Tailoring surface properties of functionalized graphene papers aiming to enzyme immobilization

he use of enzymes as catalysts requires recovery and reuse to make the process viable. Enzymatic immobilization changes enzyme stability, activity, and specificity. It is very important to explore new substrates for immobilization with appropriate composition and structure to improve the efficiency of the immobilized enzymes. This work explores the use of two different graphene oxide papers, one produced by oxidation route (GO) and the other by electrochemical synthesis (EG), aiming for β-galactosidase immobilization. The chemical and structural properties of these two papers were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Atomic force microscopy images showed that EG paper ensured more efficient immobilization of the enzymes on the surface of the paper. Cyclic voltammetry was used to monitor the reaction of conversion of lactose to glucose in the free enzyme solution and graphene paper immobilized enzyme solutions. The cyclic voltammetry analysis showed that immobilized enzymes on GO paper showed an improvement in the activity of β-galactose when compared to free enzyme solution, as well as enzyme immobilized on a glassy carbon electrode

Immobilization of β-galactosidases on grafene oxide membranes

The use of enzymes as catalysts requires recovery and reuse to make the process viable. Enzymatic immobilization changes enzyme stability, activity and specificity. There is no single method or support applicable to all enzymes and their various applications. It is very important to explore new substrates for immobilization with appropriate composition and structure in order to improve the efficiency of the immobilized enzymes. In this work, the use of graphene oxide membranes produced by chemical route (GO) and electrochemistry (EG) for immobilization of β-Galactosidases was investigated. For the membrane’s characterization, the techniques of atomic force microscopy, Raman spectroscopy, X-ray excitation and X-ray diffraction spectroscopy were used. The electrochemical technique of cyclic voltammetry was used to monitor the reaction of conversion of lactose to glucose as well as to evaluate the influence of the use of plasma treatment on the membranes. The AFM images showed that the EG membranes had better immobilization of the enzymes on the surface. This membrane was treated with different plasmas to obtain improved substrates, however, the argon plasma was destructive and the plasma jet contributed to the reduction of the defects of the graphene sheets, interfering in the interaction between the same and the active center of the enzymes, making it difficult to evaluate the activity by cyclic voltammetry. Finally, the unmodified EG membrane was the best substrate for immobilization.A utilização de enzimas como catalizadores requer a recuperação e reutilização para tornar o processo viável. A imobilização enzimática altera a estabilidade, atividade e especificidade enzimática. Não existe um método ou suporte único aplicável a todas as enzimas e suas várias aplicações. É de suma importância explorar novos substratos para imobilização com composição e estrutura apropriadas de forma a melhorar a eficiência das enzimas imobilizadas. Neste trabalho, a utilização de membranas de óxido de grafeno produzidas por rota química (GO) e eletroquímica (EG) para imobilização de βGalactosidases foi investigada. Para caracterização das membranas, foram utilizadas as técnicas de microscopia de força atômica, espectroscopia Raman, espectroscopia de fotoelétrons excitados por raios-X e difração de raios-x. A técnica eletroquímica de voltametria cíclica foi utilizada para acompanhamento da reação de conversão da lactose em glicose assim como para avaliar a influência da utilização de tratamento por plasma nas membranas. As imagens de AFM mostraram que as membranas de EG tiveram uma melhor imobilização das enzimas na superfície. Então essa membrana foi tratada com diferentes plasmas para obtenção de suportes melhorados, porém, o plasma de argônio foi destrutivo e o jato de plasma contribuiu para a diminuição dos defeitos das folhas de grafeno, interferindo na interação entre o mesmo e o centro ativo das enzimas, dificultando avaliação da atividade por voltametria cíclica. Por fim, a membrana de EG sem modificação foi o melhor substrato para imobilização

Análisis del informe de cumplimiento tributarío de una empresa de servicios de comida rápida ubicada en la ciudad de Guayaquil durante el ejercicio fiscal 2007

