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Cation induced changes to the structure of cryptophane cages
Oscar H Lloyd Williams1, Claudia S Cox1, Meng Yuan Zhang1
1School of Chemistry, UNSW Sydney, Sydney, NSW, 2052, Australia. n.rijs@unsw.edu.au.
Dalton Transactions (Cambridge, England : 2003)
|October 1, 2024
Summary
Complexes of anti-cryptophanes with cations show surprising size changes. Gas phase studies reveal competing physical effects influencing encapsulation and structural trends.
Area of Science:
- Supramolecular Chemistry
- Physical Chemistry
- Analytical Chemistry
Background:
- Cryptophanes are macrocyclic molecules capable of encapsulating guest species.
- Understanding host-guest interactions is crucial for molecular recognition and sensing.
- Gas-phase studies offer unique insights into complex formation distinct from condensed-phase behavior.
Purpose of the Study:
- To investigate the gas-phase complexation of anti-cryptophanes with various monocationic guests.
- To determine the structural trends and encapsulation mechanisms of these complexes using ion-mobility mass spectrometry.
- To compare gas-phase findings with condensed-phase complexation data.
Main Methods:
- High-resolution ion-mobility mass spectrometry (HR-IM-MS) was employed to measure the mobilities and derive collisional cross sections of cation-cryptophane complexes.
- Density functional theory (DFT) calculations were used to model and confirm encapsulation pathways.
- Isothermal titration calorimetry (ITC) and other condensed-phase techniques provided comparative data.
Main Results:
- A paradoxical trend of structural contraction was observed with increasing cation size for most alkali metal and ammonium cations.
- Lithium cation (Li+) exhibited a preference for linker coordination over full encapsulation, resulting in larger structures.
- Protonated cryptophanes formed significantly larger, imploded structures compared to cation complexes.
- Gas-phase results corroborated trends observed in condensed-phase studies.
Conclusions:
- Competing physical effects, including cation size, coordination preferences, and cryptophane structural flexibility, dictate the observed non-periodic size trends of the complexes.
- Gas-phase experimental data, supported by DFT, provide a detailed understanding of cryptophane encapsulation mechanisms.
- The study highlights the utility of HR-IM-MS in elucidating host-guest interactions in the gas phase.
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