The antioxidant potential of modified quercetins and quercetin-metal complexes

Corinne M. Spickett, Agnieszka Wojton, Maria Kopacz, Barbara Oleksyn

Research output: Contribution to journalMeeting abstract

Abstract

Quercetin is a naturally occurring polyphenol compound present in grapes, red wine, tea, apples and some vegetables. Like other flavonoids, it has been found to have antioxidant activity in studies in vitro, although there is still much debate about the bioavailability of flavonoids in the diet and their in vivo antioxidant activity. In general, it is thought that the antioxidant efficiency of polyphenols increases with increasing hydroxylation of the rings, but there have been few studies of other substitutions. We have prepared several derivatives of quercetin, to test the effect of modification on their antioxidant potential. Sodium salts of quercetin-5-sulfonate and quercetin-5,8-sulfonate, and transition metal complexes of quercetin-5-sulfonate were analysed for their total antioxidant potential using the FRAP assay, and compared to unmodified quercetin. It was found that quercetin-5-sulfonate complexes with Zn, Cu(II), Fe(II) and Mg were all significantly better antioxidants than quercetin, quercetin-5-sulfonate was comparable to quercetin, whereas the sodium salt of quercetin-5,8-sulfonate had a decreased total antioxidant potential. Kinetic studies of the FRAP reaction showed no significant differences between quercitin and any of the derivatives. The reaction of all the quercetins in the FRAP assay was found to be slower to reach completion than ascorbate, and appeared to have biphasic
characteristics. These results suggest that transition metal ions may facilitate the transfer of electrons from the polyphenol ring system to the oxidant, while substitution with S03 is electron-withdrawing and destabilizes the ring system. This is important both for understanding the antioxidant ability of flavonoids, and for the design of novel antioxidant compounds. Further work is being carried out to assess the ability of the quercetin complexes to protect cultured cells from oxidative stress.
Original languageEnglish
Article number556
Pages (from-to)S209-S210
Number of pages2
JournalFree Radical Biology and Medicine
Volume33
Issue number2, Suppl.1
Early online date29 Jun 2002
DOIs
Publication statusPublished - 15 Jul 2002
Event11th Meeting of the Society for Free Radical Research International - Paris, France
Duration: 16 Jul 2002 → …

Fingerprint

Coordination Complexes
Quercetin
Antioxidants
Polyphenols
Flavonoids
Transition metals
Assays
Substitution reactions
Salts
Sodium
Electrons
Derivatives
Hydroxylation
Oxidative stress
Wine
Vitis
Vegetables
Malus
Tea
Nutrition

Keywords

  • antioxidant potential
  • modified quercetins
  • quercetin-metal complexes
  • Pharmacy and materia medica

Cite this

Spickett, Corinne M. ; Wojton, Agnieszka ; Kopacz, Maria ; Oleksyn, Barbara. / The antioxidant potential of modified quercetins and quercetin-metal complexes. In: Free Radical Biology and Medicine. 2002 ; Vol. 33, No. 2, Suppl.1. pp. S209-S210.
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The antioxidant potential of modified quercetins and quercetin-metal complexes. / Spickett, Corinne M.; Wojton, Agnieszka; Kopacz, Maria; Oleksyn, Barbara.

In: Free Radical Biology and Medicine, Vol. 33, No. 2, Suppl.1, 556, 15.07.2002, p. S209-S210.

Research output: Contribution to journalMeeting abstract

TY - JOUR

T1 - The antioxidant potential of modified quercetins and quercetin-metal complexes

AU - Spickett, Corinne M.

AU - Wojton, Agnieszka

AU - Kopacz, Maria

AU - Oleksyn, Barbara

PY - 2002/7/15

Y1 - 2002/7/15

N2 - Quercetin is a naturally occurring polyphenol compound present in grapes, red wine, tea, apples and some vegetables. Like other flavonoids, it has been found to have antioxidant activity in studies in vitro, although there is still much debate about the bioavailability of flavonoids in the diet and their in vivo antioxidant activity. In general, it is thought that the antioxidant efficiency of polyphenols increases with increasing hydroxylation of the rings, but there have been few studies of other substitutions. We have prepared several derivatives of quercetin, to test the effect of modification on their antioxidant potential. Sodium salts of quercetin-5-sulfonate and quercetin-5,8-sulfonate, and transition metal complexes of quercetin-5-sulfonate were analysed for their total antioxidant potential using the FRAP assay, and compared to unmodified quercetin. It was found that quercetin-5-sulfonate complexes with Zn, Cu(II), Fe(II) and Mg were all significantly better antioxidants than quercetin, quercetin-5-sulfonate was comparable to quercetin, whereas the sodium salt of quercetin-5,8-sulfonate had a decreased total antioxidant potential. Kinetic studies of the FRAP reaction showed no significant differences between quercitin and any of the derivatives. The reaction of all the quercetins in the FRAP assay was found to be slower to reach completion than ascorbate, and appeared to have biphasiccharacteristics. These results suggest that transition metal ions may facilitate the transfer of electrons from the polyphenol ring system to the oxidant, while substitution with S03 is electron-withdrawing and destabilizes the ring system. This is important both for understanding the antioxidant ability of flavonoids, and for the design of novel antioxidant compounds. Further work is being carried out to assess the ability of the quercetin complexes to protect cultured cells from oxidative stress.

AB - Quercetin is a naturally occurring polyphenol compound present in grapes, red wine, tea, apples and some vegetables. Like other flavonoids, it has been found to have antioxidant activity in studies in vitro, although there is still much debate about the bioavailability of flavonoids in the diet and their in vivo antioxidant activity. In general, it is thought that the antioxidant efficiency of polyphenols increases with increasing hydroxylation of the rings, but there have been few studies of other substitutions. We have prepared several derivatives of quercetin, to test the effect of modification on their antioxidant potential. Sodium salts of quercetin-5-sulfonate and quercetin-5,8-sulfonate, and transition metal complexes of quercetin-5-sulfonate were analysed for their total antioxidant potential using the FRAP assay, and compared to unmodified quercetin. It was found that quercetin-5-sulfonate complexes with Zn, Cu(II), Fe(II) and Mg were all significantly better antioxidants than quercetin, quercetin-5-sulfonate was comparable to quercetin, whereas the sodium salt of quercetin-5,8-sulfonate had a decreased total antioxidant potential. Kinetic studies of the FRAP reaction showed no significant differences between quercitin and any of the derivatives. The reaction of all the quercetins in the FRAP assay was found to be slower to reach completion than ascorbate, and appeared to have biphasiccharacteristics. These results suggest that transition metal ions may facilitate the transfer of electrons from the polyphenol ring system to the oxidant, while substitution with S03 is electron-withdrawing and destabilizes the ring system. This is important both for understanding the antioxidant ability of flavonoids, and for the design of novel antioxidant compounds. Further work is being carried out to assess the ability of the quercetin complexes to protect cultured cells from oxidative stress.

KW - antioxidant potential

KW - modified quercetins

KW - quercetin-metal complexes

KW - Pharmacy and materia medica

U2 - 10.1016/S0891-5849(02)00945-0

DO - 10.1016/S0891-5849(02)00945-0

M3 - Meeting abstract

VL - 33

SP - S209-S210

JO - Free Radical Biology and Medicine

JF - Free Radical Biology and Medicine

SN - 0891-5849

IS - 2, Suppl.1

M1 - 556

ER -