Monitoring the hydrolysis of toxic organophosphonate nerve agents in aqueous buffer and in bicontinuous microemulsions by use of diisopropyl fluorophosphatase (DFPase) with 1H–31P HSQC NMR spectroscopy
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The enzyme diisopropyl fluorophosphatase (DFPase, EC 18.104.22.168) from the squid Loligo vulgaris effectively catalyzes the hydrolysis of diisopropyl fluorophosphate (DFP) and a number of organophosphorus nerve agents, including sarin, soman, cyclosarin, and tabun. Until now, determination of kinetic data has been achieved by use of techniques such as pH-stat titration, ion-selective electrodes, and a recently introduced method based on in situ Fourier-transform infrared (FTIR) spectroscopy. We report the use of 1D 1H–31P HSQC NMR spectroscopy as a new method for real-time quantification of the hydrolysis of toxic organophosphonates by DFPase. The method is demonstrated for the agents sarin (GB), soman (GD), and cyclosarin (GD) but can also be used for V-type nerve agents, for example VX. Besides buffered aqueous solutions the method was used to determine enzymatic activities in a biodiesel-based bicontinuous microemulsion that serves as an example of complex decontamination media, for which other established techniques often fail. The method is non-invasive and requires only limited manual handling of small volumes of liquid (700 μL), which adds to work safety when handling highly toxic organophosphorus compounds. Limits of detection are slightly below 100 μmol L−1 on a 400 MHz spectrometer with 16 FIDs added for a single time frame. The method is not restricted to DFPase but can be used with other phosphotriesterases, for example paraxonase (PON), and even reactive chemicals, for example oximes and other nucleophiles, as long as the reaction components are compatible with the NMR experiment.
KeywordsPhosphotriesterases Enzymes Nerve agents NMR DFPase Hydrolases
The German Ministry of Defense supported this work under contract number E/UR3G/6G115/6A801. The authors thank Dr Harri Koskela (Verifin, University of Helsinki, Finland) for kindly providing pulse sequence files for 1H–31P HSQC NMR experiments and Professor Julian C.-H. Chen (Institute of Biophysical Chemistry, University of Frankfurt, Germany) for his support and productive discussions.
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