Design, Synthesis and Optimization of Hybrid Organic-Inorganic Polyoxometalates

The project of this thesis was focused on both the design and synthesis of organic-inorganic POM hybrids, based on the Lindqvist and Anderson-Evans platform. Polyoxometalates (POMs) are inorganic clusters of early transition metals like W, Mo, V in their highest oxidation states, connected by oxo- bridges to form tridimensional structures. This class of compounds exhibits a broad variety of structures and tunable properties according to the synthetic parameters and elements chosen. Owing interesting features as an excellent redox activity, nano-dimensions, polyanionic charge and rigidity, plus additional properties brought by the presence of eventual heteroatoms, POMs find several applications and are attractive compounds in different research fields, for instance catalysis, material science and medicine. The aim of the work, is to evaluate if the Lindqvist POVs structures could serve as platforms capable of incorporating peptide chains, similarly to what has been accomplished with the Anderson-Evans structures in the past. It will be assessed if a free carboxylic acid functional group can be introduced onto an hexavanadate core. This hybrid typology is far less explored than the Anderson-Evans one, due to the lower reaction yields and frequent side redox reactions and it has never been functionalized with a peptide. But it could be an interesting platform in the design of POM-peptide bioconjugates, thanks to its intrinsically higher anticancer activity; besides, its lesser negative charge (−2 vs. −3) compared to the Anderson-Evans counterpart should reduce the folding of the peptide chain and thus may enable a better cell recognition. Concurrently, the synthesis of asymmetric organic-inorganic POM hybrids has been taken into consideration and the possible synthetic approaches that could be used to create hybrids bearing two distinct functionalities have been examined. The Anderson-Evans structure has been selected for this difficult task, as its TRIS-based hybrids exhibit numerous advantages with respect to other POM structures: (i) said hybrids are very stable to air, water and light, making them easy to handle; (ii) their Class II nature offers a better control at the molecular level and a greater chance of maintaining the hybrid properties from the solid to the liquid state; (iii) hybrids with this structure usually crystallize well, permitting a good purification; (iv) synthesis of the symmetric hybrid counterparts relies on well-established protocols; (v) examples of Anderson-Evans asymmetric hybrids are present in the literature. The end goal is to be able to create hybrids bearing two distinct organic moieties (peptides, fluorophores, chromophores, metal complexes, etc.), creating novel structures which can be exploited for various applications