Helicity control of a polyaromatic coordination capsule through stereoselective CH-π interactions

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Chiral Recognition

Background:

• Square-planar ML4 units are key for coordination cages, but controlling nanostructure chirality and helicity is challenging.
• Non-covalent interactions are crucial for designing complex supramolecular architectures.

Purpose of the Study:

• To achieve helicity control in M2L4 polyaromatic capsules using stereoselective CH-π interactions.
• To investigate the selective binding of monosaccharides within these capsules.
• To correlate monosaccharide configuration with capsule helical conformation.

Main Methods:

• Synthesis of M2L4 polyaromatic capsules from metal ions and bent bispyridine ligands.
• Host-guest complexation studies with various permethylated monosaccharides in water.
• Spectroscopic analysis (CD, NMR) and theoretical calculations to determine structure and interactions.
• Chiroptical spectroscopy to probe induced helicity.

Main Results:

• Quantitative binding of monosaccharides (Ka up to >10^8 M^-1) via host-guest CH-π interactions.
• Selective recognition of β-glucose from α/β mixtures (>80:20 ratio) through equatorial anomeric group binding.
• Stereoselective binding observed for galactose derivatives as well.
• Monosaccharide axial/equatorial configurations dictate capsule helical conformation.
• α-glucose encapsulation induces strong single-handed host helicity, evidenced by an intense Cotton effect.
• β-galactose binding induces inverse capsule helicity.

Conclusions:

• Stereoselective CH-π interactions provide a powerful strategy for controlling the helicity of polyaromatic capsules.
• The M2L4 capsule acts as a chiral host capable of discriminating between monosaccharide anomers.
• This work demonstrates a novel method for creating tunable chiral nanostructures in solution.