Optimizing a Bifurcating [NiFe]-Hydrogenase System for Light-Driven Hydrogen Production Öffentlichkeit

Abstract

      Electron confurcation is a recently discovered biological mechanism that enables an unfavorable electron transfer by coupling it with a favorable electron transfer to produce high-energy intermediates without using ATP. [NiFe]-hydrogenase in the anaerobic bacteria Acetomicrobium mobile uses electron confurcation to reversibly convert protons and electrons to hydrogen gas. We probe its mechanism and develop an artificial photosynthetic system for light-driven hydrogen production by coupling A. mobile hydrogenase with photosensitive semiconductor nanomaterials. CdSe quantum dots with the desired optical and electronic properties were engineered, and we demonstrate their ability to initiate electron confurcation in hydrogenase when illuminated. We tested numerous reaction conditions to optimize H2 production and found evidence that the CdSe quantum dots bind to hydrogenase and inhibit its ability to perform electron confurcation. This adds support to the theory that conformational changes are key to electron confurcation in A. mobile hydrogenase.

Table of Contents

Chapter 1: An Introduction to Hydrogenase and Electron Bifurcation                               1

1.1 The Energy Crisis                                                                                                         1

1.1.1      Motivation: The Need for Renewable Energy and Challenges                  1

1.1.2      Energy Conversion in Nature                                                                  3                                       

1.2 Overview of Hydrogenase Metalloenzymes                                                        3

1.2.1      Properties of [NiFe]-Hydrogenases                                                                  3

1.2.2      Acetomicrobium mobile Hydrogenase: Properties                                   4

1.3 Electron Bifurcation                                                                                             5

1.3.1      An Overview of Electron Bifurcation                                                     5

1.3.2      Acetomicrobium mobile Hydrogenase: Mechanism                               6

1.4 Proposed Model System                                                                                     8

1.5 Scope and Aims                                                                                                  8

1.6 References                                                                                                            9

Chapter 2: Developing Photosensitive Semiconductor Nanomaterials                                11

2.1 Introduction                                                                                                          11

2.2 Methodology                                                                                                       13

2.2.1      CdSe Quantum Dot Synthesis                                                                 13

2.2.2      CdSe/CdS Dot-in-Rod Synthesis                                                             13

2.2.3      Ligand Exchange                                                                                     14

2.2.4      Nanomaterial Characterization and Quantum Efficiency Evaluation       14

2.2.5      Steady-State Photoreduction of Ferredoxin                                            15

2.3 Results and Discussion                                                                                        16

2.3.1      Characterization of Nanomaterials                                                         16

2.3.2      Steady-State Photoreduction of Ferredoxin                                            18

2.4 References                                                                                                           20

Chapter 3: Optimizing System Parameters for Light-Driven Hydrogen Production          22

3.1 Introduction                                                                                                          22

3.2 Methodology                                                                                                       23

3.2.1      Hydrogenase Activity Assay                                                                   23

3.2.2      Preparation of Sample for Hydrogen Production Assay                        24

3.2.3      Effect of FMN Concentration on Electron Bifurcation Rate                  24

3.2.4      Photoluminescence Quenching of CdSe Quantum Dots                         25

3.3 Results and Discussion                                                                                       25

3.3.1      Hydrogenase Activity Assays                                                                25

3.3.2      Hydrogen Production Assays                                                                 26

3.3.3      Effect of FMN Concentration on Electron Bifurcation Rate                  30

3.3.4      Photoluminescence Quenching of CdSe Quantum Dots                        31

3.4 References                                                                                                          32

Chapter 4: Conclusions and Perspectives                                                                              33

4.1 Aim 1: Engineering Effective Photosensitive Nanomaterials                                  33

4.2 Aim 2: Achieving Light-Driven Reduction of Amo Ferredoxin                               33

4.3 Aim 3: Identifying Conditions for H2 Production via Electron Confurcation          34

4.4 Implications and Future Directions                                                                            34

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Physical Chemistry, Inorganic Chemistry, Biochemistry
Stichwort	Electron Bifurcation Artifical Photosynthesis [NiFe]-Hydrogenase
Committee Chair / Thesis Advisor	R. Brian Dyer, Emory University
Committee Members	Frank McDonald, Emory University Katherine Davis, Emory University

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