Conformational, electronic and antioxidant properties of lucidone, linderone and methyllinderone: DFT, QTAIM and NBO studies

Abstract

Theoretical studies on lucidone, linderone and methyllinderone were performed to investigate factors that contribute to structural stability and to elucidate the antioxidant properties and mechanisms. The study was performed in different media utilising the density functional theory with different functionals and the 6-311 + G(d,p) basis set. The antioxidant activity has been considered through the electron transfer and metal chelation mechanisms. The results show that the stability of the tautomers and conformers is due to the presence of several intramolecular hydrogen bonds. The ionisation potential values suggest that the antiradical activity increases with the increase in the number of OCH 3 groups substituted on the cyclopentene-1,3-dione ring. In vacuo, the spin density of the Fe(II) cation upon ligand coordination decreases to 3.0−3.5, whereas the ligand spin density approaches 1, indicating that it is oxidised to a radical cation. The metal ion affinity (MIA) is influenced by the position and number of OCH 3 substituted on the acylcyclopentene-1,3-dione ring. A very favourable MIA, in vacuo, is obtained when Fe(II) is chelated between the sp 2 O and sp 3 O atoms. An estimation of MIA in an aqueous solution shows a remarkable decrease with respect to the results in vacuo.

Antioxidant and antimalarial properties of butein and homobutein based on their ability to chelate iron (II and III) cations: a DFT study in vacuo and in solution

“…The formation of a stable complex structure, as a result of the interaction of the antioxidant with the transition metal ion, shields biological targets from the free transition metal ion (e.g. Fe 2+ , Fe 3+ and Cu 2+ ), thereby preventing metal-catalysed free radical reactions [30][31][32][33][34][35]. The implication of metal chelation, as an antioxidant mechanism, is that the chelated metal ions are removed from catalytic sites and therefore are not available to interact with other compounds and initiate biologically damaging reactions, such as the Fenton reaction, to produce hydroxyl radicals that are damaging to cells [30][31][32][33].…”

“…In a similar manner, the para substituted OH group (O4H4) in ring B can interact with neighbouring O3 to form an IHB, here called the second H-bond and denoted as HB2. IHBs are known to stabilise conformations [47][48][49][50][51][52][53][54][55] as well as to influence the biological activities of compounds, such as antioxidant activity [24,25,32,34].…”

DFT Study on Antioxidant Action Mechanisms of Naphthoquinone-Urazole Hybrids

“…The density functional theory (DFT) method have been successfully used to calculated physiochemical descriptors of polyphenolic compounds and to investigate the structureactivity relationship (SAR) for phenolic antioxidants [21][22][23]. The investigated naphthoquinone-urazole hybrids ( Fig.1) and their corresponding radical and ionic species, the most stable conformers were optimized without symmetry restrictions by the B3LYP/6-311++G (d,p) level in the gas phase and in water.…”

Quantum Chemical Investigation on the Antioxidant Activity of Neutral and Anionic Forms of Juglone: Metal Chelation and Its Effect on Radical Scavenging Activity

“…With the aim of determining the nature of all the stationary points, frequency calculations were performed on all the optimized geometries at the same level of theory. The DFT/B3LYP method was used because it is frequently employed for the studies on metalation of natural antioxidant [9][10][11]26]. The calculations on closed shell systems were performed by the means of the Restricted Kohn-Sham formalism whereas the Unrestricted Kohn-Sham approach was used for open shell systems [23,27].…”

“…This binding process occurs through an acid-base reaction in which the metal ion acts as the Lewis acid and the polyphenol functions as the Lewis base. The above-mentioned solutions toward mitigating the excesses of transition metal ions in living organisms have been subject to many studies [9][10][11][12].…”