Supramolecular gels from phosphonic acid-containing two-component gelators: efficient phase-selective gelation of aromatic and aliphatic hydrocarbons

Abstract

We report the efficient supramolecular gelation of multiple organic solvents by the two-component gelators comprising of phenyl phosphonic acid and the two amino acid derivatives – (S)-2-amino-N-hexadecyl-3-phenylpropanamide and (S)-2-amino-N-hexadecyl-3-methylbutanamide. Significantly, these gelators induced phase-selective gelation of several types of aromatic, aliphatic, and mixed aromatic/aliphatic hydrocarbon solvents from the respective two-phase aqueous mixtures. Thus, these gelators can separate aromatic and aliphatic hydrocarbons from aqueous mixtures. Detailed characterisations of some selected gels were performed using SEM, FTIR, rheology, and XRD techniques. We propose that multiple non-covalent interactions – H-bonding, ionic, hydrophobic, π–π interactions – are responsible for self-aggregation, gel formation and stabilization. Interestingly, a closely related analogue phenyl phosphinic acid in combination with the same amino acid derivatives displayed modest gelation ability. In these two-component systems, the diprotic phenyl phosphonic acid is considerably more effective than the monoprotic phenyl phosphinic acid. This study convincingly demonstrates that phosphonic acid derivatives are highly promising for developing efficient functional two-component gelators and will provide an invaluable method for designing new small-molecule gelators.

Graphical Abstract