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Unleashing radical sites in non‐covalent complexes: The case of the protonated S ‐nitrosocysteine/18‐crown‐6 complex
Author(s) -
Osburn Sandra,
O'Hair Richard A. J.
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6745
Subject(s) - chemistry , radical , homolysis , photochemistry , covalent bond , radical ion , protonation , dissociation (chemistry) , radical disproportionation , crown ether , molecule , ion , organic chemistry , disproportionation , catalysis
RATIONALE Introducing radicals onto gas‐phase non‐covalent complexes and studying their chemistry is a relatively unexplored frontier. In generating these radicals via bond homolysis reactions, it is important that the energy necessary for forming the radical does not exceed the energy required for dissociating the complex itself. Based on this consideration, new approaches for creating these radicals will probably have to involve incorporation of weak bonds that can easily undergo homolysis. METHODS The formation of a radical cation, via collision‐induced dissociation, of protonated S ‐nitrosocysteine non‐covalently bound to the crown ether 18‐crown‐6 is described here. The radical cation of this complex was isolated and subjected to collisional activation and ion‐molecule reactions with allyl iodide. The results were compared with those of the radical cation of 'bare' cysteine. RESULTS Collisional activation of the radical cation of the cysteine/crown complex led to fragmentation of cysteine as well as of the crown ether. Ion‐molecule reactions of the radical cation of the complex with allyl iodide led to products arising from I and allyl abstraction. Isolation and CID of the former product ion led to the loss of iodocysteine. CONCLUSIONS Cleavage of the weak S–NO bond has allowed the formation of a radical site onto a non‐covalent complex. Ion‐molecule reactions and collisional activation were utilized to probe the chemistry of this radical cation. The approach adopted here for incorporating a radical onto a cysteine/crown complex shows promise for the introduction of radical sites onto other biological non‐covalent complexes. Copyright © 2013 John Wiley & Sons, Ltd.