Metal-organic frameworks catalyze the hydrolysis of chemical nerve agents
Phosphorous-based chemical warfare agents (CWAs) are volatile chemicals known to inhibit acetylcholinesterase by phosphonylating its catalytic serine-203 –OH group, which leads to accumulation of the neurotransmitter acetylcholine in receptors and consequences of overstimulation, including death. While enzymatic approaches to detoxify CWAs by catalyzing their hydrolysis have been demonstrated, the high sensitivity of enzymes to environmental conditions has inspired efforts to design and implement more robust alternative catalysts, with theoretical molecular engineering at the atomic level an especially useful tool for rapidly surveying platforms with potential for deployment in the field.
Mohammad Momeni, Ph.D., a postdoctoral scholar working with Professor Christopher Cramer, has characterized a detailed mechanistic scheme for the aqueous remediation of the CWA Sarin, which belongs to the G-series of nerve agents, catalyzed by defective metal-organic frameworks (MOFs) with open Zr metal sites in their Zr6 nodes. By identifying a dual role for water molecules as both hydrolyzing agents and inhibitors at the active sites of the catalytic MOFs, the research rationalized experimental results, including temperature and pH effects, as well as varying reactivities observed for different MOF structures. Armed with insights from this mechanistic study, Momeni and Cramer employed theory to show that defective Zr12 MOFs with unique double-node topologies possess superior catalytic activity compared to all Zr6 alternatives. These predictions will advance the design and implementation of more robust and reactive heterogeneous catalysts for real-world applications.