Supramolecular Synthon Approach in Designing Organic Sulfonates as Supramolecular Gelators: An Easily Accessible Topical Gel with Antibacterial Properties

The supramolecular synthon approach in the context of the crystal engineering rationale has been exploited to synthesize a new series of primary ammonium sulfonate salts derived from primary alkyl amines with varying alkyl chain lengths (A_n = CH₃–(CH₂)_n–NH₂; n = 2–11, 13–15, 17) and naphthalene-2-sulfonic acid (N2S) as potential supramolecular gelators. The sulfonate salts A_nN2S with n ≥ 9 showed the ability to immobilize a number of polar and nonpolar solvents including dimethyl sulfoxide/water, resulting in supramolecular gels which were characterized by dynamic rheology and transmission electron microscopy. Single-crystal X-ray diffraction studies carried out on eight such salts confirmed the presence of gel-inducing hydrogen bonded supramolecular synthons. Anti-bacterial studies (zone inhibition, turbidity, and tetrazolium assays) revealed that the salt A₁₄N2S had the ability to kill the Gram-positive bacterium Staphylococcus aureus. Laser scanning confocal microscopy and flow cytometry data taken under various staining conditions suggested reactive oxygen species-mediated RNA depletion as the plausible cause of bacterial cell death in the presence of the gelator salt. Shear thinning of the aqueous gel of A₁₄N2S along with its anti-bacterial activity indicated that it could be a potential candidate for topical application.