Hydrogen Peroxide in Deep Waters of the North Pacific Ocean

Hydrogen peroxide is a reactive oxygen intermediate that can play a role in a variety of redox cycles. In the ocean, it is generally considered to be dominantly photo-produced with negligible concentrations in deep waters. We have utilized a highly sensitive analytical method to investigate hydrogen peroxide in deep waters of the North Pacific Ocean. We present evidence that hydrogen peroxide exists in low nanomolar concentrations in these deep waters with an apparent minimum in the depth range of the oxygen minimum. A consideration of possible mechanisms and rates suggests both a short (similar to12 day) residence time as well as a biological origin for this deep hydrogen peroxide. Hydrogen peroxide is probably of minor importance to metal cycling in the deep ocean except in low oxygen environments

Distribution of Hydrogen Peroxide In the Northwest Pacific Ocean

[1] Hydrogen peroxide (H2O2) is a reactive oxygen intermediate involved in the cycling of metals and dissolved organic matter. Because little is known of its distribution in the North Pacific Ocean, we determined H2O2 in surface waters continuously and obtained vertical profiles at nine stations during a cruise from Japan to Hawaii. Surface water H2O2 varied from less than 10 to more than 250 nmol dm(-3). A diel cycle in surface water H2O2 (similar to 25 nmol dm(-3)) was observed only on one day during the monthlong cruise. This is contrary to expectations based on the usual assumption of photo-production as the dominant input of H2O2. Experiments were also conducted during the cruise to examine both photo-production and dark decay. The net rate of photo-production at a station near Hawaii was determined to be 8 nmol dm(-3) h(-1), similar to rates reported for the central Atlantic Ocean and Antarctic. However, this maximum estimate of photo-production is also similar to probable rates of H2O2 input by other mechanisms ( biological production and rain). The pseudo-first-order rate constant for dark decay varied from 0.1 to 0.2 d(-1), which is toward the low end of previous reports of H2O2 decay rates, and was observed to increase proportionately to the dissolved organic carbon concentration. Taken together, these results suggest that photo-production of H2O2 in open ocean waters may be less important than previously thought and therefore H2O2 is likely less of an indicator of the photo-chemical reactivity of surface waters than hoped for. Furthermore, we observed that the H2O2 inventory for the upper 200 m of the water column has a maximum at midlatitudes. We suggest that this results from diminished inputs at high latitude as well as increased decay rates at low latitudes

Using metal-ligand interactions to access biomimetic supramolecular polymers with adaptive and superb mechanical properties

Natural Science Foundation of China [21074103]; Fundamental Research Funds for the Central Universities [2010121018]; Scientific Research Foundation for Returned ScholarsThe development of polymer materials that exhibit excellent mechanical properties and can respond to environmental stimuli is of great scientific and commercial interest. In this work, we report a series of biomimetic supramolecular polymers using a ligand macromolecule carrying multiple tridentate ligand 2,6-bis(1,2,3-triazol-4-yl)pyridine (BTP) units synthesized via CuAAC in the polymer backbone together with transition and/or lanthanide metal salts. The metal-ligand complexes phase separate from soft linker segments, acting as physical crosslinking points in the materials. The metallo-supramolecular films exhibit superb mechanical properties, i.e., high tensile strength (up to 18 MPa), large strain at break (>1000%) and exceptionally high toughness (up to 70 MPa), which are much higher than those of the ligand macromolecule and are tunable by adjusting the stoichiometric ratio of Zn2+ to Eu3+ and the stoichiometry of metal ion to ligand. The metal-ligand hard phase domains are demonstrated to be thermally stable but mechanically labile, similar to the behaviors of covalent mechanophores. The thermal stability and mechanical responsiveness are also dependent on the compositions of metal ions. The disruption of the hard phase domains and the dissociation of metal-ligand complexes under stretching are similar to the unfolding of modular domains in modular biomacromolecules and are responsible for the superb mechanical properties. In addition, the biomimetic metallo-supramolecular materials display promising responsive properties to UV irradiation and chemicals. These well designed, created and characterized robust structures will inspire further accurate tailoring of biomimetic responsive materials at the molecular level and/or nanoscale

Seasonal Variation in Precipitation Patterns to the Global Ocean: An Analysis of the GPCP Version 2 Data Set

An analysis of temporal and spatial variation of oceanic precipitation was conducted on the GPCP version two data set. While the precipitation patterns observed are generally similar to the previous climatologies, new features and greater detail of global precipitation were revealed from out analysis of the GPCP data set. High precipitation waw observed in the inter-tropical convergence zone, the South Pacific convergence zone, and the storm tracks in the North Pacific and Atlantic Oceans. Low precipitation was observe in the Polar regions and in the subtropics of the East Pacific, East Atlantic, and the Southeast and Northwest Indian Ocean. The spatial coverage of these high and low precipitation regions changed thruough the year. A strong seasonal cycle or precipitation was observed for the Northern and the Southern Hemispheres and for each ocean basin. Global precipitation also varied significantly with both latitude and longitude, with a latitudinal maximum at 56 degrees South, 39 degrees South, 4 degrees South, 6 degrees North, 39 degrees North, and 56 degress North, and a longitudinal maxiumum over each ocean. The seasonal varying precipitation patterns are a foundation for evaluating the effect of wet deposition on ocean circulation, flux of chemical species, and its effect on marine ecosystems

Determination of Subnanomolar Levels of Hydrogen Peroxide in Seawater by Reagent-Injection Chemiluminescence Detection

