Kaempferol antioxidant activity

A catechol moiety in the B-ring is essential for a high antioxidant activity, whereas the presence of a pyrogallol moiety or a single OH group in the B-ring reduces the activity. The TEAC values were 4.72, 3.12, 2.55, and 1.34 mM for respectively quercetin, myricetin, morin, and kaempferol. 

The C2-C3 double bond enhances the activity by stabilization of the flavonoid aroxyl radical through electron delocalization across the molecule. Taxifolin (dihydroquercetin) had a TEAC value of 1.9 mM compared to 4.72 mM for quercetin. In the absence of a catechol moiety, the C2-C3 double bond has no significant influence on the antioxidant activity. The TEAC values of kaempferol (1.34 mM) and dihydrokaempferol (1.39 mM) were quite similar, because of the low hydrogen-donating capacity of a monophenolic B-ring. 

Antioxidant activity of flavonol derivatives kaempferol, quercetin, morin, myricetin, and rutin has been suggested to explain their anti-inflammatory, antiallergic, antiviral, as well as anticancer activities. It has been confirmed that quercetin, kaempferol, and apigenin (Fig. 4) can induce cellular antioxidant system by increasing intracellular glutathione levels [83]. 

Kaempferol and morin had antioxidative activity equal to myricetin, quercetin and fisetin in the presence of Cu ions, but were much less effective for Fe, V, or Cd ions (Sugihara et al. 1999). 

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