Free radical scavenging activity of hydroxyflavone sodium salts compared to the activity of hydroxyflavones themselves

Different studies have demonstrated that the bioactivity of hydroxyflavones is due to their antioxidant and free radical scavenging activity. Recently, most interest has been devoted to structure-activity relationships; however, the main problems encountered in these studies are the low solubility of some hydroxyflavones in aqueous solution and the pro-oxidant character of the hydroxyl group at the 3 position. In the present investigation, these problems have been resolved by preparing the corresponding hydroxyflavone sodium salts. In this way, the hydroxyl free radical (OH)(center dot) scavenging activity of different hydroxyflavone salts were studied using the Fenton reaction model, and the superoxide (O-2)(center dot-) scavenging activity was studied using the xanthine oxidase model. The results obtained show clearly that the (OH)(center dot) scavenging activity of the hydroxyflavone salt form is at least two times that of the corresponding hydroxyflavone itself. Considering the (O-2)(center dot-) scavenging activity, the salt form of hydroxyflavone is as good as the corresponding hydroxyflavone. Moreover, it was observed that for a good scavenging activity the hydroxyl at the 3' position must be free, and only the hydroxyl groups of 3 and 4' have to be substituted by sodium when the sodium salt of hydroxyflavone at position 7 does not have an important role in radical scavenging. The salt forms of hydroxyflavones are interesting free radical scavenger compounds showing a hydrophilic character.