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Kinetic study of the photosensitized oxygenation of the flavanone naringin and its chalcone

Paper ID Volume ID Publish Year Pages File Format Full-Text
28516 44079 2007 10 PDF Available
Title
Kinetic study of the photosensitized oxygenation of the flavanone naringin and its chalcone
Abstract

The kinetic of the O2(1Δg)-photosensitized oxidation of the flavanone naringin (7-rhamnoglucosyl-4′,5-dihydroxyflavanone, FL) and its chalcone isomer (4′-rhamnoglucosyl-2′,6′,4-trihydroxychalcone, CH) in neutral and 1 mM NaOH ethanol solutions was studied using Rose Bengal as photosensitizer. The rate constants for the chemical quenching of O2(1Δg) by the flavonoids (kr) were determined using either UV–vis absorption spectroscopy or HPLC techniques, and for the total (physical + chemical) quenching (kt) were determined using time-resolved phosphorescence detection of O2(1Δg) at 1270 nm.A larger reactivity towards O2(1Δg) of CH than for FL in neutral ethanol solutions was observed, due to the extra conjugated double bond in CH. However, in alkaline media the reactivity of both isomers was larger than in neutral conditions. This behavior was associated to the increment of electron density by the formation of a carbanion in FL and to the presence of the extended conjugated π-system in the CH isomer by deprotonation of phenolic groups. In all cases, the formation of 4-hydroxybenzoic acid as ending product was detected by HPLC. Based on reported mechanisms of O2(1Δg)-mediated oxidation of flavonoids, the formation of 7-rhamnoglucosyl-5,4′-dihydroxyflavonol as primary photo-oxidation product was proposed.The reactivity towards O2(1Δg) of the aglycone of naringin (5,7,4′-trihydroxyflavanone or naringenin, NG) in alkaline conditions was lower than for the parent naringin, due to incapability of NG to form a carbanion species.These results are expected to have significance in biosynthesis, antioxidant properties and stability of naturally occurring flavonoids.

Keywords
DMA, 9,10-dimethylanthracene; CH, chalcone isomer; FL, flavanone or naringin; NG, naringenin; RB, Rose Bengal; S, sensitizer molecule; TRPD, time-resolved phosphorescence detectionNaringin; Flavanones; Chalcones; Singlet oxygen; Photo-oxidations
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Kinetic study of the photosensitized oxygenation of the flavanone naringin and its chalcone
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 186, Issue 1, 5 February 2007, Pages 47–56
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
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Online Support
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