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Buenos Aires, Argentina

Okulik N.B.,National University of the Chaco Austral | Jubert A.H.,CEQUINOR | Castro E.A.,INIFTA
Journal of Molecular Modeling | Year: 2012

A theoretical study on the series of compounds "PhSeX", where Ph=phenyl, Se=selenium and X=Cl, Br, I, CN or SCN, is reported and compared with previously reported experimental data. The molecular geometry for these PhSeX compounds was studied at the DFT/B3LYP level of calculation by means of the 6-311G(d,p) basis set. The equilibrium structures of the molecules were dependent on the method employed to compare the known solid structures. A topological study of the calculated PhSeX species, based on the AIM theory, was carried out to gain a deeper insight into the bonding nature and to find an explanation for the structural diversity exhibited by these PhSeX compounds. The results reported herein illustrate the subtle differences in the solid-state structures of PhSeX compounds. © Springer-Verlag 2011. Source

Ruiz D.L.,Laboratorio Of Estudio Of Compuestos Organicos Ladecor | Albesa A.G.,INIFTA | Ponzinibbio A.,Laboratorio Of Estudio Of Compuestos Organicos Ladecor | Allegretti P.E.,Laboratorio Of Estudio Of Compuestos Organicos Ladecor | Schiavoni M.M.,Laboratorio Of Estudio Of Compuestos Organicos Ladecor
Journal of Physical Organic Chemistry | Year: 2010

Solvent effects on tautomeric equilibria in several β-ketonitriles has been investigated using nuclear magnetic resonance (NMR) spectroscopy and theoretical methods. The experimental chemical shifts were compared with theoretical values obtained by using gauge-including atomic orbital (GIAO) calculations, implemented at Density Functional Theory (DFT) level with hybrid functionals, B3LYP calculations. The solvent effect on the calculated structures has been taken into account through the polarized continuum model (PCM) for chloroform, acetone and dimethyl sulfoxide (DMSO). Also, some structural parameters were calculated in gas phase and in three different solvents. Copyright © 2010 John Wiley and Sons, Ltd. Source

Sarabadani J.,Max Planck Institute for Polymer Research | Milchev A.,Max Planck Institute for Polymer Research | Milchev A.,Bulgarian Academy of Science | De Virgiliis A.,INIFTA | Vilgis T.A.,Max Planck Institute for Polymer Research
Soft Materials | Year: 2014

We investigate the dynamic and static properties of a polymer melt near solid surfaces. The melt, composed of linear chains, is confined between two solid walls with one of the walls being repulsive; whereas the opposite, attractive wall, is characterized by different degrees of roughness, caused by an array of short perpendicular pillars with variable grafting density. We demonstrate the remarkable fact that the conformations of chains in the melt at the interfaces are mostly unaffected by the strength of substrate/polymer attraction. Moreover, they practically coincide with the conformations of a single end-grafted chain at the critical point of adsorption, in agreement with Silberbergs hypothesis. This agreement is corroborated by the analysis of the size distributions of trains, loops, and tails of melt chains at the walls that are found to be perfectly described by analytical expressions pertaining to end-grafted single chains at critical adsorption. The adsorbed amount at the attractive bottom surface is found to scale with macromolecule length as regardless of adsorption strength. We also find that the pressure of the melt PN decreases as PN - P∞ α N-1 (where P∞ is the extrapolated pressure for N → ∞) with growing length N of the chains whereas the surface tension γ at both walls is found to decline as γN α N-2/3. Eventually, a study of the polymer dynamics at the rough interface reveals that surface roughness leads to dramatic drop of the coefficient for lateral diffusion whenever the separation between obstacles (neighboring pillars) becomes less than where Rg is the unperturbed radius of gyration of chains in the bulk. © Taylor & Francis Group, LLC. Source

Bordon A.G.,University del Nordeste | Profeta M.I.,University del Nordeste | Romero J.M.,University del Nordeste | Jorge N.L.,University del Nordeste | Castro E.A.,INIFTA
Current Organic Synthesis | Year: 2014

3,6-diphenyl-1,2,4,5-tetraoxane(DFT) has been prepared in order to study the effect of temperature on the reaction kinetics in methylcellosolve solution. The thermolysis reaction fulfills a kinetic law of the first order up to conversions approximately 60 % of the DFT. The values of ∆H#=20.2±1.0 kcal mol-1 and ∆S#= -25.3±1.4 cal mol-1 K-1 of the rupture of one O-O bond in the diperoxide molecule were obtained by measuring the remanent diperoxide at different reaction times by GC technique. Benzaldehyde and benzoic acid were detected by GC as the major organics products of the reaction. © 2014 Bentham Science Publishers. Source

Sancho M.I.,National University of San Luis | Sancho M.I.,CONICET | Gasull E.,National University of San Luis | Blanco S.E.,National University of San Luis | And 2 more authors.
Carbohydrate Research | Year: 2011

A thermodynamic study of the inclusion process between 2-chlorobenzophenone (2ClBP) and cyclomaltoheptaose (β-cyclodextrin, β-CD) was performed using UV-vis spectroscopy, reversed-phase liquid chromatography (RP-HPLC), and molecular modeling (PM6). Spectrophotometric measurements in aqueous solutions were performed at different temperatures. The stoichiometry of the complex is 1:1 and its apparent formation constant (K c) is 3846 M -1 at 30 °C. Temperature dependence of K c values revealed that both enthalpy (δH° = -10.58 kJ/mol) and entropy changes (δS° = 33.76 J/K mol) are favorable for the inclusion process in an aqueous medium. Encapsulation was also investigated using RP-HPLC (C18 column) with different mobile-phase compositions, to which β-CD was added. The apparent formation constants in MeOH-H 2O (K F) were dependent of the proportion of the mobile phase employed (50:50, 55:45, 60:40 and 65:35, v/v). The K F values were 419 M -1 (50% MeOH) and 166 M -1 (65% MeOH) at 30 °C. The thermodynamic parameters of the complex in an aqueous MeOH medium indicated that this process is largely driven by enthalpy change (δH° = -27.25 kJ/mol and δS° = -45.12 J/K mol). The results of the study carried out with the PM6 semiempirical method showed that the energetically most favorable structure for the formation of the complex is the 'head up' orientation. © 2011 Elsevier Ltd. All rights reserved. Source

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