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Castro M.E.,Institute Ciencias | Caballero N.A.,TecMilenio University | Guevara-Garcia J.A.,Autonomous University of Tlaxcala | Scior T.,Autonomous University of Puebla
Inorganica Chimica Acta | Year: 2014

The molecular structures, IR spectroscopy, 1H, 13C and 51V NMR spectroscopy of three bis-peroxo-oxovanadate species containing histidine peptides were studies on theoretical grounds. The geometry optimizations and IR spectra in gas phase were carried out with the DFT (B3LYP functional) method and the spectra of the peptides under study were obtained with the gauche-including atomic orbital (GIAO) method as implemented in the GAUSSIAN 09 package. The standard 6-31+G* basis set and core-valence effective core potential Lanl2dz were employed. New coordination modes were found in the potential curves for the rotation through the V-N coordination bond. They bent up and down (Bu, Bd) with the imidazole ring aligned with the V-O(peroxo) bond and also bent with respect to the VO group. In addition, the parameters describing quadrupolar and chemical shift anisotropy interactions are determined theoretically. In particular, this results help to solve apparent inconsistencies found in the 51V NMR solution spectroscopy of the three bis-peroxo-oxovanadate complexes. The gathered evidence furthers the understanding of the electronic implications and structure-activity relationships in the case of histidine peptide-containing bis-peroxo-oxovanadate structures. © 2014 Elsevier B.V. All rights reserved.

Urzua O.,Institute Ciencias | Percino M.J.,Institute Ciencias | Chapela V.M.,Institute Ciencias
International Journal of Quantum Chemistry | Year: 2010

Ab initio methods at the levels HF/cc-pVDZ, HF/6-31G(d,p), MP2/cc-pVDZ, and MP2/6-31G(d,p), as well as methods based on density functional theory (DFT) employing the hybrid functional B3LYP with the basis sets cc-pVDZ and 6-31G(d,p), have been applied to study the conformers of 2,6-distyrylpyridine. Bond distances, bond angles, and dihedral angles have been calculated at the B3LYP level. The calculated values were in good agreement with those measured by X-ray diffraction analysis of 2,6-distyrylpyridine. The values calculated using the Hartree-Fock method and second-order perturbation theory (MP2) were inconsistent. The optimized lowest energy geometries were calculated from the reported X-ray structural data by the B3LYP/cc-pVDZ method. Three conformations, A, B, and C, were proposed for 2,6-distyrylpyridine. Calculations at the three levels of theory indicated that conformation A was the most stable structure, with conformations C and B being higher in energy by 1.10 and 2.57 kcal/mol, respectively, using the same method and basis function. The same trend in the relative energies of the three possible conformations was observed at the two levels of theory and with the different basis sets employed. The reported X-ray data were utilized to optimize total molecular energy of conformation A at the different calculation levels. The bond lengths, bond angles, and dihedral angles were then obtained from the optimized geometries by ab initio methods and by applying DFT using the two basis functions cc-pVDZ and 6-31G(d,p). The values were analyzed and compared. The calculated total energies, the relative energies of the molecular orbitals, the gap between them, and the dipole moment for each conformational structure proposed for 2,6-distyrylpyridine are also reported. © 2009 Wiley Periodicals, Inc.

Prutskij T.,Institute Ciencias | Makarov N.,Institute Ciencias | Attolini G.,CNR Institute of Materials for Electronics and Magnetism
Journal of Luminescence | Year: 2016

Ternary and quaternary III-V alloys obtained by metal-organic vapor-phase epitaxy (MOVPE) grow very often with some degree of atomic ordering. Atomic ordering reduces the symmetry of the crystal lattice and thus drastically changes optical properties of the alloy. Moreover, the photoluminescence (PL) emission becomes polarized and its study helps to understand the atomic arrangement within the crystal lattice. In this work we experimentally studied the polarization of the PL emission from different crystallographic planes of several quaternary III-V semiconductor alloys grown on GaAs substrates by MOVPE. We compare the measured PL emission polarization angular patterns with those calculated with a model made for ternary alloys and discuss the limits of application of this model for quaternaries. It is found that the experimentally obtained polarization patterns are consistent with the existence of different ordering crystallographic planes for III- and for V-group atoms. © 2015 Elsevier B.V. All rights reserved.

