Teses e Dissertações

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Navegando Teses e Dissertações por Autor "005.482.048-02"

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    Determinação voltamétrica de catequina por eletrodo de carbono impresso modificado com nanotubo de carbono funcionalizado
    (Universidade Federal do Maranhão, 2014-01-22) SILVA, Ana Luisa; SILVA, Quésia Guedes da; 649.943.423-20; TAKANA, Auro Atsushi; 005.482.048-02
    The catechin compound is a phenolic that has a great oxidant action,it is found in a different kinds of food such as wine, juice and tea, its application to inhibit ultraviolet radiation, reduces the level of cholesterol, among others. Currently, techniques are used for determining catechin as a gas chromatography, high performance liquid chromatography, although the electrochemical detection method is a promising yet, because it is less cumbersome and can distinguish between the oxidized and the reduced form of catechin. A growing number of studies has shown the necessity for a hurry procedure to availible the content of catechin and electrochemical techniques have been successfully employed. The research activities carried out in this study were the characterization and optimization of the parameters used for the determination of catechin in a printed carbon electrode modified with functionalized carbon nanotube by means of cyclic voltammetry technique and application in the quantification of this analyte in a sample of black tea. The best results were obtained at a concentration of 1x10-3 mol L-1 through catechin phosphate buffer 0.1 mol L-1 pH 7.0 using a potential sweep rate of 0.05 V s-1. From these conditions an analytical curve was obtained by linear response over the concentration range of catechin between 2.0 × 107 to 1.68 × 10-5 mol L-1, as limits of detection and quantification of 9.2 x10-8 and 3.0x10-7 mol L-1, respectively. The oxidation of catechin showed a peak located around 0.15 V vs. Ag / AgCl potential being near the peak shown in the literature.
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    ESTUDO DE FÁRMACOS ANTICANCERÍGENOS NITROSUREIAS E AVALIAÇÃO IN SITU DE SUAS INTERAÇÕES COM DNA UTILIZANDO BIOSSENSORES ELETROQUÍMICOS DE DNA.
    (Universidade Federal do Maranhão, 2019-07-01) CARVALHO, Paulina Andréa Viana de; LOPES, Ilanna Campelo; 840.689.733-34; http://lattes.cnpq.br/9543261878791947; TANAKA, Auro Atsushi; 005.482.048-02; http://lattes.cnpq.br/1460765270568999; TANAKA, Auro Atsushi; 005.482.048-02; http://lattes.cnpq.br/1460765270568999; YAMANAKA, Hideko; http://lattes.cnpq.br/1923726000036625; NUNES, Gilvanda Silva; http://lattes.cnpq.br/5833210771020427; SANTANA, Sirlane Aparecida Abreu; http://lattes.cnpq.br/1052349578152491; LIMA, Roberto Batista de; http://lattes.cnpq.br/4982744838486744
    Lomustine (CCNU) and carmustine (BCNU) belong to the class of nitrosureas, which are nnitro compounds capable of alkylate DNA structures. They are lipophilic and can go through the blood-brain barrier, and due to these characteristics, they are used in the treatment of brain tumors and other neoplasms. To understand the interaction mechanisms of these compounds with DNA, voltammetric techniques and DNA-electrochemical biosensors were used. Firstly, the study of the electrochemical behavior of CCNU and BCNU and their degradation in aqueous solution on a glassy carbon electrode (GCE) was performed using voltammetric techniques. From this study, the in situ interaction of both with deoxyribonucleic acid (dsDNA) was investigated in incubated solutions, using dsDNA-electrochemical biosensors and the comet test. Both CCNU and BCNU underwent electrochemical reduction in two irreversible redox processes, diffusion-controlled, pH dependent involving the transfer of two electrons and one proton, each. There was no formation of electroactive reduction products. At pH ≥ 10, the peak potential for the two processes tends to be pH independent by involving only electrons. A reduction mechanism of the CCNU and BCNU in neutral media was proposed. In addition, both antineoplastics underwent spontaneous degradation in aqueous solution over the incubation time, without the formation of electroactive degradation products. The CCNU and BCNU degradation process was more evident in a basic medium. The in situ interaction of CCNU and BCNU with dsDNA showed these pro-drugs interacted with DNA initially causing the condensation of the double helix strands and then the unwinding of these strands. Moreover, free guanine (Gua) was released and oxidative damage caused to dsDNA by both compounds were observed, since 8-oxoguanine (8-oxoGua) and 2,8-dihydroxyadenine (2,8-DHA) were detected. These results were confirmed by the poly (dA)- and poly [dG]-electrochemical biosensors, which demonstrated the oxidative damage caused by dsDNA in both bases, guanine and adenine, by the CCNU degradation product(s). BCNU caused oxidative damage only in the guanine. The comet assay indicated breaks in the single strand of DNA, corroborating with the studies performed by differential pulse voltammetry.