Quercetin and its analogues: optical and acido-basic properties
Quercetin and its analogues: optical and acido-basic properties
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DOI：
10.1039/c7cp03845c
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发表时间：
2017-10-21
影响因子：
3.3
通讯作者：
Kubala, Martin
中科院分区：
文献类型：
--
作者：
Biler, Michal;Biedermann, David;Kubala, Martin
本文主要研究了八种结构相似的天然类黄酮，它们具有广泛的生物活性，在制药、化妆品和食品工业中具有广泛的应用价值。使用实验和理论方法，我们将它们的基本物理化学性质与结构基序联系起来，特别关注紫外/可见吸收性质和pH依赖性。我们强调了C2-C3双键的作用，它的存在或不存在负责在UVB和UVA区域的吸收带之间切换，这是由所涉及的分子轨道的强烈修饰所合理的。在碱性环境中去质子化后，观察到在最大吸收波长处的典型强度开关（λ (max)），从而可以计算具有C2-C3单键的化合物的pK(a)值，而对于含有C2-C3双键的化合物，观察到λ (max)随pH值的显色位移。这些行为也被MO分析合理化和理解。有趣的是，高pH值（蛇葡萄素高于11，杨梅素高于9）诱导由双重和/或三重去质子化引起的长波长峰的形成。在C3位置被羟基取代对杉木素和环二醇的λ (max)几乎没有影响，而对槲皮素和木犀草素的影响较大。在C3处附加的糖段具有稳定作用，只引起光谱行为的微小变化。
This study is focused on eight structurally analogous natural flavonoids that exhibit a wide range of biological activities, which are of interest in pharmacy, cosmetics and the 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 regions, which is rationalized by strong modification of the involved molecular orbitals. After deprotonation in an alkaline environment, a typical switch in intensity at the maximum absorption wavelength (lambda(max)) is observed enabling the calculation of pK(a) values for compounds with a C2-C3 single bond, whereas a bathochromic shift of lambda(max) 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 the formation of a long-wavelength peak arising from double and/or triple deprotonation. Substitution at position C3 by the OH group has almost no effect on lambda(max) for taxifolin and eriodictyol, whereas the effect is larger for quercetin and luteolin. An additional sugar moiety at C3 has a stabilizing effect and induces only minor changes in spectral behavior.