Gerhard Swiegers

Mechanical Catalysis (eBook, PDF)

Methods of Enzymatic, Homogeneous, and Heterogeneous Catalysis

• Format: PDF

Produktbeschreibung

* Provides a clear and systematic description of the key role played by catalyst reactant dynamism including: (i) the fundamental processes at work, (ii) the origin of its general and physical features, (iii) the way it has evolved, and (iv) how it relates to catalysis in man-made systems. * Unifies homogeneous, heterogeneous, and enzymatic catalysis into a single, conceptually coherent whole. * Describes how to authentically mimic the underlying principles of enzymatic catalysis in man-made systems. * Examines the origin and role of complexity and complex Systems Science in catalysis--very hot topics in science today.

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Produktdetails

• Verlag: John Wiley & Sons
• Seitenzahl: 384
• Erscheinungstermin: 8. Oktober 2008
• Englisch
• ISBN-13: 9780470384183
• Artikelnr.: 37291805

Autorenporträt

Gerhard F. Swiegers, PhD, earned his doctorate at the University of Connecticut in 1991 and then worked at the Australian National University and the University of Wollongong, Australia. In 1998, he joined the Commonwealth Scientific and Industrial Research Organization (CSIRO), the major government laboratory in Australia. From 1998 to 2006, he was involved with designing anti-counterfeiting devices for bank notes. In 2005, one of his inventions was commercialized as a spin-off company known as Datatrace DNA Pty Ltd, and in 2006, Dr. Swiegers joined the firm as Vice President, Strategic Research. Several of Dr. Swiegers's inventions are currently used by national governments and major companies around the world.

Inhaltsangabe

Preface xxi
Contributors xxv
Glossary xxvii
1 Introduction to Thermodynamic (Energy-Dependent) and Mechanical
(Time-Dependent) Processes: What Are They and How Are They Manifested in
Chemistry and Catalysis?
Gerhard F. Swiegers
1.1 Thermodynamic (Energy-Dependent) and Mechanical (Time-Dependent)
Processes 1
1.2 What Is a Thermodynamic Process? 5
1.3 What Is a Mechanical Process? 7
1.4 The Difference between Energy-Dependent (Thermodynamic) and
Time-Dependent (Mechanical) Processes 9
1.4.1 Time-Dependent (Mechanical) Processes Are Path-Reliant and
Spatiotemporal in Character 9
1.4.2 Time-Dependent (Mechanical) Processes Have a Flat Underlying Energy
Landscape (or Are Unaffected by the Energy Landscape) 10
1.4.3 Time-Dependent (Mechanical) Processes Display Deterministic Chaos;
This Causes Them to be Stochastic and Complex 11
1.4.4 Time-Dependent (Mechanical) Processes Often Involve Synergies of
Action 14
1.4.5 Time-Dependent (Mechanical) Processes Characterize Numerous Aspects
of Human Experience 15
1.5 Time- and Energy-Dependence in Chemistry and Catalysis 17
1.5.1 The Origin of Time- and Energy-Dependent Processes in Chemistry 17
1.5.2 Examples of Time-Dependent Processes in Chemistry 19
1.5.3 Time- and Energy-Dependent Processes in Catalysis 21
1.5.4 Is There Such a Thing as a Time-Dependent Process in Catalysis? 23
1.6 The Aims, Structure, and Major Findings of this Series 24
1.6.1 Summary of the Key Finding: Many Enzymes Seem to be Time-Dependent
Catalysts 25
1.6.2 The Aims and Structure of this Series. Summary: Other Major Findings
