The thermal degradation kinetics of avocado seed biomass (Persea americana) was investigated at the heating rates of 5, 15, 20 and 25 ºC min-1 using thermogravimetric (TGA) and differential thermogravimetric (DTG) analysis techniques in the temperature range from ambient to 780 ºC. Chemical analysis of the avocado seed resulted in: 51.4% cellulose, 42.4% hemicellulose, 20.1% lignin, 2.1% ash, 5.6% extractives. The pyrolysis products were characterized via FTIR, SEM/EDS. The isoconversional methods of Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) have yielded activation energy, Eα, varying from 36-323 kJ mol-1, respectively. The calorific value of biochars produced in the present study in the range of 265 to 475 ºC was 16,17 to 20,24 MJ kg-1, respectively, which are comparable to those reported values in the literature. Analyzing the DTG simultaneously with the addition of thermal energy, it can be seen that low molecular weight compounds represent the first degradation curves, followed by hemicellulose, cellulose and, lignin. The results obtained in the present work indicate that its feasible to prepare biochars with tunable properties from residual avocado seeds using a slow pyrolysis process, adding commercial value and reducing the environmental impact caused by the inadequate disposal of lignocellulosic materials.

A flow-injection preconcentration system using detection by the thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS) is proposed. Cd2+ are adsorbed on avocado seed activated carbon (ASAC) packed into a cylindrical mini-column and eluted using HCl solutions for the detection system. A 25–1 fractional factorial and Doehlert matrix design were employed to determine the optimum conditions for cadmium preconcentration (pH 7.68, buffer concentration (Tris/Tris-HCl) of 0.023 mol L-1, eluent concentration (HCl) of 2.0 mol L-1, the adsorbent mass of 100.0 mg and preconcentration flow rate of 4.8 mL min-1). The preconcentration method presents linearity within the range of 0.41-15.00 µg L-1, limits of quantification and detection of 0.41 and 0.12 µg L-1, respectively, preconcentration factor of 10.7, consumption of index of 0.93 mL and sample throughput of 26 h-1. The precision assessed as the relative standard deviation (RSD) were found to be 0.48, 0.90 and 2.30% for inter-day precision (n = 2), and 0.30, 0.44 and 2.48% for intra-day precision (n = 6) for respective cadmium concentration of 0.50, 5.00 and 15.00 µg L-1. The proposed method was applied satisfactorily in samples of cigarette (62.84 ± 11.28 µg kg-1), human hair (69.61 ± 2.38 µg kg-1) and water samples [lake (0.65 ± 0.01 µg L-1), tap and mineral].

A mesoporous, high surface area and conductive silica/titania graphite composite modified with chitosan and functionalized with tyrosinase was prepared. The composite was obtained by the sol-gel method and the surface of the resultant material was modified with chitosan solutions containing 5, 10 and 15% by mass. The textural characterization showed that even after modification with chitosan, the composite maintains a pore volume near 0.70 cm3 g-1 and pore diameter between 10 and 50 nm, adequate for enzyme immobilization. The tyrosinase was immobilized on the composite that was modified with 5% chitosan solution. A carbon ceramic electrode was manufactured with this material and was used as an electrochemical biosensor for phenolic compounds, showing low detection limits in the linear range from 40 to 350 µmol L-1 and good sensitivity of 0.284, 0.141 and 0.165 µA µmol-1 L for catechol, dopamine and pyrogallol, respectively. In this composite the enzyme showed to be operative and stable after several months.

A modificação experimental para a síntese do MESG (2-amino-6-mercapto-7-metilpurina ribonucleosídeo) 1 foi realizada com sucesso e sua caracterização total apresentada. ESI(+)-MSMS em alta resolução foram realizados indicando que a clivagem nucleosídica como principal e um possível mecanismo S N1. Cálculos ab initio baseados em estados de transição blueprint corroboram com a proposta de um mecanismo S N1 e descartam a possibilidade de um mecanismo S N2. Ensaios com a enzima purina nucleosídica fosforilase (PNP, tanto humana como de M. tuberculosis) indicam a eficiência do substrato na reação de fosforilação do MESG e permitem a determinação de fosfato inorgânico em tempo real em ensaios biológicos.

