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

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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.