Rate Of Oxide Formation Research Articles

Reactive oxygen species, vascular oxidative stress, and redox signaling in hypertension: what is the clinical significance?

Metabolism of oxygen by cells generates potentially deleterious reactive oxygen species (ROS). Under normal conditions the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between prooxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of oxidant overproduction that overwhelms the cellular antioxidant capacity. The kidney and vasculature are rich sources of NADPH oxidase-derived ROS, which under pathological conditions play an important role in renal dysfunction and vascular damage. Strong experimental evidence indicates that increased oxidative stress and associated oxidative damage are mediators of renovascular injury in cardiovascular pathologies. Increased production of superoxide anion and hydrogen peroxide, reduced nitric oxide synthesis, and decreased bioavailability of antioxidants have been demonstrated in experimental and human hypertension. These findings have evoked considerable interest because of the possibilities that therapies targeted against free radicals by decreasing ROS generation or by increasing nitric oxide availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress hypertensive end-organ damage. This article highlights current developments in the field of ROS and hypertension, focusing specifically on the role of oxidative stress in hypertension-associated vascular damage. In addition, recent clinical trials investigating cardiovascular benefits of antioxidants are discussed, and some explanations for the rather disappointing results from these studies are addressed. Finally, important avenues for future research in the field of ROS, oxidative stress, and redox signaling in hypertension are considered.

A Model of Cu-CMP

AbstractCMP has been described qualitatively in terms of alternating cycles of chemical formation and mechanical removal of a thin layer on the wafer surface. A quantitative model of CMP has been developed2-7 which is based on mechanisms for surface kinetics, treating mechanical removal as one step in the mechanism. This model has been used successfully to explain removal rates for tungsten and thermal oxide CMP. In particular, for tungsten CMP the removal rate increases steeply with increasing oxidizer concentration at low concentrations, and then approaches an asymptotic maximum removal rate at high concentrations. The model explains this by starting with the assumption that mechanical abrasion removes only tungsten oxide but not tungsten metal. It then focuses on the fraction of wafer surface covered by a tungsten oxide layer. At low oxidizer concentrations, the oxide formation rate is small compared the removal rate, so only a small fraction of the surface is oxidized and the removal rate is small. At high oxidizer concentrations, the oxide formation rate is large compared to the removal rate, so most of the surface is oxidized and the removal rate is large. Increasing the oxidizer concentration in the high oxidizer concentration region does not significantly increase the surface fraction of tungsten oxide, and the removal rate approaches a constant value.

Inhibition of arterial contraction by dinitrosyl–iron complexes: critical role of the thiol ligand in determining rate of nitric oxide (NO) release and formation of releasable NO stores by S-nitrosation

The inhibition of arterial tone produced by two nitric oxide (NO) derivatives of biological relevance, dinitrosyl–iron complexes with cysteine (DNIC-CYS) or with glutathione (DNIC-GSH), was compared. Both compounds induced vasorelaxation within the same concentration range (3–300 nM) in endothelium-denuded rat aortic rings. Consistent with a faster rate of NO release from DNIC-CYS than from DNIC-GSH, the relaxant effect of DNIC-CYS was rapid in onset and tended to recover with time, whereas the one of DNIC-GSH developed slowly and was sustained. In addition, DNIC-GSH (0.3 and 1 μM) but not DNIC-CYS (1 μM) induced, even after washout of the drug, a persistent hyporesponsiveness to vasoconstrictors and a relaxant effect of low molecular weight thiols like N-acetylcysteine (NAC, which can displace NO from preformed NO stores). Both effects of DNIC-GSH were associated with elevation of cyclic GMP content and were attenuated by NO scavengers or a cyclic GMP-dependent protein kinases inhibitor. In rings previously exposed to DNIC-GSH, addition of mercuric chloride (which can cleave the cysteineNO bond of S-nitrosothiols) elicited relaxation, completely blunted the one of NAC and also abolished the persistent elevation of NO content. In conclusion, this study shows that whereas both DNIC-CYS and DNIC-GSH elicited a NO release-associated relaxant effect in isolated arteries, only DNIC-GSH induced an inhibition of contraction which persisted after drug removal. The persistent effect of DNIC-GSH was attributed to the formation of releasable NO stores in arterial tissue, most probably as S-nitrosothiols. Thus, the nature of the thiol ligand plays a critical role in determining the mechanisms and duration of the effect of LMW-DNIC in arteries.

