THE UNIVERSITY OF HULL ELECTRO-CATALYTIC REACTIONS Being a Thesis submitted for the Degree of Doctor of Philosophy THE UNIVERSITY OF HULL by Carlos Lledo-Fernandez (June 2009) Declaration The work described in this thesis was carried out in the Department of Chemistry, University of Hull under the supervision of Professor G.M. Greenway and Dr. J. Wadhawan between October 2004 and September 2008. Except where indicated by references, the work is original and has not been submitted for any other degree. Carlos Lledo-Fernandez June 2009 2 Table of Contents TITLE 1 DECLARATION 2 TABLE OF CONTENTS 3 ACKNOWLEDGEMENTS……………………………………………………. 8 ABSTRACT……………………………………………………………………... 10 CHAPTER 1-INTRODUCTION……………………………………………… 13 1 AIMS OF THE THESIS……………………………………………………………... 14 1.1 DYNAMIC ELECTROCHEMISTRY………………………………………….. 14 1.1.1 INTRODUCTION…………………………………………………………………….. 14 1.1.2 THE INTERFACIAL REGION AND ELECTROLYTE DOUBLE LAYER………... 15 1.2 ELECTROCHEMICAL CELL AND REACTIONS……………………………. 17 1.3 CELL DESIGN AND ELECTRODE PLACEMENT……………………………. 20 1.4 MATERIAL TRANSPORT……………………………………………………….. 21 1.4.1 DIFFUSION…………………………………………………………………………….. 23 1.4.2 CONVECTION………………………………………………………………………... 25 1.4.3 MIGRATION………………………………………………………………………….. 27 1.5 CYCLIC VOLTAMMETRY……………………………………………………… 27 1.5.1 THEORY AND APPLICATIONS OF THE CYCLIC VOLTAMMETRY FOR 29 MEASURAMENT OF ELECTRODE REACTIONS KINETICS……………………………….. 1.5.2 CYCLIC VOLTAMMETRY AT PLANAR ELECTRODES………………………… 29 1.5.2.1 CYCLIC VOLTAMMETRY WITH REVERSIBLE SYSTEM………………………………………. 30 1.5.2.2 CYCLIC VOLTAMMETRY WITH IRREVERSIBLE SYSTEM……………………………………. 32 1.5.2.3 CYCLIC VOLTAMMTRY WITH QUASI-REVERSIBLE SYSTEM……………………………….. 34 1.5.2.4 COMPARISON BETWEEN REVERSIBLE AND IRREVERSIBLE VOLTAMMOGRAMS……… 36 1.6 AMPEROMETRIC DETECTION………………………………………………... 37 1.7 POTENTIAL STEP : CHRONOAMPEROMETRY…………………………….. 37 1.8 HYDRODYNAMIC ELECTRODES……………………………………………... 39 1.8.1 LIMITING CURRENTS………………………………………………………………. 40 1.8.2 ROTATING DISC ELECTRODE…………………………………………………...... 40 1.8.3 THE CHANNEL ELECTRODE……………………………………………………… 42 1.9 MICROELECTRODES……………………………………………………. 44 1.10 CHEMILUMINESCENCE AND ELECTROGENERATED 46 CHEMILUMINESCENCE……………………………………………………………. 1.10.1 CHEMILUMINESCENCE…………………………………………………………... 46 1.10.2 CHEMILUMINESCENCE REACTIONS…………………………………………... 51 1.10.2.1 CHEMILUMINESCENCE DETECTION FOR SEPARATION PROCESS………………………... 52 3 1.10.2.2 TRIS (2, 2’-BIPYRIDYL) RUTHENIUM (II)……………………………………………………… 53 1.11 ELECTROGENERATED CHEMILUMINESCENCE (ECL)………………… 53 1.11.1 ECL IN INORAGNIC COMPOUNDS-ELECTRO TRANSFER REACTIONS OF 54 TRANSITION METAL COMPLEXES…………………………………………………………... 2+ 1.11.1.1 METHODS FOR THE GENERATION OF Ru(bpy)3 ……………………………………………... 57 1.11.1.2 CHEMICAL AND PHOTOCHEMICAL OXIDATION…………………………………………….. 58 1.11.1.3 ELECTROCHEMICAL OXIDATION………………………………………………………………. 58 1.11.1.4 IN SITU GENERATED ELECTROCHEMILUMINESCENCE……………………………………. 58 1.11.2 ECL APPLICATIONS OF CONVENTIONAL CHEMILUMINESCENCE………… 59 REACTIONS……………………………………………………………………………………… 1.11.3 CATHODIC LUMINESCENCE…………………………………………………….. 61 2+ 1.12 ANALYTICAL APPLICATIONS OF Ru(bpy)3 ……………………………… 61 ELECTROCHEMILUMINESCENCE……………………………………………….. 1.12.1 AMINO ACIDS AND PROTEINS………………………………………………….. 