Supramolecular chemistry of beta- and gamma- cyclodextrin dimers.

Abstract

Native and modified cyclodextrins (CDs) act as robust hosts for a variety of guest species in water, and therefore are at the centre of supramolecular chemistry. Covalently linked CD dimers provide many advantages over native CDs in complexation of guest species in terms of their stability, selectivity or flexibility. The studies underpinning this thesis are based on the β-cyclodextrin dimers, N,N’-bis((2AS,3AS)-3A-deoxy-β-cyclodextrin-3A-yl) succinamide, 33βCD₂suc, and N,N′-bis(6A-deoxy-B-cyclodextrin-6A-yl) succinamide, 66βCD₂suc, and the γ-cyclodextrin dimers, N,N′-bis((2AS,3AS)-3A-deoxy-γ-cyclodextrin-3A-yl) succinamide, 33γCD2suc, and N,N′’-bis(6A-deoxy-γ-cyclodextrin-6A-yl) succinamide, 66γCD2suc, in which the two βCD or γCD cavities are joined together through either the C₃A or C₆A carbons of altropyranose or glucopyranose units, respectively. Often in supramolecular systems, several competing equilibria exist, as exemplified by host–guest complexation and guest aggregation. The complexation of dimerising cationic pyronines B and Y, PB⁺ and PY⁺, by βCD and the βCD dimers, 33βC₂suc and 66βCD₂suc, has been studied by UV–vis, fluorescence and ¹H NMR spectroscopy. The complexation constants for the 1:1 host–guest complexes are reported as are the dimerisation constants for PB⁺ and PY⁺. The modes of complexation, dimerisation and fluorescence quenching are discussed in light of the structural differences and the 1D and 2D ¹H NMR spectroscopic data. The competitive equilibria between the dimerisation and host–guest complexation of hematoporphyrin, HP²⁻, by γCD and two newly synthesised γCD dimers, 33γCD₂suc and 66γCD₂suc, have been simultaneously quantified by UV–vis and fluorescence spectroscopy. The competing equilibrium constants, thermodynamic parameters and molecular modelling are reported and the nature of interaction between HP²⁻ and γCD and the γCD dimer hosts is discussed. The new 3% randomly substituted 1-naphthyl-sulfonamide poly(acrylate)s, PAA1NSen and PAA1NShn, have been prepared by 3% random substitution of either N-(2- aminoethyl)-1-naphthyl-sulfonamide or N-(6-aminohexyl)-1-naphthyl-sulfonamide onto the poly(acrylate) backbone. The complexation of the 1-naphthyl substituents by βCD and γCD and their succinamide–linked dimers, 33βCD₂suc, 66βCD₂suc, 33γCD₂suc and 66γCD₂suc, have been quantified by fluorescence spectroscopy. The competition between 1-naphthyl substituent aggregation and host–guest complexation by the linked CD dimers and the 1-naphthyl substituents in forming inter–polymer strand cross–links is examined in aqueous solution at the macroscopic level by rheology and at the molecular level by 2D ¹H NOESY NMR and fluorescence spectroscopy.