A technique to estimate the rate of whole body nitric oxide formation in conscious mice

Objective. We have established a technique to estimate the total rate of nitric oxide (NO) formation in mice, based on inhalation of a stable oxygen isotope ( 18O 2). Changes of NO production with age were also studied. Methods. The experiments were performed in eight-week- ( n=6) and eight-month-old ( n=6–7), respectively, female (C57/Bl6 × CBAca) mice. Pairs of conscious mice were kept in an air-tight closed system allowing breathing of a mixture containing 18O 2. The 18O 2-technique was validated by l-NAME (10 mg/kg) and lipopolysaccharide (LPS, 8 mg/kg) administration. The concentrations of O 2 and CO 2 in the system were controlled and plasma nitrate analyzed by GC/MS technique. Results. NO formation was similar in young and old mice (young=7.68 ± 1.47 vs. old = 6.25 ± 1.49 μmol/kg/h, n.s.). Total NO production was reduced after l-NAME treatment in young animals by 91% and in old animals by 71% ( p<0.05 for both), whereas LPS administration increased NO production (114 ± 17%, p<0.05). Conclusion. NO formation is unaltered with age in mice. The 18O 2-technique is a valid and specific technique to estimate whole body NO production in conscious mice.

Single crystal experiments on grains of polycrystalline materials: oxide formation on Zr and Ta.

Passivation on polycrystalline Zr (hcp) and Ta (bcc) depends on the crystallographic orientation of the individual grains, determined by electron back scattering diffraction (EBSD). Microelectrochemical experiments yield characteristic data, such as oxide formation potentials, formation factors, capacities, and thicknesses, of local oxide formation on single grains. Strong differences occur on Zr, for Ta only a small influence of crystallographic orientation is observed. The rate of oxide formation, determined from potentiodynamic and capacitive measurements, and EBSD pattern quality, increases with decreasing surface atom density. The dominating influence can be described by the Euler angle phi, the second angle phi2 has a smaller influence. The differences in surface atom density lead to a specific current-dependent potential drop during oxide growth and therefore to a shift in the oxide formation potential. Furthermore the crystallinity and epitaxy of the oxides can depend on the orientation of the base metal causing a variation in ion conductivity.

Synthesis of titanium silicalite (TS-1) from the TPABr system and its catalytic properties for epoxidation of propylene

Titanium silicalite (TS-1) was successfully synthesized by using tetra-propylammonium bromide (TPABr) and n-butylamine as the template and the base, respectively. XRD, IR, SEM, 13 C CP/MAS NMR, UV–VIS, and UV-Raman techniques were used to characterize the synthesized products. The results show that TS-1 has MFI structure with high crystallinity and large crystal size, and with two kinds of titanium species. Using epoxidation of propylene as the probe, the catalytic properties of TS-1 in the present work were investigated. The crystal size of TS-1 affects much the initial reaction rate of propylene oxide (PO) formation. The effects of reaction conditions on PO reveal that the PO formation is greatly influenced by the solvent and the solution pH value. Methanol is the most preferable solvent, and a portion of water (<30%) in solution does not have much impact on the reaction. Moreover, the addition of base used to neutralize the residual acidity of the catalyst favor the reaction, the catalyst shows high activity and selectivity upon the adequate amount of base and the catalyst can be used repeatedly without regeneration. In the fixed-bed reactor, using ammonium water as the neutralizer, after 200 h of reaction, both the conversion and the utilization of H 2O 2 is about 95%, the selectivity of PO is about 90%.

Investigation of titanium corrosion in concentrated NaOH solutions

The rate of both spontaneous and polarization assisted formation of oxide films on commercially grade titanium, DIN 3.7025, was studied in concentrated, 1 - 5M NaOH solutions, with particular attention to the early stages of oxide formation. Simultaneous chemical dissolution of oxides was considered. The rate of spontaneous oxide formation was examined with cyclic voltammetry as an in-situ method. The shape of potentiodynamic curves recorded in different alkaline solutions indicated that the electrolyte concentration affects the oxide composition. Titanium electrodes were covered with oxide films of different thickness, and the time dependence of polarization resistance was measured under a fixed anodic polarization. The polarization resistance may either increase or decrease tending to attain a stationary value, which, for a fixed polarization, depends on both the initial thickness and the NaOH concentration. (orig.)

