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Molecules 2018, 23(3), 694; https://doi.org/10.3390/molecules23030694

π-π Conjugation Enhances Oligostilbene’s Antioxidant Capacity: Evidence from α-Viniferin and Caraphenol A

1,2,†,* , 1,2,†
,
1,2
,
1
and
3,4,*
1
School of Chinese Herbal Medicine, Guangzhou University of Chinese Medicine, Waihuan East Road No. 232, Guangzhou Higher Education Mega Center, Guangzhou 510006, China
2
Innovative Research & Development Laboratory of TCM, Guangzhou University of Chinese Medicine, Waihuan East Road No. 232, Guangzhou Higher Education Mega Center, Guangzhou 510006, China
3
School of Basic Medical Science, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
4
The Research Center of Basic Integrative Medicine, Guangzhou University of Chinese Medicine, Waihuan East Road No. 232, Guangzhou Higher Education Mega Center, Guangzhou 510006, China
These authors contributed equally to this work.
*
Authors to whom correspondence should be addressed.
Received: 9 February 2018 / Revised: 15 March 2018 / Accepted: 18 March 2018 / Published: 19 March 2018
(This article belongs to the Special Issue The Antioxidant Capacities of Natural Products)
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Abstract

α-Viniferin and caraphenol A, the two oligostilbenes, have the sole difference of the presence or absence of an exocyclic double bond at the π-π conjugative site. In this study, the antioxidant capacity and relevant mechanisms for α-viniferin and caraphenol A were comparatively explored using spectrophotometry, UV-visible spectral analysis, and electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC–ESI–Q–TOF–MS/MS) analysis. The spectrophotometric results suggested that caraphenol A always gave lower IC50 values than α-viniferin in cupric ion-reducing antioxidant capacity assay, ferric-reducing antioxidant power assay, 1,1-diphenyl-2-picryl-hydrazl radical (DPPH•)-scavenging, and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical-scavenging assays. In UV-visible spectra analysis, caraphenol A was observed to show enhanced peaks at 250–350 nm when mixed with Fe2+, but α-viniferin exhibited no similar effects. UPLC–ESI–Q–TOF–MS/MS analysis revealed that α-viniferin mixed with DPPH• produced radical adduct formation (RAF) peak (m/z = 1070–1072). We conclude that the antioxidant action of α-viniferin and caraphenol A may involve both redox-mediated mechanisms (especially electron transfer and H+-transfer) and non-redox-mediated mechanisms (including Fe2+-chelating or RAF). The π-π conjugation of the exocyclic double bond in caraphenol A can greatly enhance the redox-mediated antioxidant mechanisms and partially promote the Fe2+-chelating mechanism. This makes caraphenol A far superior to α-viniferin in total antioxidant levels. View Full-Text
Keywords: oligostilbene; stilbene trimer; α-viniferin; caraphenol A; antioxidant; conjugative double bond oligostilbene; stilbene trimer; α-viniferin; caraphenol A; antioxidant; conjugative double bond
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Li, X.; Xie, Y.; Xie, H.; Yang, J.; Chen, D. π-π Conjugation Enhances Oligostilbene’s Antioxidant Capacity: Evidence from α-Viniferin and Caraphenol A. Molecules 2018, 23, 694.

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