NSF-DFG Confine: Diffusion of Water Confined in Patterned Hydrophilic-Hydrophobic Nanopores

在化学系化学结构、动力学和机理a （CSDM-A）项目的支持下，芝加哥大学的Laura Gagliardi教授和加州大学伯克利分校的Omar Yaghi教授正在结合先进的分子模拟和化学分析工具，如核磁共振（NMR），探索和表征金属有机框架（mof）内水分子的运动。水对生命至关重要，了解水分子如何在密闭空间中运动具有重要意义。本研究的重点是具有明确定义的吸引水（亲水）和排斥水（疏水）网格状平铺区域交替模式的mof。该项目旨在首次揭示水在这个图案空间内扩散的分子水平细节，以及亲疏水区域之间的相互作用。Gagliardi教授，她的学生和德国的合作者（洪堡大学的Joachim Sauer教授）将进行量子力学计算来预测水- mof相互作用，Yaghi教授和他的学生将用核磁共振光谱技术表征水- mof相互作用。这个项目的发现可能会导致MOF材料的各种有用的应用，包括液体和气体的分离和净化，水收集和二氧化碳捕获。除了正式的研究培训活动外，Gagliardi小组还寻求通过“拓展你的视野”芝加哥分会激励未来几代具有国际意识的科学家。这个合作项目将为参与的学生提供丰富的跨学科和国际经验。Gagliardi教授和她的学生从从头算自由能计算出吸附点阵上水分子的化学精确吸附常数；他们还用从头算过渡态理论计算了水分子在吸附位点之间跳跃的化学精确扩散速率常数。为了定义基本的扩散步骤，他们定义了吸附细胞，并考虑了在所有晶体学方向上相邻细胞中位点之间的所有可能的跳跃途径。最后，他们分别使用大正则蒙特卡罗（GCMC）和动力学蒙特卡罗（kMC）模拟预测了吸附等温线和扩散系数作为负载的函数。绍尔教授提供了从头计算的势能面，以提高GCMC和kMC模拟的准确性。Yaghi教授和他的学生将合成MOF材料，并利用脉冲磁场梯度核磁共振测量研究不同水负载下MOF孔隙中水的自扩散。这将允许与预测的孔内扩散常数进行直接比较。此外，他们将采用准弹性中子散射（QENS）来深入了解不同负载下纳米孔中的水迁移率。重要的是，QENS将提供关于MOF孔中扩散模型和机制的独家信息。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

With support from the Chemical Structure, Dynamics and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professors Laura Gagliardi of the University of Chicago and Omar Yaghi of the University of California at Berkeley are combining advanced molecular simulation and chemical analysis tools such as nuclear magnetic resonance (NMR) to explore and characterize the motion of water molecules inside metal-organic frameworks (MOFs). Water is essential to life and understanding how water molecules move in confined spaces is of fundamental interest. This research focuses on MOFs with well-defined patterns of alternating water attracting (hydrophilic) and water repelling (hydrophobic) grid-like tiled regions. This project seeks to reveal for the first time the molecular level details of the diffusion of water within this patterned space and the interplay between the hydrophilic and hydrophobic regions. Professor Gagliardi, her student and a collaborator in Germany (Professor Joachim Sauer, Humboldt University) will perform quantum mechanical calculations to predict water-MOF interactions, and Professor Yaghi and his student will characterize the water-MOF interactions with NMR spectroscopic techniques. The discoveries of this project could lead to a variety of useful applications of MOF materials, including liquid and gas separations and purification, water harvesting, and CO2 capture. In addition to formal research training activities, the Gagliardi group also seeks to inspire future generations of internationally aware scientists through the Chicago chapter of Expanding Your Horizons. This collaborative project will provide the students involved with a rich interdisciplinary and international experience. Professor Gagliardi and her student compute chemically accurate adsorption constants for water molecules on a lattice of adsorption sites from ab initio free energies; they also compute chemically accurate diffusion rate constants for jumps of water molecules between adsorption sites using ab initio transition state theory. To define elementary diffusion steps, they define adsorption cells and consider all possible jump pathways between sites in neighbored cells in all crystallographic directions. Finally, they predict adsorption isotherms and diffusivities as a function of loading using Grand Canonical Monte Carlo (GCMC) and kinetic Monte Carlo (kMC) simulation, respectively, on a lattice of sites. Professor Sauer is providing ab initio-calculated potential energy surfaces to augment the accuracy of the GCMC and kMC simulations. Professor Yaghi and his student will synthesize MOF materials and study the water self-diffusion at different water loadings in the MOF pores using pulsed magnetic field gradient NMR measurements. This should allow for a direct comparison with the predicted intrapore diffusion constants. Additionally, they will employ quasi-elastic neutron scattering (QENS) to gain more insight about the water mobility in the nanopores at different loadings. Importantly, QENS would provide exclusive information about the diffusion model and mechanism in the MOF pores.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.