Preface ...................................................... xiii
CHAPTER 1 Single Electron Transfer at an Electrode .............. 1
1.1. Introduction ............................................... 1
1.2. Cyclic Voltammetry of Fast Electron Transfers.
Nernstian Waves ............................................ 2
1.2.1. One-Electron Transfer to Molecules Attached to
the Electrode Surface ............................... 2
1.2.2. One-Electron Transfer to Free-Moving Molecules ...... 5
1.3. Technical Aspects ......................................... 10
1.3.1. The Cyclic Voltammetry Experiment. Faradaic and
Double-Layer Charging Currents. Ohmic Drop ......... 10
1.3.2. Other Techniques. Convolution ...................... 20
1.4. Electron Transfer Kinetics ................................ 28
1.4.1. Introduction ....................................... 28
1.4.2. Butler-Volmer Law and Marcus-Hush Model ............ 30
1.4.3. Extraction of Electron Transfer Kinetics from
Cyclic Voltammetric Signals. Comparison with
Other Techniques ................................... 44
1.4.4. Experimental Testing of the Electron Transfer
Models ............................................. 57
1.5. Successive One-Electron Transfers vs. Two-Electron
Transfers ................................................. 62
1.5.1. Introduction ....................................... 62
1.5.2. Cyclic Voltammetric Responses. Convolution ......... 64
1.5.3. Response of Molecules Containing Identical and
Independent Reducible or Oxidizable Groups ......... 69
1.5.4. An Example of the Predominating Role
of Solvation: The Oxidoreduction of Carotenoids .... 70
1.5.5. An Example of the Predominating Role of
Structural Changes: The Reduction of
trans-2,3-Dinitro-2-butene ......................... 73
References and Notes ...................................... 75
CHAPTER 2 Coupling of Electrode Electron Transfers with
Homogeneous Chemical Reactions ....................... 78
2.1. Introduction .............................................. 78
2.2. Establishing the Mechanism and Measuring the Rate
Constants for Homogeneous Reactions by Means of Cyclic
Voltammetry and Potential Step Chronoamperometry .......... 80
2.2.1. The EC Mechanism ................................... 80
2.2.2. The CE Mechanism ................................... 92
2.2.3. The Square Scheme Mechanism ........................ 94
2.2.4. The ECE and DISP Mechanisms ........................ 96
2.2.5. Electrodimerization ............................... 102
2.2.6. Homogeneous Catalytic Reaction Schemes ............ 106
2.2.7. Electrodes as Catalysts ........................... 119
2.2.8. Numerical Computations. Simulations. Diagnostic
Criteria. Working Curves .......................... 121
2.3. Application of Redox Catalysis to the Kinetic
Characterization of Fast Follow-up Reactions ............. 125
2.3.1. Principle and Achievements of the Method .......... 125
2.3.2. Comparison with Fast Cyclic Voltammetry and
Laser Flash Photolysis ............................ 128
2.3.3. Determination of the Standard Potential for
the Formation of Very Unstable Primary
Intermediates ..................................... 129
2.3.4. Redox Catalysis of Electrocatalytic Processes ..... 131
2.4. Product Distribution in Preparative Electrolysis ......... 132
2.4.1. Introduction ...................................... 132
2.4.2. General Features .................................. 133
2.4.3. Product Distribution Resulting from
Competition Between Follow-up Reactions ........... 136
2.4.4. The ECE-DISP Competition .......................... 138
2.4.5. Other Reactions Schemes ........................... 139
2.5. Chemical Classification and Examples of Coupled
Reactions ................................................ 140
2.5.1. Coupling of Single Electron Transfer with Acid-
Base Reactions .................................... 140
2.5.2. Electrodimerization ............................... 148
2.5.3. Electropolymerization ............................. 151
2.5.4. Reduction of Carbon Dioxide ....................... 152
2.5.5. H-Atom Transfer vs. Electron + Proton Transfer .... 154
2.5.6. The SrN1 Substitution. Electrodes and Electrons
as Catalysts ...................................... 158
2.5.7. Conformational Changes, Isomerization, and
Electron Transfer ................................. 163
2.6. Redox Properties of Transient Radicals ................... 167
2.6.1. Direct Electrochemical Approach ................... 167
2.6.2. Application of Laser Flash Electron Injection ..... 172
2.6.3. Photomodulaltion Voltammetry ...................... 175
2.6.4. Application of Redox Catalysis .................... 177
