Abstract

Bidens pilosa plant has been shown to produce okanin flavanone glycoside and its chalcone derivative. In most other plants, due to chalcone isomerase enzyme, the flavanone tends to exist in higher proportions than their chalcone precursors. Herein we have utilized liquid chromatography–mass spectrometry approach and shown that within the leaves of Bidens pilosa plant the two okanin glycosides exist in unusual equal proportional distribution, which indicates that Bidens pilosa plant is an alternative rich source of these highly sought-after antioxidant molecules. The aglycone okanin chalcone (ONC) and okanin flavanone (ONF) have experimentally been shown to exhibit antioxidant activity. However, experimental findings have not conclusively determined which of the two compounds is a more potent antiradical than the other. Herein, the density functional theory (DFT) method is utilized to establish, from structural and thermodynamic energetic considerations, the preferred antioxidant molecule between the two aglycone okanins. A theoretical study on the antioxidant properties of ONC and ONF has been performed by considering their radical scavenging and metal cation (Mⁿ⁺, where M = Cu(II) or Fe (III)) chelation ability. The study has been performed using B3LYP/6-31 + G(d,p) method. In the case of the metal chelation mechanism, the LANL2DZ pseudo-potential was selected to describe the selected Mⁿ⁺ cations. The results of the study suggest that ONC is a better radical scavenger than ONF because of the extended electron delocalization on its neutral radical, which is due to the presence of conjugation within the ONC neutral radical after hydrogen atom abstraction. In the metal chelation mechanism, it is noted that the binding energies depend on the media, the nature of the ligand and the cation and the cation coordination site on the ligand. The charge and the spin density on Mⁿ⁺ decrease on coordination to the ligand. The ability of the ligands to reduce Mⁿ⁺ cations, coupled with the strong Mⁿ⁺ binding properties, has significant implication on the antioxidant ability of both okanins. However, since ONC⋅⋅⋅M⁺ⁿ interaction results in higher binding energy than ONF⋅⋅⋅M⁺ⁿ interaction, the implication is that ONC is a preferred free metal ion chelator than ONF.

摘要

Bidens pilosa植物已被证明可生产 okanin 黄烷酮糖苷及其查耳酮衍生物。在大多数其他植物中，由于查耳酮异构酶，黄烷酮的存在比例往往高于其查耳酮前体。在本文中，我们利用液相色谱-质谱法表明，在Bidens pilosa植物的叶子中，两种 okanin 苷以不同寻常的等比例分布存在，这表明Bidens pilosa植物是这些备受追捧的抗氧化分子的替代丰富来源。苷元 okanin 查尔酮 (ONC) 和 okanin 黄烷酮 (ONF) 已在实验中显示出抗氧化活性。然而，实验结果尚未最终确定这两种化合物中的哪一种比另一种更有效。在此，利用密度泛函理论 (DFT) 方法，从结构和热力学能量考虑，建立了两种苷元之间的优选抗氧化分子。已经通过考虑它们的自由基清除和金属阳离子 (M ⁿ⁺，其中 M = Cu(II) 或 Fe (III)) 螯合能力。该研究是使用 B3LYP/6-31 + G(d,p) 方法进行的。在金属螯合机制的情况下，选择 LANL2DZ 赝势来描述所选的 Mn ⁺阳离子。研究结果表明，ONC 是比 ONF 更好的自由基清除剂，因为在其中性自由基上扩展了电子离域，这是由于在氢原子提取后 ONC 中性自由基内存在共轭。在金属螯合机制中，注意到结合能取决于介质、配体和阳离子的性质以及配体上的阳离子配位点。M ⁿ⁺上的电荷和自旋密度与配体的配位降低。配体减少 M ⁿ⁺阳离子的能力，加上强的 M ⁿ⁺结合特性，对两种奥卡宁的抗氧化能力具有重要意义。然而，由于ONC⋅⋅⋅M ^{+ N}比ONF⋅⋅⋅M更高的结合能量相互作用的结果^{+ N}相互作用，其含意是ONC比ONF一个优选的无金属离子螯合剂。