Elements of Molecular and Biomolecular Electrochemistry

JEAN-MICHEL SAVÉANT is a Professor of Chemistry at Denis Diderot University of Paris, France, a member of the French Academy of Sciences, and a foreign associate of the National Academy of Sciences of the USA. CYRILLE COSTENTIN is a Professor of Chemistry at Denis Diderot University of Paris, France.

• Preface xv1 Single-Electron Transfer at an Electrode 11.1 Introduction 11.2 Cyclic Voltammetry of Fast Electron Transfers: Nernstian Waves 21.2.1 One-Electron Transfer to Molecules Attached to the Electrode Surface 21.2.2 One-Electron Transfer to Free-moving Molecules 61.3 Technical Aspects 101.3.1 The Cyclic Voltammetry Experiment – Faradaic and Double-Layer Charging Currents. Ohmic Drop 101.3.2 Other Techniques. Convolution 211.4 Electron Transfer Kinetics 291.4.1 Introduction 291.4.2 Butler–Volmer Law and Marcus–Hush–Levich (MHL) Model 311.4.3 Extraction of Electron Transfer Kinetics from Cyclic Voltammetric Signals. Comparison with Other Techniques 461.4.4 Experimental Testing of the Electron Transfer Models 591.5 Successive One-Electron Transfers vs. Two-Electron Transfers 641.5.1 Introduction 641.5.2 Cyclic Voltammetric Responses: Convolution 661.5.3 Response of Molecules Containing Identical and Independent Reducible or Oxidizable Groups 721.5.4 An Example of the Predominating Role of Solvation: The Oxidoreduction of Carotenoids 721.5.5 An Example of the Predominating Role of Structural Changes: The Reduction of trans-2,3-Dinitro-2-butene 75References 772 Coupling of Electrode Electron Transfers with Homogeneous Chemical Reactions 812.1 Introduction 812.2 Establishing the Mechanism and Measuring the Rate Constants for Homogeneous Reactions by Means of Cyclic Voltammetry and Potential Step Chronoamperometry 832.2.1 The EC Mechanism 832.2.2 The CE Mechanism 972.2.3 The Square Scheme Mechanism 992.2.4 The ECE and DISP Mechanisms 1002.2.5 Electrodimerization 1072.2.6 Homogeneous Catalytic Reaction Schemes 1132.2.6.1 Homogeneous Electron Transfer as the Rate-Determining Step 1142.2.6.2 Homogeneous Catalytic EC Mechanism 1172.2.6.3 Deactivation of the Mediator 1202.2.7 Electrodes as Catalysts: Electron-transfer Catalyzed Reactions 1222.2.8 Numerical Computations: Simulations, Diagnostic Criteria, Working Curves 1252.3 Product Distribution in Preparative Electrolysis 1292.3.1 Introduction 1292.3.2 General Features 1302.3.3 Product Distribution Resulting from Competition Between Follow-Up Reactions 1332.3.4 The ECE–DISP Competition 1352.3.5 Other Reactions Schemes 1362.4 Classification and Examples of Electron-Transfer Coupled Chemical Reactions 1372.4.1 Coupling of Single Electron Transfer with Acid–Base Reactions 1372.4.2 Electrodimerization 1462.4.3 Electropolymerization 1502.4.4 Reduction of Carbon Dioxide 1512.4.5 H-Atom Transfer vs. Electron + Proton Transfer 1532.4.6 The SRN1 Substitution: Electrodes and Electrons as Catalysts 1572.4.7 Conformational Changes, Isomerization and Electron Transfer 1622.5 Redox Properties of Transient Radicals 1672.5.1 Introduction 1672.5.2 The Direct Electrochemical Approach 1672.5.3 Laser Flash Electron Injection 1722.5.4 Photomodulation Voltammetry 1762.6 Electrochemistry as a Trigger for Radical Chemistry or for Ionic Chemistry 177References 1793 Coupling Between Electron Transfer and Heavy Atom-Bond Breaking and Formation 1833.1 Introduction 1833.2 Dissociative Electron Transfer 1853.2.1 Thermodynamics: Microscopic Reversibility 1853.2.2 The Morse Curve Model 1883.2.3 Values of the Symmetry Factor and Variation with the Driving Force 1933.2.4 Entropy of Activation 1953.3 Interactions Between Fragments in the Product Cluster 1963.3.1 Influence on the Dynamics of Dissociative Electron Transfers 1973.3.2 A Typical Example: Dissociative Electron Transfer to Carbon Tetrachloride 1983.3.3 Stabilities of Ion-radical Adducts as a Function of the Solvent 2013.3.4 Dependency of In-cage Ion-radical Interactions on the Leaving Group 2033.4 Stepwise vs. Concerted Mechanisms 2053.4.1 Introduction 2053.4.2 Diagnostic Criteria 2063.4.3 How Molecular Structure Controls the Mechanism? 