Shashank Saraf, Sudipta Seal, Ankur Gupta, Rameech Mccormack, Michael D. Sevilla, Nicholas Eliason, Alex Petrovici, Soumen Das, Craig Neal, Julian Ortiz, Swetha Barkam, Amitava Adhikary, Cameron Hanson
In this work, we tested our hypothesis that surface chemistry and antioxidant properties of cerium nanoparticles (CNPs) are affected by the presence of counterions. We first employed various precursor cerium(III) (Ce(III)) salts with different counterions (acetate, nitrate, chloride, and sulfate) to synthesize CNPs following the same wet chemical methodology. Electron spin resonance (ESR) studies provided evidence for the formation of radicals from counterions (e.g., NO3•2– from reduction of NO3– in CNPs synthesized from Ce(III) nitrate). Physicochemical properties of these CNPs, e.g., dispersion stability, hydrodynamic size, signature surface chemistry, superoxide dismutase (SOD)-mimetic activity, and oxidation potentials, were found to be significantly affected by the anions of the precursor salts. CNPs synthesized from Ce(III) nitrate and Ce(III) chloride exhibited higher extent of SOD-mimetic activities. Therefore, these CNPs were studied extensively employing in situ ultraviolet (UV)–visible spectroelectrochemistry and changing the counterion concentrations affecting the oxidation potentials of these CNPs. Thus, the physicochemical and antioxidant properties of CNPs can be modulated by anions of the precursor. Furthermore, our ESR studies present evidence of the formation of guanine cation radical (G•+) in 5′-dGMP via UV-photoionization at 77 K in the presence of CNPs synthesized from Ce(III) nitrate and chloride, and CNPs act as the scavenger of radiation-produced electrons.