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...

Hydrogen atoms cannot hide from x-rays anymore but can instead be detected very reliably in routine measurements.

Articles you may be interested inHydrogen bond spectroscopy in the near infrared: Outofplane torsion and antigeared bend combination bands in (HF)2High resolution UV spectroscopy of phenol and the hydrogen bonded phenolwater cluster Dynamics of hydrogenbonded liquids confined to mesopores: A dielectric and neutron spectroscopy study Important progressive alterations in chemical bonding are often realized through correlations with shifts in the x-ray photoelectron spectroscopy ͑XPS͒ binding energies of key elements. For example, there are useful general XPS shifting schemes for such systems as oxides, nitrides, halides, and even various functional groups in organics. Very general patterns, based upon location in the periodic table, exist for many of these materials even when the structure is not strongly considered. Unfortunately, apparently because of the lack of direct XPS detection of hydrogen, there seems to be no general statements in the literature for describing hydrogen-containing compounds, despite the fact that synergistic shifts obviously exist in the XPS spectra of elements attached to hydrogen ͑e.g., for M-O-H vs M-O-M units, where M is a typical metal͒. While not attempting a complete review paper, in the present work we use XPS shifting patterns to evolve a series of interrelated covalency/ionicity arguments to help explain the progressive, periodic changes in XPS peak locations for such common cases as M-O-H-and M-N-H-containing systems. These arguments are followed by consideration of the less dramatic XPS shifting patterns exhibited by metal and metalloid hydrides, including organic bonding. The formalism concludes with a discussion of hydrogen bonding detected by XPS. After a select review of the infrequent use made by others to attribute XPS peak shifts to hydrogen bonding, we consider in some detail two cases recently published by members of our group. One case involves the formation of -N-H-N-bonds in proton sponge organic systems, while the other uses XPS to examine the formation of surface oriented -O-H---O-bonds in the adsorption of peptides on oxidized metals. In the present article, the XPS patterns for these two seemingly divergent cases are explained by closely related arguments that may have far reaching generalities.

Experimental charge density distributions in a series of ionic complexes of 1,8-bis(dimethylamino)naphthalene (DMAN) with four different acids: 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), 4,5-dichlorophthalic acid, dicyanoimidazole, and o-benzoic sulfimide dihydrate (saccharin) have been analyzed. Variation of charge density properties and derived local energy densities are investigated, over all inter- and intramolecular interactions present in altogether five complexes of DMAN. All the interactions studied [[O...H...O](-), C[bond]H...O, [N[bond]H...N](+), O[bond]H...O, C[bond]H...N, C pi...N pi, C pi...C pi, C[bond]H...Cl, N[bond]H(+)] follow exponential dependences of the electron density, local kinetic and potential energies at the bond critical points on the length of the interaction line. The local potential energy density at the bond critical points has a near-linear relationship to the electron density. There is also a Morse-like dependence of the laplacian of rho on the length of interaction line, which allows a differentiation of ionic and covalent bond characters. The strength of the interactions studied varies systematically with the relative penetration of the critical points into the van der Waals spheres of the donor and acceptor atoms, as well as on the interpenetration of the van der Waals spheres themselves. The strong, charge supported hydrogen bond in the DMANH(+) cation in each complex has a multicenter character involving a [[Me(2)N[bond]H....NMe(2)](+)....X(delta-)] assembly, where X is the nearest electronegative atom in the crystal lattice.