TOP - um programa de cálculo de descritores topológicos para uso em correlações entre estrutura e atividade

A computational interface, using sybyl format as an input file, was created in order to calculate connectivity indexes. After generation and classification of all substructures, which derive from the molecular structure, this interface calculates all possible orders from zero up to the maximun number of bonds in the molecule. Other topological indexes such as Wiener and Schultz indexes can also be calculated.

Construção e otimização de um sistema para produção e aplicação de ozônio em escala de laboratório

This paper shows the assembly of an ozonization system to be used in laboratory scale, mainly to study effluent treatability. The system is simple, practical and provides easy acquisition of data when interfaced to a microcomputer. The performance of ozone generation and K La values are also described.

Otimização de um mecanismo fotoquímico para a simulação da atmosfera urbana brasileira

A photochemical reaction mechanism for the description of air quality in Brazilian urban regions is described and evaluated by comparison with chamber experiments. The mechanism was developed for use in ozone modeling and application of control strategies. The oxidation of ethanol and methyl-ter-butyl-ether is also considered. Using this chemical model, a trajectory simulation of Brazil Avenue, Rio de Janeiro, was performed. The model predicts that ozone should reach a maximum of 22.4 ppb at 14:57 h. This value is in good agreement with the experimental measurements of 22.5 ppb for 14:00 h and 22.3 ppb for 15:00 h.

Uma abordagem robusta de cálculo aplicada a um sistema potenciométrico de medida de concentrações hidrogeniônicas em soluções aquosas

The data analyzed in this work were generated following the methodology developed by Molina et al.(J. Electroanal. Chem., 1979) for the calibration of a potentiometric system of measurement of hydrogen-ion concentrations resulting from neutralizations, at 25 ºC, of acidic or alkaline solutions at constant ionic strength (0.1 mol.l-1) held with NaClO4. The observed data present a serious deviation in relation to the mathematical model derived from the Nernst equation, for pH values ranging from 3 to 11, where pH=-log[H+]. We show that the minimization of the sum of the absolute values of the residuals gives estimates that are not influenced by outlying values.

Construção e otimização de um reator de baixo custo para a fotodegradação da matéria orgânica em águas naturais e sua aplicação no estudo da especiação do cobre por voltametria

This work describes the construction of a home-made low-cost reactor, using easily available materials, capable of destroying efficiently dissolved organic matter. Just 30 minutes of irradiation were sufficient to destroy more than 99% of the humic acids present in a solution of 4 mg C L-1. Copper speciation was evaluated in natural waters of different salinities to test the reactor's efficiency in destroying organically complexed metal species. The effect of the organic matter concentration, salinity, dissolved oxygen and temperature in the photo-oxidation process is discussed.

Un análisis comparativo del papel del bucle fonológico versus la agenda visoespacial en el cálculo en niños de 7-8 años = A comparative analysis of the phonological loop versus the visuo-spatial sketchpad in mental arithmetic tasks in 7-8 y.o. children

En esta investigación se ha estudiado la relación entre dos subsistemas de la memoria de trabajo (buclefonológico y agenda viso-espacial) y el rendimiento en cálculo con una muestra de 94 niños españolesde 7-8 años. Hemos administrado dos pruebas de cálculo diseñadas para este estudio y seis medidassimples de memoria de trabajo (de contenido verbal, numérico y espacial) de la «Batería de Testsde Memoria de Treball» de Pickering, Baqués y Gathercole (1999), y dos pruebas visuales complementarias.Los resultados muestran una correlación importante entre las medidas de contenido verbaly numérico y el rendimiento en cálculo. En cambio, no hemos encontrado ninguna relación con las medidasespaciales. Se concluye, por lo tanto, que en escolares españoles existe una relación importanteentre el bucle fonológico y el rendimiento en tareas de cálculo. En cambio, el rol de la agenda viso-espaciales nulo

El papel de la memoria de trabajo en el cálculo mental un cuarto de siglo después de Hitch = The role of working memory in mental arithmetic a quarter of century after Hitch

Desde que Hitch (1978) publicó el primer estudio sobre el rol de la memoria de trabajo en el cálculo han idoaumentando las investigaciones en este campo. Muchos trabajos han estudiado un único subsistema, pero nuestroobjetivo es identificar qué subsistema de la memoria de trabajo (bucle fonológico, agenda viso-espacial o ejecutivocentral) está más implicado en el cálculo mental. Para ello hemos realizado un estudio correlacional en el quehemos administrado dos pruebas aritméticas y nueve pruebas de la “Bateria de Test de Memòria de Treball” dePickering, Baqués y Gathercole (1999) a una muestra de 94 niños españoles de 7-8 años. Nuestros resultadosindican que el bucle fonológico y sobretodo el ejecutivo central inciden de forma estadísticamente significativa enel rendimiento aritmético

Emprego de planejamento fatorial para a otimização das temperaturas de pirólise e atomização de Al, Cd, Mo e Pb por ETAAS

