The Interaction Between Cucurbit[6]Uril And Polyelectrolyte

Because of fundamental importance of polyelectrolytes,polyelectrolytes have been the object of a continued interest since the early days of polymer science. Cucurbit[6]uril(CB[6]),which is a macrocycle comprising six glycoluril units interconnected with twelve methylene bridges,has a hydrophobic cavity that is accessible through two identical carbonyl-fringed portals.The polar carbonyl groups at the portals and a hydrophobic cavity allow CB[6]to form stable host-guest complex with small molecules such as protonated aminoalkanes,diaminoalkanes.Moreover, CB[6]and polyelectrolyte can interact with each other to form complex,they usually display intriguing and fascinating features,which are different from polyelectrolyte or CB[6].In this doctoral dissertation,the detailed supermolecule interaction between CB[6]and polyelectrolytes has been investigated.Brief research background of this work is introduced,in which the history and recent progress in cucurbituril and polyelectrolyte as well as the application of CB[6]in polyelectrolyte are reviewed from a worldwide angle of view.The objective and the scientific significance of this doctoral dissertation are also pointed out.(1) A novel complex pseudorotaxane monomer(BAMACB) by the self-assembly of the host molecule of CB[6]and guest molecule of butyl ammonium methacrylate (BAMA) was synthesized.A series of copolymers of acrylamide(AM) with complex pseudorotaxane monomer BAMACB were synthesized via conventional free radical polymerization in aqueous media using 4,4 '-azobis(4-cyanopentanoic acid) as initiator. The copolymers(PAM/BAMACB) were characterized extensively via ¹H NMR, Elementary Analysis,Fourier Transform Infrared(FT-IR),Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry(DSC).Compositional analysis by ¹H NMR spectroscopy and Elementary Analysis revealed that copolymers with the mole ratio of BAMACB/AM 1/32.9,1/52.9,1/82.8 and 1/87.8 were achieved.The results showed that the bulky steric hindrance of CB[6]can damage the hydrogen bond of the amide groups,leading to the decrease of decomposition temperature of amide groups. However,the T_g of PAM/BAMACB increased,which was the results of the enhanced rigidity and the bulky steric hindrance of side chain of PAM/BAMACB.The results of Dynamic Light Scattering(DLS) showed that the aggregation of PAM/BAMACB occured.In aqueous solutions,intermolecular aggregation is dominant;transition between the intrachain and interchain association appear in 0.1 mol/L NaCl solutions. The copolymer chains first undergo the intrachain complexation at low copolymer concentration;while in the case of a high polymer concentration,the interchain complexation becomes dominant and apparent.At higher NaCl concentration, aggregation can be suppressed by the added NaCl.(2) The interaction between alginate and CB[6]was investigated.The interaction between polysaccharide alginate dilute solution and CB[6]has been investigated by Static Fluorescence Spectroscopy,DLS,Transmission Electron Microscopy(TEM), Circular Dichroism(CD) and Zeta Potential.Results showed that the interactions between alginate and CB[6]lead to the formation of micelle-like nanometer-sized aggregates due to electrostatic interaction and ion-dipole interaction.Micelle-like core-shell aggregates with physical cross-link segments as core and dissociated carboxyl in alginate as shell were obtained.In our experiment,when the concentration of sodium alginate was 0.05 wt%,the uniform micelle-like aggregates were achieved.DLS and TEM results both showed that isolated and clusters coexist in the blend solutions of CB[6]and alginate.Isolated micelle-like aggregates prevailed at low CB[6] concentration and clusters were predominant with increasing CB[6]concentration due to the decrease of charges at surface of micelle-like aggregates.A novel CB[6]mediated alginate physical hydrogel bead was prepared for the