In this thesis, a novel electrochemical array is reported. The array consists of two planar halves, each having four carbon screen-printed band electrodes (SPEs), orthogonally facing each other and separated by a spacer to yield 16 two-electrode electrochemical cells with 1 mm² working electrode areas. The 16 counter electrodes were converted to Ag/AgCl by electrodeposition and anodization. These electrodes were stable for at least 30 days with potentials under the current densities used in our experiments. The 16 working electrodes were modified by Au electrodeposition, and were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). <br /><br /> Immobilization strategies for biomolecules are of paramount importance for successful fabrication of biosensors. This thesis reports a new immobilization method that is based on patterned deposition of alkyl thiosulfates (Bunte salts). Monolayers were formed through electrochemical oxidation of Bunte salts at Au-modified electrodes. Single-component and mixed monolayers were investigated, where the mixed monolayers involved one component with a terminal carboxylic acid functional group to allow immobilization of biomolecules. <br /><br /> Applications of the newly developed immobilization method to an enzyme-based biosensor and an immunosensor were investigated. Glucose and biotin were chosen as model analytes, respectively. Glucose oxidase (GOx) and avidin were covalently immobilized onto the mixed-monolayer-modified electrodes through the carboxylic acid groups. Under the optimized conditions for the fabrication and operation of the biosensors, the new electrochemical array showed linearity up to 10 mM glucose with a sensitivity of 4. 7 nA mM^-1 and a detection limit of 0. 8 mM (S/N=3), and linearity up to 12. 8 µM biotin with a detection limit of 0. 08 µM (S/N=3).

In this thesis, a novel electrochemical array is reported. The array consists of two planar halves, each having four carbon screen-printed band electrodes (SPEs), orthogonally facing each other and separated by a spacer to yield 16 two-electrode electrochemical cells with 1 mm² working electrode areas. The 16 counter electrodes were converted to Ag/AgCl by electrodeposition and anodization. These electrodes were stable for at least 30 days with potentials under the current densities used in our experiments. The 16 working electrodes were modified by Au electrodeposition, and were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). <br /><br /> Immobilization strategies for biomolecules are of paramount importance for successful fabrication of biosensors. This thesis reports a new immobilization method that is based on patterned deposition of alkyl thiosulfates (Bunte salts). Monolayers were formed through electrochemical oxidation of Bunte salts at Au-modified electrodes. Single-component and mixed monolayers were investigated, where the mixed monolayers involved one component with a terminal carboxylic acid functional group to allow immobilization of biomolecules. <br /><br /> Applications of the newly developed immobilization method to an enzyme-based biosensor and an immunosensor were investigated. Glucose and biotin were chosen as model analytes, respectively. Glucose oxidase (GOx) and avidin were covalently immobilized onto the mixed-monolayer-modified electrodes through the carboxylic acid groups. Under the optimized conditions for the fabrication and operation of the biosensors, the new electrochemical array showed linearity up to 10 mM glucose with a sensitivity of 4. 7 nA mM^-1 and a detection limit of 0. 8 mM (S/N=3), and linearity up to 12. 8 µM biotin with a detection limit of 0. 08 µM (S/N=3).

Este trabalho teve como foco a preparação de compostos orgânicos de selênio, fundamentado em plataformas estruturais de moléculas pequenas que pudessem ter suas preparações viabilizadas em reduzido número de etapas, a partir de matérias primas comerciais ou de fácil preparação e economicamente viáveis. O trabalho ficou dividido em 3 partes, sendo que na primeira, optou-se por preparar compostos fundamentados em estruturas derivadas dos ácidos acético, propiônico e butírico. As estratégias de preparação ficaram centradas na geração de HSeNa ou Se2Na2, por reação de selênio e borohidreto de sódio em água ou etanol. As espécies nucleofílicas foram então submetidas a reação com cloro-acetato de sódio ou de etila, levando aos correspondentes diorgano-selenetos ou disselenetos. Também foram preparados derivados de ácido propiônico, &#945;-hidroxilados. Para isso duas abordagens foram empregadas, sendo que em uma mantivemos a estratégia de substituição nucleofílica de um haleto terminal por reação com MeSeLi, levando ao &#946;-metilseleno-&#945;-hidroxipropóide. Na outra, optamos por fazer reacão de abertura de um epóxido glicídico. Neste caso observamos mistura de regioisômeros quando MeSeLi foi empregado. Quando o Grignard correspondente foi usado na reação de abertura do epoxido além de mistura de regioisômeros, também se observou como produto majoritário, o monoseleneto dimérico (provavelmente oriundo de uma de-metilação). Por fim, empregou-se também abertura da &#947;-butirolactona com disselenolato de sódio, levando ao disselenodi-ácido correspondente. Esses compostos foram submetidos a ensaios preliminares de atividade antioxidante. Destes, o seleno-diacetato de etila apresentou alta seletividade para reação com HOCl, mesmo frente a outras espécies oxidantes e em experimento in vitro com células Hela-60. Além disso foi preparado um seleno-diglicosídeo, também empregando hidrogenoselenolato de sódio, gerado in situ à partir de selênio elementar e borohidreto de sódio. Esse composto foi submetido a ensaios de atividade anticâncer, em associação com &#946;-glucana, levando a ótimos resultados para os experimentos envolvendo câncer de mama e pulmão. Cabe mencionar que nesse caso foram feitos experimentos in vivo com ratos, acrescendo o derivado seleno-açucar e glucana, à dieta dos animais. Por último, foram investigadas estratégias de preparação de sais de Bunte (tiossulfatos orgânicos) de diferentes padrões de substituição. Nessa parte do estudo, tivemos como propósito investigar alguns fatores de reatividade desses compostos frente a espécies nucleofílicas e eletrofílicas de selênio e telúrio, a fim de preparar seleno- e telurosulfetos. Esses por sua vez devem ser submetidos a ensaios biológicos variados. Das estratégias investigadas observamos uma serie de subprodutos das reações envolvendo os sais de Bunte com espécies nucleofílicas de selênio, sendo o que o produto principal foi formado apenas em baixo rendimento e alguns derivados se mostraram bastante instáveis. Em contrapartida, reação bastante seletiva e bons rendimentos foram observados para os casos em que o sal de Bunte agiu como nucleófilo em reações com cátions de selênio e telúrio, gerados por clivagem do dicalcogeneto por persufato de amônio em solvente protônico. Alguns exemplos dos dicalcogenetos puderam ser preparados e caracterizados. / This work was devoted to the preparation of organic selenides, based on structural platforms of small molecules taking in account scalable synthetic procedures in a small steps numbers, from commercial raw materials or from easily prepared and economically viable starting materials. The work was divided into 3 parts, and in the first, it was decided to prepare compounds based on structures derived from acetic, propionic and butyric acids. The preparation strategies were centered on the generation of HSeNa or Na2Se2, by reaction of elemental selenium and sodium borohydride in water or ethanol. The nucleophylic species were then subjected to reaction with sodium chloroacetate, leading to the corresponding diorgano-selenides or disselenides. They were also prepared from &#945;-hydroxylated propionic acid derivatives. For this purpose, two approaches were employed, and in one we maintained the nucleophylic substitution strategy of a terminal halide by reaction with MeSeLi, leading to &#946;-methylseleno-&#945;- hydroxy-propoide. In the other, we chose to perform an epoxi-glycidic opening reaction. In this case, we observed a mixture of regioisomers when MeSeLi was employed. When the corresponding seleno-Grignard was used in the epoxide opening reaction besides a mixture of regioisomers, it was also observed as a major product, the symmetric monoselenide (probably originated from a de-methylation reaction). Finally, it was also used the &#947;-butyrolactone opening reaction with sodium disselenolate, leading to the corresponding disseleno-diacid. These compounds were submitted to preliminary assays of antioxidant activity. The ethyl Seleno-diacetate showed high selectivity for reaction with HOCl, even in the presence of other oxidant species and in an in vitro experiment with Hela-60 cells. In addition, a Selene-diglycoside was prepared, also employing sodium hydrogen selenide, generated, in situ from elemental selenium and sodium borohydride. It was subjected to anticancer activity assays, in association with &#946;-glucan, leading to great results for experiments involving breast and lung cancer. It is worth mentioning that inthis case experiments were made in vivo with rats, adding our seleno-sugar/glucan system to the diet of the animals. Finally, strategies for the preparation of Bunte salts (organic thiosulphates) of different substitution patterns were investigated. In this part of the study, we intend to investigate some factors of reactivity of these compounds through nucleophilic and electrophilic selenium and tellurium species, in order to prepare seleno- and telluro-sulfides. Opportunely, these compounds should be submitted to biological assays. Under the investigated reaction conditions, we observed a series of by-products of reactions involving the Bunte salts with nucleophilic selenium species, and the main product was formed only in low yield and some derivatives showed to be quite unstable. On the other hand, a fairly selective reaction and good yields were observed for cases in which the Bunte salt was used as the nucleophile in reactions with selenium and tellurium cations, generated by the cleavage of the dichalcogenide by ammonium peroxysulphate in protonic solvent. Some examples of dichalcogenides were prepared and characterized.