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Quercetin and its analogues: Optical and acido-basic properties

Abstract

This study is focused on eight structurally analogous natural flavonoids that exhibit wide range of biological activities, which are of interest in pharmacy, cosmetics or food industry. Using both experimental and theoretical approaches, we relate their fundamental physico-chemical properties to the structural motifs, with particular focus on UV/Vis absorption properties and pH dependence. We highlight the role of the C2-C3 double bond, whose presence or absence is responsible for the switch between absorption bands in the UVB and UVA region, which is rationalized by strong modification of involved molecular orbitals. After deprotonation in alkaline environment, typical switch in intensities at maximum absorption wavelength (λmax) is observed enabling to calculate pKa values for compounds with the single C2-C3 bond, whereas a bathochromic shift of λmax vs. pH is observed for the C2-C3 double bond containing compounds. These behaviors are also rationalized and understood by MO analysis. Interestingly, high pH (above 11 for ampelopsin and above 9 for myricetin) induces formation of a long-wavelength peak arising from double and/or triple deprotonation. Substitution at position C3 by OH group has almost no effect on λmax for taxifolin and eriodictyol, whereas the effect is larger for quercetin and luteolin. Additional sugar moiety at C3 has a stabilizing effect and induces only minor changes in spectral behavior.

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Publication details

The article was received on 08 Jun 2017, accepted on 07 Sep 2017 and first published on 07 Sep 2017


Article type: Paper
DOI: 10.1039/C7CP03845C
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Quercetin and its analogues: Optical and acido-basic properties

    M. Biler, D. Biedermann, K. Valentova, V. Kren and M. Kubala, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP03845C

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