| dc.description.abstract | Molecular recognition plays a crucial role in many natural processes, such as substrate binding to receptor proteins, antigen–antibody interactions, signal induction by neurotransmitters, and cellular recognition. This recognition is facilitated by the formation of highly specific intermolecular non-covalent bonds, including hydrogen bonds, π–π interactions, and van der Waals forces. These interactions allow substrates to be positioned closely within the pockets of enzymes, resulting in high substrate reactivity. Additionally, the specificity of these interactions contributes to the high selectivity observed in enzymatic reactions. To emulate the properties of such biomolecules, scientists have been developing different artificial analogues which will be able to encapsulate molecules inside their cavity. These compounds are often termed as “cages”.
Cage compounds are defined as “polycyclic compounds having the shape of a cage”. Such compounds have been synthesized by various methods and can be classified into two broad categories based on the synthetic technique used to make them. In first category the cage molecules are formed using covalent synthetic strategies using reactions that do not show dynamic nature. This synthetic approach is often termed as direct synthesis approach and generally involves multiple synthetic steps. This technique has certain advantages and disadvantages. The cages formed through this method are highly robust and can withstand a wide range of pH, further such cages are also much less cytotoxic and are more suitable for biological applications. However, this synthetic approach suffers from tedious multi-step reaction procedures with complex purification techniques leading to low yields. This hinders their applicability and thus a different strategy is often used.
In the second strategy, self-assembly processes are used to create cages through various non-covalent interactions, such as hydrogen bonding, π-π stacking, and metal-ligand coordination. These interactions have enabled the synthesis of numerous cages with diverse building blocks and functionalities. Among these, metal-ligand coordination-driven self-assembly is the most widely utilized and one of the most effective methods for constructing complex structures. This method is noted for its simple design principle, predictable directionality, high bond enthalpy, and its capacity to produce pre-designed supramolecules in high yields under mild conditions. Over the years, it has facilitated the creation of a broad range of topologically intricate structures using different metal acceptors.
These intricate structures also include molecules known as Mechanically Interlocked Molecules (MIMs). Such molecules are interlocked or intertwined by bond topology in such a way that these interlocked molecular fragments cannot be separated from one another without breaking the whole molecule. These interlocked molecules have been synthesized predominantly by self-assembly strategy and direct strategy for synthesis of such molecules are rare.
Such cages are often used for the encapsulation of molecules known as guest molecules. The encapsulation properties of cages are determined by the structures of the molecule. A large internal cavity surrounded by an aromatic core creates an ideal environment for encapsulating various guest molecules or serving as nano-reactors for different organic transformations. The microenvironment provided by these cages can be utilized to recognize molecules selectively. Although guest encapsulation by cages have been studied over the years, the use of mechanically interlocked molecules as host for such encapsulation in rare. Such molecules have narrow cavity due to their intertwined structure and encapsulation inside their microenvironment would require the fulfilment of more stringent conditions. Thus using such interlocked cages, greater selectivity in molecular recognition might be possible.
Several factors starting from the size and shape of the cavity to the interactions between host and guest, the hydrophobicity of the cavity, and the symmetry elements of the host and guest molecules all play an important role in determining the host-guest interactions inside a cage. The use of such host-guest interactions to tune the efficiency of different processes or to bias the outcome a chemical transformation has largely been unexplored.
This thesis is divided into two parts. Part 1 (Chapters 2 and 3) concerns with the fabrication of discrete water-soluble interlocked architectures and their applications. Whereas Part 2 (Chapters 4 and 5) focuses on the use of water-soluble cages as host to alter the chemical reactivity of the guests by leveraging various host-guest interactions. | en_US |
