Primary ammonium monocarboxylate synthon in designing supramolecular gels: a new series of chiral low-molecular-weight gelators derived from simple organic salts that are capable of generating and stabilizing gold nanoparticles.

The primary ammonium monocarboxylate (PAM) synthon has been exploited to generate a new series of PAM salts from the free amine of L-phenylalanine-3-pyridyl amide, (S)-2-amino-3-phenyl-N-(pyridine-3-yl)propanamine (designated as "B"), and various substituted benzoic acids (designated as "A(R)"; R=4-Me, 4-Cl, 4-Br, 4-NO2, 3-Me, 3-Cl, 3-Br, 3-NO2, 2-Me, 2-Cl, 2-Br, 2-NO2). The 4- and 3-substituted benzoate salts showed moderate-to-excellent gelation ability with a number of polar and apolar solvents. The gels were characterized by DSC, rheology, SEM and TEM, FTIR spectroscopy, etc. Structure-property studies based on single-crystal powder X-ray diffraction (PXRD) and FTIR data provided insights into the role of the PAM synthon in the formation of the gel networks. Interestingly, some of the gels were capable of forming and stabilizing gold nanoparticles at room temperature without the use of any exogenous reducing agents.