Abstract:
The generation and reactivity of a new 1-methyl-5-(trifluoromethyl)azafulvenium methide are described. Under microwave-induced pyrolysis conditions this intermediate could be trapped by dipolarophiles, acting either as a 4π or as an 8π dipole. Quantum chemical calculations carried out at the DFT level of theory allowed the rationalization of the results observed in the cycloaddition of 1-methyl-5-(trifluoromethyl)azafulvenium methide and N-substituted maleimides. The study revealed that for 1,7-cycloadducts the major products are obtained in the trans configuration through the unusual exo-cycloaddition mode, whereas for 1,3-cycloadducts the cis counterparts are obtained from this unexpected approach. In addition, under flash vacuum pyrolysis or conventional thermolysis conditions 1-methyl-5-(trifluoromethyl)azafulvenium methide undergoes an allowed suprafacial sigmatropic [1,8]H shift leading to the formation of 2-methyl-3-(trifluoromethyl)-1-vinyl-1H-pyrrole.
Author affiliation: Argüello, Gustavo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Authors: Borosky, Gabriela Leonor; Laali, Kenneth K.
Publication Date: 2009.
Language: English.
Abstract:
A density-functional theory (DFT) study aimed at understanding structure-reactivity relationships in the oxidized metabolites of isomeric dibenzopyrenes (DBPs) and naphthopyrene (NP) is reported, These large polycyclic aromatic hydrocarbons (PAHs) contain a pyrene moiety and two benzannelated rings or a naphtho ring, and depending on the annelation mode, possess a fjord region (DB[a,i]P and N[1,2-Ci]P) or two or three bay-regions (DB[a, h]P, DB[a,i]P, and DB[a,e]P). Relative energies of the resulting carbocations were examined and compared, taking into account the available biological activity data on these compounds. Geometrical, electronic and conformational issues were considered. Charge-delocalization modes in the resulting carbocations were deduced, by the changes in charges derived from, natural population analysis (NPA). The reported biological activity of these toxic PAHs was found, to correlate with the degree of deviation from planarity of the aromatic system, in accord with the higher bioactivity of the fjord- and methylated bay-region compounds. On the other hand, relative formation of the possible carbocations derived from, each PAH, as well as the activity order for compounds presenting similar distortions, were explained by their relative carbocation stabilities. The covalent adducts formed via the fjord-region diol epoxide of DB[a,I]P and the exocyclic amino group and the N-7 of guanine were computed, and relative energies and geometries of the resulting adducts were examined. Furthermore, PAH-purine base adduct formation was modeled inside a DNA fragment by means of the ONIOM method.
Author affiliation: Borosky, Gabriela Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina
Author affiliation: Laali, Kenneth K.. Kent State University; Estados Unidos
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Authors: Forti, M. D.; Alonso, Paula Regina; Gargano, Pablo Hugo; Balbuena, Perla Beatriz; Rubiolo, Gerardo Hector
Publication Date: 2016.
Language: English.
Abstract:
The adhesion at Fe/Fe3O4 interface is one of the critical pieces of information that is often lacking upon designing the protective magnetite layer on the inner surfaces of carbon steel piping or upon modeling the scale removal mechanism for optimization of industrial descaling of the wire or strip surface of carbon steel after hot rolling process. In this context, we have performed ab initio DFT calculations to determine the atomic structure, work of separation (γ), and bonding character of the Fe(001)/Fe<sub>3</sub>O<sub>4</sub>(001) interface. Three candidate interface geometries were considered, including Fe and FeO<sub>2</sub> terminations of the oxide. The minimization of the forces resulted in substantial changes to the atomic structure of the metal and oxide layer at both side of the interface, and also of the subsurface layer of the oxide in the case of Fe-terminated oxide slab. Moreover, the relaxation of the geometry in one of the two considered Fe-terminated oxide interface leads to completely unstable interface structures. By applying several methods of analysis, we have thoroughly characterized the electronic structure and have determined that the dominant bonding mechanism is the metallic-ionic interaction between the iron atoms of both metal and oxide slabs. Our calculations predict γ ≈ 1.42 J/m<sup>2</sup> regardless of the interfacial stoichiometry.