of this Series 28
References 34
2 Heterogeneous, Homogeneous, and Enzymatic Catalysis. A Shared Terminology
and Conceptual Platform. The Alternative of Time-Dependence in Catalysis 37
Gerhard F. Swiegers
2.1 Introduction: The Problem of Conceptually Unifying Heterogeneous,
Homogeneous, and Enzymatic Catalysis? Trends in Catalysis Science 37
2.2 Background: What Is Heterogeneous, Homogeneous, and Enzymatic Catalysis
38
2.2.1 Homogeneous and Heterogeneous Catalysis 38
2.2.2 Hybrid Homogeneous-Heterogeneous Catalysts 40
2.2.3 Enzymatic Catalysis 41
2.2.4 Theories and Mimicry of Enzymatic Catalysis 42
2.3 Distinctions Within Homogeneous Catalysis: Single-Centered and
Multicentered Homogeneous Catalysis 44
2.3.1 Single-Centered Homogeneous Catalysts. Most Manmade Homogeneous
Catalysts Are Single-Centered Catalysts 44
2.3.2 Multicentered Homogeneous Catalysts: Most Enzymes Are Multicentered
Homogeneous Catalysts 46
2.4 The Distinction between Single-Site/Multisite Catalysts and
Single-Centered/MultiCentered Catalysts in Heterogeneous Catalysis: An
Important Convention Used in This Series 48
2.4.1 A Key Convention Used in This Series: A Catalytic Site Is a
Collection of Atoms about Which a Reaction Is Catalyzed. A Catalytic Center
Is an Atom Within that Site Which Binds and Facilitates the Transformation
of a Reactant 48
2.5 The Alternative of Time-Dependence in Catalysis 48
References 52
3 A Conceptual Description of Energy-Dependent ("Thermodynamic") and
Time-Dependent ("Mechanical") Processes in Chemistry and Catalysis 55
Gerhard F. Swiegers
3.1 Introduction 55
3.2 Theoretical Considerations: Common Processes in Uncatalyzed Reactions
56
3.2.1 Reactions as Collisions Between Molecules 56
3.2.2 The Fundamental Origin of Energy-Dependent and Time-Dependent
Reactions 57
3.2.3 Time-Dependent and Energy-Dependent Domains Were First Observed in
Unimolecular Gas-Phase Reactions 58
3.2.4 The Pathway of the Reaction Is also Controlled by the Least-Likely
Step in the Sequence 59
3.2.5 Transition State Theory (TST) Describes the Pathway and Rate of
Energy-Dependent Reactions. Transition State Theory Corresponds to the
High-Pressure Limit of Hinshelwood-RRK Theory 61
3.2.6 Time-Dependent Reactions in the Liquid Phase: Some Examples 63
3.2.7 The Transition between Energy-Dependence and Time-Dependence as a
Function of Temperature. Curvature in Arrhenius Plots 65
3.2.8 Methods of Creating Time-Dependent Reactions 67
3.2.9 Summary: The Key Properties of Time-Dependent and Energy-Dependent
Reactions 68
3.3 Theoretical Considerations: Common Processes in Catalyzed Reactions 68
3.3.1 Catalyzed Reactions Are More Likely to be Time-Dependent than Are
Uncatalyzed Reactions 68
3.3.2 Catalysis Changes the Reaction Processes 69
3.3.3 Physical Manifestation of Time- and Energy-Dependence in Catalysts 72
3.3.4 The Distinction Between Time-Dependent Catalysis and
Diffusion-Controlled Catalysis 72
3.3.5 Energy-Dependent and Time-Dependent Control of Catalysis 73
3.3.6 The Influence of the Product Release Step 74
3.4 Conclusions: Energy- and Time-Dependent Catalysis 75
Acknowledgments 75
References 76
4 Time-Dependence in Heterogeneous Catalysis. Sabatier's Principle
Describes Two Independent Catalytic Realms: Time-Dependent ("Mechanical")