2.7. Electrochemistry as a Trigger for Radical Chemistry
or Ionic Chemistry ....................................... 178
References and Notes ..................................... 179
CHAPTER 3 Electron Transfer, Bond Breaking, and Bond
Formation ........................................... 182
3.1. Introduction ............................................. 182
3.2. Dissociative Electron Transfer ........................... 184
3.2.1. Thermodynamics. Microscopic Reversibility ......... 184
3.2.2. The Morse Curve Model ............................. 187
3.2.3. Values of the Symmetry Factor and Variation
with the Driving Force ............................ 192
3.2.4. Entropy of Activation ............................. 193
3.3. Interactions Between Fragments in the Product Cluster .... 194
3.3.1. Influence on the Dynamics of Dissociative
Electron Transfers ................................ 195
3.3.2. Typical Example: Dissociative Electron
Transfer to Carbon Tetrachloride .................. 197
3.3.3. Stabilities of Ion-Radical Adducts as
a Function of the Solvent ......................... 199
3.3.4. Dependency of In-Cage Ion-Radical Interactions
on the Leaving Group .............................. 200
3.4. Stepwise vs. Concerted Mechanisms ........................ 203
3.4.1. Introduction ...................................... 203
3.4.2. Diagnostic Criteria ............................... 204
3.4.3. How Molecular Structure Controls the Mechanism .... 206
3.4.4. Passage from One Mechanism to the Other upon
Changing the Driving Force ........................ 209
3.4.5. Photoinduced vs. Thermal Processes ................ 213
3.4.6. Does a Concerted Mechanism Mean That the
Intermediate "Does Not Exist"? .................... 216
3.4.7. π and σ Ion Radicals. Competition Between
Reaction Pathways ................................. 216
3.5. Cleavage of Ion Radicals. Reaction of Radicals with
Nucleophiles ............................................. 218
3.5.1. Introduction ...................................... 218
3.5.2. Heterolytic Cleavages. Coupling of Radicals
with Nucleophiles ................................. 218
3.5.3. Homolytic Cleavages ............................... 225
3.6. Role of Solvent in Ion-Radical Cleavage and in
Stepwise vs. Concerted Competitions ...................... 229
3.6.1. Introduction ...................................... 229
3.6.2. Experimental Clues ................................ 230
3.6.3. A Simplified Model System ......................... 235
3.7. Dichotomy and Connections between SN2 Reactions
and Dissociative Electron Transfers ...................... 239
3.7.1. Introduction ...................................... 239
3.7.2. Experimental Approaches ........................... 240
3.7.3. Theoretical Aspects ............................... 244
References and Notes ..................................... 248
CHAPTER 4 Molecular Catalysis of Electrochemical Reactions .... 251
4.1. Introduction ............................................. 251
4.2. Homogeneous Molecular Catalysis .......................... 252
4.2.1. Contrasting Redox and Chemical Catalysis .......... 252
4.2.2. The Reduction of Vicinal Dibromides. Outer- and
Inner-Sphere Catalysts. Rates and
Stereoselectivity ................................. 254
4.2.3. Homogeneous Chemical Catalysis of the Reduction
of Carbon Dioxide. Synergistic Effect of
Bronsted and Lewis Acids .......................... 260
4.2.4. Two-Step Chemical Catalysis of the Reduction of
Alkyl Halides by Low-Valent Cobalamins and
Cobinamides ....................................... 264
4.3. Supported Molecular Catalysis (Immobilized Catalysts) .... 268
4.3.1. Redox and Chemical Catalysis at Monolayer and
Multilayer Coated Electrodes ...................... 268
4.3.2. Catalysis at Monolayer Coated Electrodes .......... 270
4.3.3. Permeation Through Electrode Coatings.
Inhibition ........................................ 279
4.3.4. Electron Hopping in Assemblies of Redox Centers ... 284
4.3.5. Catalysis at Multilayer Coated Electrodes ......... 287
4.3.6. Combining an Electron-Shuttling Mediator with
a Chemical Catalyst in a Multilayer Electrode
Coating ........................................... 292
References and Notes ..................................... 296
CHAPTER 5 Enzymatic Catalysis of Electrochemical Reactions .... 298
5.1. Introduction ............................................. 298
5.2. Homogeneous Enzymatic Catalysis .......................... 299
5.2.1. Introduction ...................................... 299
5.2.2. The Ping-Pong Mechanism. Kinetic Control by
Substrate and/or Cosubstrate ...................... 300