first time,which is based on the electrostatic attraction and ion-dipole interaction between concentrated sodium alginate solution and CB[6].These alginate/CB[6]gel beads are useful in controlled drug delivery and other biomedical applications.The rheological results show that the gel can be obtained at given CB[6]concentration.At lower CB[6]concentration,the gel is impossible.The process of the formation of alginate/CB[6]gel beads was recorded by Digital Cameras,which suggested that the process of gellation is controlled by the diffusion of CB[6].CB[6]diffused through outer thin film into the center of the beads. The structure and thermal stability of alginate/CB[6]gel beads were studied by FT-IR, X-Ray Powder Diffraction(XRD),and TGA.The results showed that alginate/CB[6] gel beads were formed through the interaction between CB[6]and G-G chains of alginate in the form of "egg-box".The potential of alginate/CB[6]gel beads as carrier for 5-Fluorouracil(5-Fu) was studied in this paper.It was found that the optimum alginate/CB[6]gel beads of drug loading is 5.94 wt%.(3) The interaction between sodium carboxymethylcellulose(CMC-Na) and CB[6] was investigated by Fluorescence Spectroscopy,DLS,TEM,and Zeta Potential.The results showed that the concentration of CMC-Na,the amount of CB[6],the added salt and pH values have effect on the aggregation of CMC-Na/CB[6]systems.Because it is impossible to form the structure of "egg-box" in CMC-Na/CB[6]system,the binding force between CMC-Na and CB[6]is smaller than the system of alginate/CB[6].The formation of nano aggregates between CMC-Na and CB[6]is slow in CMC-Na/CB[6] system.Irregular nano aggregates were obtained after a long time placement.The interaction between concentrated CMC-Na solution and CB[6]could not induce the formation of gel bead.In concentrated CMC-Na solution,floccule was separated out from CMC-Na/CB[6]system and visible with naked eyes after placement.(4) CB[6]can complex with butyl ammonium hydrochloride(BA) to form stable pseudorotaxane(CB[6]/BA).The interaction between CB[6]-based pseudorotaxane (CB[6]/BA) and O-carboxymethyl chitosan(O-CMCS) in aqueous solution was investigated by Steady-State Fluorescence,Resonance Light Scattering(RLS), Ultraviolet Absorption Spectra(UV) and DLS.The interaction between CB[6]/BA and O-CMCS depended on pH values,the concentration of CB[6]/BA and the added salt.In aqueous solution,when pH value was 2.32,the conformations of polymer chains expanded.In the mixtted solution of O-CMCS and CB[6]/BA at pH value of 7.05 and 8.35,CB[6]/BA act as "stickers" to interact with the O-CMCS chains.At low CB[6]/BA concentration,the intra-aggregate complexation was expected to be dominant, CB[6]/BA first undergo the intra-aggregate complexation through the -NH₂ or -NH₃⁺ and carboxylic groups,which might make the aggregates of O-CMCS form more compact structure.In the case of a high CB[6]/BA concentration,the inter-aggregate complexation became dominant and apparent.The inter-aggregate complex points result in the further aggregation of the O-CMCS chains,leading to larger clusters.In 0.1 mol/L NaC1 solution,Na⁺ may complex with bare carbonyl of CB[6]/BA by ion-dipole interaction,leading to the appearance of ⁺NH₃CB[6]/BANa⁺.⁺NH₃CB[6]/BANa⁺ tended to complex with two -COO^- to form(-COO^-)⁺NH₃CB[6]/BANa⁺(^-OOC-) complex point and formation of bridges.The interaction between -COO^- and ⁺NH₃CB[6]/BANa⁺ can lead to the distinct conformational change of polymer chains.In 0.1 mol/L NaCl solution,interaction between O-CMCS and CB[6]/BA was dominated by either the intra-aggregate or inter-aggregate complexation.At low CB[6]/BA concentration,the intra-aggregate complexation was expected to be apparent,while in the case of high CB[6]/BA concentration,the inter-aggregate complexation became dominant and apparent.The inter-aggregate complex points resulted in the further aggregation of the O-CMCS chains.The larger clusters were obtained.