Alcóxidos como precursores na síntese de novos materiais através do processo sol-gel

An overview about the role of alkoxides in the most recent uses of the sol-gel process in the synthesis of new materials is presented. Special attention is focused on the uses of silicon, aluminum, zirconium and titanium alkoxides. This review shows that the alkoxides enable the synthesis of new matrices with controlled surface area, acidity and porosity, as well as some unusual properties. The property associated with the solubility of metal alkoxides opens enormous possibilities of combining them for the synthesis films of powders with a very large range of metal compositions.

Especiação analítica de compostos de arsênio empregando métodos voltamétricos e polarográficos: uma revisão comparativa de suas principais vantagens e aplicações

This paper provides a review on voltammetric and polarographic methods for the speciation analysis of inorganic and organic arsenic compounds in different matrices. A discussion on the main advantages of electroanalytical methods in comparison with other analytical methods employed for arsenic speciation is presented. The mechanistic aspects of the most relevant techniques employing cathodic and anodic stripping voltammetry as well as polarographic methods published in the last twenty five years are summarized and discussed. The bibliographic references cited in this work were selected from the Web of Science (published by the ISI) and the main journals of analytical chemistry.

Adsorção/dessorção do explosivo tetril em turfa e em argissolo vermelho amarelo

This paper presents the study of adsorption/desorption of the explosive tetryl (2,4,6-trinitrophenylmethyl-nitramine) in different matrices, such as in natura soil, roasted soil, humic acid of soil, in natura peat, roasted peat and humic acid of peat. The aim of the study is to evaluate the interaction capacity of those matrices with the explosive. The analytic technique used was HPLC (high performance liquid chromatography), with UV-detection at 230 nm. The Freundlich isotherms were utilized for the mathematical treatment of the data. The results indicated that in natura soil and in natura peat (with organic substances) are excellent matrices for the retention of tetryl, adsorbing it and keeping it immovable, preventing it from contaminating the groundwater. The largest adsorption of the explosive ocurred in in natura soil, while the smallest desorption was observed in in natura peat. After the calcination of the matrices, the smallest adsorption was observed, indicating that the retention occurs in the organic substance.

PARAFAC: uma ferramenta quimiométrica para tratamento de dados multidimensionais. Aplicações na determinação direta de fármacos em plasma humano por espectrofluorimetria

Since the last decade, the combined use of chemometrics and molecular spectroscopic techniques has become a new alternative for direct drug determination, without the need of physical separation. Among the new methodologies developed, the application of PARAFAC in the decomposition of spectrofluorimetric data should be highlighted. The first objective of this article is to describe the theoretical basis of PARAFAC. For this purpose, a discussion about the order of chemometric methods used in multivariate calibration and the development of multi-dimensional methods is presented first. The other objective of this article is to divulge for the Brazilian chemical community the potential of the combination PARAFAC/spectrofluorimetry for the determination of drugs in complex biological matrices. For this purpose, two applications aiming at determining, respectively, doxorrubicine and salicylate in human plasma are presented.

Desafios da química analítica frente às necessidades da indústria farmacêutica

The development of liquid chromatography-mass spectrometric (LC-MS) techniques in the last few decades has made possible the analysis of trace amounts of analytes from complex matrices. With LC, the analytes of interest can be separated from each other as well as from the interfering matrix, after which they can be reliably identified thanks to the sensitivity and specificity of MS. LC-MS has become an irreplaceable tool for many applications, ranging from the analysis of proteins or pharmaceuticals in biological fluids to the analysis of toxic substances in environmental samples. In different segments of Brazilian Industry mass spectrometry has an important role, e.g. in the pharmaceutical industry in the development of generic formulations, contributing to the growth of Industry and social inclusion. However, the Brazilian chemists until this moment don't have an effective role in this new segment of the analytical chemistry in Brazil. The present paper shows the actual scenario for mass spectrometry in the pharmaceutical industry, emphasizing the need of a revision of graduation courses to attend the needs of this growing market.

