Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Gordana Dukovic

Second Advisor

Tanja Cuk

Third Advisor

Niels Damrauer

Fourth Advisor

Paul King

Fifth Advisor

Sandeep Sharma

Abstract

Nanocrystals are an emergent strategy for providing electrons to redox enzymes for catalysis. In this dissertation I present my work on the investigation of how nanocrystals can be used to drive active site chemistry of two different enzymes. In the first project I present for the first time the direct coupling of cadmium sulfide nanorods (CdS NRs) to a CO2 reduction enzyme for the creation of new carbon-carbon bonds using light. Under optimal conditions, the maximum turnover frequency (TOFmax) for CO2 reduction is similar to that obtained in the native system where the native electron donor ferredoxin is used; however, high excitation frequencies are needed to reach TOFmax resulting in low quantum yields of 1%. The electron transfer dynamics are investigated as a means to understand this limitation on quantum yield, and we find that the electron transfer rates are dependent on whether the enzyme is bound to reactants. The implications of this new finding are discussed within the context of available crystal structures for the enzyme, and conclusions are drawn about the nature of nanocrystal-protein interactions when the enzymatic catalyst undergoes dynamic conformational changes during light-driven turnover. In the second project I present work performed to promote fast electron transfer in a more well-studied system of CdS NRs and Hydrogenase enzyme (CaI). In this work I substitute an ultrashort, sulfide ligand in place of more conventional 3-mercaptopropionate (MPA) at the interface of the nanocrystal and enzyme to shorten the tunneling barrier to electron transfer. The excited state decay of the CdS-CaI complex is investigated to determine the quantum efficiency of electron transfer (QEET). The QEET is then compared with light-driven H2 production to understand the overall impact of ultrashort ligands on the photocatalytic activity. This work concludes with a summary of these important findings and a projection for the future implementation of nanocrystals in photochemical schemes where biological enzymes are used as catalysts.

Share

COinS