This thesis presents an investigation into the synthesis of metal complexes of (Nheterocyclic carbene)-based cyclophanes. There were three main areas of focus: synthesis and complexation of bis(4,5-dihydroimidazolium) salts; the synthesis and complexation of phenol-functionalised imidazolium cyclophanes; and the synthesis and complexation of (N-heterocyclic carbene)-based cyclophanes by C-C bond activation of biimidazolium salts with electron-rich metals. The synthesis of xylyl-linked bis(4,5-dihydroimidazolium) salts was investigated. Attempts to prepare these compounds by the cyclisation of a tetraamine (linear or macrocyclic) were unsuccessful due difficulties in preparing the tetraamines. The target compounds could be prepared by adapting the methods developed for the synthesis of bis(imidazolium) salts however problems associated with purification and stability of the products prevented complexation studies. A series of phenol-, phenoxide- and anisole-functionalised imidazolium cyclophanes were prepared. Their structural properties were investigated using dynamic nmr studies and X-ray crystallography. Complexation of the functionalised cyclophanes was investigated. The phenol cyclophane I formed a dinuclear complex with mercury(II). This complex is the first example of a complex derived from a phenol-functionalised imidazolium cyclophane. However the anisole cyclophane II and the unsymmetrical phenol/ortho cyclophane III were unable to form complexes possibly due to steric hindrance and instability of the cyclophane respectively. Preliminary complexation studies of the bis(imidazolium)phenol V suggested that complexation with palladium(II) and mercury(II) were possible but more work is required to determine the optimum reaction conditions. A series of biimidazolium salts VI (both new and known) were prepared. Previously reported biimidazolium salts have very low solubility in common solvents therefore the incorporation of long alkyl chains to the bridging group was investigated as a means to improve the solubility. The structure of the salts was explored using a range of techniques including dynamic nmr spectroscopy, cyclic voltammetry, UV/Visible spectroscopy, X-ray crystallography and mass spectrometry. Some of the biimidazolium salts were able to rotate about the C2-C2' bond and the free energy of activation for this process was estimated using dynamic nmr studies. C-C bond activation of the biimidazolium salts with palladium(0) was used to form a series of palladium(II) complexes (VII) of (NHC)-based cyclophanes. These reactions are the first examples of the synthesis of bis(NHC) complexes by C-C bond activation. The reactivity of the biimidazolium salts with palladium(0) was compared to their solution structure and it was found that only the biimidazolium that were able to rotate about the C2-C2' bond could react with palladium(0).

A titanium dioxide powder co-doped with boron and zirconium was prepared by mechanical ball milling. Photocatalytic performance of the powder was evaluated by degradation of methylene blue (MB) solution under UV illumination. XRD patterns were refined by Rietveld analysis method to obtain accurate lattice parameters and position of the atoms in the crystal structure of TiO2. XRD analysis indicated that the B and/or Zr doped TiO2 powders composed of anatase and did not exhibit any additional phase. Rietveld analysis suggested that dopant B and Zr elements were successfully weaved into crystal structure and distorted the lattice of TiO2. The highest distortion was obtained by co-doping. SEM investigations confirmed that mechanical ball milling technique led to a decrease in particle size of TiO2 powder. XPS analysis revealed that dopant B and Zr atoms did not appear in any form of compound including Ti and O elements. Results of photocatalytic activity test suggested that boron and zirconium co-doped TiO2 particles exhibited a better visible light response and photocatalytic activity than that of mono element doped TiO2 (i.e. B-TiO2 and Zr-TiO2) and undoped TiO2 particles. A 20% improvement in photocatalytic activity of reference TiO2 powder (powder ball milled without dopant addition) was achieved by B and Zr co-doping. The enhanced photocatalytic activity is attributed to synergistic effects of B-Zr co-doping the lattice of TiO2 as well as particle size reduction.

