(561e) Heterogeneous Dephosphorylation Using Ceria Nanocatalysts: Identifying the Active Site and the Rate-Determining Step

As an essential element in living systems, phosphorus is crucial for cell division and growth, energy storage and conversion, respiration, photosynthesis, and other biological processes. Phosphorus is found naturally in soil, but concentrations can fall to low levels depending on geographic conditions, and artificial phosphorus fertilizers are demanded to sustain the growth of crops. Before the early 1900s, most of the world’s phosphorus was derived from animal wastes. Today the vast majority (nearly 80%) of phosphorus in fertilizers comes from phosphate rocks, which are primarily harvested in the remote Western Sahara region. It is predicted that the production of phosphate rocks will reach its peak before 2040 and the reserves will be completely depleted by the end of this century. Therefore it is imperative to develop innovative and sustainable methods for production of phosphorus from renewable sources.

One solution toward this sustainability challenge is to extract phosphorus from phosphorylated biomolecules (e.g., phospholipids and nucleic acids) and recycle it for fertilizer production. This is conventionally done via fermentation, which produces struvite, a precipitate that can be processed to make phosphorus fertilizers. Alternatively, a more robust approach is catalytic dephosphorylation. By hydrolytic cleavage of the phosphate ester bond, free phosphate anions can be released from biomass and agriculture wastes, which can then be captured and regenerated as chemical streams for further applications. Previously studies of cerium oxide (CeO₂) nanocrystals for biological applications (e.g., cancer therapy, pharmacology and toxin mitigation) have shown that these nanomaterials can function as artificial phosphatases and catalyze the dephosphorylation of nucleic acids, peptides, DNA and RNA under ambient conditions. Thereby CeO₂ is believed to be a promising catalyst for dephosphorylation and recovery of phosphorus from biomass and organic wastes

Here we report on catalytic dephosphorylation for recovery of phosphates from organic and biological molecules. Ceria (CeO₂) nanocrystals were synthesized with shape control and applied as “artificial phosphatases” to cleave the phosphate ester bond in para-nitrophenyl phosphate (p-NPP) and release free phosphate anions in aqueous solutions. After a fundamental study on this model reactant, CeO₂ nanocrystals were also applied to feedstocks to phospholipids and nucleic acids. The dephosphorylation reaction was studied on the CeO₂ nanocrystals at various temperatures to evaluate the dependences of rate constant, activation energy and recyclability on the particle shape. The structure-property relationship established in these studies suggests that the oxygen vacancies on the surface of CeO₂ are the active sites for dephosphorylation. Adsorption studies of poisoning species allow for the proposal of a potential rate-determing step in this reaction.