Romano-Trujillo R.,Institute Ciencias | Rosendo E.,Institute Ciencias | Ortega M.,National Polytechnic Institute of Mexico | Morales-Sanchez A.,CIMAV | And 6 more authors.
Nanotechnology | Year: 2012

Lead selenide nanoparticles (PbSe NPs) have been obtained through an easy and low cost route using colloidal synthesis in aqueous solution. The synthesis was carried out at room temperature using Extran (Na 5P 3O 10, NaOH and H 2O) as surfactant. Hydrochloric acid (HCl) was used to eliminate the generated by-products. The size of PbSe NPs was varied by changing the Pb:Se molar concentration. The PbSe NPs were characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The XRD measurements showed that the PbSe NPs have the face-centered cubic phase structure. The crystal size was found to be between 14 and 20nm as calculated from the XRD patterns and these values were corroborated with SEM and TEM. Additionally, HRTEM micrographs showed crystalline planes at (200), (220) and (111) of the PbSe NPs, in agreement with the XRD results. © 2012 IOP Publishing Ltd.

Prutskij T.,Institute Ciencias | Pelosi C.,CNR Institute of Materials for Electronics and Magnetism
Crystal Research and Technology | Year: 2010

The temperature behavior of the integrated intensity of photoluminescence (PL) emission from ordered GaInP2 epitaxial layer was measured at temperatures of 10 - 300 K. Within this temperature range the PL emission is dominated by band-to-band radiative recombination. The PL intensity temperature dependence has two regions: at low temperatures it quenches rapidly as the temperature increases, and above 100 K it reduces slowly. This temperature behavior is compared with that of disordered GaInP2 layer. The specter of the PL emission of the disordered layer has two peaks, which are identified as due to donor-accepter (D-A) and band-to-band recombination. The PL intensity quenching of these spectral bands is very different: With increasing temperature, the D-A peak intensity remains almost unchanged at low temperatures and then decreases at a higher rate. The intensity of the band-to-band recombination peak decays gradually, having a higher rate at low temperatures than at higher temperatures. Comparing these temperature dependencies of these PL peaks of ordered and disordered alloys and the temperature behavior of their full width at half maximum (FWHM), we conclude that the different morphology of these alloys causes their different temperature behavior. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Escobedo-Martinez C.,National Autonomous University of Mexico | Concepcion Lozada M.,Metropolitan Autonomous University | Hernandez-Ortega S.,National Autonomous University of Mexico | Villarreal M.L.,Autonomous University of the State of Morelos | And 3 more authors.
Magnetic Resonance in Chemistry | Year: 2012

From the stem bark of Mangifera indica, seven cycloartane-type secondary metabolites were isolated. Compound 1 has been isolated for the first time from M. indica, whereas compounds 2 (2a and 2b, as an epimeric mixture), 3, and 4 are new triterpenoid-type cycloartanes. Unambiguous 13C and 1H NMR assignments for these compounds and the known compounds mangiferonic acid (compound 5), isomangiferolic acid (compound 6), ambolic acid (compound 7), and friedelin (compound 8) are reported; the latter because full NMR data for these compounds are not available in the literature. © 2012 John Wiley & Sons, Ltd.

Acosta G.,University of Buenos Aires | Caridi I.,University of Buenos Aires | Guala S.,Institute Ciencias | Marenco J.,Institute Ciencias
Physica A: Statistical Mechanics and its Applications | Year: 2012

The Full Strategy Minority Game (FSMG) is an instance of the Minority Game (MG) which includes a single copy of every potential agent. In this work, we explicitly solve the FSMG thanks to certain symmetries of this game. Furthermore, by considering the MG as a statistical sample of the FSMG, we compute approximated values of the key variable σ2N in the symmetric phase for different versions of the MG. As another application we prove that our results can be easily modified in order to handle certain kinds of initial biased strategy scores, in particular when the bias is introduced at the agents' level. We also show that the FSMG verifies a strict period two dynamics (i.e., period two dynamics satisfied with probability 1) giving, to the best of our knowledge, the first example of an instance of the MG for which this feature can be analytically proved. Thanks to this property, it is possible to compute in a simple way the probability that a general instance of the MG breaks the period two dynamics for the first time in a given simulation. © 2011 Elsevier B.V. All rights reserved.