Unraveling peroxynitrite formation in biological systems

Peroxynitrite promotes oxidative damage and is implicated in the pathophysiology of various diseases that involve accelerated rates of nitric oxide and superoxide formation. The unambiguous detection of peroxynitrite in biological systems is, however, difficult due to the combination of a short biological half-life, limited diffusion, multiple target molecule reactions, and participation of alternative oxidation/nitration pathways. In this review, we provide the conceptual framework and a comprehensive analysis of the current experimental strategies that can serve to unequivocally define the existence and quantitation of peroxynitrite in biological systems of different levels of organization and complexity.

Photochemical reactivity of aquatic macrophyte leachates: abiotic transformations and bacterial response

We evaluated the influence of UV radiation exposure time on abiotic transformations of leachates from 2 aquatic macrophytes: Phragmites australis and Hydrocaris morsus-ranae. In addition, we studied the influence of phototransformations of DOM on bacterial growth. Sterile filtered leachates were exposed to UV radiation for 5, 10, 24, 48, 72 and 120 h or kept in the dark. Dissolved inorganic carbon (DIC), hydrogen peroxide and low molecular weight carboxylic acids (oxalic, formic, malonic and acetic acids) were measured. After UV or dark treatment, the leachates were inoculated with bacteria and incubated in the dark. Based on the observed DIC and hydrogen per oxide formation rates, we concluded that phototransformations are initially more rapid in H. morsus-ranae DOM than in P. australis DOM. On the other hand, production of DIC after more than 48 h of UV exposure was strongly reduced for H. morsus-ranae DOM, whereas DIC production was only slightly reduced for P. australis DOM. The differences in the photoreactivity between DOM from P. australis and H. morsus-ranae DOM were also reflected in the bacterial growth response to DOM phototransformations. The lowest bacterial growth efficiencies (BGE) were found in the irradiated leachate of P, australis exposed for more than 48 h and in the irradiated leachate of H, morsus-ranae exposed for 10 h, which coincided with the highest concentrations of hydrogen peroxide for both types of leachates. (Less)

Anodic oxidation behaviour of Al–Ti alloys in acidic media

The anodic oxidation behaviour of Al–Ti alloys in several acidic solutions was investigated. The influence of conditions such as alloy composition, electrolytic solution, electrolyte temperature and formation current density on the formation rate of oxides on Al–Ti alloys and the dielectric properties of the anodic films were analysed. It was shown that the oxide formation rate for the Al–Ti alloy containing 54 at % aluminium was the highest and the dielectric property of its anodic oxide was also the best. In addition, by means of several surface analytical techniques, the chemical composition of the films were determined as (TiO2) n (Al2O3) m . AES (Auger electron spectroscopy) profiling analysis data showed that Al–Ti alloys had preferential oxidation behaviour, that is, the aluminium was oxidized preferentially.

Nitrate reductase and nitrous oxide production by Fusarium oxysporum 11dn1 under aerobic and anaerobic conditions.

The fungus Fusarium oxysporum 11dn1 was found to be able to grow and produce nitrous oxide on nitrate-containing medium in anaerobic conditions. The rate of nitrous oxide formation was three to six orders of magnitude lower than the rates of molecular nitrogen production by common denitrifying bacteria. Acetylene and ammonia did not affect the release of nitrous oxide release. It was shown that under anaerobic conditions fast increase of nitrate reductase activity occurred, caused by the synthesis of enzyme de novo and protein dephosphorylation. Reverse transfer of the mycelium to aerobic conditions led to a decline in nitrate reductase activity and stopped nitrous oxide production. The presence of two nitrate reductases was shown, which differed in molecular mass, location, temperature optima, and activity in nitrate- and ammonium-containing media. Two enzymes represent assimilatory and dissimilatory nitrate reductases, which are active in aerobic and anaerobic conditions, respectively.

