Reactivity and kinetic studies of (NH4)2(MoS4) in acidic aqueous solution: Possible relevance to the angiostatic function of the MoS42- ligand

Although addition of mineral acids to WS42- in water is known to lead to aggregation and formation of various polynuclear thiotungstate anions, acid hydrolysis of the MoS42- anion is reported to give mainly MoS3 or MoS2 as hydrolysis products. Knowledge of the resulting product(s) from such reactions has implications on the use of tetrathiomolybdate (MoS42-) as both a potential anti-tumor drug and for the treatment of Wilson’s disease. In this investigation, reaction of HCl with MoS42- in water was monitored as a function of time. Reaction mixtures of both 1:1 and 2:1 mole ratios of the acid to MoS42- were examined, as well as MoS42- reactions in simulated human stomach fluids at pH of ∼2 and 3. Monitoring by electrospray mass spectrometry (ESMS), Fourier transform infrared (FTIR), and UV–visible spectroscopy clearly has revealed the formation of complex mixtures of polynuclear thiomolybdates (Mo2–Mo18). Generally, a two-stage consecutive reaction sequence occurs. A faster stage (k = 7.0–7.9 × 10−2 min−1), which seems to extend to trinuclear thiomolybdate species, followed by a slower second stage (k = 5.4–15.2 × 10−4 min−1) to higher polynuclear thiomolybdates. Under acidic conditions (e.g. pH ∼ 3) that could also mimic some human stomach fluids, and under anaerobic atmosphere where the generated hydrogen sulfide is prevented from escaping from the reaction vessel, Mo3S92- predominates over an extended reaction period. In similar reactions under aerobic conditions and where the hydrogen sulfide is irretrievably lost from the reaction mixture the binuclear (Mo2OaS10-a2-;a=0–3) and trinuclear (Mo3ObS9-b2-;b=1–3) anions predominate.