Investigation of the reaction of thiomolybdate and copper by electrospray-trapped ion mobility-mass spectrometry (ESI-TIMS-MS).

Molecular mass spectrometry was utilized for the first time to gather information of formed compounds consisting of tetrathiomolybdate (TTM) and Cu in the context of Wilson's disease (WD). Electrospray ionization (ESI)-mass spectrometry was used to elucidate four in vitro-formed TTM-Cu compounds, including MoS4Cu-, (MoS4)2Cu3-, (MoS4)3Cu5-, and (MoS4)4Cu7-. Based on the ions' net charges, it could be concluded that Cu(II) had been reduced to Cu(I), which then binds to TTM. By increasing the potential applied to the ESI source, it was observed that the heavier compounds fragment into MoS4Cu-, which hints to the possibility of TTM and Cu(I) forming oligomeric species in solution, with MoS4Cu- being a possible base structure. Trapped ion mobility spectrometry-mass spectrometry in conjunction to collision-induced dissociation was used to conclude that the heavier species can also fragment into the lighter ones, corroborating the assumption of an oligomeric species. Further fragmentation experiments provided additional insight into the behaviour of these compounds in the gas phase, as product ions could be identified which necessitate the reduction of Mo(VI) during or after fragmentation of these structures. Using glutathione as a model compound, it could be shown that TTM and Cu(I) can bind to glutathione disulfide, which was likely formed by a Cu-initiated oxidation of glutathione. The identification of various TTM-Cu species as well as TTM-Cu-glutathione disulfide demonstrates that molecular mass spectrometry can be used to elucidate reactions between TTM, Cu, and biomolecules related to WD.