Chemistry Seminar with Dr. Mike Reppert from Purdue University at 4:00pm

Please join us as Dr. Mike Reppert from Purdue University delivers his seminar titled “Spectrum, Form, Function:  Structural Tuning Mechanisms in Photosynthetic Light Harvesting”

Abstract: 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.