Repositório RCAAP

This work developed a flow system for pre-concentration and determination of fluoride by molecular absorption spectrophotometry using SPADNS method in water samples. The method is based on the reaction of fluoride ions with the complex zirconium and the trisodium salt of 1,8-dihydroxy-2- (4-sulfophenylazo) -naphthalene-3,6-disulphonic acid (SPADNS), leading to discoloration. The samples were pre-concentrated in a Tygon® minicolumn tube with 5 cm long and 2.0 mm internal diameter, containing Layered Double Hydroxides (NO3.Mg-Al LDH) used as adsorbent for the retention of fluoride ions. Thereafter, the fluorine ions were eluted with sodium hydroxide 0.5 mol L-1 and determined by SPADNS method. The flow system was constructed of solenoid valves, in order to improve analytical performance, as each independent valve injects the solutions so leading to a more efficient use of the reagents. The variables that affect the system such as the mass of adsorbent, type of eluent, eluent flow rate and pre-concentration, SPADNS concentration and pH effect were evaluated. The material was characterized by a variety of techniques, including Mid-Infrared Spectroscopy (FT-MIR) and Scanning Electron Microscopy (SEM). Surface area and the average diameter of the particles was also determined. The results of the optimal conditions, selected with the compromise between sensitivity and the analytical speed, was mass of adsorbent 150 mg; pre-concentration flow rate 3 mL min-1; elution flow rate 1 mL min-1, using as the eluent sodium hydroxide 0.5 mol L-1; hydrochloric acid concentration in SPADNS 1.8 mol L-1. The detection limit was 15 ug L-1, the limit of quantification of 50 ug L-1, relative standard deviation of 0.8 %, linear range of 50-500 ug L-1 and pre-concentration factor of 10.3. The accuracy of the method was evaluated by analysis of certified material ALPHA APS 1076 (Simulated Rain Water), the values were not significantly different at a 95% level of confidence with the certified value. The method was applied in the analysis of water and the levels found were below the maximum values established by Brazilian regulation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

There are no reports in the literature of electroanalytical methods for analysis of pharmaceutical formulations containing amlodipine besylate (AML) and atenolol (ATN). In this context, this study aimed to use the boron-doped diamond (BDD) electrode and the batch injection analysis (BIA) system for sequential determination of these compounds in pharmaceutical formulations. The sequential determination of the two compounds was performed by applying two potentials as a function of time using BR buffer pH 2.0 as supporting electrolyte. AML was selectively detected at +1.00 V and ATN at +1.65 V. An additional potential pulse (0.0 V / 300 ms; pulsed amperometric detection) was applied to avoid contamination/passivation of the BDD electrode surface. Under these conditions both compounds showed a linear response range of 5 to 25 μmol L-1 (r> 0.99), good repeatability (RSD < 3.2 %; n = 10), limits of detection 0.074 μmol L-1, limits of quantification 0.25 μmol L-1 and high analytical frequency (> 70 injections h-1). The results obtained with the proposed method were compared to those obtained by HPLC and similar results were obtained (at 95% of confidence level).

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

In this study were obtained pure and doped indium oxide (In2O3) nanoparticles with different concentrations of La3+ and Er3+, rare-earth ions (RE), from the preparation of the hydroxide indium (In(OH)3) by microwave hydrothermal method followed by calcination in a microwave oven. The precursors, pure In(OH)3 and RE-doped In(OH)3, were synthesized at 140 °C with a short time reaction of 2.0 minutes, and from the calcination of such materials in a microwave oven at 350 °C for 2.0 min particles were obtained pure and doped In2O3. The X-ray diffraction showed the formation of the cubic phase for the pure In2O3 and two phases, cubic and rhombohedral, for the samples doped with different concentrations of La3+ and Er3+ ions, indicating that the addition of the RE ions in the In2O3 lattice leads to a structural rearrangement with the formation of the second phase. The characteristic Raman modes for the cubic and rhombohedral In2O3 structures were observed for the pure and doped samples, respectively, and the presence of RE ions generates local distortions, causing a disorder to short range in the In2O3 structure. The structural changes resulting from the effect of the incorporation of the Er3+ and La3+ were also observed in the images of electron diffraction patterns. Nanoparticles around 10 nm from rounded to cubic shapes, wherein the sample doped with a higher concentration of La3+ ions exhibited a more regular cubic morphology, was observed by scanning and transmission electronic microscopy. Uv-vis spectra revealed absorption bands resulting from the Er3+ f-f transitions, which are intensified with increasing concentration of these ions incorporated into the In2O3 network, while the samples doped with La3+ ions were characterized by the absence of absorption in the visible region. All samples showed photoluminescent properties with a broad band emission in the visible region and maximum peak in the orange region mainly attributed to the presence of oxygen vacancies. The photoluminescence phenomenon is related to structural defects on medium and short ranges that may be generated during the preparation of the materials in the presence of different concentrations of La3+ and Er3+ added in the crystalline In2O3 lattice. These defects exert important role related to semiconductor features, in this study the influence of doping on photocatalytic performance of the synthesized materials was verified.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

