Free radicals are produced in lignin during mechanical treatment and irradiation with light of various wavelengths. During mechanical treatment, the lignin macromolecule is degraded severely as revealed by ESR and viscosity measurements. Several types of mechano-radicals are produced in lignin during the mechanical process. Among these the phenoxy radicals are rather stable, where carbon-radicals are labile at ambient conditions. Transient mechano-radicals reacted readily with oxygen molecules to produce peroxy radicals even at 77°K, but they decayed rapidly at ambient temperature. Photodegradation of lignin was observed when macromolecule was irradiated with light of λ<3500 Å as revealed by ESR, viscosity, and weight loss. Phenoxy radicals are the predominant intermediates in the photoirradiated lignin as shown by ESR studies. Elimination of side chains of lignin phenyl propane units took effect in α-carbonyl group bearing molecules. By contrast, β aryl ether substituents adjacent to α-carbonyl groups caused ether cleavage under identical conditions of photoirradiation. This is attributed to energy transferred from excited α-carbonyl groups to the ether bonds. The α-carbonyl groups also functioned as photosensitizers accelerating photochemical reactions of lignin. Termination and decomposition reactions of mechano-radicals and photoinduced free radicals in lignin ultimately lead to the formation of para- and ortho-quinones, carbonyl groups, and double bonds which cause the color of lignin. These potential choromophoric groups can be partially removed from lignin by using ultraviolet light of λ> 4000 Å; and they can be completely removed by irradiation of lignin in the presence of dioxane-water with light of λ>3500 Å. Experimental findings suggest chat chromophoric groups in lignin were being trapped or blocked by dioxanyl radicals resulting in brightening. However, the photoreduced lignin-adduct suffered color reversion. This adverse effect can be prevented by using 2-hydroxy-4-methoxy-benzophenone as a photostabilizer. The feasibility of applying photoreduction techniques to high- yield pulps was demonstrated. However, optimal experimental conditions for photoreduction of lignin in high-yield pulps have not been established yet. / Ph. D.

Radical reactions play central roles in regulating regional air quality and global climate. Some potentially important gas phase radical reactions are being investigated in this research project, including Cl reactions with acetone, butanone, 3-pentanone, pyridine, and dimethyl selenide (DMSe), HO2 complex formation and dissociation with formic and acetic acids, and reactive and non-reactive quenching of O(1D) by the potent greenhouse gases SO2F2, NF3, and SF5CF3. The involved radicals are generated by laser flash photolysis (LFP). Temporal profiles of either the radical reactant or a product are monitored in "real time" using atomic resonance fluorescence spectroscopy (RF), time-resolved UV-visible absorption spectroscopy (TRUVVAS), or tunable diode laser absorption spectroscopy (TDLAS), allowing kinetic and mechanistic information of these reactions to be obtained. These studies provide new knowledge of the investigated radical reactions and facilitate a better understanding of their significance in atmospheric chemistry.

