Sodium Metatungstate

Like ammonium metatungstate (AMT), sodium metatungstate is an important compound of the transition metal tungsten. It is a polymeric metatungstate formed by acidifying an isotungstate solution, exhibiting excellent physicochemical properties and widely used in density separation studies in geology, soil science, and marine biology.

Sodium metatungstate, also known as sodium metatungstate hydrate, polytungstate sodium, or sodium polytungstate, is a typical metatungstate composed of the transition metal tungsten, alkali metal sodium, non-metal oxygen, and hydrogen. It is a white crystal or powder and an effective inhibitor of ectonucleoside triphosphate diphosphohydrolase. Its English name is Sodium Metatungstate or Sodium Metatungstate Hydrate, with a molecular formula of 3Na₂WO₄·9WO₃·xH₂O or Na₆O₃₉W₁₂, a molecular weight of 2968.00, and a CAS number of 314075-43-9.

Sodium metatungstate appears as a white crystal or powder, non-toxic and odorless but slightly irritating, with a density of approximately 3.1 g/mL and a refractive index of about 1.5555. It is soluble in water and exhibits strong bioactivity. Notably, while it remains stable at room temperature, under normal pressure, or in weakly acidic solutions, it should be stored away from strong oxidants such as nitric acid, chlorine, and fluorine to avoid reactions.

The preparation of sodium metatungstate involves the following steps: first, preparing a sodium tungstate solution; then using ion exchange to remove some sodium ions, yielding a Na₆O₃₉W₁₂ solution; finally, concentrating, purifying, and drying through evaporation to obtain high-purity Na₆O₃₉W₁₂ powder.

The production of the sodium tungstate solution includes: purifying raw tungsten blocks to remove impurities, converting them into a tungstic acid solution, then adding an excess of hot sodium hydroxide solution for alkali boiling, and finally adding tungstic acid solution dropwise until the pH reaches 7.

Beyond its use in producing heteropolytungstates, sodium metatungstate is applied in geology, soil science, marine biology, fuel cell electrodes, cigarette filters, fire-resistant textiles, and biomedicine. In geology, it is primarily used for separating minerals and sedimentary rocks. In biochemistry, it has Ki values of 2.58 μM, 3.26 μM, and 28.8 μM against NTPDase1 (CD39), NTPDase3, and NTPDase2, respectively. It can inhibit the decomposition of ammonium paratungstate, block central synaptic transmission, and abolish renal protection induced by ischemic preconditioning.

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