Mechanically Interlocked Superstructures in Aqueous Solution: Daisy Chains and Rotaxanes

The hydrophobic effect is of fundamental importance for the self-assembly of functional units in biological systems. Eventually all life depends on the properties which are owed to the chemistry beyond covalently bound structures. Artificial supramolecular systems may be designed to mimic biological assemblies or to fulfill purposes unknown in the natural biological realm. This includes the template-directed self-assembly of rotaxanes, which can profit from the versatile applicability of the hydrophobic effect. In order to render organic compounds water-soluble and enable well-defined recognition modes, a particularly thoughtful molecular design is required. This work aims towards the synthesis of aqueous-based rotaxane-type structures, in particular rigid molecular daisy chains. Diederich-type cyclophanes were chosen as receptor components and suitable functionality for copper-catalyzed azide-alkyne cycloaddition (CuAAC) is introduced in all structures. The cyclophane part is ideally suited to accommodate rigid, π conjugated structures. These key structural elements are thought to provide a suitable basis in the search towards building blocks for aqueous rotaxane synthesis. Three publications have resulted from these investigations, which are included in this thesis. After an introductory part, an overview of mechanically interlocked structures incorporating π-conjugated subunits is given. This is followed by Assembly of [2]Rotaxanes in Water, a publication in European Journal of Organic Chemistry, where the first investigations of aqueous-based rotaxane synthesis were published. Synthesis of molecular daisy chains is presented under Aqueous Assembly of Zwitterionic Daisy Chains. This article was published in Chemistry – A European Journal. As an invited contribution to the special issue of 50 Years of Rotaxanes in European Journal of Organic Chemistry, a manuscript prepared for submission was originally included under Slow Formation of Pseudorotaxanes in Water: Large Influence of the Substitution Pattern. The article was meanwhile published and is included in form of the peer-reviewed and edited final version. All chapters are followed by the corresponding supporting information, which contains the experimental data. To conclude, possible design considerations for aqueous-based, molecular daisy chains based on the preceding findings are given. The chapter Outlook: Towards Kinetically Controlled Assembly of Molecular Daisy Chains contains not only these design considerations but also the latest state of synthetic investigations towards a possible target structure.