Chirality Induction in a Hydrophilic Metallohelicate

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Host-Guest Chemistry

Background:

• Development of novel metallohelicates for molecular recognition.
• Understanding host-guest complexation dynamics and cooperativity.
• Investigating chirality transfer in supramolecular systems.

Purpose of the Study:

• To synthesize and characterize a triply stranded iron(III) metallohelicate.
• To investigate the host-guest complexation behavior of chiral cations (G1 and G2) with the metallohelicate.
• To elucidate the mechanisms of cooperativity, molecular recognition, and chirality transfer.

Main Methods:

• Synthesis of calix[4]arene-based ligands and iron(III) metallohelicates.
• Host-guest complexation studies with chiral cations.
• Density Functional Theory (DFT) calculations for structural and interaction analysis.
• Circular Dichroism (CD) spectroscopy for chirality induction studies.

Main Results:

• The metallohelicate 1_Fe successfully incorporates up to two chiral guests (G1 and G2).
• G1 exhibits positive cooperativity, while G2 shows noncooperativity, despite G2's higher affinity.
• DFT calculations reveal cavity expansion upon first guest binding, facilitating second guest encapsulation.
• Chirality of guests is transferred to the metallohelicate via hydrogen bonding, inducing specific helicity.
• Nonlinear CD intensity indicates guest-induced preorganization enhances binding of a second, similarly chiral guest.

Conclusions:

• The metallohelicate demonstrates tunable host-guest interactions and cooperativity based on guest structure.
• Conformational changes and intermolecular interactions within the cavity dictate molecular recognition.
• Efficient chirality transfer from guest to host is achieved through specific hydrogen bonding interactions.
• The study provides insights into the design principles for sophisticated supramolecular systems with controllable recognition and chirality properties.