Abstract Molecular mass spectrometry was utilised for the first time to gather information of formed compounds consisting of tetrathiomolybdate and Cu in the context of Wilson’s disease. Electrospray ionisation-mass spectrometry was used to elucidate four in vitro-formed tetrathiomolybdate-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 tetrathiomolybdate. By increasing the potential applied to the electrospray ionisation source, it was observed that the heavier compounds fragment into MoS4Cu−, which hints to the possibility of tetrathiomolybdate and Cu(I) form 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 a 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 tetrathiomolybdate and Cu(I) can bind to glutathione disulfide, which was likely formed by a Cu-initiated oxidation of glutathione. The identification of various tetrathiomolybdate-Cu species as well as tetrathiomolybdate-Cu-glutathione disulfide demonstrates that molecular mass spectrometry can be used to elucidate reactions between tetrathiomolybdate, Cu, and biomolecules related to Wilson’s disease.
Bendieck et al. (2026) studied this question.