resumo
Pyrano-flavylium compounds are flavylium derivatives with occurrence in processed foodstuffs such as wine and red fruit juices. In this work, the chemical equilibria of "bio-inspired" pyrano-3deoxyanthocyanin dyes (4-8), presenting different substituent groups in D ring (10-methyl, 10-catechol, 10-dimethylaminophenyl, 10-carboxy) as well as in B ring (3',4'-dihydroxy, 4'-carboxy), were studied for the first time in aqueous solutions by UV-Vis spectroscopy. The presence of a methyl group at C-10 (pigment 4) seems to stabilize the flavylium cation (AH(+)) shifting the deprotonation of 7-OH to a higher pK(a1) (pK(a1) = 5.0 0.1). On the other hand, the quinoidal bases (A, A(-)) were more stabilized for the pigments which undergo the first acid-base equilibrium at C-10 substituent, as could be observed by the pICa2 constants (pK(a2) = 8.4 +/- 0.1 and pK(a2) = 8.1 +/- 0.1, pigments 6 and 8, respectively). (C) 2017 Elsevier Ltd. All rights reserved.
palavras-chave
ANTHOCYANIN-DERIVED PIGMENTS; WINE PIGMENTS; COLOR; PH; PYRANOANTHOCYANINS; CHEMISTRY; SYSTEM; FORMS; PHOTOCHROMISM; METABOLITE
categoria
Chemistry
autores
Sousa, JLC; Gomes, V; Mateus, N; Pina, F; de Freitas, V; Cruz, L
nossos autores
agradecimentos
The authors thank Dr. Zelia Azevedo for the MS analysis and Dr. Mariana Andrade for the NMR analysis. This research was supported by a research project grant (PTDC/QEQ-QFI/1971/2014) with financial support from FCT/MEC through national funds and co-financed by FEDER, under the Partnership Agreement PT2020 (UID/QUI/50006/2013 - POCI/01/0145/FEDER/007265). Luis Cruz gratefully acknowledges FCT for his post-doc grant (SFRH/BPD/72652/2010) and an investigator contract (NORTE-01-0145-FEDER-000011).