CAS: Elucidating How Nanocrystal Structure Controls Electron Flow in Nanocrystal-Enzyme Complexes

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) program in the Division of Chemistry, Professor Gordana Dukovic of University of Colorado Boulder is combining synthesis, advanced laser techniques, and high-resolution microscopy to follow the flow of electrons in nanocrystal-enzyme complexes capable of light-driven hydrogen production. To make hydrogen, the nanocrystal is first excited by light, increasing the energy of its electrons. These excited electrons must then hop from the nanocrystal to the enzyme, and then make their way to the enzyme's reaction center by hopping from one site to another, like crossing a stream by jumping from stone to stone. Each of these electron hops is important for hydrogen production, but they are difficult to observe and control. Professor Dukovic and her students will measure the times of the critical electron hopping events, and how they depend on nanocrystal structure, surface properties, and binding to the enzyme. Their discoveries could lead to new ways to use sunlight to make chemicals, including solar fuels. Additionally, the project is helping to foster the Nation's science, technology, engineering, and mathematics (STEM) workforce by supporting career development of junior faculty and scientists, as well as the undergraduate education of students from a variety of backgrounds. This project will elucidate the electron pathways involved in photochemical H2 generation that occurs when photoexcited semiconductor nanocrystals transfer electrons to the adsorbed enzyme hydrogenase, which catalyzes proton reduction to H2. The project will examine how properties of nanocrystalline quantum dots (QDs) such as composition, diameter, and surface chemistry impact the QD binding with the enzyme, the transfer of photoexcited electrons, and other critical processes for H2 production, such as hole scavenging and back-electron transfer from the enzyme. The outcome of the project will be an improved understanding of how nanocrystals drive enzyme catalysis. This, in turn, will lead to design principles for how to use the immense tunability of nanocrystal structure and properties to adapt them to drive complex, multi-step light-driven chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.