Structures and fragmentations of cobalt(II)-cysteine complexes in the gas phase

The electronebulization of a cobalt(II)/cysteine(Cys) mixture in water/methanol (50/50) produced mainly cobalt-cationized species. Three main groups of the Co-cationized species can be distinguished in the ESI-MS spectrum: (1) the cobalt complexes including the cysteine amino acid only (they can be singly charged, for example, [Co(Cys)(n)- H](+) with n = 1-3 or doubly charged such as [Co + (Cys)(2)] (2+)); (2) the cobalt complexes with methanol: [Co(CH3OH)(n)-H](+) with n = 1-3, [Co(CH3OH)(4)](2+); and (3) the complexes with the two different types of ligands: [Co(Cys)(CH3OH) - H](+) Only the singly charged complexes were observed. Collision-induced dissociation (CID) products of the [Co(Cys)(2)](2+), [Co(Cys)(2) - H](+) and [Co(Cys) - H](+) complexes were studied as a function of the collision energy, and mechanisms for the dissociation reactions are proposed. These were supported by the results of deuterium labelling experiments and by density functional theory calculations. Since [Co(Cys) - H](+) was one of the main product ions obtained upon the CID of [Co(Cys)(2)](2+) and of [Co(Cys)(2) - H](+) under low-energy conditions, the fragmentation pathways of [Co(Cys) - H](+) and the resulting product ion structures were studied in detail. The resulting product ion structures confirmed the high affinity of cobalt(II) for the sulfur atom of cysteine. Copyright (c) 2007 John Wiley & Sons, Ltd.