The effect of an antioxidant depends on (i) the reaction rate between the radical and the antioxidant and (ii) the number of radicals that can be scavenged by the antioxidant (i.e. the capacity). The importance of the reaction rate relative to that of the capacity is expected to depend on the conditions. To elaborate on this, we compared the activity of Trolox and a Trolox dendrimer containing 8 Trolox moieties in one molecule, in several assays.

In the ABTS radical scavenging assay, that gives the number of ABTS radicals scavenged, the capacity of the Trolox dendrimer was 8 times as high as that of Trolox. This indicates that linking Trolox in the dendrimer does affect the capacity of Trolox, and that the ABTS assay indeed gives the capacity of the molecules. 

In the peroxynitrite scavenging assay, the Trolox dendrimer was approximately equally active as Trolox. This indicates that here the rate of the molecule to scavenge the peroxynitrite generated radicals is involved.

The activity of the dendrimer in the protection of AAPH induced hemolysis of red blood cells was approximately 8 times as high as that of Trolox. This indicates that in this more ‘physiological’ assay, the capacity of the antioxidant is the predominant factor.

These results show that the importance of the reaction relative to the capacity depends on the condition. In ‘open’ dynamic living systems, where energy originating from e.g. consumed food can be used to efficiently recycle antioxidants, it is expected that the reaction rate is the predominant factor. Nevertheless, our result obtained in the red blood hemolysis experiment indicate that the capacity might here also be relevant. The relevance of the capacity will be relatively high in ‘closed’ systems, such as processed food.