Nitrogen-saturated Conditions Research Articles

Effect of Ultrahigh Dose Rate on Biomolecular Radiation Damage.

Dose rate is one of the important parameters in radiation-induced biomolecular damage. The effects of dose rate have been known to modify radiation toxicity in biological systems. The rate and extent of sublethal DNA damage (e.g., base damage and single-strand breaks) repair and those of cell proliferation have been manifested by dose rate. However, the recent preclinical application of ultrahigh dose rate [(UHDR) ca. 40 Gy/s and higher] radiation modalities have been shown to lower the type and extent of radiation damage to biological systems. At these UHDR, radiation-induced physicochemical and chemical processes are expected to differ from those observed after irradiation at conventional dose rates (CONV). It is unclear whether these UHDR conditions can affect the quality (type) and quantity (extent) of biomolecular damage such as DNA lesions. Here, we comparatively study the influence of indirect effects of CONV and UHDR on the formation of DNA strand breaks and clustered damage including densely accumulated lesions in an aerated and an anoxic dilute aqueous solution of a plasmid DNA model under low and high hydroxyl radical (•OH) scavenging conditions. Aqueous solutions of purified supercoiled plasmid DNA (pUC19) were prepared in either air- or nitrogen-saturated conditions, with Tris buffer added as the radiation-produced •OH scavenger at low and high scavenging capacities. These DNA samples were irradiated using kV X-ray systems at CONV (0.1 Gy/s) and high dose rate (HDR, 25 Gy/s) as well as UHDR (55 and 125 Gy/s) under different scavenging and environmental conditions. DNA lesions including strand breaks and clustered damage including densely accumulated lesions were quantified by gel electrophoresis and the yields of these lesions were calculated from the dose-response curve. Non-DSB clustered damage including densely accumulated lesions were evaluated by treating DNAs using bacterial endonuclease enzymes (Fpg and Nth) prior to gel electrophoresis. UHDR of 55 and 125 Gy/s induced lower amounts of both isolated strand breaks and clustered DNA damage including densely accumulated lesions at doses >40 Gy in the presence of oxygen, compared to the abundance of these lesions induced by 0.1 and 25 Gy/s irradiation under the same dose conditions. Overall, the strand break and clustered damage including densely accumulated lesions yields decreased by factors of 1.3-3.5 after UHDR. We did not observe these differences either via •OH scavenging or by removing oxygen from the solution. In addition, our results point out that the inter-track recombination reactions did not contribute to the observed dose-rate effects on DNA damage. The effects of dose rate on DNA damage are highly dependent on the total dose, as expected, but also on the •OH scavenging capacity that is employed in the aqueous DNA solutions. These important variables may be relevant in biological systems as well. On a practical level, our in vitro plasmid DNA model, which permits to precisely vary the scavenging capacity and gassing conditions (air saturated vs. N2 saturated) can help to differentiate dose-rate effects on biomolecular damage. Our results indicate that the radical-radical reactions are important in understanding the dose-rate effect on DNA damage.

Influence of Post-Curing in Nitrogen-Saturated Condition on the Degree of Conversion and Color Stability of 3D-Printed Resin Crowns.

Post-curing is the process of applying extra light to complete the polymerization process of 3D printing. The mechanical properties of light-cured three-dimensional (3D) printed resin can be improved by decreasing the oxygen concentrations during post-curing, and nitrogen-saturated post-curing has been applied for this purpose. This study aimed to evaluate and compare the color stability of 3D-printed resin crowns that were post-cured in both normal air and nitrogen-saturated conditions. Crowns were fabricated with a 3D printer and post-cured in normal air (control group; air) or nitrogen-saturated conditions (experimental group; nitrogen). The specimens in each group were subdivided into four subgroups, each exposed to different discoloration agents: distilled water, coffee, wine, and curry. Post-immersion color changes were measured using a digital spectrophotometer and analyzed using repeated-measures ANOVA. Fourier transform infrared (FT-IR) spectroscopy evaluated the degree of conversion of resin over immersion times for both post-curing conditions. Upon comparing the effects of post-curing conditions, a significant difference between the control and experimental groups in terms of immersion time in the wine and curry subgroups was found. FT-IR analysis showed a significant difference in the degree of conversion between the air and nitrogen groups from 10 to 300 s. These findings suggest that nitrogen-saturated post-curing can potentially enhance the conversion rate of 3D-printed resin crowns, thereby improving their color stability.

