Organophosphate Hydrolysis Catalyzed by Molybdate and Molybdate/Hydrogel Hybrid

Abstract

The hydrolysis of organophosphate (OP) esters is critical for both environmental detoxification and the understanding of fundamental biological processes. This study investigates the catalytic activity of molybdate for the hydrolysis of two structurally related OP substrates: p-nitrophenyl phosphate (pNPP), a DNA model compound, and dimethyl p-nitrophenyl phosphate (DMNP), a chemical warfare agent simulant. Notably, we report the first example of DMNP hydrolysis catalyzed by molybdate. Kinetic analyses revealed divergent pH dependencies; optimal pNPP hydrolysis occurred at pH 4.8, whereas DMNP hydrolysis rates increased alongside pH. Mechanistic investigations using 31P{H} NMR spectroscopy demonstrated that pNPP forms stable monodentate and bidentate complexes with molybdate due to its available coordinating hydroxyl groups. In contrast, DMNP lacks these groups, and no stable intermediate complexes were observed, highlighting a strictly substrate-dependent catalytic mechanism. To mitigate the environmental toxicity associated with homogeneous molybdate, we developed a heterogeneous catalytic system by electrostatically immobilizing the active species within a polyethylenimine/polymethylvinylether-co-maleic anhydride (PEI/PMVEMA) hydrogel. This hybrid material significantly accelerated the degradation of both OPs, achieving reaction kinetics comparable to those of the free catalyst in solution. This work elucidates the structural factors governing molybdate catalysis and presents a stable, scalable heterogeneous platform for the sustainable remediation of organophosphorus pollutants.