The Role of Sodium Cations and Covalent Decoration in the Dissociation of Supramolecular Polymers and a Rational Strategy to Improve Their Stability

Heterotypic supramolecular hydrogels are soft materials obtained by mixing at least two monomers in aqueous solution that self-assemble via hydrogen bonds (HBs) into polymeric fibers. Despite attempts to obtain stable hydrogels, some systems precipitate over time. In this work, we uncover the role of sodium cations and covalent modifications on the stability of three supramolecular polymers based on cyanuric acid (Cy) and triaminopyrimidine (TAP). Our computational experiments show that sodium cations penetrate the polymer and break the inner HBs, thus perturbing the stability of the structure. The longer and more flexible hexanoic acid (Co6) side group-compared to the butanoic acid (Co4) group on the Cy moiety- promotes more favorable hydrophobic close contacts with each other. Based on these results, we designed in silico a system based on CyCo6 and a triaminotriazine (TAT) moiety modified with a succinate group (sa). In this new polymer, the TATsa molecules effectively coordinate the cations on the outer surface of the polymer, avoiding their entry into the channel and thereby improving the HB strength of the rosettes and the stability of the polymer. Overall, our findings provide an understanding of the physicochemical factors that cause the precipitation of supramolecular hydrogels.