High current anodization of magnesium and magnesium alloys Ellen Angharad Carter Pure magnesium and three magnesium alloys containing different amounts of aluminium (2-9%) plus zinc and manganese were anodized with constant current density in sodium hydroxide solution with and without fluoride or phosphate ions. Electric field strengths of resultant anodic films were calculated from galvanostatic transients. These transients showed three characteristic features: linear voltage increase, noisy high voltage signals accompanied by sparking, and sawtooth-like events characterized by instantaneous voltage drops followed by slower voltage increases. Each feature was linked to certain physical processes occurring in the metal/film/solution system. Oxidation of magnesium and magnesium alloys formed anodic films with bilayer structures: a passive barrier layer adhering to the metal electrode, topped by a porous secondary layer. Cation injection into the barrier film across the metal/oxide interface was the rate determining step for film growth. Interstitial cations migrated through the film under the influence of the electric field. At the film/solution interface they reacted with electrolyte species and either thickened the film or dissolved in solution. Electric field strength was constant for particular metal/solution combinations and was independent of applied current density. Changing the electrode material altered the resultant electric field strength: pure magnesium produced oxides with lower electric field strengths than films formed on the three magnesium alloys. Changing the electrolyte had no discernable effect on the electric field strength. Charge efficiency of the film growth process was investigated by oxygen gas evolution; efficiency decreased during sparking. Ion beam analysis (Rutherford backscattering, fluorine depth profiling and nuclear reaction analysis) coupled with X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction studies and Raman spectroscopy gave information about the anodic film surface. These techniques showed that oxides formed on magnesium-aluminium alloys were thinner than those formed on pure magnesium caused by aluminium dissolution. Fluorine depth profiling revealed that concentration profiles for fluorine in anodic oxides formed in fluoride-containing solution altered depending on the aluminium content of the electrode material.

The mechanisms proposed for the Clemmensen reduction of simple ketones are critically examined, and the Clemmensen reduction of difunctional ketones is reviewed. The Clemmensen reduction of a number of 1,4-diketones has shown that the products formed depend on the conformation of the carbonyl groups: (a) syn or anti-periplanar alignment of the carbonyl groups within the C2-C3 bond favours fragmentation e.g. cyclohexane-1,4-dione leads to hexane-2,5-dione and hex-5-oF-2-one, (b) with 1,2-diacetyl systems formation 3f alcohols and furans predominates e.g. hexane-2,5-dione gives hexan-2-ol, and 2,5-dimethyltetrahydrofuran, (c) when both carbonyl groups are in a large ring (≥C7) formation of cyclobutanediols is possible e.g. 2,6,6-trimethylcycloheptane-1,4-dione is reduced to 3,3,6-trimethylbucyclo[3,2,0]-1β-diol, (d) when none of these conditions is satisfied normal reduction occurs e.g. cholestane-3,6-dione yields cholestan-6-one. A mechanism is proposed for the formation of hexan-2-ol, hex-4-on-2ol, and 2,5-dimethyltetrahydrofuran from the Clemmensen reduction of hexane-2, 5-dione. The production of a number of similarly constructed 1,4-diketones and Y-functionalised ketones is also examined. The synthetic visibility of the fragmentation reaction, previously observed to occur under Clemmensen conditions, is investigated and it is shown that this is of limited value for the preparation of large rings. The stereochemical requirements for the reaction are verified and the mechanism is further studied. A review of the synthesis of 1,4-diketones is given and the preparation of the compounds used in this study is discussed in detail. The Clemmensen reduction of two 1,5-diketones is examined. The formation of cyclopropanediols and cyclopropanols from the Clemmensen reduction of some monocyclic formyl-ketones and β-hydroxy-ketones is discussed. The Clemmensen reduction of hexane-2,5-dione and pentane-2,4-dione with different metals is investigated.

