Bacterial Photosynthetic Design Probed by Multidimensional Spectroscopies

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Photosynthetic organisms employ elaborate antenna arrays to harvest solar energy and transfer it to reaction centers with ~95% efficiency. At the heart of this stunning efficiency is the energy landscape that provides directional ultrafast transfer of energy between the antennae and reaction centers, and directional charge separation within reaction centers. Recently two-dimensional electronic spectroscopy (2DES) has emerged as a powerful method for studying energy transfer and charge separation in photosynthesis. 2DES and other spectroscopic measurements have suggested that key electronic-vibrational dynamics may enhance photosynthetic efficiency. The proposed work will enhance the experimental tools for studying energy transfer and charge separation in natural and artificial systems. The extensive experimental characterization of bacterial photosystems will drive the development of theoretical models of the electronic structure and dynamics of multichromophoric assemblies. The understanding gained from purple bacteria as a model system will inform our understanding of the more complex plant photosystems and may guide the design of artificial light-harvesting materials. The proposed work will provide extensive scientific training for graduate and undergraduate students and will also support a wide range of outreach activities. These include the organization and participation in the APS Conferences for Undergraduate Women in Physics (CUWiPs). These meetings bring together undergraduate women from the across the country, educating them about career opportunities and state-of-the-art research in Physics, thereby strengthening the network of women in Physics in the US. The proposal aims to foster a love of physics among children from diverse age groups and backgrounds through participation in the yearly Physics Olympiad and science exploration days for Girl Scouts troops. This project aims to push the frontiers of multidimensional spectroscopy to address the following open questions about bacterial photosynthesis: i) Do key protein or cofactor dynamics enhance energy transfer and charge separation in purple bacteria? ii) How do purple bacteria remodel their energy-landscape to regulate energy transfer under high and low light conditions? To address question i) bacterial reaction centers will be studied in unprecedented detail with a palette of electronic and vibrational multidimensional spectroscopies, providing a dynamical picture of the pigments and surrounding protein during charge separation. Moving beyond studies of the isolated components to address question ii) 2DES of whole cells will be used to map the complete energy transfer and charge separation pathways of purple bacteria: from the visible to near-infrared wavelengths with ultrafast time resolution. The rich spectroscopic data to be obtained in the proposed experiments will provide critical feedback to theoretical modeling of energy transfer and charge separation in purple bacteria. This project is being jointly supported by the Physics of Living Systems program in the Division of Physics and the Molecular Biophysics Cluster in the Division of Molecular and Cellular Biosciences.