Nerve Agent Simulant Dimethyl Methylphosphonate Research Articles

Chitosan-Based Molecularly Imprinted Polymers for Effective Trapping of the Nerve Agent Simulant Dimethyl Methylphosphonate

A molecular imprinted polymer (MIP) fabricated from a biomaterial (chitosan) was successfully created for the selective trapping of dimethyl methylphosphonate (DMMP) in the thousands of parts per million. DMMP is an organophosphorus compound that can be used in the production of chemical weapons and is the accepted surrogate to test filters and protective clothing designed to trap organophosphorus compounds. Computational calculations (density functional theory: B3LYP/6-31G) were used to calculate the optimum ratio of chitosan to DMMP that would produce the most energetically stable template–monomer complex. Gas chromatography mass spectrometry was used to model the DMMP concentration in the gas phase and to determine the DMMP trapped by the MIP, non-imprinted polymer (NIP), and activated charcoal. The MIP trapped 4554 (±227) ppm (4.55 mg/g) DMMP and outperformed both the NIP (156 (±20) ppm (0.16 mg/g)) and activated charcoal (82 (±17) ppm (0.08 mg/g)). Acetic acid, ammonium hydroxide, acetone, ethanol, and 2-propanol were introduced into the system as interferents and did not significantly affect the amount of DMMP trapped by the MIP: 4286 (±74) ppm (4.29 mg/g). Reusability of the MIP is affected by the extraction process but does not significantly affect the intended use as a filter for hazardous materials. Scanning electron microscopy was used to study the surface morphology of the MIP, and after MeOH extraction, the surface of the MIP became coarser, illustrating the alteration of the material. Overall, the trapping capabilities of the MIP are far superior to activated charcoal 50-fold and can be used as a filling agent in gas masks or gas filters.

Study on the formulations for Topical Skin Protectant against Liquid-Phase Chemical Warfare Agents

Chemical warfare agents(CWA) such as nerve agents and vesicating agents show lethality by skin contamination. Skin protection, therefore, is one of the top priorities to deal with the growing threat from CWA. In an attempt to develop the most effective topical skin protectant(TSP), candidate substances including PFPE(perfluorinated polyether), PTFE(polytetrafluoroethylene), glycerin, and polysaccharides were evaluated in forms of various formulations against nerve agent simulant DMMP(dimethylmethyl phosphonate) penetration. The protective efficacy of the formulation against DMMP penetration was estimated as the onset time of color change of the KM9 chemical agent detection paper. Based on this study, it was found that several PFPE- and glycerin-based formulations exhibit remarkably superior efficacy as a protective cream. This protective cream is expected to be used as TSP for military application after further research.

Study of Light-Activated Regioregular Poly(3-Hexyltiophene) Photoconductive Polymer Sensing Properties in Nerve Agent Simulant (DMMP) Detection†.

In the present work, we report the use of regioregular poly(3-hexyltiophene) polymer (RR-P3HT) as a potential light-activated material for sensing the chemical nerve agent simulant dimethyl methylphosphonate (DMMP). The electrical response of thick films of RR-P3HT, deposited by spray-coating method onto a porous laminate substrate at room temperature, to DMMP vapours was investigated. The studied material was activated by light-emitting diodes that emitted light of different wavelengths. The sensing properties of RR-P3HT are considerably enhanced upon exposure to blue and yellow light. However, excitation by the low wavelength light (blue) caused degeneration of the material, resulting in lowered stability. In the case of the yellow light, degeneration was much slower and the limit of detection was 0.4 ppm. The studied material exhibited high selectivity, as it did not respond to 6 ppm of acetone and methanol vapours.

Adsorption and Destruction of the G-Series Nerve Agent Simulant Dimethyl Methylphosphonate on Zinc Oxide

Organophosphorus chemical warfare agents (CWAs) are extremely toxic compounds that are nominally mitigated with gas mask filtration employing metal oxide impregnated activated carbon filtration mat...

Ultrafast coherent vibrational dynamics in dimethyl methylphosphonate radical cation.