Reactions of oxygen atoms and molecules with Au, Be, and W surfaces

In this study, the adsorption of atomic oxygen on polycrystalline gold, tungsten and single crystalline beryllium (0001) surfaces is investigated at room temperature and compared with molecular oxygen. The O atoms are produced by microwave discharge in pure O 2. The gaseous reactants effuse into a UHV chamber. The adsorption or chemical reaction of the oxygen atoms and molecules impinging on the metal surfaces is monitored by X-ray photoelectron spectroscopy (XPS). The main observations of this study are summarized as follows. The gold surface is inert to molecular oxygen but adsorbs O atoms up to a coverage of one monolayer. Beryllium adsorbs both molecular and atomic oxygen and is also oxidized by both species. The rate of oxide formation is significantly larger for O atoms. In the case of tungsten, there is no difference between atoms and molecules in the amount of oxygen adsorbed. Neither species, however, forms any phase of tungsten oxide. Only tungsten binding energies characteristic of the pure metal and for oxygen adsorbed within the first atomic layer are detected.

In Situ Infrared Observation of Etching and Oxidation Processes on Si Surfaces in NH 4 F Solution

We use infrared absorption spectroscopy in the multiple internal reflection geometry to investigate in situ and in real‐time the chemical process at Si(100) surfaces that are immersed in a dilute solution of ammonium fluoride, . We have followed spectral changes in the Si‐H stretch vibration region of the surface during immersion in the solution. Infrared spectroscopic data show that the native oxide on the surface is initially removed by solution and subsequently, H‐terminated Si(111) microfacets are increasingly populated. Long‐term immersion in dilute leads to oxide formation on the surface. The rate of oxide formation strongly depends on the concentration of ; oxide formation is enhanced at concentrations below 10% and it does not occur at concentrations above 20%. We suggest that oxide formation and subsequent oxide removal proceed on Si surfaces in dilute solution and that at low concentration, the rate of oxide formation is higher than that of oxide removal. © 2000 The Electrochemical Society. All rights reserved.

Smoothing, passivation and re-passivation of silicon surfaces by anodic oxidation: a low thermal budget process

The anodic oxidation of silicon surfaces as a low thermal budget process was investigated. The anodic oxidation leads to a smoothing effect of the surface due to the electric field enhanced growth process. This behavior leads to an increase of the breakdown voltage with respect to the thermally grown oxides. The rate of oxide formation depends on the amount of water in the solution, the temperature of the solution and the current density. The electronic properties (oxide charge and interface state density) depend only slightly on the temperature and current density, but they are strongly influenced by the amount of water. The oxidation rate is strongly increased by the water content of the electrolyte, which then leads to a higher defect concentration at the interface. The final oxide thickness depends on the applied potential and the amount of water in the electrolyte. The liquid contact allows the passivation and re-passivation of highly structured Si surfaces.

Oxidative stress and vascular damage in hypertension.

Metabolism of oxygen by cells generates potentially deleterious reactive oxygen species, including superoxide anion radical, hydrogen peroxide, and hydroxyl radical. Under normal physiologic conditions the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between prooxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of the overproduction of oxidants that overwhelms the cellular antioxidant capacity. There is increasing evidence that an elevation of oxidative stress and associated oxidative damages are mediators of vascular injury in various cardiovascular pathologies, including hypertension, atherosclerosis, and ischemia-reperfusion. This review focuses on the vascular effects of reactive oxygen species and the role of oxidative stress in vascular damage in hypertension.

Characteristics of nitric oxide formation rates in turbulent nonpremixed jet flames

The formation of oxides of nitrogen, NO x , in turbulent nonpremixed flames is experimentally analyzed making use of velocity, temperature, and major species concentration measurements in jet propane flames. The analysis considered the contributions of Zeldovich (thermal) and Fenimore (prompt) mechanisms at different locations of attached vertical flames with Reynolds numbers of 20,400 and 37,600. The analysis of NO mass formation rates suggests that prompt mechanism dominates NO formation throughout the flames, with peak formation rates occurring in the rich flame region, at locations r/ x approximately equal to 0.08, where r and x are the radial and axial coordinate, respectively. NO concentrations are shown to decrease with Reynolds number, as the gas residence times are reduced, although mass flow rates of NO x per unit mass flow rate of fuel are independent of Reynolds number.

