Solution Dynamics of Hybrid Anderson–Evans Polyoxometalates

Abstract

Understanding the stability and speciation of metal-oxo clusters in solution is essential for many of their applications in different areas. In particular, hybrid organic–inorganic polyoxometalates (HPOMs) have been attracting increasing attention as they combine the complementary properties of organic ligands and metal–oxygen nanoclusters. Nevertheless, the speciation and solution behavior of HPOMs have been scarcely investigated. Hence, in this work, a series of HPOMs based on the archetypical Anderson–Evans structure, δ-[MnMo6O18{(OCH2)3C–R}2]3–, with different functional groups (R = −NH2, −CH3, −NHCOCH2Cl, −NCH­(2-C5H4N) {pyridine; −Pyr}, and −NHCOC9H15N2OS {biotin; −Biot}) and countercations (tetrabutylammonium {TBA}, Li, Na, and K) were synthesized, and their solution behavior was studied in detail. In aqueous solutions, decomposition of HPOMs into the free organic ligand, [MoO4]2–, and free Mn3+ was observed over time and was shown to be highly dependent on the pH, temperature, and nature of the ligand functional group but largely independent of ionic strength or the nature of the countercation. Furthermore, hydrolysis of the amide and imine bonds often present in postfunctionalized HPOMs was also observed. Hence, HPOMs were shown to exhibit highly dynamic behavior in solution, which needs to be carefully considered when designing HPOMs, particularly for biological applications.

Polyoxometalate–peptide hybrid materials: from structure–property relationships to applications

“…The Parac-Vogt group has recently studied the stability of Mn-AE hybrids, which will aid to strengthen the bases for the AE chemistry. 65 POVs behave similarly to the AE scaffold and readily react with TRIS derivatives yielding a large pool of combinations. From the chemical point of view, the work of Hill and coworkers has focused on the esterication reaction that takes place in the V 3 -substituted phosphotungstate Wells-Dawson, [P 2 V 3 W 15 O 58 ] 5− .…”

“…Moreover, the AE scaffold has been derivatised with different chemical functional groups and metallic heteroatom centres e.g., Fe 3+ , Mn 3+ , Al 3+ to name just those most widespread. The Parac-Vogt group has recently studied the stability of Mn-AE hybrids, which will aid to strengthen the bases for the AE chemistry 65. POVs behave similarly to the AE scaffold and readily react with TRIS derivatives yielding a large pool of combinations.…”

Latest progress in covalently modified polyoxometalates-based molecular assemblies and advanced materials

“…It was worth noting that POMs possessed rich modified sites to incorporate functional groups, which can endow POMs with various properties such as controllable hydrophilicity and tunable counter-cations, etc. [16,17] , thus providing more potential to modify by rational design. Generally, polymers [18,19] , organic molecules [20] , and other organic/inorganic clusters [21,22] can be grafted on the POMs to fabricate the building blocks with different compositions and shapes by organic synthesis strategy.…”

Robotic synthesis of peptides containing metal-oxide-based amino acids

“…To achieve this goal, we chose polyoxometalates (POMs), a large group of clusters built from multiple transition metal ions linked by shared oxo or hydroxo anions; 30 their molecular nature means they introduce higher charge densities, 31 redox activity, 32,33 and additional coordination/catalytic sites into the peptide chain, 34 leading to exciting new opportunities for protein biochemistry and inorganic medicinal chemistry. [35][36][37][38] Incorporation of redox-active POMs into sequences may further impart POM peptides with tuneable redox responsiveness, which is useful in redox bio-catalysis, redox-mediated self-assembly, and hybrid flow battery. To date there are two major methodologies to introduce POMs into peptide chains: non-covalent assembly 34,39,40 or covalent conjugation.…”

“…To date there are two major methodologies to introduce POMs into peptide chains: non-covalent assembly 34,39,40 or covalent conjugation. 28,29,[36][37][38] However, the bespoke conditions required, unpredictable reactions, and the potential for many by-products greatly limit the exploration of biochemical activity of hybrid inorganic peptides (see Figure 1).…”