The influence of the framework: an anion-binding study using fused [n]polynorbornanes

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Host-Guest Chemistry

Background:

• Bis-thiourea functionalized polynorbornanes are investigated for their anion binding capabilities.
• Understanding host-guest interactions is crucial in supramolecular chemistry.

Purpose of the Study:

• To synthesize a series of bis-thiourea-functionalized [n]polynorbornane hosts with varying sizes.
• To evaluate the anion-binding properties of these hosts towards acetate and dihydrogenphosphate.
• To elucidate the influence of the host framework size on binding stoichiometry and cooperativity.

Main Methods:

• Synthesis of bis-thiourea-functionalized [n]polynorbornane hosts.
• ¹H NMR spectroscopic titration to assess binding affinities and stoichiometries.
• Job's plot analysis to determine binding modes and cooperativity.

Main Results:

• Larger bis-thiourea-[3]polynorbornane scaffolds (4 and 5) exhibited 1:1 cooperative binding with acetate.
• Smaller norbornane host 2 showed 1:2 independent binding with acetate, despite similar preorganization.
• Framework size did not affect the binding of dihydrogenphosphate by the hosts.

Conclusions:

• The size of the polynorbornane framework significantly influences the binding mode and cooperativity of acetate.
• Host framework architecture plays a subtle yet critical role in modulating host-guest interactions.
• These findings provide insights into the design principles for selective anion recognition systems.