Utilização de técnicas eletroanalíticas na determinação de pesticidas em alimentos

The aim of this work is to discuss selected applications of electroanalytical techniques for the detection of pesticides in foods and beverages, published in the last ten years. The applications involved different working electrodes for the electroanalytical determination of pesticides, namely amperometric biosensors, cholinesterase-based biosensors, polymer-modified electrodes, ultramicroelectrodes and hanging mercury drop electrodes. They were used for several voltammetric and amperometric techniques in different analytical procedures for the detection and quantification of different classes of pesticides in different food matrices.

Azul de metileno imobilizado na celulose/TiO2 e SiO2/TiO2: propriedades eletroquímicas e planejamento fatorial

The electrochemical properties of methylene blue immobilized on cellulose/TiO2 and mixed oxide SiO2/TiO2 matrices were investigated by means of cyclic voltammetry. The electron mediator property of the methylene blue was optimized using a factorial design, consisting of four factors in two levels. The experimental observations and data analyses on the system indicate that the lowest peak separation occurs for Sil/TiOAM, 1.0 mol L-1 KCl solution and 20 mV s-1 scan rate, while values of current ratio closest to unity were found for Cel/TiOAM independent of electrolyte concentration, 0.2 or 1.0 mol L-1, and scan rate, 20 mV s-1 or 60 mV s-1.

New approximation to the third-order density : application to the calculation of correlated multicenter indices

In this work we present the formulas for the calculation of exact three-center electron sharing indices (3c-ESI) and introduce two new approximate expressions for correlated wave functions. The 3c-ESI uses the third-order density, the diagonal of the third-order reduced density matrix, but the approximations suggested in this work only involve natural orbitals and occupancies. In addition, the first calculations of 3c-ESI using Valdemoro's, Nakatsuji's and Mazziotti's approximation for the third-order reduced density matrix are also presented for comparison. Our results on a test set of molecules, including 32 3c-ESI values, prove that the new approximation based on the cubic root of natural occupancies performs the best, yielding absolute errors below 0.07 and an average absolute error of 0.015. Furthemore, this approximation seems to be rather insensitive to the amount of electron correlation present in the system. This newly developed methodology provides a computational inexpensive method to calculate 3c-ESI from correlated wave functions and opens new avenues to approximate high-order reduced density matrices in other contexts, such as the contracted Schrödinger equation and the anti-Hermitian contracted Schrödinger equation

Fotoluminiscencia visible debida a capas de SiO2. implantadas con silicio y carbono

Se ha n realizado implantaciones de silicio y de carbono + silicio en matrices aislantes de SÍO2 térmico, las cuales, después de un recocido a alta temperatura precipitan en forma de nanocristales de tamaños comprendidos entre 30 y 60 Á. Estas estructuras presentan una intensa fotoluminiscencia en el rojo profundo (1.4-1.6 eV) y el verde (2.0-2.2 eV). La energía e intensidad de las bandas depende fuertemente de la temperatura y duración del recocido. Diferentes comportamientos se han encontrado para las bandas roja y verde, incluyendo la cinética de desexcitación y el origen estructural. Los experimentos de absorción infrarroja, Raman y microscopía electrónica demuestran que los nanocristales son los responsables de la banda roja mientras que agregados amorfos de carbono son los responsables de la verde.

Coordenadas cartesianas moleculares a partir da geometria dos modos normais de vibração

A simple method to obtain molecular Cartesian coordinates as a function of vibrational normal modes is presented in this work. The method does not require the definition of special matrices, like the F and G of Wilson, neither of group theory. The Eckart's conditions together with the diagonalization of kinetic and potential energy are the only required expressions. This makes the present approach appropriate to be used as a preliminary study for more advanced concepts concerning vibrational analysis. Examples are given for diatomic and triatomic molecules.

Utilização da extração em fase sólida (SPE) na determinação de hidrocarbonetos policíclicos aromáticos em matrizes aquosas ambientais

Polycyclic aromatic hydrocarbons (PAHs) are a great environmental concern mainly because of their toxic, mutagenic and carcinogenic potential. This paper reports utilization of the solid-phase extraction (SPE) technique to determine PAHs in environmental aqueous matrices. The recovery from environmental aqueous matrices fortified with PAHs varied from 63.7 to 93.1% for atmospheric liquid precipitation, from 38.3 to 95.1% for superficial river water, and from 71.0 to 95.5% for marine water. No negative matrix effect was observed for the recovery of PAHs from atmospheric liquid precipitation and marine water, but was observed for superficial river water, particularly for PAHs possessing 5 and 6 aromatic rings.

