Binding ability and assembly behavior of beta-cyclodextrin complexes with 2,2'-dipyridine and 4,4'-dipyridine

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Host-Guest Chemistry

Background:

• Beta-cyclodextrin (beta-CD) is a well-known host molecule capable of forming inclusion complexes.
• Dipyridines, such as 2,2'-dipyridine and 4,4'-dipyridine, are versatile ligands in coordination chemistry and supramolecular self-assembly.
• Understanding the interplay between host structure and guest molecule isomerism is crucial for designing novel supramolecular architectures.

Purpose of the Study:

• To synthesize and characterize two distinct channel-type supramolecular aggregations (1 and 2) using beta-cyclodextrin with 2,2'-dipyridine and 4,4'-dipyridine.
• To comprehensively investigate the binding ability and assembly behavior of these complexes in both solution and solid states.
• To elucidate the role of intermolecular interactions, such as hydrogen bonds and pi-pi stacking, in the formation of these supramolecular structures.

Main Methods:

• X-ray crystallography for solid-state structural analysis.
• Proton Nuclear Magnetic Resonance ((1)H NMR) spectroscopy for solution-state characterization.
• Circular dichroism (CD) spectroscopy to probe chiral interactions and conformational changes.
• Microcalorimetric titration to determine binding thermodynamics.

Main Results:

• Two channel-type supramolecular aggregations (1 and 2) were successfully prepared.
• Hydrogen bonds and pi-pi stacking interactions were identified as critical forces driving the self-assembly process.
• The positional isomerism of nitrogen atoms in the dipyridine guests led to different crystal systems (monoclinic for 1, triclinic for 2) and space groups (C2 for 1, P-1 for 2).
• Distinct binding modes and thermodynamic parameters were observed for the complexation of 2,2'-dipyridine and 4,4'-dipyridine with beta-cyclodextrin in aqueous solution.

Conclusions:

• The study demonstrates the significant impact of guest molecule isomerism on supramolecular assembly and crystal packing.
• Hydrogen bonding and pi-pi stacking are essential non-covalent interactions for constructing beta-cyclodextrin-dipyridine supramolecular systems.
• The findings provide valuable insights into the rational design of supramolecular materials with tailored properties based on host-guest chemistry.