Kinetics and proposed mechanisms of hexafluoropropylene oxide dimer acid (GenX) degradation via vacuum-UV (VUV) photolysis and VUV/sulfite processes

We investigated the degradation of hexafluoropropylene oxide dimer acid (GenX) in water via VUV photolysis and VUV/sulfite reactions under nitrogen-saturated conditions. Approximately 35% and 90% of GenX were degraded in 3 h in the VUV photolysis and VUV/sulfite reaction. While GenX removal rate was highest at pH 6 in VUV photolysis, it increased under alkaline pHs, especially at pH 10, in VUV/sulfite reaction. Radical scavenging experiments showed that, while both eaq- and •H contributed to VUV photolysis, eaq- played a significant role and •OH had a negative effect during VUV/sulfite reaction. Two transformation products (TPs) (TFA and PFPrA) were identified in VUV photolysis, whereas five TPs (TFA, PFPrA, TP182, TP348, and TP366) were identified in VUV/sulfite reaction by LCMS/MS and LCQTOF/MS. Defluorination of GenX was observed with the defluorination efficiency after 6 h reaching 17% and 67% in the VUV photolysis and VUV/sulfite reactions, respectively. Degradation mechanism for GenX based on the identified TPs and the theoretical calculation confirmed the susceptibility of GenX to nucleophilic attack. The initial reactions for GenX decomposition were C–C and C–O bond cleavage in both reactions, whereas sulfonation followed by decarboxylation was observed only in the VUV/sulfite reaction. ECOSAR ecotoxicity simulation showed that the toxicities of the TPs were not as harmful as those of GenX.

Light, nitrogen supply, and neighboring plants dictate costs and benefits of nitrogen fixation for seedlings of a tropical nitrogen-fixing tree.

The ability to fix nitrogen may confer a competitive advantage or disadvantage to symbiotic nitrogen-fixing plants depending on the availability of soil nitrogen and energy to fuel fixation. Understanding these costs and benefits of nitrogen fixation is critical to predicting ecosystem dynamics and nutrient cycling. We grew inoculated (with symbiotic bacteria) and uninoculated seedlings of Pentaclethra macroloba (a nitrogen-fixing tree species) both in isolation and with Virola koschnyi (a nonfixing species) under gradients of light and soil nitrogen to assess how the ability to fix nitrogen and fixation activity affect growth, biomass allocation, and responses to neighboring plants. Inoculation itself did not provide a growth advantage to nitrogen fixers, regardless of nitrogen limitation status. Higher nitrogen fixation rates increased biomass growth similarly for nitrogen-limited and nitrogen-saturated fixers. Nodule production was offset by reduced fine-root biomass for inoculated nitrogen fixers, resulting in no change in total belowground allocation associated with nitrogen fixation. Under nitrogen-limited conditions, inoculated nitrogen fixers partially downregulated fixation in the presence of a nonfixing neighbor. These results suggest that nitrogen fixation can provide a growth advantage, even under nitrogen-saturated conditions, and that nitrogen fixers may reduce fixation rates to minimize facilitation of neighbors.

Application of radiation crosslinking technique to development of gelatin scaffold for tissue engineering

The potential of a radiation crosslinking technique for developing gelatin scaffolds for tissue engineering was evaluated by comparing it with a chemical crosslinking method. Radiation-crosslinked gelatin exhibited higher visible light transmittance as compared to chemically crosslinked gelatin. The radiation crosslinking efficiency of the gelatin was estimated to be 91%; it was affected by hydroxyl (OH) radicals formed by γ-radiolysis of the aqueous gelatin solution under nitrous oxide or nitrogen-saturated conditions. The proportions of phenylalanine, tyrosine, and histidine in the gelatin decreased significantly with increasing absorbed dose. At the same time, the amounts of 12 other amino acids remained almost unchanged after γ-ray irradiation, and these amino acids did not participate in the crosslinking reactions. The contents of tyrosine, phenylalanine, and histidine in gelatin were the most important factors for radiation crosslinking. Cell adhesion of the radiation-crosslinked gelatin would be maintained before and after γ-ray irradiation because there was no decrease in the proportion of the cell adhesion active sequence (arginine-glycine-aspartic acid, RGD motif). The yield for dityrosine formation was estimated to be 0.030 µmol l−1 Gy−1, and this is considered to be the point at which crosslinking occurred in the radiation-crosslinked gelatin. As the crosslinked gelatin and degradation products have no absorption bands in the visible region, the radiation crosslinking technique, unlike chemically crosslinking techniques, can modify the gelatin while maintaining high transparency.

Sphagnum growth under N saturation: interactive effects of water level and P or K fertilization.