5.2.3. A Model Example: Glucose Oxidase with Excess
Glucose ........................................... 306
5.2.4. Molecular Recognition of an Enzyme by
Artificial One-Electron Cosubstrates .............. 307
5.2.5. Deciphering a Complex Electroenzymatic Response:
Horseradish Peroxidase ............................ 311
5.3. Immobilized Enzymes in Monomolecular Layers .............. 315
5.3.1. Introduction ...................................... 315
5.3.2. The Ping-Pong Mechanism with an Immobilized
Enzyme and the Cosubstrate in Solution ............ 315
5.3.3. Antigen-Antibody Immobilization of Glucose
Oxidase. Kinetic Analysis ......................... 323
5.3.4. Application to the Kinetic Characterization
of Biomolecular Recognition ....................... 325
5.3.5. Immobilized Horseradish Peroxidase ................ 332
5.3.6. Immobilization of Both the Enzyme and the
Cosubstrate. Electron Transfer and Electron
Transport in Integrated Systems ................... 336
5.4. Spatially Ordered Multimonomolecular Layered Enzyme
Coatings ................................................. 340
5.4.1. Step-by-Step Antigen-Antibody Construction of
Multimonomolecular Layer Enzyme Coatings .......... 340
5.4.2. Reaction Dynamics with the Cosubstrate in
Solution. Evidence for Spatial Order .............. 342
References and Notes ..................................... 346
CHAPTER 6 Appendixes .......................................... 348
6.1. Single Electron Transfer at an Electrode ................. 348
6.1.1. Laplace Transformation. Useful Definitions and
Relationships ..................................... 348
6.1.2. Cyclic Voltammetry of One-Electron Nernstian
Systems. Current- and Charge-Potential Curves ..... 348
6.1.3. Double-Layer Charging in Cyclic Voltammetry.
Oscillating and Nonoscillating Behavior ........... 353
6.1.4. Effect of Ohmic Drop and Double-Layer Charging
on Nernstian Cyclic Voltammograms ................. 357
6.1.5. Potential Step and Double Potential Step
Chronoamperometry of Nernstian Systems ............ 361
6.1.6. Overlapping of Double-Layer Charging and
Faradaic Currents in Potential Step and Double
Potential Step Chronoamperometry. Oscillating
and Nonoscillating Behavior ....................... 361
6.1.7. Solvent Reorganization in Marcus-Hush Model ....... 363
6.1.8. Effect of the Multiplicity of Electronic States
in the Electrode .................................. 368
6.1.9. Cyclic Voltammetry of Two-Electron Nernstian
Systems. Disproportionation ....................... 371
6.2. Coupling of Homogeneous Chemical Reactions with
Electron Transfer ........................................ 373
6.2.1. The EC Mechanism .................................. 373
6.2.2. The CE Mechanism .................................. 379
6.2.3. Double Potential Step Responses for Processes
Involving First- or Second-Order Follow-up
Reactions ......................................... 382
6.2.4. The ECE and DISP Mechanisms ....................... 383
6.2.5. Electrodimerization ............................... 391
6.2.6. Competition Between Dimerization of and
Electron Transfer to Intermediates ................ 398
6.2.7. Homogeneous Catalysis ............................. 403
6.2.8. Product Distribution in Preparative
Electrolysis ...................................... 414
6.3. Electron Transfer, Bond Breaking, and Bond Formation ..... 438
6.3.1. Contribution of the Cleaving Bond Stretching to
Internal Reorganization of the First Step of
the Stepwise Mechanism ............................ 438
6.3.2. Morse Curve Model of Intramolecular
Dissociative Electron Transfer .................... 439
6.4. Analysis of Supported Molecular Catalysis by
Rotating Disk Electrode Voltammetry and Cyclic
Voltammetry .............................................. 441
6.4.1. Catalysis at Monolayer Electrode Coatings ......... 441
6.4.2. Inhibition of Electron Transfer at Partially
Blocked Electrodes ................................ 444
6.4.3. Equivalent Diffusion and Migration Laws for
Electron Hopping Between Fixed Sites .............. 445
6.4.4. Catalysis at Multilayered Electrode Coatings ...... 446
6.5. Enzymatic Catalysis Responses ............................ 452
6.5.1. The Ping-Pong Mechanism in Homogeneous
Enzymatic Catalysis ............................... 452
6.5.2. Catalysis and Inhibition in Homogeneous Systems ... 457
6.5.3. Catalysis at Multilayered Electrode Coatings ...... 462
References and Notes .......................................... 469
Glossary of Symbols ........................................... 470
Index ......................................................... 481
|