Author affiliation: Forti, M. D.. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina
Author affiliation: Alonso, Paula Regina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina
Author affiliation: Gargano, Pablo Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina
Author affiliation: Balbuena, Perla Beatriz. Texas A&M University; Estados Unidos
Author affiliation: Rubiolo, Gerardo Hector. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Publication Date: 2011.
Language: English.
Abstract:
15N and 13C NMR chemical shifts were computed by GIAO-DFT and GIAO-MP2 for a series of p-substituted benzenediazonium mono- and dications in order to probe the electronic effects of the substituents on the diazonium moiety. Optimized geometries and N/N vibrational frequencies werealso considered for comparison. The GIAO-DFT derived15N chemical shifts correlate more closely with the experimental values as compared to GIAO-MP2. Energyminimizations at the B3LYP/6-311+G(2d,p), M062X-6-311+G(2d,p), MP2/6-311+G(2d,p), G2(MP2), and CBS-Q levels were carried out. Relative dication stability order HCO+ > HOMe+ > HN(Me) 2+ > HOH+ > HCN+ > HNO 2+ was derived from isodesmic proton transfer reactions. The Nβ-protonated dications were less stable than the corresponding p-R+ dications. Among the regioisomeric N β-protonated dications (with R = -F, -Cl, and -CN), those with the R group in the para position were preferred. For the regioisomeric, ring-protonated benzenium-diazonium dications, the meta-protonated dications were more favored (by DFT and MP2). Influence of the counterion and solvent on the computed 15N NMR chemical shifts in PhN2+ X- were also assessed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Author affiliation: Borosky, Gabriela Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina
Author affiliation: Okazaki, Takao. Mie University; Japón
Author affiliation: Laali, Kenneth K.. University of North Florida; Estados Unidos
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Publication Date: 2011.
Language: English.
Abstract:
Density functional theory st udies were performed to und erstand the early stage of graphene like structures nucleation and growth on Pd. Th e adsorption of C atoms on four Pd(111) surface models was examine d. We found adsorption energies ranging from -479 kJmol -1 , for a top site on a Pd( 111) surface, to -804 kJmol -1 , for a hollow-hcp site for Pd step-edge (111) surfaces. Local density of state curves analysis showed significant carbon/palladium bond hybridization. When in corporating new C atoms, these were attracted by the adatoms simulating a hexagonal ring. The calculations using a surface model containing steps, terrace and clusters su ggested that the nucleation of atomic C is promoted.
Author affiliation: Quiroga, Matías Abel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina
Author affiliation: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina
Author affiliation: Sanchez, Miguel Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Publication Date: 2002.
Language: English.
Abstract:
The adhesion of Pt overlayers in pseudomorphic epitaxy on hcp Co(0 0 0 1) and fcc Co(1 0 0) was investigated with first-principles calculations. This was compared to the adhesion of the Pt surface layers on Pt(1 1 1) and Pt(1 0 0). We show that adhesion can be analyzed by taking into account the interplay between the chemical and structural properties at the interface. The free Pt planes with the bulk Pt-Pt distance are submitted to tensile stress which can be relaxed by 6.6% and 9.1% contraction for the (1 1 1) and (1 0 0) symmetries respectively. This results in equilibrium interatomic distances which are not far from that of the Co substrate. Consequently the stress energy in a pseudomorphic Pt monolayer on a Co substrate is lower than the stress energy of pure Pt(1 1 1) or Pt(1 0 0) surfaces. However, this is at the expense of the Pt chemical reactivity towards the Co substrate. This is in agreement with the general dependence between chemical reactivity and stress of a metal surface. © 2001 Elsevier Science B.V. All rights reserved.
Author affiliation: Légaré, P.. Universite Louis Pasteur; Francia
Author affiliation: Castellani, Norberto Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina
Author affiliation: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Authors: Pieslinger, German Eduardo; Alborés, Pablo; Slep, Leonardo Daniel; Baraldo Victorica, Luis Mario
Publication Date: 2013.
Language: English.
Abstract:
The NIR and IR spectroscopic properties of the cyanide-bridged complex, trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ (py=pyridine, dmap=4-dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed-valence species, the first example reported of a cyanide-bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ ion and confirms its delocalized nature.
