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  • 1
    Electronic Resource
    Electronic Resource
    On the problem of a suitable definition of the cluster in embedded-cluster treatments of defects in crystals (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4195-4204 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbed-cluster embedding scheme [J. Chem. Phys. 92, 7448 (1990)] adopts a self-consistent procedure where, at each cycle, a molecular cluster solution is calculated, and subsequently corrected for realizing its coupling to the crystalline environment. In the present work, it is shown that a proper design of the cluster is of critical importance for the scheme to work satisfactorily. Indications are given for defining clusters that are at the same time "self-satisfied,'' and optimally fitted to the environment, so that correction terms are minimized. The procedure is tested in the case of defects in crystalline silicon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463922
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio approach to molecular crystals: A periodic Hartree–Fock study of crystalline urea (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7402-7411 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of crystalline urea (two molecules, 16 atoms per unit cell) is investigated at an ab initio level with CRYSTAL, a Hartree–Fock linear combination of atomic orbitals (LCAO) program for periodic systems. The influence of the basis set and of the computational parameters which control the treatment of the Coulomb and exchange series and the reciprocal space integration is documented; results include total and interaction energy, Mulliken analysis data and interaction (solid minus molecules) density maps, band structure, and density of states. The crystal field modifies the electronic structure of the isolated molecule, the main effect being an increase in the ionicity of bonds. The interaction energy obtained with a 6-21** basis set is 28 kcal/mol, (16 kcal/mol after a correction of the basis set superposition error by using the counterpoise method) to be compared with 21±0.5 kcal/mol from experiment. This preliminary application shows that accurate ab initio calculations of hydrogen bonded molecular crystals with a relatively small unit cell (less than 30 atoms/cell) are now within reach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458592
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  • 3
    Electronic Resource
    Electronic Resource
    Adsorption energies of NH3 and NH+4 in zeolites corrected for the long-range electrostatic potential of the crystal (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5865-5874 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The calculation of adsorption energies in zeolites in the cluster approximation has the advantage of a reduced computational effort compared to that of the periodic approach. However, in the cluster approximation, the long-range electrostatic effects of the infinite crystal are ignored and there are boundary effects. In order to remove a part of the disadvantages of the cluster approach, we developed a method to embed a cluster in a zeolite crystal by imposing an electrostatic potential on it. This potential adds the long-range electrostatic effects of the crystal and subtracts the electrostatic potential of the boundary of the cluster. It is calculated from the charge distribution of the crystal obtained with an ab initio calculation using the crystal program. We calculated the adsorption energies of NH3 and NH+4 on three different clusters embedded in the potential of a chabazite crystal, and we have compared them with the adsorption energies of NH3 and NH+4 in the crystal. If a cluster is used that has dangling bonds four, or more, bonds away from the adsorbate, i.e., the adsorption site is described well covalently, embedding the cluster reduces the error in adsorption energies (relative to the crystal calculations) from ≈20 to ≈2–3 kJ/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467303
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  • 4
    Electronic Resource
    Electronic Resource
    Dose-dependent absorption and elimination of gamma-hydroxybutyric acid in healthy volunteers (1993)
    Springer
    European journal of clinical pharmacology 45 (1993), S. 353-356 
    Details
    ISSN: 1432-1041
    Keywords: Gamma-hydroxybutyric acid ; pharmacokinetics ; dose-proportionality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Gamma-hydroxybutyric acid (GHB) is effective in treatment of the alcohol and opiate withdrawal syndromes. Its absorption and disposition kinetics have been studied in 8 healthy male volunteers following oral administration of single doses of 12.5, 25 and 50 mg kg−1. The AUC increased disproportionately with the dose and so the apparent oral clearance decreased significantly as the dose was increased, whereas the terminal half-life and mean residence time increased. The peak plasma concentrations normalised to the lowest dose fell significantly with increasing doses, whilst the corresponding peak times increased. These findings suggest that both the oral absorption and the elimination of GHB are capacity-limited processes. GHB did not bind to significant extent to plasma proteins over the therapeutic concentration range. The pharmacokinetic parameters in healthy volunteers were not significantly different from those previously observed in alcohol-dependent patients with compensated alcoholic liver disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00265954
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of age on single- and multiple-dose pharmacokinetics of erythromycin (1990)
    Springer
    European journal of clinical pharmacology 39 (1990), S. 161-164 
    Details
    ISSN: 1432-1041
