On-POM Ring-Opening Polymerisation of N-Carboxyanhydrides.

The ring-opening polymerisation of α-amino acid N-carboxyanhydrides (NCAs) offers a simple and scalable route to polypeptides with predicted and narrow molecular weight distributions. Here we show how polyoxometalates (POMs)-redox-active molecular metal-oxide anions-can serve as inorganic scaffold initiators for such NCA polymerisations. This "On-POM polymerisation" strategy serves as an innovative platform to design hybrid materials with additive or synergistic properties stemming from the inorganic and polypeptide component parts. We have used this synthetic approach to synthesise a library of bactericidal poly(lysine)-POM hybrid derivatives that can be used to prevent biofilm formation. This versatile "On-POM polymerisation" method provides a flexible synthetic approach for combining inorganic scaffolds with amino acids, and the potential to tailor and improve the specificity and performance of hybrid antimicrobial materials.

Antifungal Activity of Polyoxometalate-Ionic Liquids on Historical Brick.

Moulds inhabiting mineral-based materials may cause their biodeterioration, contributing to inestimable losses, especially in the case of cultural heritage objects and architectures. Fungi in mouldy buildings may also pose a threat to human health and constitute the main etiological factor in building related illnesses. In this context, research into novel compounds with antifungal activity is of high importance. The aim of this study was to evaluate the antifungal activity of polyoxometalate-ionic liquids (POM-ILs) and their use in the eradication of moulds from historical brick. In the disc diffusion assay, all the tested POM-ILs inhibited growth of a mixed culture of moulds including Engyodontium album, Cladosporium cladosporioides, Alternaria alternata and Aspergillus fumigatus. These were isolated from the surfaces of historical brick barracks at the Auschwitz II-Birkenau State Museum in Oswiecim, Poland. POM-IL coatings on historical brick samples, under model conditions, showed that two compounds demonstrated very high antifungal activity, completely limiting mould growth and development. The antifungal activity of the POM-ILs appeared to stem from their toxic effects on conidia, as evidenced by environmental scanning transmission electron microscopy observations. The results herein indicated that POM-ILs are promising disinfectant materials for use not only on historical objects, but probably also on other mineral-based materials.

Water Purification and Microplastics Removal Using Magnetic Polyoxometalate-Supported Ionic Liquid Phases (magPOM-SILPs).

Filtration is an established water-purification technology. However, due to low flow rates, the filtration of large volumes of water is often not practical. Herein, we report an alternative purification approach in which a magnetic nanoparticle composite is used to remove organic, inorganic, microbial, and microplastics pollutants from water. The composite is based on a polyoxometalate ionic liquid (POM-IL) adsorbed onto magnetic microporous core-shell Fe2 O3 /SiO2 particles, giving a magnetic POM-supported ionic liquid phase (magPOM-SILP). Efficient, often quantitative removal of several typical surface water pollutants is reported together with facile removal of the particles using a permanent magnet. Tuning of the composite components could lead to new materials for centralized and decentralized water purification systems.

Polyoxometalate-Ionic Liquids (POM-ILs) as Anticorrosion and Antibacterial Coatings for Natural Stones.

Corrosion of stone by acid rain and deterioration from biofilms are global problems for industrial and residential buildings as well as cultural heritage, such as statues or historic buildings. Herein we show how typical building stones can be protected from corrosion ("weathering") and biofilm formation ("biodeterioration") by application of thin films of polyoxometalate-based ionic liquids (POM-ILs). Stone samples are coated with hydrophobic, acid resistant POM-ILs featuring biocidal properties. Exposure of the samples to simulated acid rain showed negligible corrosion compared to the significant deterioration of unprotected samples; in addition the biocidal properties of the POM-ILs suppress the formation of biofilms on coated stone slabs. A new class of modular molecular materials for protecting stones can now be developed for use in construction, environmental protection, and cultural heritage preservation.

Evaluating the durability and performance of polyoxometalate-ionic liquid coatings on calcareous stones: Preventing biocolonisation in outdoor environments.