Serkin V.N.,Institute Ciencias | Belyaeva T.L.,National Autonomous University of Mexico
Journal of Modern Optics | Year: 2010

The fundamental concept of colored nonautonomous solitons in nonlinear and dispersive nonautonomous physical systems is introduced. Novel soliton solutions for the nonautonomous nonlinear Schrodinger equation models with linear and harmonic oscillator potentials substantially extend the concept of classical solitons and generalize it to the plethora of nonautonomous solitons that interact elastically and generally move with varying amplitudes, speeds and spectra adapted both to the external potentials and to the dispersion and nonlinearity variations. The parallels between nonlinear guided wave phenomena in optics and nonlinear guided wave phenomena in Bose condensates are clearly demonstrated by considering optical and matter wave soliton dynamics in the framework of nonautonomous evolution equations. The exact analytical solutions and numerical experiments reveal many specific features of nonautonomous solitons. Fundamental laws of the soliton adaptation to the external potentials are derived. Bound states of colored nonautonomous solitons are studied in detail and a comparison of the canonical Satsuma-Yajima breather dynamics with a nonautonomous 'agitated' breather is presented. The nonautonomous soliton concept can be applied to different physical systems, from hydrodynamics and plasma physics to nonlinear optics and matter waves, and offer many opportunities for further scientific studies © 2010 Taylor & Francis.

Acosta G.,University of Buenos Aires | Caridi I.,University of Buenos Aires | Guala S.,Institute Ciencias | Marenco J.,Institute Ciencias
Physica A: Statistical Mechanics and its Applications | Year: 2013

We analyze two well-known related aspects regarding the sequence of minority sides from the Minority Game (MG) in its symmetric phase: period-two dynamics and quasi-periodic behavior. We also study the sequence of minority sides in a general way within a graph-theoretical framework. In order to analyze the outcome dynamics of the MG, it is useful to define the MGprior, namely an MG with a new choosing rule of the strategy to play, which takes into account both prior preferences and game information. In this way, each time an agent is undecided because two of her best strategies predict different choices while being equally successful so far, she selects her a priori favorite strategy to play, instead of performing a random tie-break as in the MG. This new choosing rule leaves the generic behavior of the model unaffected and simplifies the game analysis. Furthermore, interesting properties arise which are only partially present in the MG, like the quasi-periodic behavior of the sequence of minority sides, which turns out to be periodic for the M Gprior. © 2013 Elsevier B.V. All rights reserved.

Mendoza C.,Institute Ciencias | Bernes S.,National Autonomous University of Mexico | Torrens H.,DEP | Arroyo M.,Institute Ciencias
Organometallics | Year: 2010

Thermolysis reactions of [Os(SC6F5) 4(P(C6H4X-4)3)] (X = CF3 1, Cl 2, F 3, H 4, CH3 5, and OCH3 6) in refluxing toluene yield compounds [OsF(SC6F5)2(SC 6F4(SC6F5)-2)(P(C6H 4X-4)3)] (1a-6a) and [Os(SC6F5) 2(SC6F4(SC6F5)-2)(C 6H4X-4)] (1b-6b). In addition, [Os(SC6F 5)3(SC6F4(SC6F 5)-2)] (c) is yielded from 1-4 and 6, compounds [OsF(SC 6F5)3(P(C6H4X-4) 3)] [X = CF3 (1e), X = Cl (2e)] are also identified as products of the thermolysis reactions of 1 and 2, while [Os(SC6F 5)2(S2C6F4)(P(C 6H4CH3-4)3)] (5d) is obtained from 5. Compounds c, e, and d are produced in low yields (ca. 2-4%). Formation of all products involves the rupture of ortho C-F bonds. The first complexes systematically detected in these thermolysis reactions are compounds a, which are isomers of the starting complexes. Thus, the C-F activation involves the metal-mediated generation of the covalent Os-F bond. Single-crystal X-ray diffraction studies of the new compounds 4a, 5a, 2b-6b, 2e, and 5d indicate that these compounds consist of five-coordinated metal ions in essentially trigonal-bipyramidal geometries. In addition, thermolysis of the isolated compound [OsF(SC6F5)2(SC6F 4(SC6F5)-2)(P(C6H4CH 3-4)3)] (5a) in refluxing toluene gives rise to [Os(SC6F5)2(SC6F4(SC 6F5)-2)(C6H4CH3-4)] (5b) and [Os(SC6F5)2(S2C 6F4)(P(C6H4CH3-4) 3)] (5d), confirming that compounds a can generate compounds b when the thermolysis is prolonged. Compounds 1a-6a, 2b-6b, 1e, and 2e are investigated in solution by NMR studies, including variable-temperature 19F NMR experiments. These molecules are fluxional. Some of the activation parameters for the dynamic processes are determined. © 2010 American Chemical Society.

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