Comparative Study of Epicatechin–Phenylalanine and Epicatechin–Alanine Interactions Using Quantum Chemistry Methods

Abstract

Aims: This research aims to analyze the interactions within Epicatechin…Phenylalanine complexes and compare them to those in Epicatechin…Alanine complexes through theoretical chemistry calculations. Methodology: The interactions between Epicatechin and Phenylalanine, an amino acid, are evaluated using theoretical chemistry methods. Calculations performed at the DFT/B3LYP/6-31+G(d,p) level are used to characterize the complexes and their individual monomers. Geometric, energetic, and spectroscopic parameters, along with QTAIM (Quantum Theory of Atoms in Molecules), NBO (Natural Bond Orbital), and NCI (Non-Covalent Interaction) topological analyses, provide insights into the nature and type of these interactions. Results: The interaction energies of Epicatechin-Phenylalanine complexes exceed those of Epicatechin-Alanine complexes. Unlike the Epicatechin-Alanine complexes, the formation of Epicatechin-Phenylalanine complexes is non-spontaneous. NBO analysis reveals that Epicatechin-Alanine complexes exhibit a greater number of interactions compared to Epicatechin-Phenylalanine complexes, including repulsive interactions attributed to the phenyl group. Moreover, the total stabilization energies of Epicatechin-Phenylalanine complexes are higher than those of their Catechin-Alanine and Epicatechin-Alanine counterparts. Conclusion: The non-covalent bonds formed in epicatechin-phenylalanine complexes are stronger and more numerous than those in catechin-alanine and epicatechin-alanine complexes.