Geoffrey A. Lawrance

Complexes of polyaza macrocycles bearing pendent coordinating groups

Presentation de travaux relatifs a la reactivite chimique de metaux de transitions vis a vis de macrocycles substitues triaza, tetraaza et pentaaza, ions Co(III) et Ni(II), principalement. Synthese bibliographique

Second order global analysis: the evaluation of series of spectrophotometric titrations for improved determination of equilibrium constants

Abstract In spectrophotometric titrations, linear or near-linear dependence of concentration profiles and the existence of minor species cause difficulties in the evaluation of the data. In the first case calculated absorption spectra and in the second case the corresponding equilibrium constants are not or only poorly defined. The result is the inability to reliably fit a reasonable model to the data. In second order global analysis, a number of spectrophotometric titrations with different initial concentrations are simultaneously analysed. In this way the concentration matrix is augmented to full rank and, secondly, conditions for the significant formation of each species can be obtained. Resulting equilibrium constants and absorption spectra are notably better defined. EQUISPEC is a computer program using the matrix based MATLAB environment for second order global analysis of spectrophotometric equilibrium data. It has been successfully tested with generated data and shown to overcome linear dependence and reproduce reported stability constants for the zinc: 1,10-phenanthroline system and to considerably improve the analysis of the complexation of Cu 2+ by diethylenetriamine (dien).

‘Green’ leaching: recyclable and selective leaching of gold-bearing ore in an ionic liquid

The recovery of gold and silver from ore in an ionic liquid is reported for the first time. The 1-butyl-3-methyl-imidazolium hydrogen sulfate ionic liquid (bmim+HSO4−) was employed, with iron(III) sulfate oxidant and thiourea added. Selective extraction of gold (≥85%) and silver (≥60%) from powdered ore (of dominantly chalcopyrite/pyrite/pyrrhotite/sphalerite mineralogy) was achieved at room temperature in 50 h, with other lower-value metals present in the ore (Cu, Zn, Pb, Fe) extracted to only low percentages. Gold extraction was similar to that achieved in aqueous H2SO4/thiourea/Fe2(SO4)3, and silver extraction was significantly better. Moreover, the ionic liquid can be recycled following selective stripping of gold and silver on activated charcoal, with reuse in at least four successive treatments leading to neither ionic liquid degradation nor any loss in extraction efficiency.

Introduction to Coordination Chemistry

Preface Preamble 1 The Central Atom 1.1 Key Concepts in Coordination Chemistry 1.2 A Whos Who of Metal Ions 1.3 Metals in Molecules 1.4 The Road Ahead Concept Keys Further Reading 2 Ligands 2.1 Membership: Being a Ligand 2.2 Monodentate Ligands - The Simple Type 2.3 Greed is Good - Polydentate Ligands 2.4 Polynucleating Species - Molecular Bigamists 2.5 A Separate Race - Organometallic Species Concept Keys Further Reading 3 Complexes 3.1 The Central Metal Ion 3.2 Metal-Ligand Marriage 3.3 Holding On - The Nature of Bonding in Metal Complexes 3.4 Coupling - Polymetallic Complexes 3.5 Making Choices 3.6 Complexation Consequences Concept Keys Further Reading 4 Shape 4.1 Getting in Shape 4.2 Forms of Complex Life 4.3 Influencing Shape 4.4 Isomerism - Real 3D Effects 4.5 Sophisticated Shapes 4.6 Defining Shape Concept Keys Further Reading 5 Stability 5.1 The Makings of a Stable Relationship 5.2 Complexation - Will it Last? 5.3 Reactions Concept Keys Further Reading 6 Synthesis 6.1 Molecular Creation - Ways to Make Complexes 6.2 Core Metal Chemistry - Periodic Table Influences 6.3 Reactions Involving the Coordination Shell 6.4 Reactions Involving the Metal Oxidation State 6.5 Reactions Involving Coordinated 6.6 Organometallic Synthesis Concept Keys Further Reading 7 Properties 7.1 Finding Ways to Make Complexes Talk - Investigative Methods 7.2 Getting Physical - Methods and Outcomes 7.3 Probing the Life of Complexes - Using Physical Methods Concept Keys Further Reading 8 A Complex Life 8.1 Lifes a Metal Ion 8.2 Metalloproteins and Metalloenzymes 8.3 Doing What Comes Unnaturally 8.4 A Laboratory-free Approach - In Silico Prediction Concept Keys Further Reading 9 Complexes and Commerce 9.1 Kill or Cure? - Complexes as Drugs 9.2 How Much? - Analysing with Complexes 9.3 Profiting from Complexation 9.4 Being Green 9.5 Complex Futures Concept Keys Further Reading Appendix One Nomenclature Appendix Two Molecular Symmetry: The Point Group Index

