Host-Guest Chemistry of Water-Soluble Coordination Cages and their Applications

Abstract

Host-guest interactions are key to enzyme-substrate recognition, where the enzyme acts as a host, providing a specific cavity for the guest to bind. Inspired by host-guest interactions observed in nature, a significant advancement is seen in designing artificial hosts. Among various design principles, metal based self-assembled cages are unique owing to their well-defined and shape-persistent cavities. These hosts, especially water-soluble cages, offer host-guest interactions akin to enzymes through non-covalent interactions, thereby exhibiting enzyme-like activity in catalysis and molecular recognition.1 In this thesis, we present our efforts in designing and synthesizing water-soluble Pd(II) coordination cages and exploring their host-guest chemistry. The well-defined hydrophobic cavity of these cages provides a confined space for encapsulating water-insoluble guest molecules and studying their properties in aqueous media. Notably, within a coordination barrel, we effectively solubilized water-insoluble zinc phthalocyanine, a well-known photosensitizer, and investigated its photodynamic properties in water.2 Additionally, we explored the potential of water-soluble cages as a reaction vessel for chemical transformations of encapsulated guests. Our findings showed that the cage assists in the selective binding and oxidation of alkyl aromatics.3 Furthermore, we investigated how cage geometry modulates host-guest interactions and affects chemical reactivity.4 Similarly, we successfully modulated the photophysical properties of encapsulated BODIHY dye by utilizing two iso-stoichiometric water-soluble coordination cages with distinct symmetries.5 This thesis highlights the versatility of water-soluble coordination cages in host-guest chemistry, with promising implications for effective solubilization, catalysis, and modulation of chemical and photophysical properties of encapsulated guest molecules.