Cationic acyclic cucurbit[n]uril-type containers: synthesis and molecular recognition toward nucleotides

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Molecular Recognition

Background:

• Acyclic CB[n]-type molecular containers are crucial in supramolecular chemistry.
• Understanding their self-association and recognition properties is key for designing new receptors.
• M2NH3 is a tetracationic analogue of the prototypical M2 container.

Purpose of the Study:

• To synthesize and characterize M2NH3, a tetracationic analogue of M2.
• To investigate the self-association and molecular recognition properties of M1NH3 and M2NH3.
• To determine the binding affinities of M1NH3 and M2NH3 towards various nucleotides.

Main Methods:

• Synthesis of M2NH3.
• Solubility studies in D2O.
• Investigation of self-association using NMR spectroscopy.
• Determination of binding constants (Ka) via 1H NMR titration with seven nucleotides.

Main Results:

• M1NH3 and M2NH3 exhibit excellent solubility and do not self-associate intermolecularly.
• An intramolecular self-complexation process was observed, driven by ion-dipole interactions and cavity inclusion.
• Binding affinities towards nucleotides were modest (10^2 - 10^3 M^-1), with M2NH3 being slightly more potent.
• Higher charged nucleotides (e.g., ATP) showed stronger complexation than lower charged ones (e.g., ADP, AMP).

Conclusions:

• The ureidyl C=O portals significantly influence the molecular recognition behavior of these acyclic CB[n]-type receptors.
• The observed intramolecular self-complexation affects binding affinities.
• Strategies like employing more highly charged arms can enhance receptor recognition of anions.