| The kinetic energy dependence of the collision-induced dissociation of M+(xBA) and M+(MALDI) complexes with Xe is studied using guided on beam tandem mass spectrometry. The xBA ligands studied include benzoic acid and all of the mono- and dihydroxy substituted benzoic acids: 2-, 3-, and 4-hydroxybenzoic add and 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dihydroxybenzoic acid. The MALDI ligands studied include: quinoline, 3-aminoquinoline, 4-nitroaniline, nicotinic acid, picotinic acid, 3-hydroxypicolinic acid, ferrulic acid, sinapic acid, alpha-cyano-4-hydroxycinnamic add, and 4-hydroxyphenylazobenzoic acid. The metal cations examined include: Na+, K+, and Ag+. The dominant dissociation pathway for the Na+(xBA), K +(xBA), Na+(MALDI), and K+ (MALDI) complexes is simple collision-induced dissociation (CID) corresponding to endothermic loss of the intact xBA or MALDI ligand. Simple CID is generally also observed for the Ag+(xBA) and Ag+(MALDI) complexes. However, low-energy activated dissociation pathways are also observed in the CID of these latter complexes.; The cross section thresholds for loss of the intact xBA or MALDI ligand are interpreted to yield zero and 298 K M+-- xBA and M+--MALDI bond dissociation energies (BDEs) for the Na+(xBA), K+( xBA), Na+(MALDI) K+(MALDI) and several of the Ag+(x8A) and Ag+(MALDI) complexes, while upper bounds for these BDEs are provided in cases where low-energy activated dissociation pathways are observed.; Ab initio and density functional theoretical calculations are performed at the B3LYP/6-310* and B3LYP/6-31G*-SRSC levels of theory to obtain structures, molecular constants, and dipole moments for the neutral xBA and MALDI M+(xBA) and M+(MALDI) complexes, and transition states between different stable conformations of these species. Theoretical estimates for the BDEs of the M+( xBA) and M+(MALDI) complexes are determined from calculations at the B3LYP and MP2(full) levels of theory using 6-311+G(2d,2p) and 6-311+G(2d,2p)-SRSC basis sets and the 63LYP/6-31G* and B3LYP/6-31G*-SRSC optimized geometries. Zero point energy and basis set super position error corrections are also included in the calculated BDEs. Theoretical estimates for the isotropic molecular polarizabilities of the neutral xBA and MALDI ligands are determined at the PBE0/6-311+G(2d,2p) level of theory using the B3LYP/6-31G* optimized geometries. The stability of the neutral xBA and MALDI ligands and their metal cationized complexes are enhanced by intramolecular hydrogen bonds formation and chelation interactions. UV visible spectra of solutions of the xBA ligands and MALDI matrices are obtained to investigate the possible use of these ligands with various lasers. The experimentally determined BDEs are compared with those calculated here and reported in the literature. |
