A new cryptophane receptor featuring three endo-carboxylic acid groups: synthesis, host behavior and structural study

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Coordination Chemistry

Background:

• Cryptophane molecules are cage-like structures with potential applications in molecular recognition and sensing.
• Previous cryptophane derivatives have shown complexation abilities, but lacked ionizable functional groups for enhanced interactions.
• The incorporation of carboxylic acid groups offers new possibilities for tuning host-guest chemistry and metal ion binding.

Purpose of the Study:

• To synthesize and characterize novel cryptophane molecules featuring aromatic bridges and endo-positional carboxylic acid groups.
• To investigate the complexation behavior of the synthesized cryptophane with low-molecular-weight alcohols.
• To evaluate the efficacy of the new cryptophane in the liquid-liquid extraction of various metal ions, including alkali, alkaline earth, and lanthanide metals.

Main Methods:

• Synthesis and characterization of cryptophane derivatives using standard organic chemistry techniques.
• X-ray crystallography to determine the structure of a cryptophane triester solvate.
• Solution-based complexation studies with alcohols.
• Liquid-liquid extraction experiments for metal ion separation.
• Molecular modeling calculations to understand cryptophane-metal ion interactions.

Main Results:

• Successful synthesis and characterization of novel cryptophane molecules with aromatic groups and three carboxylic acid functions.
• Formation of a channel inclusion compound (solvate) with trichloromethane and water, with its X-ray crystal structure elucidated.
• Demonstrated complexation of the cryptophane with low-molecular-weight alcohols in solution.
• Effective liquid-liquid extraction of various metal ions (Na+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Eu3+, Yb3+) was achieved.
• Molecular modeling provided insights into the structural and binding properties of the cryptophanes and their metal complexes.

Conclusions:

• The newly synthesized cryptophane molecules represent a significant advancement in cryptophane chemistry due to the incorporation of ionizable carboxylic acid groups.
• These cryptophanes exhibit promising capabilities for selective molecular recognition of alcohols and efficient extraction of a wide range of metal ions.
• The combination of synthetic accessibility, structural characterization, and functional properties makes these cryptophanes attractive candidates for applications in separation science and sensing.