Rock-based materials exposed to outdoor environments are naturally colonised by an array of microorganisms, which can cause dissolution and fracturing of the natural stone. Biocolonisation of monuments and architectures of important cultural heritage therefore represents an expensive and recurring problem for local authorities and private owners alike. In this area, preventive strategies to mitigate biocolonisation are generally preferred to curative approaches, such as mechanical cleaning by brush or high-pressure cleaning, to remove pre-existing patina. The aim of this work was to study the interaction between biocidal polyoxometalate-ionic liquid (POM-IL) coatings and calcareous stones and evaluate the capacity of these coatings to prevent biocolonisation through a series of accelerated ageing studies in climate chambers, carried out in parallel with a two-year period of outdoor exposure in north-eastern France. Our experiments show that POM-IL coatings did not affect water vapour transfer nor significantly alter the total porosity of the calcareous stones. Simulated weathering studies replicating harsh (hot and wet) climatic weather conditions demonstrated that the colour variation of POM-IL-coated stones did not vary significantly with respect to the natural uncoated stones. Accelerated biocolonisation studies performed on the weathered POM-IL-coated stones proved that the coatings were still capable of preventing colonisation by an algal biofilm. However, a combination of colour measurements, chlorophyll fluorescence data, and scanning electron microscopy imaging of stones aged outdoors in northern France for two years showed that coated and uncoated stone samples showed signs of colonisation by fungal mycelium and phototrophs. Altogether, our results demonstrate that POM-ILs are suitable as preventative biocidal coatings for calcareous stones, but the correct concentrations must be chosen to achieve a balance between porosity of the stone, the resulting colour variation and the desired duration of the biocidal effect over longer periods of time, particularly in outdoor environments.

Hybrid Antimicrobial Films Containing a Polyoxometalate-Ionic Liquid.

The increasing resistance of pathogenic microorganisms against common treatments requires innovative concepts to prevent infection and avoid long-term microbe viability on commonly used surfaces. Here, we report the preparation of a hybrid antimicrobial material based on the combination of microbiocidal polyoxometalate-ionic liquids (POM-ILs) and a biocompatible polymeric support, which enables the development of surface coatings that prevent microbial adhesion. The composite material is based on an antibacterial and antifungal room-temperature POM-IL composed of guanidinium cations (N,N,N',N'-tetramethyl-N″, N″-dioctylguanidinum) combined with lacunary Keggin-type polyoxotungstate anions, [α-SiW11O39]8-. Integration of the antimicrobial POM-IL into the biocompatible, flexible, and stable polymer poly(methyl methacrylate) (PMMA) results in processable films, which are suitable as surface coatings or packaging materials to limit the proliferation and spread of pathogenic microorganisms (e.g., on public transport and hospital surfaces, or in ready-to-eat-food packaging).

Decoupling manufacturing from application in additive manufactured antimicrobial materials.

3D printable materials based on polymeric ionic liquids (PILs) capable of controlling the synthesis and stabilisation of silver nanoparticles (AgNPs) and their synergistic antimicrobial activity are reported. The interaction of the ionic liquid moieties with the silver precursor enabled the controlled in situ formation and stabilisation of AgNPs via extended UV photoreduction after the printing process, thus demonstrating an effective decoupling of the device manufacturing from the on-demand generation of nanomaterials, which avoids the potential aging of the nanomaterials through oxidation. The printed devices showed a multi-functional and tuneable microbicidal activity against Gram positive (B. subtilis) and Gram negative (E. coli) bacteria and against the mould Aspergillus niger. While the polymeric material alone was found to be bacteriostatic, the AgNPs conferred bactericidal properties to the material. Combining PIL-based materials with functionalities, such as in situ and photoactivated on-demand fabricated antimicrobial AgNPs, provides a synergistic functionality that could be harnessed for a variety of applications, especially when coupled to the freedom of design inherent to additive manufacturing techniques.

Preventing fungal growth on heritage paper with antifungal and cellulase inhibiting magnesium oxide nanoparticles.

Microorganisms such as bacteria, fungi, algae and moulds are highly proficient at colonizing artistic and architectural heritage. The irreparable damage they cause to unique artefacts results in immeasurable cultural and societal losses to our shared cultural heritage, which represent an important social and economic resource for Europe. With the overall aim of preventing fungal deterioration of paper artefacts, we report the use of magnesium oxide nanoparticles (MgO NPs) of average diameter 12 nm as potent antifungal agents against fungi commonly found colonising paper heritage: A. niger, C. cladosporioides and T. reesei. Dispersions of MgO NPs on original 18th century paper samples from the Archives of the Spanish Royal Botanic Garden were effective at preventing fungal colonisation without altering the appearance of the paper artefacts. Importantly, MgO NPs also inhibit cellulase activity in the filamentous fungi T. resei and A. niger, two of the principle biodeteriogens of cellulosic materials. In addition, our report provides three simple new procedures for studying the fungal colonisation prevention properties of nanomaterials on paper samples. Overall this opens the door to the use of colourless, low-cost, and scalable nanomaterials for preventing biodeterioration in cellulose-based artefacts.