On the structure of cooperative and competitive solutions for a generalized assignment game

We study cooperative and competitive solutions for a many- to-many generalization of Shapley and Shubik (1972)'s assignment game. We consider the Core, three other notions of group stability and two al- ternative definitions of competitive equilibrium. We show that (i) each group stable set is closely related with the Core of certain games defined using a proper notion of blocking and (ii) each group stable set contains the set of payoff vectors associated to the two definitions of competitive equilibrium. We also show that all six solutions maintain a strictly nested structure. Moreover, each solution can be identified with a set of ma- trices of (discriminated) prices which indicate how gains from trade are distributed among buyers and sellers. In all cases such matrices arise as solutions of a system of linear inequalities. Hence, all six solutions have the same properties from a structural and computational point of view.

Estabilidad de la glucosa oxidasa en sistemas amorfos formados por los disacáridos sacarosa, maltosa y trehalosa

Glucose-oxidase (GOD), suffers conformational change during freeze-drying. In order to determine the protection level granted by amorphous matrices (AM) of saccharose, maltose, trehalose and their combinations, the thermal inactivation constants (K D) of GOD trapped in these systems were determined. For its evaluation, GOD samples were balanced at different water activities and heated up to 30, 50 and 70 ºC. The best AM found for GOD stability was saccharose-trehalose (5/10% p/v). The K D values (K D.10-4) at a w = 0.0 were 3 at 30 ºC and 6 at 70 ºC. For non-protected GOD under the same conditions these values were 48 at 30 ºC and 257 at 70 ºC.

O enfoque da metrologia química em análises toxicológicas na atividade turfística: validação de método analítico para determinação de cafeína em matrizes biológicas

This paper proposes an alternate method to detect forbidden doping substances present in biological matrices of horseracing. The method was fully validated for caffeine, identified as the most frequent forbidden substance in the analysis conducted by the Antidoping Laboratory of the Brazilian Jockey Club, which adopts a zero threshold limit according to national and international horseracing practices. The metrological reliability of the method applied to toxicological analysis in biological matrices is discussed. Although the analytical method proposed for detection of a zero threshold level of the doping substance is qualitative, it was validated for the determination of the limiting value (also known as quantification limit value) introducing a criterion that prevents the issuing of incorrect results ("false-positives" and "false-negatives").

Experiència dels cuidadors i les cuidadores principals informals que tenen cura d'un familiar vell amb demència des de fa més de quatre anys

El treball que es presenta vol respondre la pregunta de quina és l’experiència dels cuidadors i les cuidadores principals informals que tenen cura d’un familiar vell amb demència des de fa més de 4 anys. Després de plantejar les hipòtesis de partida, es defineixen els objectius generals i específics i s’expliquen l’interès, la justificació, la rellevància i l’aportació d’aquest estudi. En l’apartat corresponent a l’estat de la qüestió i la fonamentació conceptual, després de fer una revisió bibliogràfica, es descriuen els elements que formen part d’aquesta temàtica: perfils dels receptors de cures i de les cuidadores, significat de tenir cura, vida quotidiana i qualitat de vida i descripció del model conceptual de Virginia Henderson. En el capítol següent s’exposen la metodologia, el paradigma i el mètode d’investigació utilitzats en aquest treball, així com les matrius d’anàlisi del contingut i del discurs. A partir d’aquí s’exposen els resultats en funció dels objectius plantejats. En la discussió, s’analitzen i s’interpreten les dades obtingudes i es contraposen amb altres estudis, a més de fer-se una reflexió personal sobre els aprenentatges adquirits i una proposta de línies de treball futures. A continuació s’exposen unes conclusions per resumir la informació obtinguda. En la secció de referències bibliogràfiques es detallen les fonts consultades, i en els annexos hi consten els models d’entrevista i de matriu per a l’anàlisi de dades, el full de consentiment informat, així com el buidatge i l’anàlisi de les entrevistes.