Reduction mechanism of mangiferin from mango (Mangifera indica L.) leaf extract in the formation of gold nanoparticles, evaluation of biological activities in vitro and in silico

For the first time, the reduction mechanism and the in silico evaluation of biological activity were investigated in the green synthesis of gold nanoparticles (AuNPs) using mango leaf extract ( Mangifera indica L.) as both reducing and stabilizing agents. The formation of AuNPs was confirmed by UV-Vis spectroscopy and FT-IR, while XRD, DLS, EDX, and TEM were used to characterize their structure and size. The total polyphenol content was quantified before and after the reaction using HPLC to clarify the reduction pathway. TEM images revealed mainly spherical nanoparticles with sizes of 15–25 nm, consistent with the crystallite size (∼7 nm) from XRD. Meanwhile, the hydrodynamic size measured by DLS was larger (∼111 nm) due to solvation and biomolecular capping. HPLC results indicated that mangiferin acted as the principal reducing agent, converting hydroxyl groups into quinone forms and reducing Au³ ⁺ to Au⁰. The obtained AuNPs exhibited strong antibacterial activity against Pseudomonas aeruginosa (IC₅₀ = 0.17 ± 0.01 μg/mL), remarkable inhibition of α-glucosidase (IC₅₀ = 0.79 ± 0.03 μg/mL), and preliminary cytotoxicity toward MCF-7 breast cancer cells. Docking analysis showed that the oxidised form of mangiferin binds specifically to the active site of α-glucosidase (PDB: 7D9B), supporting its inhibitory effect with ΔG = -6.10 kcal/mol and K i = 33.95 μM.