Dayse Carvalho da Silva

Spectral, electrochemical, and catalytic properties of a homologous series of manganese porphyrins as cytochrome P450 model: The effect of the degree of β-bromination

A homologous series of beta-brominated porphyrins derived from meso-tetrakis(4-carbomethoxyphenyl)porphyrinatomanganese(III) chloride, i.e., Mn(III)(Br(x)TCMPP)Cl (x=0,2,4,6, and 8), was prepared and investigated as cytochrome P450 models. Hydroxylations of cyclohexane by iodosylbenzene (PhIO) and iodobenzene diacetate (PhI(OAc)(2)) in the presence or absence of water were carried out as P450 model reactions. The influence of the degree of beta-bromination of the macrocycle on the UV-vis spectra, the Mn(III)/Mn(II) reduction potential, and the catalytic properties of the Mn(III)(Br(x)TCMPP)Cl (x=0,2,4,6, and 8) series were examined. The catalytic efficiency does not correlate with the Mn(III)/Mn(II) reduction potential and shows a bell-shaped behavior, where the best results are achieved with the hexabrominated complex. Better hydroxylation yields were achieved by using PhI(OAc)(2) as oxygen donor, but at expenses of catalyst recovery; addition of water to this system resulted in a increase in the reaction rate. Recycling of the more oxidatively robust complexes Mn(III)(Br(6)TCMPP)Cl and Mn(III)(Br(8)TCMPP)Cl is feasible when using PhIO as oxygen donor. Selectivity and UV-vis data suggested that hydroxylation by both PhIO and PhI(OAc)(2) share closely related active species and mechanism. We also show that the Mn(III)/Mn(II) reduction potentials are inappropriate predictors of P450-type activity of Mn porphyrin-catalyzed oxidations.

As práticas educativas e seus personagens na visão de estudantes recém-ingressados nos cursos de Química e Biologia

Resumo: Desenvolvemos o presente trabalho com o objetivo de identificar concepcoes sobre as relacoes em sala de aula apresentadas por alunos recem-ingressados nos cursos de Quimica e Biologia. Baseados em Bruner, usamos a narrativa como instrumento investigativo dessas concepcoes, solicitando aos alunos que se imaginassem professores e relatassem como seria um dia de suas vidas. Pela analise dos relatos, percebemos que o professor e aquele que estuda e se prepara para as aulas, transmite conhecimentos, motiva, contextualiza, tem uma boa relacao com os alunos e e admirado por eles. Alem disso, esse professor e considerado um profissional em tempo integral, trabalhando, sobretudo, no Ensino Medio, com alunos interessados e atenciosos. Entender como essas concepcoes se formaram e problematiza-las na formacao inicial e importante. Palavras-chave: Ensino de Quimica. Ensino de Biologia. Relacoes em sala de aula. Narrativas. Concepcoes.

Ensinar e aprender Química: a percepção dos professores do Ensino Médio

O presente trabalho buscou investigar a percepcao dos professores da educacao basica sobre as praticas pedagogicas em sala de aula e na escola, as dificuldades enfrentadas e as possiveis maneiras de soluciona-las, assim como as formas por eles utilizadas para se manterem atualizados. A investigacao envolveu 93 professores do Ensino Medio de escolas do estado de Minas Gerais, durante a realizacao da Olimpiada Mineira de Quimica (OMQ) 2008. A analise dos comentarios feitos pelos professores, no instrumento de coleta de dados utilizado, mostrou que os mesmos tendem a associar as dificuldades que enfrentam principalmente a escola, aos alunos e a questoes externas a escola, ou seja, nao se assumem como parte dos problemas. Percebemos, tambem, que associam as principais melhorias na educacao basica a infra-estrutura da escola e que nem todos participaram de eventos que promovessem a atualizacao profissional nos ultimos dois anos.

Professor de ensino superior: o entendimento a partir de narrativas de pós-graduandos em química

The quality of higher education has raised growing interest among researchers and experts in education. In the present work we have emphasized the correlation between the growing specialization offered by graduate programs in Chemistry and the improvement in the quality of university teachers, trying to understand how the graduate students themselves imagine the teaching activity. For that, graduate students in Chemistry from the Federal University of Minas Gerais were invited to construct narratives about a fictitious situation in which they imagined themselves as teachers. The analysis of the reports was made by grouping the facts described under three categories: the preparation for approval in the admission exam, the classes taught, and the activities developed during the first four months of work. Results have shown that students pay less attention to the teaching activity and tend to value research and the activities that foster it. This shows that future professionals, even taking up the post of teachers, are more predisposed to act as researchers than to exercise the teaching activity. Such indication seems to be related to the demands made during the selection process for higher education teachers and to the current work situation in most universities, which evaluate qualitatively the intellectual production in the form of articles, whereas classes are evaluated in a more quantitative manner.