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Synthesis and equilibrium multistate of new pyrano-3-deoxyanthocyanin-type pigments in aqueous solutions
Tetrahedron ( IF 2.1 ) Pub Date : 2017-09-01 , DOI: 10.1016/j.tet.2017.08.051
Joana L.C. Sousa , Vânia Gomes , Nuno Mateus , Fernando Pina , Victor de Freitas , Luís Cruz

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 pKa1 (pKa1 = 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 pKa2 constants (pKa2 = 8.4 ± 0.1 and pKa2 = 8.1 ± 0.1, pigments 6 and 8, respectively).



中文翻译:

新型吡喃-3-脱氧花青素型颜料在水溶液中的合成及平衡多态

吡喃黄酮化合物是黄酮衍生物,存在于诸如葡萄酒和红色果汁等加工食品中。在这项工作中,“生物启发式”吡喃-3-脱氧花青素染料(4-8)的化学平衡为D环(10-甲基,10-邻苯二酚,10-二甲基氨基苯基,10-羧基)具有不同的取代基。以及在B环(3',4'-二羟基,4'-羧基)中,都是通过UV-Vis光谱法在水溶液中进行的首次研究。C-10(颜料4)上存在一个甲基似乎可以稳定黄酮阳离子(AH +),从而将7-OH的去质子化转移至更高的p K a1(p K a1  = 5.0±0.1)。在另一方面,醌型碱基(A,A -)对于在C-10取代基处经历第一酸碱平衡的颜料,更稳定,这可以通过p K a2常数(p K a2  = 8.4±0.1和p K a2  = 8.1±0.1,颜料68分别)。

更新日期:2017-09-01
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