Journal Article Palmitoylated amino acids as low-molecular-weight gelators for ionic liquids

Restu, Witta Kartika  ,  Nishida, Yuki  ,  Kataoka, Toshikazu  ,  Morimoto, Masahiro  ,  Ishida, Kenji  ,  Mizuhata, Minoru  ,  Maruyama, Tatsuo

295 ( 7 )  , pp.1109 - 1116 , 2017-07 , Springer Verlag
We report palmitoylated amino acids (glycine, l-valine, l-isoleucine, l-aspartic acid, l-glutamic acid, l-methionine, l-phenylalanine, l-lysine) as low-molecular-weight gelators for ionic liquids (ILs). The palmitoylated amino acids gelate ammonium- and imidazolium-based ILs, at gelation concentrations of 0.3-1.6 wt.%, despite their simple molecular structures. Eight types of gelators are synthesized, with palmitoylated methionine (Pal-Met) and palmitoylated phenylalanine (Pal-Phe) exhibiting high gelation ability toward the tested ILs. Scanning electron microscopy and confocal laser scanning microscopy observations suggest that the gelator molecules self-assemble into nanofibers within the ILs, which leads to gelation. The ionogels exhibit reversible thermal transition and viscoelastic properties, which are typical of gels. Fourier-transform infrared spectra recorded at various temperatures reveal that hydrogen bonding and van der Waals interactions between gelator molecules are important in the self-assembly. Incorporating gelators of varying concentrations do not affect the intrinsic conductivities of the ILs.

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