Screening protocol for identifying inorganic oxides with anti-oxidant and pro-oxidant activity for biomedical, environmental and food preservation applications

Free radicals are known to play a key role in the human body. When considering potential biomaterials, their interaction with free radicals needs to be considered at an early exploratory stage. In this contribution, we identify inorganic oxides that exhibit a free radical scavenging capacity. A convenient screening protocol was developed for identifying the anti-oxidant properties of highly dispersed inorganic materials. The method compares the degradation of an organic dye with radicals in the absence and presence of the material under investigation. The radicals are generated via Fenton chemistry over a heterogeneous goethite catalyst in a phosphate buffer. The procedure conveniently evaluates the anti- or pro-oxidant capacity of a large set of materials with routine laboratory equipment. Semi-quantitative EPR measurements of the radical concentration using a spin-trapping agent were used to validate the screening procedure. Besides the documented cerium oxide, four other materials were identified to exhibit comparable or even better anti-oxidant activity: aluminium titanate, antimony oxide, titanium silicalite-1 zeolite and titanium xonotlite; pro-oxidant activity was demonstrated for several zeolites.