Computational Chemistry for Fluids Confined in Nanoporous Materials

摘要：本提案申请基金，以继续一个成功的研究计划，计算化学的流体限制在纳米多孔材料。在这项研究中，我们从量子力学出发，获得了吸附分子和纳米多孔材料之间的精确力场，然后利用这些力场在平衡（蒙特卡罗）和动态（分子动力学）模拟中预测了两类新型纳米多孔材料：金属有机框架和稳定蛋白质晶体中气体、离子和药物分子的吸附、渗透性和分离因子。该方法和结果有可能对工程和生物工程分离技术中新型纳米多孔材料的设计和开发产生重大影响。智力优势：由于几何限制和表面的接近，纳米多孔材料中的流体表现出一系列富相现象和扩散速率，与散装流体明显不同。计算机模拟为理解这种行为提供了一个有用的工具。目前在这一领域的研究通常使用经验力场，例如碳材料，通过对比测量在平面石墨上的吸附行为而发展起来。然而，模拟得到的结果非常依赖于所使用的力场，我们从我们的研究中了解到，由于高度弯曲的表面、键应变、环结构和杂交的差异，碳纳米结构材料中的吸附物所经历的力场与平面石墨表面上的力场有很大的不同。正是由于这个原因，我们不使用经验势，而是使用第一原理层次方法，从力场的量子力学发展开始，然后（使用模拟）进行宏观行为的预测。四个具体的智力目标是：1)进一步发展先进的计算方法，以获得纳米结构材料中受限流体微观行为的原子分辨率、时间分辨率的见解；2)从量子化学的角度为纳米多孔基质中的客体流体建立精确的力场，然后预测工程中感兴趣的平衡和动态（输运）性质；3)开发一种普遍适用的方法来研究限制在任何类型的纳米多孔基质中的流体；4)详细研究了最近开发的两种纳米多孔材料，金属有机框架和稳定（通过交联）蛋白质晶体的吸附和运输。更广泛的影响：了解纳米多孔材料、有机和无机纳米管、容器和细胞中流体的行为对催化、纳米电子学、生物系统和其他新兴技术领域具有重要意义。在本提案中，我们将通过量子化学计算和分子模拟相结合，研究最近开发的两种新型纳米多孔材料，金属有机框架和蛋白质晶体中的各种物理和化学现象，如吸附，运输，相变和化学反应。对所涉及的现象有更好的分子水平的理解，有助于对无机、有机和生理通道和毛细血管中的流体进行准确的描述，也有助于设计和优化定制的纳米多孔材料，用于气体储存、分离、用作分子筛和催化剂支撑以及相关领域的特定应用。我们将通过使用最先进的计算化学来开发精确的力场，然后将其用于日益复杂的实际系统。

AbstractThis proposal requests fund for the continuation of a successful research program on thecomputational chemistry for fluids confined in nanoporous materials. In this research, we start with quantum mechanics to obtain accurate force fields between adsorbing molecules and nanoporous materials, and then use these force fields in equilibrium (Monte Carlo) and dynamic (molecular dynamics) simulations to predict adsorption, permeability, and separation factors of gases, ions, and pharmaceutical molecules in two new classes of nanoporous materials: metal-organic frameworks andstabilized protein crystals. The methodology and results have the potential to have a significant impact on the design and development of new nanoporous materials for engineering and bioengineering separation technologies.Intellectual Merit: Due to the geometric confinement and proximity of the surface, fluids in nanoporous materials exhibit a range of rich phase phenomena and diffusion rates that are significantly different from those of bulk fluids. Computer simulation provides a useful tool for understanding such behavior. Current research in this area has generally used empirical force fields, e.g., for carbon materials, developed by correlating measured adsorption behavior on planar graphite. However, results obtained from simulation are very dependent on the force field used, and we have learned from our research that asa result of the highly curved surfaces, bond strains, differences in ring structure and hybridization, the force field an adsorbate experiences in a carbon nanostructured material is very different from that on a planar graphite surface. It is for this reason that instead of using empirical potentials, we will use a firstprinciples hierarchal approach of starting from the quantum mechanical development of a force field, andproceeding (using simulation) to the prediction of macroscopic behavior. Four specific intellectual goals are:1) to further develop advanced computational approaches to obtain atomic-resolution, time-resolved insights into the microscopic behavior of confined fluids in the nanostructured materials;2) to develop accurate force fields from quantum chemistry for guest fluids in the nanoporous substrates, and then to predict equilibrium and dynamic (transport) properties of interest in engineering;3) to develop a generally applicable method for the study of fluids confined in any type of nanoporous substrate; and4) to examine in detail adsorption and transport in two recently developed nanoporous materials, metal-organic frameworks and stabilized (by cross linking) protein crystals.Broader Impact: Understanding the behavior of fluids confined in nanoporous materials, organic and inorganic nanotubes, vessels, and cells is important in catalysis, nanoelectronics, biological systems, and in other emerging technology areas. In this proposal, by integrating quantum chemical calculations and molecular simulations, we will investigate various physical and chemical phenomena such as adsorption,transport, phase transitions, and chemical reactions in two recently developed novel nanoporous materials, metal-organic frameworks and protein crystals. Better molecular-level understanding of the phenomena involved can help in developing accurate descriptions of the fluids in inorganic, organic and physiologic channels and capillaries, as well as in the design and optimization of tailored nanoporous materials for specific applications in gas storage, separations, for use as molecular sieves and catalystsupports, and related areas. We will do this by using state-of-the-art computational chemistry to develop accurate force fields that will then be used for real systems of increasing degree of complexity.