Molecular mechanisms in metal oxide nanoparticle Tryptophan interactions

Abstract One of the crucial metabolic processes for both plant and animal kingdoms is oxidation of amino acid tryptophan (TRP) that regulates the plant growth and controls hunger and sleeping patterns in animals. Here, we report revolutionary insights into how this process can be crucially effected by interactions with metal oxide nanoparticles (NP), creating a toolbox for a plethora of important biomedical and agricultural applications. Molecular mechanisms in TRP-NP interactions were revealed by NMR and optical spectroscopy for ceria and titania, and by X-ray single crystal and a computational study of a model TRP-polyoxometalate complexes. Nanozyme activity, involving concerted proton and electron transfer to the NP surface for oxides with high oxidative potential, CeO2 or WO3, converted TRP into a tricyclic organic acid resembling natural plant hormones, auxins. TiO2, a much poorer oxidant, was strongly binding TRP without concurrent oxidation in the dark, but oxidized it non-specifically via release of reactive oxygen species (ROS) in daylight.