Unleashing radical sites in non-covalent complexes: the case of the protonated S-nitrosocysteine/18-crown-6 complex.
BACKGROUND
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.
School of Chemistry, The University of Melbourne, Victoria, 3010, Australia; Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Victoria, 3010, Australia; ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, The University of Melbourne, Victoria, 3010, Australia.
Sandra
S
Osburn
Richard A J
RA
O'Hair
D002412:Cations / Q000737:chemistry*; D043844:Crown Ethers / Q000737:chemistry*; D003545:Cysteine / Q000031:analogs & derivatives* / Q000737:chemistry; D026403:S-Nitrosothiols / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
D002412:Cations; D043844:Crown Ethers; D026403:S-Nitrosothiols; C015762:18-crown-6; C021315:S-nitrosocysteine; D003545:Cysteine