Catalysis and Energy-Dependent ("Thermodynamic") Catalysis 77
Gerhard F. Swiegers
4.1 Introduction 77
4.2 Sabatier's Principle in Heterogeneous Catalysis 79
4.2.1 Volcano Plots 79
4.2.2 Some Important Points about Volcano Plots 82
4.2.3 Time-Dependent Catalysis in Volcano Plots 82
4.2.3.1 How Is Time-Dependence Created on the Left-Hand Side of the Volcano
Plot? 82
4.2.3.2 Why Do Volcano Plots Slope Upward on the Left 84
4.2.3.3 The Rate-Determining Step in a Time-Dependent Catalyst 86
4.2.3.4 The Physical Manifestation of Time-Dependent Catalysis.
"Saturation" of a Time-Dependent Catalyst 87
4.2.4 Energy-Dependent Catalysis in Volcano Plots 88
4.2.4.1 How Is Energy-Dependence Created on the Right-Hand Side of the
Volcano Plot? 88
4.2.4.2 Why Do Volcano Plots Slope Downward on the Right? 88
4.2.4.3 The Rate-Determining Step in an Energy-Dependent Catalyst 89
4.2.4.4 The Physical Manifestation of Energy- Dependence. Saturation in an
Energy-Dependent Catalyst 89
4.2.5 The Physical Origin of Sabatier's Principle 89
4.2.6 Other Plots Illustrating Sabatier's Principle 90
4.2.7 Modeling of Volcano Plots 91
4.2.8 Reaction Pathway as a Function of the Most-Favored Transition State
92
4.3 Exceptions to Sabatier's Principle 93
4.4 Sabatier's Principle in Homogeneous Catalysis 93
4.5 Conclusions. Sabatier's Principle Describes Two Independent Catalytic
Domains: Energy- and Time-Dependent Catalysis 94
Acknowledgments 95
References 95
5 Time-Dependence in Homogeneous Catalysis. 1. Many Enzymes Display the
Hallmarks of Time-Dependent ("Mechanical") Catalysis. Nonbiological
Homogeneous Catalysts Are Typically Energy-Dependent ("Thermodynamic")
Catalysts 97
Robin Brimblecombe, Jun Chen, Junhua Huang, Ulrich T. Mueller-Westerhoff,
and Gerhard F. Swiegers
5.1 Introduction 97
5.2 Historical Background: Are Enzymes Generally Energy-Dependent or
Time-Dependent Catalysts? 99
5.3 The Methodology of This Chapter: Identify, Contrast, and Rationalize
the Common Processes Present in Biological and Nonbiological Homogeneous
Catalysts 100
5.4 Does Michaelis-Menten Kinetics in Enzymes Indicate that They Are
Time-Dependent Catalysts? 102
5.4.1 Michaelis-Menten Kinetics 102
5.4.2 Kinetics in Most Nonbiological Catalysts 103
5.4.3 The Contradiction of Saturation Kinetics in Enzymes 103
5.4.4 Saturation in Time- and Energy-Dependent Catalysts. Saturation
Kinetics Is Necessarily an Indication of Time-Dependence 104
5.4.5 Physical Studies of the Rate Processes in Enzymes Are Consistent with
a Time-Dependent Action 106
5.4.6 A Time-Dependent Catalyst Cannot Become an Energy-Dependent Catalyst,
or vice versa, Without Changing the Temperature or Chemically Altering the
Reactivity of the Reactants 107
5.4.7 The Current View of Michaelis-Menten Kinetics Is Flawed by an
Unwarranted Assumption 107
5.4.8 Summary: Michaelis-Menten Kinetics Is Characteristic of
Time-Dependent Catalysis. Time-Dependent Catalysis Provides an Explanation
for Michaelis-Menten Kinetics in Enzymes 109
5.5 Other General Characteristics of Catalysis by Enzymes and Comparable
Nonbiological Homogeneous Catalysts 110
5.5.1 Enzymes Employ Weak and Dynamic Individual Binding Interactions with
Their Substrates. Nonbiological Catalysts Do Not 110
