Supramolecular Self-assembly Of C₆₀ Derivative And The Study On Bioactivity

Fullerene, as the third carbon allotrope, has attracted increasing attention because of its exciting physical and chemical properties, which endow fullerene-containing materials with broad and promising applications in superconductor, ferromagnet, lubrication, photoconductor, catalysts, and molecular medicines. C60, the most representative member of the fullerene family, has been studied in various fields of biomedicine for its unique properties. As a"free radical sponge", C60 has been demonstrated excellent ability to quench various free radicals more efficiently than conventional antioxidants. Furthermore, many fullerene-based compounds prepared artificially have shown potential practical value, for instance, reduction of injury on ischemic reperfusion of the intestine, a decrease in number of cells undergoing apoptosis, reduction in free radical levels in organ perfusate, and neurprotective effects. Though, in recent years, people are having much more interest in studying potential bioactive water-soluble fullerene derivatives emphasizing on their capacity to quench free radicals, the extreme hydrophobicity is a serious barricade for the broad prospects on bio-medical research and application. Therefore, a mass of representative works focus on functionalizing fullerene with negatively charged carboxylic, positively charged quaternary ammolonium, and non-charged functional group as ethylene glycol groups and polymers, etc. to enhance the water solubility of fullerenes. Another approach to overcome the insolubility is to encapsulate the respective monomer species in supramolecular structure with host moiety, such as cyclodextrin, surfactants, gels, or polymers, etc. Besides those approaches, fullerene can be stabilized in water as nano-scale colloidal assemblies through routes. For example, nanoscale colloid of C60 can be formed in the following steps. Firstly, dissolve C60 in water-miscible polar organic solvents such as tetrahydrofuran (THF) and mix with water, subsequently remove the transfer solvent via distillation or dialysis. However, the first two avenues seemed to be more promising in application of fullerene in biomaterial field.For the extreme hydrophobicity of C60, most of water-soluble derivatives of C60 are amphiphilic, while amphiphilic molecular organization is one of the widely used methods in supramolecular chemistry to construct nano-architectures. This method uses the balanced hydrophilic-hydrophobic structural motifs to give rise to micells, bilayers and further vesiclar structures, and its advantage makes it possible to solubilize the extremely hydrophobic C60 in polar media and to utilize the propensity of amphiphilic fullernenes to form prominent assemblies.1. Supramolecular complex of C60 derivative with ability of thermo-responseWe applied thermo-responsive copolymer consisting of host sites, which could recognize guest molecules, to conjugate insoluble derivative of C60 in contrast to conventional water-soluble C60, for the purpose of realizing its solubility. The fabrication of thermo-responsive assemblies was based on the complex consisting of thermo-responsive polymer and derivative of fullerene with adamantyl moiety. The complex can self-assemble to vesicles for its amphiphilic structure.It is noteworthy that the morphology of assemblies could be tuned reversibly from vesicles to nano-spheres when temperature changed. Furthermore, the assemblies have an excellent ability to scavenge hydroxyl radicals of biological system due to the introduction of the derivative of fullerene into the complex, and the scavenging efficiency could be obviously influenced by the change of temperature owing to the thermo-responsive property of the supramolecualr complex.2. Self-assambly of amphiphilic C60 derivativeLots of fullerene derivatives can self-assemble as some morphology in aqueous, because the all-carbon fullerene is completely hydrophobic and hydrphobicity can be the force to form assemblies. Tetra-Ad-C60, as a derivative of C60 that we synthetized, can self-assemble in aqueous for the ethylene glycol group which is hydrophilic. It was proved that tetra-Ad-C60 can self-assemble as vesicle in the method of DLS, SEM and TEM.. Furthermore, the vesicles can assemble as higher degree assemblies in the case of the presence of bridged cyclodextrin.3. Supramolecular derivative of C60 with GPx activityBeacuase cyclodextrin is easy to be derivated and many functional groups can be linked on it, we synthetized a derivative of cyclodextrin with GPx active site to construct supramolecules with C60 derivative. The complex we constructed can quench hydroxyl radicals efficiently for the fullerene moiety, and it can protect mitochondria from oxidative damage. Furthermore, the complex as a model of enzyme showed a high GPx activity and a remarkable rate enhancement of 24-fold compared to the well-known GPx mimic ebselen was observed. Compared with other bifunctional enzyme mimics, this supramolecular artificial enzyme has its obvious advantage: simple preparation process and remarkable catalytic activity.