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Martinez-Araya J.I.,Pedro de Valdivia University | Salgado-Moran G.,Andrés Bello University | Glossman-Mitnik D.,CIMAV
Journal of Physical Chemistry B | Year: 2013

A density functional theory study of eight oxicams was carried out in order to determine their global and local reactivities. These types of reactivities were measured by means of global and local reactivity descriptors coming from the conceptual density functional theory. Net electrophilicity as a global reactivity descriptor and local hypersoftness as a local reactivity descriptor were the used tools to distinguish reactivity and selectivity among these oxicams. Globally, isoxicam presents the highest electron donating capacity; meanwhile, the highest electron accepting capacity is exhibited by droxicam. Locally, two oxicams present neither nucleophilic nor electrophilic relevant reactivity in their peripheral pyridine ring, droxicam and tenoxicam, so that their more reactive zones are found on the respective fused rings. Oxicams have been divided into two subgroups in order to facilitate the local analysis of reactivity. One group is characterized because their most important condensed values for local hypersoftnes are well-separated: 4-meloxicam, lornoxicam, meloxicam, and normeloxicam. Meanwhile, the opposite situation is found in droxicam, isoxicam, piroxicam, and tenoxicam. As a whole, the nucleophilic characteristic noticeably predominates in these eight oxicams instead of an electrophilic behavior, thus meaning a greater tendency to donate electrons rather than withdrawing them; a consequence of this behavior implies a favorable interaction with a hypothetical receptor bearing one or more electron acceptor functional groups rather than electron donor functional groups; this would imply a maximization of this interaction from the covalent point of view. © 2013 American Chemical Society.

Martinez-Araya J.I.,Pedro de Valdivia University | Salgado-Moran G.,Andrés Bello University | Glossman-Mitnik D.,CIMAV
Journal of Chemistry | Year: 2013

The M06 family of density functionals has been assessed for the calculation of the molecular structure and properties of the Naringin molecule. The chemical reactivity descriptors have been calculated through Conceptual DFT. The active sites for nucleophilic and electrophilic attacks have been chosen by relating them to the Fukui function indices and the dual descriptor f (2) (r). A comparison between the descriptors calculated through vertical energy values and those arising from the Koopmans' theorem approximation has been performed in order to check for the validity of the last procedure. © 2013 Jorge Ignacio Martínez-Araya et al.

Martinez-Araya J.I.,Pedro de Valdivia University | Martinez-Araya J.I.,Centro Para La Investigacion Interdisciplinaria Avanzada En Ciencias Of Los Materiales | Quijada R.,Centro Para La Investigacion Interdisciplinaria Avanzada En Ciencias Of Los Materiales | Quijada R.,University of Chile | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

A density functional theory study of the ethylene polymerization mechanism catalyzed by metallocene methyl cations based on group IVB (Ti, Zr, and Hf) is presented. The concept called reaction force was applied in order to decompose the activation energy into two parts with the aim of distinguishing the predominance of structural or electronic effects within intervals along the reaction coordinate on each step of the polymerization process. This has implied an alternative rational analysis of elementary chemical reactions associated with the polymerization mechanism under the assumption that the Cossée-Arlman's mechanism is operating along the whole process. Three reaction models representing elementary chemical reactions of the polymerization process (initiation, propagation, and termination) were used through molecular quantum mechanical calculations. The simplest of metallocene methyl cations (built up by two cyclopentadienyl groups and one methyl group linked to the metal) was used as a catalytic molecular model. Since the main goal was focused on getting information of intrinsic global reactivity of catalytic systems, both solvent and co-catalyst were not modeled in the present work. As a result, energy profiles indicate that ethylene polymerization reactions are better catalyzed by the respective metallocene cation based on Ti, whereas the catalysts based on Zr and Hf present similar characteristics among them, thus supporting experimental results where the molecular weight of polyethylene obtained by means of metallocene cation based on Ti approximately doubles the molecular weights of polyethylene catalyzed by metallocenes based on Zr and Hf. However propagation and termination steps are better catalyzed by metallocene complexes based on Zr and Hf, thus masking the influence of initiation step upon the molecular weight of the obtained polymer and providing more importance to termination step rather than propagation step. This would help to better understand differences presented in the average molecular weight of a same polymer obtained with each of these catalytic systems. As some key steps of the polymerization process would be more favored with one type of metallocene rather than other one, the use of reaction force would help to better understand how to modify energetic barriers and or global changes in energy by perturbating geometrical or electronic structure of catalytic systems. The latter suggests that the ideal polymerization process should be carried out with different catalytic systems depending on the step of polymerization and not with a unique catalyst as has been commonly performed up to now. That might lead to the obtention of a more wide range of new polymeric materials. © 2012 American Chemical Society.

Lazcano H.G.,Pedro de Valdivia University | Quintana M.G.B.,Knowledge Computing
International Journal of Engineering Education | Year: 2014

This research is focused on developing an approach for learning activities in a virtual learning environment employing Web 2.0. These activities are incorporated into the design of a course intended to contribute to the development of generic and specific competencies. Input from subject experts was utilized in developing the approach. A pilot project was implemented and assessed in aCivil Engineering and Informatics course at the Universidad Católica de la Santísima Concepción. The approach was assessed through a developed guide to the most effective course design based on learning theories relating instructional design to learning outcomes. © 2014 TEMPUS Publications.