This work describes a factorial design for the optimization of pyrolysis and atomization temperatures in ETAAS. As examples, Cd and Pb were determined using lower pyrolysis and atomization temperatures and Al and Mo with higher pyrolysis and atomization temperatures. Good results were obtained for Cd employing Rh (m o = 1.4 pg) as a permanent modifier with pyrolysis and atomization temperatures of 640 and 1500 °C, respectively. For Zr, W or Zr+W, the Cd pyrolysis and atomization temperatures were 500 and 1500 °C, respectively, with m o = 1.4 pg using Zr or W and 1.5 pg using Zr+W. The best results for Pb were those using Rh, Zr, W and Zr+Rh, obtaining characteristic masses of 42, 37, 34 and 36 pg, respectively. Pyrolysis and atomization temperatures of 910 and 1850 °C, respectively, were achieved for this metal. For Al, the best results were obtained when Zr or Zr+W were used. Mo was also tested as a possible permanent modifier for Al, but the results were not satisfactory. The results obtained for Mo without modifier were similar to those with conventional modifiers (Mg or Pd+Mg) and the results obtained using permanent chemical modifiers were not satisfactory. In all situations, the experiments were performed faster than those using the univariate procedure.

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.

Espectroscopia vibracional: sistemática para o cálculo dos estiramentos CO de complexos carbonílicos e determinação da sua atividade IV e Raman

IR bands related to M-C stretchings are not diagnostically significant for the identification of carbonyl groups in the spectra of carbonyl complexes. Otherwise, the frequency, intensity and number of bands for the CO stretchings provide very useful informations about the number of CO ligands and many others structural proprieties, like the presence of bridged CO groups. We report about a relatively simple and useful method for the determination of the CO stretchings of carbonyl complexes, which considers only the bond stretching internal coordinates of the CO groups.

Sociabilidad, estrategias de relación y cálculo económico: tres estudios de caso

El segundo número de la Revista Naveg@mérica incorpora, además de otros trabajos en cada una de sus secciones, un dossier formado por tres trabajos que se refieren al papel jugado por comerciantes y productores en la sociedad argentina en la transición del orden colonial al republicano. Las tres investigaciones se interesan por buscar en el pasado algunas claves que expliquen el presente económico del país, visto este problema desde el interior de la Argentina. Así, uno de los mayores méritos de los trabajos es ofrecernos una mirada que contrasta con la homogeneidad que siempre se ha concedido a los estudios sobre Buenos Aires como supuestamente "representativos" de lo que ocurría en el país.

Cálculo ab initio de intensidades Raman dinâmicas utilizando a teoria da resposta linear

In this paper a methodology for the computation of Raman scattering cross-sections and depolarization ratios within the Placzek Polarizability Theory is described. The polarizability gradients are derived from the values of the dynamic polarizabilities computed at the excitation frequencies using ab initio Linear Response Theory. A sample application of the computational program, at the HF, MP2 and CCSD levels of theory, is presented for H2O and NH3. The results show that high correlated levels of theory are needed to achieve good agreement with experimental data.

Aplicação da equação de Poisson-Boltzmann ao cálculo de propriedades dependentes do pH em proteínas

The ability of biomolecules to catalyze chemical reactions is due chiefly to their sensitivity to variations of the pH in the surrounding environment. The reason for this is that they are made up of chemical groups whose ionization states are modulated by pH changes that are of the order of 0.4 units. The determination of the protonation states of such chemical groups as a function of conformation of the biomolecule and the pH of the environment can be useful in the elucidation of important biological processes from enzymatic catalysis to protein folding and molecular recognition. In the past 15 years, the theory of Poisson-Boltzmann has been successfully used to estimate the pKa of ionizable sites in proteins yielding results, which may differ by 0.1 unit from the experimental values. In this study, we review the theory of Poisson-Boltzmann under the perspective of its application to the calculation of pKa in proteins.

Otimização dos parâmetros de extração para determinação multiresíduo de pesticidas em amostras de água empregando microextração em fase sólida

In this study the factors that affect the extraction of pesticide residues from water samples for their determination by solid-phase micro-extraction (SPME) and GC/MS were optimized. The fiber polymer, the extraction mode, the ionic strength, the stirring rate, the pH and the extraction time were the most significant parameters evaluated. The recovery obtained with the proposed method ranged from 94 to 110% and the sensitivity of the method, determined by calculating the detection limit (DL), ranged from 0.004 to 0.1 mug l-1. The results obtained with spiked real samples, at the 0.1 mug l-1 level, showed acceptable conformity with the expected values.

Otimização da preparação de eletrodo de pasta de carbono contendo riboflavina imobilizada em suporte inorgânico

The aim of this work was to optimize the preparation of electrodes with riboflavin (RF) immobilized on a silica surface modified with niobium oxide and carbon paste. Electrode preparation was optimized employing a factorial design consisting of two levels and three factors. The electrochemical properties of immobilized RF were investigated by cyclic voltammetry. The factorial analysis was carried out analysing the current intensity (Ipa). It was possible to optimize the electrode to get the best reversibility in the redox process, i. e. the lowest separation between anodic and cathodic peak potentials and a current ratio close to unity. The concentration of supporting electrolyte has a small effect. The proportion has the highest effect and the interaction factor between proportion and mixture has also a significant effect on the current intensity.