Abstract

European Journal of Mass Spectrometry
Volume 10 Issue 6, Pages 949–962 (2004)
doi: 10.1255/ejms.694

Gas-phase kinetic measurements of the ligation of Ni⁺, Cu⁺, Ni(pyrrole)_1,2⁺ and Cu(pyrrole)_1,2⁺ with CO₂, D₂O, NH₃ and NO

Michael J. Y. Jarvis, Voislav Blagojevic, Gregory K. Koyanagi and Diethard K. Bohme^*
Department of Chemistry, Centre for Research in Mass Spectrometry and Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada, M3J 1P3. E-mail: dkbohme@yorku.ca

The rate and equilibrium kinetics of the reactions of the biologically important metal species M⁺, M⁺(pyrrole) and M⁺(pyrrole)₂ (M = Ni, Cu) have been investigated with the biological gases CO₂, D₂O, NH₃ and NO in the gas phase at 295 ± 2 K in helium buffer-gas at a pressure of 0.35 ± 0.01 Torr. The measurements were taken with an Inductively Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Only ligation was observed for the reactions of bare Ni⁺ and Cu⁺ with CO₂, D₂O and NH₃ with rates consistent with the known strengths of the resulting ligand–metal bonds. Both metal cations appeared to be oxidized and produce N₂O in interesting reactions that are second order in NO. One pyrrole ligand was observed to increase the rate of ligation by as much as a factor of 100 and to switch off the oxidation with NO. Equilibrium was achieved for the ligation of CO₂, D₂O and NO to both Ni⁺(pyrrole) and Cu⁺(pyrrole), and so it was possible to determine absolute values for the standard free energies of ligation. No ligand substitution was observed with M⁺(pyrrole). M⁺(pyrrole)₂ was observed to be generally unreactive towards the small molecules investigated: a notable exception is ammonia. Very fast ligand substitution reactions were observed for reactions of M⁺(pyrrole)₂ with NH₂