Femtosecond pump-probe measurements of the nerve agent simulant dimethyl methylphosphonate (DMMP) demonstrate the preparation of a robust coherent vibrational state in the corresponding radical cation. The oscillations in the transient ion yields have a period of 45 fs (750 cm-1), which is at least 3 times faster than any previously observed oscillations in polyatomic radical cations. Use of 1200-1600 nm, as opposed to 800 nm, wavelengths for ionization increases the oscillation amplitude by a factor of 5 and doubles the number of visible oscillation periods from 6 to 12, indicating that an adiabatic ionization mechanism significantly enhances preparation of the coherent state. The coherent motion is assigned to a bending mode in DMMP+ with frequency in the range of 742.2-754.7 cm-1 based on the results of DFT calculations. The observation of coherent nuclear dynamics in the dissociation of DMMP+ suggests the potential utility of coherent control schemes for controlling the dissociation of DMMP and related molecules, which has important implications for developing detection and decontamination technologies for organophosphorus chemical warfare agents.

Synthesis of functionalized mesoporous TiO2-SiO2 with organic fluoroalcohol as high performance DMMP gas sensor

Mesoporous TiO2-SiO2 functionalized with p-hexa-fluoroisopropanol aniline (HFIP) was designed and synthesized to achieve highly sensitive and selective sensing toward nerve agent simulant dimethyl methylphosphonate (DMMP) due to a hydrogen bonding between target DMMP and TiO2-SiO2-HFIP. The sensing experiments were conducted by coating compounds onto quartz crystal microbalance (QCM) transducers. It was found that the observed frequency shifts gradually and turned saturated in the range from 10 to 60ppm. Gas sensing test results revealed that sensors had enhanced sensitivity due to the decoration of HFIP on TiO2-SiO2 in a ppb level. Furthermore, when the doping of HFIP reached 20wt%, the sensors achieved the best sensing performance. In conclusion, the QCM sensor coated with mesoporous TiO2-SiO2-HFIP exhibited fast response, excellent reversibility and high selectivity to nerve agent stimulant DMMP vapor, implying that mesoporous TiO2-SiO2-HFIP may be a good candidate for sensing DMMP.

Oxidation, Destruction, and Persistence of Multilayer Dimethyl Methylphosphonate Films during Exposure to O(3P) Atomic Oxygen

We present work detailing the oxidative reactivity of the nerve agent simulant dimethyl methylphosphonate (DMMP) with atomic oxygen using time-resolved in situ reflection–absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). When exposed to a supersonic beam containing O(3P) with average translational energy of 0.12 eV, thermally annealed DMMP films (less than 50 layers) on single-crystal Au(111) are observed to react, likely via hydrogen abstraction, and followed by various secondary reactions with resultant hydroxyl and DMMP-derived radicals. This reaction is accompanied by the appearance of hydrogen bonding interactions with the DMMP phosphoryl (P═O) groups on the film surface, and it is also observed to result in both a loss of carbon and an uptake of oxygen by the film. These trends, when considered with the additional thermal stability of reaction products left on the surface, suggest that the mechanism entails reaction with DMMP methyl groups and the formation of vari...

4-(Hexafluoro-2-hydroxy isopropyl)aniline functionalized highly sensitive flexible SWCNT sensor for detection of nerve agent simulant dimethyl methylphosphonate

Dimethyl methylphosphonate (DMMP) is widely used as a simulant of nerve agent Sarin, which is an organophosphorus compound. In the present work, flexible single walled carbon nanotube (SWCNT) resistive sensor is functionalized with 4-(Hexafluoro-2-hydroxy isopropyl)aniline (HFiP-1) to enhance the response of the sensor towards DMMP vapors. Sensing properties of pristine and HFiP-1 functionalized flexible SWCNT resistive sensors for DMMP vapors are investigated at room temperature. The response of HFiP-1 functionalized sensor is enhanced towards DMMP due to the presence of strong hydrogen-bonding between the organophosphonate and HFiP-1. The response of functionalized sensor is 16.0% for 24 ppm of DMMP and increased 3.7 folds as compared to pristine sensor. The observed results indicate that, HFiP-1 plays a significant role in enhancement of SWCNT film sensor response towards DMMP. In addition, the flexible sensor fabricated by vacuum filtration method and functionalized using drop cast method gives repeatable response over five cycles that have been studied.

