Semiconductor Nanoparticle-Protein Hybrid Systems for Solar Hydrogen Production and Photo-Triggered Mechanistic Studies Open Access
Chica, Bryant (2017)
Abstract
We describe a hybrid photocatalytic system for hydrogen production consisting of nanocrystalline CdSe/CdS dot-in-rod (DIR) structures coupled to [NiFe] soluble hydrogenase I (SHI) from Pyrococcus furiosus. Electrons are shuttled to the catalyst by a redox mediator, either methyl viologen (MV2+, E0 = -446 mV vs. NHE) or propyl-bridged 2-2'-biyridinium (PDQ2+, E0 = -550 mV vs. NHE). H2 production in the PDQ2+ system is highly efficient, with an internal quantum efficiency (IQE) as high as 77% and a TONSHI of 1.1 x 106 under mild (RT, pH = 7.35) conditions. Detailed characterization reveals the mechanisms responsible for such high efficiencies. The high efficiency and robustness of this system enabled its use as a novel methodology for photo-triggering SHI reactivity and enabling time resolved and steady-state spectroscopic studies of the SHI active site. This enabled reproduction of previously reported active site dynamics through laser initiated chemical potential jump studies on the SHI active site. It also provided a novel method to gain insight into the reductive reactivation of the aerobically inactivated enzyme and the nature of the inactive states by systematically lowering the solution reduction potential in "light titrations". We thus establish nanocrystalline semiconductor nanostructures as powerful tools to study redox enzymes and potentially more general catalyst systems.
Table of Contents
Table of Contents
Chapter 1 - Introduction 1 1.1 - Climate change, clean energy and solar fuels 21.2 - Hydrogenases 5
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1.2.1 - Hydrogenases in Photocatalytic H2 Production 5
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1.2.2 - Hydrogenase Mechanism 7
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1.2.3 - Catalytic Bias in Hydrogenase 9
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1.2.4 - Oxygen sensitivity in Hydrogenase 11
1.4 - References 14
Chapter 2 - Experimental Methodology 21 2.1 - Introduction 222.2 - Protein expression and purification 22
2.2.1 - Pyrococcus furiosus SHI 22 2.3 - Materials 22 2.3.1 - PDQ2+ synthesis 22 2.3.2 - Nanomaterials Synthesis 23 2.3.2.1 - CdSe/CdS nanorods and ligand exchange 23 2.4 - Analytical Methods 25 2.4.1 - UV-Vis 25 2.4.2 - FTIR and Light Titrations 26 2.4.3 - Hydrogen Production and Detection 27 2.4.4 - Photoluminescence Titrations 28 2.4.5 - Mediator Photoreduction 29 2.4.6 - Photo driven hydrogen production 29 2.4.7 - Time resolved photoluminescence 30 2.4.8 - Ultrafast visible transient absorbance 30 2.4.9 - ns to ms visible and infrared transient absorbance 31absorbance
2.5 - Data Analysis 32 2.5.1 - Fitting and SVD analysis of broadband ns transient 32 2.5.2 - Global fitting of FTIR light titration data. 342.6 - References35
Chapter 3 - Efficient Photocatalytic Hydrogen Production in 36
CdSe/CdS Nanorod-[NiFe] H2ase Assemblies
3.1 - Introduction 37 3.2 - Results and Discussion 41 3.2.1 - Photocatalytic Hydrogen Production 42 3.2.2 - Electron Transfer Dynamics 51 3.2.3 - Hole Transfer Dynamics 56 3.2.4 - pH Dependence and Energetics 58 3.2.5 - Stability of the Photochemical System 62 3.3 - Conclusions 663.4 - References69
Chapter 4 - Semiconductor Nanocrystals as Tools to Probe Enzyme 76Structure and Dynamics
4.1 - Introduction 77 4.2 - Results and Discussion 794.2.1 - CdSe/CdS nanorod photo-sensitization of sub-TOF 79
H2ase dynamics4.2.2 - Insights into Pf SHI oxygen tolerance and 84
spectroscopic characterization of photochemical
reactivation
4.4 - References101
Chapter 5 - Charge Transfer in Cytochrome C-Quantum Rod Conjugates 107 5.1 - Introduction 1085.2 - Results and Discussion 111
5.2.1 - Reduction potential control through heme ligation 111
5.5.2 - Photoreduction of M80C 113 5.3 - Conclusions 1185.4 - References 121
Chapter 6 - Conclusion 124 6.1 - Conclusion125About this Dissertation
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