EXTRAORDINARY STABILITY OF COPPER(I)-TETRATHIOMOLYBDATE COMPLEXES: POSSIBLE IMPLICATIONS FOR AQUATIC ECOSYSTEMS

摘要

An extraordinary affinity of MoS_4~(2-) for Cu accounts for Mo-induced Cu deficiency in ruminants (molybdenosis) and offers an approach to treating Wilson's disease in humans. Evidence of thiomolybdates in sulfidic natural waters, and possibly even as raetastable traces in oxic natural waters, raises the question of how Cu-Mo affinity might affect Cu availability or toxicity in aquatic ecosystems. Stabilities of inorganic Cu-MoS_4~(2-) complexes are characterized and quantified here for the first time. Two remarkably stable Cu~I dissolved complexes are identified (r=23℃ ± 2℃): Cu_2(HS)_2MoS_4~(2-) and Cu_2S_2MoS_4~(4-). In addition, the solubility constant for a precipitate (NH_4CUM0S_4) was measured. Under the extremely reducing conditions in rumen fluids, these complexes will greatly suppress Cu~+ activity, supporting prior conclusions about the mechanism of molybdenosis. In sulfidic natural waters, they help to prevent complete Cu impoverishment, as might otherwise occur by sulfide mineral precipitation. On the other hand, the complexes discovered here are HS~- -dependent and could not be important in oxic natural waters (with HS~- concentrations < 10~(-9) M) even if metastable, biogenic MoS_4~(2-) indeed were present as previously conjectured.