Noncovalent interactions between metal ions and model systems for biologically relevant molecules: Threshold collision-induced dissociation and theoretical studies.

摘要

Threshold Collision-induced dissociation of M+(L) _x, x = 1–2, with xenon is studied using guided ion beam mass spectrometry involving three major different studies. In first study, M+(azine) complexes are employed for the experiments. M+ include the following alkali metal ions: Li+, Na+, and K+. The azines include pyridine, pyridazine, pyrimidine, pyrazine, 1.3.5-triazine. Second major study involves M +(pyridine) and M+(pyrimidine) complexes, where M + include Mg+, Al+, and Sc+ through Zn+, first row transition metal ion series. In all cases, the primary dissociation pathway is endothermic loss of intact neutral ligand. Only other significant product observed is the result of ligand exchange to form M+Xe. Additional minor reaction pathways are observed in several M+(pyrimidine) and Cr+(pyridine) systems. The cross-sections thresholds are interpreted to yield 0 and 298 K bond energies for M+-azine after accounting for the effects of multiple ion-neutral collisions, internal energy of the reactant ions, and dissociation lifetimes. Ab initio calculations at the MP2(full)/6–31 G* and density functional theory B3LYP/6–31 G* levels of theory are used to determine the structures of M+(azine) and M+(pyrimidine) and M+(pyridine) complexes, respectively, and provide molecular constants necessary for the thermodynamic analysis of the experimental data.; Threshold collision-induced dissociation of M+(arene) x, x = 1–2, with xenon are the other studies performed here. M+ include Li+, Na+, K+, Rb+, and Cs+ and arenes are toluene, fluorobenzene, aniline, phenol, anisole, and naphthalene. Endothermic loss of an intact neutral ligand is the observed dominant and lowest energy dissociation channel. Sequential dissociation of a second neutral ligand is observed at elevated energies in the bis-complexes. The cross-section thresholds for the primary dissociation channel interpreted to yield 0 and 298 K bond dissociation energies for (arene)_x−1 M+-arene, x = 1–2 after accounting for the effects of multiple ion-neutral collisions, internal energy of the reactant ions, and dissociation lifetimes. Structures of these complexes and molecular constants required for the thermodynamic analysis of experimental data, are obtained by performing density functional theory calculations at B3LYP/6–31G* level of theory. Theoretical bond dissociation energies are determined from single point calculations at the MP2(full)/6–311+G(2d,2p) level using B3LYP/6–31G* geometries including zero-point energy corrections and basis set superposition errors. Effective core potentials are employed for Rb and Cs metal ions. (Abstract shortened by UMI.)