This thesis is presented in three parts. The first is concerned with the solution and attempted refinement of the structure of prostratin, a toxic anti-tumour chemical extracted from the New Zealand tree pimelia prostrata. The second is concerned with the analysis of the structures of three inorganic compounds of current interest. These are; 1. bisethylenediaminenickel(II) hemioxalate nitrate 2. dipropylenetriaminezinc(II) hemioxalate perchlorate 3. diethylenetriaminecopper(II) hemioxalate perchlorate. The last section deals with the theory and programming of five of the more important computer programs developed during the course of the work.

A range of compounds related to the diquaternised salts of 2,2'-dtpyridine and 4,4'-dipyridine was studied in the present investigation. The effect of the change in the redox-state of the compounds was determined by vibrational spectroscopic and molecular orbital techniques. The investigation of 2,7-dimethylthieno[2,3-c:5,4-c'] dipyridinium diiodide monohydrate was undertaken by X-ray diffraction, vibrational spectroscopic and molecular-orbital techniques. These investigations showed that the thiophenic portion of the dication exhibited partial aromaticity. On formation of the radical monocation, a pattern of bond length changes consistent with the formation of a quinoidal structure was predicted by molecular-orbital calculations. This suggests that the electron delocalisation occurs over the entire molecule. The resonance Raman spectrum of the cation monoradical exhibits bands which may be assigned to the thiophenic portion, which suggests that this portion is associated with the chromophore. IR spectroscopic investigations into the electrogenerated radical of N,N'-diheptyl 4,4' - pyridinium, which has been investigated as the coloured component of electrochromic displays, were performed. The reflectance IR spectra of the radical monocations were obtained through bulk-sampling potential subtraction (PS) and surface-selective polarisation modulation (PM) techniques. The comparison between PS and PM spectra of the radical generated as a solid film in an aqueous medium, with the PS spectrum of the radical generated in acetonitrile revealed differences. These were interpreted in terms of an equilibrium between monomeric and aggregated forms of the radical. Similar results were obtained for the related compounds, methyl viologen and its dicyano substituted salt. The simplicity in the pattern of bands in the PS IR spectra of the monomeric radicals of methyl- and dicyanomethyl viologens was investigated by calculating the IR spectra of the dications and cation radicals of these compounds by molecular orbital techniques. The intense spectral features could be interpreted in terms of a charge-oscillation of the radical electron across the pyridine rings. The dipole moment of such modes is large and leads to the enhancement of these modes. The effect of various counterions associated with heptyl viologen was investigated by Raman and IR techniques. The pattern of bands in the Raman spectrum exhibited little variation with differing the counterions. The PS IR spectra exhibited disappearance features associated with the counterion in contrast to the PM spectra where no such bands were observed. PS IR spectra were also obtained by synchronising data acquisition with potential sweeps. The intensity of disappearance features in the PS IR spectra attributable to the CH modes varied at a similar rats to bands assigned to the radical aggregate. This suggested that a reorientation of the dipyridine ring and the quaternising alkyl chain probably occurs on reduction to form the radical. The lack of reversibility associated with the degradation of viologen films was investigated by PS IR techniques. The effect is probably associated with changes in the composition of the solid rather than a change in the concentrations of the monomeric and aggregated forms of the viologen radical. Dialkyl bridged diquaternary compounds of 2,2'-dipyridine were investigated by IR and theoretical techniques. The observation that the calculated dihedral angles for the dications and cation radicals were similar allowed the trends in the electronic absorption maxima (ultra-violet) and electrode potentials to be interpreted. Selective enhancements of bands in the PS IR spectra of the radicals suggest that a charge-oscillation mechanism may also be operative in these compounds. The utility of a combination of structural, theoretical and vibrational spectroscopic studies is demonstrated in these studies.

