Contribuição ao estudo de uma metodologia alternativa para obtenção de dioxissulfeto de terras raras

In the last decade, many method has been developed to obtain oxysufides. However, theses materials were obtained by reaction involved gaseous toxics, CO, CS2, H2S and S. In the present work, the synthesis of lanthanum oxysufides actived by europium (III) through an alternative method has been made. This method involve the rare earth sulfate reduction under an atmosphere of argon contained 10% hydrogen using the thermogravimetric technique. The results showed the formation of the phase TR2O2S (TR = La and Eu) at temperatures which depend upon the heating rate, respectively 650 - 830ºC at 5ºC min-1 and 680 - 800ºC at 10ºC min-1. The oxysufides obtained are characterized by infrared spectroscopy. The method developed is more economic than the usual industrial methods and the environmental problems during the synthesis are also better controled.

Reflexões sobre a contribuição da Carnot à primeira lei da termodinâmica

The classical interpretations of Nicolas Léonard Sadi Carnot on some physical principles involved in the operation of heat engines were fundamental to the development and formulation of the Second Law of Thermodynamics. Moreover, an accurate historical survey clearly reveals that Carnot was, by that time, also well aware about some new concepts, which were further worked out by other scientists to lead to what was, some time later, known as the mechanical equivalent of heat and the conservation of energy. Benoit Paul Émile Clapeyron recognized these original concepts in the first of Carnot´s monographs, published in 1824, but no explicit citation is found in any post-Carnot classical texts dealing with the First Law of Thermodynamics, including those by Julius Robert Mayer, James Prescott Joule and Hermann Ludwig Ferdinand von Helmholtz. The main objective of the present work is to point out some historical evidences of the pioneering contribution of Carnot to the modern concept of the First Law of Thermodynamics.

De Francisco a Marco Antonio Aldana pasando por Gaspar

It is traditionally considered that the «Aldana», whom Gaspar Gil Polo praises at the end of his «Canto de Turia» (1564), was Francisco de Aldana, the «divino». It is nonetheless more probable that it was in fact rather the Valencian poet, Marco Antonio Aldana, almost forgotten today, but very much in the public eye within the cultivated circles of the end of the sixteenth century Valencia

Contribuição à organização da pesquisa em Química e os desafios da interação com outras áreas do conhecimento

This article provides some aspects that allow making a current reading of the situation of the Brazilian Chemistry that permit us considerate it as a strategic area. They are still presented some initial proposals related to the organization of the research as well as to win the challenges of the relationship with the other areas of the knowledge.

Fatores que governam a especiação do cobre em ambientes aquáticos urbanos: evidências da contribuição de sulfetos solúveis

Copper speciation and behavior in different rivers located in the city of Curitiba were evaluated in this work. Sampling locations were selected to cover different levels of urbanization regarding their anthropogenic occupation and land use. Results showed that in highly-developed areas, both organic matter and dissolved sulfides were able to control copper speciation. Dissolved sulfide species were the major complexing agent in areas where dissolved oxygen levels are low. Finally, it was demonstrated that in urban areas anthropogenic factors such as sewage inputs and occupation of the drainage basin are the key aspects controlling copper dynamics and speciation in river waters.

Química Medicinal Moderna: desafios e contribuição brasileira

The main aspects of the modern Medicinal Chemistry, among the classic and industrial paradigms, used in the drug discovery process will be treated. The contribution of the Brazilian science in the knowledge generation in Medicinal Chemistry will be demonstrated, with base in searches accomplished in the portal Web of Science® 7.10 and in the directory of groups of research of CNPq.

Avaliação da qualidade de sedimentos - estudo de caso: sub-bacia do Ribeirão Espírito Santo, afluente do Rio São Francisco

This study evaluated the environmental impact resulting from surface water and sediment contamination by metals in a watershed affected by a tailing basin that controls effluents coming from a zinc-ore beneficiation plant. The studies combined assessments of sediment chemistry (exceedances of sediment quality guidelines), benthic assemblage structure and acute and chronic ecotoxicity. The results showed that the levels of metal contamination in sediments are not yet enough to cause deleterious effects to the biota. However, the ecotoxicity tests indicated the occurrence of chronic effects, demonstrating that other factors, as the use of fertilizers, could also be a source of contamination.

