In nature, the light-harvesting (LH) antenna systems of photosynthetic organisms at its core are made up of two fundamental building blocks—proteins and pigments—that self-assemble into a large variety of structures. This structural diversity is believed to enable the photosynthetic organisms to survive and thrive, even under extreme and constantly changing environmental conditions. While the light absorbing pigment complexes have been studied extensively, less is known about the role of the pigments’ surrounding protein scaffold. This protein scaffold is thought to protect the pigments from photo-oxidation, assist in highly efficient energy transport, and aid in dissipation of excess heat energy. However, the exact role of the protein scaffold in the LH antenna’s functionality has not been resolved yet.<br/>In my talk, I will present a biomimetic model system that we designed to allow for direct experimental investigation of the protein scaffold’s functionality: well-defined LH nanotubes self-assembled from cyanine dye molecules (to mimic the light-absorbing pigments) encapsulated with a polymer scaffold (to mimic the protein scaffold environment). CryoTEM and steady-state absorption spectroscopy divulged homogenous encapsulation without altering the LH nanotube’s delicate supramolecular structure. Broadband femtosecond transient absorption spectroscopy revealed exciton coherence was not significantly affected by the polymer scaffold. Interestingly, we found that the polymer scaffold not only offered a passive protective layer against photo-oxidation and degradation of internal structure, but in addition, the scaffold promoted structural diversity in response to environmental triggers such as temperature change. In fact, the encapsulated LH nanotubes were able to undergo supramolecular rearrangement during heating without significant degradation, and “recovered” during the annealing process. We attribute this robustness to self-healing via hierarchical re-assembly, and to the scaffold stabilizing this conformation. CryoTEM revealed dense fiber formation upon heating and annealing while high resolution Near-field Scanning Optical Microscopy (NSOM) showed that this fiber network is only formed by the polymer scaffold. We believe the formation of fiber network may increase the system’s thermal and mechanical strength, which is also supported by the investigations from our prototype dye sensitized solar cell device.

Robust light-harvesting in biomimetic nanotubes through scaffold-assisted self-healing

2019 Fall National Meeting

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