Dissociations of gas-phase complexes of deprotonated glutathione with Co2+, Ni2+, Cu2+ and Zn2+: The importance of metal ion reduction

► We electrosprayed 1:1 complexes of deprotonated glutathione (GSH−H)−, and the metal dications Co2+, Ni2+, Cu2+ and Zn2+. ► Both positive, [M(GSH−H)]+, and negative, [M(GSH−3H)]−, complexes were observed, where M is the transition metal. ► These metal complexes, [M(GSH−H)]+, and bare (GSH−H)− were exposed to multi-collisional dissociation (CID). ► CID of complexes with M = Co, Ni, Zn found to be similar to CID (GSH−H)−, so M2+ binds at cysteine with ligand mostly unchanged. ► Unique CID of Cu2+ complexes was attributed to ligand radical structures formed by the reduction of intra-complex Cu(II).