2083.4.4 Passage from One Mechanism to the Other Upon Changing the Driving Force 2123.4.5 Photoinduced vs. Thermal Processes 2173.4.6 Does Concerted Mechanism Mean that the Intermediate “Does Not Exist”? 2193.4.7 π and 𝜎 Ion Radicals: Competition Between Reaction Pathways 2203.5 Cleavage of Ion Radicals: Reaction of Radicals with Nucleophiles 2213.5.1 Introduction 2213.5.2 Heterolytic Cleavages: Coupling of Radicals with Nucleophiles 2223.5.3 Homolytic Cleavages 2303.6 Role of Solvent in Ion Radical Cleavage and in Stepwise vs. Concerted Competitions 2353.6.1 Introduction 2353.6.2 Experimental Clues 2363.6.3 A Simplified Model System 2413.7 Dichotomy and Connections Between SN2 Reactions and Dissociative Electron Transfers 2463.7.1 Introduction 2463.7.2 Experimental Approaches 2473.7.3 Theoretical Aspects 251References 2554 Proton-Coupled Electron Transfers 2594.1 Introduction 2594.2 Fundamentals 2604.2.1 Concerted and Stepwise Pathways in Proton-Coupled Electron Transfer Reactions 2604.2.2 Thermal (Electrochemical and Homogeneous) and Photoinduced Reactions 2624.2.3 Modeling Concerted Proton Electron Transfers 2644.3 Examples 2684.3.1 PCET in Hydrogen Bounded Systems: H-bond Relays 2684.3.2 PCET in Water 2714.4 Breaking Bonds with Protons and Electrons 279References 2835 Molecular Catalysis of Electrochemical Reactions 2855.1 Introduction 2855.2 Homogeneous Molecular Catalysis 2875.2.1 Contrasting Redox and Chemical Catalysis 2875.2.2 Applications of Homogeneous Redox Catalysis to the Characterization of Short-Lived Intermediates 2885.2.2.1 Principle and Achievements of the Method 2885.2.2.2 Comparison with Fast Cyclic Voltammetry and Laser Flash Photolysis 2915.2.2.3 Determination of the Standard Potential for the Formation of Very Unstable Primary Intermediates 2935.2.2.4 Redox Catalysis of Electrocatalytic Processes 2945.2.3 Overpotential, Turnover Frequency, Catalysts’ Benchmarking, Catalytic Tafel Plots, Maximal Turnover Number 2965.2.4 Inhibition by Intermediates and Other Secondary Phenomena. Remedies 2995.2.5 Multi-Electron Multistep Mechanisms 3015.2.6 Competition Between Heterolytic and Homolytic Catalytic Mechanisms 3195.2.7 Intelligent Design of Molecular Catalysts 3255.2.7.1 Redox vs. Chemical Catalysis: The Reduction of Vicinal Dibromides. Rates and Stereoselectivity 3255.2.7.2 Correlation Between Catalysis Kinetics and Thermodynamics: The “Iron Law” Restraining Through-Structure Substituent Effect Within a Catalyst Family 3265.2.7.3 Escaping the “Iron Law”: Through-Space Substituent Effects 3295.3 Supported Molecular Catalysis (Immobilized Catalysts) 3325.3.1 Redox and Chemical Catalysis at Monolayer and Multilayer-Coated Electrodes 3325.3.2 Catalysis at Monolayer-Coated Electrodes 3335.3.3 Permeation Through Electrode Coatings. Inhibition 3425.3.4 Electron Hopping Conduction in Assemblies of Redox Centers 3495.3.5 Ohmic Conduction in Mesoporous Electrodes 3525.3.6 Catalysis at Multilayer-Coated Electrodes 3565.3.7 Combining an Electron-shuttling Mediator with a Chemical Catalyst in a Multilayer Electrode Coating 374References 3796 Enzymatic Catalysis of Electrochemical Reactions 3836.1 Introduction 3836.2 Homogenous Enzymatic Catalysis 3846.2.1 Introduction 3846.2.2 The “Ping-Pong” Mechanism. Kinetic Control by Substrate and/or Cosubstrate 3856.2.3 A Model Example: Glucose Oxidase with Excess Glucose 3926.2.4 Molecular Recognition of an Enzyme by Artificial One-Electron Cosubstrates 3946.2.5 Deciphering a Complex Electroenzymatic Response: Horseradish Peroxidase 3986.3 Immobilized Enzymes in Monomolecular Layers 4026.3.1 Introduction 4026.3.2 The “Ping-Pong” Mechanism with an Immobilized Enzyme and the Cosubstrate in Solution 