No description available.

Computational methods are combined with synchrotron-based techniques to analyze the structure and bonding of water and water plus hydroxyl at metal surfaces under UHV and at near-ambient conditions. Water-metal interaction plays a crucial role in a multitude of cosmic, atmospheric and biological phenomena as well as heterogeneous catalysis, electrochemistry and corrosion. A spotlight of renewed interest has recently been cast on water-metal systems due to their relevance for surface chemical reactions related to the production and utilization of hydrogen as a clean energy carrier. In particular, H2O and OH are essential reaction intermediates in the renewable production of hydrogen from sunlight and water and in fuel cell electrocatalysis. Fuel cells are considered one of the most promising power generation technologies for a sustainable energy future. A mechanistic understanding of the oxygen reduction reaction (ORR) pathway, including the role of electronic and geometric structure of the catalyst, is essential to the design of more efficient fuel cell catalysts. This is intimately connected to fundamental factors that affect the ability to form water-metal bonds as well as the site occupation and orientation of the adsorbed H2O and OH at active metal surfaces. Key relationships related to critical issues in the fuel cell reaction are illuminated by the synergy of theory and experiment in this thesis. We emerge with a detailed understanding of the structure of the water-metal interface and the factors that rule the wettability of a metal surface, including geometric and electronic structure effects and the influence of coadsorbed species. We show that the preferred microscopic orientation of the water monolayer has consequences for macroscopic properties, and reveal the origin of the hydrophobic water layer. Finally, we identify a cooperativity effect that drives the stability of the mixed water/hydroxyl layer at metal surfaces, an important ORR intermediate.

Choline oxidase catalyzes the flavin-dependent, two-step oxidation of choline to glycine betaine via the formation of an aldehyde intermediate. The oxidation of choline includes two reductive half-reactions followed by oxidative half-reactions. In the first oxidation reaction, the alcohol substrate is activated to its alkoxide via proton abstraction and oxidized via transfer of a hydride from the alkoxide α-carbon to the N(5) atom of the enzyme-bound flavin. In the wild-type enzyme, proton and hydride transfers are mechanistically and kinetically uncoupled. The role of Ser101 was investigated in this dissertation. Replacement of Ser101 with threonine, alanine, cysteine, or valine demonstrated the importance of the hydroxyl group of Ser101 in proton abstraction and in hydride transfer. Moreover, the kinetic studies on the Ser101Ala variant have revealed the importance of a specific residue for the optimization of the overall turnover of choline oxidase. The UV-visbible absorbance of Ser101Cys suggests Cys101 can form an adduct with the C4a atom of the flavin. The mechanism of formation of the C4a-cysteinyl adduct has been elucidated. D-arginine dehydrogenase (DADH) catalyzes the oxidation of D-amino acids to the corresponding imino acids, which are non-enzymatically hydrolyzed to α-keto acids and ammonia. The enzyme is strick dehrogenase and deoesnot react with molecular oxygen. Steady state kinetic studies wirh D-arginine and D-histidine as a substrate and PMS as the electron acceptor has been investigated. The enzyme has broad substrate specificity for D-amino acids except aspartate, glutamate and glycine, with preference for arginine and lysine. Leucine is the slowest substrate in which steady state kinetic parameters can be obtained. The chemical mechanism of leucine dehydrogenation catalyzed by DADH was explored with a combination of pH, substrate and solvent kinetic isotope effects (KIE) and proton inventories by using rapid kinetics in a stopped-flow spectrophotometer. The data are discussed in the context of the crystallographic structures at high resolutions (<1.3 Å) of the enzyme in complex with iminoarginine or iminohistidine.