5.5.2 Enzymes Display Transition State Complementarity. Nonbiological
Catalysts Do Not 111
5.5.3 Enzymatic Catalysis Is "Structure-Sensitive." Nonbiological Catalysis
Is "Structure-Insensitive" 112
5.5.4 Enzymes Transform Catalytically Unconventional Groups into Potent
Catalysts. Nonbiological Catalysts Use Only Conventional Catalytic Groups
113
5.5.5 Enzymes Catalyze Forward and Reverse Reactions. Nonbiological
Catalysts Do Not 113
5.5.6 Enzymes Display High Selectivity and Activity. Nonbiological
Catalysts Do Not 115
5.5.7 Enzymes Display Convergent Synergies. Nonbiological Catalysts Display
Complementary Synergies 115
5.5.8 Summary 116
5.6 Rationalization of the Underlying Processes. The Mechanism of Action in
Time-Dependent and Energy-Dependent Catalysts 117
5.6.1 Common Processes in Multicentered Homogeneous Catalysts 117
5.6.2 The Influence of the Strength of the Individual Catalyst-Reactant
Binding Interactions 119
5.6.3 The Coexistence of Transition State Complementarity,
Structure-Sensitive Catalysis, and Unconventional Catalytic Groups in
Enzymes Is Caused by their Weak Individual Binding Interactions 122
5.6.4 The Origin of the Time-Dependence and the Synergies of Enzymes 123
5.6.5 The Mechanism of Time-Dependence in Enzymes Resolves the
Contradiction of a Kinetically Observed Rapidly Forming and Dissociating
Intermediate in the Face of Strong Overall Substrate Binding 125
5.6.6 Catalysis in Enzymes Involves Synchronization of Enzyme Binding and
Enzyme Flexing 125
5.6.7 Summary: The Origin of the General Properties of Enzymes 127
5.6.8 Catalysis in Nonbiological Analogues Depends on the Activation Energy
E a 127
5.6.9 Enzymatic Selectivity and Synergies Derive from Time-Dependence 128
5.6.10 Enzymatic Activity Is Consistent with Time-Dependence 129
5.7 All Generalizations Support Time-Dependence in Enzymes 129
5.8 Time-Dependence in a Nonbiological Catalyst Generates the Distinctive
Properties of Enzymes 130
5.9 Conclusion: Many Enzymes Are Time-Dependent Catalysts 133
Acknowledgments 134
References 134
6 Time-Dependence in Homogeneous Catalysis. 2. The General Actions of
Time-Dependent ("Mechanical") and Energy-Dependent ("Thermodynamic")
Catalysts 137
Robin Brimblecombe, Jun Chen, Junhua Huang, Ulrich T. Mueller-Westerhoff,
and Gerhard F. Swiegers
6.1 Introduction 137
6.2 Time- and Energy-Dependent, Multicentered Homogeneous Catalysts 139
6.3 The Action of Energy-Dependent, Multicentered Homogeneous Catalysts 141
6.4 The Action of Time-Dependent, Multicentered Homogeneous Catalysts 146
6.4.1 The Activation Energy E a Does Not Provide a True Measure of the
Threshold Energy in Time-Dependent Catalysts 148
6.4.2 Weak and Dynamic Binding and Activation Is Sufficient to Fulfill the
Threshold Energy in Time-Dependent Catalysts 149
6.4.3 Transition State Formation in a Time-Dependent Catalyst Can Be
Thought of as a Coordinated Mechanical Process 150
6.4.4 Time-Dependent Catalysts Are Machine-Like (Mechanical) in Their
Catalytic Action 150
6.4.5 The Origin of Michaelis-Menten Kinetics in Time-Dependent Catalysts
151
6.4.6 Time-Dependent Catalysts like Many Enzymes Display All of the
Characteristic Hallmarks of Mechanical Processes 153
