Water-soluble rotaxanes : identifiying suitable building blocks for molecular daisy chains

Structurally diverse rotaxane-based systems have been investigated extensively for applications as molecular machines and functional nanomaterials. Although the vast majority of functional molecules were assembled and function in organic solvents, to date the most efficient and sophisticated molecular machines are biomolecules which function in aqueous media. Many vital processes, such as protein folding and assembly, rely on hydrophobic interactions and are only possible in aqueous environment. From a supramolecular chemistry perspective, the hydrophobic effect is an appealing driving force for host-guest association as it potentially leads to high complexation affinities and no extra binding sites need to be installed into the respective components. Appealing macrocyclic candidates for the preparation of mechanically interlocked molecules in aqueous media are the synthetically modifiable, water-soluble cyclophanes developed and comprehensively studied by Diederich et al..
The focus of this doctoral thesis was to identify suitable guest molecules for Diederich-type cyclophanes, allowing for the assembly of rotaxanes and also molecular daisy chains. The first part of the thesis describes the investigation of the aggregation behavior of amphiphiles based on OPE guests which are potentially capable of forming molecular daisy chains (Chapter 2). A deeper insight into the system was obtained through a series of rotaxane model compounds, basically relying on the main components of the previously examined amphiphiles (Chapter 3). The investigation of an extended scope of potential guest molecules via 1H NMR complexation studies resulted in an optimization of the molecular guest design and revealed some important features of suitable candidates (Chapter 4). Based on these results a water-soluble 2,6-disubstituted naphthalene derivative was found to function as (pseudo)rotaxane axle and enabled the isolation and characterization of a [2]rotaxane (Chapter 5). The results obtained throughout this doctoral thesis allow to obtain guidelines for the successful preparation of interlocked molecular daisy chains.