Sodium decavanadate describes any member of the family of

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

s with the formula Na₆ ₁₀O₂₈H₂O)_n. These are

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

salts of the orange-colored decavanadate

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

₁₀O₂₈sup>6−. Numerous other decavanadate salts have been isolated and studied since 1956 when it was first characterized.

Preparation

The preparation of decavanadate is achieved by acidifying an aqueous solution of ortho- vanadate: :10 Na₃ O₄ + 24 HOAc → Na₆ ₁₀O₂₈ + 12 H₂O + 24 NaOAc The formation of decavanadate is optimized by maintaining a pH range of 4–7. Typical side products include metavanadate, O₃sup>−, and hexavanadate, ₆O₁₆sup>2−, ions.

Structure

The decavanadate ion consists of 10 fused VO₆ octahedra and has D_2h symmetry. The structure of Na₆ ₁₀O₂₈�18H₂O has been confirmed with

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. The decavanadate anions contains three sets of equivalent V atoms (see fig. 1). These include two central VO₆ octahedra (V_c) and four each peripheral tetragonal-pyramidal VO₅ groups (V_a and V_b). There are seven unique groups of oxygen atoms (labeled A through G). Two of these (A) bridge to six V centers, four (B) bridge three V centers, fourteen of these (C, D and E) span edges between pairs of V centers, and eight (F and G) are peripheral. The

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

vanadium Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

in decavanadate is +5.

Acid-base properties

Aqueous vanadate (V) compounds undergo various self-condensation reactions. Depending on pH, major vanadate anions in solution include VO₂(H₂O)₄²⁺, VO₄³⁻, V₂O₇³⁻, V₃O₉³⁻, V₄O₁₂⁴⁻, and V₁₀O₂₈⁶⁻. The anions often reversibly protonate. Decavanadate forms according to this equilibrium: :H₃V₁₀O₂₈³⁻ ⇌ H₂V₁₀O₂₈⁴⁻ + H⁺ :H₂V₁₀O₂₈⁴⁻ ⇌ HV₁₀O₂₈⁵⁻ + H⁺ :HV₁₀O₂₈⁵⁻_(aq) ⇌ V₁₀O₂₈⁶⁻ + H⁺ The structure of the various protonation states of the decavanadate ion has been examined by ⁵¹V NMR spectroscopy. Each species gives three signals; with slightly varying

chemical shift In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...

s around −425, −506, and −523 ppm relative to

vanadium oxytrichloride Vanadium oxytrichloride is the inorganic compound with the chemical formula, formula VOCl3. This yellow distillable liquid hydrolyzes readily in air. It is an oxidizing agent. It is used as a reagent in organic synthesis. Samples often appear r ...

; suggesting that rapid proton exchange occurs resulting in equally symmetric species. The three protonations of decavanadate have been shown to occur at the bridging oxygen centers, indicated as B and C in figure 1. Decavanadate is most stable in pH 4–7 region. Solutions of vanadate turn bright orange at pH 6.5, indicating the presence of decavanadate. Other vanadates are colorless. Below pH 2.0, brown V₂O₅ precipitates as the hydrate. :V₁₀O₂₈⁶⁻ + 6H⁺ + 12H₂ ⇌ 5V₂O₅

Potential uses

Decavanadate has been found to inhibit phosphoglycerate mutase, an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

which catalyzes step 8 of

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...

. In addition, decavandate was found to have modest inhibition of ''

Leishmania ''Leishmania'' () is a genus of parasitic protozoans, single-celled eukaryotic organisms of the trypanosomatid group that are responsible for the disease leishmaniasis. The parasites are transmitted by sandflies of the genus '' Phlebotomus'' ...

tarentolae'' viability, suggesting that decavandate may have a potential use as a topical

inhibitor Inhibitor or inhibition may refer to: Biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotransmi ...

of protozoan parasites.

Related decavanadates

Many decavanadate salts have been characterized. NH₄⁺, Ca²⁺, Ba²⁺, Sr²⁺, and group I decavanadate salts are prepared by the acid-base reaction between V₂O₅ and the oxide, hydroxide, carbonate, or hydrogen carbonate of the desired positive ion. :6 NH₃ + 5 V₂O₅ + 3 H₂O ⇌ (NH₄)₆ ₁₀O₂₈ Other decavanadates: :(NH₄)₆ ₁₀O₂₈�6H₂O :K₆ ₁₀O₂₈�9H₂O :K₆ ₁₀O₂₈�10H₂O :Ca₃ ₁₀O₂₈�16H₂O :K₂Mg₂ ₁₀O₂₈�16H₂O :K₂Zn₂ ₁₀O₂₈�16H₂O :Cs₂Mg₂ ₁₀O₂₈�16H₂O :Cs₄Na₂ ₁₀O₂₈�10H₂O :K₄Na₂ ₁₀O₂₈�16H₂O :Sr₃ ₁₀O₂₈�22H₂O :Ba₃ ₁₀O₂₈�19H₂O : C₆H₅)₄P₃V₁₀O₂₈·4CH₃CN :Ag₆ ₁₀O₂₈�4H₂O Naturally occurring decavanadates include: :Ca₃V₁₀O₂₈·17 H₂O ( Pascoite) :Ca₂Mg(V₁₀O₂₈)·16H₂O ( Magnesiopascoite) :Na₄Mg(V₁₀O₂₈)·24H₂O ( Huemulite)

References

{{reflist Vanadates Sodium compounds