A modified experimental procedure for the synthesis of MESG (2-amino-6-mercapto-7-methylpurine ribonucleoside) 1 has been successfully performed and its full characterization is presented. High resolution ESI(+)-MSMS indicates both the nucleoside bond cleavage as the main fragmentation in the gas phase and a possible S N1 mechanism. Ab initio transition state calculations based on the blue print transition state support this mechanistic rationale and discard an alternative S N2 mechanism. Assays using purine nucleoside phosphorylase (PNP) enzyme (human and M. tuberculosis sources) indicate its efficiency in the phosphorolysis of MESG and allow the quantitative determination of inorganic phosphate in real time assay.

Neste trabalho, o corante azul de metileno foi imobilizado na superfície do acetato de celulose modificado com dióxido de titânio produzindo um material híbrido sólido denominado de CA-TiO2MB. O experimento produziu uma quantidade de 1,8 mmol g-1 de TiO2 incorporado no acetato de celulose e uma quantidade de 0,170 ± 0,005 mmol g-1 de azul de metileno adsorvido na superfície do CA-TiO2. Um eletrodo de pasta de carbono desse material foi usado para estudar a oxidação eletrocatalítica do ácido ascórbico pelas técnicas de voltametria cíclica e cronoamperometria. O pH da solução não afetou o potencial de pico de anódico nem a corrente de pico anódico ao variar de 3,0 a 7,0. A oxidação do analito ocorreu em 75 mV versus ECS em solução de KCl 1,0 mol L-1 e pH 7,0. A intensidade da corrente de pico anódico variou com a concentração de ácido ascórbico na faixa de 5,0 × 10-4 mol L-1 to 4,5 × 10-3 mol L-1, sendo observada uma correlação linear com um limite de detecção de 15 µmol L-1, limite de quantificação de 50 µmol L-1 e uma sensibilidade de 7,1 µA L mol-1. A resposta do eletrodo foi muito rápida, com um tempo decorrido de 1,0 s, mostrando potencial para ser utilizado como um sensor eletroquímico para a determinação de ácido ascórbico em produtos comerciais.

In this work, methylene blue dye was immobilized on the surface of cellulose acetate modified with titanium dioxide, producing a solid hybrid material designated as CA-TiO2MB. The experiment yielded an amount of 1.8 mmol g-1 of TiO2 incorporated in the cellulose acetate and an amount of 0.170 ± 0.005 mmol g-1 of methylene blue adsorbed onto CA-TiO2 surface. A carbon paste electrode of this material was used to study the electrocatalytic oxidation of ascorbic acid by cyclic voltammetric and chronoamperometric techniques. The pH of the solution had no effect on the anodic peak potential and anodic peak current when ranging from 3.0 to 7.0. The oxidation of the analyte occurred at 75 mV versus SCE in 1.0 mol L-1 KCl solution and pH 7.0. The intensity of the anodic peak current varied with the concentration of ascorbic acid from 5.0 × 10-4 mol L-1 to 4.5 × 10-3 mol L-1 and a linear correlation was observed, with a detection limit of 15 µmol L-1, quantification limit of 50 µmol L-1 and a sensitivity of 7.1 µA L mol-1. The electrode response was very fast, with an elapsed time of about 1.0 s, showing the potentiality to be utilized as an electrochemical sensor for determination of ascorbic acid in commercial samples.

In order to reduce the total number of experiments for achieving the highest amount of adsorbed Cu2+ (qmax) using pecan nutshells (Carya illinoensis) as biosorbent, a full 2(4) factorial design with two central points was carried out (mass of biosorbent- m, pH, initial metallic ion concentration- C0, time of contact- t). In order to continue the optimization of the system, a central composite surface analysis design with two factors and five central points was carried out. The maximum amount of Cu2+ taken up by the pecan nutshells was 20 mg g-1. These results were confirmed by determining a Cu2+ isotherm using the best conditions attained by the statistical design of experiments.

