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Gas‐Phase Unimolecular Dissociation Reveals Dominant Base Property of Protonated Homocysteine Sulfinyl Radical Ions
Author(s) -
LoveNkansah Chasity B.,
Tan Lei,
Francisco Joseph S.,
Xia Yu
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502642
Subject(s) - chemistry , protonation , dissociation (chemistry) , photochemistry , collision induced dissociation , tandem mass spectrometry , hydroxyl radical , radical ion , fragmentation (computing) , homocysteine , moiety , combinatorial chemistry , ion , mass spectrometry , stereochemistry , radical , organic chemistry , biochemistry , chromatography , computer science , operating system
Homocysteine sulfinyl radical ( SO⋅ Hcy) is a reactive intermediate involved during oxidative damage of DNA in the presence of high concentrations of homocysteine (Hcy). The short lifetime of SO⋅ Hcy makes its preparation, isolation, and characterization challenging using traditional chemical measurement tools. Herein, we demonstrate the first study on mass‐selected protonated SO⋅ Hcy ions in the gas phase by investigating its unimolecular dissociation pathways from low energy collision‐induced dissociation (CID). Tandem mass spectrometry (MS/MS), stable‐isotope labeling, and theoretical calculations were employed to rationalize the observed fragmentation pathways. The dominant dissociation channel of protonated SO⋅ Hcy was a charge‐directed H 2 O loss from the protonated sulfinyl radical (‐SO⋅) moiety, forming a thiyl radical (‐S⋅), which further triggered sequential radical‐directed ⋅SH loss through multiple pathways. Compared to cysteine sulfinyl radical ( SO⋅ Cys), the small structural change induced by one additional methylene group in the side chain of SO⋅ Hcy significantly promotes its base property while reducing the radical reactivity of sulfinyl radical. This observation provides new insight into studying reactions of SO⋅ Hcy with biomolecules, which are critical in understanding toxicity induced by high levels of Hcy in biological conditions.