E. A. Castro

National Scientific and Technical Research Council, Buenos Aires, Buenos Aires F.D., Argentina

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Publications (157)174.91 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This communication describes a novel structural-type that could be the basis for a potentially new allotrope of C. The novel structural-type is called “exocyclobutadieneite”, and it is thus named for the 1,3-dimethylenecyclobutane generating fragment that the lattice is based upon. It is a 3-,4-connected network consisting of slightly distorted tetrahedral vertices, and slightly distorted pairs of trigonal planar vertices. The lattice can be derived from a known mineral structure called Cooperite (PtS or PdO) by a topologically isomorphic substitution of trigonal planar atom pairs, for square planar vertexes, in the parent Cooperite unit cell. As such, the new pattern bears a distinct counterpoint relationship with its sibling structural-type called the glitter lattice, which has already been described by the authors in several other papers. And whereas glitter is generated by a topologically isomorphic substitution of trigonal planar atom pairs for the square planar vertices in the Cooperite unit cell, in a fashion that extends the unit cell vertically along the crystallographic c-axis, the exocyclobutadieneite structure is generated, in counterpoint, by such an isomorphic substitution that extends the unit cell horizontally along the a- and b-axes. Both the resulting glitter and exocyclobutadieneite structural-types possess AB $_{2}$ stoichiometry (where A is a tetrahedral vertex and B is a trigonal planar vertex) and both occur in the tetragonal symmetry space group P4 $_{2}$ /mmc (#131). The networks differ, however, in the special positions adopted by the vertices in the resultant unit cells, and in their respective topology, as is evidenced by consideration of the Wells point symbols and Schläfli symbols for the 2 tetragonal networks. These differences are illustrated further in the course of the discussion to follow.
    Journal of Mathematical Chemistry 03/2013; 51(3). DOI:10.1007/s10910-012-0115-6 · 1.27 Impact Factor
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    Pesticides - The Impacts of Pesticides Exposure, 01/2011; , ISBN: 978-953-307-531-0
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    ABSTRACT: The thermal decomposition study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide) was carried out in 2-methoxyethanol solution in the 130-166 °C temperature range. The overall reaction follows a first-order kinetic law up to at least 75% diperoxide conversion. The activation parameters (ΔH# = 22.5 ± 0.7 kcal⋅mol–1 and ΔS# = -25.6 ± 0.5 cal⋅mol–1⋅K–1) for the unimolecular rupture of the O–O bond in the diperoxide molecule were obtained by measuring the remnant diperoxide at different reaction times by the CG technique. Acetone was detected by GC as the major organic product of the reaction. Keywordsacetone cyclic diperoxide-diacetone diperoxide-tetroxane-thermolysis
    Chemistry of Heterocyclic Compounds 12/2010; 45(12):1455-1459. DOI:10.1007/s10593-010-0449-6 · 0.70 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2010; 22(5):21-21. DOI:10.1002/chin.199105021
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2010; 22(5):22-22. DOI:10.1002/chin.199105022
  • 12/2009; 6(4). DOI:10.4314/jophas.v6i4.48556
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    ABSTRACT: QSPR constitutes one of the major areas within computational chemistry and refers to the process of correlating chemical structure of compounds with their physicochemical properties. To achieve this, it employs a wide range of computational programmes and computer softwares including DRAGON, MATLAB, HYPERCHEM and RECKON. Experimental data are first generated from which models or equations are derived that now help to predict the properties of known or unknown compounds whose properties are hitherto unknown. It is a very useful tool in the search for new compounds with improved physicochemical properties like melting point, boiling point, free energy, activation energy, partition coefficient,diffusion coefficient and the like.
    12/2009; 6(4). DOI:10.4314/jophas.v6i4.48560
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    ABSTRACT: Molecular modeling has proved an indispensible tool in exact science research utilizing tested computational theories. One important area of application of molecular modeling is in the physics discipline. It has been used extensively in understudying some physics based principles which have often proved difficult to unravel by laboratory experimental studies. Use is made of theories and models like density functional theory, molecular mechanics method, Thomas Fermi model and molecular dynamics. Several computer softwares have been employed in physics-based modeling and include: Ascalaph, BOSS, CHARMM, COSMOS, Ghemical, GROMOS, GROMACS, MDynaMix, NAMD, STR3DI32, TINKER, Zodiac, X-PLOR.
    12/2009; 6(3). DOI:10.4314/jophas.v6i3.48512
  • M. J. Bucknum, E. A. Castro