An electrochemical determination methodology of Parathion was investigated based on the amperometric detection of multiple pulses in a flow injection analysis system (FIA). A propulsion system without pulsation and an electrochemical detector for flow analysis systems were built and investigated for this determination. Studies of the electrochemical behavior of Parathion on carbon electrodes were investigated in function of the pH and of the supporting electrolyte type. Glassy carbon electrode and citric acid 0.1 mol L-1 supplied the more favorable experimental conditions for the amperometric detection of Parathion. The studies of the amperometric detection of multiple pulses, in the generator-collector mode, under flow analysis conditions, showed that this detection mode increases the sensitivity and the selectivity of the electrochemical determination of Parathion. Stable amperometric signs and of greater sensitivity were obtained when pulse potentials were applied in the sequence: -0.5 V, +0.4 V and -0.1 V, during 30 ms each pulse. The application of these potential pulses involved the following electrode processes, respectively: reduction of RNO2 to RNHOH, oxidation of RNHOH to RNO and reduction of RNO to RNHOH. The relative standard deviation of the amperometric signs obtained at -0.5 V, +0.4 V and -0.1 V was, respectively: 1.5%, 2.0% and 1.4%. The studies showed that the amperometric detection of multiple pulses in the generator-collector mode also increases the selectivity of the nitrophosphates detection, because it allows to differentiate the amperometric sign due to these compounds through the amperometric sign of the electroative products formed at -0.5 V. An increase of the sensitivity of the analytical sign was reached through the algebraic sum, in module, of the amperometric signs obtained in -0.5 V, + 0.4 V and 0.1 V. Limit detection of 0.14 mg L-1 for Parathion and a linear range from 10 to 50 mg L-1 were obtained. These findings indicate that the methodology investigated in this work presents good repeatability, selectivity and sensibility, and it can be used for the determination of total nitrophosphates in natural waters. Recovery studies carried out with water samples of river (Rio Uberabinha) spiked with Parathion at level of 20 mg L-1 showed a recovery of 102%, with relative standard deviation of 1.7%.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This work turns on the process of intercalation of two types of dyes in DNA, the Brilliant Blue FCF, an food dye and the Coomassie Blue G-250, that is habitually used in biochemists assays. Data gotten through assays of the spectroscopy of absorption in the region of the UV/Vis and of infrared with regard to the complex formed between DNA/ Brilliant Blue show an effective interaction between Brilliant Blue FCF and the DNA, strengthening the possibility of the dye to be intercalating enter the bases of the DNA, occupying mainly the site of guanine. So excellent alterations in the absorptions with regard to the formed complex had not been observed enter the DNA/Coomassie Blue. We can conclude that the Coomassie Blue G-250 can be binding through electrostatic interaction in the surface of the DNA, that is, binding to the phosphate groups.

