Soman Research Articles

Characterization of the Zirconium Metal-Organic Framework (MOF) UiO-66-NH2 for the Decomposition of Nerve Agents in Solid-State Conditions Using Phosphorus-31 Solid State-Magic Angle Spinning Nuclear Magnetic Resonance (31P SS-MAS NMR) and Gas Chromatography – Mass Spectrometry (GC-MS)

UiO-66-NH2 was synthesized in situ and analyzed as a reactive sorbent for nerve agent removal in the solid-state environment. UiO-66-NH2 had the smallest pore sizes, centered at 7 Å with added pores at 13 and 15 Å, indicating a hierarchically microporous structure. The in situ reaction was examined using phosphorus-31 solid state-magic angle spinning nuclear magnetic resonance (31P SS-MAS NMR) and further confirmed by gas chromatography – mass spectrometry (GC-MS). The results show that the nerve agents were decomposed via hydrolysis by UiO-66-NH2 and the overall rates were reduced for solid-phase reactions. Of the characterized components O-pinacolyl methylphosphonofluoridate (GD), N, N-dimethylphosphoramidocyanidate (GA), and O-ethyl S-diisopropylaminomethyl methylphosphonothioate (VX), GD was decomposed faster than GA and VX by UiO-66-NH2. Specifically, GD was decomposed to O-pinacolyl-methylphosphonic acid (PMPA) with a half-life of approximately 430 min in the presence of neat UiO-66-NH2. However, GA and VX were slowly hydrolyzed, forming reaction products such as ethylphosphate and dimethylphosphoramidic (DMPA) acid monoethylester from GA, and ethyl methylphosphonic acid (EMPA), methylphosphonic acid (MPA), and 2-(Diisopropylamino)ethyldisulfide (DES)2 from VX, respectively. This work describes the processes involved for these materials when they are deployed to protect against a nerve agent release, implying the practical application of UiO-66-NH2 for a broad range of filtration applications in the field.

Simultaneous Time-concentration Analysis of Soman and VX Adducts to Butyrylcholinesterase and Albumin by LC-MS-MS.

A sensitive method for the purification and determination of two protein adducts, organophosphorus (OP)-BChE and OP-albumin adducts, in a single sample using a simultaneous sample preparation method was developed and validated using liquid chromatography-tandem mass spectrometry. First, we isolated O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate (VX) and O-pinacolyl methylphosphonofluoridate (soman, GD)-BChE adducts using an immunomagnetic separation (IMS) method and the HiTrap™ Blue affinity column was subsequently used to isolate and purify VX and GD-albumin adducts from the plasma of rhesus monkeys exposed to nerve agents. Additionally, we examined the time-concentration profiles of two biomarkers, VX and GD-nonapeptides and VX and GD-tyrosines, derived from OP-BChE and OP-albumin adducts up to 8 weeks after exposure. Based on the results, we determined that VX and GD-tyrosine is more suitable than VX and GD-nonapeptide as a biomarker owing to its longevity. This integrated approach is expected to be applicable for the quantification of other OP-BChE and OP-albumin adducts in human plasma, thus serving as a potential generic assay for exposure to nerve agents.