A study of how mediators interact with the catabolic pathways of microbes was undertaken with a view towards improving the performance of microbial fuel cells. The use of mediators is known to improve the power density in microbial fuel cells, but this work suggests that no single mediator is ideally suited to the task. Instead, a carefully selected mixture of two targeted mediators (Methylene Blue and Neutral Red) might be optimal. To test this hypothesis, a yeast-catalyzed microbial fuel cell was built and empirically evaluated under different mediation conditions while keeping all other parameters constant. The results clearly show that an appropriate mix of the two mediators mentioned could indeed achieve significantly superior performance, in terms of power-density, than when either mediator is used singly. All tests were carried out using the same overall mediator concentration.

Current Texas Department of Transportation (TxDOT) procedures for evaluating coarse aggregate for portland cement concrete (PCC) have been in place for over 39 years. Item 421 in the TxDOT "Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges" describes the tests and test limits that must be met by aggregates before they can be approved for use in portland cement concrete applications. The intention of Item 421 is to ensure that only strong, durable aggregates are used in concrete so that the life of concrete is not cut short by common distress mechanisms which ultimately lead to costly repairs and replacements. The two main tests currently used by TxDOT to evaluate aggregates are the magnesium sulfate soundness test and the Los Angeles abrasion and impact test. These tests are meant to characterize the overall soundness and resistance to abrasion and impact of an aggregate respectively. Unfortunately, past research has shown that the magnesium sulfate soundness and test and the Los Angeles abrasion and impact test are not able to successfully predict the field performance of an aggregate in concrete. The requirements of item 421 have thus far done a reasonably good job of ensuring long-lasting concrete; however the current tests and test limits may be unnecessarily precluding the use of some local materials. As high quality aggregate sources are depleted and transportation costs increase, it will become more necessary to distinguish good performers from marginal and poor performers in the future. If aggregate tests can be found that demonstrate better correlations with field performance, it may be possible to use more local aggregate sources and still provide the desired level of reliability for pavements, bridges, and other TxDOT concrete applications. Researchers are in the processing of collecting coarse and fine aggregates commonly used in Texas and testing these aggregates on a variety of alternative tests. Researchers will attempt to relate this test data to concrete behavior and ultimately recommend tests for improved TxDOT aggregate specifications. / text

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Alzheimer's disease (AD) is associated with decreased brain energy metabolism. Hypometabolism in the posterior cingulate cortex (PCC) occurs before the onset of memory deficits in subjects at genetic risk for AD who are not yet cognitively impaired. There is a specific inhibition in cytochrome oxidase (C.O.) in the PCC, an area involved in spatial navigation. Creating an animal model that exhibits the early pathophysiology of AD is important for developing and testing drugs that could reverse memory problems associated with such deficits. Methylene blue (MB) is a compound that improves C.O. activity and memory retention in rats. This dissertation had three specific aims: 1) to examine if isolated PCC hypometabolism causes spatial memory deficits in rats; 2) to find a dose of MB that improves memory without nonspecific behavioral effects; and 3) to prevent memory deficits from PCC hypometabolism with low dose MB. PCC hypometabolism was produced by focal administration of sodium azide, an inhibitor of C.O. activity. PCC hypometabolism resulted in impaired spatial memory in a hole board food-search task, increased oxidative damage, and neurotoxicity in the PCC. In addition, PCC hypometabolism resulted in reduced inter-regional correlations in brain activity. Our second set of studies examined the dose-response effects of MB. Our findings demonstrated that a low dose of MB: 1) enhanced memory in open field habituation and object recognition tasks; 2) did not affect general locomotor activity, exploration, motivation, or anxiety; and 3) increased brain oxygen consumption 24 hr after in vivo administration. Finally, our last study found that low dose MB prevented the deficits caused by PCC hypometabolism. MB did not prevent PCC inhibition or cell loss caused by sodium azide. Inter-regional correlations of brain metabolic activity suggested that rats treated with MB were using a different, but equally efficient, strategy for memory retrieval. This animal model of C.O. hypometabolism in the PCC can provide information to understand the mechanisms that regulate early pathological degeneration and reveal new therapeutic strategies aimed at reducing or preventing cognitive decline. Studies of low dose MB in humans are needed to examine its effects in AD patients.

