Counterion dependent hydrogelation of amino acid based amphiphiles: switching from non-gelators to gelators and facile synthesis of silver nanoparticles

With the growing importance of hydrogels in scientific applications, the search for low molecular weight hydrogelators (LMWH), with simultaneous logical structural correlation is continuously increasing. In the present work, counterion variation of amino acid based amphiphiles was done to qualitatively evaluate its contribution towards hydrogelation. Further changes in the molecular skeleton of the amino acid amphiphile were done along with counterion variation to establish the importance of pi-pi interactions of aromatic planar ring in hydrogelation. An efficient conversion of a non-gelator to gelator molecule was achieved simply by changing the counterions to aromatic carboxylates. Role of the counterion in the mechanism of gelation process through the self-assembly of amino acid based amphiphiles has been discussed. The formation of supramolecular structures during hydrogelation was investigated by FESEM, CD, FT-IR, luminescence, 2D-NOESY and rheological studies. Interestingly, the L-tryptophan containing amphiphile hydrogelators were further utilized for synthesis of Ag nanoparticles under mild conditions without any need for high temperature, alkaline medium and external reducing agent. The nanoparticles obtained were characterized by UV-Vis, TEM, AFM and XRD experiments.