Assessment of brain oxygenation imbalance following soman exposure in rats

Nerve agents (NAs) are potent organophosphorus (OP) compounds with applications in chemical warfare. OP compounds act by inhibiting acetylcholinesterase (AChE). Soman (O-pinacolyl methylphosphonofluoridate) is one of the most potent NAs. It is well known that small doses of NAs can be lethal, and that even non-lethal exposure leads to long-term mental debilitation/neurological damage. However, the neuropathology following exposure to sub-lethal nerve agents is not well understood.In this study, we examined changes in tissue oxygenation (pO2) in the cortex and hippocampus after a sub-lethal dose of soman [80–90 μg/kg; subcutaneous]. pO2 changes can provide information regarding oxygen delivery and utilization and may be indicative of a disruption in cerebral blood flow and/or metabolism. Changes in oxygenation were measured with chronically implanted oxygen sensors in awake and freely moving rats. Measurements were taken before, during, and after soman-induced convulsive seizures.Soman exposure resulted in an immediate increase in pO2 in the cortex, followed by an even greater increase that precedes the onset of soman-induced convulsive seizures. The rise in hippocampus pO2 was delayed relative to the cortex, although the general pattern of brain oxygenation between these two regions was similar. After convulsive seizures began, pO2 levels declined but usually remained hyperoxygenated. Following the decline in pO2, low frequency cycles of large amplitude changes were observed in both the cortex and hippocampus. This pattern is consistent with recurring seizures.Measuring real-time changes in brain pO2 provides new information on the physiological status of the brain following soman exposure. These results highlight that the measurement of brain oxygenation could provide a sensitive marker of nerve agent exposure and serve as a biomarker for treatment studies.

Cerium oxide for the destruction of chemical warfare agents: A comparison of synthetic routes

Four different synthetic routes were used to prepare active forms of cerium oxide that are capable of destroying toxic organophosphates: a sol–gel process (via a citrate precursor), homogeneous hydrolysis and a precipitation/calcination procedure (via carbonate and oxalate precursors). The samples prepared via homogeneous hydrolysis with urea and the samples prepared via precipitation with ammonium bicarbonate (with subsequent calcination at 500°C in both cases) exhibited the highest degradation efficiencies towards the extremely dangerous nerve agents soman (O-pinacolyl methylphosphonofluoridate) and VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate) and the organophosphate pesticide parathion methyl. These samples were able to destroy more than 90% of the toxic compounds in less than 10min. The high degradation efficiency of cerium oxide is related to its complex surface chemistry (presence of surface OH groups and surface non-stoichiometry) and to its nanocrystalline nature, which promotes the formation of crystal defects on which the decomposition of organophosphates proceeds through a nucleophilic substitution mechanism that is not dissimilar to the mechanism of enzymatic hydrolysis of organic phosphates by phosphotriesterase.

Penehyclidine hydrochloride and organ protection during cardiopulmonary bypass

Background Penehyclidine hydrochloride (PHC),which is derived from hyoscyamine is a new anticholinergic drug,has both antimuscarinic and antinicotinic activities and retains potent central and peripheral anticholinergic activities.Clinical data showed that PHC had good curative effect for the pesticides poison of organic phosphorus and soman poisoning,asthma and chronic obstructive pulmonary disease,septic shock,the diseases of gastrointestinal tract and drug addiction,et al.Additionally,recent studies have suggested that PHC has protective effects of hepatic,renal and lung injury and brain ischemia/reperfusion injury (I/RI).Objective The protective effect of PHC on organs during cardiopulmonary bypass (CPB) is briefly reviewed.Content The pharmacological actions of PHC,and effects on organs during CPB and the mechanism of its action are discussed.Trend Further studies of PHC for prevention of organ injury during CPB in patients with open-heart surgery are needed. Key words: Penehyclidine hydrochloride; Organ protection; Cardiopulmonary bypass

Detection of Chemical Warfare Nerve Agents via a Beckmann Fragmentation of Aldoxime

A new (E)-pyrene-1-carbaldehyde O-tert-butyldimethylsilyl oxime 3 was synthesized for the detection of chemical warfare nerve agents, O-isopropyl methylphosphonofluoridate (GB) and O-pinacolyl methylphosphonofluoridate (GD). 1H NMR spectrum showed that the tert-butyldimethylsilyl (TBDMS) group was deprotected using TBAF and the oximate supernucleophile was made. Upon addition of chemical warfare agents (GB and GD) (50 mol%), the reaction was completely finished within 5 min and also the color change of reaction mixture was observed under a hand-held UV lamp with the naked eye.

