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 (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.