Synthesis and Host-Guest Chemistry of Organically-Functionalized Polyoxomolybdate Wheels

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Host–guest encapsulation processes in chemistry assisted by supramolecular interactions are of importance in drug delivery, separation processes and sensing applications. Polyoxometalates (POMs) are discrete, anionic metal-oxo clusters and attractive for host-guest chemistry because of the ease of controlling their molecular properties, such as size, shape, composition, charge, acidity, redox potential and solubility in aqueous and organic media. POMs have been shown to be highly effective as antiviral, antitumor, antibacterial, and antidiabetic agents both in vitro and in vivo. Very large, discrete wheel- or ball-shaped polyoxomolybdates (e.g. {Mo154} wheel, {Mo132} ball) have been known for >20 years, and some limited insight has been obtained on their role as hosts for guest encapsulation. However, systematic studies on guest uptake and release all the way to drug delivery applications using discrete POM wheels as hosts are largely unexplored. The first key aim of this project is to design and synthesize discrete, organically-functionalized molybdenum-oxo wheels and utilize them for bio-medical applications via host-guest interactions, in analogy to organic hosts such as crown ethers, cyclodextrins, calixarenes and cucurbiturils. We will also explore their sensing behaviour for various thiol contaminants and nitro-explosives, as well as their catalytic activities in reactions, such as the oxidation of organic sulfides and epoxidation of olefins. The second key aim of this project is the construction of POM-wheel-based extended, porous framework materials known as metal-organic frameworks (MOFs), using individual POMs as secondary building units. This represents a promising strategy for generating POM-based MOF materials, which merge the merits of both POMs and MOFs, and hence give rise to highly attractive, host-guest based properties in areas such as proton conduction, catalysis and bio-medicine. This project hence deals with a completely new research field, which is likely to result in the discovery of promising multi-functional materials with the potential for clinical and/or industrial applications.