Browsing by Subject "Physical Chemistry"

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    Computer modelling of the chemical speciation in seawater
    (1990) Van der Meulen, Karen; Linder, Peter W; Jackson, Graham Ellis
    The primary aim of this thesis is to establish a computer model of the chemical elements in seawater and to use this model to gain insight into the chemical processes controlling dissolution, precipitation, redox levels and coordinative interactions in surface seawater. In order to accomplish this task a relatively extensive database consisting of about 580 complexation equilibria arising from 32 inorganic and 10 organic components has been set up. Constants have been selected from critical compilations. Included in these equilibria are solubility products for the formation of potential solids, redox reactions and interactions with the atmospheric gases carbon dioxide and oxygen.
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    Computer simulation of metal-ion equilibria in biochemical systems : models for blood plasma
    (1976) May, Peter Michael; Linder, P W
    This thesis describes an investigation, by computer simulation, into the nature of the metal ion binding to low molecular weight ligands in blood plasma. A successful attempt is made to accommodate the effects of metal protein binding on the computed distribution that is obtained. An evaluation of the results is undertaken. The value and some applications of the knowledge arising from this kind of study are examined. The collection, assembly and processing of the data is described. A computer program is written to cope with the very large equilibrium systems that are simulated. The experimentally determined values for the formation constants of the metal ion ligand complexing reactions in the biofluid are found in the literature. These are corrected whenever they are not applicable to physiological conditions of temperature and ionic strength. Where no experimental values were available, formation constants for complexes that seemed likely to be important were estimated using certain types of chemical trend. The results of the blood plasma model may be summarized as follows. Copper and ferric iron are found to exist exclusively as ternary complexes except that the copper dihistidinato complex is important. With copper, these ternary complexes always involve histidine whilst citrate plays an analogous role in the ferric complex formation. Calcium, magnesium and manganese do not appear to exist as ternary complexes. With these three cations the bicarbonate species predominate although the binding is weak; as a consequence of the relatively high ligand concentration in plasma. Zinc and lead form both binary and ternary complexes. The ternary zinc cysteinate citrate complex is found to account for a significant percentage of the low molecular weight complex fraction of this metal. This result is in contrast to those of previous models.
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    Physico-chemical studies of solutions of some acids in acetone
    (1964) Sadie, Francois Gustaves du Bois; Spong, A H; Hotz, M C B
    The work of Hotz showed the lack of knowledge of the behaviour of electrolytes in acetone solutions as well as the uncertainty as to the possibility of preparing anhydrous acetone and the stability of this solvent, if it could be prepared. An extensive study was therefore undertaken in which the efficiency of various desiccants was studied in producing acetone as anhydrous as could be obtained. A very efficient still was designed and the average water content of the acetone produced was of the order of 0.006 per cent which is much lower than reported by any previous investigator. Moisture determinations were done using a modified Karl Fischer reagent.
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    Scientific aspects of urolithiasis : quantitative stone analyses and crystallization experiments
    (1986) Wandt, Michael Alexander Erich; Rodgers, Allen L
    This thesis describes two aspects of the various scientific approaches to the study of urolithiasis. In the first instance, the theory, development and results of three quantitative analytical procedures are described while in the second, crystallization experiments in a rotary evaporator are presented. Of the different methods of quantitative X-ray powder diffraction analyses, the 'internal standard method' and a microanalytical technique were identified as being potentially the two most useful procedures for the quantitative analysis of urinary calculi. 'Reference intensity ratios' for 6 major stone phases were determined and were used in the analysis of 20 calculi by the 'internal standard method'. It is concluded that the attainment of accurate results using this procedure is not easily achieved because of problems such as the unavailability of standards which realistically mimic stone composition, sample preparation, overlap of reflections from sample components and standards and the requirement of 'infinitely thick' specimens ( > 250 mg). For the microanalytical technique, micro-quantities of 10 calculi from the original 20 were deposited on silver filters and were quantitatively analysed using both, the attenuation of the Ag peak and the separately measured absorption coefficients μ*· Inductively coupled plasma atomic emission spectroscopic (ICP-AES) methods were also investigated, developed and used in this study. Various procedures for the digestion of calculi were tested and a mixture of HNO₃ and HClO₄ was eventually found to be the most successful. The major elements Ca, Mg, and Pin 41 calculi were-determined. For the determination of trace elements, a new microwave-assisted digestion procedure was developed and used for the digestion of 100 calculi. Thereafter the major elements Ca, Mg and P together with the minor and trace elements Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn in all 100 stones were simultaneously determined. The data so obtained were subjected to 3 types of statistical analyses involving direct correlations, scatter plots and a relatively new multivariate analysis of logarithmic data known as a 'covariance biplot'. Several interesting correlations were obtained. Fluoride concentrations in two stone collections - 20 calculi from India and 42 from South Africa - were determined using a fluoride-ion sensitive electrode and the HNO₃/HClO₄ digestion procedure used for the ICP study. Direct measurement of fluoride proved unsuccessful thereby necessitating the investigation and development of a diffusion technique. Using this method the fluoride content of both collections was determined. A series of crystallization experiments involving a standard reference artificial urine was carried out in a rotary evaporator. The effect of pH and urine composition was studied by varying the former and by including certain components (uric acid, urea, creatinine, MgO, methylene blue, chondroitin sulphate A, fluoride) in the reference solution. Crystals formed in these experiments were subjected to qualitative and semi-quantitative X-ray powder diffraction analyses. Scanning electron microscopy of several deposits was also carried out. Similar deposits to those observed in calculi were obtained with the fast evaporator. The results presented suggest that this system provides a simple, yet very useful means for studying the crystallization characteristics of urine solutions. The quantitative analytical procedures described in detail in this thesis can serve as model techniques for other workers involved in stone research. Together with other approaches such as the crystallization experiments discussed, these procedures can lead to a better understanding of the aetiological processes which govern stone formation.
