Semiconductor Nanoparticle-Protein Hybrid Systems for Solar Hydrogen Production and Photo-Triggered Mechanistic Studies Open Access

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 2

1.2 - Hydrogenases 5

1. 1.2.1 - Hydrogenases in Photocatalytic H2 Production 5

2. 1.2.2 - Hydrogenase Mechanism 7

3. 1.2.3 - Catalytic Bias in Hydrogenase 9

4. 1.2.4 - Oxygen sensitivity in Hydrogenase 11

1.3 - Hypothesis and scope of this thesis 13

1.4 - References 14

Chapter 2 - Experimental Methodology 21 2.1 - Introduction 22

2.2 - 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 31

absorbance

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. 34

2.6 - 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 66

3.4 - References69

Chapter 4 - Semiconductor Nanocrystals as Tools to Probe Enzyme 76

Structure and Dynamics

4.1 - Introduction 77 4.2 - Results and Discussion 79

4.2.1 - CdSe/CdS nanorod photo-sensitization of sub-TOF 79

H2ase dynamics
4.2.2 - Insights into Pf SHI oxygen tolerance and 84

spectroscopic characterization of photochemical
reactivation

4.3 - Conclusions 98

4.4 - References101

Chapter 5 - Charge Transfer in Cytochrome C-Quantum Rod Conjugates 107 5.1 - Introduction 108

5.2 - Results and Discussion 111

5.2.1 - Reduction potential control through heme ligation 111

5.5.2 - Photoreduction of M80C 113 5.3 - Conclusions 118

5.4 - References 121

Chapter 6 - Conclusion 124 6.1 - Conclusion125

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	PhD
Submission	Dissertation
Language	English
Research Field	Chemistry, Inorganic Chemistry, Physical Nanoscience
Keyword	Hydrogenase CdSe Photocatalysis Quantum Dot Solar Fuels
Committee Chair / Thesis Advisor	Dyer, Brian, Emory University
Committee Members	Evangelista, Francesco , Emory University MacBeth, Cora E., Emory University

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