Correlation of solution and gas phase complexation assessed by electrospray ionization mass spectrometry: Application to one-, two-, and three-ring macrocycles

Electrospray ionization mass spectrometry (ESI-MS) was used to probe multiple cation complexation by C12H25(N18N)(CH2)(12)(N18N)(CH2)(12)(N18N)C12H25,2, and (18N)CH2C6H4CH2(N18), 3. Complexation of two cations (2Na(+), 2 K+, or Na+ and K+) by 3 and three cations by 2 (3 Na+, 3 K+, and mixtures) as well as mixed proton-metallic cation complexes of both were observed. The K+/Na+ cation-binding selectivity of 18-crown-6 was studied by ESI-MS of a methanol solution, and the selectivity profile was favorably compared with data obtained previously by ion-selective electrode techniques in the same solvent.