Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

abstract / Chemistry / Doctoral / Doctor of Philosophy

The transient receptor potential channels, ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1), are non-selective cation-permeable channels that have retained their function as chemical sensors since their first appearance in metazoan species several hundred million years ago. In vertebrates, TRP channels have evolved multiple functions which make it difficult to understand exactly how they transmit signals to the brain that are interpreted very differently. For example, TRPA1 and TRPV1 are sensitive to various chemicals and activation of these channels produce sensations with opposing effects. Pain is felt when TRPV1 is activated by spider toxins, but activation by plant cannabidiol results in a pain-relieving sensation. Similarly, TRPA1 activation by delta-tetrahydrocannabinol is reported to relieve symptoms of pain, but TRPA1 activation by the active ingredient in wasabi results in a repulsive or noxious sensation. Much of what we know about TRPA1 and TRPV1 comes from the use of plant products or exposure to substances that cause or alleviate pain and inflammation. In this study, whole-cell voltage clamp recordings of heterologously expressed human TRPA1 and human TRPV1 were tested for sensitivity to a hallucinogenic plant compound, salvinorin A and an arthropod-defensive compound, para-benzoquinone. Neither compound has yet been reported to activate TRP channels but both are known to be involved in pain and inflammation signaling in humans. I show that the arthropod compound, para-benzoquinone, activates and desensitizes TRPA1 in a cysteine-dependent manner, but activation of TRPV1 is not dependent on cysteine reactivity. Although salvinorin A is known to be a potent agonist of the kappa-opioid and cannabinoid receptors, here I show that it also acts as a highly potent agonist of both TRPA1 and TRPV1. Its interaction with TRP channels may contribute to its antinociceptive effects in behavioral studies with animals that are reported to be independent of opioid signaling.

The aim of this research was to provide a comprehensive evaluation of the heavy metal removal performance of two synthetic zeolites, Zeocros CA150 and Zeocros CG180. Detailed laboratory investigations of the key parameters known to affect zeolitic ion exchange were performed with respect to lead, zinc, copper, cadmium and nickel by means of batch equilibrium tests. The study into the effect of contact time suggests that a near equilibrium state was reached within two hours. As metal hydroxide precipitation was minimal at pH 6.0 and the structural integrity of the zeolite was maintained, metal removal at this pH is predominantly by ion exchange rather than chemical precipitation. Fluctuations in both silicon and aluminium release from the zeolites suggest that partial dissolution may occur under mildly acidic conditions, an observation discussed elsewhere in the literature. Heavy metal removal decreased with increasing metal loading, with the zeolites exhibiting Significantly lower operating exchange capacities compared to the theoretical ones. Exchange capacities varied between 1.3-4.9 meq/g and 0.5-4.6 meq/g for CA 150 and CG180 respectively for the five metals studied. Throughout all of the experimental investigations, lead was removed preferentially (>99%) and nickel removal effiCiencies were the lowest «20%). The results from the mixed metal studies demonstrated that lead removal was the least affected by the presence of other heavy metals whereas cadmium, copper and zinc removal was suppressed in comparison to that from Single metal solutions. The presence of competing ions was not found to adversely affect lead removal by CA 150 and CG180, with copper and cadmium removal showing the most suppression in the presence of calcium, magnesium, potassium and sodium. Zinc uptake by both zeolites proved the most sensitive to the addition of hardness ions even under soft water conditions. The zeolites were also demonstrated to achieve up to 100% removal from real effluents, outperforming a natural zeolite, clinoptilolite. Overall, this research has demonstrated the considerable potential of these synthetic zeolites to selectively remove heavy metals from complex contaminated effluents, indicating their possible application as a tertiary technology for effluent treatment.

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