Roberto F. S. Freitas

Temperature sensitive gels as extraction solvents

Crosslinked poly(N-isopropylacrylamide) gel and crosslinked copolymers of 97% N,N-diethylacrylamide and 3% sodium methacrylate which are swollen with water collapse abruptly at 33°C and near 55°C, respectively. These collapses apparently occur because each gel is near its lower critical solution temperature. The gels can be used to extract water and low molecular weight solutes from macromolecular solutions. After they have extracted the water, the gels can be regenerated by warming to release the absorbed water. The resulting separation process is effective for proteins and other polymers, and may be operated with waste heat which is usually discarded.

Phase behavior of poly(N-isopropylacrylamide) in binary aqueous solutions

Abstract In this work, the phase behavior of linear poly(N-isopropylacrylamide) (PNIPA) in water–solvent mixtures was investigated. Several solvents, including low molecular weight alcohols, were selected and phase separation temperatures were determined through cloud point measurements. All the studied systems exhibited the cononsolvency effect, i.e. lower PNIPA compatibility within definite ranges of composition in water-rich mixtures. However, it was first detected that the coexistence of phase separation temperatures—a lower critical solution temperature (LCST) with an upper critical solution temperature (UCST)—at higher solvent concentrations in most systems, depend on the hydrophobic nature of the solvent. The change from a LCST to a UCST was correlated with the competition between polymer–water and polymer–solvent interactions mediated by compositional factors. The effects produced by the different solvents tested were qualitatively compared, considering aspects related to their particular molecular structures, such as the potential to form hydrogen bonds and the implications of the size and shape of non-polar groups for hydrophobic hydration.

Temperature Sensitive Gels as Size Selective Absorbants

Abstract We have used crosslinked polymer gels as extraction solvents for aqueous solutions. The gels swell to many times their dry weight by absorbing water and low molecular weight solutes, but excluding proteins and other high molecular weight solutes. The swollen gel is removed by filtration. When it is slightly warmed, it collapses, releasing most of the absorbed material. This sudden change of swelling with temperature occurs because the gel is near a critical point. After the gel is separated from the desorbed water by filtration, it is cooled and then can be reused.

Síntese e caracterização térmica e química do copolímero poli(D,L-lactídeo-co-glicolídeo)

O copolimero poli(D,L-lactideo-co-glicolideo) apresenta-se como um dos polimeros de maior interesse para aplicacao na area medica. O fato de ser biorreabsorvivel, biocompativel, atoxico e ter uma cinetica de degradacao que pode ser modificada pela razao entre os monomeros na copolimerizacao justifica tal interesse. Neste trabalho, os copolimeros foram sintetizados a 175 oC, por meio da abertura dos aneis dos dimeros ciclicos dos monomeros D,L-lactideo e glicolideo, na presenca do iniciador octanoato de estanho e do co-iniciador alcool laurilico. O controle eficiente do vacuo no meio reacional, aliado a adequada agitacao, foram fundamentais para o sucesso da sintese. Para caracterizacao dos copolimeros sintetizados foram empregadas as tecnicas de calorimetria exploratoria diferencial (DSC), termogravimetria (TG) e espectroscopia na regiao do infravermelho (FTIR). Foram analisados nao somente os produtos de reacao, mas tambem os monomeros de partida. A nova rota de sintese utilizada mostrou-se adequada, sendo os copolimeros poli(D,L-lactideo-co-glicolideo) obtidos com sucesso.