In-situ epoxidation using dioxiranes: evaluation of reactivity and selectivity

The epoxidation of cyclohexene to cyclohexene oxide by dioxiranes in the ketone/oxone system was studied. The catalytic activities of acetone, butan-2-one, pentan-2-one and 1,1,1-trifluoroacetone were investigated. A monophasic and a biphasic system were investigated for this reaction, namely tetrahydrofuran (THF)/water and dichloromethane/water. The THF/water system was found to be more efficient at converting cyclohexene to cyclohexene oxide. It was found that the rate of cyclohexene oxide formation increased in proportion to increasing ketone concentration using 1,1,1-trifluoroacetone, acetone and butan-2-one. Turnover frequencies were in the range 0–2·75 h−1, in sharp contrast to the perceived reactivity of this system. The greater the solubility of a ketone in water the greater its catalytic activity. The selectivity in terms of cyclohexene conversion to cyclohexene oxide was always 100% but the selectivity in terms of KHSO5 utilisation was generally less than 60%, even in the best experimental conditions. © 1998 SCI

The Role of Nitrous Oxide in the Mechanism of Thermal Nitric Oxide Formation within Flame Temperature Range

The thermal nitric oxide formation in a one-dimensional tubular flow reactor has been investigated. A mixture of oxygen and nitrogen was continuously supplied into an electrically heated reactor of wall temperature within the range 1653-I798K. Five different reactor diameters made of two materials were used. The measured rate of nitric oxide formation was much higher than the calculated by the Zeldovich thermal mechanism with the available rate constants. During the experiments no fuel was supplied into the reactor, thus the concept of the Fenimore prompt NO could not be used to clear up these discrepances. Also the nitrous oxide mechanism with the recommended rate constants could not explain the results. The observed rate of nitric oxide formation has been described by a sequence of five reactions formed of the Zeldovich mechanism and the proposed by Malte and Pratt N2O mechanism: for which the rate constants of reactions (1) and (7) with the assumption of O radicals in equilibrium were tested. Because these reactions proceed independently of the combustion process it is proposed to call them as an extended thermal mechanism. The rate of nitric oxide formation through the extended thermal mechanism is much faster than by the Zeldovich thermal mechanism (reactions 1 and 2) within the flame temperature range. The role of nitrous oxide for the thermal NO build up is crucial in temperatures below 1800K, while of the Zeldovish mechanism (reactions 1 and 2) above 2000K.

Regional measurements of NO formed in vivo during brain ischemia.

Nitric oxide formed in vivo in the rat brain regions of hippocampus, striatum, neocortex and cerebellum was spin trapped and measured ex vivo by cryogenic electron paramagnetic resonance spectroscopy. In non-ischemic control animals the rate of nitric oxide (NO) formation in the individual brain regions ranged from 15 to 42 pmol.g-1.min-1. During exposure to global ischemia for 7 min the generation of NO increased in all parts of the brain. In the hippocampus the rate of NO formation during ischemia increased by 6-fold from a control rate of 19 pmol.g-1.min-1. This increase was attenuated 47% by pretreatment with the NO synthase antagonist 7-nitroindazole, whereas pretreatment with the non-NMDA receptor anatogonist NBQX and the Ca2+ channel blocker NS638 did not influence the NO formation. The data show that short-duration ischemia elicits a significant, NO-synthase-dependent formation of NO in all brain regions.

The catalytic activity of cytochrome P450cam towards styrene oxidation is increased by site-specific mutagenesis

The styrene oxidation activity of cytochrome P450cam has been greatly improved by rational protein engineering. Compared to the wild-type enzyme, the active-site mutants Y96A and Y96F bound styrene more tightly, consumed NADH more rapidly, and were more efficient at utilising reducing equivalents for product formation. Styrene oxide formation rates were enhanced 9-fold in the Y96A mutant relative to wild-type, and 25-fold in the Y96F mutant, thus demonstrating the effectiveness of active-site redesign in improving the activity of a haem monooxygenase towards an unnatural substrate.©1997 Federation of European Biochemical Societies.