Bifunctionalization of l-Lysine with Aromatic and Aliphatic Moieties Converts It into a Super Organogelator in DMSO

Organogels are soft materials that have been gaining increased attention due to their wide range of applications in various fields. While the gelation of several organic solvents has been successfully achieved using polymer and low molecular weight (LMW) gelators, forming gels of dimethyl sulfoxide (DMSO) remains challenging due to its high polarity and its ability to disrupt hydrogen bonding. This is particularly challenging because LMW gelators primarily rely on intermolecular hydrogen bonding along with hydrophobic interactions for gelation. In this study, we demonstrate that the bifunctionalization of l-lysine with fluorenylmethoxycarbonyl and palmityl groups at the N_α and N_ϵ amino groups of l-lysine (FmKPal) respectively, induces organogelation in neat DMSO. Notably, the minimum gelation concentration (MGC) of FmKPal in DMSO is as low as 0.2 wt %, which is significantly lower than the typical 1-2 wt % observed for most LMW organogelators. This low MGC classifies FmKPal as a "super" organogelator. Electron microscopy reveals a nanofibrillar network formed through the self-assembly of FmKPal, resulting in a stable gel. Various biophysical characterizations indicate that aromatic π-π and hydrophobic interactions drive the self-assembly of the FmKPal. Interstingly, despite DMSO's hydrogen bond-disrupting nature, intermolecular hydrogen bonding between the carbamate and amide groups of FmKPal remains intact. This preservation is likely due to the synergistic effects of aromatic π-π and hydrophobic interactions. Furthermore, blending the FmKPal DMSO gel with lubricant oil retained the gel behavior, highlighting its potential for oil-based applications. The current finding of DMSO gelation by an LMW gelator provides additional insights into supramolecular gel formation and offers a lead for designing similar gelators with broader applications such as lubrication and related fields.