title: Structure and reactivity of the N-acetyl-cysteine radical cation and anion: does radical migration occur?
abstract: The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol(-1) lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M - 2H)( •- ). IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol(-1)) position, and does not rearrange.
authors.affiliation: Department of Chemistry and Biochemistry, and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, IL 60115, USA.
authors.forename: Sandra
authors.initials: S
authors.lastname: Osburn
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.forename: Richard A J
authors.initials: RA
authors.lastname: O'Hair
authors.forename: Victor
authors.initials: V
authors.lastname: Ryzhov
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry*; D000498:Allyl Compounds / Q000737:chemistry; D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D013058:Mass Spectrometry; D008968:Molecular Conformation; D013055:Spectrophotometry, Infrared; D013329:Structure-Activity Relationship
chemical_list: D000498:Allyl Compounds; D000838:Anions; D002412:Cations; D004220:Disulfides; C021181:dimethyl disulfide; C050431:allyl bromide; D000111:Acetylcysteine