Spectroscopy of Early Intermediates in Nitrogenase Catalysis - From Steady State to Femtoseconds

化学部的生命过程化学项目获此殊荣，支持加州大学戴维斯分校的Stephen P.Cramer博士利用先进的高速振动光谱学技术对生物固氮和CO还原的早期阶段进行表征。这些物种要么通过捕获中间体的闪光光解，要么通过底物或电子的光化学传递来制备。红外光谱已经观察到了各种CO物种，但有些反应发生得太快，用停流FT-IR方法看不到。取而代之的是，使用光谱仪和阵列探测器来推进亚毫秒级的时间尺度。至于氮气中间体，没有关于氮气结合的最早步骤的信息，采用红外光谱和飞秒泵浦-探针法相结合的方法来寻找这些物种。固氮酶是一种含有金属的酶，具有非凡的催化活性。例如，它可以将氮(N2)还原为氨(NH3)，这是其他任何酶都不能做到的。但是，它也可以将二氧化碳(CO2)还原为甲烷(CH4)，将CO还原为烯烃(所谓的费托化学)，最终产生氢气。尽管这些净反应已经确定，但具体步骤如何发生却鲜为人知。大约1-2%的工业能源生产用于固定氮。生物过程的任何改进或优化都会带来巨大的潜在经济和社会效益。即使是自然氮气固定的微小改进，或者将固氮酶用于费托燃料生产或作为一种有效的氢酶，都将有助于具有巨大的经济和环境杠杆作用的领域。该项目允许研究生和博士后研究员获得激光和高速光谱学方面的专门培训。他们还与世界各地的科学家同行互动，包括米兰、马德里、柏林和日本。在夏天，他们分享自己的技能，帮助培训来自全国各地的本科生。

With this award, the Chemistry of Life Processes Program in the Chemistry Division supports Dr. Stephen P. Cramer at the University of California, Davis to characterize the earliest stages of biological nitrogen fixation and CO reduction using advanced, high-speed vibrational spectroscopy techniques. These species are prepared either by flash photolysis of trapped intermediates or by photochemical delivery of substrates or electrons. A variety of CO species have already been observed by IR spectroscopy, but some reactions occur too fast to be seen by stopped-flow FT-IR methods. Instead, a spectrograph and array detector are used to push into sub-millisecond time scale. As for N2 intermediates, there is no information about the earliest steps in N2 binding, and a combination of IR and femtosecond pump-probe methods is utilized to search for these species.Nitrogenase is a metal-containing enzyme with extraordinary catalytic activities. For example, it can reduce nitrogen (N2) to ammonia (NH3), something that no other enzyme can do. But, it can also reduce carbon dioxide (CO2) to methane (CH4) and CO to alkenes (so-called Fischer-Tropsch chemistry), and finally, it can produce hydrogen. Although these net reactions are well established, the detailed steps for how this occurs are poorly understood. Some 1-2% of industrial energy production is used to fix nitrogen. Any improvement or optimization of the biological process offers enormous potential economic and societal benefits. Even small improvements in natural N2 fixation, or use of nitrogenase for Fischer-Tropsch fuels production or as an efficient hydrogenase, would contribute to areas with enormous economic and environmental leverage. This project allows graduate students and postdoctoral fellows to acquire specialized training in lasers and high-speed spectroscopy. They also interact with fellow scientists around the world, including Milan, Madrid, Berlin and Japan. During the summer they share their skills and help train undergraduates from around the country.