Introduction: General. The family Solanaceae, to which the Solanurn genus belongs, is comprised of some 70 genera and approximately 2000 species. Its members, which are herbs, erect or climbing shrubs and, occasionally, small trees, are distributed in the tropical and extend to the temperate regions, the greatest concentration being in Central and Southern America. The family's chief point of interest chemically is the fact that many of its members contain alkaloids, well known examples being Atropa belladonna (containing atropine), Datura strammonium(daturine), Nicotiana tobacum (nicotine), and Solmum tuberosum (solanine). The Solanum (Latin - solamen, solace or quieting) genus is made up of some 1,200 species, three of which, S. tuberosum (potato), S. lycopersicum = Lycopersicum esculentum Mill. ( tomato), and S . nigrum (a common weed of cultivation), are especially well known. New Zealand has one endemic species, namely S. aviculare Forst. Agriculturally, mainly because of S. tuberosum and S. lycopersicum, the genus is of course an important one but in addition several species are used in horticulture, e.g. S. pseudocapsicum and S. macrmthum, and a few species, e.g. S. mammosum and S. dulcamara, are reported as being of medicinal value. Chemically it is unique, in that may species contain glycosidic steroidal alkaloids and most attention has been devoted to the characterisation of these substances, although various other constituents, e.g. commarins and anthocyanins, have been reported.

This study concerns the synthesis, structure and reactivity of complexes of d⁶ and d⁸ osmium. The reactivity of certain ligands coordinated to low-valent osmium has also been investigated. Various hydride complexes of osmium(II) were prepared as potential precursors of osmium(O). OsH₄(PPh₃)₃ reacts with p-tolylisocyanide (TIC) and 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (ETPO) to yield OsH₂(L)(PPh₃)₃ from which were derived OsH₂(L’)(L)(PPh₃)₂ (L, L’=CO, TIC, ETPO). Attempts to eliminate hydrogen from the dihydrides failed. OsHCl(CO) (PPh₃)₃ reacts with neutral ligands L (=TIC, ETPO, P(OMe)₃, P(OPh)₃, PPh₂Me) to give OsHCl(CO)(L)(PPh₃)₂ which, with silver perchlorate (L=TIC, ETPO only) afford OsH(OClO₃)(CO)(L)(PPh₃)₂. The labile perchlorate ligand can be replaced by ligands L’ affording [OsH(CO)(L)(L’)(PPh₃)₂]ClO4 (L=TIC, L’=CO, TIC, PPh₃ L=ETPO, L’=CO, ETPO). OsHCl(CO)(PPh₃)₃ reacts with silver perchlorate in acetonitrile to yield [OsH(CO)(CH N)₂(PPh₃)₂]ClO4, which in turn reacts with neutral ligands to give [OsH(CO)(CH₃N)(L)(PPh₃)₂]ClO₄ (L=CO, TIC, ETPO, PPh₃). Cationic [OsH(CO)₂(PPh₃)₃]+ and [OsH(TIC)₂(PPh₃)₃]+ can be prepared from the action of PPh₃ on [OsH(CO)₂(CH₃N)(PPh₃)₂]+ and TIC on OsH(O₂CCH₃)(PPh₃)₃ respectively. With base, [OsH(CO)(CH₃N)(PPh₃)₃]ClO4 affords OsH(OH)(CO)(PPh₃)₃ from which a series of hydroxide complexes OsH(OH)(CO)(L)(PPh₃)₂ (L=CO, TIC ETPO) can be obtained. The hydroxide group in OsH(OH)(CO)(PPh₃)₃ is cleaved by acids HX to yield OsHX(CO)(PPh₃)₃ (X=F, Br, Cl, I, CH₂, CF₂, SC₇H₇, OClO₃). Those members of the series with X=CN, N₃, OCN, SCN were obtained from OsH(OClO₃)(CO)(PPh₃)₃ and the appropriate anion. From the values of vCO for this series can be gained some understanding of the bonding properties of the anionic ligands.

