Reactivity and kinetic studies of (NH 4) 2(MoS 4) in acidic aqueous solution: Possible relevance to the angiostatic function of the [formula omitted] ligand

Abstract

Although addition of mineral acids to WS 4 2 - in water is known to lead to aggregation and formation of various polynuclear thiotungstate anions, acid hydrolysis of the MoS 4 2 - anion is reported to give mainly MoS 3 or MoS 2 as hydrolysis products. Knowledge of the resulting product(s) from such reactions has implications on the use of tetrathiomolybdate ( MoS 4 2 - ) as both a potential anti-tumor drug and for the treatment of Wilson’s disease. In this investigation, reaction of HCl with MoS 4 2 - in water was monitored as a function of time. Reaction mixtures of both 1:1 and 2:1 mole ratios of the acid to MoS 4 2 - were examined, as well as MoS 4 2 - 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 (Mo 2–Mo 18). 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, Mo 3 S 9 2 - 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 ( Mo 2 O a S 10 - a 2 - ; a = 0 – 3 ) and trinuclear ( Mo 3 O b S 9 - b 2 - ; b = 1 – 3 ) anions predominate.