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Issue 25, 2010
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Complexation of apigenin and luteolin in weld lake: a DFT/TDDFT investigation

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Abstract

A DFT-TDDFT investigation on the aluminium complexation of apigenin and luteolin has been carried out. We have focused our attention on these hydroxyflavonoids, which are the main components of weld, one of the earliest natural dyestuff used in art. In particular, weld, upon complexation with Al(III) forms a highly prized lake which has been widely used in medieval manuscripts and easel paintings for its rich yellow colour and transparency. The experimental spectra of apigenin and luteolin upon addition of increasing [Al3+] show a general red-shift of the lowest absorption bands of both flavonoids spectra, associated with the presence of two and three isosbestic points for apigenin and luteolin, respectively. The molecular geometries of all the Al-apigenin and -luteolin complexes have been optimized, followed by calculation of the formation Gibbs free energies and UV–vis absorption spectra. The comparison between the computed absorption spectra of the Al-flavonoid complexes and the experimental ones corresponding to various limit [Al3+] concentrations has been used to discriminate between the possible complexation modes as well as the stoichiometry ratio. We have thus been able to associate specific Al-apigenin (-luteolin) complexes with the experimental absorption spectra as a function of the [Al3+] concentration, thus providing insights into the aluminium complexation of these hydroxyflavonoids and most importantly into the weld lake composition.

Graphical abstract: Complexation of apigenin and luteolin in weld lake: a DFT/TDDFT investigation

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Supplementary files

Article information


Submitted
08 Dec 2009
Accepted
05 Mar 2010
First published
23 Apr 2010

Phys. Chem. Chem. Phys., 2010,12, 6672-6684
Article type
Paper

Complexation of apigenin and luteolin in weld lake: a DFT/TDDFT investigation

A. Amat, C. Clementi, C. Miliani, A. Romani, A. Sgamellotti and S. Fantacci, Phys. Chem. Chem. Phys., 2010, 12, 6672
DOI: 10.1039/B925700D

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