Speciation atlas of polyoxometalates in aqueous solutions

Abstract

Speciation is the key parameter in solution chemistry that describes the composition, concentration, and oxidation state of each chemical form of an element present in a sample. The speciation study of complex polyatomic ions has remained challenging because of the large number of factors affecting stability and the limited number of direct methods. To address these challenges, we developed the speciation atlas of 10 polyoxometalates commonly used in catalytic and biological applications in aqueous solutions, where the speciation atlas provides both a species distribution database and a predictive model for other polyoxometalates to be used. Compiled for six different polyoxometalate archetypes with three types of addenda ions based on 1309 nuclear magnetic resonance spectra under 54 different conditions, the atlas has revealed a previously unknown behavior of polyoxometalates that may account for their potency as biological agents and catalysts. The atlas is intended to promote the interdisciplinary use of metal oxides in various scientific fields.

All‐Inorganic Polyoxometalates Act as Superchaotropic Membrane Carriers

“…[ 53 ] First, their long‐term (24 h and longer) fate in aqueous solution (slightly acidic and neutral) was investigated by applying the active NMR nuclei in their composition (Table S9 and Figures S24–S37, see the Supporting Information for details). As previously described [ 11,38 ] the Keggin anions [PW 12 ] 3‒ and [SiW 12 ] 4‒ were found to be fully hydrolyzed at neutral or even slightly acidic pH to their monolacunary forms (Figures S35–S37, Supporting Information), but they were included as negative controls, to exclude potential carrier activity arising from degradation products. The other selected POMs were stable at neutral pH (7.5) or were only slowly hydrolyzed on a long‐time scale, as summarized in Table 1 .…”

“…For example, their unspecific interactions with proteins [ 32,33 ] and lipids [ 34–36 ] have recently been interpreted in terms of the chaotropic effect and their superchaotropic character. [ 15 ] On the other hand, the omnipresent tendency for speciation and degradation of POMs in aqueous solution, frequently pronounced near neutral pH, [ 11,37,38 ] hinder their biological and in particular clinical use, [ 29 ] which until today is largely focused on antimicrobial or toxic effects, including anticancer, [ 28,39 ] antiviral, [ 40–42 ] antibacterial, [ 27,43 ] and enzyme inhibitory [ 33,44–46 ] activity. Herein we report the development of POMs which are sufficiently stable near neutral pH to act as membrane carriers.…”

Experimental and Theoretical Studies on Two Dual-Functional Organic–Inorganic Hybrids Based on [V4O12]4– Clusters

“…For the hydrothermal/solvothermal synthesis, many conditions, such as the molar ratio of the raw material, acidity, ligand, transition metal, and solvent, can determine the growth and final structures of target materials. Gumerova and Rompel’s papers have guided us to understand more speciation of POVs . Two hybrids were synthesized under similar POVs/Cu/N-heterocyclic ligand reaction processes, except for N-donor ligands and acidity: dpy for 1 and tpy for 2 (Figure ).…”

Reactivity of metal–oxo clusters towards biomolecules: from discrete polyoxometalates to metal–organic frameworks

“…57,333–336 Therefore, additional studies on the impact of MOCs on living organisms and on their stability in biological systems are needed to develop them for these applications. 337,338 These studies could benefit from the molecular-level insights discussed in this review by establishing a link between reactivity and cytotoxicity, which has been scarcely investigated in detail. Additionally, the study of the cytotoxicity of POMs and the development of biocompatible POMs with low off-target toxicity is of primordial importance for their implementation in biomedical applications since clinical trials of POM-based inorganic drugs have been largely hampered by their cytotoxicity.…”