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Studies on Hollow Nanospheres, Micells and Dendrimers Based on Supramolecular Self-assembly

Author: HaWei
Tutor: Tian; LiBangJing
School: Lanzhou University
Course: Organic Chemistry
Keywords: Host-Guest Inclusion Supramolecular Self-assembly Natural Polysaccharide Cyclodextrins Rod-Coil Part Hollow Spheres Amphipatic Micell Drug Delivery and Release Dendrimer
CLC: O621.3
Type: PhD thesis
Year: 2011
Downloads: 132
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Abstract


Novel hollow nanospheres, amphipatic micelles and dendrimer were constructed and successfully applied in enzyme immobilization, microreactor and drug deleviery area. These systems all constructed via supramolecular self-assembly which based on the inclusion complexion between cycodextrins and various gurest molecules and some natural polysaccharides.Chapter 1:Macromolecular Self-assembly via Host-Guest InclusionRencent progress in macromolecular self-assembly based on host-guest inclusion have been reviewed according to various intereactions in host-guest inclusion process, which include metal-dipole intereactions, hydrogen bond, vander Waals interactions, hydrophilicity or hydrophobicity intereactions andπ-πintereactions. In addition, some novel host molecules and guest molecules were discussed according to various mechansim of action and their potential applications of the resultant assemblies.Chapter 2:Self-assembly Hollow Nanosphere for Enzyme Encapsulation and Selective Membrane Permeability Properties of Self-assembly Hollow NanospheresThis chapter describes a kind of hollow nanosphere prepared by self-assembly of rod-coil complexes, in which the rod-like segments were formed by inclusion a-cyclodextrins (a-CDs) and poly(ethylene glycol) (PEG) chains grafted on alginate-graft-PEG (Alg-g-PEG). The Alg-g-PEG/a-CD hollow spheres were extended to investigate the encapsulation behavior of enzyme. It was found that the hollow spheres not only enable a high loading of enzyme, but also show semi-permeability which could prevent the enzyme from leaving while allowing substrates and products to pass through. Although protected in hollow spheres, the encapsulated enzyme can still exert its activity and the affinity between the substrate and encapsulated enzyme was lightly increased. Furthermore, the encapsulation of L-asparaginase widened the optimum reactive temperature and pH range of the enzyme, and the encapsulated L-asparaginase showed significantly higher stability in an acidic environment as compared to the native enzyme. The permeability properties of Alg-g-PEG/a-CD hollow nanospheres were investigated by encapsulating different probes. Results showed that the molar mass cutoff (MMCO) of these hollow nanospheres was between 20 and 40 kDa. The encapsulation capability of Alg-g-PEG/a-CD hollow nanospheres was also investigated, the results indicated a maximal values for L-asparaginase encapsulation is 4 mg per 4 mL Alg-g-PEG/a-CD (0.25%/6%) solution. Furthermore, the encapsulation behavior for L-asparaginase showed PEG graft density (GD) dependence.Chapter 3:Self-aggregates of Cholesterol-modified Carboxymethyl Konjac Glucomannan Conjugate:Preparation, Characterization, and Preliminary Assessment as a Carrier of EtoposideIn this chapter, various cholesterol (CH) bearing carboxymethyl konjac glucomannan (CKGM) amphiphilic conjugates (denoted CHCKGM) were synthesized using CKGM and CH as hydrophilic and hydrophobic segments. Structural characteristics of these CHCKGM conjugates were investigated using FTIR,1H NMR and thermogravimetric analysis (TGA). The properties of these self-aggregates were analysed by dynamic laser light-scattering (DLS), zeta potential, transmission electron microscopy (TEM) and the fluorescence probe technologies. The critical aggregation concentration (cac) of CHCKGM conjugates (2.59×0-3-5.89×10-3 mg/ml) was comparatively low, suggesting that the cholesterol fragment was very effective for forming aggregates. Etoposide was physically entrapped into the CHCKGM nanoparticles by sonication method. The in vitro release behavior of etoposide from CHCKGM nanoparticles revealed a sustained release property. Furthermore, these self-aggregated nanoparticles showed pH-and ionic strength-dependent properties which caused a considerable change in their radius.Chapter 4:Self-assembled Hollow Spheres Based on Chitosan and the Preliminary Application as a Protein CarrierIn this chapter we present a convenient approach to construct hollow spheres with chiostan as the backbone. The strategy for fabrication based on the self-assembly of rod-coil complexes, in which the rod-like segments were formed by inclusion a-cyclodextrins (a-CDs) and poly(ethylene glycol) (PEG) chains grafted on chiostan-graft-PEG(CS-g-PEG). The hollow sphere indicates great promise in the area of protein delivery systems. Those self-aggregated hollow spheres showed pH-dependent properties. This pH-switchable control of the polyelectrolyte envelopes can be used to trigger the release of encapsulated drugs. To further investigate the potential of CS-g-PEG/a-CD hollow spheres in bionic area, the CFoFl-ATPase was isolated, purified successfully from spinach leaves. The reconstitution of CFoFl-ATPase onto membrane of the hollow spheres to functionalize the enzyme is in progress.Chapter 5:Dendrimers Based on Host-Guest ChemistryThe inclusion between cyclodextrins and different guest molecules are designed to construct dendrimers in place of traditional covalent bond. The surface functional groups, tailored sanctuary and dendrimer core are all constructed by host-guest inclusion in this dendrimer. Obviously, this method is simple, straightforward and have great advantages compared to traditional dendrimer. Now, the work of self-assembly between each unit was in progress.

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