Computational Modeling of Carbon Monoxide Dehydrogenase Model Systems for Carbon Dioxide Fixation

项目摘要 大气中的二氧化碳浓度已经达到了迄今为止的最高水平， 对环境和人类健康的所有领域的后果。基于这些迫在眉睫且不断增长的威胁， 迫切需要将我们目前的基础设施从化石燃料转向可再生能源。在 在这种情况下，太阳能或可再生电力可以用来驱动CO2和H2O的催化转化 转化为富含能量的化学物质（类似于生物系统），能量以化学键的形式无限储存 用于按需使用。将CO2化学还原为具有更高化学能的其他碳化合物 将关闭碳循环，并提供与现有基础设施兼容的化学燃料。然而，在这方面， 现有的CO2催化剂通常具有非常高的过电位、低的转换频率和差的底物 在H2O存在下的选择性相比之下，一氧化碳脱氢酶（CODH）酶，如一氧化碳脱氢酶（CODH）酶， 来自Carboxydothermus hydrogenoformans的镍-一氧化碳脱氢酶II能够提取能量 以便以高速率和选择性进行CO到CO2的可逆转化 同时在热力学势附近操作。Ni-CODHCh II的晶体结构揭示了存在一种 铁硫簇与镍原子结合，称为C簇。这个C-簇的一个结构特征是 存在Fe 3S 4簇，其将镍和铁原子桥接在一起。这种合作的刘易斯酸碱 对被认为是Ni-CODHCh II异常活性的关键特征。这项提案的长期目标是 是利用计算化学结合互补的实验努力来设计 创新的催化剂，模拟CODH酶的基本结构特征和功能， 在H2O存在下将CO2转化为CO。我们建议通过以下方式实现这一目标： 具体目标：（一）研究由大环氧化还原活性配体支持的地球丰富的材料;和（二） 通过使用仲链中的带电官能团催化一氧化碳的产生， 协调领域。更具体地说，这一建议概述了合理设计创新催化剂的计划 用于基于热力学和动力学性质的CO2至CO转化。这些原则 被认为是多相催化的关键。例如，在Sabatier原则中， 在关键中间体中的金属处的底物结合能与总催化剂速率有关。使用 分子催化剂将使我们能够调整这些关键的键能，以达到最佳值。在这 电子结构计算将提供一种直接的方法来研究关键的热力学 和动力学性质，所述动力学性质是开发具有（i）对反应物的高选择性的分子催化剂所需的。 所需产物;和（ii）在长时间内的快速动力学。成功实现这些目标将产生 基于基本热力学和动力学性质的下一代设计的一般准则 用于将CO2还原成CO或任何高价值C1产物的分子催化剂。

Project Abstract Atmospheric CO2 concentrations have reached their highest to date, which holds immediate and dire consequences for the environment and all areas of human health. Based on these imminent and growing threats, there is an urgent need to transition our current infrastructure from fossil fuels to renewable energy sources. In this context, solar energy or renewable electricity could be used to drive the catalytic conversion of CO2 and H2O into energy-rich chemicals (similar to biological systems) whereby energy is stored indefinitely in chemical bonds for on-demand use. The chemical reduction of CO2 to other carbon compounds with higher chemical energy would close the carbon cycle and deliver chemical fuels that are compatible with existing infrastructure. However, existing CO2 catalysts often suffer from very high overpotentials, low turnover frequency and poor substrate selectivity in the presence of H2O. In contrast, carbon monoxide dehydrogenase (CODH) enzymes, such as the nickel-carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans are able to extract energy from their environments in order to carry out the reversible conversion of CO to CO2 at high rates and selectivity while operating near the thermodynamic potential. Crystal structure of Ni-CODHCh II reveals the presence of an iron-sulfur cluster combined with a nickel atom, called C-cluster. One structural feature of this C-cluster is the presence of a Fe3S4 cluster, which bridges the nickel and iron atoms together. This cooperative Lewis acid-base pair is considered a key feature for the exceptional activity of Ni-CODHCh II. The long-term goal of this proposal is to employ computational chemistry in combination with complementary experimental efforts to design innovative catalysts that mimic essential structural features and functions of CODH enzymes for the selective conversion of CO2 to CO in the presence of H2O. We propose to accomplish this goal through the following specific aims: (i) To investigate earth-abundant materials supported by macrocyclic redox-active ligands; and (ii) To catalyze the production of carbon monoxide through the use of charged functional groups in the secondary coordination sphere. More specifically, this proposal outlines a plan for the rational design of innovative catalysts for CO2-to-CO conversion based on thermodynamic and kinetic properties. These principles have been established as critical in heterogeneous catalysis. For instance, in the Sabatier principle, the magnitude of the substrate binding energy at the metal in critical intermediates is related to the overall catalyst rate. The use of molecular catalysts will allow us to tune these crucial bond energies in order to achieve optimal values. In this context, electronic structure calculations will provide a straightforward approach to study the key thermodynamic and kinetic properties that are required in the development of molecular catalysts with (i) high selectivity for the desired product; and (ii) fast kinetics over a long period of time. Successful completion of these aims will produce general guidelines based on fundamental thermodynamic and kinetic properties for the design of next generation molecular catalysts for CO2 reduction to CO or any high value C1 product.