Antioxidant and chelating properties of phenolic compounds of agro-industrial waste of Carapa guianensis: theoretical insights for food and pharmaceutical applications

Abstract

Context

This study investigates the antioxidant behavior and chelating properties of thirteen phenolic compounds identified in Carapa guianensis agro-industrial waste. Using quantum mechanical methods, we analyzed the molecular structure and solvent effects, revealing potential applications in the food and pharmaceutical industries. Approximately 85% of these compounds demonstrated superior antioxidant performance compared to the phenol backbone, with three compounds rivaling quercetin and ascorbic acid in all tested environments. Solvent polarity significantly influenced the antioxidant mechanism: while hydrogen atom transfer (HAT) dominated in the gas phase, sequential proton loss electron transfer (SPLET) became prevalent in polar solvents. Hydrogen abstraction occurred primarily at the meta position, though polar solvents increased activity at the para site. These predictions are confirmed by simulating the chemical reactions between the aromatic compounds and free OH radicals. The analysis of the hydrogen abstraction reactions indicates that the inclusion of Hartree-Fock exchange-correlation and dispersion corrections is essential to describe hydrogen abstraction by explicitly free radicals. These findings not only underscore the commercial potential of Carapa guianensis waste but also provide a comprehensive understanding of its antioxidant mechanisms, contributing to the sustainable use of natural resources for health and environmental benefits.

Methods

This is a two-step methodology. First, we select the best antioxidant molecules through thermochemical analysis. Then, we explore the hydrogen scavenging mechanism using transition state theory. All quantum mechanics and thermodynamic analyses were carried out within the framework of the density functional theory using the M06-2X, \(\omega \)B97, \(\omega \)B97XD, and CAM-B3LYP variants associated with the Pople’s 6-311++G(d, p) basis set. The effects of the solvent are also systematically investigated by considering the Solvent Density Model for different polar and nonpolar environments. Naturally, the unrestricted wave-function formalism is accounted for once the thermodynamic description of the antioxidant mechanisms involves optimizing open-shell structures. Additionally, the chemical reaction of the hydrogen abstraction due to OH radicals is ensured by applying the Synchronous Transit-Guided Quasi-Newton Method, which allows us to estimate the transition state structures and the energy barrier of the reaction. At this stage, DFT methods like CAM-B3LYP and \(\omega \)B97XD were applied in association with the 6-31+G(d). All calculations were carried out taking advantage of the Gaussian 16 program.