Molecularly imprinted polymer for determination of lumefantrine in human plasma through chemometric-assisted solid-phase extraction and liquid chromatography

Lumefantrine is the first-choice treatment of Falciparum uncomplicated malaria. Recent findings of resistance to lumefantrine has brought attention for the importance of therapeutic monitoring, since exposure to subtherapeutic doses of antimalarials after administration is a major cause of selection of resistant parasites. Therefore, this study focused on the development of innovative, selective, less expensive and stable molecularly imprinted polymers (MIPs) for solid-phase extraction (SPE) of lumefantrine from human plasma to be used in drug monitoring. Polymers were synthesized by precipitation polymerization and chemometric tools (Box-Behnken design and surface response methodology) were employed for rational optimization of synthetic parameters. Optimum conditions were achieved with 2-vinylpyridine as monomer, ethylene glycol dimethacrylate as crosslinker and toluene as porogen, at molar ratio of 1:6:30 of template/monomer/crosslinker and azo-bisisobutyronitrile as initiator at 65 °C. The MIP obtained was characterized and exhibited high thermal stability, adequate surface morphology and porosity characteristics and high binding properties, with high affinity (adsorption capacity of 977.83 μg g-1) and selectivity (imprinting factor of 2.44; and selectivity factor of 1.48 and selectivity constant of 1.44 compared with halofantrine). Doehlert matrix and fractional designs were satisfactorily used for development and optimization of a MISPE-HPLC-UV method for determination of lumefantrine. The method fulfilled all validation parameters, with recoveries ranging from 83.68% to 85.42%, and was applied for quantitation of the drug in plasma from two healthy volunteers, with results of 1407.89 and 1271.35 ng mL-1, respectively. Therefore, the MISPE-HPLC-UV method optimized through chemometrics provided a rapid, highly selective, less expensive and reproducible approach for lumefantrine drug monitoring.

Síntese e caracterização de MIP com fenilalanina visando sua aplicação na técnica de SPE

Polimeros Molecularmente Impressos (MIPs) sao polimeros sinteticos que apresentam alta seletividade a uma molecula de interesse. O objetivo deste trabalho foi a sintese e caracterizacao de MIPs para aplicacao na extracao em fase solida (SPE), visando a determinacao de fenilalanina. Os MIPs foram sintetizados a partir do MAA, fenilalanina, EGDMA, AIBN, em cloroformio. Tambem foi sintetizado o polimero nao-impresso (NIP), para controle da seletividade dos MIPs. A dessorcao da fenilalanina foi realizada em extrator Soxhlet. Os MIPs e NIP foram caracterizados pelas tecnicas de analise: FTIR, UV-Vis, MEV, DSC e TG. O MIP apresentou maior capacidade adsortiva a fenilalanina do que o NIP, com uma taxa media de adsorcao de 55% comparada a 11% para o NIP. Por MEV o MIP apresentou superficie mais porosa, importante caracteristica para aplicacao em SPE. Os estudos realizados mostraram que o MIP sintetizado apresentou grande potencial para aplicacao em tecnica de SPE.

ESTUDO REOLÓGICO DE ÓLEOS LUBRIFICANTES AUTOMOTIVOS POR MEIO DE REOMETRIA

Neste trabalho, foi feito um estudo reologico de dezoito oleos comerciais, de diferentes marcas e classificacoes SAE. Os oleos foram submetidos a testes em regime estacionario de tensao, utilizando um reometro AR-G2. A tensao de cisalhamento foi variada de 0 a 600Pa, a temperatura fixa de 25C. Foi observado que a viscosidade de todos os oleos lubrificantes diminuiu com o aumento da tensao de cisalhamento. A partir destes testes em regime estacionario, os oleos foram separados em tres grupos, de acordo com as suas curvas de viscosidade, com os do Grupo A apresentando as maiores viscosidades, em qualquer tensao aplicada, seguidos dos do Grupo B, e os do Grupo C com as menores viscosidades. Os oleos, classificados no Grupo A, sao aqueles com maior grau SAE e com viscosidade cinematica maior que 250cSt. Os resultados obtidos mostram uma correspondencia entre o estudo reologico dos oleos por reometria e os testes convencionais usados para classificacao dos oleos. Considerando tais resultados, a eficiencia, a rapidez e a facilidade do metodo, pode-se concluir pela vantagem da utilizacao deste metodo para testes preliminares na formulacao de oleos lubrificantes. 1. INTRODUCAO