<i>In vivo</i> and <i>in vitro</i> studies on numerous types of blood vessels obtained from a variety of vascular beds and species have demonstrated that oxygen free radicals (OFRs) can evoke both vasodilation and vasoconstriction. Specific OFRs have been shown to elicit different and often times opposite effects on vascular smooth muscle. Therefore, this thesis attempts to define the vascular actions and mechanism of oxygen free radicals (OFRs) [superoxide anion (O₂^-), hydrogen peroxide (HO₂) and hydroxyl radical (OH)] on isolated rabbit aorta. This thesis will examine the role of OH in Ach- and nitroglycerin (NTG)-induced relaxation of isolated rabbit aorta. Superoxide anions generated by xanthine (X) plus xanthine oxidase (XO) produced concentration-dependent contractions of isolated rabbit aorta. The contractile response to O₂^- was completely abolished in preparations denuded of endothellum or pretreated with superoxide dismutase (SOD), a scavenger of O₂^-. The contractile response was reduced by indomethacin (I), a cyclooxygenase inhibitor. These results suggest that O₂^- mediated by vasoconstrictor arachidonic acid metabolites. Hydrogen peroxide generated by glucose and glucose oxidase produced contraction (low concentrations) and relaxation followed by contraction (high concentrations) in isolated rabbit aorta. The contractile response was abolished in the presence of catalase, a scavenger of H₂O₂ however the relaxant effect was exaggerated. Indomethacin markedly reduced the H₂O₂-induced contraction. Relaxation was completely prevented by de-endothelialization or pretreatment with N^G-monomethyl-L-arginine (LNMMA), an inhibitor of nitric oxide synthetase. These results suggest that H₂O₂ in large concentrations produces a biphasic response, relaxation followed by contraction. Relaxation is endothelium dependent and is mediated by endothelium-derived relaxing factor (EDRF), nitric oxide (NO). The contractile response is endothelium independent and is mediated by vasoconstrictor arachidonic acid metabolites of smooth muscle. Hydroxyl radicals generated by dihydroxyfumarate (DHF), ferric chloride (FeCl₃) and adenosine diphosphate (ADP) (DHF/FeCl₃-ADP) produced concentration dependent relaxations of NE-precontracted rabbit aorta. Mannitol (Ml) completely inhibited OH-induced relaxation. Relaxation was markedly reduced in aortic rings mechanically denuded of endothelium. The relaxant effect was reduced by an inhibitor of NO synthesis (LNMMA), by an inhibitor of guanylate cyclase (methylene blue), by an inhibitor of cyclooxygenase (indomethacin) and by an inhibitor of an ATP-sensitive K⁺ channel blocker (glyburide). These results indicate that OH produces relaxation that is endothelium-dependent and partially mediated by an endothelium-derived relaxing factor (NO), vasodilatory arachidonic acid metabolites and an ATP-sensitive K⁺ channel. We hypothesized that Ach-induced vascular relaxation is mediated by OH derived from the interaction of NO and O₂^-. To test this hypothesis we investigated the effect of Ach and NTG on NE-precontracted isolated rabbit aortic preparations in the absence or presence of scavengers of O₂^- (SOD), and OH (dimethylthiourea (DMTU) or mannitol or Garlicin). The OFR scavengers (SOD, dimethylthiourea, mannitol, garlicin and histidine) alone or the combination of SOD and DMTU markedly reduced Ach- or NTG-induced relaxation. However, the combination of histidine, (a ¹O₂ scavenger) SOD and DMTU completely abolished Ach-induced relaxation.

No description available.

The protic acid-catalyzed polymerization of 1,6-anhydro-6-D-glucopyranose (I) was first reported one-half century ago; however, the mechanism of this reaction has not been resolved and is the topic under investigation in this thesis. In an attempt to resolve this mechanism, a number of 1,6-anhydrides structurally related to 1,6-anhydro-B-D-glucopyranose (I) were prepared and polymerized. The C-2, C-3, or C-4 hydroxyl group was either specifically blocked, replaced by a hydrogen atom or positioned different sterically. The relative rates of disappearance of monomer in the polymerization reaction were measured and this information used to propose a reaction mechanism.

No description available.

