Yulia Pushkar - US grants

The Chemistry of Life Processes Program and the Molecular Biophysics Program are funding Dr. Yulia Pushkar of Purdue University for research towards a detailed mechanism for photosynthesis, the process by which plants produce substances such as sugars from carbon dioxide, water and sunlight. The understanding of this key life process can advance the development of alternative energy sources through the design of better water-splitting catalysts that enable artificial photosynthesis. The work employs various physical measurements to determine the molecular details of this important process in real time and, as such, is at the interface of physics, chemistry and the biological sciences. Consequently, the broader impact of the research is also on several scientific areas including bioinorganic chemistry and molecular biophysics. Additionally, the work has consequences on science education at the high school level through the involvement of the research team in the design of lesson modules about photosynthesis that high school science teachers can adopt and use. Inquiry-based educational modules that incorporate the results of the research are developed for the "Physics of the Green Leaf" program.

The research is focused on the study of the light-induced function of the oxygen evolving complex (OEC) in Photosystem II. The light-induced water splitting by the Mn4Ca cluster of the oxygen evolving complex is a fundamental biological process that sustains our biosphere. Laser pump X-ray probe time-resolved X-ray emission and X-ray absorption spectroscopy are used to monitor changes in the electronic structure of the OEC in real time during catalysis. Transient intermediates in Photosystem II protein are trapped by ultra-fast freeze-quenching and their structure is characterized using the extended X-ray absorption fine structure (EXAFS) method. The research aims are to determine aspects of both the dynamics of the change in electronic structure and the geometry of the manganese cluster and, when combined with DFT calculations, to provide details of the mechanism of catalytic water splitting.

In this project supported by the Chemical Structure, Dynamic & Mechanism,B Program of the Chemistry Division, Professor Yulia Pushkar of the Department of Physics and Astronomy at Purdue University studies the time-resolved mechanism of dioxygen (O2) formation in artificial photosynthesis. In artificial photosynthesis, solar energy is converted into chemical energy through generation of the clean fuels hydrogen and oxygen, a process which requires rearrangement of chemical bonds. Fundamental understanding of this process is required for the development of new catalysts and devices which are able to mimic natural photosynthesis. The development of artificial photosynthesis and its large-scale implementation can address energy needs of modern society. This research lies at the interface of physics, chemistry and materials science, with results expected to impact diverse fields and contribute to fundamental science, education and national energy security. Planned research and educational activities are designed to increase participation of under-represented students from economically disadvantaged backgrounds, improve experiences of female students in STEM (Science, Technology, Engineering and Mathematics), enhance training of students via integration of research results into curricula and to deliver teaching modules to schools.

Research in this project focuses on the complex multi-electron chemical process of artificial photosynthesis. A major project goal is to determine the structure, electronic configurations and dynamics of the critical intermediates involved in water oxidation. In this multi-scale approach, time-resolved techniques monitor the evolution of structure and electronic states in newly designed ruthenium catalysts, with a focus on the key mechanism of oxygen-oxygen bond formation and its dependence on ligand structure. The relationship between molecular structure and catalytic activity is tested by a combination of experiments and quantum-mechanical computational models. Experimental techniques in this study of in situ catalytic water oxidation are synchrotron-based X-ray spectroscopy, including X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagnetic resonance (EPR) and multi-wavelength kinetic resonance Raman spectroscopy. These experimental techniques deliver information on the structure of the intermediates and their electronic configuration as they evolve during the catalytic process.

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.

Purdue University Molecular Biophysics Training Program PROJECT SUMMARY In 2015, the Zika virus outbreak emerged as an international public health crisis. In less than a year, scientists at Purdue University published the structure of the mature Zika virus capsid, providing immunologists and drug discovery experts with a sophisticated molecular understanding of how to rationally develop selective anti-viral agents. This remarkably fast transition from the discovery of a novel disease to an atomic model was made possible by a cutting-edge electron microscopy facility, a deep understanding of the theory and application of biophysics, and a diverse team of researchers spearheaded by a well-trained predoctoral student. Successful molecular biophysics training programs will instill upon its trainees many of the same qualities that made this example so effective. To this end, the mission of the Purdue University Molecular Biophysics Training program is to bring together 27 preceptors from six different departments to train an outstanding cohort of graduate students in the underlying theory and practice of cutting-edge biophysical techniques. The program's chief objectives are: (i) to provide enhanced training in the application of molecular biophysics in a rigorous and reproducible way to modern problems in human health and disease, (ii) to foster effective and inclusive teamwork, and (iii) to provide career development opportunities tailored to the goals of individual trainees. To achieve these objectives, selected trainees (6 in each year of the award, typically beginning in their 2nd year of study and supported for up to 2 years) will take a new two-semester gateway class that merges theory with team- based project design and implementation, participate in and help implement an interdepartmental biophysics seminar series that will showcase student-invited external speakers and trainee research on campus, and plan, develop, and implement Purdue's annual biophysics symposium called the Hitchhiker's Guide to the Biomolecular Galaxy. Examples of key activities that support the professional development of these trainees are exercises in teamwork built into program coursework and symposium planning, active development and implementation of detailed individual development plans reviewed and revised annually in collaboration with the mentor, personalized teaching and/or internship opportunities, a grant-writing class tailored to biophysical topics, training in the responsible conduct of research, and participation in the recruitment and retention of underrepresented and/or disabled students. By leveraging Purdue's expertise in Biology Education and self- assessment, the training program and its individual activities will be evaluated annually and refined to ensure that the program is meeting its objectives and the needs of the scientific community.

