Guilherme Andrade Marson

An efficient, one‐pot acylation of cellulose under homogeneous reaction conditions

Cellulose samples from cotton linters, sisal, and sugar cane bagasse have been successively acylated (acetate, propionate, butyrate, and acetate/butyrate) under homogeneous reaction conditions, in LiCl/N,N-dimethylacetamide (DMAC), by the following procedure: (i) cellulose and LiCl are heated under reduced pressure, at 110°C; (ii) cellulose is dissolved in LiCl/DMAC by heating at 155°C, followed by cooling to 40°C; (iii) the solubilized polymer is acylated at 60°C for 18 h. Attractive features of this one-pot procedure include: easy control and high reproducibility of the degree of substitution; elimination of base catalyst; negligible degradation of the natural polymer; and recovery/recycling of high purity DMAC and acid anhydride. Reaction conditions employed for the present celluloses are different from those previously used for Avicel PH 101 microcrystalline cellulose because their fibrous nature, higher indices of crystallinity and higher molecular weights retard their dissolution and decrease their rates of acylation by acid anhydrides.

A novel, efficient procedure for acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicel PH101) was successfully acylated under homogeneous solution conditions by the following novel procedure: 2.0 g of cellulose and 5.0 g of LiCl were introduced into a glass reactor, magnetic stirring was started, the pressure was reduced to 2 mmHg, the temperature was raised to 110°C in 30 min, and the reactor was kept under these conditions for another 30 min. N,N-Dimethylacetamide, 60 mL, was introduced, atmospheric pressure was restored, and the temperature was raised to 150°C in 30 min. The system was kept under these conditions for 1 h, then the temperature was decreased to 40°C; in 2 h a clear cellulose solution was obtained. Acid anhydride was added, and the solution was stirred at 60°C for additional 18 h. Acetates, propionates, butyrates, and acetate/butyrate mixed ester were prepared with excellent reproducibility of the degree of substitution, from 1 to 3. The degree of polymerization of cellulose is negligibly affected by these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit follows the order C6 > C2 > C3. Features relevant to the industrial application of this novel procedure are discussed.

Some aspects of acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicell PH101) was successfully acylated under homogeneous solution conditions by the following procedure: 2.0 g of cellulose were stirred with 75 mL of N,N-dimethylacetamide for 1 h at 150°C, 3.5 g of LiCl were added, the temperature was raised to 170°C, ca. 18.5 mL of the solvent were distilled and the suspension was cooled to room temperature and stirred overnight. The temperature of the clear cellulose solution was raised to 110°C, kept at that temperature for 1 h, an acid anhydride was added and the solution stirred at 110°C for additional 4 h. Acetates, propionates, butyrates, and acetate/propionate mixed ester were prepared with excellent control of the degree of substitution, DS, 1 to 3 for acetates, 2 and 3 for propionates and butyrates, and 3 for acetate/propionate. The degree of polymerization of cellulose is negligibly affected under these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit shows a preference for the C6 position.

Cellulose dissolution in lithium chloride/N,N‐dimethylacetamide solvent system: Relevance of kinetics of decrystallization to cellulose derivatization under homogeneous solution conditions

Rate constants and activation parameters for decrystallization of Avicel PH-101 cellulose, and bagasse-based cellulose in presence of LiCl/N,N-dimethylacetamide solvent system have been determined from dependence of the index of crystallinity of cellulose, Ic, on time, under nonisothermal conditions. Calculated rate constants and activation parameters are negligibly dependent on the degree of polymerization of the natural polymer. Under experimental conditions used, derivatization of cellulose can be started after 3 h of cellulose–solvent contact. The relevance of our results to the industrial application of derivatization under homogeneous solution conditions is discussed.

A quick guide for computer-assisted instruction in computational biology and bioinformatics.

Computational Biology and Bioinformatics (CBB) are indispensable components in the training of life scientists [1]–[3]. Current curricula in the life sciences should prepare graduates who master quantitative and computer skills for increased levels of performance [4]–[6]. Equally important is that the application of the curricula is driven by an appropriate instructional paradigm and effective learning experiences. Teaching and learning with computers bring specific issues that should be considered beforehand by any instructor. The following Quick Guide for Computer-Assisted Instruction (CAI) outlines ten principles for effective teaching. The principles are aligned with current developments on human cognition and learning [7] and have been drawn from our own experience using CAI in seminars, tutorials, and distance education, in courses on Molecular Life Sciences at the undergraduate level, taught to majors in biology or in other subjects (e.g., nutrition, teaching of physics and chemistry, teaching of biology, sports). The Guide refers to the preparation, presentation, and assessment of CAI. It should be an aid for those who teach CBB with CAI in class, and it is expected to stimulate student motivation and deeper learning in CBB, thus making class time more effective and improving satisfaction of both students and instructors.

Visualização no ensino de química: apontamentos para a pesquisa e desenvolvimento de recursos educacionais

Visualization is a fast-growing field in science education. This review covers 171 articles published between 2001 and 2010 in 14 science education journals. Major findings include: i - despite the predominance of English speaking countries, interest in the topic has increased in several countries; ii - qualitative research is increasing, but quantitative methodologies prevail; iii - the role of peer interaction in group activities is little investigated; iv - research on the way students and teachers use visualization tools is increasing, but most publications focus on the tools; v - structure of matter remains the most common subject covered.

Química Nova Interativa - QNInt - o portal do conhecimento da SBQ: conectando ciência e educação

The Quimica Nova Interativa (QNInt) portal was launched in 2009 by the Brazilian Chemical Society (SBQ) to offer free quality content for broad audiences. QNInt provides peer-reviewed articles from SBQ journals on science & society, chemical concepts, classroom activities and educational research. With 3,000,000 visits, QNInt also offers a unique library of interactive molecules. In the International Year of Chemistry QNInt served for distributing pH kits and registering data from IUPACs Global Water Experiment, yielding Brazil the largest share of the global pH data set. The portal performance makes QNInt a valuable resource for connecting science to education.

IMAGEM PÚBLICA E DIVULGAÇÃO DA QUÍMICA: DESAFIOS E OPORTUNIDADES

Chemical knowledge plays a central role in the economical and social development of a nation. Chemistry is considered a key science, which provides the means and meanings that fuel the advancement of other fields of knowledge. However, the public image of chemistry is often associated with negative facts and misconceptions. This paper addresses and discusses the public image of chemistry with two case studies: the public image of chemistry depicted in two major Brazilian newspapers and the Brazilian project for the International Year of Chemistry (IYC). Analysis of the newspaper data strongly suggests that the public image of chemistry is related to both the way news is written and the ability of the reader to identify the chemical knowledge actually present in the text. Analysis of IYC related data in the second case study depicted an optimistic panorama for the divulgation of chemistry at both national and local levels. A model for broad and effective initiatives for dissemination of chemistry is discussed. The need to keep science divulgation as the top agenda of the scientific community is also highlighted.