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The formation of a series of doubly charged pyridyl ngand-polyether-transition metal complexes was studied using electrospray ionization (ESI) methods. Both doubly charged mixed-ligand dimer and trimers were observed. Differences in the electronic structures of the metal ions and the nature of the polyether and pyridyl ligands influence the types of complexes formed. Despite the large differences in the solution binding constants of pyridyl and polyether ligands, mixed-ligand complexes were efficiently formed, suggesting that the ESI process itself may enhance the formation of certain types of complexes that might not be favored in solution. Charge reduction of the metal ion within the mixed-ligand complexes was not observed, although charge reduction of Cu 2+ occurred for the singleligand polyether and pyridyl complexes.

The competitive proton-binding abilities of a series of pyridyl and polyether ligands were examined by application of ligand-exchange and collisionally activated dissociation (CAD) methods. Many of the ligands of interest are multidentate, thus giving them enhanced capabilities for coordinating the proton, and they also may undergo a substantial loss of entropy, predominantly in rotational and vibrational modes of freedom, when binding a proton because the electrostatic interactions between donor atoms and the proton create a degree of organization of the ligand. The presence of dominant mixed-dimer complexes formed during the ligand-exchange reactions provides key evidence that multiple hydrogen-bond formation is operative for one or both ligands. Although CAD provides some insight into the factors which influence proton-binding strengths of the ligands in dimers, several general issues emerge when applying the CAD (i.e. the kinetic method) to estimate proton affinities of multidentate ligands. Owing to the severe impact of entropic effects upon dissociation of the dimers involving multidentate ligands, the ratio of product ions does not reflect the order of proton affinities of the ligands involved in the dimer. The CAD experiments give the order of gas-phase basicities at a higher temperature in which the entropy term is much more significant. This effect is especially significant when one of the ligands is floppy and multidentate and the other is rigid or monodentate. © 1998 John Wiley & Sons, Ltd.

The analysis of hydantoin and succinimide anticonvulsants was carried out using techniques of chemical ionization and collision activated dissociation (CAD) in a quadrupole ion trap. Dimethyl ether was used as the chemical ionization reagent gas to generate [M + H] + and [M + 13] + products, with the objective of determining whether the protonation and methylene substitution reactions occurred at the same site and whether the products provided the same structural information. CAD, including MS 3 , SWIFT double resonance experiments and deuterium-labeling studies suggest that protonation occurs on a nitrogen atom or carbonyl oxygen while methylene substitution occurs predominantly on the phenyl substituents. Both [M + H] + and [M + 13] + ions dissociate by similar pathways in which typically the attached proton or methylene group remains a spectator.