4026.3.3 Antigen–Antibody Immobilization of Glucose Oxidase: Kinetic Analysis 4116.3.4 Application to the Kinetic Characterization of Biomolecular Recognition 4136.3.5 Immobilized Horseradish Peroxidase 4206.3.6 Immobilization of Both the Enzyme and the Cosubstrate: Electron Transfer and Electron Transport in Integrated Systems 4256.4 Spatially Ordered Multi-monomolecular Layered Enzyme Coatings 4306.4.1 Step-by-Step Antigen–Antibody Construction of Multi-monomolecular Layer Enzyme Coatings 4306.4.2 Reaction Dynamics with the Cosubstrate in Solution: Evidence for Spatial Order 432References 4367 Appendices 4397.1 Single-Electron Transfer at an Electrode 4397.1.1 Laplace Transformation: Useful Definitions and Relationships 4397.1.2 Cyclic Voltammetry of Nernstian Systems: Current– and Charge–Potential Curves 4397.1.3 Double-Layer Charging in Cyclic Voltammetry: Oscillating and Nonoscillating Behaviors 4467.1.4 Effect of Ohmic Drop and Double-Layer Charging on Nernstian Cyclic Voltammograms 4487.1.5 Potential Step and Double Potential Step Chronoamperometry of Nernstian Systems 4517.1.6 Overlapping of Double-Layer Charging and Faradaic Currents in Potential Step and Double Potential Step Chronoamperometry. Oscillating and Nonoscillating Behaviors 4537.1.7 Solvent Reorganization in Marcus–Hush–Levich Model 4557.1.8 Effect of the Multiplicity of Electronic States in the Electrode 4607.1.9 Cyclic Voltammetry of Two-Electron Nernstian Systems. Disproportionation 4637.2 Coupling of Homogeneous Chemical Reactions with Electron Transfer 4657.2.1 The EC Mechanism 4657.2.2 The CE Mechanism 4717.2.3 Double Potential Step Responses for Processes Involving First- or Second-Order Follow-Up Reactions 4747.2.4 The ECE and DISP Mechanisms 4757.2.5 Electrodimerization 4837.2.6 Competition Between Dimerization of and Electron Transfer to Intermediates 4907.2.7 Homogeneous Catalysis 4957.2.7.1 Homogeneous Electron Transfer as the Rate-Determining Step 4957.2.7.2 Homogeneous Catalytic EC Mechanism 4997.2.7.3 Deactivation of the Mediator 5007.2.8 Product Distribution in Preparative Electrolysis 5027.3 Electron Transfer, Bond Breaking, and Bond Formation 5257.3.1 Contribution of the Cleaving Bond Stretching to Internal Reorganization of the First Step of the Stepwise Mechanism 5257.3.2 Morse Curve Model of Intramolecular Dissociative Electron Transfer 5267.4 Proton-Coupled Electron Transfers 5287.4.1 Rate Law for Electrochemical CPET 5287.4.2 Current–Potential Relationship for PCET in Water 5337.4.3 Competition Between Dimerization and CPET Kinetics 5387.5 Analysis of Supported Molecular Catalysis by Rotating Disk Electrode Voltammetry and Cyclic Voltammetry 5417.5.1 Catalysis at Monolayer Electrode Coatings 5417.5.2 Inhibition of Electron Transfer at Partially Blocked Electrodes 5447.5.3 Equivalent Diffusion and Migration Laws for Electron Hopping Between Fixed Sites 5457.5.4 Ohmic Conduction in Mesoporous Electrodes 5477.5.5 Catalysis at Multilayered Electrode Coatings: RDVE 5567.5.6 Ohmic Transport in Electrocatalytic Film 5627.5.6.1 Governing Equations 5627.5.6.2 Dimensionless Formulation 5637.5.6.3 Semianalytical Resolution 5647.5.6.4 Asymptotes of the Catalytic Tafel Plots for E → ±∞ 5677.5.7 Catalysis at Multilayered Electrode Coatings: Cyclic Voltammetry 5687.5.7.1 Formulation 5687.5.7.2 Resolution in the Absence of Substrate Consumption 5697.5.7.3 Resolution in Pure Kinetics Conditions (Fast Kinetics) with Possible Substrate Consumption 5717.5.7.4 Resolution in Fast-conducting Conditions with Possible Substrate Consumption 5777.6 Enzymatic Catalysis Responses 5807.6.1 The “Ping-Pong” Mechanism in Homogeneous Enzymatic Catalysis 5807.6.2 Catalysis and Inhibition in Homogeneous Systems 5857.6.2.1 Derivation of Eq. (6.10) 5857.6.2.2 Control by Substrate Diffusion 5897.6.3 Catalysis at Multilayered Electrode Coatings 591References 597Glossary of Symbols 599Index 611