Detection of dimethyl methylphosphonate by thin water film confined surface-enhanced Raman scattering method

It is important and necessary to effectively detect the chemical warfare agents, such as highly toxic never agent sarin. However, based on the surface-enhanced Raman scattering (SERS) effect, detection of nerve agent simulant dimethyl methylphosphonate (DMMP) which is weakly interacted with SERS-active substrate has been the most challenge for the routine SERS detection method. To overcome this challenge, we put forward a thin water film confined SERS strategy. Under the space-confinement of water film, Raman measurements are carried out in the water evaporation process. The subsequent water evaporation induces concentrating of the DMMP molecules, which are thus successfully restricted within the strong electromagnetic field enhanced area above the SERS substrates, leading to the enhancement of their Raman signals. This study provides a new way to achieve the efficient SERS-based detection of the target molecules weakly interacted with the metal substrates.

Fluoroalcohol and fluorinated-phenol derivatives functionalized mesoporous SBA-15 hybrids: high-performance gas sensing toward nerve agent

Two new mesoporous SBA-15/organic hybrids featuring fluoroalcohol and fluorinated-phenol derivatives were successfully synthesized via a co-condensation route. Hexafluorobisphenol and hexafluoroisopropanol were chosen to graft onto mesostructured silica, respectively. The as-synthesized hybrids preserve their mesoscopic structures with relative large surface areas and pore volume, as confirmed by SAXS, TEM and N2 adsorption–desorption porosimetry. Moreover, FT-IR and solid-state MAS NMR spectroscopy proved covalent anchoring of the organic functional groups onto the SBA-15. In order to confirm the potential application of the hybrids in gas sensing, investigations on the sensing properties toward the nerve agent simulant dimethyl methylphosphonate (DMMP) were carried out by QCM transducer. The QCM sensors based on hybrid materials exhibit excellent sensitivity toward trace DMMP vapour down to 26 ppb. In comparison with pristine SBA-15, the hybrids also show remarkably enhanced selectivity to DMMP due to suitable H-bonding interactions. Therefore, the well-defined mesoscopic porosity of the organic–inorganic hybrids together with the grafted fluoroalcohol and fluorinated-phenol derivatives lead to excellent sensing properties to DMMP vapour, and show great potential in the area of nerve agent detection.

Polymer‐coated piezoelectric quartz crystal sensor for sensing the nerve agent simulant dimethyl methylphosphonate vapor

AbstractA chemical vapor sensor based on a quartz crystal microbalance was fabricated with a 10‐MHz quartz crystal oscillator. The quartz crystals were coated with four newly synthesized polymers and were studied for the detection of the nerve agent simulant dimethyl methylphosphonate vapor. The sensor was tested for immediate and extended periods of time. Various sensing parameters (e.g., the sensitivity, response time, and recovery time) were evaluated with respect to different coating materials. All the polymers showed fairly good baseline stability even after several cycles. The highest frequency drift of 23.8 Hz/kHz was observed for one of the polymers, whereas another polymer showed the best sensing stability over an extended period of 250 days. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Specifics of solvation of sulfonated polyelectrolytes in water, dimethylmethylphosphonate, and their mixture: A molecular simulation study

Sulfonated polyelectrolyte membranes (PEMs), such as Nafion and styrene-olefin block copolymers, are explored as permselective membranes for fuel cells as well as suitable barrier materials against chemical agents. The permselective properties of PEM are determined by their microphase segregation into hydrophilic and hydrophobic domains. We performed classical molecular dynamics simulations of solvation of the hydrophilic fragments of PEM exemplified on sulfonated polystyrene (sPS) with potassium, calcium, and aluminum as counterions, in water, phosphor-organic nerve agent simulant dimethylmethylphosphonate (DMMP), and their binary mixture. The force field for the sulfonate group has been developed by optimizing the potential parameters to fit the benzenesulfonate conformations obtained from the density functional theory. For a comparison, we considered perfluorosulfonate oligomers representing fragments of Nafion polymer. We found a noticeable difference between the geometries of the polymer backbone in different solvents. The polymer backbone is stiffer in DMMP for both sPS and Nafion. An anisotropic structuring of the solvent around the phenylsulfonate group is substantially stronger than around the Nafion sidechain due to the rigidity and the anisotropy of the phenylsulfonate group. The counterion significantly affects the conformations of solvated sPS: the rigidity of the backbone increases when potassium or calcium ions are replaced by trivalent aluminum ions.

