Guanidinium-Responsive Crown Ether-Based Macrocyclic Amphiphile in Aqueous Medium

Abstract

Supramolecular assemblies based on oligo(ethylene glycol) (OEG) building blocks are well-known for their neutral chemical property and thermal-responsive behavior. Here, the cyclic "CLOSED" and linear "OPEN" typologies of OEGs led to dramatic difference in the sensitivity to guanidinium-containing species. From thermodynamic studies, the association constant (K a ) between the "CLOSED" form amphiphile and guanidinium salt was determined to be 28.7 M −1 , whereas there was no detectable binding affinity for the "OPEN" form. Therefore, considering ion specificity, the present results establish that crown ether derivatives with "CLOSED" and "OPEN" topologies provide an easy-to-access model pair with designed ion-recognition sites and special functional moieties and geometries (like the binding pockets of enzymes or ion channels in cellular members) that allow the manipulation of the intercrossed relationship between supramolecular solutes, waters, and guanidinium salts. These supramolecular forces in aqueous solution offered an alternative strategy to fabricate thermal-responsive systems in ionic medium.

The aqueous supramolecular chemistry of crown ethers

“…A benzo-27-crown-9 ether (C9OH) system was used to explore the "size-fitting"-induced host-guest complexation between C9 and guanidinium. A similar coexisting salting-in and salting-out effect can be extended to guanidinium-type ions, such as guanidinium chloride and arginine (Pan et al, 2021).…”

“…On-going research has further demonstrated the general principles of the spatial topology factor and site-fitting effect in CE-containing ionic systems (Huang et al, 2018;Luo et al, 2019;Pan et al, 2021). Chen et al observed a similar coexisting salting-in and salting-out effect (Huang et al, 2018) when C7 was functionalized on a poly (vinyl alcohol) polymer system, demonstrating that CEs can serve as general building blocks to control ion specificity in aqueous media.…”