Síntese, caracterização e agregação de líquidos iônicos mono- e dicatiônicos derivados de aminoácidos

Abstract

This study presents the synthesis and characterization of mono and dicationic ionic liquids (ILs), with anions derived from amino acids (Arginine, Glycine, Lysine and Serine). The influence of the molecular structure of ILs in the aggregates formation in solution were also realized. The characterization of ILs was performed using 1H and 13C Nuclear Magnetic Resonance (NMR), Electrospray Ionization Mass Spectrometry (ESI- MS-MS), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The results showed that monocationic ILs have lower thermal stability than dicationic ILs, with the exception of [BisDec(MIM)2][GLI]. All ILs are less stable than analogous ILs with counterion bromide. From DSC, it was observed that the ILs presented only glass transition in the monitored temperature range. The aggregation behavior in aqueous solution of ILs was investigated using electrical conductivity and 1H NMR. The results showed that dicationic ILs aggregate more easily than monocationic ones. This result was related to the anions hydrophobicity of the anion influenced CAC more than the hydrophobicity of the cation. The chemical shift of the 1H of the imidazole (polar head) and the side/spacer chain (apolar part) of the ILs showed an increase in the chemical shift. Except for the IL [BisDec(MIM)2][2GLI] that all 1H signals showed a decrease as the aggregation occurred. The CAC obtained by conductivity and 1H NMR showed the same trend. The higher the hydrophobicity of the anion, the lower the CAC.