Flavio F. Contreras-Torres

Low-symmetry structures of Au32Z (Z = +1, 0, -1) clusters.

In this work, we have explored new stable structures of the Au32Z (Z = +1, 0, -1) clusters. Theoretical calculations using density functional theory within the generalized-gradient approximation were performed. Our results show that, in the anion state (Au32-), low-symmetry (disordered) structures are preferred over the caged fullerene-like isomer. In addition, the cationic cluster (Au32+) also exhibits a disordered low-symmetry structure as its lowest energy configuration, but it is much closer in energy to the fullerene-like isomer. These results, obtained at T = 0 K, indicate that disordered structures for the Au32- and Au32+ clusters may be detected not only at room temperature, as was experimentally verified for the Au32- one, but also at much lower temperatures.

Nanostructured Diamine−Fullerene Derivatives: Computational Density Functional Theory Study and Experimental Evidence for their Formation via Gas-Phase Functionalization

Nanostructure derivatives of fullerene C(60) are used in emerging applications of composite matrices, including protective and decorative coating, superadsorbent material, thin films, and lightweight high-strength fiber-reinforced materials, etc. In this study, quantum chemical calculations and experimental studies were performed to analyze the derivatives of diamine-fullerene prepared by the gas-phase solvent-free functionalization technique. In particular, the aliphatic 1,8-diamino-octane and the aromatic 1,5-diaminonaphthalene, which are diamines volatile in vacuum, were studied. We addressed two alternative mechanisms of the amination reaction via polyaddition and cross-linking of C(60) with diamines, using the pure GGA BLYP, PW91, and PBE functionals; further validation calculations were performed using the semiempirical dispersion GGA B97-D functional which contains parameters that have been specially adjusted by a more realistic view on dispersion contributions. In addition, we looked for experimental evidence for the covalent functionalization by using laser desorption/ionization time-of-flight mass spectrometry, thermogravimetric analysis, and atomic force microscopy.

DNA insertion in and wrapping around carbon nanotubes

The interaction of carbon nanotubes (CNTs) with biomolecules has been a subject of great interest during the last decades, for the wide range of applications profiting their novel properties; particularly, it has been pointed out their ability to interact with living cells for different purposes. The study of the interactions between CNTs and DNA is an active research subject, given the remarkable properties of the DNA molecule and its potential use in biologic materials. Theoretical calculations have become an essential task in the study of such interactions; hence, computational simulations provide a powerful tool, which in turn yields powerful insights on the underlying phenomena of nanoscale processes occurring on these composites. This work reviews some of the latest efforts on theoretical simulations of DNA functionalized CNTs composites. Among the different theoretical approaches used in computational modeling of nanocomposites there are some that were found not fitted for analyzing CNTs, given the large number of molecules present in an ordinary CNT; often these routines are very resource consuming and long computation times are frequently required for accurate analysis. Recent works using density functional theory (DFT) and molecular dynamics (MD) have proven to be of great value when dealing with DNA modified CNTs. We discuss some of the latest results of these treatments, namely, on the DNA insertion in and wrapping around single‐walled carbon nanotubes (SWNTs) and envision some of their current applications such as nanocarriers for therapeutical uses, selective imaging, and biological sensing.

Regioselectivity in Azahydro(60)fullerene Derivatives: Application of General-Purpose Reactivity Indicators

To attempt theoretical predictions of the regioselectivity pattern in molecules with multiple reactive sites, the energies of formation of all possible isomers are usually considered. This means that the computing becomes highly demanding if high theoretical levels are used. The study objective was to predict the regioselectivity in the reaction of hydrogen addition onto azahydro[60]fullerene C 59H n+1 N ( n = 0-4) systems using a new reactivity indicator termed general-purpose reactivity indicator, Xi Delta N<or=0,alpha (kappa), proposed by Anderson et al. ( J. Chem. Theory Comput. 2007, 3, 358). Because Xi Delta N<or=0,alpha (kappa) combines the information from the electrostatic potential and the Fukui function, this indicator is a two-parameter model that depends on the atomic charges and Fukui values calculated. We used the gradient-corrected BLYP and BOP functionals to approximate the electronic density of the systems, and these densities were employed to determinate the parameters. In terms of regioselectivity, the preferential addition sites at every hydrogenation step on C 59H n+1 N ( n = 0-4) shows that 1,4-adducts are more stable than 1,2-adducts. However, we show that the multiple additions are only feasible up to a C 59H 5N (tetraddition) product. Consequently, the application of this indicator not only helps to avoid systematic computational studies by comparing energies of formation in several isomersmany of which are not currently supported by experimental resultsbut also provides an insight of how the pattern of addition is achieved. Comparisons with traditional indicators show that the application of Xi Delta N<or=0,alpha (kappa) performs much better for predicting reactivity in the aza[60]fullerene derivatives studied.

