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Tyler Bennett1 Michael Vaughn1 Dibyendu Mukherjee1 Bamin Khomami1

1, University of Tennessee, Knoxville, Tennessee, United States

During photosynthesis plants and algae use Photosystem I (PSI), a supra-molecular protein complex, to harness solar energy with 100% quantum efficiency and drive stable charge separation. The unique photoactive electrochemical properties of PSI make it a promising candidate for applications in biohybrid materials and devices. Many works have achieved organized two-dimensional assemblies of PSI for photovoltaic electricty or solar fuel generation. However, three-dimensional architecture to house PSI, such as the native folded thylakoid membrane, has yet to be achieved in artificial systems. Metal organic frameworks (MOFs) are an increasingly explored category of hybrid material with the unique properties of high crystallinity and exceptionally high porosity, which allow for diverse functionality whose applications are rapidly expanding. These materials are formed from solutions of metal ion nodes connected by organic linkers to form infinite 3D porous networks. This work employs the zinc-based MOF, ZIF-8, as a scaffold to both coordinate 3D assembly of PSI and serve as a protective coating due to its robust chemical and thermal stability. Optimized reaction conditions for a mixture of the MOF constituents and PSI together in solution lead to the formation of ZIF-8 microparticles encapsulating PSI trimers. X-ray diffraction and BET isotherms confirm the quality and porosity of our hybrid material. The ensuing changes in absorption and fluorescence behavior of embedded PSI contribute to our understanding of chromophore network confinement. Pump-probe spectroscopy was utilized to measure the electron turnover rate of PSI, establishing the activity of ZIF-8/PSI compared to free PSI in both benign and protein denaturing environments.

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