Royal Military College of Canada
Materials Science & Engineering
Reactive Surfaces for Detoxification of Chemical Warfare Agents
By: Dr. James Wojtyk
Recent world events have focused the attention of the political and scientific communities on the threat of Chemical Warfare (CW) agents. While there are many CW agents, mustard gas (HD) and the organophosphate (OP)-based nerve agents (Sarin, Soman,Tabun and VX) are commonly considered since they are readily synthesized, known to be stockpiled, and are extremely toxic.
As the economical and technical barriers towards acquiring these agents have decreased, there have been concerted efforts to develop novel methods for the detection, protection and decontamination of these materials. However, the conventional approaches of decontamination, i.e. incineration and/or hydrolysis/oxidation, are plagued by environmental and public safety concerns. Similarly, protective garments are cumbersome and provide limited protection capacity due to their reliance on activated carbon adsorption. Thus, there remains a strong need for materials that can eliminate CW agents without addition of reagents to advance detection and protection technologies.
In an effort to find safer and more efficient alternatives, attention has focused on the enzymatic degradation of CW agents due to inherent enzyme-substrate specificity and rapid turnover rates. Organophosphorous Hydrolase (OPH) was found to hydrolyze CW agents containing P-O, P-S, P-CN and P-F bonds. Because of its unique reactivity towards nerve agents, immobilization and encapsulation strategies have been pursued to increase OPH stability and activity.
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Unlike the OP nerve agents, enzymatic degradation of mustard gas is not currently possible. The only methods for detoxification are nucleophilic substitution (eg. amine) at the aliphatic chlorine or by partial oxidation of the sulfide to the sulfoxide. Stoichiometric systems of this type are limited in their protective capacity because the reaction is irreversible and the reactive material is consumed.
In realistic applications involving CW detoxification and detection, OPH activity must be maintained in the presence of other CW agents. However, mustard gas results in irreversible deactivation and denaturation of enzymes. Therefore, in order to harness all of the advantages of OPH, a parallel mechanism for deactivating mustard gas must be incorporated into any device.
This project is focused on the development of a thin-film technology that is capable of simultaneously sensing and detoxifying mustard gas and nerve agents. The formation of organic monolayers on semiconductor surfaces (e.g. silicon) is an attractive route for introducing stable chemical and biochemical functionalities onto a surface. The reaction of n-alkenes with Si-H surfaces under photochemical conditions is a simple route towards passivation of the surface and can be used to incorporate a carboxylate functional group into the monolayer if the alkene used is undecylenic acid. Monolayers formed are flat on the Angstrom level and have an increase in hydrolytic stability (HF, KOH) due to a higher structural order. This inherent stability is crucial if the intrinsic semiconductor properties are to be exploited for sensor development.
Hydrolytic enzymes specific to organophosphorous esters will be immobilized onto micropatterned surfaces and the rate of vapor- and liquid-phase CW simulant deactivation using spectrophotometric techniques will be investigated. This work is being performed in collaboration with the National Research Council of Canada.
For further information on this project, please contact Dr. James Wojtyk: James.Wojtyk@rmc.ca