Protective Effects of Aerosolized Scopolamine Against Soman-Induced Acute Respiratory Toxicity in Guinea Pigs

The protective efficacy of the antimuscarinic agent scopolamine was evaluated against soman (o-pinacolyl methylphosphonofluoridate [GD])-induced respiratory toxicity in guinea pigs. Anesthetized animals were exposed to GD (841 mg/m(3)) by microinstillation inhalation exposure and treated 30 seconds later with endotracheally aerosolized scopolamine (0.25 mg/kg) and allowed to recover for 24 hours. Treatment with scopolamine significantly increased survival and reduced clinical signs of toxicity and body weight loss in GD-exposed animals. Analysis of bronchoalveolar lavage (BAL) fluid showed normalization of GD-induced increased cell death, total cell count, and protein following scopolamine treatment. The BAL fluid acetylcholinesterase and butyrylcholinesterase levels were also increased by scopolamine treatment. Respiratory dynamics parameters were normalized at 4 and 24 hours post-GD exposure in scopolamine-treated animals. Lung histology showed that scopolamine treatment reduced bronchial epithelial and subepithelial inflammation and multifocal alveolar septal edema. These results suggest that aerosolized scopolamine considerably protects against GD-induced respiratory toxicity.

Desorption electrospray ionization mass spectrometric analysis of organophosphorus chemical warfare agents using ion mobility and tandem mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) has been applied to the direct analysis of sample media for target chemicals, including chemical warfare agents (CWA), without the need for additional sample handling. During the present study, solid-phase microextraction (SPME) fibers were used to sample the headspace above five organophosphorus CWA, O-isopropyl methylphosphonofluoridate (sarin, GB), O-pinacolyl methylphosphonofluoridate (soman, GD), O-ethyl N,N-dimethyl phosphoramidocyanidate (tabun, GA), O-cyclohexyl methylphosphonofluoridate (cyclohexyl sarin, GF) and O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate (VX) spiked into glass headspace sampling vials. Following sampling, the SPME fibers were introduced directly into a modified ESI source, enabling rapid and safe DESI of the toxic compounds. A SYNAPT HDMS instrument was used to acquire time-aligned parallel (TAP) fragmentation data, which provided both ion mobility and MS(n) (n = 2 or 3) data useful for the confirmation of CWA. Unique ion mobility profiles were acquired for each compound and characteristic product ions of the ion mobility separated ions were produced in the Triwave transfer collision region. Up to six full scanning MS(n) spectra, containing the [M + H](+) ion and up to seven diagnostic product ions, were acquired for each CWA during SPME fiber analysis. A rapid screening approach, based on the developed methodology, was applied to several typical forensic media, including Dacron sampling swabs spiked with 5 microg of CWA. Background interference was minimal and the spiked CWA were readily identified within one minute on the basis of the acquired ion mobility and mass spectrometric data.

Gene Expression Profiling of Rat Hippocampus Following Exposure to the Acetylcholinesterase Inhibitor Soman

Soman (O-pinacolyl methylphosphonofluoridate) is a potent neurotoxicant. Acute exposure to soman causes acetylcholinesterase inhibition, resulting in excessive levels of acetylcholine. Excessive acetylcholine levels cause convulsions, seizures, and respiratory distress. The initial cholinergic crisis can be overcome by rapid anticholinergic therapeutic intervention, resulting in increased survival. However, conventional treatments do not protect the brain from seizure-related damage, and thus, neurodegeneration of soman-sensitive brain areas is a potential postexposure outcome. We performed gene expression profiling of the rat hippocampus following soman exposure to gain greater insight into the molecular pathogenesis of soman-induced neurodegeneration. Male Sprague-Dawley rats were pretreated with the oxime HI-6 (l-(((4-aminocarbonyl)pyridinio)methoxyl)methyl)-2-((hydroxyimino)methyl)-pyridinium dichloride; 125 mg/kg, ip) 30 min prior to challenge with soman (180 microg/kg, sc). One minute after soman challenge, animals were treated with atropine methyl nitrate (2.0 mg/kg, im). Hippocampi were harvested 1, 3, 6, 12, 24, 48, 72, 96, and 168 h after soman exposure and RNA extracted to generate microarray probes for gene expression profiling. Principal component analysis of the microarray data revealed a progressive alteration in gene expression profiles beginning 1 h postexposure and continuing through 24 h postexposure. At 48 h to 168 h postexposure, the gene expression profiles clustered nearer to controls but did not completely return to control profiles. On the basis of the principal component analysis, analysis of variance was used to identify the genes most significantly changed as a result of soman at each postexposure time point. To gain insight into the biological relevance of these gene expression changes, genes were rank ordered by p-value and categorized using gene ontology-based algorithms into biological functions, canonical pathways, and gene networks significantly affected by soman. Numerous signaling and inflammatory pathways were identified as perturbed by soman. These data provide important insights into the molecular pathways involved in soman-induced neuropathology and a basis for generating hypotheses about the mechanism of soman-induced neurodegeneration.

