formation of the final bicarbonate complex by an internal (intramolecular) proton transfer is only possible in the simplest of all model systems, namely {[Im3Zn(OH)]+·CO2}. The energy of activation for this process, however, is 36.8 kcal·mol−1 and thus too high for enzymatic catalysis. Therefore, we conclude that within the limitations of the model systems presented and the level of theory employed, the overall mechanism for the formation of the bicarbonate complex comprises an initial direct nucleophilic attack of zinc-bound hydroxide to carbon dioxide followed by a rotation-like rearrangement of the bicarbonate ligand via a penta-coordinate Zn2+ transition state structure, including the participation of an extra active site water molecule.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s008940050094
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  • 2
    Digitale Medien
    Digitale Medien
    Kinetic, structural and electrostatic aspects of the reduction of pentacyanoferrate(III) complexes by myoglobin (1999)
    Springer
    JBIC 4 (1999), S. 302-310 
    Details
    ISSN: 1432-1327
    Schlagwort(e): Key words Pentacyanoferrate(III) complexes ; Oxymyoglobin ; Electron transfer ; Kinetics ; Electrostatic potential
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract  The mechanism of the reduction of pentacyanoferrate(III) complexes by oxymyoglobin has been studied by conventional and high-pressure kinetic methods, and also by structural modelling. The results of this and an earlier study show that an outer-sphere mechanism is operating for electron transfer between oxymyoglobin and FeIII(CN)5L n –, independent of the lability of the ligand L. The electron transfer process is preceded by precursor formation at a specific site on the protein close to the protein heme pocket.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s007750050316
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  • 3
    Digitale Medien
    Digitale Medien
    X-ray and Solution Structure of Inosine 5' -Monophosphate Coordinated to (Ethylenediamine)palladium(II).  - the Importance of Intramolecular Hydrogen Bonding (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1551-1555 
    Details
    ISSN: 0009-2940
    Schlagwort(e): Antitumor agents ; Nucleotides ; Palladium ; Hydrogen bonds ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The compound [Pd(en)(5′-IMP-N7)2].11 H2O, where 5′-IMP = inosine 5′-monophosphate, crystallizes in the tetragonal space group P4322 with the unit cell parameters: a = b = 12.060(5) and c = 28.510(5) Å, V = 4147(3) Å3, Z = 4. A head-to-tail orientation with A configuration is observed for the nucleotides which are coordinated through the N(7) positions such that d[Pd-N(7)] = 2.053(8) Å. The sugar moieties exhibit anti orientations toward the purine bases while their pukkers adopt C(3)′-endo conformation. The overall conformation about the phosphate backbone is gauche+. Intramolecular hydrogen bonding is observed between the phosphates and the NH groups of the en ligand with a donor-acceptor distance of 2.88 Å. The coordination mode of the solid-state structure is shown to be identical to that observed by 1H-NMR spectroscopy in solution under slightly acidic conditions, where the N (l) positions of the nucleotides are protonated. The results are discussed in reference to closely related systems reported in the literature with emphasis on the importance of hydrogen bonding in such complexes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cber.19971301032
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  • 4
    Digitale Medien
    Digitale Medien
    A Spectroscopic and Mechanistic Study of the Enolization and Diol Formation of Hexafluoroacetylacetone in the Presence of Water and Alcohol (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 315-320 
    Details
    ISSN: 0009-2940
    Schlagwort(e): Acetylacetone, hexafluoro- ; Diol formation / Enolization ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Eine spektroskopische und mechanistische Untersuchung der Enolisierung und Diol-Bildung von Hexafluoracetylaceton in Gegenwart von Wasser und AlkoholDie Reaktionen von Hexafluoracetylaceton (Hfac) (6) mit Wasser, Methanol, Ethanol und Isopropylalkohol wurde im einzelnen anhand von 1H-, 13C-, 17O-, 19F-NMR- und UV-VIS-Spektroskopie untersucht. Dabei konnten die Zwischen- und Reaktionsprodukte bei der Enolisierung und Diol-Bildung spektroskopisch identifiziert werden. Die vorgeschlagenen Reaktionswege werden unter Bezug auf früher in der Literatur berichtete Daten diskutiert. Ein wichtiges Ergebnis dieser Untersuchung ist der direkte Nachweis für die Bildung der Addukt-Spezies Hfac(OH)4 (10), Hfac(OMe)2 (13a) und Hfac(OEt)2 (13b).
    Notizen: The reactions of hexafluoroacetylacetone (hfac) (6) with water, methanol, ethanol, and isopropyl alcohol were studied in detail using 1H-, 13C-, 17O-, 19F-NMR, und UV-VIS spectroscopy. The reported spectra enable the identification of intermediate and product species, and allow a mechanistic analysis of the enolization and diol formation. The suggested mechanisms are discussed with reference to earlier data reported in the literature. An important feature of this study is the direct evidence presented for the formation of the adduct species hfac(OH)4 (10), hfac(OMe)2 (13a), and hfac(OEt)2 (13b).
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cber.19891220218
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  • 5
    Digitale Medien
    Digitale Medien
    Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes - The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 643-650 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cobalt(III) complexes ; Tetrapodal pentadentate ligand ; Hydrolysis ; Kinetics ; Mechanism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Multi-wavelength stopped-flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square-pyramidal coordination cap [L = 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second-order kinetics, rate = kOH [2][OH-], with kOH = 0.139 ± 0.001 M-1s-1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M-1s-1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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