Functional Hybrid Biotic/Abiotic Materials

第一部分： 非技术总结该项目的目标是开发混合生物/非生物功能材料，实现光驱动，多电子还原二氧化碳（CO2）甲酸盐-甲酸衍生的阴离子。CO2是现代社会的主要化石燃料能量载体的不可避免的氧化产物，出于环境和经济原因，将其还原为有用的烃产物如甲酸盐是期望的。然而，由于CO2是一种在热力学和动力学上都非常稳定的分子，因此很难活化CO2进行还原。为了实现这一目标，需要新的催化剂和将它们与可再生能源偶联的方法。人造材料如金属氧化物表面是低效的催化剂，并且缺乏对CO2底物超过H+的特异性和干扰析氢反应。相比之下，自然界已经进化出用于选择性CO2还原而没有竞争性H2释放的高效催化剂。甲酸脱氢酶（FDH）是一类来自原核生物的酶，其可逆地催化CO2还原为甲酸盐，甲酸盐是甲醇或甲烷生产的前体，并且其本身是潜在的能源。然而，在自然界中，FDH酶并不自然地被光激活，而是需要一些其他的能量输入。Dyer团队将开发混合生物/非生物材料，将纳米晶体半导体（量子点）与FDH酶整合在一起，以实现光驱动的CO2减排。生物/非生物界面已经在自然界中进化，以实现从生物膜到光子晶体和结构材料的功能设计。人工杂交非生物/生物材料可以被合理地设计以实现新的和紧急的功能。 整合生物分子和非生物结构是创造功能材料的有力途径。本工作的主要目标是将生物酶FDH偶联到非生物光敏剂组分上（量子点）将太阳能转化为反应性电子，以生产功能材料，这些功能材料可以优化用于高效的光驱动CO2转化为燃料。技术概述该基金的中心目标是开发基于甲酸脱氢酶（FDH）的生物/非生物混合功能材料酶偶联到纳米晶体半导体（NCS）光敏剂，用于光驱动的多电子还原CO2为甲酸盐。第一个目标是设计，合成和表征混合NCS：FDH材料，将光转化为活性电子，然后有效地将它们转移到催化剂。界面电子转移（ET）将通过使用三种不同的方法控制NCS：FDH相互作用来优化：1）经由N-末端His-标签直接附接至NCS表面; 2）使用紫精衍生物氧化还原介体优化ET效率和3）共价“分子线”至远端FeS簇。界面ET也将通过NCS结构（点、核壳、棒、棒中点结构）的波函数工程以及封端配体和界面电荷的性质来优化。最后，光驱动的CO2还原的效率将与界面ET效率和混合界面的底层结构相关。该基金的第二个目标是阐明混合NCS：FDH材料光驱动CO2减排的机制。这些混合材料的固有光敏性将被利用来光学触发ET和酶周转，从而研究所有相关过程的动力学，包括多激子产生和提取，界面电子转移和酶周转。这些实验将验证一个重要的假设，即量子限制NCS可以作为一个多电子光敏剂的多激子产生和提取。该方法也将用于阐明FDH酶的CO2还原机制。Dyer实验室为此开发了一种独特的能力，该能力基于激光诱导电位跳跃，结合结构特异性、时间分辨方法，包括超快红外和荧光光谱。最后，这些材料将被集成到光电极中，以展示持续的光驱动二氧化碳减排，而不受使用牺牲电子供体的限制。该奖项反映了NSF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。

PART 1: NON-TECHNICAL SUMMARYThe goal of this project is to develop hybrid biotic/abiotic functional materials that achieve light driven, multi-electron reduction of carbon dioxide (CO2) to formate - an anion derived from formic acid. CO2 is the inevitable oxidation product of the primary fossil fuel energy vectors of modern society and reducing it back to useful hydrocarbon products such as formate is desirable for both environmental and economic reasons. It is difficult to activate CO2 towards reduction, however, because it is a very stable molecule, both thermodynamically and kinetically. New catalysts and a method for coupling them to a renewable energy source are required to achieve this goal. Man-made materials such as metal oxide surfaces are inefficient catalysts and suffer from lack of specificity for CO2 substrate over H+ and the interfering hydrogen evolution reaction. In contrast, nature has evolved highly efficient catalysts for selective CO2 reduction without competitive H2 evolution. Formate dehydrogenases (FDH), are a class of enzymes from prokaryotes that reversibly catalyze the reduction of CO2 to formate, a precursor to methanol or methane production and a potential energy source itself. In nature, however, FDH enzymes are not naturally activated by light, but require some other input of energy. The Dyer group will develop hybrid biotic/abiotic materials that integrate a nanocrystalline semiconductor (quantum dot) with the FDH enzyme to achieve light driven CO2 reduction. Biotic/abiotic interfaces have evolved in nature to achieve functional designs that range from biofilms to photonic crystals and structural materials. Artificial hybrid abiotic/biotic materials may be rationally designed to achieve novel and emergent functions. Integrating biomolecular and abiotic structures is a powerful approach to create functional materials. The major goal of this work is to couple the biological enzyme FDH to an abiotic photosensitizer component (quantum dot) that converts solar energy into reactive electrons, to produce functional materials that can be optimized for highly efficient light driven conversion of CO2 to fuel.PART 2: TECHNICAL SUMMARYThe central goal of this grant is to develop hybrid biotic/abiotic functional materials based on a formate dehydrogenase (FDH) enzyme coupled to a nanocrystalline semiconductor (NCS) photosensitizer for light driven, multi-electron reduction of CO2 to formate. The first objective is to design, synthesize and characterize hybrid NCS:FDH materials that convert light to reactive electrons and then efficiently transfer them to the catalyst. The interfacial electron transfer (ET) will be optimized by controlling the NCS:FDH interaction using three different approaches: 1) direct attachment to the NCS surface via an N-terminal His-tag; 2) optimization of ET efficiency using a viologen derivative redox mediator and 3) a covalent "molecular wire" to the distal FeS cluster. Interfacial ET will also be optimized by wave-function engineering of the NCS structure (dot, core shell, rod, dot-in-rod structures) and the nature of the capping ligands and interfacial charge. Finally, the efficiency of light-driven CO2 reduction will be correlated to the interfacial ET efficiency and to the underlying structure of the hybrid interface. The second objective of the grant is to elucidate the mechanism of light driven CO2 reduction by hybrid NCS:FDH materials. The intrinsic photosensitivity of these hybrid materials will be exploited to optically trigger the ET and enzyme turnover and thereby study the dynamics of all of the relevant processes, including multi-exciton generation and extraction, interfacial electron transfer and enzyme turnover. These experiments will test the important hypothesis that a quantum confined NCS may act as a multi-electron photosensitizer by multi-exciton generation and extraction. This approach will also be used to elucidate the CO2 reduction mechanism by the FDH enzymes. The Dyer lab has developed a unique capability for this purpose, based on the laser induced potential jump coupled with structure-specific, time-resolved methods including ultrafast infrared and fluorescence spectroscopy. Finally, these materials will be integrated into photo-electrodes to demonstrate sustained light-driven CO2 reduction without the limitations imposed by the use of a sacrificial electron donor.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.