With this award, the Chemistry of Life Processes Program of the Chemistry Division is supporting Dr. Yulia Pushkar of the Department of Physics and Astronomy at Purdue University to study the mechanism of dioxygen (O2) formation in the naturally-occurring photosynthetic protein Photosystem II. This protein uses the energy of sunlight to split water molecules into protons, electrons and oxygen molecules, providing the majority of the oxygen in the Earth?s atmosphere. Plants subsequently use the electrons and protons in chemical processes resulting in CO2 fixation. The chemical center of Photosystem II responsible for water-splitting contains manganese and calcium ions, that work together in the crucial chemical catalysis process that sustains our biosphere. Establishing the fundamental mechanism of this process in molecular detail could enable the design of new methods for CO2-neutral sunlight-powered energy production. The planned educational activities focus on increasing opportunities for and the participation in research activities for students from backgrounds underrepresented in STEM careers. Dr. Pushkar advises in research students who participate in the Minority Access to Research Careers and Access Internally for Minorities, the Louise Stokes Alliance for Minority Participation, and Research Experiences for Undergraduate Programs. She also mentors student recipients of Summer Undergraduate Research Fellowships, Discovery Park Undergraduate Research Internships, and the Edward S. Akeley Award and Lijuan Wang Award for Women in Physics and contributes to the training of young women scientists through research and presentations in Purdue?s Women in Physics and Women in Science Programs.

Research in this project focuses on the use of laser pump X-ray probe time-resolved X-ray emission, absorption and scattering to study the oxygen-evolving complex (OEC) of Photosystem II, which participates in the O-O bond formation and O2 evolution, the critical step of photosynthesis. The analysis of the electronic structure of the Mn4Ca cluster is conducted with microsecond (µsec) time resolution and the structural changes in the cluster are determined with ~0.02 Å precision. Critical technology developments are made in high-resolution, high-sensitivity X-ray spectrometers, nanoliter drop-on demand sample delivery systems, and biological time-resolved X-ray spectroscopy at newly developed high-flux synchrotron beamlines. The experimental results are interpreted in the framework of currently available structural models of the OEC. Complementary DFT calculations are conducted to monitor the energy profile of the proposed chemical transformations in the OEC. Elucidation of the structural changes in the OEC that accompany the critical catalytic step of O-O bond formation and elucidation of the nature of the species activating water by combined experimental data and DFT modeling are stepping stones for understanding the details of the mechanism of catalytic water-splitting.

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.

With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Yulia Pushkar of Purdue University, Professor Jeremy Smith of Indiana University and Associate Professor Elena Jakubikova of North Carolina State University are studying catalysts that will use electrical energy for the conversion of aqueous nitrate to useful or benign products such as ammonia. Nitrate is a water pollutant that occurs largely as a result of agricultural fertilizer use. The proposed research takes a first step to addressing this problem through the development of robust and efficient electrocatalysts that to convert nitrate to desirable compounds via reductive chemistry. Scientific insights gained through these studies will likely impact the development of other electrocatalysts for other useful electrochemical conversions. Outreach activities include a partnership with the public radio program “A Moment of Science” and the development of YouTube videos on the nitrogen cycle.

This project combines the expertise of three research groups in synthetic, electrochemical, spectroscopic, and computational studies on the development of environmentally relevant electrocatalysts. A modular class of graphite-conjugated macrocyclic complexes will be characterized by a range of physical methods, including synchrotron-based X-ray spectroscopy. Together with experimentally calibrated electronic structure calculations, these data will provide information on the coordination environment, structure, and electron configuration of the metal ion. Redox properties will be characterized by electrochemical measurements, with computational methods providing detailed insights into the electronic structures of different oxidation states. In addition to standard electrochemical and computational methods for mechanistic interrogation, in situ spectroscopic characterization is expected to provide detailed information on the nature of intermediates in the catalytic cycle. Mechanistic investigations into materials that are selective for nitrate reduction will provide insight that is expected to aid in the rational design of catalysts having improved activity. Outreach activities are to including a partnership with a public radio broadcast and the development of publicly accessible educational videos are expected to reach a wide audience and inform the public broadly about electrocatalysis and its utility in developing environmentally beneficial reductive nitrogen chemistry.

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.