Degradation of Chemical Warfare Agents by Reactive Polymers

Nucleophilic hydrolysis of chemical warfare agents (CWA), S-2-(diisopropylamino)ethyl O-ethyl methylphosphonothioate (VX), O-pinacolyl methylphosphonofluoridate (soman, or GD), and isopropyl methylphosphonofluoridate (sarin, or GB) by polyacrylamidoxime (PANOx) and poly(N-hydroxyacrylamide) (PHA) has been demonstrated. The reactive PANOx and PHA were obtained by one-step oximation of polyacrylonitrile and polyacrylamide, respectively. The polymers were converted to their respective oximate salts at pH values greater than the pKa of oximate or amidoximate groups of 7.5 and 10.8, respectively. Although the PANOx and PHA exhibited spontaneous hydrolysis at ambient temperature and humidity, the conversion of the hydroxamate into the unreactive carboxylic groups was insignificant even at prolonged storage, so that the polymers maintained reactivity at ambient conditions. When exposed to ambient air or 100% humidity, the polymers imbibed up to 65 wt % water, which dramatically enhanced the polymer reactivity to...

Acute Toxicity of Organophosphorus Compounds in Guinea Pigs Is Sex- and Age-Dependent and Cannot Be Solely Accounted for by Acetylcholinesterase Inhibition

This study was designed to test the hypothesis that the acute toxicity of the nerve agents S-[2-(diisopropylamino)ethyl]-O-ethyl methylphosphonothioate (VX), O-pinacolyl methylphosphonofluoridate (soman), and O-isopropyl methylphosphonofluoridate (sarin) in guinea pigs is age- and sex-dependent and cannot be fully accounted for by the irreversible inhibition of acetylcholinesterase (AChE). The subcutaneous doses of nerve agents needed to decrease 24-h survival of guinea pigs by 50% (LD(50) values) were estimated by probit analysis. In all animal groups, the rank order of LD(50) values was sarin > soman > VX. The LD(50) value of soman was not influenced by sex or age of the animals. In contrast, the LD(50) values of VX and sarin were lower in adult male than in age-matched female or younger guinea pigs. A colorimetric assay was used to determine the concentrations of nerve agents that inhibit in vitro 50% of AChE activity (IC(50) values) in guinea pig brain extracts, plasma, red blood cells, and whole blood. A positive correlation between LD(50) values and IC(50) values for AChE inhibition would support the hypothesis that AChE inhibition is a major determinant of the acute toxicity of the nerve agents. However, such a positive correlation was found only between LD(50) values and IC(50) values for AChE inhibition in brain extracts from neonatal and prepubertal guinea pigs. These results demonstrate for the first time that the lethal potencies of some nerve agents in guinea pigs are age- and sex-dependent. They also support the contention that mechanisms other than AChE inhibition contribute to the lethality of nerve agents.