ONIOM Studies of Esterification at Oxidized Carbon Nanotube Tips

Esterification of oxidized carbon nanotubes (CNTs) can open a new route for the separation of zigzag and armchair nanotubes. We studied theoretically (by using hybrid DFT within the ONIOM embedding protocol) the reactions of monocarboxy-substituted oxidized tips of zigzag and armchair single-walled CNTs (SWCNTs) with methanol. According to the calculated values of activation energy, Gibbs free-activation barriers, and enthalpies of formation for the SWCNT-(COOH)H5 models, the zigzag nanotube isomer is more reactive as compared to its armchair counterpart. For other models we obtained variable results.

Structure of Methyl (1S, 6S) 6-(4-chlorophenyl)-4-(4-methylphenyl) cyclohex-3-en-2-one-1-carboxylate

1 Instituto de Quimica, Universidad Nacional Autonoma de Mexico, Mexico D.F., A. Postal, 04510,Mexico.2 Department of Chemistry, The University of Arizona, Tucson, AZ 85721 USA.3 Laboratorio de Sintesis Organica, Facultad de Farmacia, Universidad Central de Venezuela, Caracas1051, Venezuela.* Author to whom correspondence should be addressed. E-mail: ajalbout@u.arizona.edu; Tel:+15206216761; Fax: +15206218047

Ultrasensitive detection of phenolic antioxidants by surface enhanced Raman spectroscopy

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful surface-sensitive technique to study the vibrational properties of analytes at very low concentrations. In this study, ferulic acid, p-coumaric acid, caffeic acid and sinapic acid were analyzed by SERS using Ag colloids. Analytes were detected up to 2.5x10-9M. For caffeic acid and coumaric acid, this detection limit has been reached for the first time, as well as the SERS analysis of sinapic acid using silver colloids.

Computational Simulation of Tumor Surgical Resection Coupled with the Immune System Response to Neoplastic Cells

Numerous mathematical and computational models have arisen to study and predict the effects of diverse therapies against cancer (e.g., chemotherapy, immunotherapy, and even therapies under research with oncolytic viruses) but, unfortunately, few efforts have been directed towards development of tumor resection models, the first therapy against cancer. The model hereby presented was stated upon fundamental assumptions to produce a predictor of the clinical outcomes of patients undergoing a tumor resection. It uses ordinary differential equations validated for predicting the immune system response and the tumor growth in oncologic patients. This model could be further extended to a personalized prognosis predictor and tools for improving therapeutic strategies.

Las revistas electrónicas: una salida oportuna hacia la difusión de la ciencia ecuatoriana

