Hybride polyoxometalaten voor toepassingen in supramoleculaire chemie en moleculaire machines

Innovations in the field of supramolecular chemistry have provided some of the most creative and efficient solutions to modern-day problems. Studying chemistry beyond the molecule allowed chemists to exploit weak intermolecular forces to tackle problems in materials science, medicine, and pharmaceuticals. Moreover, supramolecular approaches have allowed us to expand our understanding of chemistry and physics toward the controlled motion of molecules at a molecular scale. This culminated in the development of the field of artificial molecular machines, where chemical and physical inputs are used to control molecular motion, such as rotation, translation, or perform other mechanical tasks. Despite remarkable achievements, most research in these fields is focused on organic molecules. Very rarely can we find works that incorporate inorganic moieties such as metal-oxo clusters in these frameworks, which is a missed opportunity. Metal oxo clusters could provide new and interesting properties that, in combination with supramolecular systems and molecular machines, could offer new properties not easily accessible using purely organic frameworks. This is especially true for polyoxometalates (POMs), which are anionic metal-oxo clusters with well-defined structures and interesting redox and catalytic properties. These characteristics make POMs potential functional building blocks in supramolecular architectures and molecular machines. In this thesis, I have explored new ways of incorporating POMs into supramolecular systems by functionalizing them with organic molecules to create hybrid polyoxometalates (HPOMs). Organic molecules were chosen based on the ability to facilitate the incorporation of the HPOM into various supramolecular architectures, including responsive materials, biochemical systems, and artificial molecular machines. Chapter 1 provides an overview of current progress in the field of responsive supramolecular systems with POMs and discusses the state-of-the-art in artificial molecular machines. In the work presented in Chapter 2, a host-guest method, based on pillar[5]arene, was developed for controlled supramolecular assembly of HPOMs. These assemblies were further applied in catalysis, highlighting their potential as functional nanoarchitectures. Derivatization with organic and bioorganic molecules was also used in Chapter 3, to achieve targeted interactions of the HPOM with an enzyme. Namely, azide, α-D-mannopyranoside, and hexyne moieties were covalently grafted onto the POM, which enabled unprecedented site-selective binding of azide and α-D-mannopyranoside functionalized POMs within the enzymatic pocket of Hen Egg White Lysozyme, a crucial antibacterial enzyme. This represents a significant finding in designing POM-based systems for bioengineering applications. Chapter 4 expands on the idea of establishing a modular approach toward creating POMs with different properties and potential applications in supramolecular chemistry. In this case, copper-catalyzed click chemistry was used to synthesize new molecules with multiple POMs covalently linked together exhibiting emergent properties not accessible through individual components. The same synthetic approach was extended to create the first example of a rotaxane-type mechanically interlocked molecule containing a POM. Such a rotaxane with incorporated POM unit could act as a scaffold for functional molecular machines that combine motion with catalysis or electron transfer. In Chapters 5 and 6, the incorporation of POMs into artificial molecular machine architectures was studied. Chapter 5 explores coupling rotary motion with POMs, which was achieved through functionalization of an HPOM with a second-generation Feringa-type motor. Chapter 6 focused on achieving controlled translation motion of a macrocycle toward POM, through photoswitching of an azobenzene attached to the POM. This thesis establishes a synthetic and conceptual framework for integrating POMs into supramolecular systems. The versatility of POMs as modular platforms for building supramolecular systems was demonstrated by combining them with organic moieties of different character, such as host-guest and light-responsive molecules. By expanding their structural diversity with tailored organic molecules, it was possible to establish control over the supramolecular behavior of the POMs. In the five experimental chapters, the developed systems demonstrate catalytic, redox, and dynamic stimuli-responsive behavior, creating new opportunities for inorganic cluster chemistry in the broader fields of molecular machines, smart materials, and nanoscale devices.