Liquid Mixtures Involving Hydrogenated and Fluorinated Alcohols: Thermodynamics, Spectroscopy, and Simulation

This article reports a combined thermodynamic, spectroscopic, and computational study on the interactions and structure of binary mixtures of hydrogenated and fluorinated substances that simultaneously interact through strong hydrogen bonding. Four binary mixtures of hydrogenated and fluorinated alcohols have been studied, namely, (ethanol + 2,2,2-trifluoroethanol (TFE)), (ethanol + 2,2,3,3,4,4,4-heptafluoro-1-butanol), (1-butanol (BuOH) + TFE), and (BuOH + 2,2,3,3,4,4,4-heptafluoro-1-butanol). Excess molar volumes and vibrational spectra of all four binary mixtures have been measured as a function of composition at 298 K, and molecular dynamics simulations have been performed. The systems display a complex behavior when compared with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes. The combined analysis of the results from different approaches indicates that this results from a balance between preferential hydrogen bonding between the hydrogenated and fluorinated alcohols and the unfavorable dispersion forces between the hydrogenated and fluorinated chains. As the chain length increases, the contribution of dispersion increases and overcomes the contribution of H-bonds. In terms of the liquid structure, the simulations suggest the possibility of segregation between the hydrogenated and fluorinated segments, a hypothesis corroborated by the spectroscopic results. Furthermore, a quantitative analysis of the infrared spectra reveals that the presence of fluorinated groups induces conformational changes in the hydrogenated chains from the usually preferred all-trans to more globular arrangements involving gauche conformations. Conformational rearrangements at the CCOH dihedral angle upon mixing are also disclosed by the spectra.

Moléculas simples com aplicação na medicina

O trabalho apresentado, foi realizado no âmbito do mestrado em Química para o ensino, da Universidade de Évora e tem como tema " Moléculas Simples de Aplicação na Medicina". A abordagem deste tema deve-se à necessidade cada vez maior de um ensino que motive os alunos e lhes proporcione um gosto maior pelo estudo das ciências, uma vez que cada vez mais os jovens estudantes revelam pouca motivação e gosto pelo estudo das áreas científicas quer ao nível do ensino secundário quer ao nível do ensino superior. Pretende-se também tentar compreender e explicar o porquê das suas desmotivações e tentar adaptar novas abordagens a temas que suscitem nos jovens um maior interesse, uma melhor compreensão da importância das ciências, da tecnologia na vida quotidiana de todos nós no que respeita ao nosso bem-estar e à nossa saúde. Numa primeira parte é feita uma revisão sobre os principais conteúdos propostos a desenvolver em sala de aula, conteúdos esses que sustentam o estudo do xénon como anestésico e dos perfluorocarbonetos como substitutos do sangue. A segunda parte integra um programa orientador, seguindo as metodologias e estrutura do programa homologado pelo ME para o 12º ano de escolaridade, e protocolos de algumas actividades de carácter experimental laboratorial propostas. Estas actividades têm como finalidade estimular a curiosidade e facilitar a consolidação das matérias. ABSTRACT: The present study was carried out under the Master's Degree in Chemistry for Teaching, taught at the University of Évora under the theme "lmplementation of Simple Molecules in Medicine". The approach to this issue is due to an increasing need for teaching that motivates students and sharpen their senses for the study of science because, increasingly, young students show little motivation and passion for the study of science, both at secondary school and higher education terms. The aim is also trying to understand and explain the reason of their discouragement and try new approaches to issues that raise young in a better understanding of the importance of science and technology in everyday life for all of us in what concerns to our welfare and our health. ln the first part there is an overview of the major content areas to develop in the classroom. These contents support the study of xenon as an anesthetic and perfluorocarbons as blood substitutes. The second part includes the syllabus, following the methodologies and structure of the curriculum approved by the ME to the 12th grade and protocols of some activities for an experimental laboratory. These activities intend to stimulate curiosity and facilitate the consolidation of materials.