Phenol acidity and ease of oxidation in isoflavonoid/ß-carotene antioxidant synergism

TY - JOUR

T1 - Phenol acidity and ease of oxidation in isoflavonoid/ß-carotene antioxidant synergism

AU - Han, Rui-Min

AU - Li, Dan-Dan

AU - Chen, Chang-Hui

AU - Liang, Ran

AU - Tian, Yu-Xi

AU - Zhang, Jian-Ping

AU - Skibsted, Leif Horsfelt

PY - 2011/9/28

Y1 - 2011/9/28

N2 - Regeneration of β-carotene from the β-carotene radical cation by the 4′-propylpuerarin anion (second-order rate constant = 1.5 × 10 9 L mol -1 s -1 in methanol/chloroform = 1:9 (v/v) solution at 25 °C as determined by laser flash photolysis) was found to be marginally slower than regeneration by the 7-propylpuerarin anion (2.3 × 10 9 L mol -1 s -1), in agreement with the 7-propylpuerarin anion being more reducing (E′ = 0.56 V vs NHE) than the 4′-propylpuerarin anion (E′ = 1.01 V vs NHE). The potentials were calculated from E° = 1.12 and 1.44 V (vs NHE) as determined by cyclic voltametry in aqueous solution and pK a = 9.51 and 7.23 obtained previously for 7-propylpuerarin and 4′-propylpuerarin, respectively. The less reducing but more acidic 4′-propylpuerarin showed less antioxidant activity in liposome of pH 7.4, but more significant antioxidant synergism with β-carotene than the more reducing but less acidic 7-propylpuerarin for oxidation initiated in the liposome lipid phase. Electrostatic effects are concluded to be important in the regeneration of β-carotene from the radical cation in the water/lipid interface because approximately 50% of 4′-propylpuerarin is present as the anion, whereas only 0.5% of 7-propylpuerarin is present as the anion. In contrast, penetration of the undissociated phenolic group into the lipid phase, more significant for 7-propylpuerarin than for 4′-propylpuerarin according to the calculated water/lipid partition coefficients, becomes important for the chain-breaking action in lipid oxidation of the puerarin derivatives as models for (iso)flavonoids and their glycosides.

AB - Regeneration of β-carotene from the β-carotene radical cation by the 4′-propylpuerarin anion (second-order rate constant = 1.5 × 10 9 L mol -1 s -1 in methanol/chloroform = 1:9 (v/v) solution at 25 °C as determined by laser flash photolysis) was found to be marginally slower than regeneration by the 7-propylpuerarin anion (2.3 × 10 9 L mol -1 s -1), in agreement with the 7-propylpuerarin anion being more reducing (E′ = 0.56 V vs NHE) than the 4′-propylpuerarin anion (E′ = 1.01 V vs NHE). The potentials were calculated from E° = 1.12 and 1.44 V (vs NHE) as determined by cyclic voltametry in aqueous solution and pK a = 9.51 and 7.23 obtained previously for 7-propylpuerarin and 4′-propylpuerarin, respectively. The less reducing but more acidic 4′-propylpuerarin showed less antioxidant activity in liposome of pH 7.4, but more significant antioxidant synergism with β-carotene than the more reducing but less acidic 7-propylpuerarin for oxidation initiated in the liposome lipid phase. Electrostatic effects are concluded to be important in the regeneration of β-carotene from the radical cation in the water/lipid interface because approximately 50% of 4′-propylpuerarin is present as the anion, whereas only 0.5% of 7-propylpuerarin is present as the anion. In contrast, penetration of the undissociated phenolic group into the lipid phase, more significant for 7-propylpuerarin than for 4′-propylpuerarin according to the calculated water/lipid partition coefficients, becomes important for the chain-breaking action in lipid oxidation of the puerarin derivatives as models for (iso)flavonoids and their glycosides.

U2 - 10.1021/jf202683n

DO - 10.1021/jf202683n

M3 - Journal article

SN - 0021-8561

VL - 59

SP - 10367

EP - 10372

JO - Journal of Agricultural and Food Chemistry

JF - Journal of Agricultural and Food Chemistry

IS - 18

ER -