Redox Processes at the Manganese Dioxide Electrode II. Slow‐Scan Cyclic Voltammetry

Slow-scan cyclic voltammetry was used to investigate the voltammetric behavior of electrolytic manganese dioxide (EMD), birnessite, chemically modified EMD (Bi-CMEMD), and birnessite (Bi-birnessite)electrodes under a variety of experimental conditions. During reduction, each electrode underwent a homogeneous reduction stage followed by a heterogeneous reduction stage. The composition at which the transition between these two stages occurred was dependent on the material under study. The initial cycle of the Bi-CMEMD electrode was similar to that of the EMD electrode. However, during the second cycle its behavior was similar to that of the Bi-birnessite electrode. This change in mechanism imparts rec argeable behavior to the Bi-CMEMD electrode. The end product of also dependent Mn(OH) 2 , except for the birnessite electrode, where Mn 3 O 4 was formed. The behavior of each electrode was also dependent on the graphite content used in the electrode, the electrolyte concentration, and the particle size of the manganese dioxide under study. The homogeneous reduction stage, which is a reaction involving a solid solution, favors a high proportion of graphite in the electrode and fine manganese dioxide particles. The heterogeneous reduction stage, which involves the formation of a soluble intermediate, was enhanced with concentrated KOH electrolytes and fine manganese dioxide particles. The influence of EMD surface area on electrode behavior was also investigated. The oxidation of Mn(OH) 2 in each electrode proceeded through a variety of solid Mn3 + intermediates to form a birnessite-like phase of manganese dioxide. The Bi 3+ ions in the chemically modified electrodes were incorporated into the structure of the oxidation product.

Redox Processes at the Manganese Dioxide Electrode I. Constant‐Current Intermittent Discharge

The reduction of electrodeposited manganese dioxide (EMD), birnessite, and Bi-birnessite electrodes was investigated using a constant-current intermittent discharge technique under conditions where major kinetic effects had been minimized. The results suggested that each type of manganese dioxide underwent a homogeneous reduction followed by a heterogeneous reduction stage. The transition between these reaction mechanisms occurred at a composition that was dependent on the manganese dioxide used. The homogeneous reduction of each electrode was a complex process involving the reduction of Mn 4+ ions within the various manganese dioxide structures. The heterogeneous reduction of the electrodeposited manganese dioxide and Bi-birnessite electrodes resulted in formation of Mn(OH) 2 , whereas heterogeneous reduction of the birnessite electrode resulted in formation of Mn 3 O 4

Direct un-mediated electrochemistry of the enzyme P-cresolmethylhydroxylase

The enzyme p-cresolmethylhydroxylase, from Pseudomonas putida, is involved in the degradative pathway of p-cresol. The direct, un-mediated reversible electron transfer between the heme of the flavocytochrome enzyme and an edge-plane graphite electrode in the presence of redox-inactive cationic species as promoters of the enzyme electrochemistry is reported. Diffusion controlled heterogeneous electron transfer is modulated by the levels and type of promoter used, which range from simple and complex cations to polyamines and aminoglycosides. The promoter-enzyme assembly affords a degree of macromolecular recognition at the electrode as both the cationic charge and the flexible nature of the promoter are important to achieve direct electron transfer. A quasi-reversible cyclic voltammetric response was observed in the absence of substrate from which the heterogeneous rate of electron transfer between the enzyme and the electrode was determined as ks~ 1.8 × 10−4 cm2 s−1. An enzyme titration with optimal concentrations of promoter and substrate p-cresol yielded a linear relationship between catalytic current and enzyme concentration up to 1.2 μM. Similarly, relationships were obtained to p-cresol and p-hydroxybenzylalcohol concentrations with fixed amounts of enzyme and promoter, both yielding a linear current vs. substrate response up to 0.5 m M. Furthermore, the magnitude of the catalytic current of p-cresol is greater than that obtained for mediation with the enzymes natural redox partner, azurin, but comparable to those obtained with a ferrocene mediator. Catalytic response was also obtained at a peptide-modified gold electrode in the presence of a promoter, spermine.