As propriedades eletroquímicas dos corantes catiônicos, azul de meldola e azul de toluidina, imobilizados na superfície do acetato de celulose modificado com dióxido de titânio foram investigadas por voltametria cíclica. Os materiais sintetizados foram empregados como eletrodos de pasta de carbono. As propriedades mediadoras redox dos eletrodos modificados quimicamente com azul de meldola e azul de toluidina foram otimizadas utilizando um planejamento fatorial consistindo de dois níveis e quatro fatores com dois pseudo-pontos centrais (n=20 experimentos). A análise fatorial foi realizada para investigar as melhores condições de reversibilidade do processo redox tais como uma diminuição na separação entre os picos de potenciais anódico e catódico e razão de corrente próxima da unidade. Os fatores que apresentaram efeitos significantes na otimização global do sistema e que permitiram alcançar as melhores condições de reversibilidade de transferência de elétrons foram os fatores principais velocidade de varredura e tipo de eletrodo (azul de meldola ou azul de toluidina) além dos fatores de interação concentração do KCl × tipo de eletrodo (B×D) e a interação pH × [KCl] × velocidade de varredura (A×B×C). As melhores condições de reversibilidade eletroquímica obtidas foram: o eletrodo CA-TiO2-MB, KCl 1,0 mol L-1 como eletrólito suporte e velocidade de varredura de 10,0 mV s-1. Adicionalmente, o eletrodo modificado CA-TiO2-MB foi testado como sensor amperométrico para a determinação de NADH com um limite de detecção de 0,1 µmol L-1.

The electrochemical properties of meldola blue and toluidine blue cationic dyes immobilized on cellulose acetate surface modified with titanium dioxide were investigated by cyclic voltammetry. The materials synthesized were employed as carbon paste electrodes. The redox mediator properties of the meldola blue and toluidine blue chemically modified electrodes were optimized using a factorial design, consisting of two levels and four factors with two pseudo-central points (n= 20 experiments). The factorial analysis was carried out by searching for better reversibility of the redox process, such as the lowest separation between anodic and cathodic potential peaks and a current ratio near unity. The factors that presented significant effects on the overall optimization of the system to achieve the best conditions of the reversibility of electron transfer were the main factors scan rate and type of electrode (meldola blue or toluidine blue), besides the interaction factors KCl concentration × type of electrode (B×D) and the pH × [KCl] concentration × scan rate (A×B×C) interaction. The best electrochemical reversibility conditions obtained were: using the CA-TiO2-MB electrode, 1.0 mol L-1 KCl as supporting electrolyte, at scan rate of 10.0 mV s-1. Afterwards, the CA-TiO2-MB modified electrode was tested as an amperometric sensor for the determination of NADH, with a detection limit of 0.1 µmol L-1.

Nesse trabalho foi estudada a influência do ácido acético na estrutura de poros e na área superficial de sílicas preparadas pelo método sol-gel. Condições experimentais de síntese, tais como temperatura de policondensação e solventes, também foram estudadas. Isotermas de adsorção de N2 das amostras foram classificadas como do tipo 1, típicas de materiais microporosos, o que explica os altos valores de área superficial obtidos. A adição simultânea dos ácidos acético e clorídrico como catalisadores e de acetona como solvente, bem como o emprego de uma temperatura de policondensação de 20 ºC, possibilitaram a preparação de sílicas amorfas com valores de área superficial de até 850 m² g-1. O alto valor de área superficial dessas amostras pode ser explicado principalmente pela microporosidade e também pelo tamanho nanométrico das partículas.

The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent, together with the use of a gelation temperature of 20 ºC, made it possible to prepare amorphous silica materials with surface area values up to 850 m² g-1. The high surface area value of these samples could be explained by the microporosity and the nanometric size of the particles.