Physical Seminar- Prof. Michael Reppert (Purdue University)

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1315 Seminar Hall, North Tower
@ 11:00 am


Title: Spectrum, Form, Function: Structural Tuning Mechanisms in Photosynthetic Light Harvesting


Mike Reppert completed his BS at Kansas State University in 2009 in Chemistry, Biochemistry, and Mathematics. It was also at Kansas State (during four years of undergrad research) where he became fascinated by the molecular mechanisms of photosynthesis. After a year of Fulbright research at the Polish Academy of Sciences in Warsaw, Poland, he went on to work in 2D IR spectroscopy and peptide structural analysis with Andrei Tokmakoff at the Massachusetts Institute of Technology and the University of Chicago. After obtaining his PhD in 2016, he worked as a Banting Scholar with Professor Paul Brumer at the Chemical Physics Theory group of the University of Toronto, exploring quantum effects in biological light harvesting. In summer 2019, he moved to Purdue to begin his own research group in Physical Chemistry, working to develop both experimental and computational tools to quantitatively understand structure/spectrum relationships in biomacromolecules, particularly photosynthetic proteins.


Biological photosynthesis offers a tantalizing glimpse of the clean-energy opportunities at the interface of synthetic biology, chemical catalysis, molecular excitonics, and soft-matter physics. However, this sophisticated system is optimized in nature for biological objectives (competitive fitness) that are often at odds with human concerns such as energy-storage efficiency. While some progress has been made in reconfiguring native photosystems for biofuel production, advances are limited by gaps in our understanding of the “structure-spectrum-function” relationship, i.e., of the mechanisms by which protein structures tune pigment optical properties and, in turn, how these optical properties translate into biological function. In this talk, I will describe recent efforts in my group to build a quantitative approach to structure-based tuning using site-directed mutagenesis, optical spectroscopy, and molecular and quantum dynamics simulations. Electrostatics and pigment chemistry are found to provide relatively simple and predictable control knobs for tuning electronic transitions, while steric ring-deformation (although likely to be important) is more difficult to predict and control. Single point mutations are seen to produce surprisingly large changes in vibrational sidebands in electronic spectra, which can be understood as an interplay between vibrational coupling and excitonic delocalization. I will close with preliminary results on tuning the lowest-energy fluorescent state of Photosystem II in cyanobacterial cells, opening the door both to characterizing the functional relevance of these states in native systems and to tuning their properties for new applications.

Keywords: photosynthesis, spectroscopy, protein structure

Host: Prof. Martin Zanni