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  • Atomic, Molecular and Optical Physics  (5)
  • Precipitation  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Precipitation of hydroxyapatite from dilute solutions upon seeding (1977)
    Springer
    Calcified tissue international 24 (1977), S. 47-57 
    Details
    ISSN: 1432-0827
    Keywords: Calcification ; Crystal growth ; Hydroxyapatite ; Kinetics ; Precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The kinetics of precipitation of hydroxyapatite, HA, was studied by seeding dilute supersaturated solutions with well characterized HA crystals. In solutions having initial degrees of supersaturation comparable to those present in human serum, the precipitation rates were related to the thermodynamic driving force (degree of supersaturation with respect to HA) and not to the solution composition. The following relationshipR 0=KA(DS) n , whereR 0=initial precipitation rate, A=amount of seeds, DS=degree of supersaturation, and K andn are parameters obtained from the experimental data, was found to apply over a DS range of 6.6×1010 to 3.3×106. These observations are consistent with the occurrence of a simple growth process on the HA seeds. No evidence for the formation of discrete calcium phosphates other than HA was detected. The Ca/P molar ratio of the precipitating phase, calculated from solution compositions, was invariably higher than that expected for HA; this result is shown to be consistent with an initial adsorption phenomenon. Anomalous kinetic behavior was observed at low seeding levels and may relate to the surface phenomenon described. It is concluded that, most probably, under physiological conditions, formation and remineralization of hard tissues occur through the reported crystal growth process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02223296
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  • 2
    Electronic Resource
    Electronic Resource
    A quantum chemical study of small beryllium hydrides and their radical anions (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 54 (1995), S. 93-98 
    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: Molecular structures of neutral and anionic beryllium hydrides have been investigated using ab initio calculations at the MP2 (geometries) and MP4 (energies)/6 - 31++G** levels. ZPE and (if possible) BSSE correction have been included. While BeH2- is not stable, the radical anion of the beryllium hydride dimer is significantly stabilized with respect to the neutral Be2H4 system. Moreover, this anion can appear in two isomeric forms with comparable stability. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560540204
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  • 3
    Electronic Resource
    Electronic Resource
    A quantum-chemical study of the LiH + LiH⋅- ⇄ LiH2- + Li⋅ reaction (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 643-648 
    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: Parts of the potential energy surface of the title process and related processes have been investigated at the SCF/6-31G**, SCF/6-31++G**, and MP2/6-31++G** levels. The investigated reaction is exothermic (-6.23 kcal/mol, MP4/6-31++G**//MP2/6-31++G** level, ZPE included): A linear intermediate radical anion, Li—H—Li—H⋅-, is significantly stabilized with respect to LiH + LiH⋅- (-38.74 kcal/mol, the same level as above). The BSSE at MP2/6-31++G**//MP2/6-31++G** amounts to 1.8 kcal/mol. The title process seems to be suitable for experimental study in molecular beams.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400507
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio calculations and absolute rate theory. Critical test for a series of elementary gas-phase reactions (1979)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 243-256 
    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: Absolute rate theory (ART) was applied to a series of reactions of the type A+BC → AB+C containing H, F, HF, H2, and F2, trans-cis isomerization of dideuteroethylene, and processes H + CH4 → H2 + CH3 and H′+CH4 → H′CH3 + H. Geometries and energies of activated complexes were taken from the best ab initio studies reported in the literature in which at least a DZ + P basis set was used and a large portion of the correlation energy was included. Vibrational frequencies needed for the zero-point energies and vibrational partition functions were estimated from the reported potential surfaces (HHF and HFF) or evaluated from SCF 4-31G calculations (HFH, FHF, twisted C2H4, and CH5 complexes). Compatability of calculated rate constants with the experimental data was examined.
    Additional Material: 39 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560160205
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  • 5
    Electronic Resource
    Electronic Resource
    Role of entropy in formation of van der Waals complexes (1979)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 257-260 
    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: The TΔS0 term has been estimated for various types of van der Waals molecules and its importance for the stability predictions has been demonstrated. With hydrogen-bonded complexes the absolute values of ΔH0 and TΔS0 are comparable at 289°K. With true van der Waals molecules the TΔS0 term even represents a dominant contribution to ΔG0.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560160206
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  • 6
    Electronic Resource
    Electronic Resource
    Van der Waals molecules: Quantum chemistry, physical properties, and reactivity (1983)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 325-338 
    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: Interaction energies ΔE accompanying the formation of van der Waals (VDW) systems may be estimated by means of the formula ΔE = ΔESCF + BSSE + ED(r-6, r-8, r-10), where BSSE is the basis set superposition error and ED is the dispersion energy in the expanded form. Twenty one stationary points were located on the potential energy surfaces of hydrogen-bonded complexes; of those, 18 were local minima and 3 were saddle points. Thermodynamic characteristics calculated on the basis of molecular constants, quantum chemically generated, were obtained for 12 hydrogen-bonded complexes and for competition equilibria between VDW molecules. The role of the VDW forces in some rate processes and in a prototype of enzyme-substrate interactions is outlined. In connection with enzymic catalysis, the intramolecular discrimination in 1,2-difluorohydrazine, and the stability of hydrogen-bonded complexes in a cation field is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560230128
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