No abstract

Cerium oxide nanoparticles (CNPs) have been demonstrated to protect biological tissues against radiation induced damage and scavenging of superoxide anions, prevent laser induced retinal damage, reduce spinal injury, possess pH dependent antioxidant properties, prevent cardiovascular myopathy, and as a tool for immunoassays and other inflammatory diseases.1a-j It is speculated that nanoceria is a regenerative radical scavenger with the ability to regenerate the active Ce 3+ oxidation state for radical scavenging which separates it from other nanomaterials based antioxidant systems such as hydroxylated and water-soluble C-60 and SWCNTs.1k, l Thus far there are no reports on controlling the regeneration of the Ce 3+ oxidation state which is the most important parameter in the application of CNPs as a reliable, regenerative radical scavenger. There is an imminent need to increase the residence time of CNPs in the body and to control the regeneration of the Ce 3+ oxidation state. PEG has been reported to increase the residence time of NPs and proteins inside cells and provide biocom-patibility.2 PEGylated counterparts of the Superoxide Dismutase (SOD) enzymes have shown improved performance over non-PEGylated enzymes. 2 Herein, we report our efforts to synthesize CNPs directly in PEG (600 MW) solution and determine the effect of increasing [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 Ce 3+ oxidation state can be regenerated and demonstrate the role of PEG on the redox chemistry of CNPs catalyzed by H 2 O 2 . Several complexes of PEGs with lanthanides have been reported and characterized.3 To evaluate the effect of [PEG] 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). All PEG solutions show higher absorption relative to the water based solution of cerium nitrate, but the observed nonspecific trend could not be ascribed to a systematic decrease in the solvent polarity or dielectric constant. This observation indicates the complexation of cerium ions with PEG. In contrast to this Uekawa et al.4a, b reported a red shift upon addition of cerium nitrate in PEG and ascribed the red shift to the complexation of PEG with cerium ions. The CNPs were synthesized as described in the experimental details (SI-2). A high resolution transmission electron micrograph (Figure 1a NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscriptdemonstrates that PEG is present as an amorphous layer on CNPs confirmed by an amorphous background around the crystalline CNPs. To confirm further, CNPs synthesized in PEG were dialyzed using a 3500 MWCO cellulose membrane and the FTIR spectrum was collected from the dried powder. Figure 1b confirms the presence of PEG on the nanoceria particles from FTIR of 20% PEG CNPs. Biocompatibility and SOD Mimetic Activity of CNPs in PEGCell viability analysis was performed for CNPs in PEG solution u...

No abstract

This review examines characterization challenges inherently associated with understanding nanomaterials and the roles surface and interface characterization methods can play in meeting some of the challenges. In parts of the research community, there is growing recognition that studies and published reports on the properties and behaviors of nanomaterials often have reported inadequate or incomplete characterization. As a consequence, the true value of the data in these reports is, at best, uncertain. With the increasing importance of nanomaterials in fundamental research and technological applications, it is desirable that researchers from the wide variety of disciplines involved recognize the nature of these often unexpected challenges associated with reproducible synthesis and characterization of nanomaterials, including the difficulties of maintaining desired materials properties during handling and processing due to their dynamic nature. It is equally valuable for researchers to understand how characterization approaches (surface and otherwise) can help to minimize synthesis surprises and to determine how (and how quickly) materials and properties change in different environments. Appropriate application of traditional surface sensitive analysis methods (including x-ray photoelectron and Auger electron spectroscopies, scanning probe microscopy, and secondary ion mass spectroscopy) can provide information that helps address several of the analysis needs. In many circumstances, extensions of traditional data analysis can provide considerably more information than normally obtained from the data collected. Less common or evolving methods with surface selectivity (e.g., some variations of nuclear magnetic resonance, sum frequency generation, and low and medium energy ion scattering) can provide information about surfaces or interfaces in working environments ( or ) or information not provided by more traditional methods. Although these methods may require instrumentation or expertise not generally available, they can be particularly useful in addressing specific questions, and examples of their use in nanomaterial research are presented.