Carmen Fernandez

Effects of probe-amphiphile interaction on pyranine proton transfer reactions in lecithin vesicles

Abstract Photoacids and photobases are powerful tools for the discrimination, in real time, between the preferential pathways in H+/OH− transfer processes in biological and biomimetic systems which can determine the origins of crucial biochemical processes. In this study, the binding of 8-hydroxy-1,3,6-pyrenetrisulphonate sodium salt (pyranine) to phosphatidylcholine (lecithin) vesicles was investigated (by time-resolved and steady state fluorometry and laser-induced pH jump measurements) as a function of the probe and electrolyte concentration to determine how these parameters affect the properties of the photoacid. The ratio (R) between the fluorescence intensities at 510 nm (dissociated form) and 440 nm (undissociated form) can be related to the excited state degree of dissociation (D (%)). The binding of the probe to the internal leaflet of lecithin small unilamellar vesicles (SUVs) is larger than that to the external leaflet. The addition of salt up to 2 M does not prevent binding even at low probe concentrations. Time-resolved emission decay measurements also show the probe-lipid interaction. The lifetime of the undissociated form is equivalent to that in alcoholic solutions (approximately 3.8 ns). The pyranine ground state re-protonation rate constant (kobs) is dependent on the probe content per vesicle. With 550 pyranine molecules per vesicle, kobs is constant within a large range of salt concentration. In this situation, an alternative route is proposed (compared with direct PO−/H+ recombination), in which proton transfer between neighbouring species maintains an unchanging recombination rate. The data presented show that careful analysis of pyranine H+ transfer data is necessary for biomimetic and biological or reconstituted systems.

Aspectos do conhecimento pedagógico do conteúdo de química verde em professores universitários de química

P C K aspects of Green C hemistry in university chemistry teachers This paper aims to document the pedagogical content knowledge (PCK) about Green Chemistry (GC) in professors from the Institute of Chemistry of the University of Sao Paulo, experts from traditional fields of chemistry and working in different undergraduate degrees — BS in Chemistry, Environmental Chemistry, Chemistry Teachers Education and Industrial Chemistry. Data were based on a questionnaire of 44 items answered by 26 teachers. Analyzes of responses were individual and collective within the areas of expertise. In Grossman’s model conceptions of purposes for teaching green chemistry were related to three models for teaching GC described in recent literature — traditional, contextualized and socio-scientific. Results revealed a significant dependence between teachers’ content knowledge and PCK in terms of consistency between the purposes and strategies for teaching GC, understanding the difficulties of students and curriculum knowledge. Teachers from Organic Chemistry area, which has a closer relationship with the contents of GC, show a preference for a socio-scientific approach and show greater alignment and consistency between the different PCK components as compared with teachers from other areas of chemistry.

Oxidation States and Structure of the Manganese Cluster in the S 0 State of the Oxygen Evolving Complex

Photosystem II (PS II) catalyzes the light driven oxidation of water to molecular oxygen and the reduction of plastoquinone to plastohydroquinone. Water oxidation occurs in the oxygen evolving complex (OEC) of PS II that is known to cycle through five different redox states, referred to as the S states (S0,..,S4). A cluster of four Mn, one Ca and Cl− is thought to form the central unit of the OEC which stores most of the oxidizing equivalents and binds the substrate water.

Proximity of calcium to the manganese cluster of the photosynthetic oxygen-evolving complex determined from strontium XAFS

Working on Photosystem II membranes from spinach, we substituted strontium for calcium and probed using Sr EXAFS for any nearby Mn. Sr EXAFS results indicate major differences between the functional (intact) and inactive (hydroxylamine-treated) samples. In intact samples, the Fourier transform of the Sr EXAFS shows a major peak that is missing in inactive samples. This interaction is best simulated by two Mn neighbors at a distance of ~3.5 A.

How to Teach Science in Emerging and Developing Environments

The complexity of science education today, particularly the areas related to chemistry, needs new teaching approaches, new teaching resources, new skills of the teacher and an alternative focus for the subject itself. All of these factors need to be considered in the context of all countries of the world. In developing countries, there are still further challenges ahead, as teachers struggle to enable their families to survive and do not always have the necessary training, while schools are overcrowded, operating multiple sittings in a day and textbooks are few and far between, with new copies often too expensive to purchase. All too often in these countries, student-centred learning is a dream that is far from being feasible and assessment systems are a burden, serving to determine how the selected few students can progress, while ignoring the exciting challenges and intrigues from stimulating learning which the subject has to offer. Despite these problems, improving science education is often regarded as a priority for developing countries — the goal is nothing less than the capacity to apply learning, whether this is knowledge, skills or values, to new situations. This chapter addresses some of the issues currently facing science education in developing countries. In so doing it draws also on ideas expressed in earlier chapters of this book.