61 1.12.2 PHARMACEUTICALS…………………………………………………………….... 61 1.12.2.1 IMMUNOASSAY AND DNA PROBE ASSAY……………………………………………………. 61 1.13 COMPARISON OF LIMITS OF DETECTION FOR ECL……………………... 62 SYSTEMS…………………………………………………………………………………. 1.14 REAGENT IMMOBILISATION………………………………..………………… 63 1.14.1 SOL GELS…………………………………………………………………………… 63 1.14.1.1 SOL GEL MECHANISMS…………………………………………………………………………... 65 1.14.1.1.1 ACID CATALYZED HYDROLYSIS…………………………………………………………………………... 65 1.14.1.2 FACTORS AFFECTING SOL GEL PROPERTIES……………………………………………........ 66 1.14.2 COVALENT ATTACHMENT………………………………………………………. 67 1.15 CONCLUSIONS OF ECL AND CL……………………………………………... 68 1.15 REFERENCES……………………………………………………………………. 70 CHAPTER 2-EXPERIMENTAL SECTION INSTRUMENTATION AND 74 PROCEDURES…………………………………………..................................... 2.1 INSTRUMENTATION…………………………………………………………….. 75 2.1.1 DEVELOPMENT OF A ELECTROGENERATED CHEMILUMINESCENCE 75 DETECTORS……………………………………………………………………………………... 2.1.1.1 EXPERIMENTAL SETUP……………………………………………………………………………. 75 2.1.1.2 POTENTIOSTATS AND ELECTRODES……………………………………………………………. 76 2.1.1.3 ELECTROCHEMILUMINESCENCE DETECTOR…………………………………………………. 77 2.1.2 PORTABLE ELECTROGENERATED-CHEMILUMINESCENCE DETECTOR….. 78 2.2 REAGENTS...............................……………………………………………………… 79 2.2.1 REAGENTS USED FOR ELECTROGENERATED CHEMILUMINESCENCE 79 DETECTOR………………………………………………………………………………………. 2.3 PROCEDURES……………………………………………………………………... 81 2.3.1 ELECTROCHEMICAL MEASURAMENTS………………………………………… 81 2.3.2 COATING PROCEDURE FOR A SOL-GEL………………………………………… 81 4 2.3.3 ELECTRODE POLISHING AND COATING PROCEDURES FOR THE 83 FORMATION OF DROPLETS IN THE ELECTRODE…………………………………………. 2.4 CONCLUSIONS……………………………………………………………………. 84 2.5 REFERENCES……………………………………………………………………... 85 CHAPTER 3-DEVELOPMENT OF A REAGENTLESS PORTABLE 86 SYSTEM FOR ANALYSING DRUGS………………………………………... 3.0 AIMS OF THE CHAPTER………………………………………………………... 87 3.1 DRUGS OF ABUSE………………………………………………………………..… 87 3.2 SELECTION OF THE EXPERIMENTAL CONDITIONS…………………….. 91 2+ 3.2.1 SELECTION OF THE Ru(BPY)3 CONCENTRATION…………………………... 91 3.2.2 DESIGNING THE ELECTROCHEMICAL CELL…………………………………... 92 3.2.3 THE SELECTION OF THE pH………………………………………………………. 93 3.2.4 EFFECTS OF THE SCAN RATE…………………………………………………….. 96 3.3 ECL DETECTION OF ROHYPNOL…………………………………………….. 98 3.4 SOL-GEL COATED ELECTRODE……………………………………………… 101 3.4.1 SOL-GEL COATING ON METALS ELECTRODES………………………………….. 101 3.4.2 SOL-GEL COATING ON GLASSY CARBON ELECTRODES …………………………. 103 2+ 3.4.2.1 DETERMINATION OF CODEINE WITH Ru(BPY)3 IMMOBILISED IN SOL-GELS………….. 105 3.4.3 ECL EMISSION………………………………………………….…………………………. 108 3.5 COVALENT ATTACHMENT OF ELECTROCHEMILUMINESCENT 110 REAGENTS IN SILICATE SOL-GELS……………………………………………… 3.5.1 VOLTAMMOGRAMS FOR COVALENTLY IMMOBILISATION………………… 111 3.5.2 ECL EMISSION FOR COVALENTLY IMMOBILISATION……………………….. 113 3.6 CONCLUSIONS……………………………………………………………………. 114 3.7 REFERENCES……………………………………………………………………... 116 CHAPTER 4-ELECTROGENERATED CHEMILUMINESCENCE AT 118 LIQUID/LIQUID INTERFACE : EVIDENCE INVERTED & PROTON- COUPLED ELECTRON TRANSFER………………………………………... 4.0 AIMS………………………………………………………………………………… 119 4.1 INTRODUCTION………………………………………………………………….. 