Isothermal titration calorimetry (ITC) and 1H NMR spectroscopy are being used to determine key thermodynamic parameters (stoichiometry, ?H, ?S, Ka) in the binding of variously sized monobenzo- and dibenzo-crown ethers with a number of dibenzylammonium (DBA) derivatives.  To date, dibenzo-24-crown-8 ether (DB24C8) and dibenzo-30-crown-10 ether (DB30C10) have been treated with DBA, difluoro-DBA, and dimethoxy-DBA to investigate the impact of ring size and substituent effects on the host-guest complexation.  Preliminary results indicate that the larger crown ether (DB30C10) binds the DBA guests more weakly than the smaller DB24C8 analog in 1:1 CHCl3/MeCN at 30.0 �C.  Relative to unsubstituted DBA, the binding weakens with electron-donating OMe substituents and strengthens with electron-withdrawing F substituents.  Detailed knowledge of these structural relationships will help in the future design of more complex supramolecular architectures.

Influence of ring size and substituent effects in the binding of benzo-crown ethers with dibenzylammonium ions

243rd National Meeting (2012)

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