Engineering Supramolecular Polymers: From Ferrocene to G-Quadruplexes

Abstract

Supramolecular polymers (SPs), emerging as non-covalent analogs of traditional covalent polymers, consist of small molecular monomers interconnected through directional and reversible non-covalent interactions, such as hydrogen bonding and metal-ligand coordination.¹ These interactions give rise to one-dimensional molecular aggregates with dynamic and stimuli-responsive properties. The strategic design of monomers plays a pivotal role in promoting efficient supramolecular polymerization by strengthening non-covalent interactions. Our investigation reveals that the ferrocene unit, with its restricted rotational flexibility, facilitates optimal intermolecular interactions in 1,1-disubstituted ferrocenes bearing non-covalent functionalities, thereby enhancing the probability of successful supramolecular polymerization.²˒³ Next, I will discuss aqueous SPs,⁴˒⁵ focusing on recent advancements in Cu(I)-induced G-quadruplex SPs, a non-canonical DNA secondary structure capable of undergoing heating-induced aqueous phase transitions. These transitions result in either a hydrogel, formed via entropically driven cross-linking of SPs, or a hydrophobic collapse-induced solid precipitate exhibiting lower critical solution temperature (LCST) behavior.5 Unlike conventional supramolecular assemblies that disassemble upon heating, our SPs exhibit LCST-driven gelation. Additionally, a folic acid-based SP produces a heat-set, self-healing gel. Inspired by proteins, we also demonstrate the salting-out behavior of SPs by introducing kosmotropic salts, which enhance their robustness.⁴ These aqueous SPs, with unique phase transition behaviors, hold potential as smart supramolecular materials for applications in materials science, nanotechnology, and healthcare.