Tetrahedron
Tetrahedron
5 years ago

Synthesis and equilibrium multistate of new pyrano-3-deoxyanthocyanin-type pigments in aqueous solutions

Synthesis and equilibrium multistate of new pyrano-3-deoxyanthocyanin-type pigments in aqueous solutions
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-3-deoxyanthocyanin 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 pK a2 constants (pK a2 = 8.4 ± 0.1 and pK a2 = 8.1 ± 0.1, pigments 6 and 8, respectively).

Publisher URL: www.sciencedirect.com/science

DOI: S0040402017309006

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