Oxide Nanocrystals with Variable Valence Ions for Hydroxyl Radical Neutralization

Cellular respiration in living cells generates biologically active molecules known as reactive oxygen species (ROS). Among these ROS, superoxide anions, hydrogen peroxide, and hydroxyl radicals are produced within mitochondria and play pivotal roles in cellular metabolism. However, an elevation in hydroxyl radical (.OH) levels, the most potent oxidants among ROS, can instigate various pathological processes within cells, ranging from heightened lipid peroxidation of cell membranes to DNA damage. Hydroxyl radicals are generated through water radiolysis during X-ray or gamma irradiation of cells. Their extremely high reactivity, coupled with an average lifespan of only a few nanoseconds in a biological environment, poses a considerable challenge for the cell's internal defense mechanisms in effectively neutralizing them. In response, we propose the utilization of three distinct types of oxide nanocrystals—containing variable valence ions (CeO
2
, TiO
2
, and GdVO
4
)—as promising materials for the efficient neutralization of hydroxyl radicals. These nanocrystals, CeO
2
, TiO
2
, and GdVO
4
, exhibit remarkable capabilities in scavenging hydroxyl radicals generated in water solutions during X-ray irradiation. Their hydroxyl radical-neutralizing properties are intricately linked to the high concentration of reduced variable valence ions (such as Ce
³⁺
in CeO
2
, Ti
³⁺
in TiO
2
, and V4
⁺
/V3
⁺
in GdVO
4
), which possess the ability to donate electrons during hydroxyl radical neutralization reactions. Small oxide nanocrystals, characterized by the presence of structural imperfections like oxygen vacancies, enable the reduction of neighboring variable valence ions, as validated by XPS experiments for all three types (CeO
2
, TiO
2
, and GdVO
4
). The proficiency of these small oxide nanocrystals containing variable valence ions (CeO
2
, TiO
2
, and GdVO
4
) in efficiently neutralizing hydroxyl radicals in aqueous solutions highlights their potential as effective antioxidants and radioprotectors within living cells. This promising avenue opens new possibilities for cellular defense and therapeutic applications.