DNA damage is important to understand since it has the potential to lead to disease if unrepaired. In particular, bulky C8 guanine adducts (addition products) are known to induce a variety of mutations due to their conformational flexibility. C-linked C8-phenoxyl-deoxyguanosine adducts (PhOH-dG) have been poorly understood despite their potential for genotoxicity. This thesis systematically develops a computational model to predict the conformational and base-pairing preferences of PhOH-dG by gradually increasing the size of the system. The structure of PhOH-dG in DNA is determined, where the bulky C8 group induces a syn conformation of the base similar to other C8-adducts. A stabilized guanine mismatch is identified for the syn adducts, which implies that the primary mechanism of genotoxicity may be base-substitution mutations resulting in G→C transversions. This thesis has contributed to a growing body of literature dedicated to understanding the role of conformational heterogeneity in the mutagenicity of bulky C8-adducts. / xix, 192 leaves : ill. (some col.) ; 29 cm

The present study was undertaken to determine the effects and possible mechanism of action of cimetidine in cancer and Alzheimer’s disease (AD). Throughout this study emphasis is placed on free radical levels since the magnitude of the relationship between diseases and the levels of free radicals vary from one disease to another. Studies were carried out to examine the effect of cimetidine on free radical levels using superoxide formation and lipid peroxidation as indicators of free radical levels. The experiments revealed that addition of cimetidine, especially in high concentrations (0.5 and 1.0 x10-6 M) significantly inhibited WHCO6 cancer cell growth rather than cancer cell growth, as no normal control was available. Free radical formation as well as hydroxyl radical formation were reduced in the deoxyribose assay. In addition, cimetidine exhibits properties of binding to metals such as copper and iron. To maintain consistency in the experiments, a WHCO6 (Wits Human Carcinoma of the Oesophagus) cell line was used to investigate the effect of cimetidine in cancer. Neurodegeneration was induced in the rat brain using neurotoxins such as cyanide to investigate the relationship between cimetidine in AD. A decrease in cancer cell growth was accompanied by a concomitant decrease in the levels of free radicals and lipid peroxidation, suggesting that the growth-inhibitory effects of cimetidine on WHCO6 cancer cells in vitro may be due to free radical scavenging properties. This proposal was further strengthened by determination of free radical levels in the rat brain. After treatment with neurotoxins to induce neurodegeneration, the levels of free radicals in the rat brain suggest that addition of cimetidine reduces free radical levels in the rat brain in a dosedependent manner. Further experiments were done in an attempt to uncover the underlying mechanism by which cimetidine exhibits free radical scavenging properties. Metal binding studies were done using electrochemical, HPLC and UV/Vis studies. The results show that cimetidine binds iron and copper. These metals have been implicated in free radical production via the Fenton reaction. By binding with cimetidine the metals become unavailable to produce free radicals and hence cimetidine indirectly reduces the formation of free radicals. The final experiment was the determination of cimetidine as a hydroxyl radical scavenger in the deoxyribose assay. Cimetidine was shown to act as a potent hydroxyl radical scavenger, thereby confirming its activity as a free radical scavenger. In addition, cimetidine protects against damage to the deoxyribose sugar, a component of DNA. Whilst there are many theories that explain the therapeutic role of cimetidine in degenerative disease, the actual mechanism of the role of cimetidine is emphasized as a free radical scavenger. Regardless of the mechanism of action, cimetidine does inhibit tumour growth according to this study and also reduce free radical levels in neurodegeneration, which suggests a role for cimetidine as a possible additive in treatment of patients with such disease states. These findings have important clinical implications, and needs to be investigated further.

An extensive study of disubstituted cycloalkanes like CnH2n where n=3,4,5 and 6 using DFT((U)B3LYP/6-31G(d) and 6-311+G(2df,2p)) calculations is presented focusing on the effect of pyramidalization of the radical center. A potential energy surface (PES) analysis shows that the radical prefers to pyramidalize anti to the two cis fluorines in the disubstituted cycloalkanes. The degree of pyramidalization for 1,2-difluorocyclopropyl radical is 43.9o away from the cis fluorines whereas for 1,3-difluorocyclobutyl radical, 1,3-difluorocyclopentyl radical and 1,3-difluorocyclohexyl radical is 3.8o, 5.4o and 14.5o respectively away from the cis fluorines. The importance of this pyramidality effect in these compounds is discussed in context with the carbon-hydrogen bond dissociation energies (BDE's) because the preference of the radical centers to pyramidalize anti to the fluorines affects the bond dissociation energy. Importance of steric effect and unfavorable electronic interactions have been extensively explored in planar permethylated cyclobutadiene (Me4CBD) and cyclooctatetraene (Me8COT) using ((U)B3LYP/6-31G(d) and 6-311+G(2df,2p)) calculations. It is thought that steric interactions dominate electronic interactions in Me8COT, while this works opposite in case of Me4CBT. Instead, in Me4CBD the number of unfavorable electronic interactions between π bonds and out-of-plane hydrogens plays the dominant role in determining the relative energies. Interactions between the π bonds of CBD and the out-of-plane hydrogens on carbons attached to the four-membered ring becomes very interesting when the ring size changes. With ethano bridge on the cyclobutadiene ring interaction with the diagonal bonds results in non-bonding AOs across the other diagonal having the opposite phase in the highest occupied (HO)MO. If the HOMO and LUMO are switched, bis-ethano-bridged tetrahedrane is formed. It is suggested that bis-ethano-bridged tetrahedrane is thermodynamically more stable than bis-ethano-bridged cyclobutadienes. While the reverse is true for unsubstituted cyclobutadienes. The ability of ethano bridges to reverse the usual order is because it causes the doubly-bonded carbons to pyramidalize.

