Copper/MCM-41 as catalyst for photochemically enhanced oxidation of phenol by hydrogen peroxide

Heterogeneous copper catalyst was developed using the mesoporous molecular sieve MCM-41 as the catalyst support. Copper was impregnated onto the support. Catalysts with different copper loadings were obtained. The performance of the developed catalysts was evaluated in photochemically enhanced oxidation of phenol using hydrogen peroxide as the oxidant. The catalyst was found to significantly increase the oxidation rate and enhance the removal level of phenol with UV light present. The effects of copper loading on the catalyst, photo (UV), H2O2 concentration, and catalyst dosage on the photo-oxidation of phenol were studied. (C) 2001 Elsevier Science B.V. All rights reserved.

Azurin of pathogenic Neisseria spp. is involved in defense against hydrogen peroxide and survival within cervical epithelial cells

Laz, a lipid-modified azurin of the human pathogens Neisseria gonorrhoeae and Neisseria meningitidis, is involved in defense against oxidative stress and copper toxicity; laz mutant strains are hypersensitive to hydrogen peroxide and copper. The N. gonorrhoeae laz mutant also has decreased survival in an ex vivo primary human ectocervical epithelial assay.

A dual catalyst bed system for the elimination of hydrogen from CO2 feed gas in urea synthesis

A dual catalyst bed system (Au/Fe2O3 + Pt-Pd/Al2O3) for eliminating hydrogen from the CO2 feed gas in urea synthesis is found to be far superior to commercially available and patented catalysts in catalytic activity. At relatively low temperatures, hydrogen is eliminated and coexistent CO is also oxidized completely to useful CO2. This can avoid effectively the accidental explosion of hydrogen-oxygen-ammonia mixed gases, thus ensuring the safety of urea synthesis.

OxyR acts as a repressor of catalase expression in Neisseria gonorrhoeae

It has been reported that Neisseria gonorrhoeae possesses a very high level of catalase activity, but the regulation of catalase expression has not been investigated extensively. In Escherichia coli and Salmonella enterica serovar Typhimurium, it has been demonstrated that OxyR is a positive regulator of hydrogen peroxide-inducible genes, including the gene encoding catalase. The oxyR gene from N. gonorrhoeae was cloned and used to complement an E. coli oxyR mutant, confirming its identity and function. The gene was inactivated by inserting a kanamycin resistance cassette and used to make a knockout allele on the chromosome of N. gonorrhoeae strain 1291. In contrast to E. coli, the N. gonorrhoeae oxyR::kan mutant expressed ninefold-more catalase activity and was more resistant to hydrogen peroxide killing than the wild type. These data are consistent with OxyR in N. gonorrhoeae acting as a repressor of catalase expression.

Cytotoxic iron chelators: Characterization of the structure, solution chemistry and redox activity of ligands and iron complexes of the di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues

Di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) and a range of its analogues comprise a series of monobasic acids that are capable of binding iron (Fe) as tridentate (N,N,O) ligands. Recently, we have shown that these chelators are highly cytotoxic, but show selective activity against cancer cells. Particularly interesting was the fact that cytotoxicity of the HPKIH analogues is maintained even after complexation with Fe. To understand the potent anti-tumor activity of these compounds, we have fully characterized their chemical properties. This included examination of the solution chemistry and X-ray crystal structures of both the ligands and Fe complexes from this class and the ability of these complexes to mediate redox reactions. Potentiometric titrations demonstrated that all chelators are present predominantly in their charge-neutral form at physiological pH (7.4), allowing access across biological membranes. Keto-enol tautomerism of the ligands was identified, with the tautomers exhibiting distinctly different protonation constants. Interestingly, the chelators form low-spin (diamagnetic) divalent Fe complexes in solution. The chelators form distorted octahedral complexes with Fe-II, with two tridentate ligands arranged in a meridional fashion. Electrochemistry of the Fe complexes in both aqueous and non-aqueous solutions revealed that the complexes are oxidized to their ferric form at relatively high potentials, but this oxidation is coupled to a rapid reaction with water to form a hydrated (carbinolamine) derivative, leading to irreversible electrochemistry. The Fe complexes of the HPKIH analogues caused marked DNA degradation in the presence of hydrogen peroxide. This observation confirms that Fe complexes from the HPKIH series mediate Fenton chemistry and do not repel DNA. Collectively, studies on the solution chemistry and structure of these HPKIH analogues indicate that they can bind cellular Fe and enhance its redox activity, resulting in oxidative damage to vital biomolecules.