Chapter One begins with an introduction to enzymology and leads into a discussion on BSSL beginning with the physical properties and the source of the enzyme. The literature concerning the kinetic properties of BSSL is reviewed, followed by a discussion on how the structure of enzymes influences their catalytic activity and specificity. The use of X-ray crystallographic techniques is addressed as a means of elucidating the three dimensional structure of enzymes. The chemicals, apparatus and standard methodologies used in this present investigation are described in Chapter Two. The means by which kinetic data measured for an enzyme-substrate system are analysed and compared are also discussed. Chapter Three describes the purification of bile salt-stimulated human milk lipase (BSSL) from whole human milk. A detailed study of the activity of the purified protein has been conducted against both lipid and ester substrates in order to monitor the progress of the purification. A further determination of the physical properties of the protein has also been conducted. Results from these studies have identified the protein as BSSL. In Chapter Four the methods used for determining the partial amino acid sequence of the enzyme are described. This study has revealed interesting homologies with enzymes from other species. The sequence of that part of the enzyme which includes the active site has been determined and has been found to be identical to the consensus sequence found in the active site of pancreatic lipase, serine proteases and cholinesterases. It may therefore be postulated that the similarity observed for some of the kinetic behaviour of enzymes arises from homology in their amino acid sequences and, in particular, those portions of the protein comprising the active site. The use of kinetic isotope effects, to gain insight as to the mechanism of BSSL catalysed hydrolysis of lipid substrates, is the subject of Chapter Five. A mechanism has been proposed which explains the observed effects and takes into account information from the literature. The mechanism also incorporates findings made from the amino acid sequence study and the literature reports on the residues involved in catalysis. Chapter Six begins within a literature survey of detergent less microemulsions and continues with an account of the kinetic properties of BSSL in this new and novel medium in which enzymic reactions involving substrates of low water solubility may be conducted. The advantage of this medium is that it allows one to monitor the reaction by spectrophotometric means. In more traditional methods of assay of lipid substrates this is not normally possible. This advantage has also been exploited in the study of the kinetics of BSSL against triolein in reversed micelles, which is the subject of Chapter Seven. A detailed description is given of an FT-IR technique which allows one to monitor the course of reaction of biologically important substrates.

A wide range of compounds elicit the sweet taste response but currently it is not known what causes this response. In Chapter 3 a number of sweeteners, and representatives of all the taste groups are investigated using NMR spectroscopy. The T1 relaxation times of the tastants were determined in aqueous solution and in solution with liposomes, a model membrane system. The observed changes in T1, values are analysed to determine which regions of the tastants are involved in the interaction with the membrane. In Chapters 4 and 5 an investigation is reported of the interaction of tastants with a liquid membrane system, which is reportedly able to distinguish between classes of chemicals. The interest lies in developing a simple experiment that will enable taste qualities to be predicted, something that is currently not possible. In Chapters 6 and 7 the NMR assignments of some sweeteners is discussed. NMR assignments are a necessary precursor before their sweetening properties can be studied by NMR.

Despite the vast amount of research reported on the acid-catalysed hydrolysis of amides, the mechanism of reaction has remained a source of controversy. The various literature results have been summarised in the introduction. Two series of amides have been studied in this investigation, one a series of N-substituted, 4-chlorobenzamides, the other a series of substituted acetanilides. Their basicity (or acid-dissociation) constants have been evaluated in sulphuric acid, and the rates of hydrolysis measured over a wide range of acid concentrations. Within each series, variation of the substituent causes the rate constant to vary in a way which is typical of a bimolecular reaction involving rate-determining nucleophilic attack of water on the protonated intermediate. By drawing a comparison between the two series of amides, (i.e. the difference in basicities and rates of hydrolysis) it becomes apparent that the 0-protonated amide, which is thermodynamically favoured, is not the kinetically active species, A new rate equation is proposed, the equation being based on a mechanism in which water attacks the carbonyl carbon in the rate-determining step. The equation confidently predicts the experimental rate-profiles for the acid-hydrolysis of simple amides. It has been applied, in two forms, to the experimental rate data; the first form allows for the involvement of three water molecules in the slow step of hydrolysis, and the second form allows for the involvement of only two water molecules. The rate equation, in these two forms, has also been applied to much of the hydrolysis data reported in the literature and again it has proved to be very successful. In contrast to the amides, ureas have not been subjected to extensive research. In this investigation, the basicity constants of a series of substituted phenylureas have been measured, (if not already available) and the hydrolysis reactions carried out over a wide range of sulphuric acid concentrations, as well as in water. The 4-methyl and 4-chloro-phenylureas have also been hydrolysed in a range of hydrochloric and perchloric acid solutions; the effects of added salt were studied and the solvent isotope effects on the rate were evaluated. All these results, together with information obtained from application of the Hammett equation to the rate data, were in agreement with a mechanism involving a pre-equilibrium protonation to form the minor, N-protonated conjugate acid. This is followed by a slow transfer of the proton attached to the alternate nitrogen atom to form the appropriately substituted phenylisocyanate, and rapid reaction of this intermediate to form products. The substituent effects on the n.m.r. spectra of the substituted acetanilides and phenylureas have also been reported.