Indiana University-Purdue University Indianapolis (IUPUI) / Fast photochemical oxidation of proteins (FPOP) is an emerging footprinting method that utilizes hydroxyl radicals. The use of hydroxyl radicals create stable labeled products that can be analyzed with mass spectrometry. The advantage of FPOP over other methods is the fast acquisition of results and the small amount of sample required for analysis. Protein structure and protein- ligand interactions have been studied with FPOP. Here we evaluated (1) the reproducibility of FPOP, (2) the effect of hydrogen peroxide concentration on oxidation and (3) the use of FPOP to evaluate protein- nucleic acid interaction with Apurinic/Apurinic endonuclease 1 (APE1) protein. APE1 is a pleotropic protein that has been crystallized and studied widely. The 35641.5 Da protein has two major functional activities: DNA repair and redox function. An intact protein study of APE1 showed consistent global labeling by FPOP and a correlation between oxidation and hydrogen peroxide concentration. Furthermore, analysis of APE1 with DNA was done in hopes of probing the DNA binding site. Although the oxidation observed was not sufficient to define the complex pocket, a dramatic effect was seen in residue oxidation when DNA was added. Interestingly, the internal residues were labeled collectively in all APE1 experiments which indicates partial unfolding of the protein as previously suggested in the literature. Hence, these findings establish the use of FPOP to capture protein dynamics and provide evidence of the existence breathing dynamics of APE1.

During aerobic cell metabolism, molecular oxygen is reduced to water through electron-transfer reactions, and the oxygen not completely reduced is transformed into a set of neutral and free radical molecules with high oxidant ability, generally denominated Reactive Oxygen Species (ROS). To regulate the cellular ROS content, organisms are endowed with an efficient endogen antioxidant system. The physiological ROS levels may be excessively increased by different factors including unbalanced diets, ionizing radiations, and tobacco smoke among others, leading to the oxidative stress, term referred to the imbalance between ROS production and its neutralization by the endogenous antioxidant system. More importantly, in vitro and in vivo studies reveal the relationship between suffering oxidative stress and the development of cardiovascular and respiratory diseases, diabetes, and cancer. To prevent and treat the oxidative stress and its adverse effects, exogenous, readily oxidizable molecules may help the organism to neutralize ROS into less dangerous species. The phenolic compounds or (poly)phenols, molecules very abundant in our diet (i.e. fruits, vegetables, and beverages such as tea and wine) may be responsible for this antioxidant activity of fruits and vegetables. Currently, (poly)phenols are regarded as natural antioxidant molecules with outstanding beneficial effects, including anti-aging activity, and the prevention of cancer and diabetes. The antioxidant activity of (poly)phenols is mainly associated with their radical scavenging activity, action conferred by the transfer of a hydrogen atom or an electron to a free radical, rendering a less reactive molecule. On the other hand, chemical probes and in vitro studies have demonstrated that some highly reacting (poly)phenols are able to generate small quantities of ROS. Phenolic compounds have shown antiproliferative activity which may be caused inter alia by their ability to scavenge or generate toxic radicals. To further understand the connection between the redox reactivity of (poly)phenols and their biological actions, studies with more sensitive and selective chemical probes may help to clarify the role of redox reactions in the physiological actions of phenolics and their metabolites. In this thesis, we have focused on the utilization of two stable radicals synthesized in our laboratory, the tris(2,4,6-trichloro-3,5-dinitropehnyl)methyl (HNTTM) and the tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl)radical (TNPTM), as chemical probes to determine the electron-transfer activity