Caracterização espectroscópica multivariada do potencial antioxidante de vinhos

In this work the antioxidant capacity of red wine samples was characterized by conventional spectroscopic and chromatographic methodologies, regarding chemical parameters like color, total polyphenolic and resveratrol content, and antioxidant activity. Additionally, multivariate calibration models were developed to predict the antioxidant activity, using partial least square regression and the spectral data registered between 400 and 800 nm. Even when a close correlation between the evaluated parameters has been expected many inconsistencies were observed, probably on account of the low selectivity of the conventional methodologies. Models developed from mean-centered spectra and using 4 latent variables allowed high prevision capacity of the antioxidant activity, permitting relative errors lower than 3%.

Determinação de misturas de sulfametoxazol e trimetoprima por espectroscopia eletrônica multivariada

In this work a multivariate spectroscopic methodology is proposed for quantitative determination of sulfamethoxazole and trimethoprim in pharmaceutical associations. The multivariate model was developed by partial least-squares regression, using twenty synthetic mixtures and the spectral region between 190 and 350 nm. In the validation stage, which involved the analysis of five synthetic mixtures, prediction errors lower that 3% were observed. The predictive capacity of the multivariate models is seriously affected by spectral changes induced by pH variations, a fact that acquires a great significance in the analysis of real samples (pharmaceuticals) that contain chemical additives.

SISTEMAS ALTERNATIVOS DE CALIBRAÇÃO PARA DETERMINAÇÃO ESPECTROFOTOMÉTRICA SIMULTÂNEA DE ESPÉCIES COM INTERFERÊNCIA ESPECTRAL

Two simple and efficient procedures have been developed for the rapid simultaneous determination of compounds with mutual spectral interference (rifampicin (RIF) and isoniazid (INH)). The first method was based on the UV–Vis spectral signal (190–600 nm) of synthetic RIF and INH aqueous solutions, whereas the second method involved the visible spectral signal registered between 350 and 800 nm after the reaction of INH with a Cu2+/neocuproine complex. Both multivariate spectrophotometric methods show excellent prevision capacity, providing results that are statistically equivalent with those provided by the standard chromatographic procedure. The methods were validated according to criteria established by ANVISA, showing precision, accuracy and robustness compatible with the requirements for new analytical methods, additionally allowing the reduction of waste generation.

Estudo das propriedades ópticas em vidros 0,3La2S3-0,7Ga2S 3

In this work we describe the synthesis and characterization of chalcogenide glass (0.3La2S3-0.7Ga2S 3) with low phonons frequencies. Several properties were measured like Sellmeier parameters, linear refractive index dispersion and material dispersion. Samples with the composition above were doped with Dy2S3. The absorption and emission characteristics were measured by electronic spectroscopy and fluorescence spectrum respectively. Raman and infrared spectroscopy shows that these glasses present low phonons frequencies and strucuture composed by GaS4 tetrahedrals. The Lines model was used for calculate the coefficients values of the non linear refractive index.

Síntese e caracterização de novos compostos de coordenação de cobre (II) com ligantes não-simétricos N,O-doadores: contribuições para o sítio ativo da galactose oxidase

The reactions of four new unsymmetrical N,O-donor ligands, {H2BBPETEN= [N-(2-hydroxybenzyl) - N,N' - bis(2 methylpyridyl) -N'-(hydroxyethyl) ethylenodiamine], H3BPETEN=[N,N'- bis(2-hydroxybenzyl) -N- (2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine], HTPETEN=[N,N,N'- tris(2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine] and H3BIMETEN=[N,N'-(2-hydroxybenzyl)-N-(1-methylimidazol-2-il-methyl)-N'- (hydroxyethyl)ethylenodiamine]}, with Cu(II) salts afforded the following mononuclear compounds: [CuII(HBBPETEN)]ClO4, [CuII(H2BPETEN)]ClO4 , [CuII(HTPETEN)](PF6)2 and [CuII(H2BIMETEN)]ClO4 . All were characterized by EPR, electronic spectroscopy and electrochemistry. The four copper (II) compounds showed interesting electrochemistry properties. All presented an anodic wave that can be attributed to the Cu (I) oxide formation at the electrode surface, or to a Cu0 sediment at the same surface or yet, to Cu(I) -> Cu(II) oxidation process with coupled chemistry reaction, due to their irreversibility. Two of the complexes are described as interesting synthetic models for the active site of the metalloenzyme galactose oxidase.

Preparação de LiNbO3 e LiNbO3:Eu3+ pelo método dos precursores poliméricos

The ferroelectric compound LiNbO3 was prepared by the polymeric precursors method in the polycrystalline form containing different concentrations of Eu3+. The compounds were characterized by X-ray diffraction, vibrational and electronic spectroscopy. Electronic spectroscopy was shown to be sensitive to small concentrations of contaminating phases allowing a good control of the compound purity. The presence of Eu3+ ions leads to the formation of the LiNb3O8 phase in the range of 500 to 800 °C. Above this temperature range LiNbO3 and tetragonal (T') EuNbO4 were obtained.

O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Synthesis, structure and physicochemical properties of zinc and copper complexes based on sulfonamides containing 8-aminoquinoline ligands

Sulfonamides obtained by reaction of 8-aminoquinoline with 4-nitrobenzenesulfonylchloride and 2,4,6-triisopropylbenzenesulfonyl chloride were used to synthesize coordination compounds with CuII and ZnII with a ML2 composition. Determination of the crystal structures of the resulting zinc and copper complexes by X-ray diffraction show a distorted tetrahedral environment for the [Cu(qnbsa)2], [Cu(qibsa)2] and [Zn(qibsa)2] complexes in which the sulfonamide group acts as a bidentate ligand through the nitrogen atoms from the sulfonamidate and quinoline groups. The complex [Zn(qnbsa)2] crystallizes with a water molecule from the solvent and the Zn is five-coordinated and shows a bipyramidal-trigonal geometry. The electrochemical and electronic spectroscopy properties of the copper complexes are also discussed.

