Engineering principles of photosystems and their practical application as long-lived charge separation in maquettes

Zhenyu Zhao, University of Pennsylvania


Light-activated electron transfer reactions between cofactors embedded in proteins serve as the central mechanism underlying numerous biological processes essential to the survival and prosperity of most organisms on this planet. These processes range from navigation, to DNA repair, to metabolism, and to solar energy conversion. The proper functioning of these processes relies on the creation of a charge-separated states lasting for a necessary length of time, from tens of nanoseconds to hundreds of milliseconds, by the arrays of cofactors in photosystems. In spite of decades of experiments and theoretical frameworks providing detailed and extensive description of the behavior of the photosystems, coherent and systematic understanding is lacking regarding the underlying structural and chemical engineering principles that govern the performance of charge-separation in photosystems, evaluated by the fraction of the input energy made available by the photosystem for its intended function. This thesis aims to establish a set of engineering principles of natural and man-made photosystems based on the fundamental theories of electron transfer and the biophysical and biochemical constraints imposed by the protein environment, and then to apply these engineering principles to design and construct man-made photosystems that can excel in charge-separation while incurring minimal cost in their construction. Using the fundamental theories of electron transfer, this thesis develops an efficient computational algorithm that returns a set of guidelines for engineering optimal light-driven charge-separation in cofactor-based photosystems. This thesis then examines the validity of these guidelines in natural photosystems, discovering significant editing and updating of these guidelines imposed by the biological environment in which photosystems are engineered by nature. This thesis then organizes the two layers of engineering principles into a concise set of rules and demonstrates that they can be applied as guidelines to the practical construction of highly efficient man-made photosystems. To test these engineering guidelines in practice, the first ever donor-pigment-acceptor triad is constructed in a maquette and successfully separates charges stably for >300ms, establishing the world record in a triad. Finally, this work looks ahead to the engineering of the prescribed optimal tetrads in maquettes, identifying what’s in place and what challenges yet remain.

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Recommended Citation

Zhao, Zhenyu, "Engineering principles of photosystems and their practical application as long-lived charge separation in maquettes" (2016). Dissertations available from ProQuest. AAI10194728.