Pentachloronitrobenzene (PCNB) is an organochlorine fungicide used either as seed dressing or for soil treatment. Research was conducted to investigate the microbial reductive transformation of PCNB with cultures developed from a contaminated estuarine sediment. The biotransformation of PCNB to pentachloroaniline (PCA) occurred under all electron accepting conditions tested. Sequential dechlorination of PCA to di- and in some cases to mono-chlorinated anilines occurred under fermentative/methanogenic conditions. Based on the use of inhibitors, methanogens were not involved in the sequential dechlorination of PCA. Based on 16S rRNA gene analysis, among five known dechlorinating bacterial groups tested, only Dehalococcoides was detected in the mixed culture. The sequential dechlorination of PCA was simulated using a branched-chain Michaelis-Menten kinetic model. The dechlorination rate (k) of the chlorinated anilines ranged from 0.25 to 1.19 uM/day and the half-saturation coefficient (KC) ranged from 0.11 to 1.72 uM at an incubation temperature of 22C and pH 6.90.1. Incubation at different temperature and pH values resulted in significant differences in the biotransformation rate and extent of PCNB in the fermentative/methanogenic enrichment culture. Incubation at 35C resulted in significantly different product distribution. The effect of temperature on the PCA dechlorination rate was modeled using an Arrhenius relationship. Dechlorination of PCA and methanogenesis were not observed in cultures amended with completely bioavailable iron sources until all Fe3+ was reduced to Fe2+. In contrast, PCA dechlorination took place at the same time with iron reduction in the same mixed, methanogenic culture amended with a less bioavailable iron source (FeOOH). PCA was sequentially dechlorinated to dichloroanilines in cultures amended with low nitrate concentrations, whereas partial dechlorination of PCA to tetrachloroanilines was observed in cultures amended with high initial nitrate concentrations due to the accumulation of reduced nitrogen species (e.g., NO, N2O). A semi-empirical molecular model (MOPAC/AM1) was used to estimate the thermodynamic and electronic properties of all chlorinated aniline congeners. These values were used to predict the sequential PCA dechlorination pathway and compare to experimentally observed dechlorination reactions. The results of this study have significant environmental implications relative to the fate and transport of PCNB, PCA and its dechlorination products in subsurface systems.

