Structure-antioxidant capacity relationship of dihydrochalcone compounds in Malus.

The antioxidant capacity (AC) of six dihydrochalcone compounds was evaluated using DPPH and ABTS assays. In water-based solution 3-hydroxyphlorizin exhibited the highest AC among all dihydrochalcones. In acetone and acidic solutions (pH = 2.5 or 2.0), presence of an o-dihydroxyl at the B-ring increased AC, whereas glycosylation at the A-ring decreased AC of dihydrochalcones. By comparing the AC of dihydrochalcones with similar structures, it was found that the o-dihydroxyl at the B-ring and 2'-hydroxyl group at the A-ring were critical for maintaining the AC of dihydrochalcones by promoting hydrogen atom transfer or single electron transfer mechanism. Sequential proton-loss electron transfer commonly occurred during free radical scavenging in water-based solution. Moreover, we report a unique phenomenon in which glycosylation at the 2'-position enhanced the dissociation ability of the 4'-hydroxyl group and increased the AC of dihydrochalcones containing o-dihydroxyl. We speculate that this increase in AC might occur through intramolecular electron transfer.