E. A. Castro

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

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Publications (165)140.14 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 01/2013; 51(3). · 1.23 Impact Factor
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    Pesticides - The Impacts of Pesticides Exposure, 01/2011; , ISBN: 978-953-307-531-0
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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;
  • 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.
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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 01/2009; 79(10):2187-2190. · 0.43 Impact Factor
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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 01/2009; 40(22).
  • 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 01/2009; 40(38).
  • Int. J. Chem. Model. 01/2009; 1(2):221.
  • 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 01/2009; 79(11):2445-2448. · 0.43 Impact Factor
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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. · 0.51 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. · 1.98 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. · 0.96 Impact Factor
  • M. J. Bucknum, E. A. Castro
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    ABSTRACT: A novel hypothetical 4,8-connected tetragonal crystalline structure with a ternary stoichiometry AB2C2 is described. The novel pattern belongs to the space group P4/mmm (no. 123). The structure includes novel 8-connected anticube-centered vertices along with ordinary 8-connected cube-centered and 4-connected square-planar vertices. The structure may be representative of a ternary bimetallic fluoride, such as MRe2F2 or MTa2F2, where M is an alkaline-earth metal. The novel structure is unusual due to the absence of strains.
    Russian Journal of General Chemistry 01/2008; 78(1):35-36. · 0.43 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 01/2008; 78(6):1273-1276. · 0.43 Impact Factor
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    ABSTRACT: The influence of temperature and solvent effects on the stability of the complex formed by two molecules of 1,2-dihydroxybenzene and one molecule of AlCl3 were experimentally and theoretically studied, by means of UV spectroscopic methods and Density Functional Theory methods. The changes of the stability constant with the temperature were analyzed using the van't Hoff equation, while the variations with the permittivity of the reaction medium were explained with an equation proposed by us. The experimental and theoretical data obtained allowed proving that the increase in the hydrogen-bond donor ability of the solvents favors a higher thermodynamic stability of the reactants with respect to the complex and, therefore a decrease in the corresponding stability constant. The non-planar structure proposed for the 2:1 ligand-metal complex is coherent with the small batochromic shift experimentally observed. In the complex molecule, the planes containing the phenyl rings are tilted by approximately 89 degrees with each other. It was concluded that the complexation reaction is an endothermic process in which the solvent-solute interactions play an essential role.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 11/2007; 68(2):387-93. · 1.98 Impact Factor
  • Anales des la Asociacion Quimica Argentina 12/2006; 94(4-6):31-45.
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    ABSTRACT: We report the experimental preparation of the 1,3-butanal-1,2,4,5-tetroxane by oxidation of glutataldehyde with oxygen peroxide in presence of concentrated sulfuric acid, following the Bayer and Viller method modified by Jorge et al. The UV and IR spectra are studied from the experimental and theoretical standpoint. A rather complete vibrational assignment was performed and the nature of the electronic transitions was discussed in detail.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 07/2006; 64(3):717-21. · 1.98 Impact Factor
  • E. A. Castro, D. A.J. Barbiric
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    ABSTRACT: This review deals with the panorama of current theoretical methods applied to study chemical and physical chemistry properties of cyclodextrins and their inclusion complexes. This study covers from 1998 to the present, with the exception of some papers not included in a rather recent review.
    Current Organic Chemistry 04/2006; 10(7):715-729. · 3.04 Impact Factor
  • M. J. Bucknum, E. A. Castro
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    ABSTRACT: In a previous report, the approximate crystalline structure and electronic structure of a novel, hypothetical hexagonal carbon allotrope has been disclosed. Employing the approximate extended Hückel method, this C structure was determined to be a semiconducting structure. In contrast, a state-of-the-art density functional theory (DFT) optimization reveals the hexagonal structure to be metallic in band profile. It is built upon a bicyclo[2.2.2]-2,5,7-octatriene (barrelene) generating fragment molecule and is a Catalan network, with the Wells point symbol (66)2(63)3 and the corresponding Schläfli symbol (6, 3.4). As the network is entirely composed of hexagons and, in addition, possesses hexagonal symmetry, lying in space group P6/mmm (space group #191), it has been given the name hexagonite. The present report describes a density functional theory (DFT) optimization of the lattice parameters of the parent hexagonite structure, with the result giving the optimized lattice parameters of a = 0.477 nm and c = 0.412 nm. A calculation is then reported of a simple diffraction pattern of hexagonite from these optimized lattice parameters, with Bragg spacings enumerated for the lattice out to fourth order. Results of a synchrotron diffraction study of carbon nanotubes which underwent cold compression in a diamond anvil cell (DAC) to 100 GPa, in which the carbon nanotubes have evidently collapsed into a hitherto unknown hexagonal C polymorph, are then compared to the calculated diffraction pattern for the DFT optimized hexagonite structure. It is seen that a close fit is obtained to the experimental data, with a standard deviation over the 5 matched reflections being given by σx = 0.003107 nm/reflection.
    Journal of Chemical Theory and Computation - J CHEM THEORY COMPUT. 03/2006; 2(3).
  • Trends in Applied Sciences Research 02/2006; 1(2):113-114.

Publication Stats

367 Citations
140.14 Total Impact Points

Institutions

  • 2013
    • National Scientific and Technical Research Council
      Buenos Aires, Buenos Aires F.D., Argentina
  • 2011
    • Universidad Nacional del Noroeste de la Provincia de Buenos Aires
      Junín, Buenos Aires, Argentina
  • 2005–2009
    • Universidad de la Cuenca del Plata
      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
  • 2007
    • Universidad Nacional de San Luis
      • Área de Química Física
      San Luis, San Luis, Argentina
  • 2001–2006
    • National University of the Northeast
      • Faculty of Natural and Exact Sciences and Surveying
      Corrientes, Corrientes, Argentina
  • 1998
    • Universidad Nacional de Mar del Plata
      Mar de Plata, Buenos Aires, Argentina
  • 1989
    • Uppsala University
      Uppsala, Uppsala, Sweden