The curious case of 12-hydroxystearic acid - the Dr. Jekyll & Mr. Hyde of molecular gelators

A comprehensive review of the features driving self-assembly of 12-hydroxystearic acid (12-HSA), a low-molecular-weight gelator, and its applications in drug delivery and as other soft innovative materials are presented herein. 12-HSA is obtained via hydrogenation of ricinoleic acid naturally found in high concentrations in castor oil. The ability of 12-HSA to self-assemble is associated with the presence, position, and enantiomeric purity of the hydroxy group along the fatty acid chain. The polarity and position of the hydroxyl group facilitates more interaction possibilities leading to its exceptional self-assembly behavior giving rise to fibers, ribbons, and tubes in a variety of solvents. Upon self-assembly, 12-HSA undergoes crystallization resulting in the formation of high aspect ratio fibrillar structures due to noncovalent, intermolecular interactions forming self-spanning, three-dimensional networks (called self-assembled fibrillar networks) in both aqueous and organic solvents. Herein, emphasis is placed on emerging applications of 12-HSA supramolecular assemblies (i.e. responsive aqueous foams, gelled complex fluids, drug delivery systems, hydrogels, organogels, xerogels, and aerogel). The vast literature is compiled associated with 12-HSA self-assembly exploring supramolecular assemblies based on one ambidextrous gelator capable of assembling in aqueous and nonaqueous solvent.