Composição química volátil, em diferentes estádios de maturação, de manga 'Tommy Atkins' produzida no Vale do São Francisco

The effect of the maturation stages on the volatile chemical composition of mango fruit cv. Tommy Atkins, cultivated in São Francisco Valley, was investigated using SPME. GC/MS and GC-FID analysis allowed the identification of 32 compounds, consisting mainly of monoterpenes. δ-3-Carene was the major component in all the stages, while α-terpinolene, trans-β-caryophyllene e α-pinene succeded each other as the second most abundant constituent, during the ripening. The aroma of the ripe fruit was characterized by presence of short-chain ethyl esters (C2-C6), whereas the green mango contained the highest concentration of δ-3-carene. Furthermore, some terpenes were detected exclusively at one of the stages.

Contribuição da fitoquímica para o desenvolvimento de um país emergente

The sustainable development of an emergent country is dependent on a consistent scientific, technologic and innovative policy, on nature and biodiversity, on a rational exploration of natural resources to feeding, social advance and economical aim along with maintenance of health and diseases treatment. Phytochemical investigations may be used to contribute with development throughout undergraduate and graduate career preparing professionals with qualification to these activities, as researcher and professor, including discovering and divulgation of new scientific knowlegments. The role of organic compounds produced by secondary metabolism of plants in the development of new drugs is presented (e. g.) throughout exposition using examples of features involved in this activity, since the recognition of a plant-derived popular medicine, until the laboratory semi-synthesis of its main constituents. Several aspects related to the use of some vegetable species in treatment of many tropical diseases are pointed. Economical and social importance of isolation, structural characterization, pharmacological investigation and chemical transformations of new natural organic substances isolated from the plants are related.

Em busca da conservação ambiental: a contribuição da percepção ambiental para a formação e atuação dos profissionais da Química

Planet transformations caused by human intervention in the last 200 years are largely due to chemical impact. Therefore, this study aimed to identify and analyze the environmental perception of undergraduate students and lecturers in the Chemistry course of the Federal University of Lavras, accounting for the topics "Environmental Definition" and "Relationship between Chemistry and Environment". Two thematic axes for discussion were proposed using theories of Social Representation and Environmental Complexity, with the aim of stimulating the conservationist reasoning and actions. Such axes were proposed to give support to the education of chemists at the undergraduate level.

Concentrações e associações geoquímicas de Pb e Zn em sedimentos do rio São Francisco impactados por rejeitos da produção industrial de zinco

Surface sediments from the River São Francisco were analyzed to investigate the impact, due to the presence of metals (Cd, Cu, Pb, Zn) in wastes from a metallurgical industry in the city of Três Marias/MG, Brazil. The concentrations and geochemical associations of Pb, Zn and trace metals associated with the minerals employed in zinc production were measured. Sediments close to discharge locations were highly contaminated with Pb (332-512 μg g-1) and Zn (7872-10780 μg g-1), with values decreasing rapidly due to dilution and hydraulic sorting. Evaluation of toxicity according to the Consensus-based Sediment Quality Guidelines indicated for Cd, Pb and Zn a high probability of adverse effects on aquatic biota at these sites.

Montagem de uma disciplina experimental: contribuição para a química geral

The purpose of this paper is to present a classification criterion for general chemistry experiments departing from a survey of 35 years of the experimental general chemistry discipline at the Chemistry Institute - UNICAMP. It is shown that by considering the most remarkable characteristics of an experiment and classifying it under Conceptual, Fundamental, Methodological or Quantitative criterion, teachers could better develop the discipline plan and prevent a subject superposition. Taking into account the system Fe3+/SCN- , the article also exemplify how is possible to modify an experimental approach and to conceive other procedures with different didactic purposes.

Aplicação da radiação ultravioleta como forma de contribuição para a química verde e construção de um reator fotoquímico alternativo e de baixo custo, para pré-tratamento de amostras

Ultraviolet radiation corresponds to a fraction of electromagnetic radiation, covering wavelengths between 1 and 400 nm. Methods based on UV irradiation have become popular because it is possible to treat samples simply by applying energy, avoiding procedures that require the use of toxic substances, thus contributing to the development of Green Chemistry. This study aimed to assess the main applications of UV radiation reported in the literature and thoroughly described the construction of an alternative and low-cost photochemical reactor to be used for the pretreatment of samples in the laboratory. The use of this new photochemical reactor in the clean-up of milk samples for spectrofluorimetric measurements was also reported.