Construction And Application Of Pegylated Supramolecular Systems

Supramolecular chemistry is a newly-developed subject based on intermolecular noncovalent interactions and aggregation, concerning self-assembly of molecules into supramolecular system with specific structure and function through weak interactions. It has now become a promising field in interdisciplinary subject of chemistry, materials and life science. Supramoleclar hosts, such as calixarenes, cyclodextrins (CDs) and branched macromolecules, etc., are one of the most important research aspects of supramolecular chemistry. Combination with polymers, they will be endowed with polymeric inherent characteristics such as amphiphility, stimuli-responsiveness and processibility, which realizes.the functionalization of these hosts and extends their applications. In this dissertation, based on the summary of previous researches on various polymer-modified supramolecular hosts, poly(ethylene glycol) (PEG) chain was introduced into hydrophobic calixarene and hyperbranched polyester, or hydrophilic cyclodextrin and hyperbranched polymer. By utilization of various noncovalent interactions such as coordination, host-guest interaction and electrostatic effects, different functional supramolecular systems were constructed. Finally, the applications of these functional supramolecular systems in nano-science and biomedicine were studied. The main results are shown as follows:1. PEGylated thiacalix[4]arene for the in-situ controlled preparation of gold nanoparticles (AuNPs)A facile controlled synthesis of AuNPs under mild conditions was developed. Firstly, a single hydrophilic PEG chain was grafted onto the phenolic group of p-tert-butyl thiacalix[4]arene for the formation of amphiphilic host. Benefiting from the phenolic groups and the sulfur linkages, PEGylated thiacalix[4]arene could be used as both reductant and stabilizer of AuNPs. We investigated the redox reaction and found the phenolic groups of host without PEG chain were oxidized to benzoquinone during the preparation of AuNPs. The size and morphology of AuNPs were characterizated by UV-Vis, DLS and TEM. By simply adjusting the feeding ratio of Au/S, AuNPs with different sizes could be readily obtained in an aqueous phase under mild conditions.2. Supramolecular polymeric micelles by the host-guest interaction of PEGylated calix[4]arene and chlorin e6 for photodynamic therapyA novel photosensitizer delivery system based on supramolecular amphiphilic carrers via host-guest interaction was carried out. Firstly, p-tert-butylcalix[4]arene was modified by removing of tert-butyl groups at the upper rims and grafting PEG chains onto phenolic groups at the lower rims. This star-like PEGylated calix[4]arene acted as a hydrophilic host and encapsulated hydrophobic guest, such as chlorine e6, then they self-assembled into micelles in aqeous solution. The equal molar ratio complexes were comfirmed by NMR titration. The size and morphology of supramolecular micelles were studied by TEM and DLS. Moreover, the cytotoxicity of photosensitizer, host and complexes was assayed by MTT in HeLa cancer cells. This photosensitizer delivery system showed very low cytotoxicity in the dark but high cytotoxicity under photo-irradiation. Thus, these supramolecular polymeric micelles can be ultilized as an efficient delivery system for photodynamic therapy.3. Hyperbranched polyrotaxanes for drug deliveryWe developed a novel supramolecular drug delivery system based on reduction-detachable hyperbranched polyrotaxanes (HPRs). HPRs were synthesized from Micheal addition polymerization of poly(ethylene glycol) diacrylate and cystamine in the presence of ?-CD. The structure of HPRs was characterized by NMR, FTIR and WXRD. The host-guest inclusion complexes were comfirmed by the existence of characteristic diffraction peak at 2θ=7.4o. Furthermore, the cytotoxicity of HPRs was assayed by MTT in NIH/3T3 cells. HPRs showed very low toxicity. The hydrophobic drug doxorubicin (DOX) could be encapsulated in the cavities of ?-CD in HPRs, and the drug-loaded efficiency reached 70%~80%. Moreover, the encapsulated drug could be released quickly in a reducing environment. The cellular uptake behaviors of DOX-loaded HPRs were investigated by flow cytometry (FCM) and confocal laser scanning microscopy (CLSM). The loaded DOX could enter into the nucleas in 15 minutes. The proliferation inhibition of Hela cells was evaluated by MTT assay.4. PEGylated hyperbranched polyester for pH-responsive drug delivery carrierWe synthesized a pH-responsive drug delivery carrier by one-step PEGylation of BoltornTM H40. The hydroxyl terminals of H40 could react with aldehyde group to form acetal linkages under InCl3 catalysis. Thus, unimolecular micelles were constructed by hydrophobic H40 core and hydrophilic PEG arms. As a pH-responsive material, the degradation rates of H40-star-PEG were inverstigated by NMR titration under neutral and acidic conditions. These amphiphilic micelles showed low toxicity when they were grafted to many PEG chains. The results were comfirmed by MTT in NIH/3T3 cells. The cell viability after treated with micelles for 24 h was up to 80% under the polymer concentration of 1 mg/mL. Critical micelle concentrations (CMC) of H40-star-PEG were measured by 1,6-diphenyl-1,3,5-hexatriene (DPH) probe. Furthermore, the size and morphology of micelles were studied by TEM. The cellular uptake behaviors of DOX-loaded micelles were investigated by FCM and CLSM. Finally, the proliferation inhibition of HeLa cells was evaluated by MTT assay. It demonstrates that H40-star-PEG is a smart and safe drug carrier.5. Cationic hyperbranched PEG for gene deliveryWe synthesized a low charge-density hyperbranched PEG (HA-PEGs) with different degree of branching by Micheal addition polymerization of poly(ethylene glycol) diacrylate and 2,2'-(ethylenedioxy)-bis(ethylamine). Then, the excess acrylate terminals were end-capped by diethylamine. The structure and properities of HA-PEGs were characterized by NMR, FTIR, DSC and SEC. As a biomaterial consisting of biocompatible PEG, its low cytotoxicity was confirmed by MTT assay in COS-7 cells. Moreover, as a polycation, we studied its DNA condensation ability by agarose gel electrophoresis (GE), atomic force microscope (AFM), and circular dichroism (CD). Since the low charge-density, DNA/HA-PEG complexes maintained a loose structure and the B-type conformation of plasmid DNA remained during the complexation. Suprisingly, HA-PEGs with low nitrogen content displayed high transfection efficiency in COS-7 cells.