Reactivity of Synthetic Iron-Sulfur Clusters

Nitrogen is an element that is essential for all living cells and forms about 78% of Earths atmosphere. Most organisms cannot make use of its molecular form, so it must be converted to ammonia first. This process is termed nitrogen fixation. Cells can then use ammonia to build more complex nitrogen- containing compounds. Until the development of the Haber-Bosch process for the production of ammonia on an industrial scale in the early 20th century, almost all of Earths ammonia was generated by microbes. For this, they use nitrogenases which are the only enzymes that are capable of breaking the nitrogen-nitrogen bond, one of the strongest covalent bonds in the universe. Nitrogenases contain clusters made of iron and sulfur which are essential for the conversion of molecular nitrogen to ammonia. These clusters can also contain molybdenum and vanadium. The mechanism of nitrogen fixation is not very well understood, and it is still unclear how nitrogen binds to an ironsulfur cluster. In addition to the reduction of nitrogen to ammonia and protons to hydrogen, nitrogenases are also capable of activating small molecules such as acetylene, carbon dioxide, and carbon monoxide. To shed light on how and where substrates bind to nitrogenases, simpler versions of molybdenum ironsulfur clusters will be synthesized and used to study the binding of dinitrogen, acetylene, and carbon dioxide. The major challenge in trying to mimic the binding of inert small molecules to an iron sulfur cluster is the fact that when the clusters are in solution, they react with themselves or the solvent instead. These undesired side reactions should be overcome by using a sterically demanding ligand environment in addition to specific reaction conditions. By and large, the project aims at answering the following questions: How do molybdenumironsulfur clusters bind nitrogenase substrates, and to what extent do they activate these substrates? Can catalytic substrate reduction be achieved at synthetic molybdenumironsulfur clusters, and how does the environment and overall structure of the cluster impact the reaction outcome? How does the cluster compositionparticularly the presence of molybdenum versus vanadiumaffect small molecule activation and reductive catalysis? A variety of spectroscopic methods as well as collaborations with other labs will help address these questions satisfactorily.

Nitrogen is an element that is essential for all living cells and forms about 78% of Earth's atmosphere. Most organisms cannot make use of its molecular form, so it must be converted to ammonia first. This process is termed 'nitrogen fixation'. Cells can then use ammonia to build more complex nitrogen-containing compounds. Until the development of the Haber-Bosch process for the production of ammonia on an industrial scale in the early 20th century, almost all of Earth's ammonia was generated by microbes. For this, they use nitrogenases which are the only enzymes that are capable of breaking the nitrogen-nitrogen bond, one of the strongest covalent bonds in the universe. Nitrogenases contain clusters made of iron and sulfur which are essential for the conversion of molecular nitrogen to ammonia. These clusters can also contain molybdenum and vanadium. The mechanism of nitrogen fixation is not very well understood, and it is still unclear how nitrogen binds to an iron-sulfur cluster. In addition to the reduction of nitrogen to ammonia and protons to hydrogen, nitrogenases are also capable of activating small molecules such as acetylene, carbon dioxide, and carbon monoxide. To shed light on how and where substrates bind to nitrogenases, simpler versions of molybdenum-iron-sulfur clusters will be synthesized and used to study the binding of dinitrogen, acetylene, and carbon dioxide. The major challenge in trying to mimic the binding of inert small molecules to an iron-sulfur cluster is the fact that when the clusters are in solution, they react with themselves or the solvent instead. These undesired side reactions should be overcome by using a sterically demanding ligand environment in addition to specific reaction conditions. By and large, the project aims at answering the following questions: How do molybdenum-iron-sulfur clusters bind nitrogenase substrates, and to what extent do they activate these substrates? Can catalytic substrate reduction be achieved at synthetic molybdenum-iron-sulfur clusters, and how does the environment and overall structure of the cluster impact the reaction outcome? How does the cluster composition-particularly the presence of molybdenum versus vanadium-affect small molecule activation and reductive catalysis? A variety of spectroscopic methods as well as collaborations with other labs will help address these questions satisfactorily.