Sphagnum biomass is a promising material that could be used as a substitute for peat in growing media and can be sustainably produced by converting existing drainage-based peatland agriculture into wet, climate-friendly agriculture (paludiculture). Our study focuses on yield maximization of Sphagnum as a crop. We tested the effects of three water level regimes and of phosphorus or potassium fertilization on the growth of four Sphagnum species (S. papillosum, S. palustre, S. fimbriatum, S. fallax). To simulate field conditions in Central and Western Europe we carried out a glasshouse experiment under nitrogen-saturated conditions. A constant high water table (remaining at 2cm below capitulum during growth) led to highest productivity for all tested species. Water table fluctuations between 2 and 9cm below capitulum during growth and a water level 2cm below capitulum at the start but falling relatively during plant growth led to significantly lower productivity. Fertilization had no effect on Sphagnum growth under conditions with high atmospheric deposition such as in NW Germany (38kgN, 0.3kg P, 7.6kgK·ha-1 ·year-1 ). Large-scale maximization of Sphagnum yields requires precise water management, with water tables just below the capitula and rising with Sphagnum growth. The nutrient load in large areas of Central and Western Europe from atmospheric deposition and irrigation water is high but, with an optimal water supply, does not hamper Sphagnum growth, at least not of regional provenances of Sphagnum.

Effective Stress Coefficient for Seismic Velocities in Carbonate Rocks: Effects of Pore Characteristics and Fluid Types

The concept of effective stress is key for understanding the dependence of rock elastic and compaction behaviors on stress and pore-fluid pressure. Previous studies on the concept largely used data acquired on siliciclastic rocks. Carbonate rocks, however, display elastic and compaction behaviors that can be very different than those of siliciclastic rocks. For example, applying most velocity-to-pore-pressure transforms in the context of carbonate reservoirs can be quite challenging. Our study used an experimental approach (a disequilibrium compaction scenario) to assess effective stress coefficient (n) for velocities in three carbonate samples displaying comparable porosities but different dominant pore types (in terms of shape and compliance). Different saturating fluids (nitrogen and distilled water) were used, one at a time, which allowed us to compare both pore and fluid type effects on the coefficient n between these rocks. We found that n is generally bounded by unity. The exception is with nVs (n derived from shear wave velocities) obtained under nitrogen-saturated conditions; nVs is higher than 1 on the three studied samples. Under nitrogen-saturated conditions, the less compliant the main pore types in a given rock are, the higher the value of nVs is. Higher-than-unity values of nVs indicate a deviation from the behavior predicted by existing theories. This could stem from (i) the fact that theoretical analyses assume a pore fluid whose properties are not comparable to those of nitrogen and/or (ii) the way the bulk volumetric strain (a main factor in elastic wave propagation) is incorporated into those theories.

Electroreduction of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid: Oriented product selectivity through the electrode material

A new insight into the electrochemical reduction mechanism of imidazolium cations is given by examining the cathodic stability of the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [BMIm][NTf2] ionic liquid at platinum, gold, copper and mercury electrodes. Potentiostatic electrolyses were performed under nitrogen-saturated conditions and the major reduction products of the BMIm+ cation were quantified by 1H NMR spectroscopy. The product selectivity is influenced by the electrode material and by the presence of an additional proton source in the medium, evidencing the key role of adsorbed hydrogen in the mechanism of BMIm+ electroreduction.

Enhanced oxidation of antibiotics by ferrate(VI)-sulfur(IV) system: Elucidating multi-oxidant mechanism

Ferrate(VI) (FeVIO42−, FeVI) is usually effective in oxidizing a wide range of antibiotics on a time scale of seconds, but some recalcitrant antibiotics such as trimethoprim (TMP) and flumequine (FLU) require a longer time and higher dose of FeVI for their removal from water. The current study presents the FeVI-sulfur(IV) (or FeVI-sulfite/bisulfite) system, which could give near-instantaneous oxidation of these two antibiotics (20.0 μM) (i.e., in 15 s time scale) at a lower dose of FeVI (100.0 μM) than is needed with FeVI oxidation alone. Experiments on the removal of TMP were performed as a function of the molar ratios of S(IV) to FeVI (0.2–15.0) and FeVI to TMP (2.0–30.0 μM) at three different pH values (7.0, 9.0 and 11.0) under both oxic (air saturated) and anoxic (nitrogen saturated) conditions. In case of oxidation of FLU under the same conditions, the molar ratios were used at 1.0 ([S(IV)]:[FeVI]) and 5.0 ([FeVI]:[FLU]) under the same solution pH. Removal of these two recalcitrant antibiotics depended on the pH and the amount of oxygen in the reaction solution. Significantly, TMP was removed by FeVI-S(IV) system under anoxic condition, whereas the removal percentage was lower than that under oxic condition. The relative amounts of the oxidized products of TMP were also different in the oxic and anoxic environments. A set of reactions that were involved in the oxidation of TMP by the FeVI-S(IV) system may demonstrate the participation of multi-oxidizing species (FeV/FeIV, SO3−, SO4− and OH) in the removal of TMP from water. Representative anions and natural organic matters had little or no significant interference on the removal of TMP by the FeVI-S(IV) technique in water.

