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Photo-degradation of trans-caffeic acid in aqueous solution and influence of complexation by metal ions

Paper ID Volume ID Publish Year Pages File Format Full-Text
26964 43990 2013 10 PDF Available
Title
Photo-degradation of trans-caffeic acid in aqueous solution and influence of complexation by metal ions
Abstract

•The photo-degradation of metal complexes of caffeic acid is compared to the photo-degradation of free caffeic acid.•The kinetics and mechanism of trans-caffeic acid photo-degradation are investigated.•The first route is a photo-isomerization which then undergoes a cyclization to form the esculetin.•Two other routes lead to protocatechuic acid and vinylcatechol formation.•Metal cations such as Al(III), Pb(II) and Cu(II) can influence the rate and mechanism of caffeic acid photo-degradation.

The photo-degradation of metal complexes of caffeic acid was compared to the photo-degradation of free caffeic acid by using UV–vis spectroscopy and HPLC–ESI-mass spectrometry. This article reports first the determination of the products that are formed from the photo-degradation of trans-caffeic acid in aqueous solution and the investigation of the mechanism by a kinetic approach. The good fit between the model and the experimental concentration profiles confirms the photo-isomerization route of the molecule to cis-caffeic acid which then undergoes a cyclization to form the esculetin photo-product. In addition, it reveals, for the first time, another route of major importance leading to the product vinylcatechol. The presence of oxygen leads to an increase of the photo-isomerization rate. Then we report that metallic cations such as Al(III), Pb(II) and Cu(II) can influence the rate and mechanism of caffeic acid photo-degradation. Al(III) ions slow down the photo-degradation whereas Pb(II) and Cu(II) ions have a promoter effect on the production of esculetin. In all cases, the photo-isomerization is reduced by the presence of metal ions and the formation of vinylcatechol does not occur.

Keywords
Caffeic acid; Humic substances; Photo-degradation; Metal complex; Mechanism; Kinetics
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 265, 1 August 2013, Pages 10–19
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
Full-text PDF Download
Online Support
Any Questions? feel free to contact us