PROCESSO REFLEXIVO E DESENVOLVIMENTO DO CONHECIMENTO PEDAGÓGICO DO CONTEÚDO NUMA INTERVENÇÃO FORMATIVA COM PROFESSORES DE QUÍMICA

O conhecimento pedagogico do conteudo (PCK) e reconhecido como aquele que representa o conhecimento profissional dos professores e se desenvolve na pratica e por processos reflexivos. Nesta investigacao analisamos o desenvolvimento do PCK de dois professores que participaram de um processo reflexivo num grupo colaborativo envolvendo acoes individuais e em grupo. Dados incluem textos escritos, videos de discussoes orais e de aulas e o ciclo reflexivo de Smyth. A analise dos dados foi baseada no Modelo Hexagonal e nas intervencoes discursivas. Os professores investigados, a partir do processo reflexivo, tomam consciencia de algumas acoes a partir da participacao do grupo colaborativo, revelando um processo de desenvolvimento de PCK de modo semelhante ao proposto no modelo de raciocinio pedagogico e acao.

O professor universitário novato: tensões, dilemas e aprendizados no início da carreira docente

O presente trabalho tem por objetivo analisar como docentes do Ensino Superior de uma universidade publica percebem os diferentes agentes do campo educacional, e como as tensoes e dificuldades sao gerenciadas no inicio da profissao, partindo da nocao de campo de Bourdieu. Nossos dados se basearam em entrevistas semiestruturadas, que foram analisadas por Analise de Conteudo. Nossos resultados revelam dificuldades relacionadas a gestao de sala de aula e semelhancas entre professores com e sem experiencia previa no que diz respeito: a inseguranca didatica, ao valor dado ao apoio (ou nao) dos colegas de trabalho, e ao numero de atividades desempenhadas. Revela-se, ainda, uma relacao de dominacao dos professores mais experientes sobre os novatos no trabalho universitario. Essas relacoes de poder refletem, claramente, a diferenciacao de capital cultural e simbolico de quem adentra um novo campo, revelando as estruturas mais gerais de um campo na perspectiva de Bourdieu

Professores novatos de química e o desenvolvimento do PCK de oxidorredução: influências da formação inicial

Abstract The learning of teaching starts from the theory, observation of the practice of teacher educators and experiences as students. The aim of this research is to elucidate the theoretical elements from disciplines and practical aspects of the trainning action of teacher educators that are incorporated by student teachers to their Pedagogical Content Knowledge (PCK) on the subject oxidation-reduction. For this we conducted a multiple case study with eight teacher formers and three pre-service chemistry teachers. Data is based on interviews, CoRe, evaluative materials and student notes produced during the disciplines. The results indicate that all teacher formers, regardless of area, influence the PCK of their students. This influence appears in the specific content, in the way of acting, in the teaching-learning conceptions and during the different ways to drive teaching activities. Thus, elements of disciplines and theoretical aspects of teaching practice trainers are embedded in PCK of undergraduates.

Reactions of 1,?-bis(2-bromopyridinium)alkanes with hydroxide ion in aqueous solutions

The reaction of OH− ion with 1,ω-bis(2-bromopyridinium)alkanes, where the reaction centers are separated by a varying number of methylene groups, was investigated to model the increased velocity of OH− attack on premicellar aggregated N-alkylpyridinium compounds. 1,ω-Bis(2-bromopyridinium)alkanes (RPBr) [R  =  propane (I), butane (II), pentane (III), hexane (IV) and octane (V)] were synthesized and characterized by standard procedures. The kinetics of I–V with OH− ion fitted two consecutive first-order reactions. The intermediate products, 1-(2-pyridone)-ω-(2-bromopyridinium)alkane, and also the final products 1,ω-bis(2-pyridone)alkanes, were isolated. Deuterium isotope effects, activation parameters and salt effects on the reaction rates suggest that OH− attack is rate limiting and there is a through-space acceleration of the initial attack due to the proximity of the positive charges. These results place an upper limit of 20-fold for the electrostatic acceleration in OH− attack in premicellar aggregates.

REVISITANDO A BASE DE CONHECIMENTOS E O CONHECIMENTO PEDAGÓGICO DO CONTEÚDO (PCK) DE PROFESSORES DE CIÊNCIAS

O Conhecimento Pedagogico do Conteudo (PCK) representa o centro dos conhecimentos profissionais de professores, aquele conhecimento que distingue um professor das demais profissoes e tem sido considerado um modelo frutifero para a investigacao sobre os professores e, como consequencia, para propostas de como desenvolve-lo durante a formacao inicial e continua. Por outro lado, existe pouca literatura em portugues e, a julgar pela sua importância no cenario internacional, pela quantidade de modelos propostos e o problema com as traducoes de alguns termos, justifica-se fornecer um panorama da literatura apresentando os componentes da base de conhecimentos de professores e do PCK, os modos estabelecidos para seu acesso e documentacao alem de apresentar uma analise critica a esses modelos.