Flavonoid B-ring chemistry and antioxidant activity: Fast reaction kinetics

Rapid scavenging of the model stable radical cation, ABTS(.+) has been appl ied to screen for the antioxidant activity of flavonoids, The reaction foll ows two distinct phases. For compounds with a monophenolic B-ring there is a rapid initial phase of reduction of ABTS(.+) within 0.1 s with no further change in the subsequent 2.9 s, In contrast, compounds with a catechol-con taining B ring follow a fast initial scavenging phase with a slow secondary phase. Flavonoids with an unsubstituted B ring do not react within this ti me scale. The findings suggest that the structure of the B ring is the prim ary determinant of the antioxidant activity of flavonoids when studied thro ugh fast reaction kinetics. (C) 2001 Academic Press.