No description available.

No description available.

No description available.

The molecular structures of two polynuclear aromatic hydrocarbons, biphenylene and coronene, have been refined from new three-dimensional data. The positional and thermal parameters of the carbon and hydrogen atoms were refined by least squares and the gross features of the structures, previously determined, were confirmed. The anisotropic thermal parameters of the carbon atoms were interpreted in terms of rigid-body vibrations, and the measured carbon-carbon bond lengths were then corrected for rotational oscillation effects. The bond lengths for biphenylene reinforce the conclusion that the molecule must be considered as a cyclobutane derivative. The bonds joining the six-membered rings measure 1.514 ± 0.003Å, and the bonds in the six-membered rings, starting with the bond in the four-membered ring, are 1.426 + 0.003Å, 1.372 ± 0.002Å, 1.423 ± 0.003Å, and 1.385 ± 0.004Å. The molecule situated at a centre of symmetry is planar, the other molecule is slightly non-planar as a result of crystal packing forces. All intermolecular contacts correspond to normal van der Waals interactions. For coronene, the bond lengths measure 1.425 ± 0.004Å in the centre ring, 1.433 ± 0.004Å for the "spokes", 1.346 ± 0.005Å and 1.415 ± 0.003Å for the two types of outer bond. Only the shortest bonds (1.346Å) are significantly less than the theoretical values predicted by valence-bond and molecular-orbital calculations and, since this discrepancy is observed also for all other polynuclear aromatic hydrocarbons for which accurate bond distances are available, an amended order/length correlation curve is suggested which improves the agreement between theory and experiment for these shorter bonds. Small, but significant, deviations from planarity, which reduce the molecular symmetry from 6/mmm to 3, may be a result of either intra- or inter-molecular forces. All intermolecular separations correspond to van der Waals interactions; the perpendicular distance between the molecular planes is 3.46Å. The crystal and molecular structure of the hydroiodide of 1,2-0-aminoisopropylidene-∝-D-glucopyranose has been determined. The iodine position was located by Patterson methods, and all carbon, nitrogen and oxygen atoms were found on successive three-dimensional electron-density distributions. The positional and isotropic thermal parameters of the seventeen I, C, N, O, atoms in the asymmetric unit were refined by least squares. The configuration of the asymmetric dioxolane 2-car-bon atom was determined and the absolute configuration is established since the compound is derived from V-glucose. The five-membered ring has an envelope conformation with C(7) displaced from the plane of the other four atoms, and the pyranose ring has a twisted chair conformation. The bond distances and valency angles are normal. The crystal is held together by a system of O-H...O, N-H...O, and O-H...I hydrogen bonds. To investigate the structure of an intermediate in an attempted removal of the 14∝-methyl group of 3-β-acetoxylanost-8-ene, the structure of the dibromo derivative of the intermediate has been determined by X-ray analysis. The bromine positions were determined by Patterson methods and all carbon and oxygen atoms were located on successive three-dimensional electron-density distributions. Positional and anisotropic temperature parameters were refined by least squares. The absolute configuration was determined by the anomalous dispersion method. The derivative is 3-β-acetoxy-7∝,11∝-dibromolanostane-8∝,9∝-epoxide. Steroid ring A is in the normal chair form and ring D has a half-chair conformation. The epoxide prevents rings B and C from adopting the chair form. The bond lengths and valency angles are normal, and the intermolecular separations correspond to van der Waals interactions. / Science, Faculty of / Chemistry, Department of / Graduate

Analysis of the sulfur dioxide long wavelength band, appearing in n-ROH or benzene and carbontetrachloride solutions, has been obtained in terms of the system:- donor + SO₂ ⇌ complex The characteristic constants for the MeOH , EtOH , n-PrOH, n-BuOH and benzene complexes and the heat of formation of the benzene and ethanol complexes with sulfur dioxide in carbontetrachloride have been estimated. Structures for the n-ROR – SO₂ complexes have been proposed along the lines of Mulliken's simple charge transfer theory. It has been shown that the spectroscopic behaviour of sulfur dioxide in mixed benzene - ethanol solutions is adequately explained in terms of the binary donor system:- benzene + SO₂ ⇌ (complex)₁ ethanol + SO₂ ⇌ (complex)₂ if it is assumed that the characteristic constants for both complexes and the molar extinction curve of free sulfur dioxide remains unchanged in passing from non - polar to polar solvents. From a similar analysis of the new band appearing in hydroquinone - sulfur dioxide - ethanol solutions, the characteristic constants and heat of formation of the hydroquinone - sulfur dioxide complex have been obtained. The value for the heat of formation of this complex is in good agreement with the reported value of the heat of decomposition of the hydroquinone - sulfur dioxide clathrate compound. This fact, together with the evidence of the binary donor character of the ethanol - benzene - sulfur dioxide system is strong evidence in favour of the proposed theory of the formation of liquid lattice penetration complexes (by penetration of the liquid lattice by sulfur dioxide). From studies of the temperature dependence of the long wavelength band in sulfur dioxide - water solutions, it has been concluded that neither Ley and Konig nor Boyd Campbell and Maass’ theories adequately describe the behaviour of the sulfur dioxide - water system. A new theory has been proposed which qualitively describes the behaviour of this system. However, attempts to obtain values for the constants involved from the absorption spectra of water-ethanol-sulfur dioxide solutions, have been unsuccessful. This has been attributed to the simultaneous formation of ethanol - water interpenetration complexes (water penetrating the ethanol lattice). / Science, Faculty of / Chemistry, Department of / Graduate