Author affiliation: Pieslinger, German Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina
Author affiliation: Alborés, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina
Author affiliation: Slep, Leonardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina
Author affiliation: Baraldo Victorica, Luis Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Authors: Brasca, Romina; Kneeteman, Maria Nelida; Mancini, Pedro Maximo Emilio; Fabian, Walter M. F.
Publication Date: 2011.
Language: English.
Abstract:
Diels-Alder reactions between the substituted furans 1a-1c and Danishefsky's diene (2), yielding 5-hydroxybenzofurans, were studied by density functional theory [B3LYP/6-31G(d) level] in benzene as solvent (SP/CPCM). The mechanistic details of these reactions, especially with respect to regio-, site-, and stereochemistry were analyzed in detail. Moreover, the extrusion of nitrous acid from the Diels-Alder cycloadducts and the formation of the aromatic products were also explained in order to give a total description of the complete domino processes. Some Diels-Alder reactions leading to 5-hydroxybenzofurans were studied at the B3LYP/6-31G(d) level of theory in benzene as solvent (SP/CPCM). DFT calculations on the transition structures were carried out for all the possible reaction channels (site, regio-, and stereoisomeric channels were included in this study). Additionally, a description of the complete domino processes was performed.
Author affiliation: Brasca, Romina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Author affiliation: Kneeteman, Maria Nelida. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Author affiliation: Mancini, Pedro Maximo Emilio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Química; Argentina
Author affiliation: Fabian, Walter M. F.. Karl Franzens Universität Graz,; Austria
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Abstract:
The conformational equilibria of cyclohexane (as well as its fluoro-, chloro-, methyl-, hydroxy-, and t-butyl derivatives), cyclohexanone, piperidine, tetrahydropyran (and its 2-hydroxy derivative) were studied by ab initio and DFT procedures. The transition states were calculated at HF/6-31G, B3LYP/6-31+G*, and B3LYP/6-311+G* levels, whereas the intrinsic reaction coordinates (IRCs) were evaluated at the B3LYP/6-31+G* level. The degree of puckering and energy data was nearly not basis set-dependent (using B3LYP) in most of the cases. However, DFT methods gave better agreement with experimental data than HF methods, as expected from electron correlation inclusion. Fluorocyclohexane and 2-hydroxytetrahydropyran showed the largest basis set-energy dependence. It was found that the conversion from chair to skew is direct in some cases, whereas in others it goes through the pseudorotational (skew/boat) pathway. The case of t-butylcyclohexane, with a skew form as stable as one of the chairs, is especially interesting. In this compound, as well as in cyclohexanone and 2-hydroxytetrahydropyran, large deviations from the known pseudorotation/inversion scheme are observed.
Author affiliation: Stortz, Carlos Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Authors: Camí, Gerardo Enrique; Chacón Villalba, Elizabeth; Colinas, Pedro Alfonso; Echeverría, Gustavo Alberto; Estiu, Guillermina Lucia; Soria, Delia Beatriz
Publication Date: 2012.
Language: English.
Abstract:
The results of the structural and electronic structure of p-cyanobenzenosulfonamide (L), and its copper(II) complex, Cu(L) 2(NH3)2 are reported. Both compounds have been prepared and their crystal structures determined. The sulfonamide crystallizes in the orthorhombic system, space group, Pnma and Z = 4, whereas the complex crystallizes in the triclinic system, P-1 and Z = 2. The coordination geometry of the copper(II) ion in the complex can be described as a distorted square planar with two N-sulfonamide and two NH3 in opposite vertices. The thermal behavior of both, the ligand and the Cu(II) complex, was investigated by thermogravimetric analyses (TG) and differential thermal analysis (DT). The experimental IR, Raman and UV-VIS spectra have been assigned on the basis of DFT calculations.
Author affiliation: Camí, Gerardo Enrique. Universidad Nacional de San Luis; Argentina
Author affiliation: Chacón Villalba, Elizabeth. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Laboratorio de Estudio de Compuestos Orgánicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina
Author affiliation: Colinas, Pedro Alfonso. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Laboratorio de Estudio de Compuestos Orgánicos; Argentina
Author affiliation: Echeverría, Gustavo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina
Author affiliation: Estiu, Guillermina Lucia. University of Notre Dame; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Author affiliation: Soria, Delia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas