Collaborative Research: Ionic Liquids- Cations in the Spotlight and Single Atom Changes with Large Consequences.

美国国家科学基金会化学分部的化学结构、动力学和机制项目支持美国国家科学基金会协会的一项合作研究。爱荷华大学化学系Claudio J. Margulis教授（P.I.）和新泽西州立大学罗格斯分校化学和化学生物学系Edward W. Castner教授（co-P.I.）。目标是详细研究离子液体的结构和动力学性质，使用马古利斯小组的理论和计算方法与卡斯特纳小组的实验研究相结合。离子液体由柔性的、不对称的分子阳离子和阴离子组成。有几份报告表明，离子液体的阳离子或阴离子组分的微小修饰可以使其性质发生巨大变化。例如，用磷原子代替四烷基铵阳离子的中心氮原子可以导致液体粘度下降两倍。我们目前对这些液体的理解并不能直接解释这些结果；我们的目标是将这些液体的x射线和核磁共振实验与详细的分子模拟和理论分析相结合，以解释这种现象。从离子液体观察到的x射线散射模式都具有相同的双（三氟甲基磺酰基）酰胺阴离子是非常相似的。这是因为阴离子比烃基阳离子有更多的富电子原子。因此，尽管阳离子可能是许多液体中最重要的组织成分，但x射线散射中的信息内容主要提供了关于阴离子的详细信息，而关于阳离子的信息只能间接获得。我们将通过制备具有较小阴离子的离子液体（如硝酸盐、二氰酰胺和醋酸盐）来扭转这种情况，以便观察到的x射线散射模式主要是由阳离子散射造成的。这将为离子液体的结构研究提供一个新的视角。它也将有助于测试和设计更好的模拟参数。虽然这项研究是基础性的，但其结果将为离子液体的设计、测试和选择提供信息，用于一系列电解质应用以及与生物分子和组件的相互作用。这些液体为能源储存、纳米技术、生物质加工和药物研究等领域的许多重大挑战提供了解决方案。本科生、研究生和博士后研究人员将接受最新实验方法的培训，包括基于同步加速器的x射线散射实验、二维核磁共振波谱、分子动力学模拟和应用于复杂液体统计物理的理论方法。

The Chemical Structure, Dynamics and Mechanisms Program of the NSF Chemistry Division supports a Collaborative Research effort by Assoc. Prof. Claudio J. Margulis (P.I.) at the University of Iowa Dept. of Chemistry and by Prof. Edward W. Castner, Jr. (co-P.I.) at the Dept. of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey. The goal is to study in detail the structural and dynamical properties of ionic liquids using a combination of theoretical and computational methods from the Margulis group with experimental investigations done by the Castner group. Ionic liquids consist of flexible, asymmetric molecular cations and anions. Several reports have shown that very small modification of either the cation or the anion components of the ionic liquid can make dramatic changes to its properties. For example replacing the central nitrogen atom of a tetralkylammonium cation by a phosphorus atom can lead to a drop in the liquid viscosity by a factor of two. Our current understanding of these liquids does not provide a straightforward explanation of these results; our goal is to combine x-ray and NMR experiments on these liquids with detailed molecular simulations and theoretical analyses to explain this phenomenon.The observed x-ray scattering patterns from ionic liquids that all share the same bis(trifluoromethylsulfonyl)amide anion are remarkably similar. This is because the anions have more electron-rich atoms than the hydrocarbon-based cations. Thus, whereas the cations may be the most important organizational components in many liquids, the information content in the x-ray scattering provides mostly detailed information about the anions with information about the cations being obtained only indirectly. We will invert this circumstance by preparing ionic liquids with smaller anions such as nitrate, dicyanamide and acetate, so that the observed x-ray scattering patterns result predominantly from scattering by the cations. This will provide a new perspective on the structure of ionic liquids. It will also help in testing and designing better parameters for simulations.While the research is of a fundamental nature, the outcomes will inform the design, testing and selection of ionic liquids for a range of electrolyte applications and interaction with biological molecules and assemblies. These liquids are providing solutions to a number of significant challenges in energy storage, nanotechnology, processing of biomass, and pharmaceutical research. Undergraduate students, graduate students and postdoctoral researchers will receive training in the latest experimental methods, including synchrotron-based x-ray scattering experiments, two-dimensional NMR spectroscopy, molecular dynamics simulations, and theoretical methods applied to the statistical physics of complex liquids.