Radical dynamics of puerarin as revealed by laser flash photolysis and spin density analysis.
Puerarin, a C-glycoside of daidzein, forms upon direct photoexcitation in acetonitrile an excited-state with a lifetime of 4.2 micros assigned by oxygen quenching and sensitized formation of triplet zeaxanthin as a triplet and phenoxyl radicals of ms lifetime insensitive to oxygen and with spin density delocalized over the ACB isoflavonoid ring system, [ACB]*, as shown by laser flash photolysis and theoretical spin density calculations. Photoexcitation of A-ring 7-phenolate puerarin yields a [AC]* radical, which converts into the [ACB]* radical with a rate constant of 3.6 x 10(5) s(-1) in 5% methanolic acetonitrile in a process triggered by B-ring deprotonation (4'-phenol). For the 7-phenolate with the 4'-phenol derivatized to yield a propyl anisole, no rearrangement of the initially formed [AC]* radical was observed. With the A-ring phenol derivatized, the 7-propyl-4'-phenolate forms a radical with spin density delocalized over the CB ring system, [CB]*, together with a minor fraction of [ACB]* due to propyl radical dissociations confirmed by BDE-calculations. Dianionic puerarin forms initially the [ACB]* radical, which is converted into the [CB]* radical in a slower process (1.6 x 10(4) s(-1)) assigned to 7-methylation. The radical dynamics is discussed in relation to puerarin/carotenoid antioxidant synergism at water/lipid interphases.
Tian
Yu-Xi
YX
Beijing National Laboratory for Molecular Science, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China.
Han
Rui-Min
RM
Fu
Li-Min
LM
Zhang
Jian-Ping
JP
Skibsted
Leif H
LH
D004583:Electrons; D005609:Free Radicals; D006027:Glycosides; D007529:Isoflavones / Q000737:chemistry*; D007700:Kinetics; D007834:Lasers; D009005:Monosaccharides; D010782:Photolysis
C438934:C-glycoside; D005609:Free Radicals; D006027:Glycosides; D007529:Isoflavones; D009005:Monosaccharides; C033607:puerarin