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    Solution equilibria of the methyldopacopper (II) system and the crystal and molecular structures of selected compounds
    (1979) Wright, Martin Robert William; Linder, P W; Nassimbeni, Luigi R
    The contents of this thesis are essentially in two parts. The first deals with solution studies relating to the methyldopa-copper(II) system and its relevance to medicinal chemistry, a full abstract of which is given on page 1 of the main text. The second part describes five single crystal x-ray investigations into some interesting compounds isolated at this university. The abstracts to these topics may be found preceding the relevant sections as they appear in the text on pages 94, 118 and 146, respectively.
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    Structure-activity relationships in Werner clathrates
    (1987) Moore, Madeleine Henrietta; Nassimbeni, Luigi R
    The synthesis and characterization of a series of inorganic coordination compounds which, upon crystallization, have the ability to include solvent or guest molecules spatially within the lattice are reported. The compounds have the following general formula: [NiX2B4] - where X is isothiocyanate or bromine and B is 4-ethylpyridine, 4-vinylpiridine or 3,5-dimethylpyridine; [NiX2B2]n - where X is isothiocyanate, B is 2-aminopyridine and n indicates it is a polymer; [NiX2AB2]2 - where X is isothiocyanate, B is 3-aminopyridine (two of these four ligands in the dimer are bridging) and A is water. The various guest molecules have been carefully chosen, according to their point symmetry, which is a key factor in yielding structures of a particular type. The structures of seventeen compounds have been elucidated by single crystal x-ray analysis. The difficulty has been found to lie in refining disordered guest molecules. Other techniques employed in the initial characterization of these compounds are Microanalysis, Mass Spectrometry and UV/Visible Spectrophotometry. An intramolecular potential energy study on the [Ni(NCS)2(3,5-diMepy)4] complex reveals that the orthohydrogens on the 3,5-dimethylpyridine ligands control the conformation of the molecule. Packing densities and volume comparisons of the [Ni(NCS)2(4-Etpy)4] and [Ni(NCS)2(4-Vipy)4] complexes and their clathrates have been carried out. The exact sizes and shapes of the cavities in which the guest molecules are located in the x-ray crystal structures have been evaluated by both intermolecular potential energy and molecular volume calculations. Thermodynamic and spectroscopic properties of the [Ni(NCS)2(4-Etpy)4] and [Ni(NCS)2(4-Vipy)4] clathrates have been studied in both solution and the solid state. The techniques used are x-ray powder diffractometry, IR spectroscopy and Thermogravimetry (including Differential Thermal Analysis).
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    A structure-reactivity study of selected phosphate esters
    (1985) Bond, Dianne Ruth; Nassimbeni, Luigi R
    A comparative X-ray analysis study of bis(4-nitrophenyl)-8-quinolinyl phosphate (4), 1-naphthyl-bis(4-nitrophenyl) phosphate (5) and 4-nitrophenyl -8-quinolinyl phosphate (5) was undertaken. In compound (4) donor-acceptor nitrogen-phosphorus interactions change the geometry of the molecule from tetrahedral to quasi trigonal bipyramidal, thus the structure may be considered as an "early stage" of the intramolecular displacement of the 4-ni trophenoxide group. In the diester (6) this interaction is replaced by intermolecular N+ -H...O- hydrogen bonding. In addition the intramolecular non-bonded potential energies of (4) and (5) were calculated and the minimum-energy conformations were compared with those determined by X-ray diffraction. These results confirm the differences observed in the intramolecular interactions operative in (4) and (5). The mass spectra of (4) and (5) are dramatically different with respect to the fragmentation involving expulsion of the 4-nitrophenoxy radical and formation of the corresponding phosphorylitum ion by nitrogen participation. Rate measurements for the base-catalysed hydrolysis of the first P-OPNP linkage show that (4) is not significantly more reactive than (5) and provide no evidence for intramolecular nucleophilic catalysis in the hydrolysis of (4). The crystal and molecular structure of 1-naphthyl acetate (7) was determined. Attempts to grow suitable crystals of 8-quinolinyl acetate (8) failed and therefore its structure could not be elucidated. Possible intramolecular nitrogen - carbonyl carbon interactions operative in (8) could therefore not be established.
