Estimation of the Noncovalent Bond Dissociation Energies of the Gas-Phase Complexes of macrocyclic Polyethers with Alkali Metal Cations Using an Electrospray Ionization/Triple Quadrupole Mass Spectrometer

An attempt to use the commercial triple quadrupole mass spectrometer, equipped with an electrospray ion source, to estimate the noncovalent bond dissociation energies of gas-phase complexes of macrocyclic polyethers with metal cations has been made. It was found that, after standardization of the experimental conditions, the collision cell voltage required for decomposition of 50% of the selected complex ions (CE50%) is proportional to the binding energies with reasonable accuracy. Even better correlation was obtained after recalculation of the CE50% values to the center-of-mass frame (ECM50%). Measurements were made for 12-crown-4, 15-crown-5, 18-crown-6, and dibenzo-18-crown-6 complexes with alkali metal cations from Li+ to Cs+. These results indicate, that it is possible to estimate values of the binding energies after correct setting of the experimental conditions and using model compounds as the reference.