Biomarkers of Low-Level Exposure to Soman Vapor: Comparison of Fluoride Regeneration to Acetylcholinesterase Inhibition

The nerve agent O-pinacolyl methylphosphonofluoridate, also known as soman or by its military designation GD, is a highly toxic organophosphorous compound that exerts its effects through inhibition of the enzyme acetylcholinesterase (AChE). In the present study, a fluoride ion based regeneration assay was developed to quantify the level of soman present in the blood of rats following a low-level whole-body inhalation exposure. It was hypothesized that the amount of regenerated nerve agent in the blood would be dose dependent in rats subjected to a whole-body inhalation exposure to a low-level dose of soman vapor, and that the fluoride ion-based regeneration method would be more sensitive for the detection of a low-level exposure to soman vapor than the measurement of whole blood AChE activity. Regenerated soman was dose-dependently detected in both the red blood cells (RBCs) and plasma of exposed rats at all concentrations tested (0.033–0.280 mg/m3 for a 240-min exposure). Significant inhibition of whole blood AChE activity did not occur below a concentration of 0.101 mg/m3, and was only depressed by approximately 10–25% at concentrations ranging from 0.101 mg/m3 to 0.280 mg/m3. This study is the first to utilize a fluoride ion-based regeneration assay to demonstrate the dose-dependent increases in soman in the blood following whole-body inhalation exposure to low levels of vapor. Additionally, the results of the present study demonstrate that the fluoride ion based regeneration assay was approximately threefold more sensitive than the measurement of AChE activity in the blood for the detection of exposure to soman, and also that miosis is a more sensitive marker of soman exposure than inhibition of AChE activity.

Enhanced stereoselective hydrolysis of toxic organophosphates by directly evolved variants of mammalian serum paraoxonase

We addressed the ability of various organophosphorus (OP) hydrolases to catalytically scavenge toxic OP nerve agents. Mammalian paraoxonase (PON1) was found to be more active than Pseudomonas diminuta OP hydrolase (OPH) and squid O,O-di-isopropyl fluorophosphatase (DFPase) in detoxifying cyclosarin (O-cyclohexyl methylphosphonofluoridate) and soman (O-pinacolyl methylphosphonofluoridate). Subsequently, nine directly evolved PON1 variants, selected for increased hydrolytic rates with a fluorogenic diethylphosphate ester, were tested for detoxification of cyclosarin, soman, O-isopropyl-O-(p-nitrophenyl) methyl phosphonate (IMP-pNP), DFP, and chlorpyrifos-oxon (ChPo). Detoxification rates were determined by temporal acetylcholinesterase inhibition by residual nonhydrolyzed OP. As stereoisomers of cyclosarin and soman differ significantly in their acetylcholinesterase-inhibiting potency, we actually measured the hydrolysis of the more toxic stereoisomers. Cyclosarin detoxification was approximately 10-fold faster with PON1 mutants V346A and L69V. V346A also exhibited fourfold and sevenfold faster hydrolysis of DFP and ChPo, respectively, compared with wild-type, and ninefold higher activity towards soman. L69V exhibited 100-fold faster hydrolysis of DFP than the wild-type. The active-site mutant H115W exhibited 270-380-fold enhancement toward hydrolysis of the P-S bond in parathiol, a phosphorothiolate analog of parathion. This study identifies three key positions in PON1 that affect OP hydrolysis, Leu69, Val346 and His115, and several amino-acid replacements that significantly enhance the hydrolysis of toxic OPs. GC/pulsed flame photometer detector analysis, compared with assay of residual acetylcholinesterase inhibition, displayed stereoselective hydrolysis of cyclosarin, soman, and IMP-pNP, indicating that PON1 is less active toward the more toxic optical isomers.