6.4.7 Additional Insights into Enzymatic Catalysis: The Bidirectionality of
Enzymatic Catalysis Originates from the Mechanical Nature of the Catalytic
Action 154
6.4.8 Additional Insights into Enzymatic Catalysis: Many Enzymes Select the
First-Encountered Transition State, Rather than the Lowest Energy
Transition State 155
6.5 The Importance of Recognizing Time-Dependent Catalysis 155
6.6 Time-Dependent Catalysis Is Very Different to Energy-Dependent
Catalysis and Therefore Seems Unfamiliar 156
6.7 Conclusions for Biology 157
6.8 Conclusions for Homogeneous Catalysis 157
6.9 The "Ideal" Homogeneous Catalyst 158
6.10 Conclusions for the Conceptual Unity of the Field of Catalysis 158
Acknowledgments 159
References 159
7 Unifying the Many Theories of Enzymatic Catalysis. Theories of Enzymatic
Catalysis Fall into Two Camps: Energy-Dependent ("Thermodynamic") and
Time-Dependent ("Mechanical") Catalysis 161
Gerhard F. Swiegers
7.1 Introduction 161
7.2 Theories of Enzymatic Catalysis 163
7.2.1 Adsorption Theory 163
7.2.2 "Lock-and-Key" Theory 163
7.2.3 Haldane's Strain Theory 164
7.2.4 Pauling's Theory of Transition State Complementarity 165
7.2.5 Koshland's Induced Fit Theory. Fersht's Concept of Stress and Strain
165
7.2.6 Intramolecularity 165
7.2.7 Orbital Steering 167
7.2.8 Entropy Traps 168
7.2.9 The Proximity (Propinquity) Effect 168
7.2.10 "Coupled" Protein Motions 168
7.2.11 The Spatiotemporal Hypothesis 169
7.3 Theories Explaining Enzymatic Catalysis Fall into Two Camps:
Energy-Dependent and Time-Dependent Catalysis 169
7.3.1 Haldane's Strain Theory and Fersht's Concept of Stress and Strain Are
Valid Explanations for Rate Accelerations but Do Not Seem to be Responsible
for the Rate Accelerations of Many Enzymes 171
7.3.2 Theories Based on Reaction Entropy Are Valid Explanations for Rate
Accelerations but Do Not Seem to be Behind the Rate Accelerations of Many
Enzymes 172
7.3.3 Experiments Studying Intramolecular Reaction Rates Were Probably
Often Conceptually Contradictory 172
7.3.4 Theories of "Coupled" Protein Motions and Machine-Like Catalytic
Actions Seem to Be Generally Accurate Descriptions of Enzymatic Catalysis
173
7.4 Studies Verifying Pauling's Theory in Model Systems Are Correct, but
Describe Energy-Dependent and not Time-Dependent Catalysis 174
7.5 The Anomaly Described in the Spatiotemporal Hypothesis Originates, in
Part, from the Onset of Time-Dependence 176
Acknowledgments 177
!References 177
8 Synergy in Heterogeneous, Homogeneous, and Enzymatic Catalysis. The
"Ideal" Catalyst 181
Gerhard F. Swiegers
8.1 Introduction 181
8.2 Synergy in Heterogeneous Catalysts 183
8.3 Single-Centered Nonbiological Homogeneous Catalysts and Their 'Mutually
Enhancing' Synergies 184
8.3.1 Facial Selectivity in Single-Centered Catalysts 184
8.3.2 Energy-Dependent, Single-Centered Homogeneous Catalysts Display
'Mutually Enhancing' Synergies 187
8.3.3 The Synergies in Time-Dependent, Single-Centered Homogeneous
Catalysts 188
8.3.4 The Selectivity of Single-Centered Catalysts 189
8.4 Multicentered, Energy-Dependent Homogeneous Catalysts and Their
Functionally Complementary Synergies 190
8.5 Enzymes and Their Functionally Convergent Synergies 194
