Domoic acid (DA) is a naturally occurring cyanotoxin, which upon ingestion, is responsible for amnesic shellfish poisoning (ASP) in both humans and animals. Produced by the marine diatom, Pseudonitzschia, DA is accumulated by a number of marine organisms including shellfish, clams and mussels which upon consumption can lead to headaches, nausea and seizures. Possessing a variety of functional groups the structure of DA contains three carboxyl groups, a pyrrole ring and a potent conjugated diene region allowing for binding to glutamate receptors in the dorsal hippocampus of the brain causing the described detrimental effects. Although limitations have been placed regarding the amount of DA that may be contained in seafood no limitations have been placed on the amount present in drinking water. Natural degradation of the toxin may occur through reactive oxygen species such as the hydroxyl radical and singlet oxygen at the conjugated diene region. In this work the photooxidation of DA via singlet oxygen has been studied using sorbic acid as a model compound. The three major reaction pathways observed during the photooxdiation process for both acids include 2 + 4 cycloaddition to produce endoperoxides , 2 + 2 reaction to afford aldehydes and ketones or an ene reaction to generate hydroperoxides. Under similar reaction conditions for SA and DA, the endoperoxide has been seen to be the major product for photoxidation of SA while the hydroperoxide has been seen to be the dominant product during photooxidation of DA.

The presences of heavy metals, organic contaminants and natural toxins in natural water bodies pose a serious threat to the environment and the health of living organisms. Therefore, there is a critical need to identify sustainable and environmentally friendly water treatment processes. In this dissertation, I focus on the fundamental studies of advanced oxidation processes and magnetic nano-materials as promising new technologies for water treatments. Advanced oxidation processes employ reactive oxygen species (ROS) which can lead to the mineralization of a number of pollutants and toxins. The rates of formation, steady-state concentrations, and kinetic parameters of hydroxyl radical and singlet oxygen produced by various TiO2 photocatalysts under UV or visible irradiations were measured using selective chemical probes. Hydroxyl radical is the dominant ROS, and its generation is dependent on experimental conditions. The optimal condition for generation of hydroxyl radical by of TiO2 coated glass microspheres is studied by response surface methodology, and the optimal conditions are applied for the degradation of dimethyl phthalate. Singlet oxygen (1O2) also plays an important role for advanced processes, so the degradation of microcystin-LR by rose bengal, an 1O2 sensitizer was studied. The measured bimolecular reaction rate constant between MC-LR and 1O2 is ~ 106 M-1 s-1 based on competition kinetics with furfuryl alcohol. The typical adsorbent needs separation after the treatment, while magnetic iron oxides can be easily removed by a magnetic field. Maghemite and humic acid coated magnetite (HA-Fe3O4) were synthesized, characterized and applied for chromium(VI) removal. The adsorption of chromium(VI) by maghemite and HA-Fe3O4 follow a pseudo-second-order kinetic process. The adsorption of chromium(VI) by maghemite is accurately modeled using adsorption isotherms, and solution pH and presence of humic acid influence adsorption. Humic acid coated magnetite can adsorb and reduce chromium(VI) to non-toxic chromium (III), and the reaction is not highly dependent on solution pH. The functional groups associated with humic acid act as ligands lead to the Cr(III) complex via a coupled reduction-complexation mechanism. Extended X-ray absorption fine structure spectroscopy demonstrates the Cr(III) in the Cr-loaded HA-Fe3O4 materials has six neighboring oxygen atoms in an octahedral geometry with average bond lengths of 1.98 Å.

Photodynamic therapy (PDT) has been investigated over the past three decades and is currently an approved therapeutic modality for skin cancer, the treatment of superficial bladder, early lung and advanced esophageal cancers, and age-related macular degeneration in a number of countries. In PDT, the absorption of light by a chromophore generates cytotoxic species such as reactive singlet oxygen, leading to irreversible destruction of the treated tissue. The measurement of the singlet oxygen quantum yield is an important determinant used to evaluate the efficiency of new photodynamic therapy agents developed in the laboratory, to screen potential photosensitizers in aqueous media.The singlet oxygen quantum yield is a quantitative measurement of the efficiency in which photosensitizers are able to use energy, in the form of light, to convert oxygen in the ground state to the reactive species singlet oxygen useful in photodynamic therapy. Singlet oxygen quantum yields of photosensitizers differ when measured in different solvents. The majority of the existing quantum yield values found in literature for various photosensitizers are documented with the sensitizers in organic solvents though values in aqueous media are more valuable for actual applications. Determination of accurate and precise quantum yield values in aqueous solution is a much more difficult problem than in organic media. Problems in aqueous solution arise primarily from the physicochemical properties of singlet oxygen in water. Singlet oxygen has a much shorter lifetime in water than it does in organic solvents, causing challenges with respect to quantitative detection of singlet oxygen.The ensuing pages are an attempt to explore the theory and document the procedures developed to provide the accurate measurement of singlet oxygen in aqueous media. Details of this experimental method and singlet oxygen quantum yield results of new compounds relative to established photosensitizers will be presented.

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