Analytical application of poly{methyl[3-(2-hydroxy-3,4-difluoro)phenyl]propyl siloxane} as a QCM coating for DMMP detection

A new material—poly{methyl[3-(2-hydroxy-3,4-difluoro)phenyl]propyl siloxane}(PMDFPS) sensitive to toxic organophosphate vapor was synthesized with 2,3-difluorophenol, allyl bromide and poly (methyl hydrosiloxane) as raw materials, via O-alkylation, Claisen rearrange reaction and hydrosilylation reaction. This novel material was then coated on a quartz crystal microbalance (QCM) to investigate its gas sensitive properties to the nerve agent simulant dimethyl methylphosphonate (DMMP) vapor, as well as known interfering vapors. When tested with competing vapors, the sensor was more than 10 times sensitive to DMMP than to other interfering vapors. Thus, high selectivity of poly{methyl[3-(2-hydroxy-3,4-difluoro)phenyl]propyl siloxane} to DMMP was demonstrated. The poly{methyl[3-(2-hydroxy-3,4-difluoro)phenyl]propyl siloxane}-QCM sensor responded linearly to DMMP vapor with a slope of 14 Hz/ppm in the 1–50 ppm range with a detection limit of 0.21 ppm (S/N = 3).

Hyperbranched polyesters with internal and exo‐presented hydrogen‐bond acidic sensor groups for surface acoustic wave sensors

AbstractThree hyperbranched aromatic polyesters carrying both internal and exo‐presented hydrogen‐bond acidic phenol, carboxylic acid, or mixed phenol/acetoxy groups were coated onto 500 MHz surface acoustic wave (SAW) sensor platforms, and sensor responses to the nerve agent simulant dimethyl methylphosphonate (DMMP) and the explosives simulant dinitrotoluene (DNT) were studied. All three hyperbranched polyesters gave strong responses to DMMP, and the hyperbranched polyester carrying carboxylic acid groups gave a particularly strong response. The hyperbranched polyester carrying phenol groups gave the best response to DNT of the three polymers studied. The DMMP and DNT responses of the three hyperbranched polyesters were also compared with hyperbranched SAW sensor polymers carrying exo‐presented phenolic sensor groups only, and also with linear SAW sensor polymers carrying phenolic sensor groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Hydrogen‐bond acidic polyhedral oligosilsesquioxane filled polymer coatings for surface acoustic wave sensors

AbstractA series of novel polyhedral oligosilsesquioxane nanofiller compounds functionalized with hydrogen‐bond acidic sensor groups was prepared, characterized by IR, 1H‐, 13C‐ and 29Si‐NMR, and MALDI‐TOF MS, and formulated into polymer coatings for 500 MHz surface acoustic wave sensor platforms. Sensor responses to the explosives simulant dinitrotoluene and to the nerve agent simulant dimethyl methylphosphonate were studied, and the performances of the polyhedral oligosilsesquioxane formulations were compared with those of conventional hydrogen‐bond acidic linear surface acoustic wave sensor polymers carrying the same sensor groups. The polyhedral oligosilsesquioxane formulations gave good initial responses to the simulants, maintained 40–65% of their original response over a period of 6 months and maintained their sensitivity down to a simulant vapor concentration of 1 ppb v. The surface compositions of the surface acoustic wave sensor coatings were characterized by sum frequency generation spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Modelling and measurements of a composite microcantilever beam for chemical sensing applications

A resonant microcantilever beam gas sensor was designed and fabricated in Carnegie Mellon University using complementary metal oxide semiconductor (CMU-CMOS) technology. The cantilever beam modified with a suitable sorbent coating was demonstrated as a chemical transducer for monitoring hazardous vapours and gases at trace concentrations. The design of the cantilever beam included interdigitated fingers to allow electrostatic actuation of the device and a piezoresistive Wheatstone bridge design to read out the deflection signal. The cantilever beam resonant frequency was modelled using the Euler-Bernoulli beam theory and ANSYS. The beam resonant frequency was measured with an optical laser Doppler vibrometer. Good agreement was obtained among the measured, simulated, and modelled resonant frequencies. A custom sorbent polymer layer was coated on the surface of the cantilever beam to allow its operation as a gas-sensing device. The frequency response as a function of exposure to the nerve agent simulant dimethylmethylphosphonate (DMMP) at different concentrations was measured, which allowed a demonstrated detection at a concentration of 20 ppb or 0.1 mg/m3. The air-polymer partition coefficient K, for DMMP was estimated and compared favourably with the known values for related polymers.

