Molecular dynamics computer simulations have been performed to identify preferred positions of the fluorescent probe PRODAN in a fully hydrated DLPC bilayer in the fluid phase. In addition to the intramolecular charge-transfer first vertical excited state, we considered different charge distributions for the electronic ground state of the PRODAN molecule by distinct atomic charge models corresponding to the probe molecule in vacuum as well as polarized in a weak and a strong dielectric solvent (cyclohexane and water). Independent on the charge distribution model of PRODAN, we observed a preferential orientation of this molecule in the bilayer with the dimethylamino group pointing toward the membrane's center and the carbonyl oxygen toward the membrane's interface. However, changing the charge distribution model of PRODAN, independent of its initial position in the equilibrated DLPC membrane, we observed different preferential positions. For the ground state representation without polarization and the in-cyclohexane polarization, the probe maintains its position close to the membrane's center. Considering the in-water polarization model, the probe approaches more of the polar headgroup region of the bilayer, with a strong structural correlation with the choline group, exposing its oxygen atom to water molecules. PRODAN's representation of the first vertical excited state with the in-water polarization also approaches the polar region of the membrane with the oxygen atom exposed to the bilayer's hydration shell. However, this model presents a stronger structural correlation with the phosphate groups than the ground state. Therefore, we conclude that the orientation of the PRODAN molecule inside the DLPC membrane is well-defined, but its position is very sensitive to the effect of the medium polarization included here by different models for the atomic charge distribution of the probe.
A evasão e a retenção universitária vêm se impondo, ao longo do tempo, como uma realidade cada vez mais ostensiva no âmbito do ensino de graduação dos cursos de ciências exatas. Com o intuito de oferecer alternativas para erradicar este problema, ações que visam à democratização e à permanência dos estudantes de ensino superior vêm sendo adotadas em algumas instituições de ensino federal brasileiras. Neste artigo descreve-se a contribuição do programa PAG-Química (Programa de Apoio à Graduação em Química), proposto pela Universidade Federal do Rio Grande do Sul (UFRGS) no âmbito do programa REUNI (Reestruturação das Universidades Federais), que tem por objetivo a busca de sanar esta dificuldade, ajudando estudantes que necessitam de apoio no processo ensino-aprendizagem em Química (é também oferecido apoio em Cálculo, Física, Português, Inglês e Produção de Textos Acadêmicos e Científicos), através de aulas de reforço proporcionadas pelo professor tutor desta disciplina e por alunos do Programa de Pós-Graduação em Química e em Ciência dos Materiais da UFRGS. Palavras-chave: química geral, evasão, programa de apoio. Title: The Undergraduate Support Program in Chemistry (PAG-Chemistry) and its contribution to the democratization and permanence of students in higher education.
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