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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
ABSTRACT:
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
Keywords:
Ni+, Cu+, pyrrole, CO2, D2O, NH3, NO, ligation,
ICP-SIFT
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