Supramolecular Polymers of Amino Triazines vs. Amino Pyrimidines in Aqueous Solution: How Key Interactions Control their Thermodynamic Stability

Supramolecular polymers (SPs) based on the stacking of hydrogen-bonded rosettes are attracting increasing attention due to their potential applications as soft materials. However, a detailed description of the interactions that give rise to these one-dimensional architectures is still scarce in the literature. In this work, we use molecular dynamics to analyze in aqueous solution the stability of two SPs based on amino triazines (AT) and amino pyrimidines (AP) modified with a hydrophilic chain of succinic acid (-saH). Our results reveal that the AT-based polymers are stable in both their neutral and anionic (succinate -sa^-) forms. In contrast, the anionic AP-based polymer is completely dissociated in the presence of sodium cations. While chloride anions can stabilize AT polymers and even induce helical coordination, sodium cations destabilize the AP polymer by penetrating its structure and coordinating with the N atoms, thereby disrupting the hydrogen bonds of the rosettes. On the contrary, the AT-sa^- monomers are able to hold back sodium cations due to their extra endocyclic N atom. The side chains are also essential for the formation of these SPs. In summary, we show how non-covalent interactions can be strategically used to control the stability of these systems.