El presente trabajo se ha titulado “Análisis del Informe de Cumplimiento Tributario de una empresa de servicios de comida rápida ubicada en la ciudad de Guayaquil durante el ejercicio fiscal 2007”. El objetivo que persigue el mismo es el de comprobar que la compañía ha cumplido adecuadamente con las obligaciones tributarias, habiendo aprovisionado correctamente los riesgos derivados de posibles contingencias fiscales. Este proyecto se divide en cuatro capítulos, que tratarán de lo siguiente: En el Primer Capítulo, se detallarán las bases legales sobre las que se desarrolló esta tesis, conceptos generales tributarios, que harán que el lector se introduzca en el tema. En el Segundo Capítulo, conoceremos a la compañía Auditada, es decir, sabremos a que se dedica, cuáles son sus principales clientes, cuáles son sus estrategias, etc. En el Tercer Capítulo, desarrollaremos en sí lo que comprende la auditoría, aquí estará incluida la planificación, la programación y la aplicación de pruebas; estas pruebas en su mayoría serán sustantivas, las cuales consisten en el examen de las declaraciones tributarias, en cuanto a la exactitud de las cifras presentadas, y la evaluación se sus soportes. Finalmente, concluiremos con un Informe Tributario, el cual determinará si la organización auditada se acerca o no a lo que dicen o estipulan las leyes o reglamentos tributarios. En este capítulo, se incluirán las conclusiones y recomendaciones efectuadas a la compañía auditada

Prototyping and Evaluation of Graphene-Based Piezoresistive Sensors

In this work, the electrical properties of graphene papers were investigated with the aim of developing pressure sensor prototypes for measuring pressures up to 2 kPa. In order to determine which graphene paper would be the most suitable, three different types of graphene papers, synthesized by different routes, were prepared and electrically characterized. The results of electrical characterizations, in terms of electrical conductivity and sheet resistance of graphene papers, are presented and discussed. Prototypes of pressure sensors are proposed, using graphene papers obtained by chemical oxidation (graphene oxide and reduced graphene oxide) and by electrochemical exfoliation. The prototypes were tested in static compression/decompression tests in the working range of 0 kPa to 1.998 kPa. The compression/decompression sensitivity values observed in these prototype sensors ranged from 20.8% ΔR/kPa for graphene sensors obtained by electrochemical exfoliation to 110.7% ΔR/kPa for those prepared from graphene oxide obtained by chemical oxidation. More expressive sensitivity values were observed for the sensors fabricated from GO, intermediate values for those made of rGO, while prototypes made of EG showed lower sensitivity

Prototyping and Evaluation of Graphene-Based Piezoresistive Sensors

In this work, the electrical properties of graphene papers were investigated with the aim of developing pressure sensor prototypes for measuring pressures up to 2 kPa. In order to determine which graphene paper would be the most suitable, three different types of graphene papers, synthesized by different routes, were prepared and electrically characterized. The results of electrical characterizations, in terms of electrical conductivity and sheet resistance of graphene papers, are presented and discussed. Prototypes of pressure sensors are proposed, using graphene papers obtained by chemical oxidation (graphene oxide and reduced graphene oxide) and by electrochemical exfoliation. The prototypes were tested in static compression/decompression tests in the working range of 0 kPa to 1.998 kPa. The compression/decompression sensitivity values observed in these prototype sensors ranged from 20.8% ΔR/kPa for graphene sensors obtained by electrochemical exfoliation to 110.7% ΔR/kPa for those prepared from graphene oxide obtained by chemical oxidation. More expressive sensitivity values were observed for the sensors fabricated from GO, intermediate values for those made of rGO, while prototypes made of EG showed lower sensitivity

Efeito da doxorrubicina e ciclofosfamida na linhagem celular de adenocarcinoma de mama MCF-7

O câncer de mama é o segundo tipo mais comum de neoplasia no mundo, sendo mais frequente entre as mulheres. O objetivo do estudo foi avaliar o efeito da interação entre doxorrubicina e ciclofosfamida na linhagem celular de carcinoma de mama MCF-7. Para isto, utilizamos o ensaio de MTT para a citotoxicidade, citometria de fluxo para distribuição de células no ciclo celular e ensaio CBMN para mutagenicidade. Os resultados mostraram que a linhagem MCF7 apresenta maior sensibilidade a doxorrubicina e que quando esta é combinada com ciclofosfamida ocorre uma potencialização do efeito. Todos os tratamentos induziram parada em G2/M e aumento de células em SubG1. Além disso, somente o tratamento combinado foi capaz de reduzir os valores de CBPI em relação ao grupo controle negativo, indicando citotoxicidade e morte celular. Assim, este estudo mostrou que o cotratamento doxorrubicina e ciclofosfamida é mais efetivo que os agentes isolados e que este efeito está associado com bloqueio das células no ciclo celular e indução de morte