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New findings in the research of Synthesis of cubane-type heteroleptic iron–sulfur clusters relevant to the FeMo cofactor

Researchers of Nanjing Normal University (NNU) have made important breakthroughs in the research of Synthesis of the FeMo Cofactor. They worked out the ligand metathesis for the synthesis of cubane-type heteroleptic iron–sulfur clusters relevant to the FeMo cofactor.

The paper entitled “Ligand Metathesis as Rational Strategy for the Synthesis of Cubane-type Heteroleptic Iron–sulfur Clusters Relevant to the FeMo Cofactor” was published in the journalProceedings of the National Academy of Sciences of the United States of America(PNAS) on April 13, 2018.

Nitrogen is one of the basic elements that make up life organisms. Nitrogen in the Earth's atmosphere must first be converted into ammonia (NH3) in order to be absorbed and utilized by an organism. This process is called nitrogen fixation. Activating nitrogen in an appropriate way and converting it into ammonia nitrogen which can participate in the metabolism of organisms is an important ecological response to maintain productivity on the earth. The currently widely used industrial nitrogen fixation——synthetic ammonia——requires high temperature and high pressure conditions and consumes a large amount of energy. However, some microorganisms can fix nitrogen by utilizing the enzyme nitrogenase to catalyze the conversion of atmospheric nitrogen (N2) to ammonia (NH3) under the mild environment of the organism. Therefore, if the artificial simulation of biological nitrogen fixation can be achieved, it will be of great significance to solve the problems facing humanity such as population, food, energy and environment.

FeMoco is the primary cofactor of nitrogenase. The active site (FeMo cofactor) is the structurally and electronically complex weak-field metal cluster [MoFe7S9C] built of Fe4S3 and MoFe3S3C portions connected by three sulfur bridges and containing an interstitial carbon atom centered in an Fe6 trigonal prism. Chemical synthesis of this cluster is a major challenge in biomimetic inorganic chemistry. The success of its chemical synthesis is an important basis for the artificial simulation of biological nitrogen fixation, and is of great significance for the in-depth study of the nitrogen fixation mechanism of biological nitrogenases. This research, however, has been stagnant in recent years because of its unusual difficulty and its difficulty lies in the embedding of non-sulfur ligands in the center of the molecule.

To solve this problem, are search group led by Prof. Xudong Chen of the School of Chemistry and Materials Science has made numerous efforts and has conducted in-depth cooperation with Professor Richard H. Holm of Harvard University.

Because the active centers of the enzyme are metal–ligand clusters, it is feasible that they are attainable by synthesis and as such are primary goals in the field of biomimetic inorganic chemistry. The research group presents a ligand metathesis strategy utilizing the periodic near-identity of molybdenum and tungsten when incorporated into analogous compounds. The approach provides a pathway for constructing heterometal heteroleptic Fe–S clusters of presumed relevance to the active site. Based on cubane-type stereochemistry, clusters have been prepared allowing alterations in structure and ligand binding, and inclusion of a light core atom. At present, the research group is conducting follow-up research.

NNU postgraduate Gan Xu, who will continue this research in his Ph.D study at NNU, is the lead author of this paper. Prof. Xudong Chen,and Prof. Richard H. Holm of Harvard University are corresponding authors. The School of Chemistry and Materials Science, NNU is the signature unit of the first author, and Harvard University the cooperation unit.

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