Hybrid Polyoxometalate Salt Adhesion by Butyltin Functionalization

Abstract

Polyoxometalate (POM)-based ionic liquids, with nearly infinite compositional variations to fine-tune antimicrobial and physical properties, function as water purification filters, anticorrosion/antibacterial coatings for natural stones, self-repairing acid-resistant coatings, catalysts, and electroactive, stable solvents. By combining hydrophobic quaternary ammonium cations (QACs; tetraheptylammonium and trihexyltetradecylammonium) with butyltin-substituted polyoxotungstates [(BuSn)3(α-SiW9O37)] via repeated solvent extraction-ion exchange, we obtained phase-pure hybrid POM salts (referred to as such because they melt above room temperature). If the solvent extraction process is performed only once, then solids with high salt contamination and considerably lower melting temperatures are obtained. Solution-phase behavior, based on POM–QAC interactions, was similar for all formulations in polar and nonpolar organic solvents, as observed by X-ray scattering and multinuclear magnetic resonance spectroscopy. However, solid thin films of the butyltin-functionalized hybrid POM salts were significantly more stable and adhesive than their inorganic analogues. We attribute this to the favorable hydrophobic interactions between the butyltin groups and the QACs. All synthesized hybrid POM salts display a potent antimicrobial activity toward Escherichia coli. These studies provide fundamental form-function understanding of hybrid POM salts, based on interactions between ions in these complex hybrid phases.

The Future Is Bright for Polyoxometalates

“…When comparing the date of the first POMs studies described against viruses and cancer, respectively, at 1971 and 1965 [39,40], the antibacterial activities can be considered recent (1993). However, insights in POMs as anti-microbial agents or adjuvants, as well as POM-ILs as antibacterial coatings, have been attracting interest by offering mechanisms of action different from other recent antibacterial therapies [41][42][43][44][45][46][47][48][49][50]. On the other hand, many POMs have poor antibacterial activity, but possess excellent redox activity, and their use as biosensors for bacterial detection has been described [51].…”

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

“…Combining with hydrophobic quaternary ammonium cations and butyltin-substituted polyoxotungstates [(BuSn)3(α-SiW9O37)], Nyman et al obtained phase-pure hybrid POMs salts, which showed strong antibacterial activity against Escherichia coli [119] .…”