120 4.1.1 FACTORS AFFECTING ELECTRODE REACTION RATE AND CURRENT…. 120 4.1.2 ELECTROCHEMISTRY OF IMMOBILISED REDOX DROPLETS…………….. 121 4.1.2.1 ELECTROCHEMISTRY AT THE THREE-PHASE BOUNDARY…………………………………. 121 4.1.2.2 ELECTRON TRANSFER PROCESSES AT THE LIQUID/ LIQUID INTERFACE………………... 122 4.1.2.3-THE CURRENT–VOLTAGE CURVES IN THE CASE OF HYDROPHILIC COMPOUNDS AND 122 ELECTROLYTE COUNTER IONS (ELECTROCHEMICALLY INDUCED ION EXPULSION PROCESS)………….. 4.2 RESULTS AND DISCUSSION……………………………………………………. 124 4.2.1 VOLTAMMETRY OF OC3N (TRIOCTYLAMINE) MICRODROPLETS………….. 124 5 2+ …4.2.2 VOLTAMMETRY OF RU(BPY)3 AT GLASSY CARBON ELECTRODES…….. 128 4.2.3 BIPHASIC ELECTRON TRANSFER………………………………………………... 129 4.2.4 AMPEROMETRIC AND ECL MEASUREMENTS IN DEUTERATED…………… 140 PHOSPHORIC AND BASIC CONDITIONS. 4.3 CONCLUSIONS……………………………………………………………………. 147 4.4 REFERENCES……………………………………………………………………... 149 CHAPTER 5-ELECTROCHEMICAL/CHEMICAL SYNTHESIS AND 151 ISOLATION OF THE FULLY REDUCED VITAMIN B12 SPECIES FOR THE CATALYTIC REDUCTION OF DBCH……………………………….. 5.0 AIMS………………………………………………………………………………… 152 5.1 INTRODUCTION TO THE CHEMISTRY OF VITAMIN B12………………… 152 5.1.1 HISTORY……………………………………………………………………………... 152 5.1.2 ISOLATION AND PURIFICATION…………………………………………………. 153 5.1.3 STRUCTURE…………………………………………………………………………. 153 5.1.4 METABOLIC ROLE, FUNCTIONS AND IMPORTANCE…………………………. 155 5.1.5 THE REDUCTION OF THE VITAMIN B12…………………………………………. 155 5.2 MECHANISM……………………………………………………………………… 156 5.3 MICROFLUIDIC DEVICES……………………………………………………… 158 5.3.1 PROPERTIES OF MIXING…………………………………………………………... 159 5.3.2 ENHANCED MIXING IN MICROREACTOR………………………………………. 161 5.4 EXPERIMENTAL…………………………………………………………………. 162 5.4.1 CHEMICAL REAGENTS…………………………………………………………...... 162 5.4.2 INSTRUMENTATION……………………………………………………………….. 162 5.4.2.1 CYCLIC VOLTAMMETRY………………………………………………………………………….. 162 5.4.2.2 BULK ELECTROLYSIS EXPERIMENTS…………………………………………………………... 162 5.4.2.3 SPECTROSCOPIC CHARACTERISATION………………………………………………………… 163 5.4.2.4 EXPERIMENTAL SET-UP EMPLOYED IN MICROFLUIDIC DEVICES………………………… 163 5.4.2.5 PROCEDURES FOR BATCH REACTIONS………………………………………………………… 164 5.4.2.5.1 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 WITH NA/AMALGAM…………………… 164 5.4.2.5.2 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 USING NABH4/20%NAOH……………… 165 5.4.2.5.3 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 WITH DL-CYSTEINE IN ALKALI………. 165 5.4.2.5.4 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 WITH ZN-DUST AND AMMONIUM 166 CHLORIDE 5.5 RESULTS AND DISCUSSION……………………………………………………. 166 5.5.1 CYCLIC VOLTAMMETRY INVESTIGATION OF THE ELECTROCATLYTIC 166 REACTION WITH VITAMIN B12 AND DBCH………………………………………………… 5.5.2 CHEMICAL REDUCTION OF THE VITAMIN B12………………………………… 170 5.5.2.1 NMR OF REACTANTS AND PRODUCTS…………………………………………………………….. 171 5.5.2.2 BATCH CATALYTIC REDUCTION OF B12 USING NABH4/20%/NAOH……………………………. 172 5.5.2.3 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 WITH DL-CYSTEINE IN ALKALI 174 SOLUTION…………………………………………………………………………………………………………………….. 5.5.2.4 BATCH CATALYTIC REDUCTION OF THE VITAMIN B12 WITH ZN-DUST IN ……………... 175 6 AMMONIUM CHLORIDE 5.5.3 APPLICATION OF THE MICROFLUIDIC DEVICE FOR THE REACTION OF 175 DBCH WITH B12S…………………………………………………………………………………