Department of Chemistry, University of Calicut, Malappuram, 673635, India.
Department of Chemistry, University of Calicut, Malappuram, 673635, India.
Comput Biol Chem. 2019 Jun;80:66-78. doi: 10.1016/j.compbiolchem.2019.03.009. Epub 2019 Mar 23.
In this study, the structural and antioxidant behavior of the three lichen-derived natural compounds such as atranorin (AT), evernic acid (EV) and diffractaic acid (DF) has been investigated in the gas and water phase using both B3LYP and M06-2X functional level of density functional theory (DFT) with two different basis sets 6-31+G (d, p) and 6-311++G (d, p). The intramolecular H-bonds (IHB) strength, aromaticity and noncovalent interactions (NCI) have been computed with the help of the quantum theory of atoms in molecules (QTAIM). This calculation gives major structural characteristics that indirectly influence the antioxidant behavior of the investigated compounds. The spin density (SD) delocalization of the unpaired electron is found to be the main stabilizing factor of neutral and cationic radical species. The main mechanisms, recommended in the literature, for the antioxidant action of polyphenols as radical scavengers such as hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were examined. The result shows that the HAT and SPLET mechanism are the most conceivable one for the antioxidant action of this class of compounds in gas and water phase respectively. Preference of SPLET over HAT in water phase is due to the significantly lower value of proton affinity (PA) compared to the bond dissociation enthalpy (BDE) value. This study reveals that O-H, O-H and O-H respectively are the most favored site of AT, EV and DF for homolytic as well as heterolytic OH bond breaking.
在这项研究中，使用密度泛函理论（DFT）的 B3LYP 和 M06-2X 两种不同的基组（6-31+G（d，p）和 6-311++G（d，p）），在气相和水相中研究了三种地衣衍生天然化合物（即，变松萝酸（AT）、evermic 酸（EV）和 diffractaic 酸（DF））的结构和抗氧化行为。借助原子在分子中的量子理论（QTAIM），计算了分子内氢键（IHB）强度、芳香性和非共价相互作用（NCI）。该计算给出了主要的结构特征，这些特征间接影响了所研究化合物的抗氧化行为。未配对电子的自旋密度（SD）离域被发现是中性和阳离子自由基物种的主要稳定因素。文献中推荐的多酚类化合物作为自由基清除剂的抗氧化作用的主要机制，如氢原子转移（HAT）、单电子转移后质子转移（SET-PT）和顺序质子损失电子转移（SPLET），进行了研究。结果表明，在气相和水相中，HAT 和 SPLET 机制分别是这类化合物抗氧化作用的最可能机制。与键离解焓（BDE）值相比，水相中质子亲和力（PA）值显著降低，导致 SPLET 比 HAT 更优先。这项研究表明，O-H、O-H 和 O-H 分别是 AT、EV 和 DF 进行均裂和异裂 OH 键断裂的最有利位点。
