Six-Cyclic Crown Ether-Type Pillar[5]Arene: Enhanced Binding Ability to Bispyridinium Derivatives

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Macrocyclic Chemistry

Background:

• Pillar[5]arenes are macrocyclic compounds with a tunable cavity.
• Crown ethers are known for their ability to bind metal cations.
• Developing new macrocyclic hosts with enhanced binding properties is crucial for molecular recognition applications.

Purpose of the Study:

• To synthesize a novel six-cyclic crown ether-type pillar[5]arene.
• To investigate the structural and thermal properties of the synthesized macrocycle.
• To evaluate the host-guest binding abilities of the new pillar[5]arene derivative with bis(pyridinium) guests and metal cations.

Main Methods:

• Synthesis of a six-cyclic crown ether-type pillar[5]arene.
• Variable-temperature Nuclear Magnetic Resonance (NMR) spectroscopy (DMSO-d6, CDCl3).
• 2D 1H-1H NOESY experiment (CDCl3).
• 1H NMR titration experiments (acetone-d6/CDCl3, CD2Cl2/methanol-d4).
• UV-vis titration experiments (CHCl3).

Main Results:

• The synthesized six-cyclic pillar[5]arene features ethylene oxide loops positioned externally, unaffected by temperature variations.
• The macrocycle demonstrates superior host-guest binding affinity towards bis(pyridinium) derivatives compared to traditional alkoxy pillar[5]arenes.
• The peripheral benzocrown ether units effectively bind metal cations.

Conclusions:

• The successful synthesis of the six-cyclic pillar[5]arene crown ether provides a new platform for supramolecular chemistry.
• The enhanced binding capabilities highlight its potential for selective molecular recognition and sensing applications.
• The structural stability and cation-binding properties make it a promising candidate for advanced host-guest chemistry.