of dietary (poly)phenols and some metabolites. The different reducing potential of the two stable radicals facilitates the quantitative evaluation of the radical scavenging capacity of each (poly)phenol, as well as the establishment of the most reactive moieties. TNPTM is a useful tool to determine the most reactive (poly)phenols as electron transfer donors, (poly)phenols that cannot be differentiate with any other chemosensor. The results obtained are compared with two well-established methods for the quantification of electron-transfer capacity. The action of these (poly)phenols on cell cultures of a colon cancer cell line is also presented, showing a correlation between those (poly)phenols detected with TNTPM and with those that produce the highest antiproliferative activity. This cell line is particularly relevant because dietary (poly)phenols are in contact with epithelial cells of this kind during their transit along the digestive tract and may exert some preventive action on colon cancer. In addition, a chemoenzymatic strategy to prepare glucuronated metabolites of (-)-epigallocatechin-3-O-gallate (EGCG), the most abundant and active (poly)phenol of green tea, was attempted, obtaining the acetylated and methylated precursor of the EGCG-4’’-glucuronide, the most abundant EGCG glucuronide obtained in the human metabolism. The final conjugated, the EGCG-4’’-glucruonide, was obtained albeit with not enough quantity to be purified. / "Estudi de la Transferència Electrònica de compostos fenòlics i la seva relació amb l’activitat biològica en cèl•lules canceroses" En el metabolisme i respiració dels organismes aeròbics, l’oxigen és utilitzat com a receptor electrònic reduint-se principalment a aigua. Una petita part d’aquest oxigen no és totalment reduint obtenint-se un conjunt d’espècies radicalàries i no radicalàries (ROS). Aquestes espècies en ser altament reactives poden malmetre macromolècules, activitat que està relacionada amb l’aparició de malalties com el síndrome metabòlic i el càncer. Per aquest motiu els organismes han desenvolupat un sistema de regulació de la seva concentració. En determinades situacions, aquest sistema no és suficient i per tant, antioxidants exògens poden ajudar a aquest sistema endògen. Els polifenols molècules abundants en la nostra dieta (fruita i verdures) són els principals candidats, i s’ha demostrat un efecte preventiu i terapèutic en la salut per la seva part. L’efecte beneficiós exercit pels polifenols pot tenir lloc per dos mecanismes de reacció; per transferència d’hidrogen i per transferència electrònica. Actualment, no hi ha cap mètode prou eficaç que ens permeti determinar la acció del polifenols exercida per transferència electrònica, mecanisme que també habilita als polifenols per a formar ROS. En el nostre laboratori hem sintetitzat dos radicals lliures estables, els radicals tris(2,4,6-tricloro-3,5-dinitrofenil)metil (HNTTM) i el tris(2,3,5,6-tetracloro-4-nitrofenil)metil (TNPTM) com a quimiosensors de transferència electrònica. Aquests radicals ens permeten mesurar la activitat antiradicalària dels polifenols, i el TNPTM ens permet detectar a aquells polifenols amb una reactivitat per transferència electrònica més elevada i que no poden ser diferenciats amb altres mètodes. S’han fet estudis d’antiproliferació per part dels polifenols en cèl•lules de càncer de còlon HT-29 i s’ha demostrat que els polifenols amb més activitat antiproliferativa són els que tenen activitat front al TNPTM. Per tant, el radical TNPTM permet determinar als polifenols amb una elevada reactivitat per a cedir electrons i es suggereix que els mecanismes de transferència electrònica juguen un paper important en els mecanismes d’ antiproliferació en cèl•lules de càncer de còlon HT-29. S’ha proposat metodologia sintètica per a obtenir els principals glucuronats de l’epigal•locatequin-3-O-gal•lat (EGCG) el més abundant i més actiu dels polifenols del te verd. S’ha obtingut el precursor acetil•lat i metil•lat del glucuronat majoritari de l’EGCG obtingut en el metabolisme humà, l’EGCG-4’’-glucurònid i s’ha obtingut el conjugat final però no amb una quantitat suficient com per a ser aïllat.