8.6 Biomimetic Chemistry and Its Pseudo-Convergent Synergies 197
8.6.1 Cyclodextrin-Appended Epoxidation Catalysts: Pseudo-Convergence in a
Nonbiological, Multicentered Catalyst 198
8.7 The Spectrum of Synergistic Action in Homogeneous Catalysis 200
8.7.1 The Relationship Between Complementary and Convergent Synergies 202
8.7.2 The Ideal Catalyst 203
8.8 Synergy in Catalysis Is Conceptually Related to Other Synergistic
Processes in Human Experience 205
References 206
9 A Conceptual Unification of Heterogeneous, Homogeneous, and Enzymatic
Catalysis 209
Gerhard F. Swiegers
9.1 Introduction 209
9.2 Diffusion-Controlled and Reaction-Controlled Catalysis 210
9.3 The Diversity of Catalytic Action in Heterogeneous Catalysts 211
9.4 The Diversity of Catalytic Action in Nonbiological Homogeneous
Catalysts 212
9.5 The Diversity of Catalytic Action in Enzymes 214
9.6 Heterogeneous Catalysis and Enzymatic Catalysis Has, Effectively,
Involved Combinatorial Experiments that Have Produced Time-Dependent
Catalysts. Nonbiological Homogeneous Catalysis Has Not 214
9.7 Homogeneous and Enzymatic Catalysts Are the 3-D Equivalent of 2-D
Heterogeneous Catalysts 215
9.8 A Conceptual Unification of Heterogeneous, Homogeneous, and Enzymatic
Catalysis 216
References 218
10 The Rational Design of Time-Dependent ("Mechanical") Homogeneous
Catalysts. A Literature Survey of Multicentered Homogeneous Catalysis 219
Junhua Huang and Gerhard F. Swiegers
10.1 Introduction 219
10.2 The Rational Design of Time-Dependent Homogeneous Catalysts 221
10.2.1 Design Criteria for a Time-Dependent Homogeneous Catalyst 221
10.2.2 The Problem of Simultaneously Identifying Suitable Catalytic Groups
and Their Active Spatial Arrangement 223
10.2.3 Time-Dependent Homogeneous Catalysis May Conceivably Be Achieved by
Mimicry of a Natural Time-Dependent Catalyst 225
10.2.4 Time-Dependent Homogeneous Catalysis May Conceivably Be Achieved in
the form of a Combinatorial Experiment Involving a "Statistical Proximity"
Effect 226
10.2.4.1 A Time-Dependent Combinatorial Catalyst May Display Unique
Kinetics 228
10.2.4.2 Previous Attempts at Concentration-Based Biomimetic Catalysis
Involved Energy-Dependent Systems 229
10.2.5 Time-Dependent Catalysis May Be Useful in Transformations of Small
Gaseous Molecules 230
10.2.6 Why Do We Need New Time-Dependent Catalysts? 230
10.3 Elements of Rational Design in Multicentered Catalysis 230
10.3.1 Modes of Binding in Multicentered Catalysts 230
10.3.2 Optimizing the Spatial Arrangement of Catalytic Groups 231
10.3.2.1 Intramolecular Catalysts 231
10.3.2.2 Intermolecular Catalysts 233
10.3.2.3 Unconventional Approaches to Optimizing the Spatial Organization
of Catalytic Groups 233
10.3.3 Creating Functionally Convergent Catalysts 234
10.3.3.1 Practical Approaches to Achieving Functionally Convergent
Catalysis 234
10.4 A Review of Nonbiological, Multicentered Molecular Catalysts Described
in the Chemical Literature 235
10.4.1 Intramolecular Catalysts 235
10.4.1.1 Functionally Convergent Catalysis (Class A Type): Cofacial and
Capped Metalloporphyrins as Oxygen Reduction Catalysts 235
10.4.1.2 Functionally Convergent Catalysis (Class B Type):
[1.1]Ferrocenophanes and Related Compounds as Hydrogen Generation Catalysts
