Degradation and Detection of the Nerve Agent VX by a Chromophore-Functionalized Zirconium MOF

Abstract

Nerve agents are among the most toxic substances known to man. Recent events in Syria, Malaysia, and the UK illustrate that the threat of these substances is real and actual. The timely detection and identification of nerve agents is of great importance to facilitate timely decontamination or medical countermeasures. In this work, an effective and sensitive detection system, based on the metal–organic framework (MOF) NU-1000, was developed for the disclosure of V-agents, a class of nerve agents that is very persistent, highly toxic, and difficult to detect. NU-1000 is a zirconium-based MOF that can hydrolyze VX into a nontoxic phosphonic acid and the thiol 2-(diisopropylamino)ethanethiol. In this work, it was hypothesized that the four noncoordinating sites that are present on each Zr-building brick of this MOF could be functionalized with the two carboxylates present in 5,5′-di-thio-bis(2-nitrobenzoic acid), DTNB. This dimeric (RS-SR) compound efficiently reacts with thiols by S–S bond exchange and results in the release of the chromophore RS-H. Thus, the target hybrid material (DTNB@NU-1000) was expected to degrade VX and at the same time give a visual color response upon reaction of the thiol-containing degradation product of VX with MOF-bound DTNB. We here report that DTNB@NU-1000 can be readily synthesized and that it is surprisingly active in the degradation of VX in neutral buffer. Moreover, the degradation of VX resulted in a color response, the intensity of which showed linear correlation with the VX concentration used. The applicability of this material was illustrated by a proof-of-concept detection kit for VX-contaminated surfaces, as exemplified with VX-contaminated metal panels coated with military paint [chemical agent resistant coating]. This procedure requires minimal training burden, and VX contamination down to a level of about 1–2 μg/cm2 could be reliably visually established, during a total handling time of 20 min.