title: A simple method for estimating activation energies using the fragmentation yield: collision-induced dissociation of iron(II)-phenanthroline complexes in an electrospray ionization mass spectrometer.
abstract: The gas-phase stabilities of Fe(Phi)3(2+) complexes, where Phi represents the 1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline ligands were investigated by collision-induced dissociation (CID) in the capillary-first skimmer region upon changing the voltage difference between the capillary and the skimmer. The loss of only one ligand from the Fe(Phi)3(2+) complexes was observed with each of the phenanthroline ligands studied. An increase in the voltage difference between the capillary and the skimmer resulted in a higher fragmentation yield as calculated from the intensity of the precursor and the fragment ion. The fragmentation yield versus capillary-skimmer voltage difference plots were evaluated by means of the Arrhenius and the Rice-Ramsperger-Kassel (RRK) model by fitting the model parameters to the experimental data. Both models yielded practically the same results. In addition, if the internal energy gained through the capillary-skimmer region is estimated correctly, the approximate value of the critical energy (activation energy) for fragmentation can be extracted from the fragmentation yield versus capillary-skimmer voltage difference plots. It was found that the gas-phase stabilities of the Fe(Phi)3(2+) complexes are nearly identical except for the more stable Fe(II)-4,7-diphenyl-1,10-phenanthroline complex. The critical energy for fragmentation was estimated to be approximately 1.2 and 0.9 eV for the Fe(II)- 4,7-diphenyl-1,10-phenanthroline, and the other complexes, respectively.
authors.affiliation: Department of Applied Chemistry, University of Debrecen, H-4010, Debrecen, Hungary.
authors.forename: Sandor
authors.initials: S
authors.lastname: Keki
authors.affiliation: Department of Applied Chemistry, University of Debrecen, H-4010, Debrecen, Hungary.
authors.forename: Lajos
authors.initials: L
authors.lastname: Nagy
authors.affiliation: Department of Applied Chemistry, University of Debrecen, H-4010, Debrecen, Hungary.
authors.forename: Janos
authors.initials: J
authors.lastname: Torok
authors.affiliation: Department of Applied Chemistry, University of Debrecen, H-4010, Debrecen, Hungary.
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Deak
authors.affiliation: Department of Applied Chemistry, University of Debrecen, H-4010, Debrecen, Hungary. zsugam@tigris.klte.hu.
authors.forename: Miklos
authors.initials: M
authors.lastname: Zsuga