Theoretical studies of reaction pathways and energy barriers for alkaline hydrolysis of phosphotriesterase substrates paraoxon and related toxic phosphofluoridate nerve agents

Ab initio molecular orbital calculations were carried out to study reaction pathways and evaluate energy barriers for alkaline hydrolysis of O,O-diethyl p-nitrophenyl phosphate (paraoxon), diisopropyl phosphorofluoridate (DFP), O-isopropyl methylphosphonofluoridate (sarin), O-pinacolyl methylphosphonofluoridate (soman) and O,O-dimethyl phosphorofluoridate. This is the first computational study on the reaction pathways for hydrolysis of phosphotriesters and their structural variants that have small pKa values for the leaving groups. The reaction coordinate calculations reveal that the hydrolysis of DFP, sarin, soman and O,O-dimethyl phosphorofluoridate proceeds through the attack of hydroxide ion at the phosphorus center to form a pentacoordinate intermediate and the decomposition of the intermediate through F leaving. The hydrolysis of paraoxon was found to occur by a one-step process, which strongly supports the conclusion, based on the previously observed primary and secondary 18O isotope effects, of an SN2-like transition state with the absence of a stable pentacoordinate intermediate during the paraoxon hydrolysis. The energy barriers calculated in the gas phase for the pentacoordinate intermediate decomposition step are slightly lower than for the formation step for DFP and sarin, and are higher for soman and O,O-dimethyl phosphorofluoridate. Solvent effects significantly increase the energy barriers for the pentacoordinate intermediate formation step and significantly decrease the energy barriers for the decomposition step. Thus, the pentacoordinate intermediate formation step of hydrolysis in aqueous solution is always rate-determining. For the hydrolysis of all the compounds examined in this study, the energy barrier, 0.8 kcal mol−1, calculated for the paraoxon hydrolysis is the lowest in the gas phase, whereas the corresponding barrier, 10.1 kcal mol−1, is the highest in aqueous solution. For the hydrolysis of sarin in aqueous solution, for which the experimental activation energy is available, the calculated energy barrier of 8.6 kcal mol−1 for the pentacoordinate intermediate formation (i.e. the rate-determining step) is in good agreement with the experimental activation energy of 9.1 kcal mol−1. Finally, the relative magnitudes of the energy barriers calculated for the alkaline hydrolysis were qualitatively compared with the relative magnitudes of the available experimental rate constants reported for the corresponding phosphotriesterase-catalyzed hydrolysis, and were employed to discuss substituent effects.

The influence of anticholinergic drug selection on the efficacy of antidotal treatment of soman-poisoned rats

The influence of some anticholinergic drugs (atropine, benactyzine, biperiden, scopolamine) on the efficacy of antidotal treatment to eliminate soman ( O-pinacolyl methylphosphonofluoridate)-induced disturbance of respiration and circulation and to protect experimental animals poisoned with supralethal dose of soman (1.5×LD 50) was investigated in a rat model with on-line monitoring of respiratory and circulatory parameters. While the oxime HI-6 in combination with atropine prevented soman-induced changes in monitored physiological parameters insuficiently and very shortly, the combination of HI-6 with benactyzine or biperiden is able to prevent soman-induced alteration of respiration and circulation much more longer. Nevertheless, only rats treated with HI-6 in combination with scopolamine were fully protected against the lethal toxic effects of soman within 2 h following soman challenge. Our findings confirm that anticholinergic drugs with the strong central antimuscarinic activity, such as benactyzine, biperiden and especially scopolamine, seem to be more effective adjuncts to HI-6 treatment of severe acute soman-induced poisoning than atropine.

γ-Hydroxyphosphonate inducing single-chain antibodies capable of catalyzing soman hydrolysis

