Synthesis and Solution Properties of Water-soluble Fullerene Polymeric Systems
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Water-soluble fullerene containing polymers comprising of poly(2-(dimethylamino) ethyl methacrylate)-fullerene (PDMAEMA-C60) with targeting moieties, poly(oligo(ethylene glycol) methyl ether methacrylate)-C60 (POEGMA-C60), nanocrystalline cellulose-fullerene (NCC-C60) and NCC-C60-POEGMA were synthesized and their solution properties were investigated. PDMAEMA-C60 with galactose targeting moiety was prepared by atom transfer radical polymerization (ATRP) and atom transfer radical addition (ATRA) processes. The self-assembly of galactose functionalized PDMAEMA-C60 structure in aqueous solutions was investigated using dynamic light scattering (DLS) at different pHs. A smaller hydrodynamic radius (Rh) was observed at pH 10 than at pH 3 due to electrostatic repulsion at low pH values. In addition, free PDMAEMA chains induced the demicellization of self-assembled nanostructures caused by the formation of charge transfer complex between PDMAEMA and C60. A well-defined poly(di(ethylene glycol) methyl ether methacrylate–stat-oligo(ethylene glycol) methyl ether methacrylate)-block-poly(di(ethylene glycol) methyl ether methacrylate ((PMEO2MA-stat-POEGMA300)-b-PMEO2) was successfully synthesized at room temperature via a two-step ATRP process. The block copolymer exhibited two thermal transitions at ~ 30 and 45 oC, which was believed to be associated with the formation of micelles and larger aggregates. The Rh of the aggregates increased from 47 to 90 nm, the aggregation number increased from 76 to ~9800 and Rg/Rh increased from 0.75 to 1.2 within the temperature range of 34 to 45oC. Well-defined statistical (PMEO2MA-stat-POEGMA300)-C60 was synthesized via ATRP and ATRA. The lower critical solution temperature (LCST) of (PMEO2MA-stat-POEGMA300)-C60 increased with methanol content in water, exhibiting lower LCSTs than PMEO2MA-stat-POEGMA300 for all methanol/water compositions. Higher critical micelle concentration (CMC) and larger spherical micelles were observed for (PMEO2MA-stat-POEGMA300)-C60 with increasing methanol content. The Rh of the micelles remained constant at temperature below the LCST and increased dramatically at temperature greater than the LCST, and (Rg/Rh) increased from ~ 0.75 to ~ 1.0. Nanocrystalline cellulose (NCC) was modified with water-soluble C60-(β-cyclodextrin) and (PMEO2MA-stat-POEGMA300)-C60) through a radical coupling reaction. NCC-C60-(PMEO2MA-stat-POEGMA300) possessed thermal responsive behavior in water and ~3.5 oC hysteresis associated with the heating/cooling cycles. No observable damage to NCC occurred during the radical coupling reaction as determined by TEM. NCC-C60-(β-cyclodextrin) possessed a similar thermal degradation behavior as NCC except it possessed a broader temperature range. Both NCC-fullerene systems demonstrated a radical scavenging activity when screened with the 2,2-diphenyl-1-picrylhydrazyl (DPPH). In addition, the drug loading and delivery using PDMAEMA-C60 with targeting moieties was explored. Two model drugs, namely fluorescein and pyrene were employed to evaluate the location of drug in the self-assembled structure of PDMAEMA-C60. It was found that the hydrophobic drugs were partitioned between the PDMAEMA shells and the hydrophobic fullerene cores. The drug delivery profiles indicated that PDMAEMA-C60 is an efficient drug carrier, however, it was cytotoxic to cells. The gene transfection efficacy of PDMAEMA-C60 to different cell lines was investigated and the results demonstrated that PDMAEMA-C60 exhibited good gene transfection performance. However, the targeting selectivity to liver cells cannot be determined in both cases. This study demonstrates that nanostructures of stimuli-responsive fullerene polymers can be controlled and manipulated by changing the external environments. Several potential applications, such as in drug and gene delivery, and free radical scavenging can be further explored.