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  • 1
    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: In order to understand the interaction mode of benzodiazepine ligands with their peripheral binding sites, the structural and electronic properties of a benzodiazepine Ro 5-4864, Alpidem, PK 11195, and some analogs are characterized at the ab initio molecular orbital level. Conformational and electronic data, with a particular emphasis on electrostatic aspects, i.e., molecular electrostatic potentials, Mulliken atomic charges, and potential-derived charges, are used as input within molecular superimpositions to elaborate the pharmacophoric elements for the peripheral benzodiazepine ligands. A putative three-dimensional (3-D) steric and electronic model is proposed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 149-165 
    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: Using molecular orbital methods, we propose various models of interactions between GABA or analogs (TACA, muscimol, isomuscimol) and an hypothetical receptor molecular fragment, a methylguanidinium ion. The respective geometries of the GABA-, TACA-, muscimol-, and isomuscimol-methylguanidinium ion complexes are optimized using the semi-empirical MNDO method. Stabilization energies of the complexes obtained by substraction of the heats of formation of the optimized complexes from those of the optimized isolated molecules differentiate the behavior of the anionic heads between the agonist and antagonist compounds. Affinity and stabilization are confirmed by computing ab initio STO-3G ionization potentials and interaction energies taking into account counterpoise corrections. Results show a decrease of the interaction energy from GABA and TACA (-54.9 and -49.4 kcal/mol) to isomuscimol (-35.6 kcal/mol), via muscimol (-46.0 kcal/mol). The low interaction energy of the 5-isoxazolols as isomuscimol compared to the 3-isoxazolols, as muscimol, may explain their antagonist character.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 1291-1326 
    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: In this paper, we present Monte Carlo and molecular dynamics simulations of water molecules inside a ferrierite-type framework. Detailed analyses of the energetic, structural, and dynamical properties are carried out and compared with liquid water results in order to study the influence of the framework on the physisorbed water molecules.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 211-225 
    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: Conformational analyses of large molecules as fatty acids and triglycerides are usually amenable by molecular mechanics. A correct evaluation of the electrostatic energy term is thus crucial in determining reliable results. In this contribution, we have considered the most abundant fatty acids in biomembranes, i.e., lauric, stearic, oleic, and elaidic acid, and the corresponding triglycerides, i.e., trilaurin, tristearin, triolein, and trielaidin, and estimated the Mulliken and potential-derived charges both at the semiempirical AM1 and ab initio HF MO STO-3G level. Atomic charges obtained by the Mulliken population analysis do not take into account the full geometry of the molecule. On the contrary, the change of conformation, due to different chains length or the presence of a trans or cis double bond, greatly influences the repartition of the potential-derived charges. A systematic comparative analysis shows that charges calculated by AM 1 are not suitable because as they do not reproduce potential-derived charges obtained by ab initio. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 57-77 
    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: Triglycerides, the major components of neutral lipids, are important biomaterials, as they take part in the edification of membranes. In this perspective, the consideration of biological membranes at a molecular level requires detailed knowledge of the preferred conformations of the triglycerides in their various polymorphic forms. In this context, we adapted a molecular modeling approach, which allows the simulation the three-dimensional structure of the different polymorphic forms (α, β′, and β) valid for any triglyceride. Their conformational analysis is based on molecular mechanics calculations, as follows: First, a large number of isolated molecular structures were generated in a systematic structuretree analysis. For their generation, atomic charges within the Mulliken scheme, calculated at the ab initio RHF-LCAO-MO-SCF level (6-31G), were considered. The lowest-energy conformers were, next, correlated with experimental data (NMR, powder X-ray diffraction) in order to select α, β′, or β structures. Then, in a second step, these selected conformers were assembled, in head-to-tail dimers in order to form a monolayer. For this step, the use of potential-derived atomic charges is known to be more suitable. In this study, we consider triglycerides derived from the predominant fatty acids, i.e., stearic, elaidic, and oleic acids. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 349-352 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Formulas fully exploiting the periodicity symmetry of the electron density of polymers are deduced. They are shown to lead to efficient algorithms for the evaluation of Coulomb and exchange interactions in those systems.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 680-693 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An algorithm for predicting the conformations of strained molecules using Artificial Intelligence techniques is described and illustrated with some typical examples.
    Additional Material: 21 Ill.
