Facile syntheses of a class of supramolecular gelator following a combinatorial library approach: Dynamic light scattering and small-angle neutron scattering studies

Abstract

Following a combinatorial library approach, 60 organic salts have been prepared by reacting 5 bile acids and 12 secondary amines. Gelation tests with various organic and aqueous solvents reveal that 16 salts are supramolecular gelators of which 6 salts are found to be ambidextrous displaying the ability to form gels with organic as well as aqueous solvents. The salt didodecylammonium cholate (1a7b) is the most versatile gelator, displaying gelation ability with a maximum number of solvents. AFM images of the xerogels of 1a7b in organic and aqueous solvents reveal the presence of fibrous aggregate including helical fibers. Dynamic and morphological behaviors of the aggregates in the gel state have been probed by dynamic light scattering (DLS) and small-angle neutron scattering (SANS) experiments on an aqueous gel (1:1 DMSO/H₂O) of 1a7b. It is revealed that the gelation takes place via the formation of flexible fibrous clusters followed by physical cross-linking. DLS and SANS results also disclose that (1) the fibrous network is formed via flexible clusters of a few tens of nanometers in length, followed by immobile network formation; (2) the network structure is self-similar irrespective of gelator concentration, C, while the gelation temperature is C dependent; and (3) the fibrous aggregates are in the solid state with a sharp boundary.