241
10.4.1.3 Pseudoconvergent Catalysis: Supramolecular, Bifunctional Catalysts
of Organic Reactions 245
10.4.1.4 Probable Functionally Convergent Catalysis: Rhodium-Phosphine
Hydroformylation Catalysts 248
10.4.1.5 Possible Functionally Convergent Catalysis: Ruthenium-Based Water
Oxidation Catalysts 249
10.4.1.6 Functionally Complementary Catalysis: Intramolecular Epoxidation
Catalysts 252
10.4.1.7 Metal Clusters in Multicentered Molecular Catalysis: Triruthenium
Dodecacarbonyl Hydrogenation Catalysts 252
10.4.1.8 Statistical Approaches to Functionally Convergent Catalysis:
Macromolecular Intramolecular Catalysts 254
10.4.2 Intermolecular Catalysts 259
10.4.2.1 Functionally Complementary Catalysis 259
10.4.2.2 Statistical Approaches to Functionally Convergent Catalysis:
Concentration Effects in Intermolecular Catalysts 260
10.4.2.3 Statistical Approaches to Functionally Convergent Catalysis:
Self-Assembled, Supramolecular Catalysts 261
10.4.3 Footnote: Unexpected Mechanistic Changes in Multicentered Catalysts
262
Acknowledgments 263
References 263
11 Time-Dependent ("Mechanical"), Nonbiological Catalysis. 1. A Fully
Functional Mimic of the Water-Oxidizing Center (WOC) in Photosystem II
(PSII) 267
Robin Brimblecombe, G. Charles Dismukes, Greg A. Felton, Leone Spiccia, and
Gerhard F. Swiegers
11.1 Introduction 267
11.2 The Physical and Chemical Properties of the Cubanes 1a-b 273
11.2.1 Chemical Structures 273
11.2.2 Stepwise Hydride Abstraction, Leading to Water Release 275
11.2.3 Dioxygen Generation 275
11.2.4 A Possible Catalytic Cycle 277
11.2.5 Other Reactions 277
11.2.6 Summary 278
11.3 Nafion Provides a Means of Solubilizing and Immobilizing Hydrophobic
Metal Complexes 278
11.4 Photoelectrochemical Cells and Dye-Sensitized Solar Cells for
Water-Splitting 279
11.5 Photocatalytic Water Oxidation by Cubane 1b Doped into a Nafion
Support 282
11.5.1 Solution Electrochemistry 282
11.5.2 Electrochemistry of 1b Doped into a Nafion Membrane 283
11.5.3 Electrocatalytic Effects Are Observed Under cv Conditions 283
11.5.4 a Photo-electrocatalytic Effect Is Observed at 1.00 v (vs. Ag/AgCl)
284
11.5.5 if the Photocurrent Is Caused by Water Oxidation Catalysis, This
Involves a Decrease in the Overpotential of 0.4 V 285
11.5.6 The Photocurrent Is Observed only in the Presence of Water. The
System Saturates at Low Water Content, Consistent with a Time-Dependent
Catalytic Action 286
11.5.7 The pH Dependence of the Photocurrent Is Consistent with Water
Oxidation 287
11.5.8 Bulk Water Is a Reactant and Oxygen Is Generated 287
11.5.9 The Quantity of Gas Generated Matches the Current Obtained. Notable
Turnover Frequencies Are Implied 287
11.5.10 Photocurrent as a Function of the Illumination Wavelength 290
11.5.11 The Photoaction Spectrum of the Catalysis Corresponds to the Main
LMCT Absorption Peak of 1b 290
11.6 The Challenge of Dye-Sensitized Water-Splitting 291
11.7 The Mechanism of the Catalysis 292
11.8 Conclusions 293
References 294
12 Time-Dependent ("Mechanical"), Nonbiological Catalysis. 2. Highly
Efficient, "Biomimetic" Hydrogen-Generating Electrocatalysts 297
Jun Chen, Junhua Huang, Gerhard F. Swiegers, Chee O. Too, and Gordon G.
