Estudo químico-computacional da reatividade de aziridinona e diaziridinona através de cálculos semi-empíricos

The results of semiempirical molecular orbital calculations performed on aziridinone and diaziridinone employing the MNDO, AM1, and PM3 molecular models are presented. The AM1 method, which best reproduces ground-state molecular properties, is used to calculate electronic parameters and the use of these parameters for the evaluation of reactivity is discussed.

Transporte de massa em polímeros intrinsecamente condutores: importância, técnicas e modelos teóricos

In this work we discuss the aspects related to the phenomenon of mass transport in thin electroactive polymer films. Such phenomenon must be considered because the properties and consequent applications of these materials largely depend on the movement of charge carriers, i.e. ions, electrons or holes. The most recent majority of the techniques, methods and theoretical models used in this type of study are gathered and discussed, providing an easy and critical way for choosing the methodology for an investigation.

Caracterização de polimorfismo em fármacos por ressonância magnética nuclear no estado sólido

This review aims to present some features about solid state NMR and its application in the field of pharmaceutical chemistry, for the characterization of polymorphism of pharmaceutical molecules.

Aplicació de tècniques de pensament computacional en aules escolars

En el present article es planteja quins mecanismes existeixen per aplicar el pensament computacional en les aules escolars i s'analitzarà com s'està duent a terme aquesta implantació en diferents països. Finalment, es proposa i es desenvolupa una aplicació web basada en eines de programari lliure per tal d'introduir als infants alguns dels fonaments del pensament computacional a les seves aules.

Fotoquímica de chalconas fluoradas no estado sólido

Chalcone and its fluorinated derivatives were synthesized and photolyzed in the solid state. UV irradiation of chalcone and its monosubstituted fluorine derivatives (3- and 4-fluorchalcone) resulted in a mixture of anti-head-head (gamma-truxinic), sin-head-tail (alpha-truxilic) and anti-head-tail (epsilon-truxilic) dimers. On the other hand, upon irradiation of 3,4- and 3,5-difluorchalcone a stereoselective formation of the alpha-truxilic photodimer was observed, whereas for 2-substituted chalcones (2,3difluorchalcone, 2,5-difluorchalcone, 2,6-difluorchalcone and 2,3,4-trifluorchalcone) the beta-truxilic dimer was stereoselectively obtained. 2',3',4',5',6'-pentafluorchalcone was the less reactive of all chalcones studied and at least one of the possible photodimers, i.e the anti-head-head isomer, was identified. Irradiation of polyfluorinated chalcones such as 2,3,5,6-tetrafluor-, 2,3,4,5,6-pentafluor-, and 2,2',3,3',4,4',5,5',6,6'-decafluorchalcone led only to polymerization and/or decomposition products.

Propelente sólido compósito polibutadiênico: I- influência do agente de ligação

In the Brazilian Complete Spacial Mission, the research of Vehicle Satellite Launcher is important. The solid propellant composite used in this vehicle is made with ammonium perchlorate, aluminiun powder and hydroxy terminated polibutadiene resin. In the propellant the bonding agent has a function to promote the interaction between solids and polimeric matrix, improving mechanical properties as stress, strain, aging characteristics and moisture embrittlement. Due its importance in propellant, bonding agent is consider as industrial secret and the literature about it is generic, without greater informations.

Estudo da geometria da uréia por métodos ab initio e simulação computacional de líquidos

A study was carried out on the urea geometries using ab initio calculation and Monte Carlo computational simulation of liquids. The ab initio calculated results showed that urea has a non-planar conformation in the gas phase in which the hydrogen atoms are out of the plane formed by the heavy atoms. Free energies associated to the rotation of the amino groups of urea in water were obtained using the Monte Carlo method in which the thermodynamic perturbation theory is implemented. The magnitude of the free energy obtained from this simulation did not permit us to conclude that urea is non-planar in water.

Técnicas de análise do perfil de execução e otimização de programas em química computacional

In this paper we review the basic techniques of performance analysis within the UNIX environment that are relevant in computational chemistry, with particular emphasis on the execution profile using the gprof tool. Two case studies (in ab initio and molecular dynamics calculations) are presented in order to illustrate how execution profiling can be used to effectively identify bottlenecks and to guide source code optimization. Using these profiling and optimization techniques it was possible to obtain significant speedups (of up to 30%) in both cases.

