Carica papaya-mediated green synthesis of ZnO nanoparticles: biological potentials and in silico investigations

Zinc oxide nanoparticles (ZnO NPs) have emerged as promising biocompatible materials for biomedical and environmental applications due to their unique physicochemical properties. In this study, ZnO NPs were synthesized via a green approach using Carica papaya leaf extract and comprehensively characterized using UV–visible spectroscopy (UV–Vis) and Fourier-transform infrared spectroscopy. Morphological and structural properties were analyzed via X-ray diffraction and scanning electron microscopy. The environmentally benign ZnO NPs were evaluated for their biological potential, demonstrating significant antibacterial activity against Helicobacter pylori, with a minimum inhibitory concentration of 40.62 μg/mL and a minimum bactericidal concentration of 162.5 μg/mL. The nanoparticles also exhibited potent antioxidant and cytotoxic properties, evidenced by a notably low IC50 value of 63.055 µg/mL. To elucidate the interaction mechanism between ZnO and DNA bases, a semiempirical computational study was performed. Interaction energy calculations revealed the strongest affinity for adenine and the weakest for guanine. Theoretical investigations, including electronic absorption spectra, vibrational spectra, electrostatic potential, and charge density analyses, indicated that ZnO interaction induced a pronounced redshift in the electronic spectra (extending to 954 nm), shifting absorption from the UV to the near-infrared region. Furthermore, charge distribution and electrostatic potential plots suggested distinct binding modes: cytosine and guanine interacted primarily through hydrogen bonding, while adenine coordinated via the electron-rich nitrogen (–N =) in its five-membered ring, facilitating electron donation to ZnO.