Micropreconcentrator for Enhanced Trace Detection of Explosives and Chemical Agents

The design, fabrication, and testing of a sorbent-coated microfabricated preconcentrator device in complementary metal-oxide-semiconductor is presented. As a sorbent-coated device, the preconcentrator is used to collect, concentrate, and deliver analyte sampled from air for analysis with a detector. The preconcentrator in this paper is based on a perforated flowthrough microhotplate structure that is coated with a sorbent layer to maximize vapor trapping efficiency. The coating sorbs the analytes of interest during the collection phase at ambient temperatures. A thermal desorption cycle is then used to rapidly heat the preconcentrator to 180 degC in 40 ms to release a concentrated wave of analyte. A finite-volume method was used to simulate the temperature distribution on a microhotplate and to model the time to reach the steady-state temperature. The experimental electrical measurements of the device were found to be in good agreement with the predicted values obtained using the finite-volume method. The preconcentrator device was demonstrated by interfacing to the front end of a handheld chemical agent detector and a handheld trace explosives detector. The preliminary results showed signal enhancement for the detection of the nerve agent simulant dimethylmethylphosphonate and the explosive 2,4,6-trinitrotoluene

Effects of high relative humidity on the dynamic adsorption of dimethyl methylphosphonate (DMMP) on activated carbon

The effects of high relative humidity (RH) on the breakthrough of the nerve agent simulant dimethyl methylphosphonate (DMMP) vapor in beds of ASC-impregnated, activated carbon were investigated. Maximum concentrations of DMMP at room temperature and RH > 60% were found to be lower by more than an order of magnitude than in dry air. The breakthrough time ( t B) of 1.2 × 10 −4 g l −1 DMMP in pre-humidified beds and humid air of RH = 90% was shortened by a factor of 1.6 relative to adsorption in dry beds and dry air. Analysis of the breakthrough curves according to the Wheeler–Jonas model indicated that the high RH lowered the dynamic adsorption capacity ( W E) but had nearly no effect on the critical bed weight ( W C). The reduction of W E by humidity correlates with the observed displacement of adsorbed water by DMMP. The use of DMMP for testing filter performance is limited to low and intermediate relative humidities. On the other hand, DMMP in dry air can be used to advantage for testing the capacity of new or used respirator filters and for the detection of filter channeling.

Adsorption and Photodegradation of Dimethyl Methylphosphonate Vapor at TiO2 Surfaces

The adsorption and degradation of the nerve agent simulant dimethyl methylphosphonate (DMMP) over UV-irradiated TiO(2) powders and thin films has been investigated. Adsorption of vapor-phase DMMP on TiO(2) powder is characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Photochemically assisted oxidation of adsorbed DMMP is carried out in situ by irradiation of samples in the DRIFTS accessory, giving kinetic data and information on specific site binding of DMMP and catalyst poisoning. Gas-phase intermediates from a static vapor phase reaction are identified by gas chromatography-mass spectrometry analysis, and surface-bound intermediates and products are analyzed by high-performance liquid chromatography-mass spectrometry, and ion chromatography of both aqueous and organic extractions from the TiO(2). Adsorbed DMMP is photodegraded in a stepwise fashion to give methylphosphonic acid, PO(4)(3-), H(2)O, and CO(2) as products. A proposed reaction pathway is consistent with a rapid degradation of DMMP but with extensive poisoning of the catalyst by surface-bound phosphonate products.

Electrostatically actuated resonant microcantilever beam in CMOS technology for the detection of chemical weapons

The design, fabrication, and testing of a resonant cantilever beam in complementary metal-oxide semiconductor (CMOS) technology is presented in this paper. The resonant cantilever beam is a gas-sensing device capable of monitoring hazardous vapors and gases at trace concentrations. The new design of the cantilever beam described here includes interdigitated fingers for electrostatic actuation and a piezoresistive Wheatstone bridge design to read out the deflection signal. The reference resistors of the Wheatstone bridge are fabricated on auxiliary beams that are immediately adjacent to the actuated device. The whole device is fabricated using a 0.6-/spl mu/m, three-metal, double-poly CMOS process, combined with subsequent micromachining steps. A custom polymer layer is applied to the surface of the microcantilever beam to enhance its sorptivity to a chemical nerve agent. Exposing the sensor with the nerve agent simulant dimethylmethylphosphonate (DMMP), provided a demonstrated detection at a concentration of 20 ppb or 0.1 mg/m/sup 3/. These initial promising results were attained with a relatively simple design, fabricated in standard CMOS, which could offer an inexpensive option for mass production of a miniature chemical detector, which contains on chip electronics integrated to the cantilever beam.