Cyclodextrin-based Molecular Devices

Abstract

In this thesis, several types of secondary-face modified beta-CD are developed and investigated. The conformational behaviours of these modified CDs were determined by 1H and 2D NMR spectroscopies. In general, this thesis presents one of the only a few studies of secondary-face modified CDs. In Chapter 1, developments in the field of supramolecular chemistry are described. The "bottom-up" approach for the fabrication of supramolecular molecular devices is discussed. This chapter also introduces the host-guest recognition properties of CDs and their roles in the development of functional molecular devices. In addition, different synthetic approaches for secondary-face modification of beta-CDs are introduced. The work in Chapter 2 describes the preparation of secondary-face modified cinnamido-CDs, where the cinnamyl substituent is covalently linked at the C3A position of beta-CD via an N-methyl amino modification. The installation of a cinnamide on an altropyranose shows the absence of intramolecular interaction in polar (D2O), organic (d6-DMSO), and in D2O in the presence of potential organic guest competitor (1-adamantanecarboxylic acid). In contrast, different conformational behaviours can be observed by substituting the cinnamido substituent on a glucopyranose unit, instead of an altropyranose, where the intramolecular interaction between the substituent and the CD cavity persists in polar (D2O), organic (d6-DMSO), and in D2O in the presence of a potential organic guest competitor (TNS). In this context, the dissociation of the substituent from the CD cavity can only be achieved by photoisomerising the trans to cis double bond. In addition, the interconversion of the cis and trans double bonds is reversible, making these cinnamido-CDs photo-sensitive and solvent-independent molecular gates. In Chapter 3, phenylpropionamide CDs were synthesised to investigate the generality of the solvent-independent intramolecular interactions observed in Chapter 2. In the work described in this chapter, the extent to which the amide bonds are constrained varies across the phenylpropionamide CDs prepared. However, intramolecular interactions can be observed between the CD cavity and the substituent in both polar (D2O) and organic solvents (CD3OD) for all the phenylpropionamide CDs. Therefore, the presence of the intramolecular interactions between the substituent installed at the secondary face with the CD cavity is solvent-independent and presumably a more general phenomenon closely related to the geometrical configuration rather than the flexibility of the substituent.