Conformational analysis and binding affinity determination for hostguest complexation of alkali metal ions with bis-crown ethers by electrospray mass spectrometry and molecular modeling

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Eur. J. Mass Spectrom. 8, 375 - 380 (2002)
DOI: 10.1255/ejms.516

Conformational analysis and binding affinity determination for hostguest complexation of alkali metal ions with bis-crown ethers by electrospray mass spectrometry and molecular modeling

Hui-Fen Wu,^* Shun-Min Huan and Chun-Fu Wu
Department of Chemistry, Tamkang University, Tamsui, Taipei Hsien, 251, Taiwan

ABSTRACT:

This study presents the application of electrospray ionization mass spectrometry (ESI/MS) to investigate the hostguest complexation phenomenon for an array of alkali metal ions with bis[(benzo-15-crown-5)-15-ylmethyl] pimelate (BBCP). The results have shown that potassium ions possess the best binding affinity with the BBCP, owing to formation of the very stable sandwich-type (1 : 1) complexes and the strong K⁺ cation-p electron interactions between the K⁺ ion and the benzene rings of BBCP. The results of the competition experiments indicate the selectivity for BBCP toward the alkali metal ions is K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺. In addition, combining the results of ESI/MS and molecular mechanics conformational searches reveal that the formation of sandwich-type (1 : 1) complexes can be observed for larger metal ions including K⁺, Rb⁺ and Cs⁺. As for Na⁺ ions, both 1 : 1 and 1 : 2 complexes can be observed.

Keywords: hostguest chemistry, conformational analysis, binding affinity, alkali metal ions, bis-crown ethers, electrospray mass spectrometry, molecular modeling

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