Degradation of Ibuprofen by Ultrasonic Irradiation and γ-Radiolysis: Kinetic Studies and Degradation Pathways

Abstract Degradation of ibuprofen (IBP) at two concentrations (0.05 and 0.1 mM) through ultrasonic irradiation at 585 kHz was studied under the air-, oxygen-, argon-, and nitrogen-saturated conditions. Effects of H2O2 on the degradation of IBP were also studied. Addition of hydroxyl radical scavengers (isopropyl alcohol and terephthalic acid) was used to derive and compare the reaction constants of IBP in the three zones (the cavitation bubble, the bulk solution, and the supercritical interface) formed during ultrasonic irradiation. Some results are as follows: first, degradation pathways proceed through first-order kinetics in all experiments by ultrasonic irradiation; second, IBP degradation rate was faster at the lower IBP concentration of 0.05 mM; third, additions of H2O2 from 0 to 5 mM could accelerate the degradation of IBP. In addition, degradation of IBP by γ-radiolysis was also compared to the degradation by ultrasonic irradiation under the air-, nitrous oxide-, and argon-saturated conditions. Re...

Degradation of diclofenac by ultrasonic irradiation: Kinetic studies and degradation pathways

Diclofenac (DCF) is a widely used anti-inflammatory drug found in various water bodies, posing threats to human health. In this research, the effects of ultrasonic irradiation at 585kHz on the degradation of DCF were studied under the air, oxygen, argon, and nitrogen saturated conditions. First, the dechlorination efficiencies under the air, oxygen, argon, and nitrogen saturated conditions were calculated to be 67%, 60%, 53% and 59%. Second, there was full mineralization of nitrogen during DCF degradation under the air, oxygen, and argon saturated conditions, but no mineralization of nitrogen under the nitrogen-saturated condition. Different from nitrogen, only partial mineralization of carbon occurred under the four gas-saturated conditions. Third, OH scavengers were added to derive the rate constants in the three reaction zones: cavitation bubble, supercritical interface, and bulk solution. Comparison of the constants indicated that DCF degradation was not limited to the bulk solution as conventionally assumed. Oxidation in the supercritical interface played a dominant role under the air and oxygen saturated conditions, while OH reactions in the cavitation bubble and/or bulk solution were dominant under the nitrogen and argon saturated conditions. After the addition of H2O2, reactions in the cavitation bubble and bulk solution kept their dominant roles under the nitrogen and argon saturated conditions, while reaction in the supercritical interface decreased under the air and oxygen saturated conditions. Finally, LC–MS analysis was used to derive the by-products and propose the main pathways of DCF degradation by ultrasonic irradiation.

Degradation of MTBE and Related Gasoline Oxygenates in Aqueous Media by Ultrasound Irradiation

Gasoline oxygenates [methyl \Itert\N-butyl ether (MTBE), di-isopropyl ether, ethyl \Itert\N-butyl ether, and \Itert\N-amyl methyl ether] in aqueous media are readily decompose upon ultrasonic irradiation (665 kHz). The optimal instrumental settings for the production of reactive radical species employing a specific reactor were determined using dosimetry. Since hydroxyl radical is generally believed to be the predominant reactive species leading to ultrasonically induced degradation of organic substrates in aqueous media, a terephthalate dosimeter was employed to selectively determine the yields of hydroxyl radicals. The decomposition of the gasolinie oxygenates and the primary decomposition products of MTBE were compared in the presence of different saturating gases (O\d2, N\d2, and Ar). The observed decomposition rates for the oxygenates were similar under Ar and O\d2 saturated conditions, but significantly slower under nitrogen saturated conditions. The observed decomposition rates for a number of the primary decomposition products of MTBE are significantly slower under N\d2 and O\d2 saturation relative to Ar saturation. All the gasoline oxygenates in this study were degraded by more than 98% within 3 h of ultrasonic irradiation under O\d2 saturationwith half-lives of 21–25 min.