After the earthquake and tsunami that struck the south-central Chile on February 27, 2010, it is necessary to anticipate the psychological consequences of disasters such causes in the population. This paper reviews the results of various studies worldwide in order to understand these consequences, focusing mainly on posttraumatic stress disorder [PTSD], their characteristics, prevalence, risk factors and interventions used for prevention and treatment. Then, we propose a model of narrative intervention, enriched by the contributions of studies on emotional expression and social support in the prevention of this disorder. This proposal has been tried before successfully for the prevention of PTSD and associated symptoms in women with breast cancer. Copyright 2010 by Sociedad Chilena de Psicología Clínica.

Caffeic acid (C9;H8.;O4;) and its conjugate base C9;H7;O4; - (anionic form-known as caffeate) were analyzed computationally through the use of quantum chemistry to assess their intrinsic global and local reactivity using the tools of conceptual density functional theory. The anionic form was found to be better at coordinating the silver cation than caffeic acid thus suggesting the use of caffeate as a complexation agent. The complexation capability of caffeate was compared with that of some of the most common ligand agents used to coordinate silver cations. Local reactivity descriptors allowed identification of the preferred sites on caffeate for silver cation coordination thus generating a plausible silver complex. All silver complexes were analyzed thermodynamically considering interaction energies in both gas and aqueous phases; the complexation free energy in aqueous phase was also determined. These results suggest that more attention be paid to the caffeate anion and its derivatives because this work has shed new light on the behavior of this anion in the recovery of silver cations that could be exploited in silver mining processes in a environmentally friendly way. © Springer-Verlag 2012.

Martinez-Araya J.I.,Pedro de Valdivia University | Martinez-Araya J.I.,University of Santiago de Chile
Journal of Physical Chemistry C | Year: 2013

Some metallocene methyl cations made of zirconium, that have been used as catalysts in polymerization of ethylene, were studied by means of the conceptual density functional theory (DFT). Up to now, catalytic activity, a pure experimental parameter, that measures the kilograms of polyethylene produced per gram of metallocene, per time unit, per temperature unit, and per pressure unit, has been mainly explained in terms of steric hindrance at least qualitatively, meaning that a catalyst having a higher steric hindrance will present a lower catalytic activity. However, there has not been a satisfactory explanation for those few cases in which the steric effect cannot be linked with the catalytic activity, thus meaning that the electronic inductive effect predominates over the steric effect. As a consequence, the electronic inductive effect must be quantified through the use of a proper descriptor based on quantum chemical calculations and, in addition, this descriptor should be able to explain high values of catalytic activities even when the steric effect seems to play an unfavorable role. This work has demonstrated that a local reactivity descriptor called local hyper-softness coming from the conceptual DFT is a suitable pure theoretical parameter that explains such anomalies in some values of catalytic activity. It is expected that the findings exposed here can help to estimate catalytic activity and lead to a more rational design of new catalysts by means of computational chemistry. © 2013 American Chemical Society.

Martinez-Araya J.I.,Pedro de Valdivia University
Journal of Molecular Modeling | Year: 2013

At present, there are two levels of approximation to compute the dual descriptor (DD). The first uses the total electronic density of the original system along with the electronic densities of the system with one more electron and one less electron, but this procedure is time consuming and normal termination of computation of total electronic densities is not guaranteed. The second level of approximation uses only the electronic densities of frontier molecular orbitals, HOMO and LUMO, to avoid the former approximation; however, the orbital relaxation implicitly included in the first level of approximation is absent in the second, thus risking an incorrect interpretation of local reactivity. Between the lowest occupied molecular orbital (LOMO) and the highest unoccupied molecular orbital (HUMO), a framework to provide an expression of the DD in terms of the electronic densities of all molecular orbitals (except HUMO and LOMO) has been proposed to be implemented by programmers as a computational code. This methodology implies another level of approximation located between the conventional approximation methods mentioned above. In this study, working equations have been oriented toward molecular closed- and open-shell systems. In addition, the mathematical expression for a closed-shell system was applied to acetylene in order to assess the capability of this approach to generate the DD. © 2012 Springer-Verlag Berlin Heidelberg.

Martinez-Araya J.I.,Pedro de Valdivia University
Journal of Molecular Modeling | Year: 2013

The intrinsic reactivity of cyanide when interacting with a silver cation was rationalized using the dual descriptor (DD) as a complement to the molecular electrostatic potential (MEP) in order to predict interactions at the local level. It was found that DD accurately explains covalent interactions that cannot be explained by MEP, which focuses on essentially ionic interactions. This allowed the rationalization of the reaction mechanism that yields silver cyanide in the gas phase. Other similar reaction mechanisms involving a silver cation interacting with water, ammonia, and thiosulfate were also explained by the combination of MEP and DD. This analysis provides another example of the usefulness of DD as a tool for gaining a deeper understanding of any reaction mechanism that is mainly governed by covalent interactions. [Figure not available: see fulltext.] © 2012 Springer-Verlag.

Martinez Araya J.I.,Pedro de Valdivia University
Chemical Physics Letters | Year: 2011

Two hierarchical working equations to calculate the dual descriptor for electronic open-shell systems were deduced based on the formalism of the Conceptual Spin-Polarized Density-Functional Theory (SP-DFT). NO and O 2 molecules were analyzed by taking into account their ground state multiplicities. The NO molecule has been used as a typical conventional example of a system with a doublet multiplicity presenting non-degenerate frontier molecular orbitals and the O2 molecule has been considered as a typical example of a system with a triplet multiplicity presenting degenerate frontier molecular orbitals. One working equation was tested in carbenes. © 2011 Elsevier B.V. All rights reserved.

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