Supramolecular Synthon Approach in Designing Organic Sulfonates as Supramolecular Gelators: An Easily Accessible Topical Gel with Antibacterial Properties
Poulami Chakraborty, Hemanta Kumar Datta, Protap Biswas, Parthasarathi Dastidar
Abstract
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 (An = CH3–(CH2)n–NH2; n = 2–11, 13–15, 17) and naphthalene-2-sulfonic acid (N2S) as potential supramolecular gelators. The sulfonate salts AnN2S 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.