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    ABSTRACT: A novel 4,6-connected network, called Hsichengia, is described. The novel network lies in the trigonal space group P3m1 (no. 156), with a = b = 3.447 Å and c = 12.948 Å; these lattice parameters were derived assuming Fe-S composition. It implies a binary AB2 stoichiometry in which the 6-connected A (Fe) atoms have octahedral configuration, and the 4-connected B (S) atoms have tetrahedral configuration. The Hsichengia network seems to be very closely related to the layered MoS2 structure-type, in which puckered MoS2 layers composed of octahedral Mo centers and trigonal-pyramidal S centers are held together by weak van der Waals forces normal to the a and b directions where the MoS2 layers extend. Thus the Hsichengia network can be generated from the MoS2 lattice by the formation of disulfide (S-S) bridges between particular layers, thereby creating a 3-dimensional network from a 2-dimensional layered structure, so that the S atoms are transformed from 3-connected trigonal-pyramidal coordination into fully 4-connected tetrahedral coordination. The Wells point symbol for the Hsichengia network is given by (4666)(4363)2, and it is thus seen to have the translated Schläfli symbol given as (5, 42/3). The latter is identical to that intrinsic to the well-known mineral structure of the pyrite network, FeS2, with the corresponding Wells point symbol (512)(56)2. Therefore, the Hsichengia network may be regarded as a topological isomer of the pyrite network, where topological isomerism is defined as occurring between unique networks possessing the same Schläfli symbol. Phase transformation between the two topological isomers is possible.
    Russian Journal of General Chemistry 11/2009; 79(11):2445-2448. DOI:10.1134/S1070363209110279 · 0.42 Impact Factor
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    María López, Eduardo Castro
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    ABSTRACT: DFT study on the the stability and reactivity of Pt(100) and Pt(111) surfaces modified by nickel UPD monolayer deposition have been carried out. We used the binding energy calculation of bimetallic structures versus the cohesion energy of the bulk adsorbate to quantify the underpotential shift (ΔEupd) to determine the stability of the bimetallic systems. The reactivity of the clean and modified surface was analized by energy levels of the highest occupied molecular orbital (HOMO), softness and local softness. We concluded that the stability of Pt(100)25Ni9 and Pt(111)25Ni10 bimetallic structures cannot be explained by excess of the metal- substrate binding energy but the instability can be explained by structural effects. We found that the modified surfaces are more reactive and the active sites are located in the centre of the cluster which favores the formation of islands of atoms onto these surfaces.
    Nature Precedings 10/2009; DOI:10.1038/npre.2009.3909.1
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    ABSTRACT: Thermal decomposition of formaldehyde diperoxide (1,2,4,5-tetraoxane) in aqueous solution with an initial concentration of 6.22 × 10−3 M was studied in the temperatures range from 403 to 439 K. The reaction was found to follow first-order kinetic law, and formaldehyde was the major decomposition product. The activation parameters of the initial step of the reaction (ΔH ≠ = 15.25 ± 0.5 kcal mol−1, ΔS ≠ = −47.78 ± 0.4 cal mol−1K−1, E a = 16.09 ± 0.5 kcal mol−1) support a mechanism involving homolytic rupture of one peroxide bond in the 1,2,4,5-tetraoxane molecule with participation of the solvent and formation of a diradical intermediate.
    Russian Journal of General Chemistry 10/2009; 79(10):2187-2190. DOI:10.1134/S107036320910017X · 0.42 Impact Factor
  • N. B. Okulik, A. H. Jubert, E. A. Castro
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 09/2009; 40(38). DOI:10.1002/chin.200938216
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    ABSTRACT: The complexation by β-cyclodextrin (β-CD) of three organophosphorus pesticides, fenitrothion, parathion and methylparathion, and of their carboxylic ester analogues was analyzed using PM3 and molecular mechanics methods. The objective was to elucidate structural features and energy changes that accompany the complexation and could possibly affect the hydrolysis process, which is catalyzed by β-CD in the case of carboxylic esters but inhibited for the pesticides, in alkaline medium. The complexation of fenitrothion was further explored, since experiments proved its hydrolysis is relatively less inhibited and progresses mainly through a different pathway than that usually accepted. The results of this study show that complex structures involving esters enable effective interactions between the guest carbonyl and the rim of the host; methylparathion and parathion, however, appear to be deeply included in the cavity of β-CD. Therefore the conditions for a nucleophilic attack by the β-CD are favorable for the carboxylic esters but not for the two pesticides. Different complex geometries resulted for fenitrothion depending on its mode of inclusion in the cavity, none apparently being prone to an attack by the β-CD, but favoring instead the approach of an external OH− group, in agreement with the experiment.
    Journal of Structural Chemistry 08/2009; 50(4):671-679. DOI:10.1007/s10947-009-0103-2 · 0.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 06/2009; 40(22). DOI:10.1002/chin.200922276
  • E V Ortiz, M B Lopez, E A Castro