A reagent-injection chemiluminescent method for the determination of hydrogen peroxide (H2O2) has been developed. The method is based on the catalytic (cobalt (IT)) oxidation of luminol by hydrogen peroxide in an alkaline solution. One mixed reagent is used for the analysis using the reagent injection method. The mixed reagent is optimized for pH and concentration of luminol and Co2+. Apart from Fe2+, none of the 14 species tested showed interference at their seawater levels. Because Fe2+ oxidation is rapid compared to the rate of decay of hydrogen peroxide, the Fe2+ interference can be eliminated by storing seawater samples for 1 h. The combination of reagents and the adaptation of reagent injection lead to a subnanomolar detection limit. The accuracy of the method is at least 0.42 nM. The precision of the method is 17 pM (for a 0.57 nM sample). The method has been used aboard ship to determine the concentrations of hydrogen peroxide in seawater samples in the open ocean as well as on the continental shelf

The Variation of Hydrogen Peroxide in Rainwater Over the South and Central Atlantic Ocean

The concentration of hydrogen peroxide in rainwater over the South and Central Atlantic Ocean was determined. The rainwater samples were collected during an Intergovernmental Oceanographic Commission (IOC) sponsored baseline expedition in May and June 1996. The concentration of hydrogen peroxide was determined on diluted samples using a cobalt-catalyzed luminol chemiluminesence method. The concentration of hydrogen peroxide in rainwater varied from 3.5 to 71 μM with an average (n=25) and standard deviation of 26 and 22 μM, respectively. These are similar to previously reported average hydrogen peroxide concentrations in marine rainwater of the Gulf of Mexico (40 μM), the western Atlantic Ocean (13 μM), and Florida Keys (28 μM). The concentration of hydrogen peroxide in rainwater varied with time of the day, with lower concentrations in early morning and higher concentrations in the late afternoon. The rainwater concentration of hydrogen peroxide also decreased during a rainstorm that may be an indication of a washout effect. The general levels of hydrogen peroxide in rainwater reported here and elsewhere together with the satellite-measured global distribution of precipitation indicate that wet deposition could affect water column hydrogen peroxide significantly in certain parts of the world

The Distribution of Hydrogen Peroxide in the Southern and Central Atlantic Ocean

The near-surface distribution and processes controlling the distribution of hydrogen peroxide were examined in the South and central Atlantic Ocean during a transect from Uruguay to Barbados in May and June 1996. Four kinds of held experiments were conducted during the cruise including diel observations, dark decay experiments, photochemical production experiments, and hydrogen peroxide-enrichment experiments. Significant diel variations (similar to 25 nM) of hydrogen peroxide were observed, with surface-water concentrations increasing during the day and decreasing at night. With a dark decay half-life of 5.5 days and a net rate of photochemical production of 8.3 nM/h at local noon, it appears that both decay rate and photo-production rate of hydrogen peroxide are much smaller in oligotrophic seawater than in coastal seawater. The experimental results indicate that: (1) the decay reaction is a second-order reaction over all, first-order with both the concentration of hydrogen peroxide and the concentration of colloidal material; (2) seawater in the study area could restore its ambient levels of hydrogen peroxide in about 4d after external perturbations. A total of 20 vertical profiles were obtained at 11 stations that can be classified as: surface maximum, surface mixed, and sub-surface maximum. Generally, the concentration of H2O2 decreased with depth to less than 5 nM below 200 m. Hydrogen peroxide also was determined in some water samples from below 200 m, which revealed a slight increase of hydrogen peroxide with depth. In the surface waters of the open ocean, hydrogen peroxide increased with latitude from about 24 nM in the south (33.8 degreesS) to about 80 nM in the north (8.9 degreesN). This latitudinal variation of hydrogen peroxide correlated with model-calculated solar irradiance, satellite-measured wet deposition, depth of the mixed layer, and possibly total organic carbon. The water-column hydrogen peroxide inventory varied from 1.5 to 6.3 x 10(-3) mol/m(2). Although the greatest shallow water concentrations were observed at stations in the Amazon plume, these stations showed a dramatic decrease in hydrogen peroxide with depth and integrated-water-column hydrogen peroxide was not significantly higher than at open ocean stations. (C) 2001 Elsevier Science Ltd. All rights reserved

Comparison of compressible and incompressible numerical methods in simulation of a cavitating jet through a poppet valve

The regime of compressible flow generally refers to the super/subsonic case. However, several remarkable cases with low Mach number could not be appropriately described with the incompressible method. It is a similar case for a cavitating jet inside a poppet valve. In order to comprehensively address the discrepancy between incompressible and compressible methods, both non-cavitating and cavitating cases are performed in experiment and calculation based on OpenFOAM. Experiment reveals a transition in flow pattern in both non-cavitating and cavitating flow. For example, for 0.7 mm openness and 30-degree poppet angle, transition happens at approximately 29 and 27 bar pressure drop for the two cases, respectively. In general, results from the compressible method exhibit better agreement with experiment regarding both flow performance and flow structure. By contrast, the incompressible method could not provide an accurate description for the transition process under the applied flow condition. A series of studies are carried out with emphasis on such discrepancy. Firstly, the deviation in flow performance is addressed based on velocity profile and turbulence level. Secondly, the disparity in flow structure is illustrated and the mechanism for cavitation inception is discussed, which combined provide an interpretation of the deficiency of the incompressible method. Thirdly, different inlet boundary conditions are applied, and the results confirm the independence of deficiency of the incompressible method for inlet fluctuation. Finally, a re-examination is proposed concerning traditional notion of compressible flow as well as the applicability of incompressible numerical method