CAS: Biologically Inspired Aminopyridine Complexes for CO2 Reduction

With the support of the Chemical Catalysis program in the Division of Chemistry, Smaranda C. Marinescu of the University of Southern California will study the development of biologically inspired catalytic systems for the conversion of harmful carbon dioxide into chemical fuels. The development of clean energy technologies as an alternative to fossil fuels is a critical need in the face of rapid planetary warming.

Solar energy has received much attention as a clean energy source, but the focus has largely been on electricity generation. This narrow focus does not adequately meet the need for renewable fuels for transportation, heating, and industrial uses, which make up ~70% of energy needs. A sustainable energy future will require a non-fossil fuel method for the formation of chemical feedstocks, and the electrochemical reduction of abundant small molecules such as carbon dioxide (CO2) and water (H2O), using the solar-derived electricity is a viable pathway to do so.

This approach will allow for storing of solar energy in chemical bonds in a similar way as nature accomplishes through photosynthesis, where the energy of photons is used to drive the reduction of CO2 to a variety of high-energy products. Inspired by biological systems, the Marinescu group will develop molecular catalysts that involve hydrogen-bonding networks which are capable of small molecule activation through multiple proton and electron transfers.

This project will focus on the development of a series of biologically inspired metal complexes with pendant amines, which will allow for understanding the effect of proton relays on multi-electron, multi-proton reactions. The ligand framework allows for excellent control of electronic and positioning effects, which will facilitate structure-activity studies.

Integrated into this research plan is an educational program focused on providing research opportunities to both students and teachers from local community colleges with a high percentage of minority students, and a mentoring program for women at the postdoctoral level to increase the participation of this underrepresented group in science. These outreach and mentoring activities will impact a significant number of individuals over the long term: teachers and generations of their students, along with researchers from USC.

Importantly, students involved in these efforts will develop a culture of contributing to their scientific and non-scientific communities that is expected to last beyond their formative years.

With the support of the Chemical Catalysis program in the Division of Chemistry, Smaranda C. Marinescu of the University of Southern California will study the effect of pendant proton relays on the CO2 reduction with cobalt aminopyridine macrocycles. Recent work in the Marinescu group has demonstrated that a series of cobalt complexes with zero to four pendant secondary amines (NH) displays a linear correlation between the rate of CO2 reduction and the number of pendant NH moieties.

Experiment and theory suggest that the pendant NH groups do not directly transfer protons to CO2, but instead bind acid molecules from solution, leading to the formation of a catalyst-acid adduct, held together through a hydrogen-bonding network, that enables direct proton transfer from acid to the activated CO2 substrate. The research goal is to understand the factors that govern the catalytic properties of these complexes, in terms of activity and selectivity for CO2 reduction, by characterizing and altering the electronic environment (the primary and secondary coordination spheres) of these metal aminopyridine macrocycles.

This project focuses on the synthesis and characterization of a variety of aminopyridine complexes with pendant hydrogen bond donors or cationic groups to understand the effects of these moieties on the catalyst activity and selectivity. The science education goals will focus on: (1) organizing a summer workshop for students from Cerritos College, a public community college with a high percentage of students from underrepresented groups and hosting a Cerritos College student in the Marinescu laboratory to perform undergraduate research for an 8-week period during the summer; and (2) developing a mentoring program for women at the postdoctoral level to increase the participation of women in science.

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.