Thermochemistry of Non-Covalent Ion–Molecule Interactions

Abstract

The thermochem. of non-covalent ion-mol. complexes has been examd. by measuring quant. bond dissocn. energies using threshold collision-induced dissocn. in guided ion beam tandem mass spectrometers (GIBMS). The methods used are briefly reviewed and several examples of the types of information and insight that can be obtained from such thermodn. information are discussed. The hydration of metal cations, both singly and doubly charged, is reviewed and the trends elucidated, mainly on the basis of electrostatic contributions. The binding of alkali metal cations to amino acids has been examd. for a range of systems, with both the overall polarizability of the amino acid and the local dipole moment of heteroat. side-chains shown to be important contributors. The gas-phase interactions of the 12-crown-4 (12C4) polyether with alkali metal cations, classic mol. recognition systems in soln., have been newly compared to previous GIBMS work. These results validate the previous hypothesis that excited conformers were present for Rb+(12C4) and Cs+(12C4) and offer clues as to how and why they are formed. [on SciFinder(R)]