# Visualizing Catalytic Oxidation of Tryptophan by Nanoceria via an Oligonuclear Cerium Oxo-Complex Model

## TL;DR

Researchers studied how a cerium complex can directly oxidize tryptophan, mimicking the activity of ceria nanoparticles in biological systems.

## Contribution

The study reveals a direct oxidation mechanism of tryptophan by a cerium oxo-complex without reactive oxygen species intermediates.

## Key findings

- A hexanuclear cerium oxo-complex (Ce-BA-DMF) was structurally characterized using X-ray crystallography.
- The CeIV/III redox couple in the complex can directly oxidize tryptophan through electron-and-proton transfer.
- This mechanism mimics the nanozyme activity of ceria nanoparticles in catalytic oxidation.

## Abstract

Metal oxide species interact with biologically relevant
molecules,
which are crucial to the life cycle of plants and animals. Metal oxides
can also act as catalysts in various reactions required for proper
plant development. In this study, we investigated the hydrolysis of
inorganic Ce(IV) precursors in the presence of carboxylic acids, leading
to the formation of oligonuclear cerium oxo-complexes. The structure
of the species was obtained by X-ray single-crystal studies and found
to be hexanuclear, with the composition Ce6O4(OH)4(H2O)2(NO3)3(C7H5O2)9(C3H7NO)4 (Ce-BA-DMF). The catalytic properties
of these complexes on the oxidation of amino acids have been investigated,
aiming to establish a transformation mechanism providing insights
into both molecular and surface interactions. A redox feature assigned
to the CeIV/III couple in the cerium oxo-complex was observed by cyclic
voltammetry and found to be sufficiently positive to oxidize tryptophan
directly, without the need for intermediate generation of reactive
oxygen species. Our findings provide new insights into the possible
molecular mechanisms and open the door for more targeted applications
of ceria nanoparticles in agriculture and biomedicine.

Oxidation of tryptophan by an oligonuclear
Ce(IV) complex
mimics the nanozyme activity of ceria nanoparticles and proceeds via
simultaneous electron-and-proton transfer.