Molecular "Darwinian" selection is initially defined as the generation of a variant molecule, within a population of self-replicating molecules, that becomes the predominant molecular form in descendent populations by virtue of its replicative superiority. The molecular biology of the replication of Qβ in vivo is presented prior to providing evidence for molecular "Darwinian" selection of Qβ-RNA in vitro. Critical experiments undertaken to prove that Qβ—replicase is capable of catalyzing the synthesis of molecular replicas of primer Qβ-RNA in vitro are described. This information is followed by a description of the experiments utilized to demonstrate the occurrence of molecular "Darwinian" selection of Qβ-RNA under different selective environments. Molecular and phenotypic properties of mutant RNA molecules are discussed. After an account of the expectations of molecular "Darwinian" selection in vivo: suppressitivity, gross alterations of DNA base composition in microorganisms' and the von Magnus effect are presented as evidence for molecular "Darwinian" selection in vivo. Suppressive respiratory-deficiency in Saccharomyces cerevisiae is taken as a model system for the investigation of suppressitivity. A literature review of the data generated by genetic and cytological analyses of suppressitivity was found to be accommodated by the hypothesis of molecular "Darwinian" selection in vivo. In addition, the author's genetic analyses of: (i) mosaic colonies, (ii) the effect of the cytoplasmically-inherited suppressive-factor on a cytoplasmically-inherited erythromycin-resistant marker, and (iii) high and low suppressitivity, were interpreted as evidence for the hypothesis. Biochemical evidence is presented that indicates that the suppressive-factor is an abnormal mitochondrial DNA with a replicative superiority to normal mitochondrial DNA. A brief discussion of the possible influence of molecular "Darwinian" selection on pre and post cellular evolution is presented. / Science, Faculty of / Botany, Department of / Graduate

The electronic emission spectra of the OH and CH molecules in applied electric fields up to 68,000 v/cm have been observed. These spectra show Stark splittings, broadenings and field-induced, parity-forbidden lines. The electric dipole moment of the molecules has been determined for OH in the ²π electronic state and CH in both the ²π and ²∆ electronic states from Stark effects on transitions to the following levels: [formula omitted] Electric fields were determined from Stark splittings in hydrogen Balmer lines. The Stark spectra were produced in the high field region of a low pressure glow discharge. This technique is well suited for the study of short lived and chemically reactive molecules in both their ground and excited, electronic states. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Cell adhesion molecules enhance Interactions between adjacent cells In order to mediate a large variety of functions of the Immune system. An antibody against the murine lymphocyte surface antigen MALA-2 has previously been shown to Inhibit mixed lymphocyte response. A λgt10 cDNA library from NS-1 cells was screened and a cDNA clone, K3-1.1, was previously isolated. It had significant homology to the human ICAM-1 gene. This thesis covers the isolation of a second cDNA clone, K4-1.1, and its comparison to K3-1.1 In terms of expression, function and distribution. The two clones are identical in sequence with the exception of the 5’ ends. Expression of these two clones was examined using a transient expression system of COS cell transfection. Cell surface expression of the K3-1.1 clone could not be detected by FACS analysis. Even when the 5' untranslated region of the K3-1.1 clone (which has 10 potential translation start sites) was removed, protein could not be detected at the cell surface, intracellularly, or extracellularly. However, K4-1.1 expression was detected at the cell surface. Northern blot analysis reveals that there are two distinct messages which are likely to be represented by the two clones. When the northern blot was probed with the 5' end of the K3-1.1 clone, only one of the messages was detected. This together with the result of Southern blot analysis suggests that the two messages are likely the result of alternate splicing. In order to examine the interactions of the murine ICAM-1 with the surface of other cells, an expression system which would produce large amounts of a secreted soluble form was established. The soluble protein was purified from the supernatant of transfected cells by an antibody-affinity column and used in preliminary binding assays. / Medicine, Faculty of / Medical Genetics, Department of / Graduate

No description available.

We present results for the solid-fluid phase equilibrium for molecular models of chain molecules using Monte Carlo computer simulation and cell theory. We were concerned primarily with the role of molecular shape and flexibility on the solid-fluid phase equilibrium. We have considered models with different intramolecular potentials to examine the effect this has on the phase diagram. Extensive calculations of the fluid and solid phase equations of state have been made and solid phase free energies have also been determined. Our results for the fluid properties are compared with various theoretical equations of state which have been proposed for these systems. A method for calculating the solid phase free energy of chain molecules has been developed based on finding a reversible path to an Einstein crystal. For models of freely jointed chains of tangent hard spheres, the dependence of the solid phase thermodynamics upon the chain conformation has been studied and solid-fluid phase diagrams for chains with lengths ranging from three through eight atoms have been determined. In the case of models of flexible united atom chains, solid-fluid phase diagrams for chains with lengths ranging from four to eight atoms have been determined for three different torsional potentials. The data for flexible united atom chain models have been used as reference systems in a generalized van der Waals or mean field calculation of the n-alkane phase diagrams. This theory reproduces trends in the triple point temperature seen in experimental data. These trends are interpreted in terms of the changes in the close packed densities of the solids with chain length and the effect of the torsional energy on the relative stability of the fluid and solid phases. A cell theory was developed that was applicable to the flexible hard sphere site united atom model. The theory was in good agreement with the Monte Carlo simulations. Finally the phase diagram of a flexible united atom model mixture was determined. The model phase diagram showed that a solid-solid mixture phase coexistence can occur in these systems. However the method for calculating [special characters omitted] a required quantity was not accurate enough to definitively calculate the phase diagram. The data showed clear overall trends that the value of [special characters omitted] at constant pressure decreased with increasing mole fraction and that as the pressure increased the slope of [special characters omitted] versus mole fraction increased. These trends were present for the two different system sizes considered.