Intravenous application of a high dose of endotoxin, such as lipopolysaccharide (LPS), results in endotoxemia and sepsis in experimental animals. LPS induces production of cytokines and free radicals, plasma leakage and systemic inflammation. But the relationship between LPS-induced plasma leakage and endothelial gap formation is still unknown. Under normal physiological and pathological conditions, the mucus of intestine plays an important role in host defense mechanism as a barrier to prevent invasion of bacteria and endotoxin. The integrity of the intestinal epithelium is an important determinant of clinical outcome in septic patients. It is reported that, after LPS application, ileal mucosa is injured consequently. Necrosis of epithelial cells is also prominent feature in the villus epithelium. However, the response of mucin-secreting goblet cells is often ignored. The present study was designed to prove (1) whether LPS application increased plasma leakage by endothelial gap formation in rat intestinal tract, (2) whether LPS application increased goblet cell secretion by compound exocytotic activity in mucosal villi of small intestine; and (3) whether hydroxyl radicals were involved in LPS-induced compound exocytosis in goblet cells and plasma leakage. First, the microcirculation of large intestine in rats was shown by using silver nitrate staining method, and India ink was used to label the leaky microvessels to express the magnitude of plasma leakage. Endothelial gaps formed between endothelial cells in the venules after LPS-induced inflammation were investigated by light and scanning electron microscopy. In saline control, the number of endothelial gaps per 1000 £gm2 endothelium of postcapillary and collecting venules was 0.2 ¡Ó 0.1 ~ 0.4 ¡Ó 0.1 / 1000 £gm2 (n = 5). At 5 minutes after LPS application, the endothelial gap density drastically increased to 12.1 ¡Ó 1.6 ~ 27.5 ¡Ó 2.2 / 1000 £gm2 (n = 5 or 6), about 43-69 times (P < 0.01) as much as control. At the same time, the magnitude of plasma leakage, expressed by area density of India ink-labeled blood vessels, in the cecum and colon of LPS-treated rats increased to 7.8-8.2 times (P < 0.01) as much as control. Unusually high degree of plasma leakage and high number of endothelial gaps persisted for at least 30 minutes after treatment. Then, a significant reduction to the baseline level occurred at 60 minutes after LPS application (P > 0.05). The results evidently indicated that LPS-induced intestinal plasma leakage and the endothelial gap formation of venules were closely related. In the following experiment, in order to obtain an actual number of goblet cells in the mucosal epithelium, an innovative and effective experimental method was developed and adopted to prepare small intestine specimens in this study. Tissue pieces with two rows of mucosal villi were taken under a dissecting microscope. Then, scanning electron microscope was used to observe goblet cells and histochemistry staining was applied to further identify mucosubstance. The degree of goblet cell secretion in the villus epithelium of the duodenum and ileum was expressed by the number of cavitated goblet cells undergoing compound exocytosis. Digital morphometric software SimplePCI was employed to measure the epithelial surface area of sampled villi and to count the number of goblet cells. In addition, hydroxyl radical scavenger ¡V dimethylthiourea (DMTU) was also applied to explore the role of hydroxyl radicals involving in LPS-induced goblet cells secretion and plasma leakage. From scanning electron microscopy study, the numbers of cavitated goblet cells per mm2 of ileal villus epithelium in rats at 5 and 30 minutes after LPS injection were 693 ¡Ó 196 (n = 6) and 547 ¡Ó 213 (n = 6), respectively, which were 5.1 and 8.4 times (P < 0.05) compared with the number of saline control. The percentage of villus cavitated goblet cell numbers, in both duodenum and ileum 5 minutes after LPS and in the ileum 30 minutes after LPS, increased significantly (P < 0.05). When DMTU was given prior to LPS, the number of cavitated goblet cells and the amount of plasma leakage was inhibited and remained at the level as control (P > 0.05). It is concluded that the mechanism of the LPS-induced increase in compound exocytotic activity of goblet cells and increase in plasma leakage during acute phases of inflammatory response in rat small intestine was associated with hydroxyl radicals.

No description available.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1942. / Includes bibliographical references (p. 106-107).