Flavonol–serum albumin complexation. Two-electron oxidation of flavonols and their complexes with serum albumin
作者:Olivier Dangles、Claire Dufour、Stephan Bret
DOI:10.1039/a810017i
日期:——
Quercetin (3,3â²,4â²,5,7-pentahydroxyflavone) and quercetin derivatives (3-methylquercetin, isoquercitrin, rutin) are strong polyphenolic antioxidants abundant in plants and in the human diet. Recent investigations have shown that significant concentrations of albumin-bound quercetin conjugates are present in the plasma of humans fed a quercetin-rich diet.In this work, binding of quercetin and quercetin glycosides to bovine serum albumin (BSA) is quantitatively investigated by fluorescence spectroscopy. The strong fluorescence enhancement of quercetin upon binding points to the fact that a significant fraction of quercetin adopts a pyrylium-like structure in the complex. On the other hand, the observation of a very efficient quenching of tryptophan fluorescence by quercetin is consistent with a binding occurring in the IIA domain.Flavonoid-derived quinones may be formed upon quenching of reactive oxygen species by flavonoids (antioxidant activity). In this work, the quinones are conveniently formed upon periodate oxidation of the selected flavonoids in methanol and in aqueous buffers with and without BSA. A kinetic investigation by UVâvisible spectroscopy shows that albumin-bound flavonoids are oxidized as quickly as free flavonoids. Interestingly, the quercetin quinone, which is merely detectable in the absence of BSA because of fast solvent addition, is efficiently stabilized in the complex by charge transfer interactions (pH 9). No evidence for quercetinâBSA conjugates could be found, thus showing that water addition (and subsequent degradation) remains the sole significant pathway of quinone transformation in the complex.
槲皮素(3,3',4',5,7-五羟基黄酮)和槲皮素衍生物(3-甲基槲皮素、异槲皮苷、芦丁)是植物和人类饮食中富含的强效多酚类抗氧化剂。最近的研究表明,在食用富含槲皮素饮食的人的血浆中存在大量结合白蛋白的槲皮素结合物。在这项工作中,通过荧光光谱定量研究了槲皮素和槲皮素糖苷与牛血清白蛋白(BSA)的结合。槲皮素在结合点处具有强烈的荧光增强作用,这表明在复合物中,很大一部分槲皮素采用吡喃结构。另一方面,槲皮素对色氨酸荧光的高效淬灭与IIA结构域中的结合相一致。黄酮类衍生的醌类可能在黄酮类化合物(抗氧化活性)淬灭活性氧时形成。在这项工作中,在甲醇和有或没有BSA的水缓冲液中,选定的黄酮类化合物在过碘酸氧化时很容易形成醌类。通过紫外可见光谱进行的动力学研究表明,结合白蛋白的黄酮类化合物与游离黄酮类化合物一样快速氧化。有趣的是,由于溶剂快速添加,槲皮素