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  • 8
    Publication Date: 2020-03-19
    Description: Ilopango caldera erupted episodically at least 13 tuff-forming eruptions with a minimum estimate volume of 1–5km3 DRE per eruption, reaching up to 150km3 DRE for the first caldera-forming eruption. All tuffs are of dacitic-rhyolitic composition. The complete pyroclastic sequence spans a range in time from 1.785 to 0.0015 Ma, and based on stratigraphy and geochronology constraints can be divided into three formations: the Comalapa, Altavista and Tierras Blancas formations. In this work, we focus on the members of the newly described Altavista Formation (middle part of Ilopango caldera volcanic sequence), which consist of six con- solidated pyroclastic deposits or tuffs. Each tuff corresponds to a specific eruption followed by a period of quiescence during which soil beds were developed on the deposits. The ages of the Altavista Formation ranges from 918 to 257ka, based on new 40Ar/39Ar, U/Pb-zircon, and U/Th-zircon analyses. The tuffs of this for- mation show similar characteristics in mineralogy and composition. They are calcalkaline, rhyodacitic tuffs, with plagioclase, clinopyroxene, and hornblende. From field mapping and descriptions of the deposits, we have inferred the eruptive styles that include pumice fallouts, pyroclastic density currents and also hydromag- matic explosions. The common vent in all tuffs was the Ilopango caldera and each member of the Altavista Formation could correspond to a caldera collapse event, except for one of the six eruptions. The volume of each member was estimated to be 〉30km3 DRE, which is the same order of magnitude than that estimated for the Tierra Blanca Joven (TBJ) eruption at about 1500 B. P, and smaller than those of the ignimbrites of the Comalapa Formation, the first three members of the Ilopango caldera reported previously. The tuffs of the Altavista Formation are visible up to 15–20 km away from the caldera's topographic margin. The recurrence interval of large explosive events at the Ilopango caldera was established by integrating the stratigraphic and geochronologic data of all 13 ignimbrites and pumice fallouts erupted from Ilopango caldera since the first one at 1.78 Ma to the last explosive event (TBJ).
    Description: Published
    Description: 100-119
    Description: 1V. Storia eruttiva
    Description: JCR Journal
    Keywords: Stratigraphy of volcanic deposits ; Ignimbrite ; Central America Volcanic Arc ; Pull-apart graben ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
    Publication Date: 2019-02-25
    Description: The Ilopango caldera is located in the central part of El Salvador, within the right-lateral El Salvador Fault System (ESFZ) and adjacent to the capital city of San Salvador. The caldera has a polygonal shape of 17 × 13 km and hosts an intra-caldera lake. Ilopango caldera had multiple collapse eruptions that formed widespread and voluminous silicic ignimbrites. Volcanic activity of the caldera has been controlled by strike-slip faults of the ESFZ. In this work we present the geological characteristics of the first three ignimbrite-forming eruptions of Ilopango caldera, pro- viding an interpretation of the origin and initial stages of the volcanic evolution of this caldera complex. An initial extensional regime of the ESFZ possibly developed a graben at or near the actual Ilopango caldera, where the graben's master faults worked as fissure vents during the first caldera collapse. The Olocuilta Ignimbrite was emplaced at 1.785 ± 0.01 Ma BP, with a Dense Rock Equivalent (DRE) volume N 50 km3 (probably ~300 km3). The ESFZ stress gradually changed from extensive to transtensive, inducing the second collapse associated with a pull-apart caldera, producing the Colima Ignimbrite at 1.56 ± 0.01 Ma BP, with a DRE volume of N11 km3. The transtensive regime increased along the ESFZ, producing the third collapse in the pull-apart graben caldera apparently affected by the newly formed strike-slip San Vicente Fault. This phase corresponds to the ex- plosive eruption that formed the Apopa Ignimbrite at ~1.34 Ma BP, with N9 km3 DRE volume. The latter ignim- brite marks a change in the eruptive style producing hydromagmatic pyroclastic flows followed by a dense ignimbrite with coignimbrite lithic breccias. These features suggest the involvement of water that could come from a paleoIlopango lake within the caldera depression associated with the second caldera collapse at 1.56 Ma BP. Ilopango is thus a multistage caldera system associated with the largest explosive events registered in El Salvador so far.
    Description: Published
    Description: 1-19
    Description: 1V. Storia eruttiva
    Description: JCR Journal
    Keywords: Central America Volcanic Arc ; Tecton Fault ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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