The conversion of carbon dioxide to carbon monoxide and the reverse conversion of carbon monoxide to carbon dioxide are extremely important industrial processes that require considerable energy. Additionally, nitrous oxide is one of the oxides of nitrogen that contribute to air pollution and smog. Its conversion to innocuous nitrogen gas has environmental importance. There are naturally occurring substances, carbon monoxide reductase (CODH) and nitrous oxide reductase (N2O reductase), that can perform both of these transformations quickly and in an energy efficient manner. In both of these the chemical transformations occur at a copper atom that is surrounded by several sulfur containing groups. Since these biological systems are very efficient, Dr. James P. Donahue, Chemistry Department of Tulane University, with the support of the Chemical Synthesis Program of the Chemistry Division, is preparing small copper/sulfur compounds that mimic the copper sites in CODH and N2O reductase. These compounds are designed to function like CODH and N2O reductase and provide new more economical ways to perform the reactions mentioned above. As a part of the project undergraduate and graduate students are trained to enter the science and technology workforce. In addition, collaborations are established with nearby, often minority serving institutions, to provide access to instrumental facilities and to provide summer research opportunities for undergraduate students from colleges where research opportunities are minimal or nonexistent.
This project targets the synthesis of small molecule analogues of the active sites of two copper-containing enzymes: CODH and N2O reductase. These metalloenzymes mediate the two electron oxidation of carbon monoxide to carbon dioxide and the two electron reduction of nitrous oxide to dinitrogen, respectively. Heterodimetallic Mo-Cu compounds with bridging carbonyl and sulfido ligands are prepared as analogues of intermediates in the catalytic cycle of CODH. This portion of the study first involves an investigation of the of CO binding to two-coordinate Cu(I) bis(thiolate) complexes. This resembles the first step of the CO oxidation pathway in CODH. The resulting three coordinate adducts are converted into the Mo-Cu compounds that resemble the active site in CODH. In connection with N2O reductase, various bis(amino) bis(thiolate) ligands are prepared and examined for their ability to support the formation of multi-copper complexes of compositional relevance to the catalytic site of N2O reductase. Variation in the steric bulkiness of the ligands and variation in the hardness of the donor atom set are probed for their effect upon the aggregation of the multicopper clusters. This work provides a breadth of experience to undergraduate and graduate students, who will be trained in synthesis and characterization methods including crystallography spectroscopy, electrochemistry, and computations. Summer students from New Orleans area institution that offer few undergraduate research opportunities are involved and these institutions, which are often minority serving, are provided access to the PI's crystallographic facility.
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.
