RUI: Bimolecular Collisions in Ionic Liquids

在这个由化学系化学结构、动力学和机理-A（CSDM-A）项目资助的项目中，加州州立大学（CSU）北岭分校的Miroslav Peric教授和他的学生正在研究溶解在室温离子液体（IL）中的分子之间的碰撞。离子液体是一类被用作挥发性有机溶剂的环境友好替代品的液体。 液体中分子碰撞的频率可以提供化学反应在该液体中发生的速度的概念。 离子液体与其他液体不同，因为它们由带正电荷和带负电荷的分子组成（带电荷的原子或分子称为“离子”，因此命名为离子液体）。 目前对离子液体中分子碰撞的理解是有限的。 水、酒精和汽油是由中性（不带电）分子组成的液体的常见例子。Peric教授将具有磁性的“探针”分子溶解到离子液体中。然后，他使用电子顺磁共振（EPR）光谱法来检测探针分子与IL碰撞时的磁性变化。 EPR测量原子或分子中电子的磁性。对离子液体中碰撞事件的详细了解，以及这些事件与离子液体结构的关系，最终可能使我们能够为特定的技术应用设计离子液体。该研究项目的本科生和研究生将获得从溶液化学到物理学和量子力学到复杂数据分析的广泛学科的宝贵机会。该项目基于EPR海森堡自旋交换（HSE）技术，可以分离粘性介质中偶极-偶极和自旋交换相互作用的影响。这种分离使得能够测量中性和带电氮氧自由基在粘性液体如离子液体中的双分子碰撞。测量了中性、单电荷和双电荷氮氧自旋探针在由不同大小的阳离子和阴离子组成的离子液体中的平移和旋转扩散随温度的变化。氮氧自由基自旋探针的选择允许了解离子液体中自旋探针的双分子碰撞的电荷效应。阳离子是取代咪唑（乙基至辛基）的同系阳离子。 这一系列阳离子使Peric团队能够澄清离子液体的疏水部分在溶液相动力学中的作用。类似地，阴离子具有两种不同的尺寸（单原子阴离子和大的多原子阴离子），以理解阴离子对离子液体中溶质分子的平移的影响。用分数斯托克斯-爱因斯坦关系和科恩-特恩布尔自由体积方程对结果进行了解释。该项目的更广泛的影响包括对离子液体中化学反应的传输特性和动力学的理解，以及CSU北岭学生获得实验研究，尖端仪器和理论经验的机会，所有这些都是有价值的，因为学生进入现代化学科学的劳动力。这个奖项反映了NSF的法定使命，并已被认为是值得支持，通过使用基金会的知识价值和更广泛的影响审查标准进行评估。

In this project funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program of the Chemistry Division, Professor Miroslav Peric and his students at the California State University (CSU) Northridge are studying the collisions between molecules dissolved in room temperature ionic liquids (ILs). ILs are a class of liquids which are being used as environmentally-friendlier substitutes for volatile organic solvents. The frequency of molecular collisions in a liquid can provide an idea of how quickly chemical reactions can take place in that liquid. ILs are different from other liquids because they are composed of positively and negatively charged molecules (charged atoms or molecules are called "ions", hence the name ionic liquid). The current understanding of molecular collisions in IL liquids is limited. Water, alcohol, and gasoline are common examples of liquids composed of neutral (non-charged) molecules. Professor Peric dissolves "probe" molecules that have magnetic properties into the ILs. He then uses Electron Paramagnetic Resonance (EPR) spectroscopy to detect changes in the probe molecule's magnetic properties as the probe collides with the IL. EPR measures the magnetic properties of electrons in atoms or molecules. A detailed understanding of collision events in ILs, and how these relate to the structure of the ILs may ultimately allow us to design ILs for specific technological applications. The undergraduate and graduate students working on this research project are gaining valuable exposure to a wide range of disciplines, from solution chemistry to physics and quantum mechanics to complex data analysis.The project is based on the EPR Heisenberg Spin Exchange (HSE) technique that can separate the effects of dipole-dipole and spin exchange interactions in viscous media. This separation enables the measurement of the bimolecular collisions of neutral and charged nitroxides in viscous liquids such as ILs. The translational and rotational diffusion of neutral, singly-charged and doubly-charged nitroxide spin probes in ILs composed of cations and anions of variable sizes is measured as a function of temperature. The choice of the nitroxide spin probes allows for an understanding of the effect of charge on bimolecular collisions of spin probes in ILs. The cations are of a homologous series of substituted imidazoles (ethyl to octyl). This series of cations allows the Peric team to clarify the role of the hydrophobic part of ILs in solution phase dynamics. Similarly, the anions are of two different sizes (single atom anions and large multi-atom anions) in order to understand the influence of the anion on the translation of solute molecules in ILs. The results are interpreted in terms of the fractional Stokes-Einstein relation and the Cohen-Turnbull free volume equation. The broader impacts of this project include an understanding of transport properties and the kinetics of chemical reactions in ILs, as well as an opportunity for the CSU Northridge students to gain experience in experimental research, cutting-edge instrumentation, and theory, all of which are valuable as the students enter the modern chemical sciences workforce.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.