The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide). The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an atmospheric degradation pathway for each alkyl bromide is qualitatively assessed. The studies of halogen atom reactions with alkenes focused on formation of weakly-bound adducts where kinetics of adduct formation and dissociation as well as non-adduct forming channels were evaluated. The elementary steps in the Br initiated oxidation of the alkenes 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-2-butene (tetramethylethylene, TME), and 1,3-butadiene have been investigated. The experimental kinetic database for these reactions is quite sparse. The kinetic results reported herein, suggests that Br reaction with the above olefins is much faster than previously thought. Analysis of the temperature dependence of the "approach to equilibrium" kinetic data in conjunction with electronic structure calculations allows for determination of enthalpy and entropy changes associated with each addition reaction. Where possible, both forward addition and reverse dissociation channels as well as H-abstraction pathways were characterized. The enthalpy change associated with the addition reaction to give the Br−isoprene and Br−1,3-butadiene adducts has been determined for the first time and the bond dissociation enthalpy obtained for the Br−TME adduct is in reasonable agreement with the only other previously reported value. It should be noted that in the case of isoprene and 1,3-butadiene, there are multiple possible adducts that could be formed. In order to help clarify which adducts are more or less likely to be formed, we rely on electronic structure calculations (see Chapter 5) to aid in our overall understanding of the adduct forming channels. Furthermore, for the Br reactions with the three alkenes above, atomic Br kinetics have been monitored directly both in the absence and in the presence of O2 which allowed, for the first time, determination of rate coefficients for the elementary steps in the overall complex mechanism including determination of the Br−olefin + O2 rate coefficient. Also included in this group of reactions is the chlorine reaction with isoprene. In addition to the well-known fact that isoprene is emitted into the atmosphere from vegetation, a potentially significant marine source of isoprene has received considerable attention. Chlorine has long been thought to exist primarily in marine environments, however, recent findings also suggest a significant Cl production rate in the middle of the continental United States. There are numerous room temperature kinetic studies for the Cl + isoprene reaction in the literature, however, there is only one temperature dependent study reported. Current recommended 298 K rate coefficients for isoprene reactions suggest the Cl reaction is ~ 4x faster than the analogous OH reaction. If indeed this is the case, the Cl reaction could play a non-neglibible role in isoprene oxidation in atmospheric locales where Cl concentrations are relatively high. In addition, the C−Cl bond strength in Cl−C5H8 is obtained from direct measurements of the forward and reversible addition rate coefficients. Our results are compared with the literature data, and the potential importance of Cl-initiated oxidation as an atmospheric sink for isoprene is assessed. The final group of reactions investigated involves reactions of Cl with DMS and DMSe. DMS and DMSe are the most prevalent sulfur and selenium compounds emitted to the atmosphere from the oceans. The oxidation of DMS has been studied extensively due to the interest in the possible role of DMS oxidation in the formation of sulfate aerosols, however, DMSe oxidation processes have hardly been studied at all. And, DMSe oxidation products are likely to be less volatile than the analogous DMS species. Selenium is an essential nutrient for many plants and animals; however, there is a fine line between enough and excess selenium which can be toxic. Most studies suggest that atmospheric deposition is an important source of Se contamination, and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. Since the majority of atmospheric Se exists in the form of DMSe, determination of the kinetics and oxidation mechanisms of DMSe will go a long way towards understanding the global biogeochemical cycle of Se. Both reversible addition and H-abstraction pathways have been characterized, and the first experimental determination of bond strength of the gas-phase DMS−Cl and DMSe−Cl adducts have been obtained.