    Keywords: erythromycin ; pharmacokinetics ; steady-state ; elderly subjects ; age effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of age on the pharmacokinetics of erythromycin was investigated by comparing its kinetic behaviour in eight young healthy adults and eight healthy elderly subjects after single and repeated oral doses of erythromycin stearate 1 g b.d. for 7 doses. The peak serum concentration and area under the serum concentration-time curve (AUC) were significantly greater in the elderly subjects than in the young controls after single and multiple doses. Accordingly, the apparent oral clearance was lower in the elderly subjects (0.31 vs 0.64 and 0.22 vs 0.69 l·h−1·kg−1 after the first and seventh administration, respectively). The mean elimination half-life was significantly longer in the elderly group only after multiple dosing (4.8 vs 2.3 h). No age-related difference was observed in the time to peak serum concentration and apparent volume of distribution. The multiple-dose regimen resulted in an almost two-fold accumulation of erythromycin in the older individuals and no accumulation in the young adults. Mean drug accumulation in elderly subjects at steady state was 43% greater than was predicted from the AUC after the first dose, suggesting a time-dependent reduction in both systemic and presystemic clearance. The results indicate that the metabolic elimination processes for erythromycin are impaired in normal elderly subjects and suggest that caution is required on administering a high dose of it to aged people.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280051
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  • 6
    Electronic Resource
    Electronic Resource
    Alprazolam attenuates metabolic stress-induced neuroendocrine and behavioral effects in humans (1991)
    Springer
    Psychopharmacology 104 (1991), S. 479-484 
    Details
    ISSN: 1432-2072
    Keywords: Metabolic stress ; Glucoprivation ; Benzodiazepines ; Cortisol ; Behavioral response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of benzodiazepine drugs and the role of their recognition site, the GABAA/benzodiazepine receptor, in acute glucoprivic stress are not known. In the present study, the effects of acute glucoprivation were examined in ten healthy human subjects. Glucoprivation was induced by infusion of the glucose analog, 2-deoxyglucose (2DG), at doses sufficient (50 mg/kg) to competitively inhibit glucose metabolism. In addition, the effects of the triazolobenzodiazepine alprazolam (1.5 mg) on the 2DG-induced stress response was assessed. 2DG produced significant elevations in plamsa cortisol (P=0.0001) and glucose (P=0.0003) levels. Alprazolam pretreatment attenuated the 2DG-related cortisol elevations (P=0.05) but did not effect 2DG-induced glucose increases. In addition, 2DG caused significant increases in hunger (P=0.01) and thirst (P=0.001), and alprazolam significantly blunted both of these responses. Lastly, 2DG had significant effects on heart rate, diastolic blood pressure and body temperature (P〈0.05). Alprazolam did not effect these physiologic indices. The significance of these data for the mechanisms involved in acute glucoprivic stress are examined and the implications of the data for the pathophysiology of affective illness and eating disorders are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02245653
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  • 7
    Electronic Resource
    Electronic Resource
    A quantum mechanical study of the perovskite structure type of MgSiO3 (1993)
    Springer
    Physics and chemistry of minerals 20 (1993), S. 407-414 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The periodic ab-initio Hartree-Fock Self Consistent Field program CRYSTAL has been used to study the electronic structure and equation of state of MgSiO3 perovskite. Three space groups were considered: Pm3m (cubic; ideal untilted SiO6 octahedra), P4/mbm (tetragonal; the octahedra are allowed to deform along and rotate about the crystallographic c cell edge) and Pbnm (orthorhombic; octahedra are allowed to deform along and rotate about the three cell edges). The calculated orthorhombic structure is the most stable, in agreement with experiment. The relative stability of the three structures and the effect of pressure on the SiO6 octahedra is interpreted in terms of bond population data and is mainly determined by the oxygen-oxygen repulsion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203110
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  • 8
    Electronic Resource
    Electronic Resource
    Letter to the Editor (1993)
    Springer
    Infection 21 (1993), S. 131-131 
    Details
    ISSN: 1439-0973
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01710751
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  • 9
    Electronic Resource
    Electronic Resource
    Density matrix of crystalline systems. II. The influence of structural and computational parameters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 419-433 
    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 one-electron density matrix (DM) of a number of crystalline systems - lithium, graphite, boron nitride, silicon, and beryllium - are considered here, as resulting from Hartree-Fock-SCF-LCAO calculations. The influence of structural and computational parameters is discussed. It is shown in particular why the structure of chemical bonds in semiconductors leads to an oscillating long-range behavior of the DM, similar to that observed in metals, where these oscillations are related to the very existence of a Fermi surface. Concerning computational parameters, the influence of the density of sampling k points and of basis set on the calculated DM is considered; it is shown that the choice of the basis set is not a very critical one as far as the DM range is concerned. Some critical aspects of the interrelation between DM range and exchange part of the Fock Hamiltonian are analyzed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380305
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  • 10
    Electronic Resource
    Electronic Resource
    Trace elements in a profile of the unsaturated zone of the São Paulo Basin (1994)
    Springer
    Journal of radioanalytical and nuclear chemistry 179 (1994), S. 259-266 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This study comprises Tertiary sediments (clays, silts, and fine clayey sands) from the unsaturated zone of the Experimental Station in the University of São Paulo, taken from a nine meters depth profile; ten samples were separated in bulk and 〈53 μm fractions. Chemical composition was determined by INAA to ascertain the distribution of trace elements throughout the sediment deposition, and to establish the background parameters, useful for mobilization studies of such elements after industrial waste disposal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02040160
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