Conocido comunmente como: canelon, Ishpink, ispingu o Ishpingu; el arbol de Ocotea quixos, es una planta perenne, pertenece a la familia de las Lauraceae [1], y constituye una variedad endemica del Ecuador. El fruto es rico en aceites escenciales, entre sus componentes principales tiene al cinemaldehido en un 27,91% y el cinamato de etilo en un 21,65%, junto con otros 42 componentes en donde se ha comprobado la presencia de una alta actividad de tipo antifungica [2]. Lamentablemente, el fruto florece solamente cuando el arbol llega a una edad madura; es decir luego de varios anos y lo hace de forma perodica, no constante. Sin embargo, en sus hojas tambien se ha logrado determinar la presencia de aceite escencial, ha sido objeto de nuestro estudio.Hablar del sistema preventivo es hablar de precaucion, es decir prever acontecimientos. El sistema preventivo salesiano basado en los tres pilares fundamentales que son: la razon, la religion y amabilidad, terminos conocidos por todos los educadores salesianos y practicados tambien por muchos no salesianos, no fueron escogidas por un mero capricho de Juan BoscoEs una planta que por no representar un rubro economico significativo para la agricultura del pais y la economia del agricultor, se ha perdido su explotacion, lo peor es que nada se hace para reactivar su cultivo o su debida propagacion en las zonas de adaptacion, por lo que este se vera afectado mas de lo que ya esta por el fenomeno de la extincion; por ello quiero en este articulo dar a conocer algunos lineamientos para la ejecucion de su cultivo.El ultrasonido se viene utilizando en el area de la Medicina Veterinaria en especies menores como perras, gatas, para observar cuerpos extranos, etc, donde se aplica la tecnica TRANSABDOMINAL.Son sustancias producidas por varias especies de microorganismos tales como: hongos, bacterias y actinomicetos.Para Ecuador, el petroleo es la principal fuente de ingresos; la produccion y las fases de la actividad petrolera pueden afectar al ambiente, pues conllevan riesgos de contaminacion por derrames, siendo ineludible remediar estos danos de alguna manera. La fitorremediacion se presenta como una tecnologia alternativa de bajo costo para limpiar suelos contaminados; en el presente trabajo se evaluan los niveles de tolerancia y potencial de fitorremediacion de Ludwigia peruviana, Mimosa polydactyla, Tessaria integrifolia y Verbena litoralis en suelo contaminado con petroleo (3 y 6% de concentracion), mediante comparacion del cambio en el contenido de hidrocarburos en tales suelos por el metodo gravimetrico. El estudio se realizo en un invernadero en la comunidad de San Luis, canton El Chaco, provincia de Napo y en los laboratorios de la Universidad Politecnica Salesiana en la ciudad de Quito. El trasplante de las plantas silvestres recolectadas se realizo a los 14 dias despues de contaminado el suelo con las diferentes concentraciones de petroleo. El diseno experimental fue de cuatro repeticiones por tratamiento y seis tratamientos para cada especie. Se encontro que los mejores resultados de actividad fitorremediadora fueron para Tessaria integrifolia y Verbena litoralis a bajas concentraciones de petroleo (3%) y con aplicacion de fertilizante.El presente articulo realiza un analisis ambiental de los agrocombustibles, argumentando no constituir una solucion al problema del calentamiento global, debido a que su proceso de produccion no representa una disminucion significativa en emisiones de CO2 y que inclusive plantea un problema ambiental mas grave, al amenazar la seguridad alimentaria y fomentar la deforestacion, los monocultivos, el uso de transgenicos, mayor uso de agroquimicos toxicos, disminucion de nutrientes naturales del suelo, disminucion de biodiversidad, contaminacion del agua y el suelo, entre otros. Asimismo, a partir de un analisis geopolitico, este documento concluye que los agrocombustibles son una alternativa propuesta principalmente por la industria agro-biotecnologica que no aborda la verdadera causa del calentamiento global, y que consecuentemente no puede resolverla. Ademas, se plantea que la promocion de los agrocombustibles es una forma de generar mercado para insumos agricolas producidos por las mismas companias que los impulsan y, eventualmente, obtener el control del principal mercado energetico mediante politicas comerciales globales y derechos de propiedad intelectual.Desde el 14 de mayo hasta el 9 de junio del presente ano, mediante resolucion del Consejo Superior de la Universidad, el ingeniero agronomo Fredi Portilla Farfan M.Sc, Decano de la Facultad de Ciencias Agropecuarias y Ambientales, conjuntamente con los otros Decanos y el Vicerrector de la UPS, realizaron un itinerario academico a diez universidades europeas: Pontificia Salesiana de Roma, La Sapienza de Roma, de Florencia, de Pavia, Universidad de Salamanca, Politecnica de Madrid, Nacional de Estudios a Distancia UNED (Madrid), de Barcelona, Universidad Abierta de Cataluna y Escuela Salesiana Tecnologica de Sarria.El uso de fertilizacion tecnica se inicio con la introduccion de especies forrajeras altamente productivas, la creciente utilizacion de fertilizantes se debe entre otros al acelerado agotamiento de la fertilidad de los suelos, debido a practicas agronomicas inadecuadas que facilitaron el desgaste erosionando el contenido nutricional. La creciente demanda de alimento para los animales, mas los costos elevados de insumos y de la tierra, han obligado al productor pecuario a ser mas eficiente en la produccion de alimento. Tambien se puede considerar que los sistemas de explotacion intensiva utilizados en paises como Nueva Zelanda, Estados Unidos y Holanda, estan sirviendo como modelo de produccion en nuestro pais, realizando manejos mas tecnicos tanto en produccion alimenticia como en el manejo de los animales y otros recursos.Las estrategias reproductivas halladas en Rubus niveus ‘mora’ superan las expectativas de cualquier amante de las especies vegetales, esta especie ha tenido un bajo per l en su ambiente natural, sin embargo, en un nuevo ecosistema, como lo son las Islas Galapagos, logro de manera rapida extender su cobertura a diferentes zonas del lugar: Isabela, Santiago, San Cristobal y Santa Cruz, convirtiendose en estas dos ultimas Islas en un gran problema para la biota local. Este articulo aborda una descripcion breve sobre algunos aspectos referentes a la especie y deja planteada una posible linea de investigacion sobre la erradicacion de la misma acudiendo a la ingenieria genetica para lograr este proposito.La contaminacion quimica de la leche se puede verificar mediante cuatro vias: a. Detergentes y desinfectantes usados en las operaciones de lavado. b.Antielminticos. c. Insecticidas y anticriptogamicos usados en agricultura. d. Elementos radioactivos, sustancias dicersas, metales.La Varroasis, causada por el acaro Varroa jacobsoni, que fue introducida al pais recientemente, es uno de los principales problemas a nivel nacional y mundial, que requiere de la atencion de todos los apicultores y politicas del gobierno nacional para su control.

Structure of Methyl 1-oxo-3,5-diphenylcyclohexene-6-carboxylate

The exploration of a simple molecule with different functionalities for the synthesis of heterocycles is a worthwhile contribution in the chemistry of heterocycles.[...]