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    ABSTRACT: The aim of this paper is to report a study of the reactivity of Pt(100) cluster and the same system modified by a nickel tetramer towards the atomic hydrogen adsorption. This study was carried out in the framework of density functional theory which provides global and local indexes that can be used to characterize the reactivity. The analyzed reactivity descriptors were: chemical potential, chemical hardness, electrophilicity index and Fukui function. The results showed that the global reactivity descriptor predicts that the platinum cluster modified by nickel is more reactive than the pure platinum cluster and that the local Fukui function provides information about the most susceptible site to electrophilic attack in platinum cluster.
    Journal of Physics Conference Series 05/2009; 167(1):012021. DOI:10.1088/1742-6596/167/1/012021
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    ABSTRACT: The review contains new data on tautomerism of organic compounds belonging to different classes, which were obtained by mass spectrometry and confirmed by quantum-chemical calculations.
    Russian Journal of Organic Chemistry 11/2008; 44(12):1725-1736. DOI:10.1134/S1070428008120014 · 0.68 Impact Factor
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    ABSTRACT: The aim of this work is to present results derived from experimental IR and UV spectra and theoretical studies of DPCH, in order to get a more deeper insight on the physicochemical properties of this compound to gain a more deep knowledge of its action, helping in the design of new compounds with antimalaric effects. Experimental results are analyzed on the basis of theoretical calculations, which allow to derive suitable interpretations of spectral data.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 10/2008; 70(4):775-9. DOI:10.1016/j.saa.2007.09.018 · 2.13 Impact Factor
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    ABSTRACT: Thermal decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane was examined in methanol solution (1.69×10−2 M) containing cuprous ions (5.05×10−7 M) in the temperature range from 130 to 166°C using UV spectroscopy as analytical method. The ion-catalyzed reaction follows first-order kinetics with respect to the peroxide and added cuprous ions. The temperature effect on the rate of thermal decomposition of the title compound was described by the corresponding Arrhenius equations, and its stability in solution was estimated on a quantitative level. The activation parameters of the initial step of decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane were determined (ΔH ≠ = 14.7±0.8 kcal mol−1; ΔS ≠ = −38.9±1.4 cal mol−1 K−1; ΔG ≠ = 31.0±0.8 kcal mol−1). Electron-transfer mechanism was proposed for the reaction under study.
    Russian Journal of General Chemistry 06/2008; 78(6):1273-1276. DOI:10.1134/S1070363208060303 · 0.42 Impact Factor
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    ABSTRACT: The apparent acidity constant of p-hydroxybenzophenone, which is a practically insoluble drug in water but of great pharmaceutical interest, was determined by reversed-phase high-performance liquid chromatography in organic solvent - water mixtures (acetonitrile-water, ethanol-water, and methanol-water), varying the reaction medium permittivity in the interval 56 to 70, at constant ionic strength (0.050) and temperature (30 °C). A combined glass electrode calibrated with aqueous standard buffers was used to obtain pH readings based on the concentration scale (swpH). The pKa values from chromatographic data were obtained using the Hardcastle-Jano equation. Moreover, excellent linear relationships between the pKa values and solvation properties of the reaction medium (relative permittivity and Acity) were used to derive acid dissociation constants in aqueous solution. It has been concluded that the pKa values extrapolated from such solvent-water mixtures are consistent with each other and with previously reported measurements. In addition, the molecular structures of all the chemical species involved in the acid-base dissociation equilibrium studied were calculated with a B3LYP/6-311++G(d,p) method that makes use of the polarizable continuum model (PCM). Taking into account the theoretical pKa values, the conclusions obtained match our experimental determinations.
    Canadian Journal of Chemistry 05/2008; 86(5-86):462-469. DOI:10.1139/v08-040 · 1.01 Impact Factor

Publication Stats

644 Citations
174.91 Total Impact Points

Institutions

  • 2013
    • National Scientific and Technical Research Council
      Buenos Aires, Buenos Aires F.D., Argentina
  • 2006–2009
    • University of Buenos Aires
      Buenos Aires, Buenos Aires F.D., Argentina
  • 1987–2009
    • National University of La Plata
      • • Facultad de Ciencias Exactas
      • • Departamento de Química
      • • Instituto de Investigaciones Físicoquímicas Teóricas y Aplicadas (INIFTA)
      Eva Perón, Buenos Aires, Argentina
  • 2008
    • IVI Buenos Aires
      Buenos Aires, Buenos Aires F.D., Argentina
  • 2005
    • Universidad de la Cuenca del Plata
      Eva Perón, Buenos Aires, Argentina
  • 2001–2002
    • National University of the Northeast
      • Faculty of Natural and Exact Sciences and Surveying
      Corrientes, Corrientes, Argentina
  • 1998
    • Universidad Nacional de Mar del Plata
      • Departamento de Química
      Mar de Plata, Buenos Aires, Argentina