The prostate cancer in initial stages is completely asymptomatic. It is detected in routine exams by digital rectal exam. The diagnosis by PSA must be followed by a rectal ultrasonography being necessary the development of diagnostic platforms that may generate fast results with specificity, sensibility and low costs, features found on biological sensors. Among these biosensors, there are those based on DNA. Polymers as poly(aminophenols) are support matrices and can be used for the immobilization of biomolecules due to their features such as excellent permeability, selectivity, reproducibility and fast response. It was possible the electropolymerization of 2-aminophenol and 3-aminophenol. This polymer presents a self-limited growth and non-conducting behavior, confirmed in solution containing the redox pair Fe2+/Fe3+ while that polymer presents a polymeric film with conducting properties. These data are corroborated by EIS through analysis of resistance values, low for poly(2-aminophenol) and high for poly(3-aminophenol). Measurements of mass made by MECQ points a greater amount of polymeric film for poly(3-aminophenol) than for poly(2-aminophenol). Increasing the pH values results in a shift on the potential of the monomer oxidation to more cathodic potentials and a decreasing on the current values. SEMs and AFMs show rough films with different thickness, thinner to poly(3-aminophenol). FTIR results suggest possible polymerization through NH2 with the presence of free OH bands, due to the possibility of C-N-C bounds of secondary aromatic amines. The detection of purinic and pyrimidinic bases, isolated and in a mix, was possible showing that the interactions between them and the polymeric films occur by a similar mechanism. Experiments of immobilization of prostate cancer specific PCR products, with 277 base pairs were performed, denatured and hybridizated with ferrocenecarboxyaldheyde as mediator for the detection process. It is possible the construction of modified electrodes with polymeric films derived from 2-aminophenol and 3-aminophenol, presenting distinct spectroscopic and electrochemical properties. The polymers can be used as DNA nitrogenated bases detection matrices and they have the possibility of being used for biosensor construction.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study had as purpose to investigate and to analyze the learning of the Chemistry pre-service teachers on chemical equilibrium identifying their difficulties to develop it, carried through in an Undergraduate Chemistry Course of a university. It was appealed to the qualitative research, with the analysis of questionnaires with opened questions, half-structuralized interviews and lesson plans done by the preservice teachers. To get the necessary data is was delimited as object of research, all of the 47 students registered in specifics subjects of Undergraduate Chemistry Course. The analysis of the data showed that the education of the topic about chemical equilibrium in the teachers formation is guided (for great part of the professors) by a conception that stimulates the mechanical way, reproductive, emphasizing much more the repetitive character than the potential to support the construction of concepts. According to the pre-service teachers reports, the professors unconsidered their previous knowledge and although this is a subject of High School, they need to deepen their knowledge in this area. The analysis of the questionnaires suggest that the students have difficulties with the conceptualization of the chemical equilibrium, the application of the rules of Le Chatelier and the equilibrium in watery way.

This study had as a principal aim, to investigate the use of different technologies in teaching Molecular Geometry and fundamentally, identify if the software ChemSketch® empowers or opposes the elaboration of more adequate models of chemical structures. To subsidize this study, it was needed to appeal to the quality research which resulted in a study of case. The study of the case was the procedure method which was adopted, aiming a 2nd high school class of 28 students, in a private school in the state of Minas Gerais. The students had the opportunity to deal with different situations while being taught chemistry with the use of technologies, and also to assess the aspects related to learning chemistry. The date was collected through questionnaires; recording of audio and video activities and the elaboration of a planning of the chemistry activities which involved the technology of blackboard and chalk, the technology of using isopor Balls and Sticks and the software ChemSketch®. The analyses were made following 2 perspectives: the evolution of the students due to the use of each of the technologies and the observations and registrations made in the learning environments. Regarding the analyses of the questionnaires, and the observations and registrations in the learning environments it was possible to realize that the development of the activities in a balanced way among the technologies supports the learning to students, due to the fact that it built the structures in a more adequate way. Although the software provided a better view of the molecules structures, the students did not come to a satisfactory performance, which suggests that in the use of the computer, the teacher performs a fundamental role.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Se estudió el potencial alelopático del extracto metanólico de hojas, raíz, tallo y espinas de timbete, con el propósito de evaluar su eficiencia en relación a inhibición de germinación de semillas de Panicum maximum, Lolium perene, Amaranthus hypochondriacus, Trifolium alexandrium y Physalis ixocarpa en placas petri y casa de invernadero, y posterior caracterización de los compuestos alelopáticos responsables por la inhibición. Fueron realizados ensayos de germinación con foto-período de 10 horas, durante 7 días, usando soluciones de los extractos en concentraciones de 25, 50, 100, 150 e 200 ppm. Después del fraccionamiento cromatográfico del extracto bruto de la raíz, las fracciones obtenidas con solventes diclorometano y con la mezcla acetato de etilo/metanol (1:1) presentaron los mejores resultados de inhibición de las semillas de Panicum maximum para los parámetros: Crecimiento de raíz, tallo, porcentaje de germinación y producción de biomasa. El extracto metanólico de la raíz y tallo presentaron mayor inhibición para la especie Amaranthus hypochondriacus y la especie Trifolium alexandrium fue menos afectada. El extracto metanólico de la raíz de Cenchrus echinatus presentó mayor eficiencia cuando comparado con el extracto de tallo, obteniendo valores de inhibición de hasta 100%. Análisis cualitativa de los metabólitos secundários presentes en el extracto metanólico de raíz de Cenchrus echinatus mostraron resultados positivos para alcaloides, glicosidos cardiotónicos y triperpenos y/o esteróides.

Mestre em Tecnologias, Comunicação e Educação