This work contains some fundamental investigations on Triton X series nonionic surfactants from different aspects. Techniques, such as viscometry, densimetry, diffusion measurement, ultra-violet spectrophotometry, differential scanning calorimetry, surface tension measurement and optical microscopy were employed to acquire the information. Some theoretical analyses were given to the results of these measurements. Triton X surfactants show different properties when they dissolve in different solvents. Aggregation can occur in some solvents, depending on the interactions between solvent and solute. The addition of a surfactant to a solvent will give rise to a solute-solvent interaction and change the solute-solute and solvent-solvent interactions as well. From mass transport properties of the surfactant solutions, these interactions were studied and the contributions to them from each species of the solutions were calculated with a transition-state theory model which is usually used for small molecule systems. Under some reasonable assumptions, a new theoretical method was set up and was able to give a reasonable explanation for the experimental results. The surfactants can also associate with some dyes in both polar and apolar media. The ultra-violet spectra of the surfactant-dye solutions show that surfactant-dye complexes might be formed in the polar and apolar media where the surfactants form regular and reversed micelles respectively. The mechanism of the complexation reactions was studied with equilibrium theory and the charge-transfer nature of the association between the surfactant and dye revealed. The surface tension and. cloud point changes due to the addition of polyethylene glycol were determined to discover the interaction between the water-soluble polymer PEG and the surfactants at the air-solution interface and in the bulk solutions respectively. The mass distribution of the two materials between the two phases produced in the segregation (at the cloud point) of the solutions were determined by their ultra-violet adsorption spectra and densities. The analysis of the cloud point changes was given with the new concepts of polysoap and depletion flocculation. The results show that the size of the micelles, the length of the polymer chains, and the structures of the intra - chain micelles can change the mechanisms of polymer-surfactant interaction and influence the properties of the polymer/surfactant solutions. In a certain range of concentrations, the surfactants aqueous solutions can form liquid crystalline structures which can be observed under a cross-polarised microscope and determined by differential scanning calorimetry. The phase diagrams and their variations with additions of the third component, such as xylene, polyethylene glycol and BaCl2 2H2O have been determined. The effects of temperature and each of the additives on the ordered structures were analysed separately in the light of concepts of spontaneous mean curvature and "salting out" effect. Osmotic coefficients of the surfactant aqueous and methanol solutions were determined with a vapour pressure osmometer, and the activity coefficient of the solvent can be calculated with the osmotic coefficients. The change of the activity coefficient with increase of surfactant concentration shows the interactions of the surfactant with the solvent. In aqueous solution, the addition of surfactant frees the solvent molecules, leading to an activity coefficient larger than 1. In methanol solution, the surfactant addition reduces the fugacity of methanol molecules, resulting in an activity coefficient less than 1. Chemical shift changes of protons of the surfactant molecules in the lH NMR spectra show some information about the configuration of the chains, hydration, and phase structure of the solution system when the surfactant concentration changes over the whole concentration range. From 40% w/w the associated water molecules begin to be lost, and the association number ratio of water molecules and the ethylene oxide unit of the surfactant is 4:1. Electric conductance of electrolytes in the surfactant aqueous solutions are reduced by the addition of the surfactants. The reduction is more significant for large size cations, and the longer the EO chain of the surfactant, the larger the reducing effect on conductance.