Evaluation of alkali metal binding selectivities of caged aza-crown ether ligands by microelectrospray ionization/quadrupole ion trap mass spectrometry

Microelectrospray ionization mass spectrometry (MESI-MS) is used to evaluat e alkali metal binding selectivities of a variety of macrocyclic compounds. Well-studied crown ethers are used to validate the MESI-MS method. A quant itative correlation between MESI mass spectral ion intensities and solution equilibrium distributions of complexes is obtained for the mixtures contai ning a single host and different alkali metal guest ions. The MESI-MS metho d is successfully applied for the determination of the alkali metal binding selectivities of a series of cage-functionalized aza-crown ethers and rele vant model compounds in methanol and chloroform solutions. The binding sele ctivities parallel previous results obtained using conventional spectrophot ometric extraction methods. Structural differences in the host compounds, s uch as the presence of a cage functionality, binding cavity size, and overa ll flexibility, cause significant changes in the binding selectivities. (J Am Soc Mass Spectrom 2000, 11, 884-891) (C) 2000 American Society for Mass Spectrometry.