Copper Catalyzed Lipid Polysaccharide Monooxygenase Biomimicry of Polysaccharide Oxidative Cleavage Restricted; Files Only

Abstract

Lipid polysaccharide monooxygenases (LPMO) can degrade glycosidic bonds via oxidative cleavage using ascorbate reagents in a redox system with a debated mechanism, and copper complex mimetics display similar capabilities with more room for optimization. This work investigates four copper complex mimetics of LPMO designed with N, N, N or N, N, O coordination spheres in terms of glycosidic cleavage capability. This work investigates their reactivity towards model substrates of cellulose and gain insight into the mechanism via reactive intermediates. It demonstrates a novel ligand-centered radical reactive capability of a proline-derived ligand on a copper complex mimetic with oxidative glycosidic capability. One copper complex LPMO mimetic was synthesized with desired reactive properties, and its abilities in oxidative cleavage using peroxide as well as ascorbic/dioxygen reagent conditions were demonstrated using 4-nitrophenyl-β-D-glucopyranoside and cellobiose as substrates. Numerous reactions to probe the mechanism revealed the reactivity of ligand-centered radicals from proline-derived ligands as central to this glycosidic cleavage capability.

Table of Contents

Chapter 1: An Introduction to Complex 4 and Cellulose Breakdown

 

1.1 The Energy Crisis

           1.1.1 The Challenges of Energy                                                                                         1

           1.1.2 Plant Biomass as an Energy Source                                                                        2

1.2 Copper Complex Mimetics                                                                                                     3

1.3 Reaction Overview                                                                                                                   5

1.4 Scopes and Aims                                                                                                                       6

1.5 References                                                                                                                                7

 

Chapter 2: Oxygen and Ascorbate as Reagents

 

2.1 Introduction                                                                                                                              8

2.2 Methodology                                                                                                                            

           2.2.1 Peroxide as a Reagent                                                                                               9

           2.2.2 Ascorbate as a Reagent                                                                                            10

2.3 Results and Discussion

           2.3.1 Peroxide as a Reagent                                                                                             11

           2.3.2 Ascorbate as a Reagent                                                                                            14

2.4 References                                                                                                                              15

 

Chapter 3: The Copper Complex

 

3.1 Introduction                                                                                                                            16

3.2 Methodology                                                                   

           3.2.1 Complex 4 Synthesis                                                                                               19

           3.2.2 Evaluation of Different Complexes in LPMO Mimetic Activity                            20

3.2.3 Complex 4 Mechanism                                                                                             20

3.3 Results and Discussion

           3.3.1 Complex 4 Synthesis                                                                                               21

           3.3.2 Evaluation of Different Complexes in LPMO Mimetic Activity                            22

3.3.3 Complex 4 Mechanism                                                                                            25

3.4 References                                                                                                                              28

 

Chapter 4: Optimizing Reaction Conditions

 

4.1 Introduction                                                                                                                            29

4.2 Methodology                                                       

           4.2.1 Reagent Concentrations                                                                                           29

4.2.2 pH stability                                                                                                              30

           4.2.3 Breakdown of Cellobiose                                                                                        30

4.3 Results and Discussion

4.2.1 Reagent Concentrations                                                                                           30

4.2.2 pH stability                                                                                                              33

           4.2.3 Breakdown of Cellobiose                                                                                        34

4.4 References                                                                                                                              35

 

Chapter 5: Conclusions and Perspectives                                                                                36

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

List of Figures

Figure 1.1 Energy consumption in the United States                                                                    1

Figure 1.2 Corn Production and Fuel Use in the United States                                                   2

Figure 1.3 LPMO Catalytic Site Structure from Panu similis and LPMO glycosidic cleavage reactions.                                                                                                                                           3

Figure 1.4 LPMO Copper Complex Mimetic                                                                             4

Figure 1.5 Complex Characterization                                                                                       5

Figure 1.6 Reaction Scheme.                                                                                                       6

Figure 2.1 The depiction of the dioxygen intermediate with a binuclear copper active site          9

Figure 2.2 Reaction Scheme for Experiment                                                                               10

Figure 2.3 Reaction Scheme for Experiment                                                                               11

Figure 2.4 Study of Oxidative Cleavage Rate and the Copper Complexes                                 12

Figure 2.5 Kinetic Data Comparison of Model Substrate Turnover in Copper Complexes         13

Figure 2.6 Absorbance Characterization of Peroxy Intermediate                                               14

Figure 2.7 Monooxygenase Activity of Complex 4 With Ascorbate and Oxygen Reagents       15

Figure 3.1 Copper Complexes analyzed for LPMO reactivity                                                    17

Figure 3.2 HRMS of Complex 4 in Water and Methanol                                                           17

Figure 3.3 EPR Evaluation of Radical Forming in Complex 4                                                    19

Figure 3.4 Mass Spectrum of Complex 4 Synthesis                                                                    22

Figure 3.5 Study of Influence of Complex Concentration on Catalysis                                      24

Figure 3.6 Influence of Ascorbate concentration in Catalysis                                                     25

Figure 3.7 Mass Spectrum of Complex4- Peroxy Intermediate with Peroxide Reagent            26

Figure 3.8 Mass Spectrum of Complex4- Peroxy Intermediate with Ascorbate Reagent          27

Figure 3.9 Absorbance Spectrum of Peroxy Intermediate of Complex 4 Using Ascorbate Reagent                                                                                                                                       28

 

Figure 4.1  Study of the Influence of Peroxide Concentration on Catalysis                            31

 

Figure 4.2  Evaluation of Different Substrate Concentration on Catalysis                                         32

 

Figure 4.3 Study of Influence of pH on Reaction Rate of Complex 4                                        33

 

Figure 4.4 Absorbance Spectrum of Complex 4 Reaction with Cellobiose Substrate              34

 

Figure 4.5 Mass Spectrum of Complex 4 Reaction Oxidative Cleavage                                    35

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Inorganic
Keyword	Chemistry Copper Complexes LPMO mimetics Renewable Fuels
Committee Chair / Thesis Advisor	Richard Brian Dyer, Emory University
Committee Members	Katherine Davis, Emory University Richard Himes, Emory University

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