Cerium oxide nanoparticles (CNPs) are regarded as universal inorganic antioxidant that is capable of scavenging multiple reactive oxygen species (ROS) such as superoxide, peroxide, nitric oxide etc. This nanozyme like activity of cerium oxide has been employed in realizing multiple applications such as treatment of tumours and cancers, radiation protection and development of sensors. The oxidation state of cerium in CNPs play an important role in determining which ROS species can be scavenged. It has been established that partially reduced CNPs with higher Ce3+/Ce4+ ratio can scavenge superoxide and nitric oxide while stoichiometric CNPs with predominant Ce4+ can scavenge peroxide species. The redox potential for oxidation/reduction of surface cerium ions plays a major role in oxidation or reduction of ROS species. In this study we show that the fundamental redox potential of CNPs can be altered by modifying its surfaces with selected ligands. CNPs with different Ce3+/Ce4+ ratios were synthesized by wet chemical synthesis and thermal hydrolysis method. As synthesized particles were functionalized with triethyl phosphate (TEP) and tris(2,4,6-trimethoxyphenyl) phosphine (TTMPP) ligands to modify its redox properties. Functionalized CNPs were characterized using light scattering, electron microscopy, UV-Vis, IR and fluorescence spectroscopy to ascertain the changes in the properties of bare nanoparticles post functionalization with ligands. It was found that the ROS scavenging properties of both reduced and stoichiometric CNPs are influenced by surface functionalization with ligands. Modification of stoichiometric CNPs with TEP increases its ability to scavenge superoxide species while leaving the properties of reduced ceria unaltered. On the other hand TTMPP imparts peroxide scavenging ability to reduced CNPs and does not alter the peroxide scavenging activity of stoichiometric ceria. Thus we conclude that the ROS scavenging of CNPs can be tuned independent of the oxidation state by changing their redox potential. TEP and TTMPP ligands with their differences in sigma donor and pi acceptor properties can differentially influence the redox properties of nanozymes (CNPs).

Ligand mediated exchange of oxidation state dependent ROS scavenging activity of cerium oxide nanoparticles

256th National Meeting (2018)

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