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

摘要

This study presents the application of electrospray ionization mass spectrometry (ESI/MS) to investigate the host-guest 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-π 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.