Cysteine Radical/Metal Ion Adducts: A Gas-Phase Structural Elucidation and Reactivity Study

Autor: Vincent Steinmetz, Philippe Maître, John T. Lawler, Justin Kai-Chi Lau, Alan C. Hopkinson, Michael Lesslie, K. W. Michael Siu, Victor Ryzhov
Rok vydání: 2016
Předmět:
Zdroj: ChemPlusChem. 81:444-452
ISSN: 2192-6506
DOI: 10.1002/cplu.201500558
Popis: The formation and investigation of sulfur-based cysteine radicals cationized by a group 1A metal ion or Ag+ in the gas phase are reported. Gas-phase ion-molecule reactions (IMR) and infrared multiple-photon dissociation (IRMPD) spectroscopy revealed that the Li+ , Na+ , and K+ adducts of the cysteine radical remain S-based radicals as initially formed. Theoretical calculations for the three alkali metal ions found that the lowest-energy isomers are Cα -based radicals, but they are not observed experimentally owing to the barriers associated with the hydrogen-atom transfer. A mechanism for the S-to-Cα radical rearrangement in the metal ion complexes was proposed, and the relative energies of the associated energy barriers were found to be Li+ >Na+ >K+ at all levels of theory. Relative to the B3LYP functional, other levels of calculation gave significantly higher barriers (by 35-40 kJ mol-1 at MP2 and 44-47 kJ mol-1 at the CCSD level) using the same basis set. Unlike the alkali metal adducts, the cysteine radical/Ag+ complex rearranged from the S-based radical to an unreactive species as indicated by IMRs and IRMPD spectroscopy. This is consistent with the Ag+ /cysteine radical complex having a lower S-to-Cα radical conversion barrier, as predicted by the MP2 and CCSD levels of theory.
Databáze: OpenAIRE
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