PEGylated Nanoceria as Radical Scavenger with Tunable Redox Chemistry
Cerium oxide nanoparticles (CNPs) have shown tremendous potential in various applications such as water gas shift catalysis, chemical mechanical planarization (CMP), solid oxide fuel cells (SOFC), solar cells4 and high temperature oxidation protection coatings1. Recently, CNPs have been demonstrated to protect biological tissues against radiation induced damage, scavenging of superoxide anions, prevention of laser induced retinal damage, reduction of spinal injury in a tissue culture model, prevention of cardiovascular myopathy, pH dependent antioxidant properties, as a tool for immunoassays as well as other inflammatory diseases2. In most biomedical applications it is speculated that nanoceria is a regenerative radical scavenger with the ability to regenerate its active 3+ oxidation state for radical scavenging. Thus far there are no reports to control the regeneration of Ce3+ oxidation state which is the most important parameter in the application of CNPs as a reliable and regenerative radical scavenger. Thus, there is an imminent need to increase the potency of CNPs to achieve higher degree of protection against reactive oxygen species (ROS), to increase the residence time of CNPs in body and to control the regeneration of 3+ oxidation state. PEG has been reported to increase the residence time of nanoparticles and proteins inside cells and provide biocompatibility3. PEGylated counterparts of the SOD enzymes have shown improved performance over non-PEGylated enzymes. Herein, we report our efforts to synthesize CNPs directly in polyethylene glycol (mol wt 600) solution and determine the effect of increasing concentration of PEG (PEG vol % as 5, 10, 20, 40, 60 and 80) on the SOD mimetic properties exhibited by nanoceria. We also report how the active Ce3+ oxidation state can be regenerated or further tuned to regenerate at faster rate. We further demonstrate the role of PEG on the redox chemistry of CNPs catalyzed by hydrogen peroxide. Several complexes of PEGs with lanthanides have been reported and characterized4. To evaluate the effect of PEG concentration on the complexation of cerium, UV-Vis spectra of the precursor salt of cerium (cerium nitrate hexahydrate) in different solutions of PEG were obtained (SI-1). It was observed that all PEG solutions showed an increase in absorption relative to the water based solution of cerium nitrate but the observed non specific trend cannot be ascribed to a systematic decrease in the solvent polarity or dielectric constant. This observation is in contrast to Uekawa et al5 who reported a red shift upon addition of cerium nitrate in PEG however, they ruled out the charge transfer between Ce4+ and oxygen. The above observation confirms the complexation of PEG with cerium ions. The CNPs were then synthesized as described in the experimental details (SI-2). High resolution transmission electron micrograph (Figure 1a) demonstrates that PEG coats as an amorphous layer on CNPs as observed from an amorphous background behind the crystalline core. To confirm further CNPs synthesized in PEG were dialyzed using a 3500 MWCO cellulose membrane and the FTIR spectrum was collected from the isolated powder. Figure 1b confirms the presence of PEG on the nanoceria particles. To facilitate the explanation, only representative spectrum from 20% PEG solution is shown.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 970356
- Report Number(s):
- PNNL-SA-67404; JACSAT; 25688; KP1704020; TRN: US201003%%519
- Journal Information:
- Journal of the American Chemical Society, 131(40):14144-14145, Vol. 131, Issue 40; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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