EVALUATION OF BINDING SELECTIVITIES OF BIS-CROWNED CLEFTS BY ELECTROSPRAY-IONIZATION QUADRUPOLE ION-TRAP MASS-SPECTROMETRY

Electrospray ionization (ESI) was used in conjunction with quadrupole ion trap mass spectrometry to measure metal binding selectivities of b is-crowned clefts in methanol solution. Each of the three cleft compou nds contained two 15-crown-5 rings separated by different quinoline sp acers. Binding selectivities were compared qualitatively with previous extraction results obtained for three bis-crown clefts complexing wit h the alkali metals sodium, potassium and rubidium in aqueous solution . The bis-crowned cleft molecules were found to form 1:1 and 2:1 metal -cleft complexes, and, in a few cases where larger alkali metals were involved, two cleft molecules were able to form 2:2 metal-left complex es cooperatively. The binding selectivity is greatly affected by the s ize of the alkali metal and by the flexibility of the quinoline bridge , factors that influence the degree of electrostatic repulsion between the two crown ether rings. (C) 1998 John Wiley & Sons, Ltd.