Caracterização e classificação do resíduo sólido "pó do balão", gerado na indústria siderúrgica não integrada a carvão vegetal: estudo de um caso na região de Sete Lagoas/MG

This research was developed by considering that the solid waste produced in the process of pig iron production represents the loss of raw materials and the increase in environmental problem. The charcoal based mini blast-furnace off gases dust named CHARCOK was collected from SIDERPA ¾ Siderúrgica Paulino Ltda, located in Sete Lagoas, Minas Gerais. The Charcok was characterized and classified according to ABNT (Associação Brasileira de Normas Técnicas) standard. The results showed that the Charcok should be classified as Class I Wastes ¾ "Hazard Wastes" because of its high concentration of phenols (54.5mg C6H5OH/kg). The Charcok had high concentration of iron and charcoal which can be used as energy source.

Estudi i simulació aerodinàmica amb programari de dinàmica de fluids computacional (CFD) en un model bàsic de vehicle de competició de la categoria CM (curses de muntanya)

Aquest projecte té com a objectiu la simulació numérica de la carrosseria d’ un vehicle de curses de muntanya de categoria CM

Qual o sítio de reação? Um experimento computacional

A computational quantum chemistry experiment is described on the determination of the most reactive atom in a molecule for a reaction. The reaction studied was the S N2 of 4-(dimethylamino)pyridine and methyl iodide. Several indexes (HOMO coefficent, (c), charges, (q), nucleophilic softness, (s+), and Fukui index, (f+)) were employed to verify which correctly describe what nitrogen will react. The calculations were made by AM1 and HF/STO-3G methods. The correct reactivity order is only reproduced by s+ and f+. The lack of agreement of FMO based indexes was discussed.

Transporte de carga em compósitos de polianilina/V2O5

In this work, composites formed from a mixture of V2O5 and polyaniline (PANI) were investigated, for applications as cathode materials for secondary lithium batteries. Electrochemical quartz crystal microbalance (EQCM) data show that charge compensation in the [PANI]0.3V2O5 nanocomposite is achieved predominantly by Li+ migration. However, the charge compensation in the [PANI]V2O5 microcomposite occurs by Li+ and ClO4- transport. Electrochemical Impedance Spectroscopy (EIS) measurements reveal several benefits of nanohybrid formation, including the achievement of shorter ionic diffusion pathways, the higher diffusion rate of the lithium ion and also the higher electronic conductivity, which are responsible for a synergetic effect of the energy storage properties.

Construção e avaliação de célula de fluxo para estudo da tensão interfacial dinâmica da interface fluxo líquido - sólido por despolarização da fluorescência

A simple low-cost flow cell was developed, built and optimized in order to observe dynamic interfacial tension of continuous flow systems. Distinct materials can be used in one of the cell walls in order to observe the intermolecular forces between the flowing liquid and the chemical constitution of the walls. The fluorescence depolarization was evaluated using Rhodamine B as fluorescent probe seeded in ethylene glycol. The effects of the positioning angles on the data acquired across the cell are reported. The reproducibility of the data was evaluated with a spectrometer assembled in-house and the relative standard deviation was below 3%.

Preparação de amostra de fígado bovino e estudo de micro homogeneidade para a determinação de Cd E Pb por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta de sólido

This work describes a systematic study for bovine liver sample preparation for Cd and Pb determination by solid sampling electrothermal atomic absorption spectrometry. Samples were prepared using different procedures: (1) drying in a household microwave oven followed by drying in a stove at 60 ºC until constant mass, and (2) freeze-drying. Ball and cryogenic mills were used for grinding. Particle size, sample size and micro sample homogeneity were investigated. All prepared samples showed good homogeneity (He < 10) even for low sample mass, but samples dried in a microwave oven/stove and ground in a ball mill presented the best homogeneity.

Pilhas a combustível de óxido sólido: materiais, componentes e configurações

In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 ºC) and intermediate (T < 800 ºC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic principles, types of fuel cell, fabrication methods, cell configurations and the development of components (cathodes, anodes, electrolytes, interconnect) and materials.