Effects of hydrogen-air non-equilibrium chemistry on the performance of a model scramjet thrust nozzle

Two aspects of hydrogen-air non-equilibrium chemistry related to scramjets are nozzle freezing and a process called 'kinetic afterburning' which involves continuation of combustion after expansion in the nozzle. These effects were investigated numerically and experimentally with a model scramjet combustion chamber and thrust nozzle combination. The overall model length was 0.5m, while precombustion Mach numbers of 3.1 +/- 0.3 and precombustion temperatures ranging from 740K to 1,400K were involved. Nozzle freezing was investigated at precombustion pressures of 190kPa and higher, and it was found that the nozzle thrusts were within 6% of values obtained from finite rate numerical calculations, which were within 7% of equilibrium calculations. When precombustion pressures of 70kPa or less were used, kinetic afterburning was found to be partly responsible for thrust production, in both the numerical calculations and the experiments. Kinetic afterburning offers a means of extending the operating Mach number range of a fixed geometry scramjet.

Comparative study of hydrogen storage in Li- and K-doped carbon materials - theoretically revisited

Hydrogen adsorption in alkali-doped carbon materials is investigated theoretically. Our calculations show that hydrogen molecules can be physically adsorbed on alkali-doped graphite at 0 K but such an adsorption is thermodynamically unfavourable. The binding energy of hydrogen adsorption decreases significantly with the increase in temperature and becomes nearly zero at ambient temperature. We suggest that it may be unlikely to observe any hydrogen uptake in alkali-doped carbon materials at or above ambient temperature in the TGA (thermogravimetric) system, the previously reported hydrogen uptake in alkali-doped carbon materials was caused by either uncyclable chemisorbed hydrogen on the defects of carbon (defects were produced by repeated heat treatment) and/or moisture adsorption. (C) 2004 Elsevier Ltd. All rights reserved.

The role of Ti as a catalyst for the dissociation of hydrogen on a Mg(0001) surface

In this paper, the dissociative chemisorption of hydrogen on both pure and Ti-incorporated Mg(0001) surfaces are studied by ab initio density functional theory (DFT) calculations. The calculated dissociation barrier of hydrogen molecule on a pure Mg(0001) surface (1.05 eV) is in good agreement with comparable theoretical studies. For the Ti-incorporated Mg(0001) surface, the activated barrier decreases to 0.103 eV due to the strong interaction between the molecular orbital of hydrogen and the d metal state of Ti. This could explain the experimentally observed improvement in absorption kinetics of hydrogen when transition metals have been introduced into the magnesium materials.

Macrophages overexpressing tartrate-resistant acid phosphatase show altered profile of free radical production and enhanced capacity of bacterial killing

Activated macrophages and osteoclasts express high amounts of tartrate-resistant acid phosphatase (TRACP, acp5). TRACP has a binuclear iron center with a redox-active iron that has been shown to catalyze the formation of reactive oxygen species (ROS) by Fenton's reaction. Previous Studies Suggest that ROS generated by TRACP may participate in degradation of endocytosed bone matrix products in resorbing osteoclasts and degradation of foreign Compounds during. antigen presentation in activated macrophages. Here we have compared free radical production in macrophages of TRACP overexpressing (TRACP +) and wild-type (WT) mice. TRACP overexpression increased both ROS levels and Superoxide production. Nitric oxide production was increased in activated macrophages or WT mice, but not in TRACP+ mice, Macrophages from TRACP+ mice showed increased capacity or bacterial killing. Recombinant TRACP enzyme was capable of bacterial killing in the presence of hydrogen peroxide. These results suggest that TRACP has an important biological function in immune defense systern.

Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

The defect effect on hydrogen adsorption on single-walled carbon nanotubes (SWNTs) has been studied by using extensive molecular dynamics simulations and density functional theory (DFT) calculations. It indicates that the defects created on the exterior wall of the SWNTs by bombarding the tube wall with carbon atoms and C-2 dimers at a collision energy of 20 eV can enhance the hydrogen adsorption potential of the SWNTs substantially. The average adsorption energy for a H-2 molecule adsorbed on the exterior wall of a defected (10,10) SWNT is similar to 150 meV, while that for a H-2 molecule adsorbed on the exterior wall of a perfect (10,10) SWNT is similar to 104 meV. The H-2 sticking coefficient is very sensitive to temperature, and has a maximum value around 70 to 90 K. The electron density contours, the local density of states, and the electron transfers obtained from the DFT calculations clearly indicate that the H-2 molecules are all physisorbed on the SWNTs. At temperatures above 200 K, most of the H-2 molecules adsorbed on the perfect SWNT are soon desorbed, but the H-2 molecules can still remain on the defected SWNTs at 300 K. The detailed processes of H-2 molecules adsorbing on and desorbing from the (10,10) SWNTs are demonstrated.