The design, synthesis, characterization, and applications of annulated bis(imidazolium) salts are described. New synthetic methodologies have been developed that allow access to a broad structural range of bis(imidazolium) salts. Initial studies focused on thee use of bis(imidazolium) salts as comonomers in the formation of mainchain organometallic polymers. Two distinct polymer scaffolds were synthesized, one featuring metal(II)dihalides in the main-chain, and the other featuring a chelated metal center. Ultimately, polymerizations were conducted under ambient atmosphere, proceeded in excellent overall yield, and provided main-chain organometallic polymers comprising Ni(II), Pd(II), and Pt(II) with molecular weights up to 106 Da. Departing polymer studies, focus was shifted toward the study of the physical and photophysical properties of the bis(imidazolium) salts. In few synthetic manipulations, a series of highly photoluminescent bis(imidazolium) salts were prepared whose substituents enable emission in solution, in the solid-state, and, uniquely, as free-flowing liquids. Importantly, these materials display excellent physical properties, such as low glass-transition temperatures (< 0 °C) and high thermal stabilities (> 300 °C). In addition, the bis(imidazolium) platform enabled access to two new fluorescent ionic liquid crystals, demonstrating an ability to also control mesomorphic properties of these materials. Further investigations were conducted regarding the photophysical properties of bis(imidazolium) salts. Focus was placed upon absorption and emission wavelength tunability, solvatochromism, red-edge excitation, and chemical stability. Through functional group modulation, the [lambda]em were varied from 329 -- 561 nm with [Phi]fs up to 0.91. Both the absorption and emission characteristics were found to display strong solventdependencies which were found to be strongly influenced by the nature of the bis(imidazolium) core. The red-edge effect was investigated for a series of bis(imidazolium) salts and was found to be similar between Br and BF4 salts, but distinctly different when MeSO4 anions were incorporated. The stability of an amphiphilic BBI was quantified in aqueous solutions of varying pH and > 85% of the emission intensity was retained after 2 h at pH levels of 3 -- 9.

The present research reports the first comprehensive map of brain networks underlying latent inhibition learning, the first application of structural equation modeling to cytochrome oxidase data, and the first effects of methylene blue, a known metabolic enhancer, on latent inhibition. In latent inhibition, repeated exposure to a stimulus results in a latent form of learning that inhibits subsequent associations with that stimulus. As neuronal energy demand to form learned associations changes, so does the induction of the respiratory enzyme cytochrome oxidase. Therefore, cytochrome oxidase can be used as an endpoint metabolic marker of the effects of experience on regional brain metabolic capacity. Quantitative cytochrome oxidase histochemistry was used to map brain regions in mice trained on a tone-footshock fear conditioning paradigm with either tone preexposure (latent inhibition), conditioning only (acquisition), conditioning followed by tone alone (extinction), or no handling or conditioning (naïve). In normal latent inhibition, the ventral cochlear nucleus, medial geniculate, CA1 hippocampus, and perirhinal cortex showed modified metabolic capacity due to latent inhibition. Structural equation modeling was used to determine the causal influences in an anatomical network of these regions and others thought to mediate latent inhibition, including the accumbens and entorhinal cortex. An uncoupling of ascending influences between auditory regions was observed in latent inhibition. There was also a reduced influence on the accumbens from the perirhinal cortex in both latent inhibition and extinction. These results suggest a specific network with a neural mechanism of latent inhibition that involves sensory gating, as evidenced by modifications in metabolic capacity, effective connectivity between auditory regions, and reduced hippocampal influence on the accumbens. The effects of methylene blue on disrupted latent inhibition were also investigated. Reduced tone-alone presentations disrupted the latent inhibition effect and led to an increase in freezing behavior. Repeated low-dose administration of methylene blue decreased freezing levels and facilitated the disrupted latent inhibition effect. Methylene blue administration also resulted in changes in metabolic capacity in limbic and cortical regions. A unique functional neural network was found in methylene blue-restored latent inhibition that emphasized sensory gating of auditory information, attention processing, and cortical inhibition of behavior. / text

published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy