Department of Chemistry, University of Venda, Thohoyandou, South Africa.
Department of Biotechnology and Food Technology, University of Johannesburg, Auckland Park, South Africa.
Free Radic Res. 2021 Jan;55(1):53-70. doi: 10.1080/10715762.2020.1859107. Epub 2020 Dec 15.
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 plant the two okanin glycosides exist in unusual equal proportional distribution, which indicates that 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 (M, 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 M 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 M decrease on coordination to the ligand. The ability of the ligands to reduce M cations, coupled with the strong M binding properties, has significant implication on the antioxidant ability of both okanins. However, since ONC⋅⋅⋅M interaction results in higher binding energy than ONF⋅⋅⋅M interaction, the implication is that ONC is a preferred free metal ion chelator than ONF.
该植物已被证明能产生奥卡宁黄酮糖苷及其查尔酮衍生物。在大多数其他植物中，由于查尔酮异构酶的存在，黄酮类化合物的比例往往高于其查尔酮前体。在此，我们利用液相色谱-质谱联用技术表明，在 植物的叶片中，两种奥卡宁糖苷以不同寻常的等比例分布存在，这表明 植物是这些备受追捧的抗氧化分子的另一种丰富来源。苷元奥卡宁查尔酮（ONC）和奥卡宁黄酮（ONF）已被实验证明具有抗氧化活性。然而，实验结果并未最终确定这两种化合物中哪一种的自由基清除能力比另一种更强。在此，利用密度泛函理论（DFT）方法，从结构和热力学能量的角度，确定了两种苷元奥卡宁之间更具抗氧化能力的分子。通过考虑其自由基清除能力和金属阳离子（M，其中 M = Cu(II) 或 Fe(III))的螯合能力，对 ONC 和 ONF 的抗氧化性质进行了理论研究。研究采用 B3LYP/6-31+G(d,p)方法进行。在金属螯合机制中，选择 LANL2DZ 赝势来描述所选的 M 阳离子。研究结果表明，由于其中性自由基上的电子离域扩展，ONC 是一种比 ONF 更好的自由基清除剂，这是由于在氢原子提取后，ONC 中性自由基中存在共轭。在金属螯合机制中，注意到结合能取决于介质、配体的性质以及配体上的阳离子和阳离子配位位。配体与 M 配位后，M 上的电荷和自旋密度降低。配体还原 M 阳离子的能力，加上与 M 的强结合特性，对两种奥卡宁的抗氧化能力有重要影响。然而，由于 ONC⋅⋅⋅M 相互作用导致的结合能高于 ONF⋅⋅⋅M 相互作用，因此可以认为 ONC 是一种比 ONF 更优的游离金属离子螯合剂。