Redox Processes at the Manganese Dioxide Electrode III. Detection of Soluble and Solid Intermediates during Reduction

The soluble and solid-state intermediates formed during redox cycling of electrodeposited manganese dioxide (EMD), birnessite and chemically modified EMD (Bi-CMEMD), and birnessite (Bi-birnessite) electrodes were investigated using a stationary detector electrode (soluble intermediates) and x-ray diffraction (solid-state intermediates). Reduction of each electrode type can be divided into a homogeneous stage followed by a heterogeneous stage. For all electrode types, homogeneous reduction was a solid-state process involving proton and electron insertion into the manganese dioxide structure, causing a lattice expansion. Toward the end of homogeneous EMD reduction, soluble species were detected, presumably due to an equilibrium shift between solid and solution phase Mn 3+ species. The homogeneous/heterogeneous transition was also electrode dependent; i.e., ∼MnO 1.55 for EMD and Bi-CMEMD, ∼MnO 1.33 for birnessite, and ∼MnO 1.33 for Bi-birnessite. Heterogeneous electrochemical behavior was also electrode dependent. Initial heterogeneous reduction of EMD, Bi-birnessite, and Bi-CMEMD proceeded through a soluble Mn 3+ intermediate to form Mn(OH) 2 . Electrolyte concentration effects were more pronounced in this stage, since more concentrated KOH electrolytes lead to greater Mn 3+ solubility. The composition at which Mn(OH) 2 was first detected in the Bi-birnessite electrode suggested that the Mn(IV) to Mn(III) and Mn(III) to Mn(II) reduction processes occurred simultaneously. Heterogeneous reduction of birnessite was a solid-state process that resulted in Mn 3 O 4 , which is electrochemically inactive. Mn(OH) 2 oxidation resulted in formation of birnessite, the exact nature of which depended on the presence or absence of Bi 3+ ions. Under these deep discharge cycling conditions, the EMD electrode behaved poorly due to the eventual formation of Mn 3 O 4 . However, the Bi-birnessite and Bi-CMEMD electrodes are rechargeable due to the presence of Bi 3+ ions, which prevent Mn 3 O 4 formation

Effect of electrolyte composition on zinc hydroxide precipitation by lime

The effect of effluent composition on the efficiency of the hydroxide precipitation of Zn2+ modelling lime (CaO) as a precipitant has been predicted using the solubility domain approach and experimentally validated. Solubility domains were based on the phases that were found to be solubility limiting for systems representing potential effluent chemical composition limits. All such phases were found to resemble their mineralized counterparts with a lower degree of structural order. The generated solubility domains generally encompassed the experimentally observed solubilities, thus providing effluent treatment quality assurance ranges for the hydroxide precipitation process. The presence of calcite (CaCO3) and gypsum (CaSO4.2H2O) as secondary precipitates had little effect on the observed residual zinc solubilities. Validation of the solubility domain approach using real industrial wastewater was accomplished.

Toward the Understanding of Chemical Absorption Processes for Post-Combustion Capture of Carbon Dioxide: Electronic and Steric Considerations from the Kinetics of Reactions of CO2(aq) with Sterically hindered Amines

The present study reports (a) the determination of both the kinetic rate constants and equilibrium constants for the reaction of CO(2)(aq) with sterically hindered amines and (b) an attempt to elucidate a fundamental chemical understanding of the relationship between the amine structure and chemical properties of the amine that are relevant for postcombustion capture of CO(2) (PCC) applications. The reactions of CO(2)(aq) with a series of linear and methyl substituted primary amines and alkanolamines have been investigated using stopped-flow spectrophotometry and (1)H NMR measurements at 25.0 °C. The specific mechanism of absorption for each of the amines, that is CO(2) hydration and/or carbamate formation, is examined and, based on the mechanism, the kinetic and equilibrium constants for the formation of carbamic acid/carbamates, including protonation constants of the carbamate, are reported for amines that follow this pathway. A Brønsted correlation relating the kinetic rate constants and equilibrium constants for the formation of carbamic acid/carbamates with the protonation constant of the amine is reported. Such a relationship facilitates an understanding of the effects of steric and electronic properties of the amine toward its reactivity with CO(2). Further, such relationships can be used to guide the design of new amines with improved properties relevant to PCC applications.