C. Tournaire et al., ANTIOXIDANT ACTIVITY OF FLAVONOIDS - EFFICIENCY OF SINGLET OXYGEN (1(DELTA)G) QUENCHING, Journal of photochemistry and photobiology.B, Biology, 19(3), 1993, pp. 205-215
Flavonoids, polyphenolic pigments widely present in plants, have been
reported to act as scavengers of various oxidizing species. However, m
ost often an overall antioxidant effect was measured. In this paper we
report the results of a systematic study of the reactivity of 13 sele
cted flavonoids (from the flavonol, flavone, flavanone and flavane fam
ilies) with singlet oxygen (O-1(2)(1DELTA(g))) in order to establish a
structure-activity relationship. The rate constants of the chemical r
eaction of these flavonoids with O-1(2)(k(r)) and their rate constants
Of O-1(2) physical quenching (k(q)) have been determined by kinetic m
easurements and neaT-IR singlet oxygen luminescence. The efficiency of
the physical quenching is mainly controlled by the presence of a cate
chol moiety on Ting B, whereas the structure of ring C (particularly t
he presence of a hydroxyl group activating the double bond) is the mai
n factor determining the efficiency of the chemical reactivity of thes
e compounds with O-1(2). The total reactivity scale is dominated by k(
q), which is in general higher than k(r). (+)-Catechin is the most eff
icient quencher of the series.