Molecular Simulation of Chemical Warfare Agent Adsorption

摘要韦恩州立大学-0522005用于检测化学战剂（CWA）和有毒工业材料（TIM）的基于半导电金属氧化物（SMO）的传感器的灵敏度约为十亿分之几。 基于SMO的传感器在尺寸、重量和成本方面具有优于其他化学剂检测方法的潜在优势。 使用SMO基传感器进行CWA/TIM检测的一个限制因素是这些材料是非选择性的。 也就是说，除了感兴趣的试剂之外，还有许多分子将产生阳性检测结果。 本论文的工作主要集中在提高半导体金属氧化物传感器的选择性和减少假阳性响应，控制CWA/IM在表面的吸附和随后通过孔的扩散以及此类器件设计中的关键因素。 这可以通过预过滤方案来完成，其中混合气体流穿过陶瓷膜或活性炭。 孔径、形状和化学组成可以定制以选择性地吸附感兴趣的分子。 在预过滤器中浓缩后，CWA/TIM通过化学置换器或热脉冲释放，并发送到SMO进行检测。 预过滤的另一种方法是使用模板形成对目标分子具有高选择性的多孔半导体金属氧化物。 本文采用分子模拟方法研究了CWA及其模拟物在MCM-41分子筛中的吸附行为。 分子模拟非常适合于有毒物质的研究，可以用来提取特定分子间相互作用在吸附过程中所起作用的信息。 由于适当的模型（力场），所以不存在感兴趣的分子，重大的努力，提出了发展可转移的联合原子力场的有机磷酸酯，包括化学战剂沙林和VX。 分子模型的开发是使用模拟用于基于SMO的传感器的设计中所需的第一步。 这些分子模型将允许使用模拟来研究孔径、形状和组成对多孔材料相对于特定CWA/TIM的选择性的影响。 原子模拟和从头算方法用于识别特定的多孔结构（形状/尺寸），具有低假阳性的CWA/TIM传感所需的高选择性。 更广泛的影响最近的世界事件，如沙林毒气释放到东京地铁系统和目前对潜在对手怀疑发展和使用化学和生物战剂的关注，强调了开发高度移动的，准确的传感器和这些材料的去污设备的重要性。 作为拟议研究的结果，PI希望通过开发必要的计算基础设施来克服该领域目前的局限性，以便在新型模板分子识别材料的设计中使用模拟。 与其他多孔材料相比，这些模板分子识别材料具有对化学战剂的高选择性和灵敏度。 对特定目标分子具有高亲和力的吸附剂的开发预期将导致改进的传感器、过滤器和催化材料。 预计这些发展将减少恐怖组织使用化学战剂的威胁，改善国家安全和公众健康。 此外，精确的力场描述探索分子和金属氧化物表面之间的相互作用，将允许其他研究小组使用分子模拟作为一个太设计新的吸附剂和催化材料用于其他目的。 鼓励本科生，特别是代表性不足的少数民族和妇女参加本科生研究项目。 本科生的研究经验被用作指导工具，以提高学生的招聘和保留在少数群体与历史上较低的保留率。

ABSTRACTWayne State University - 0522005Semi-conducting metal oxide (SMO) based sensors for the detection of chemical warfare agents (CWA) and toxic industrial materials (TIM) exhibit sensitivities on the order of parts per billion. SMO based sensors have potential advantages over other methods of chemical agent detection in terms of size, weight and cost. One limiting factor in the use of SMO based sensors for CWA/TIM detection is that these materials are non-selective. That is, there are many molecules, in addition to the agent of interest, which will yield positive detection results. The proposed work is focused on improving the selectivity of semi-conducting metal oxide sensors and the reduction of false positive responses.Controlling the adsorption of CWA/IM onto the surfaces and their subsequent diffusion through the pores and key factors in the design of such devices. This can be done via a pre-filtering scheme, where a mixed gas stream in passed through a ceramic membrane or activated carbon. Pore size, shape and chemical composition can be tailored to selectively adsorb the molecule of interest. After being concentrated in the pre-filter, the CWA/TIM is released by a chemical displacer or a thermal pulse and sent to the SMO for detection. An alternative approach to pre-filtering is to use templating to form porous semi-conducting metal oxides with high selectivity to the target molecule. In the proposed work, molecular simulation is used to determine the absorption behavior of CWA and their simulants in the molecular sieve MCM-41.The difficult nature of performing experiments on CWA/TIM motivates the proposed use of computational methods. Molecular simulations is well suited to the study to the toxic material and can be used to extract information on the roles specific intermolecular interactions play in the adsorption process. Because appropriate models (force fields) so not exist for the molecules of interest, significant effort is proposed on the development of transferable united-atom force fields for organophosphates, including the chemical warfare agents sarin and VX. The development of molecular models is a required first step in use of simulation for the design of SMO based sensors. These molecular models will allow for the use of simulation to investigate the effects of pore size, shape and composition on the selectivity of porous materials with respect to specific CWA/TIM. Atomistic simulations and ab initio methods are used to identify specific porous structures (shape/size) with the high selectivity necessary for the sensing of CWA/TIM with low false positives. Broader ImpactsRecent world events, such as the release of sarin gas into the Tokyo subway system and the current concern over potential adversaries suspected development and use of chemical and biological warfare agents underscore the importance of developing highly mobile, accurate sensors and decontamination equipment for these materials. As an outcome of the proposed research, the PI expects to overcome the current limitations of the field by developing the necessary computational infrastructure for the use of simulation in the design of novel templated molecular recognition materials. These templated molecular recognition materials hold the promise of high selectivity and sensitivity to chemical warfare agents compared to other porous materials. Development of adsorbents with high affinity to a specific target molecule is expected to result I improved sensors, filters and catalytic materials. Such developments are expected to reduce the threat of the use of chemical warfare agents by terrorist organizations, improving national security and public health. Furthermore, accurate force fields describing the interactions between quest molecules and metal oxide surfaces will allow other research groups to use molecular simulation as a too to design novel adsorbent and catalytic materials for other purposes.This research is integrated with education. Undergraduates, particularly underrepresented minorities and women, are encouraged to participate in undergraduate research projects. The undergraduate research experience is used as a mentoring tool to improve the recruitment and retention of students in minority groups with historically low retention rates.