Wallace
12.1 Introduction 297
12.2 Monomer and Polymer Preparation 301
12.3 Catalytic Experiments 302
12.3.1 PPy-9 and PPy-12 Display Anodic Shifts in the Most Positive
Potential for Hydrogen Generation 302
12.3.2 PPy-9 and PPy-12 Increase the Rate of Hydrogen Generation on Pt by
ca. 7-Fold after 12 Hat20.44 V 304
12.3.3 PPy-9 and PPy-12 Increase the Rate of Hydrogen Generation on Pt per
Unit Area by ca. 3.5-Fold 307
12.3.4 The Mechanism of Catalysis in PPy-9. Is PPy-9 a Combinatorial
("Statistical Proximity") Catalyst? 308
12.3.5 Polypyrrole Is Likely Involved in the Catalytic Cycle 309
12.3.6 Other Evidence for the Involvement of Polypyrrole in the Catalytic
Cycle 311
12.3.7 The Pyrrole in Polypyrrole Is a Powerful, Time-Dependent,
Combinatorial, "Statistical Proximity" Catalyst 313
12.4 Conclusions: A Combinatorial "Statistical Proximity" Catalyst Was
Obtained as a Bulk, Hybrid Homogeneous-Heterogeneous Catalyst 316
Acknowledgments 317
References 317
13 Time-Dependent ("Mechanical"), Nonbiological Catalysis. 3. A Readily
Prepared, Convergent, Oxygen-Reduction Electrocatalyst 319
Jun Chen, Gerhard F. Swiegers, Gordon G. Wallace, and Weimin Zhang
13.1 Introduction 319
13.2 Cofacial Diporphyrin Oxygen-Reduction Catalysts 321
13.3 Vapor-Phase Polymerization of Pyrrole as a Means of Immobilizing High
Concentrations of Monomeric Catalytic Groups at an Electrode Surface 323
13.4 Preparation and Catalytic Properties of PPy- 3 324
13.4.1 Vapor-Phase Preparation of Polypyrrolle-Co Tetraphenylporphyrin,
PPy- 3 324
13.4.2 Electrochemistry of, and Oxygen Reduction by, Polypyrrolle-Co
Tetraphenylporphyrin, PPy- 3 324
13.4.3 Rotating Disk Electrochemistry (RDE) of Polypyrrolle-Co
Tetraphenylporphyrin, PPy- 3 326
13.4.4 Rotating Ring Disk Electrochemistry (RRDE) of Polypyrrolle-Co
Tetraphenylporphyrin, PPy- 3 328
13.4.5 The Product Distribution Relative to the Proportion of 3 in the
Polypyrrolle-Co Tetraphenylporphyrin, PPy- 3 329
13.5 PPy-3 as a Fuel Cell Catalyst 330
13.5.1 PPy-3 on Carbon Fiber Paper 330
13.5.2 Electrochemical Characterization of PPy-3 on Carbon Fiber Paper 330
13.5.3 Morphology of the PPy-3 Carbon Fiber Composite Film 330
13.5.4 Oxygen-Reduction Catalysis by the PPy- 3 Carbon Fiber Composite Film
in Simple Fuel Cell Test Apparatus 331
13.6 Conclusions 334
References 335
Appendix A Why Is Saturation Not Observed in Catalysts that Display
Conventional Kinetics? 337
Appendix B Graphical Illustration of the Processes Involved in the
Saturation of Molecular Catalysts 341
Index 347

Rezensionen

This book is a useful addition to the library of any individual working with functionalized catalysts, especially those that may undergo conformational changes during the reaction process. This text is especially informative for those working with enzymes, biomimetic, and organometallic based catalysts. It also unifies many of the kinetic models that have been put forth to describe heterogeneous, homogeneous, and enzymatic catalysis. ( Journal of the American Chemical Society , October 2009)