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    Structures of Werner clathrates
    (1989) Taylor, Michael William; Nassimbeni, Luigi R
    This work is predominantly devoted to the 4-phenylpyridine ligand and the role that it plays in the formation of a series of inorganic coordination complexes termed Werner Clathrates. The synthesis and characterization by single crystal X-ray diffraction techniques are reported for 18 structures, the majority of which, upon crystallization, have the ability to include solvent or guest molecules within the host framework. The compounds are divided into four broad classes with the host complex of each as follows: Class A [Ni(NCS)₂(4-PhPy)₄]; Class B [NiCl₂(4-PhPy)₄]; Class c [Ni(NCS)₂(4-MePy)₂(4-PhPy)₂]; Class D [NiX₂(dmso)₂(4-PhPy)₂] where X= Ncs- or Cland [Ni(NCS)₂(4-RPy)₄] where R = 4-t-Bu or 4-Bz. The guest molecules, anionic ligand and substituent on the pyridine ligand have all been varied to try to establish the role that they each play in the formation of a structure. Much effort has been spent on the location and refinement of disordered guest molecules. Use has been made of statistical disorder and molecular scattering factors to try and successfully model these guests. The shapes of the cavities containing the guest molecules have been mapped by volume calculations and comparisons made between the packing of the compounds. Several of the complexes pack in space groups which are subsets of others and attempts have been made to determine the cause of the reduction in symmetry. A new technique to analyze competition experiments, with two guest solvents competing for occupation of the voids within the host lattice, has been established. Preliminary results for competition between p-xylene/benzene, p-xylene/toluene and p-xylene/ethylbenzene with the host complex [Ni(NCS)₂(4-ViPy)₄] are reported. The ability of the host complex [Ni(NCS)₂(4-MePy)₂(4-PhPy)₂] to separate a series of straight chain alcohols is demonstrated. The preference, by this host complex, for guest molecules containing a linear skeleton of 5 non-hydrogen atoms, is explained in terms of potential energy and residual volume calculations. Thermal analysis, consisting of thermogravimetry and differential thermal analysis, has been performed on several of the compounds. Temperatures of guest release, host decomposition and the enthalpies involved at each of these steps are reported.
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    A study of liquid clathrates
    (1987) Joao, Heidi Caroline; Nassimbeni, Luigi R; Bond, D
    Use was made of Nuclear Overhauser effects (nOe) and crystallography to determine the structure and packing in novel liquid clathrate systems. The stoicheiometry of the clathrates was investigated by various chemical methods including: thermogravimetric analysis, differential thermal analysis and proton nuclear magnetic resonance spectroscopy.
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    A study of secondary bonding effects in Werner clathrates
    (1988) Suckling, Adrian Philip; Nassimbeni, Luigi R; Niven, Margaret Lilian
    The crystal structures of Ni(NCS)₂(4-ViPy)₂.nG where nG = 2CH₂Cl₂ (I), 2CCl₄ (II), 1.8CH₂I₂ (III) and CHI₃ (IV), as well as the crystal structure of [Ni(NCS)₂(4-ViPy)₄]. [Ni(NCS)₂(4-ViPy)₃(thf)].2CHI₃ (V) have been elucidated. The diiodomethane guest molecules in STRUCTURE III were severely disordered at room temperature and so this structure was solved at -40°C. The dichloromethane clathrate is isomorphous with the chloroform clathrate of the same host, and both these clathrates have a similar packing to the carbon tetrachloride clathrate. There is significant secondary bonding between the sulphur (donor) of the isothiocyanate ligand of the host and the iodines (acceptor) of the halogenated guest molecules in compounds III, IV and V. The iodoform clathrates, compounds IV and V, also show strong similarities in their packings. Particular attention has been paid to the shape and size of the cavities in which the guest molecules find themselves, in order to gain a better understanding of the nature of these clathrates. This has also shed some light on the probable cause of the disordered diiodomethane molecules in STRUCTURE III. Packing densities and volume comparisons of the [Ni(NCS)₂(4-ViPy)₂] clathrates have been carried out. Solid - state U.V/visible spectroscopy was used to obtain information on the host conformation, and thermal analysis (thermogravimatry and differential thermal analysis) was used to obtain insight into the host - guest interactions of these clathrates.