Thesis (PhD) -- Macquarie University, Division of Environmental and Life Sciences, Dept. of Chemistry and Biomolecular Sciences, 2007. / Bibliography: leaves 295-322. / Generation of peroxide groups in proteins exposed to a wide variety of reactive oxygen species (ROS) requires an initial formation of protein carbon-centred or peroxyl free radicals, which can be reduced to hydroperoxides. Both protein radicals and protein hydroperoxides are capable of oxidizing important biomolecules and thus initiate biological damage. In this study, we investigated the inhibition of protein hydroperoxide formation by ascorbate and GSH in gamma-irradiated HL-60 cells.--We used HL-60 cells as a model for general protection of living organisms by ascorbate (Asc) and glutathione (GSH) from the deleterious effects of protein hydroperoxides generated by radicals produced by gamma radiation. Measurement by HPLC indicated that incubation of HL-60 cells with Asc in the presence of ascorbate oxidase resulted in the accumulation of intracellular Asc. The intracellular Asc levels were lowered by irradiation, demonstrating intracellular consumption of Asc by the radiation-generated radicals. Exposure of HL-60 cells to increasing gamma irradiation doses resulted in increasing accumulation of protein peroxides in the cells. This was measured by the FOX assay. A significant decrease in intracellular protein hydroperoxides was noted when the cells were treated with ascorbic acid before irradiation. A dose-dependent protective effect of Asc was observed. Asc loading also provided strong protection from radiation-generated protein hydroperoxides independently of the composition of the external medium, showing that only the radicals formed within the cells were effective in oxidizing the cell proteins. Similarly, protein peroxidation was inhibited in cells with enhanced levels of GSH and increased when the intracellular GSH concentration was reduced. These findings indicate that ascorbate and GSH are important antioxidants in protecting cells from oxidative stress associated with the generation of protein hydroperoxide. / Mode of access: World Wide Web. / xxix, 322 leaves ill

Dehydroepiandrosterone, a C-19 steroid, is found endogenously with the highest circulating serum levels. It is converted to important steroids such as the sex hormones oestrogen and testosterone. DHEA has come under the spotlight as a purported “fountain of youth” due to its well-characterised age-related decline. The supplementation of DHEA in both the elderly and those with a pathophysiological deficiency has been shown to be of benefit, particularly with regard to wellbeing and depression. The role of DHEA in the periphery has not been elucidated beyond its role as a precursor hormone in sex steroid biosynthesis, though it has been established as a neuroactive neurosteroid, capable of exerting neuroprotective effects in the brain. Since the importance of free radicals in aging and neurodegeneration is well established, investigations were conducted on the ability of DHEA to inhibit free radical generation or scavenge existing free radicals. DHEA was able to significantly inhibit quinolinic acid-induced lipid peroxidation, a measure of membrane damage, over a range of concentrations, although the reduction did not appear to be dose-dependent. This was observed in both in vitro and in vivo studies. Thus, the ability of a compound to reduce the degree of lipid peroxidation may indicate its value as a neuroprotectant. However, DHEA did not significantly reduce cyanide induced generation of the superoxide free radical, suggesting that DHEA is not an effective free radical scavenger of the superoxide anion and that the reduction in lipid peroxidation does not occur through a scavenging mechanism. Apoptosis is a physiological process which is necessary for development and homeostasis. However, this form of programmed cell death can be initiated through various mechanisms and too much apoptotic cell death results in deleterious effects in the body. DHEA was shown not to induce apoptosis. Even the lowest concentration of DHEA investigated in this thesis shows a remarkable decrease in the degree of apoptosis caused by intrahippocampal chemical insult by the neurotoxin quinolinic acid. Cresyl violet was used to visualise tissue for histological examination which revealed that DHEA is able to preserve the normal healthy morphology of hippocampal cells which have been exposed to quinolinic acid. Cells maintained their integrity and showed little evidence of swelling associated with necrosis. Organ culture studies were performed by assessing the impact of DHEA on several pineal metabolites. The study revealed that DHEA exerted an effect on the metabolism of indoleamines in the pineal gland. Melatonin, the chief pineal hormone, did not appear to be affected while the concentrations of N-acetylserotonin, serotonin and methoxytryptamine showed significant alterations. Thus, the neuroprotective mechanism of DHEA does not appear to be mediated by an increase in the presence of melatonin. The biological importance of metal ions in neurodegeneration is also well established and thus the potential interaction between DHEA and metal ions was considered as a mechanism of action. Spectroscopic and electrochemical analyses were performed to determine whether DHEA is able to interact with metal ions as a ligand. These reveal that DHEA does not form a strong bond with the metals investigated, namely copper (II) and iron (III), but that a weak interaction is evident. These investigations were conducted in a rodent model, which has neither large amounts of endogenous DHEA, nor the enzymatic infrastructure present in humans. Thus, the theory that DHEA exerts its effects through downstream metabolic products is unlikely. However, these investigations reveal that there is merit in the statement that DHEA itself is a neuroprotective molecule, and confirm that the further investigation of DHEA is an advisable strategy in the war against neurodegeneration and aging.