Linked beta-cyclodextrin trimers: from molecular recognition to polymer network hydrogels
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Date
2014
Authors
Nguyen, Trang Thi Hanh
Editors
Advisors
Lincoln, Stephen Frederick
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Theses
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Abstract
The thesis describes the construction and characterisation of a variety of polymer network hydrogels based on β-cyclodextrin (β-CD) trimers and modified poly(acrylate)s. Chapter 1 extensively reviews in cyclodextrin (CD) fields from its history from beginning in 1981 until 2013. The most significant work is highlighted as well as the field of polymer hydrogel, including the novel field of CD based polymer hydrogel. In Chapter 2, a UV-vis and ¹H NMR spectroscopic study of the host-guest complexation by β-cyclodextrin (β-CD), 1,3,5-N,N,N-tris-(6ᴬ-deoxy-6ᴬ-β-cyclodextrin)-benzene (β-CD₃bz), and 1,3,5-N,N,N-tris(6ᴬ-(2-aminoethyl)amino-6ᴬ-deoxy-6ᴬ-β -cyclodextrin)- benzene (β-CDen₃bz) of cationic crystal violet (CV⁺) and pyronine B (PB⁺) and zwitterionic rhodamine B (RB) in aqueous phosphate buffer at pH 7.0 and I = 0.10 mol dm³ is described. The complexation constants and the associated ∆H₁₁ and T∆S₁₁ for all nine complexes coincide with an entropy-enthalpy compensation plot for the formation of a wide range of β-CD and modified β-CD host-guest complexes reported in the literature. Crystal violet also forms (β-CD)₂.CV⁺, (β-CD₃bz)₂.CV⁺ and (β-CDen₃bz)₂.CV⁺ complexes characterized by 10⁻²K₂₁ (298.2 K) = 2.14, 4.57and 3.86 dm³ mol⁻¹ and analogous (β-CD)₂.PB⁺ , (β-CDen₃bz)₂.PB⁺ and (β-CDen₃bz)₂.RB complexes also form, but the (β-CD₃bz)₂.PB⁺, (β-CD)₂.RB, and (β-CD₃bz)₂.RB complexes were not detected. The effects of the structures of the hosts and guests on the complexation processes are discussed. In Chapter 3 the characterisation stability of constants and thermodynamic patterns in polymer hydrogels based on host-guest complexation of the linked β-CD trimers with the dodecyl (C12) and octadecyl (C18) 3% randomly substituted poly(acrylate)s PAAC12 and PAAC18 in aqueous solution are discussed. These studies compare hydrophobic interactions of the C12 and C18 substituted poly(acrylate)s and their interaction with β-CD and linked β-CD trimers. The complexation processes were studied by 2D NOESY ¹H NMR spectroscopy, ITC, dynamic light scattering and rheology. These data are used to establish the extent to which these interactions influence hydrogel formation in more concentrated solutions. In Chapter 4 the supramolecular chemistry of polymer hydrogel based on host-guest chemistry of the linked β-cyclodextrin trimers and four adamantyl substituted poly(acrylate)s with different linker tether lengths is discussed. 2D NOESY ¹H NMR spectroscopy, isothermal titration calorimetry and rheological studies show that the β-CD groups of the two linked β-cyclodextrin trimers, β-CD₃bz and β-CDen₃bz, complex the adamantyl substituents and their tethers in 3.0% substituted poly(acrylate)s to form intra and inter-poly(acrylate)s strand cross-links in aqueous solution. The structures of the linked-β-cyclodextrin trimers and the length of the tether between the adamantly substituent and the poly(acrylate)s backbone have substantial effects on the complexation constants, K₁₁, and the associated thermodynamic parameters. This is partially shown for the complexation by β-CD₃bz of the adamantyl substituents as tether length varies from -CONH- (3.45 × 10⁴) through -CONH(CH₂)NHCO- where n = 2 (2.09 × 10⁵), 6 (3.17 × 10⁵) or 12 (7.46 × 10⁴) in 0.13 – 0.37 wt.% substituted poly(acrylate)s solutions and the figures in brackets are the K₁₁ in dm³ mol⁻¹ at 298.2 K. For the same sequence of substituted poly(acrylate)s the variation of viscosity is: 0.03, 3.78, 3.48, and 2.03 Pa s⁻¹ at 500 s⁻¹ shear rate at 298.2 K for 5.0 wt.% substituted poly(acrylate)s solutions in which the β-CD groups of β-CD₃bz and the adamantyl substituents are equimolar at 1.5 × 10⁻² mol dm⁻³. The eight data sets for the β-CD₃bz and β-CDen₃bz systems are discussed in terms of host-guest interactions between the host β-CD groups and the guest adamantyl substituents of the substituted poly(acrylate)s and are compared with those for the analogous β-CD systems. In chapter 5, the supramolecular chemistry of the poly(acrylate)s hydrogels based on host-guest complexations of the linked β-CD₃bz and β-CDen₃bz trimers with the dansyl substituent guests (DS) attached through tethers of three different lengths containing 2, 6 and 12 methylene groups in 3.0% randomly substituted, PAADSen, PAADShn and PAADSddn are discussed. The six systems have been characterized at the molecular level by 2D NOESY ¹H NMR, isothermal titration calorimetry, fluorescence spectroscopy and time-resolved fluorescence, and at the macroscopic level by dynamic light scattering and rheology. The data gathered are consistent with individual dansyl substituents forming aggregates and being complexed by the linked β-CD₃bz and β-CDen₃bz trimers in within poly(acrylate)s strands in dilute solutions and between poly(acrylate)s strands in hydrogels. The trends in β-CD₃bz and β-CDen₃bz complex stability constants fluorescence life times and viscosities of six systems are discussed. Chapter 6 describes the experimental methodology deployed in the study.
School/Discipline
School of Chemistry and Physics
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2014.
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