Kinetics and Mechanism of the Antioxidant Activities of C. olitorius and V. amygdalina by Spectrophotometric and DFT Methods

Abstract

The kinetics and mechanism of the antioxidant activities of the methanolic extract of the leaves of two vegetables [ Corchorus olitorius ( C. olitorius ) and Vernonia amygdalina ( V. amygdalina )] have been studied using experimental and theoretical approaches. The kinetics (second order and pseudo-first order) of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of the leaf extracts at varying times (30–90 min) were determined using the UV–visible spectrophotometry method at λ max = 517 nm, whereas the mechanism was studied by density functional theory at two levels of functionals (B3LYP and LC-ωPBE) using bond dissociation enthalpy and adiabatic ionization potential values. Molecular properties such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, electronegativity (χ), electrophilicity (ω), hardness (η), and softness ( S ) of the predominant phenolic antioxidants were also compared. The second-order kinetics is favored by both plants rather than pseudo-first order; however, V. amygdalina with a second-order rate constant k 2 of 0.0152 (mM) −1 min –1 is faster in scavenging DPPH radicals than C. olitorius with a k 2 value of 0.0093 (mM) −1 min –1 . Chlorogenic acid and luteolin-7-O-β-glucuronide, which are the most abundant phenolic acid antioxidant in C. olitorius and V. amygdalina , both preferably scavenge the DPPH radical via a hydrogen atom transfer mechanism. This is evident from their lower bond dissociation enthalpy values than the adiabatic ionization potential values. Successful molecular docking of these phenolic compounds indicates that both compounds form favorable interactions with the therapeutic target, xanthine oxidase.

Antioxidant Efficacy of Natural Ubiquinol Compared to Synthetic References – In Vitro Study

“…Compared with phenolics, Mathew et al (2015) [43] also proved that their radical-scavenging ability increased in first minutes of time reaction but stagnated over time. In our research, obtained results are consistent with the study of Poderoso et al (1999), [44] who described that the reaction of ubiquinol with free radicals lead to formation of intermediates, namely ubisemiquinone, ubiquinone-2 and ubiquinone-0. Besides, they evaluated that the oxidation kinetics of ubiquinol are measurable in minutes.…”

“…Second-order rate constants of UQH 2 _S and α-tocopherol were significantly higher compared than those reported by Yusuff et al (2019) [44] for vegetable extracts, although overall behaviour of radical scavenging was comparable with our results. Kancheva (2009) [45] summarized second-order rate constants of fifty phenolic antioxidants including α-tocopherol determined by H-donating and chain-breaking activity.…”

Green Synthesis of Gold and Silver Nanoparticles Using Leaf Extract of Capsicum chinense Plant

“…So far, a wide range of vegetal species from different families have been used for the synthesis of nanoparticles [ 5 , 6 , 7 ]; between them, different species from the genus Capsicum [ 7 , 8 ]. The genus Capsicum belongs to the Solanaceae family, and it counts with [ 9 , 10 , 11 , 12 ] species among which five have been domesticated and harvested. Capsicum annuum , C. frutescens , C. pubescens , C. baccatum and C. chinense are species native to the tropical and template zones of America, including Mexico.…”

“…On the other hand, it is well known that the reduction process of nanoparticles by green synthesis, using phytochemical extracts, is mediated by the reducing capacity of several compounds [ 28 , 29 ]. Recently, several authors have evaluated the antioxidant capacity of the nanoparticles once synthesized [ 10 , 11 , 12 ]. However, there are very few works where authors try to evaluate the changes in the antioxidant activity after the synthesis of nanoparticles or the groups of compounds implicated in the reduction process.…”

Quality Assessment and Biological Activity Evaluation of Different Brands of Olive Oil

“…The DPPH (2, 2-Diphenyl-1-picrylhydrazy) method was employed to assess the VOO sample's antioxidant activity [17,18]. The solutions of the DPPH (0.1 mM) and VOO (different concentrations in mg of oil/mL) in ethanol and diethyl ether mixture (4:1) were prepared.…”