In molecular magnetism, rational design and serendipity have played complementary roles in the synthesis of complexes which display a breadth of interesting physical characteristics. These range from the basic understanding of magneto‐structural correlations, to more complicated phenomena such as slow relaxation of the magnetisation, spin frustration effects, and tuning magnetic interactions with a view to spintronics. The inherent physical properties of these complexes has already afforded molecules which can behave as single‐molecule magnets, singlechain magnets, single‐ion magnets, magnetic metal‐organic frameworks, magnetic refrigerants, and molecular qubits. Even when the building blocks are well known, the rational design of magnetic clusters can be extremely difficult, with the shape and nuclearity often dominated by several internal and external factors. Metallosupramolecular processes proffer an attractive strategy to the rational design of these clusters by making use of structurally‐rigid precursors which, when combined in the correct stoichiometric ratio, can be used to construct various predefined discrete two‐ and three‐dimensional polygons and polyhedra. In particular, the use of metalloligands as structurally‐rigid precursors is appealing, not only because of their often‐straightforward synthesis, but because of their ability to be easily modified in order to create comparable building blocks with different chemical and physical properties. It is therefore surprising that there are limited examples of magnetic architectures built through this approach. Each chapter of this thesis aims to exploit the use of acetylacetonate‐based paramagnetic metalloligands for the synthesis of structurally analogous magnetic coordination capsules, with inherently different magnetic properties. Chapter 2 describes the structural and magnetic studies of fourteen tetradecanuclear coordination cubes, synthesised using the paramagnetic metalloligand [MIIIL3] (MIII = Cr, Fe; HL = 1‐(4‐pyridyl)butane‐1,3‐dione). The heterometallic [MIII8MII6L24]n+ (MII = Co, Ni, Cu, and Pd; n = 0‐ 12) cubes formed from the reaction of [MIIIL3] and a “naked” MII salt are all topologically similar, with the MIII ions occupying the corners of the cubes and the MII ions occupying the faces. Excluding the PdII‐based cube, all of the complexes display magnetic exchange interactions at low temperatures. Due to the enormous size of these clusters and their resulting matrices, the magnetic fitting was done using the process of statistical spectroscopy. Chapter 3 describes the structural and magnetic studies of five [MIII2MII3L6]n+ (MIII = Cr, Fe, and Al; MII = Co, Zn, and Pd; HL = 1‐(4‐pyridyl)butane‐1,3‐dione; n = 0‐6) trigonal bipyramids, built using the diamagnetic and paramagnetic metalloligands [MIIIL3]. [FeIII2CoII3L6Cl6] represents the first magnetic trigonal bipyramid synthesised through the pyridyl‐based metalloligand approach. SQUID magnetometry studies show a weak antiferromagnetic exchange interactions between the FeIII and CoII ions, while EPR spectroscopy measurements demonstrate a small increase in the zero‐field splitting parameter of the FeIII ion upon coordination of [FeIIIL3] to a MII ion. Complete active space self‐consistent field (CASSCF) calculations show the axial zero‐field splitting parameter of CoII to be ≈‐14 cm‐1, which is consistent with the magnetothermal and spectroscopic data. Chapter 4 describes the synthesis and characterisation of six magnetic trigonal bipyramids, synthesised through dynamic covalent reactions of the metalloligand [FeIIILNH23] (HLNH2 = 1‐(4‐ aminophenyl)butane‐1,3‐dione) with either a dialdehyde or diacyl dichloride. The three [FeIII2MII3Lim3]n+ (MII = Co, Ni; n = 0‐6) imine‐based cages are formed from the reaction of the metalloligand with 2,6‐pyridinedicarboxaldehyde in the presence of a templating MII salt and a catalytic amount of acid, whereas the three [FeIII2Lam3] amide‐based cages are formed from the reaction of the metalloligand with isophthaloyl chloride in the presence of a base. The [FeIII2NiII3Lim3]n+ trigonal bipyramid displays weak antiferromagnetic interactions between FeIII and NiII ions, with JFe‐Ni = ‐0.12 cm‐1 and DNi = 8.93 cm‐1, while the [FeIII2Lam3] amide‐based cages display interesting configurational features dominated by the enthalpic gain from a series of intermolecular interactions.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / A methodology for estimating hydrogen-bond preferences and binding affinities in solution, based on molecular electrostatic potential surfaces (MEPS), is presented using tritopic hydrogen bond acceptor and a series of aromatic carboxylic acids. The plot of calculated MEPS values against experimentally determined binding constants produces a goodness-of-fit of over 0.93 and a similar positive correlation is obtained between MEPS values and binding enthalpies. A series of tritopic N-heterocyclic compounds were synthesized and subjected to systematic co-crystallizations with selected multi-topic aliphatic and aromatic carboxylic acids to determine if ditopic and tritopic donors formulate assemblies with desired stoichiometries. The co-crystals formed contained the COOHᐧᐧᐧBzim synthon, and we observe vacant sites on the acceptor molecules. A series of co-crystallizations between tritopic N-heterocyclic compounds and perfluoroiodoarenes were carried to map out structural landscapes. At least one potential binding site on the acceptor is left vacant on all the four structures obtained. The absence of halogen bonds to all sites can be ascribed primarily due to deactivation of the σ-hole on the iodo-arene donors and partially due to steric hindrance. Four nonsteroidal anti-inflammatory (NSAID) drugs were chosen due to the presence of the COOH moiety, to establish if aqueous solubility can be modulated by systematic solubility measurements of the complex. Two different solids were obtained with a 1:1 and 1:3 stoichiometry. The solubility of the 1:1 co-crystal decreased by 12-fold compared to pure aspirin (3mg/mL at 20 °C) indicating that co-crystals can offer promising new solid forms of pharmaceutically relevant compounds. A series of hydrogen- and halogen bonding Tröger’s base derivatives were synthesized using aromatic N-heterocycles and the iodoethynyl functionality, followed by a series of co-crystallization between aliphatic dicarboxylic acids and symmetric ditopic acceptors. The results suggest that reducing the number of binding sites from three to two facilitates the formation of co-crystals with the desired stoichiometry. The results indicate that directed assembly can be achieved more easily when the molecular building blocks are conformationally rigid.

A prospective study of two combined oral contraceptives was conducted in the Sudan. No pregnancies occurred. Overall incidence of side effects was low. Headache was most frequently reported. Elevations were observed for weight, systolic and diastolic blood pressures, and SGOT and SGPT values while a decrease was seen for hemoglobin levels. Menstrual irregularities were not a problem for the users. Total 6-month use discontinuation rates were low for both pill groups.

Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under continuous irradiation by the electron beam. Temperature-dependent measurements were used to determine the activation energies for the electron irradiation-induced effects. The latter energies were found to be consistent with the involvement of deep acceptor states. Based on these findings, the effects of electron irradiation are explained via the mechanism involving carrier trapping on these levels. Solid-state electron injection was also shown to result in a similar increase of minority carrier lifetime and diffusion length. Solid-state injection was carried out by applying the forward bias to a ZnO homojunction and resulted in a significant improvement of the peak photoresponse of the junction. This improvement was unambiguously correlated with the increase of the minority carrier diffusion length due to electron injection.

