Smart materials based on cyclodextrins

Abstract

In the Introduction Chapter, the field of molecular self-assembly and supramolecular chemistry is introduced. The importance and advantages of supramolecular chemistry with noncovalent interactions to trigger the development of artificial molecular machines and the improvement of materials science is discussed. A brief summary of molecular machines is presented with relevant examples from the literatures. Also introduced are cyclodextrin (CD) and the development of CD based molecular machines and daisy chains. Isothermal titration calorimetry (ITC) and nuclear magnetic resonance (NMR) methods are described and their usage as analytical methods to get insight into the selfassembly behaviour of noncovalent interactions is presented. A brief introduction of amides is presented at the end. In the Discussion and Results Chapter 1, a three station photochemically switchable trans 2rotaxane and its photoisomer cis 2rotaxane were studied under various conditions with the aim of achieving unidirectional motion in a rotaxane. 1D and 2D NMR technology was used to analyze the conformational behaviour of the trans 2rotaxane and cis 2rotaxane. In D2O and methanold4 the CD moves with directional selectively, but which direction could not be determined. The successful preparation of a hetero c2 rotaxane consisting of two different light stimuli hermaphrodites with potential to act as a four-station molecular muscle is presented in Discussion and Results Chapter 2. A combined NMR and UVvisible spectroscopic method was used to analyze the conformation and the photolysis of the hetero c2 rotaxane. The conformation of the hetero c2 rotaxane has the CD sitting over the stilbene and azobenzene moieties. However, the hetero c2 rotaxane was not photolabile in MilliQ H2O upon photoirradiation. The possible explanation and solutions are discussed. The Discussion and Results Chapters 3 to 6 described the design and preparation of three types of the substituted CDs with the aim of creating a molecular daisy chain in solution. trans Cinnamido substituted beta CDs only form c1 complexes in aqueous solution. Chapter 3 investigated the solvent effects on their c1complexes. NMR and ITC experiments suggested that the amount of organic solvent required to dissociate the c1 complex also prevents intermolecular complexation. From this, stilbenylamido-substituted alpha CDs were designed and synthesised towards daisy chains by avoiding the c1 complex. Investigation of alkyl steric effects on the amide isomer ratios, and correlation of this with formation of complexes suggested that trans stilbenylamido substituted alpha CDs only form the c2 complexes in aqueous solution. A mechanically interlocked form of the complex constructed by trans stilbenylamido substituted alpha CDs was prepared and examined. This in turn, gave a c2 rotaxane, which was identified by NMR spectroscopy and Mass spectrometry. Finally, trans cinnamido substituted alpha CDs were designed and used in continued pursuit of a molecular daisy chain. The architectures and sizes formed by cinnamido-substituted alpha CDs were studied by advanced microscopy, NMR spectroscopy and ITC measurements in both aqueous solution and organic solvents. Obtained results clearly reveal the formation of supramolecular structures through daisy chain formation in aqueous solution. Gelation in methanold4 is proposed to be driven by other effects. Show more