A γ-hydroxyphosphonate P 6 ( O 1 -methyl- O 2 -(1, 2, 2-trimethylpropyl)-2-hydroxy-5- nitrophenyl methylphosphonic acid) which is proposed to be an analog of the transition state in hydrolysis of soman was synthesized. Artificial antigens were obtained by conjugating P 6 to the carrier proteins BSA (bovine serum albumin) and LPH ( Limulus polyphenus hemocyanin). Mice were immunized with P 6 -LPH and recombinant single-chain antibody phage display library was constructed. After 4 rounds of panning against P 6 -BSA and competitive inhibition enzyme immunoassay, more than 70 strains of phage antibodies capable of binding soman were obtained and 11 of them can accelerate the hydrolysis reaction of soman. One of them (EP 6 ) was studied further. Soluble single-chain antibody was prepared and purification was performed by gel filtration and ion exchange chromatography. The kinetic experiment was carried out showing that the turnover number k cat = 198 min -1 and the rate enhancement k cat / k uncat = 122 419. When 0.16 mg mL -1 EP 6 was preincubated in vitro with 0.132 mmol L -1 (220 mg kg -1 = 1.1×LD 95 ) of soman prior to the administration to mice by subcutaneous route, all animals (19 mice) survived whereas all the control mice (14) treated with PBS and soman died within 30 min. Furthermore, EP 6 could prolong the latent time of spasm and death when mice were passively immunized with EP 6 intravenously 15 min before 1×LD 95 of soman challenge. These results demonstrate that EP 6 is able to increase the rate of soman degradation and protect against soman's toxicity, especially in vitro.

Reaction Products of Acetylcholinesterase and VX Reveal a Mobile Histidine in the Catalytic Triad

Reaction Products of Acetylcholinesterase and VX Reveal a Mobile Histidine in the Catalytic Triad

Spectrophotometric determination of paraoxonase within mouse carrier red blood cells.

A method has been developed to continuously measure paraoxonase activity spectrophotometrically in carrier red blood cells (RBCs) containing paraoxonase. This enzyme has a broad substrate specificity that includes parathion, paraoxon, soman, sarin, di-isopropyl fluorophosphate and many other organophosphorus compounds. Paraoxon is hydrolysed by paraoxonase to the less toxic 4-nitrophenol and diethyl phosphate. Determination of enzymic activity was based on the liberation of 4-nitrophenol in the presence of mouse RBCs. Paraoxonase was encapsulated within murine RBCs by hypotonic dialysis with subsequent resealing and annealing. The enzyme within resealed RBCs actively hydrolyses paraoxon in biological fluids to its less toxic metabolites. Paraoxonase incorporated within RBCs, like other enzymes, was found to be quite stable once encapsulated into RBCs and this formed the basis for this spectrophotometric method. Increasing absorbance at 400 nm indicated paraoxon hydrolysis and was the basis employed to determine enzymic activity. The Km of the enzyme within erythrocytes was 0.04 mM. This method offers a convenient, rapid and continuous way to monitor paraoxonase activity inside the carrier cell.

The effect of various compounds on the motor performance of mice impaired by phosphonofluoridic acid, methyl-,1,2,2-trimethylpropyl ester(soman)

The effect of various compounds on the motor performance of mice impaired by phosphonofluoridic acid, methyl-,1,2,2-trimethylpropyl ester(soman)

A19F NMR STUDY OF THE HYDROLYSIS OF ORGANOPHOSPHORUS FLUORIDATES IN AQUEOUS SOLUTION Doubling of the19F nmr in Diastereoisomeric Mixtures

Abstract 1H and 19F nmr spectra of two series of organophosphorus esters containing a P–F bond were studied. 2-Fluoro-4-methyl 1,3,2-dioxaphosphorinane 2-oxide (2) was found to be a mixture of two diastereoisomers in the ratio of trans/cis = 4. Stereospecific catalysis of phosphate and maleate anions in the hydrolysis of 2 was observed, leading to enrichment of the non-hydrolysed fluoridates with the trans isomer. The 19F nmr spectra of O-2-butyl methylphosphonofluoridate (7) and O-pinacolyl methylphosphonofluoridate (8), showed doubling of the 19F nmr spectra, giving rise to two sets of double quartets of equal intensity. 1:1 mixtures of diastereoisomers account for the doubling of the resonance rather than sterically hindered rotation. The applicability of nmr spectroscopy to the study of stereospecific displacement reactions at tetrahedral phosphorus is discussed.