Yes / The association constants for formation of 1 : 1 complexes between a H-bond donor, 1-naphthol, and a diverse range of charged and neutral H-bond acceptors have been measured using UV/vis absorption and fluorescence emission titrations. The performance of 1-naphthol as a dual colorimetric and fluorescent molecular recognition probe for determining the H-bond acceptor (HBA) parameters of charged and neutral solutes has been investigated in three solvents. The data were employed to establish self-consistent H-bond acceptor parameters (β) for benzoate, azide, chloride, thiocyanate anions, a series of phosphine oxides, phosphate ester, sulfoxide and a tertiary amide. The results demonstrate both the transferability of H-bond parameters between different solvents and the utility of the naphthol-based dual molecular recognition probe to exploit orthogonal spectroscopic techniques to determine the HBA properties of neutral and charged solutes. The benzoate anion is the strongest HBA studied with a β parameter of 15.4, and the neutral tertiary amide is the weakest H-bond acceptor investigated with a β parameter of 8.5. The H-bond acceptor strength of the azide anion is higher than that of chloride (12.8 and 12.2 respectively), and the thiocyanate anion has a β value of 10.8 and thus is a significantly weaker H-bond acceptor than both the azide and chloride anions. / Supported by the ESPRC.

No description available.

The oil from the Exxon Valdez incident is still observed in different Prince William Sound beaches over two decades. The persisting oil is slightly weathered and highly toxic to the environment. Several studies investigated the reasons for lingering oil. Different remediation techniques were tried and the results were not satisfactory. Recently, it was found that the oil is stranded in a low permeability layer. Detailed explorations showed that the exchange of the nutrients and oxygen is limited in this layer. The main objective of the present study is to explain the effect of oxygen and nutrients on the degradation phenomena in the Alaskan beaches. The general approach for this study is a combination of the field experiments and lab analysis. As it is important to eliminate any cross-layer contamination, a unique sampling method was developed. The applied method involves collecting samples from the oily layer (low permeability layer), measuring oxygen levels in the field and comparing them with the nutrient samples analyzed in the lab. The findings showed that the nutrients levels were low in the beach but the lack of effective electron acceptor is the major factor limiting the biodegradation of the oil. The seawater is responsible for delivering the oxygen and nutrients to the beach during the high tide while during low tide the landward freshwater discharges to the beach. The study of the sulfate and nitrate in the beach revealed that the levels of the alternative electron acceptors were not sufficient to support anaerobic biodegradation. Finally, for successful biodegradation of the Exxon Valdez oil, adequate levels of nutrients (nitrogen and phosphorous) and along with oxygen are required. / Civil Engineering

No description available.

The work presented in this thesis concerns surface energy modification and patterning of the surfaces of conjugated polymers. Goniometry and Wilhelmy Balance techniques were used to evaluate the surface energy or wettability of a polymer’s surface; infrared reflectionabsorption spectroscopy (IRAS) was used to analyse the residuals on the surface as modified by a bare elastomeric stamp poly(dimethylsiloxane) (PDMS). The stamp was found to be capable of modifying a polymer surface. Patterning of a single and/or double layer of conjugated polymers on the surface can be achieved by surface energy controlled dewetting. Modification of a conjugated polymer film can also be carried out when a sample is subjected to electrochemical doping in an aqueous electrolyte. The dynamic surface energy changes during the process were monitored in-situ using the Wilhelmy balance method. This thesis also concerns studies of conjugated polymer-based optoelectronics, including light-emitting diodes (PLEDs), that generate light by injecting charge into the active polymer layer, and solar cells (PSCs), that create electrical power by absorbing and then converting solar photons into electron/hole pairs. A phosphorescent metal complex was doped into polythiophene to fabricate PLEDs. The energy transfer from the host polymer to the guest phosphorescent metal (iridium and platinum) complex was studied using photoluminescence and electroluminescence measurements performed at room temperature and at liquid nitrogen temperature. PSCs were prepared using low-bandgap polyfluorene copolymers as an electron donor blended with several fullerene derivatives acting as electron acceptors. Energetic match is the main issue affecting efficient charge transfer at the interface between the polymers and the fullerene derivatives, and therefore the performance of the PSCs. Photoluminescence, luminescence quenching and the lowest unoccupied molecular orbital (LUMO) together with the highest occupied molecular orbital (HOMO) of the active materials in the devices were studied. A newly synthesized fullerene, that could match the low-bandgap polymers, was selected and used as electron acceptor in the PSCs. Photovoltaic properties of these PSCs were characterised, demonstrating one of the most efficient polymer:fullerene SCs that generate photocurrent at 1 μm. / On the day of the defence the status of article number III was Manuscript and article VII was Accepted.