Investigação da interação entre a polianilina e líquidos iônicos derivados de sais de amônio e aminoácidos

Abstract

In this work, 18 quaternary ammonium salts (QAS), which are potential ionic liquids (ILs) containing three different cations and six amino acids were prepared and characterized. Amino acids that present different characteristics: L-proline, L-leucine, L-phenylalanine, Ltyrosine, L-histidine, and L-aspartic acid (acids, basics, charged and that form hydrogen bonds). And ammonium halides containing different groups bounded to quaternary nitrogen: hexadecyltrimethylammonium bromide (CTAB), hexadecylethyldimethylammonium bromide (EDAB) and hexadecylbenzyldimethylammonium chloride (BDAC). Different side chains of the precursors were used to evaluate how these features influence in ILs properties. These salts were characterized by Raman spectroscopy, infrared (FT-IR), and nuclear magnetic resonance (NMR). To assist in the characterization of ILs, we also performed the spectroscopic characterization of the amino acid precursors (AAs) and the CTAB, EDAB, and BDAC. The preparation of QAS with AAs consists of the ion exchange of the CTAB, EDAB, or BDAC halide for hydroxyl ions and following acid-base reaction with the respective AAs. The spectroscopic data of the quaternary ammonium hydroxides exhibit that the presence of a bulkier R group decreases the anionic influence on the electronic density of the H neighbors to the quaternary nitrogen. And, it noticed the change in the ions packaging of the different hydroxides. The vibrational spectra of QAS samples with AAs indicate that AAs is in the anionic form. Also, the interactions of the ions are weak and non-specific but induced a conformation change in the cations. The results indicated that the side chain could interact with the anion and on the presence of water or residual solvents from the drying procedure is capable of modifying the molecular structure. Emeraldine salt (ES-PANI) and emerald-based nanofibers (EB-PANI) were synthesized. The UV-VIS-NIR, Raman, and FT-IR were employed to study the interaction of EB-PANI nanofibers with CTAB and BDAC derivatives. Spectroscopic data showed that QASs interact with EB-PANI's quinoid segments and are capable of inducing changes in PANI conformation and/or causing oxidation of the polymer. Besides, it noticed that the presence of solvents such as ethanol and chloroform induce the formation of semiquinoid segments in the PANI system that containing the SAQs derived from BDAC with the AAs: L-aspartic acid and L-histidine.