This Research award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports work by Professor George Richter-Addo at the University of Oklahoma and Professor Michael Shaw at Southern Illinois University at Edwardsville to determine the electrochemical behavior of metalloporphyrins containing the NO ligand. Both the NO molecule and metalloporphyrins (e.g., the heme group in the liver enzyme cytochrome P450) are biochemically relevant and undergo electron-transfer reactions. However, the effects of the NO ligand on the electron transfer properties of metalloporphyrins are not well understood. New and innovative spectroelectrochemical methodologies are being developed to provide, for the first time, the needed spectral data for complete characterization of important intermediates to gain insight on the location of electron addition and removal, and to determine the fate of the redox-generated intermediates.
Electrochemistry is being used in this work as a tool to inculcate the broader community with fundamental concepts in chemistry in a way that brings chemistry into the home. The research and instructional outreach programs extend to communities in East St. Louis and to Langston University that have large numbers of underrepresented minority populations, and to K-12 home schooled students and their parents. Students involved in this project develop a mature understanding of modern electrochemical methods and issues which prepare them for careers in fields which involve the interaction of chemistry with electrodes, including modern batteries, fuel cells, and photocells. Knowledge of how electrochemistry provides insight into the chemical properties of materials is essential to a broader understanding of how nature utilizes electron transfer for critical processes such as photosynthesis and respiration.
Living organisms depend on complex chemical reactions for the metabolism of a plethora of small molecules. Many of these chemical reactions depend on the presence and action of metal-containing complexes (metal cofactors) that act as biological catalysts. The heme group is an iron-containing cofactor that is found in the blood, the muscle, the liver, and in other parts of the body. Our bioinorganic approach deals with the study of a class of model hemes based on the more stable ruthenium analogues. Here, we combine chemistry and spectroelectrochemistry to define the action of ruthenium analogs of heme that interact with a biological small molecule, namely nitric oxide (NO). Our project is highly collaborative between the Ph.D.-granting Department of Chemistry and Biochemistry at the University of Oklahoma, and the primarily undergraduate Department of Chemistry at the Southern Illinois University Edwardsville. Intellectual Merit The complex and diverse reactions in which heme engage in are, to a large degree, dependent on the structure and electronic properties of the heme cofactor in its particular environment at any given time. For example, hemes can either simply bind oxygen (or NO) or can destroy its O-O bond (or couple two NO groups to detoxify NO into nitrous oxide) depending on the environment of the heme. We have prepared new representative model Ru-hemes of the form (porphyrin)Ru(NO)X, where the X group is an O-ligand, a halide, or a carbon-based ligand. We have shown, through solid-state crystallography and electrochemistry, that these model hemes differ in structure and electronic properties in ways that affect their subsequent chemistry and, hence, biological relevance. We developed new electrochemical and spectroelectrochemical methodology to probe the redox properties of these compounds and to access spectra of unstable redox intermediates that form at the electrode surface. The compounds studied are structural models for the heme cofactor in blood (for the hemoglobin protein), in muscle (for the myoglobin protein), in the liver (for the cytochrome P450 protein), and in some bacteria (for the NO reductase protein). Our research delineated the sites of redox behavior (e.g., porphyrin- vs. metal-centered) and provided insight into the stabilities of these redox products, and helps provide an understanding of why NO may be beneficial to humans and how bacteria can use heme to detoxify NO. Broader Impacts A primary goal of our project was to develop new tools that could bring Ph.D.-level research to a level that is hands-on and understandable by undergraduates. Prior to our entry into spectroelectrochemistry method development, the technique was commonly seen as "beyond the reach of undergraduates" due to its difficult-to-comprehend methodology. We spent considerable time writing new software programs and constructing simple hardware that allowed for the development of a user-friendly spectroelectrochemical setup; this way, the identification of unstable redox intermediates can be better accomplished without the normal hassle. We presented some of our research, in an educational General Chemistry setting, to a freshman class at Langston University in Oklahoma. We also participated actively in the SIUE Science Olympiad, the Science Fair, and the St. Louis "Day at the Science Center" events, among others. We are currently continuing the development of cheap and simple-to-use "pocket potentiostats" that, hopefully, will be utilized at the high-school level. We believe that our work has, indeed, began to make electrochemistry and spectroelectrochemistry more readily accessible to the non-expert.
