Pulse radiolysis was conducted to investigate: several fundamental reactions of a natural flavonoid, rutin, and its glycosylated form (αG-rutin) as a basis for their radiation protection properties; the reactions with •OH (radical scavenging) and dGMP radical, dGMP• (chemical repair), which was used as a model of initial and not yet stabilised damage on DNA. Three absorption peaks were commonly seen in the reactions of the flavonoids with •OH, showing that their reactive site is the common structure, i.e. aglycone. One among the three peaks was attributed to the flavonoid radical produced as a result of the removal of a hydrogen atom. The same peak was found in their reactions with dGMP•, showing that dGMP• is chemically repaired by obtaining a hydrogen atom supplied from the flavonoids. Such a spectral change due to the chemical repair was as clear as never reported. The rate constants of the chemical repair reaction were estimated as (9 ± 2)×108 M-1 s-1 and (6 ± 1)×108 M-1 s-1 for rutin and αG-rutin, respectively. The rate constants of the radical scavenging reactions towards •OH were estimated as (1.3 ± 0.3)×1010 M-1 s-1 and (1.0 ± 0.1)×1010 M-1 s-1 for rutin and αG-rutin, respectively. In addition, there was no obvious difference between rutin and αG-rutin, indicating that the glycosylation does not change early chemical reactions of rutin.
Keywords: Chemical repair; flavonoid; pulse radiolysis; radiation protection; radical scavenging; rutin.