Control of hypersonic turbulent skin friction by boundary-layer combustion of hydrogen

Shvab-Zeldovich coupling of flow variables has been used to extend Van Driest's theory of turbulent boundary-layer skin friction to include injection and combustion of hydrogen in the boundary layer. The resulting theory is used to make predictions of skin friction and heat transfer that are found to be consistent with experimental and numerical results. Using the theory to extrapolate to larger downstream distances at the same experimental conditions, it is found that the reduction in skin-friction drag with hydrogen mixing and combustion is three times that with mixing alone. In application to flow on a flat plate at mainstream velocities of 2, 4, and 6 knits, and Reynolds numbers from 3 X 10(6) to 1 x 10(8), injection and combustion of hydrogen yielded values of skin-friction drag that were less than one-half of the no-injection skin-friction drag, together with a net reduction in heat transfer when the combustion heat release in air was less than the stagnation enthalpy. The mass efficiency of hydrogen injection, as measured by effective specific impulse values, was approximately 2000 s.

Sources of hydrogen sulfide in groundwater on reclaimed land

Fisherman Islands is an area of reclaimed land at the mouth of the Brisbane River in Queensland, Australia. Ongoing groundwater monitoring has found elevated concentrations of hydrogen sulfide (H2S) in the groundwater on the island. The presence of H2S on Fisherman Islands is of concern because of its toxic nature, the potential for acid sulfate soil formation, and its noxious odor. The aim of this study was,to, identify the sources of H2S within the groundwater on Fisherman Islands. It was hypothesized that the H2S is being formed by sulfate reducing bacteria acting on sulfate from seawater, rather than the introduction of sulfide with the dredge sediments. Groundwater and soil samples were collected and analyzed for sulfide, sulfate, and organic carbon contents. Elevated concentrations of sulfides coincide with,elevated concentrations of sulfate in the groundwater and elevated concentrations of organic carbon in the sediments, supporting the hypothesis that sulfide formation is the result of heterotrophic, sulfate reducing organisms.

Ab initio studies of hydrogen desorption from low index magnesium hydride surface

The low index Magnesium hydride surfaces, MgH2(001) and MgH2(110), have been studied by ab intio Density Functional Theory (DFT) calculations. It was found that the MgH2(110) surface is more stable than MgH2(001) surface, which is in good agreement with the experimental observation. The H-2 desorption barriers vary depending on the crystalline surfaces that are exposed and also the specific H atom sites involved-they are found to be generally high, due to the thermodynamic stability of the MgH2, system, and are larger for the MgH2(001) surface. The pathway for recombinative desorption of one in-plane and one bridging H atom from the MgH2(110) surface was found to be the lowest energy barrier amongst those computed (172 KJ/mol) and is in good agreement with the experimental estimates. (c) 2006 Elsevier B.V. All rights reserved.

Catalytic effects of subsurface carbon in the chemisorption of hydrogen on a Mg(0001) surface: an ab-initio study

Ab initio density functional theory (DFT) calculations are performed to explore possible catalytic effects on the dissociative chemisorption of hydrogen on a Mg(0001) surface when carbon is incorporated into Mg materials. The computational results imply that a C atom located initially on a Mg(0001) surface can migrate into the subsurface and occupy an fcc interstitial site, with charge transfer to the C atom from neighboring Mg atoms. The effect of subsurface C on the dissociation of H-2 on the Mg(0001) surface is found to be relatively marginal: a perfect sublayer of interstitial C is calculated to lower the barrier by 0.16 eV compared with that on a pure Mg(0001) surface. Further calculations reveal, however, that sublayer C may have a significant effect in enhancing the diffusion of atomic hydrogen into the sublayers through fcc channels. This contributes new physical understanding toward rationalizing the experimentally observed improvement in absorption kinetics of H2 when graphite or single walled carbon nanotubes (SWCNT) are introduced into the Mg powder during ball milling.