Chiroptical properties of cryptophane-111.

Area of Science:

• Supramolecular Chemistry
• Chiroptical Spectroscopy
• Computational Chemistry

Background:

• Cryptophane-111 (1) is a simplified cryptophane derivative with high xenon binding affinity.
• Understanding the chiroptical properties and solution-phase behavior of enantiomers is crucial for their applications.
• Previous studies on cryptophane derivatives like cryptophane-222 (2) showed solvent-dependent chiroptical properties.

Purpose of the Study:

• To separate the enantiomers of cryptophane-111 (1) and characterize their chiroptical properties.
• To determine the absolute configurations of cryptophane-111 enantiomers in solution and solid states.
• To investigate the influence of solvent on chiroptical properties and compare with cryptophane-222 (2).
• To demonstrate xenon encapsulation using Raman optical activity (ROA).

Main Methods:

• High-Performance Liquid Chromatography (HPLC) with chiral stationary phases for enantiomer separation.
• Polarimetry, Electronic Circular Dichroism (ECD), Synchrotron Radiation Circular Dichroism (SRCD), Vibrational Circular Dichroism (VCD), and Raman Optical Activity (ROA) experiments.
• Time-Dependent Density Functional Theory (TDDFT) and Density Functional Theory (DFT) calculations for configuration assignment.

Main Results:

• Separation of cryptophane-111 enantiomers ([CD(+)₂₅₄]-1 and [CD(-)₂₅₄]-1) achieved.
• Absolute configurations in solution ([CD(-)₂₅₄]-PP-1 and [CD(+)₂₅₄]-MM-1) determined and confirmed in the solid state.
• Chiroptical properties of cryptophane-111 enantiomers were solvent-independent, unlike cryptophane-222.
• Xenon encapsulation by cryptophane-111 evidenced by ROA via a symmetric breathing mode at 150 cm^-1.

Conclusions:

• The solvent-independent chiroptical behavior of cryptophane-111 is attributed to the absence of solvent molecules within its cavity.
• ROA spectroscopy is a viable method to detect xenon encapsulation by cryptophane-111.
• Cryptophane-111 enantiomers exhibit distinct chiroptical signatures useful for structural elucidation and host-guest chemistry.