Organização supramolecular da ftalocianina de cobalto(II) e seu efeito na oxidação do aminoácido cisteína

The interest in the chemistry of cobalt (II) tetrasulfonated phthalocyanine (PcTsCo) comes mainly from its macrocycle-ligand structure combined with their special chemical characteristics, such as high solubility, well-defined redox reactions and remarkable optical absorption in the visible region. In this work, we use layer-by-layer technique in order to assemble CoTsPc and poly(allylaminehydrochloride) (PAH) in hybrid supramolecular system. The electronic spectroscopy and cyclic voltammetry techniques were utilized to study PAH/CoTsPc multilayers growth and the cysteine catalytic oxidation. PAH/CoTsPc showed high electrochemical stability and worthwhile to mention is the remarkable influence of supramolecular arrangement on the final redox properties of the system.

Abordagem teórico-experimental da teoria do campo cristalino na disciplina de síntese inorgânica

We describe herein the synthesis and characterization of the complexes KNiF3, [Ni(en)3]I2, [Ni(en)3]Cl2, [Ni(acac)2(H2O)2], [Ni(en)2(H2O)2]Cl2 and [Ni(NH3)6](BF4)2 (en = ethylenediamine, acac- = acetylacetonate) performed in the inorganic synthesis major course at the Chemistry Institute of UFRGS (Universidade Federal do Rio Grande do Sul). The compounds were characterized by infrared and electronic spectroscopy and the electrolytic conductivity was measured. The parameters 10Dq and B were obtained from the electronic spectra and the nefelauxetic and spectrochemical series were determined. The obtained spectrochemical series was F- < acac- < NH3 < en and the nefeulaxetic series was en < NH3 < acac- < F-.

Simultaneous spectrophotometric determination of lamivudine and zidovudine in fixed dose combinations using multivariate calibration

The simultaneous determination of two or more active components in pharmaceutical preparations, without previous chemical separation, is a common analytical problem. Published works describe the determination of AZT and 3TC separately, as raw material or in different pharmaceutical preparations. In this work, a method using UV spectroscopy and multivariate calibration is described for the simultaneous measurement of 3TC and AZT in fixed dose combinations. The methodology was validated and applied to determine the AZT+3TC contents in tablets from five different manufacturers, as well as their dissolution profile. The results obtained employing the proposed methodology was similar to methods using first derivative technique and HPLC.

Application of fourier transform infrared spectroscopy, chemical and chemometrics analyses to the characterization of agro-industrial waste

Agroindustrial waste in general presents significant levels of nutrients and organic matter and has therefore been frequently put to agricultural use. In this context, the objective of this study was to determine the chemical composition, nitrogen, phosphorus, potassium, calcium, magnesium and carbon content, as well as the qualitative characteristics through Fourier transform infrared spectroscopy of four samples of poultry litter and one sample of cattle manure, from the southwestern region of Paraná, Brazil. Results revealed that, in general, the poultry litter presented higher amount of nutrients and carbon than the cattle manure. The infrared spectra allowed identification of the functional groups present and the differences in degree of sample humification. The statistical treatment confirmed the quantitative and qualitative differences revealed.

Sample surveys via electronic mail: a comprehensive perspective

Although postal questionnaires, personal interviewing, and telephone interviewing are the main methods of survey-based research, there is an increasing use of e-mail as a data collection medium. However, little, if any, published Western research in general and that of Turkish in particular have investigated e-mail survey technique from pure survey research perspective. Attempting to develop a framework to assess e-mail as a data collection mean, the purpose of this study is to explore e-mail-based questionnaire technique from complementary angles. To this goal, sample representativeness, data quality, response rates, and advantages and disadvantages of e-mail surveying are discussed.

Electronic government policies in Brazil: context, ICT management and outcomes

The State Reform processes combined with the emergence and use of Information and Communication Technology (ICT) originated electronic government policies and initiatives in Brazil. This paper dwells on Brazilian e-government by investigating the institutional design it assumed in the state's public sphere, and how it contributed to outcomes related to e-gov possibilities. The analyses were carried out under an interpretativist perspective by making use of Institutional Theory. From the analyses of interviews with relevant actors in the public sphere, such as state secretaries and presidents of public ICT companies, conclusions point towards low institutionalization of e-gov policies. The institutional design of Brazilian e-gov limits the use of ICT to provide integrated public services, to amplify participation and transparency, and to improve public policies management.

Sensitivity analysis for unmeasured confounders using an electronic spreadsheet

In studies assessing the effects of a given exposure variable and a specific outcome of interest, confusion may arise from the mistaken impression that the exposure variable is producing the outcome of interest, when in fact the observed effect is due to an existing confounder. However, quantitative techniques are rarely used to determine the potential influence of unmeasured confounders. Sensitivity analysis is a statistical technique that allows to quantitatively measuring the impact of an unmeasured confounding variable on the association of interest that is being assessed. The purpose of this study was to make it feasible to apply two sensitivity analysis methods available in the literature, developed by Rosenbaum and Greenland, using an electronic spreadsheet. Thus, it can be easier for researchers to include this quantitative tool in the set of procedures that have been commonly used in the stage of result validation.