A review of selected phenolic compounds and metal complexes in tea, emphasizing their significance through the analysis of quantum chemical parameters

Polyphenols display diverse chemical properties due to their phenolic hydroxyl groups, which enable hydrogen bonding and interactions such as hydrophobic, electrostatic, and pH-responsive behaviors. These compounds can form stable coordination complexes with metal ions, acting as polydentate ligands with high charge density. Their ability to chelate metals like iron(III) makes them useful for developing functional materials and flexible surfaces, with less biotoxicity compared to other metals. Polyphenols found in tea—especially black, green, and oolong varieties—offer notable health benefits, including cancer prevention. Oolong tea polyphenols have been shown to inhibit gastric carcinoma and sarcoma cell growth through antioxidant and immune mechanisms. This study explores catechin derivatives, including Catechin (EC), Epicatechin (EC), Epicatechin gallate (ECG), and Epigallocatechin gallate (EGCG), using Density Functional Theory (DFT) and Monte Carlo simulations to analyze their structural, electronic, and adsorption properties on Fe(110) surfaces. Molecular geometries were optimized with the Gaussian09 software and Material Studio using the B3LYP functional and 6-311++G(d,p) basis set. Key electronic parameters like bandgap energy, ionization energy, and electron affinity were calculated. Monte Carlo simulations identified the most stable adsorption configurations, providing insights into molecule-metal interactions and electron transfer processes crucial for corrosion inhibition. Catechin's superior electron-donating ability and strong adsorption on metal surfaces are linked to its high EHOMO, low ΔE, and abundant hydroxyl groups, forming effective inhibitory layers. Catechins, especially EGCG, demonstrate strong radical scavenging activity due to their hydroxyl groups and aromatic rings, which inhibit oxidative damage and extend food shelf life. The bond dissociation enthalpy (BDE) of catechins is vital to their antioxidant efficiency; EGCG shows the lowest BDE and highest antioxidant activity, making it valuable for food preservation and health applications.