Nutritional assessment of a forest fertilisation experiment in northern Sweden by root bioassays

Roots were excised from long-term nitrogen, phosphorus and potassium fertilisation experiments in a Pinus sylvestris plantation in northern Sweden, and tested for their ability to take up 15N, 32P or 86Rb from solutions of ammonium chloride, potassium dihydrogen phosphate and rubidium chloride. High levels of uptake in these tests indicate low nutrient status. At this site, lower uptake rates in the trees from the fertilised treatments showed they had responded to the addition of all three nutrients, although the nitrogen test could not detect a difference in root response between trees from the two higher nitrogen treatments, which, according to other criteria, were high enough to create nitrogen-saturated conditions. There was no evidence from the nitrogen uptake measured that this was affected by phosphorus or potassium fertiliser treatment, suggesting that correcting the supply of these elements did not induce further nitrogen demand. Conversely, trees receiving high nitrogen additions did not show any increased demand for phosphorus or potassium. This is in agreement with data on tree growth and nitrogen retention of the stands. Trees from plots treated with acid 16–21 years previously or lime 21 years previously did not respond differently from trees in control plots, unless nitrogen, phosphorus and potassium fertiliser were also added, when demand for the three nutrients was reduced. The results suggest that, in spite of difficulties in sampling tree roots in an area with a rich ground flora, the method is a useful test of the long-term nutrient status in forest fertilisation experiments.

Vertical changes in soil solution chemistry in soil profiles under coniferous forest

Soil solution samples from six layers in a brown forest soil were collected regularly over a four year period in a Cryptomeria japonica D. Don plantation, Shiga prefecture, Japan. Samples were analyzed for inorganic N, organic N, total P, Cl −, SO 2− 4, Ca 2+, Mg 2+ and Na +. Inorganic N mainly consisted of NO − 3 in the soil solutions. NO − 3, Ca 2+ and Mg 2+ were predominant in the soil solutions. over the study period. NO − 3, Ca 2+ and Mg 2+ concentrations and fluxes showed a clear seasonal pattern with peaks in late autumn to early winter in the Ah horizon throughout the study period. Nitrification potentials in the six soil layers were estimated. Nitrification occurred mainly in the Ah horizon. Nitrification in the Ah horizon accounted for about 90% of the total NO − 3 production in the soil. In the Ah horizon, the temporal variations in NO − 3 concentrations and fluxes were attributed to the seasonal nitrification processes. While in the Bw horizon, the patterns were variable, and were attributed to the percolation processes of NO − 3 produced in the Ah horizon. NO − 3 fluxes from the Bw horizon were estimated and ranged from 81 to 186 kg N ha −1 yr −1. The estimated high fluxes of NO − 3 reflected the fertile and nitrogen saturated soil conditions in the Cryptomeria plantation.

Aspects of the electrochemistry of lead in acid media Part II. Active dissolution in oxygenated and deoxygenated perchloric acid solutions

Steady-state current-potential, double-layer capacity and impedance measurements have been made on lead in 0.1 M and 5 M perchloric acid solutions under nitrogen and oxygen saturated conditions. It is shown that the metal dissolution reaction is a quasi-reversible process. Evidence for a charge-transfer mechanism involving two consecutive one-electron transfers is given with Pb [1] as an intermediate. A large enhancement in the rate of dissolution in the presence of oxygen is confirmed, although there is no evidence for a change in the reaction mechanism. It is suggested that these results will have consequences with regard to the operation of lead-acid batteries since, in particular, passivation processes at the negative are likely to affected.

Aspects of the electrochemistry of lead in acid media: Part II. Active dissolution in oxygenated and deoxygenated perchloric acid solutions

Steady-state current-potential, double-layer capacity and impedance measurements have been made on lead in 0.1 M and 5 M perchloric acid solutions under nitrogen and oxygen saturated conditions. It is shown that the metal dissolution reaction is a quasi-reversible process. Evidence for a charge-transfer mechanism involving two consecutive one-electron transfers is given with Pb [1] as an intermediate. A large enhancement in the rate of dissolution in the presence of oxygen is confirmed, although there is no evidence for a change in the reaction mechanism. It is suggested that these results will have consequences with regard to the operation of lead-acid batteries since, in particular, passivation processes at the negative are likely to affected.

Gamma irradiation of coumarin in aqueous solution

Abstract Aqueous solutions of coumarin become fluorescent on gamma irradiation. The main fluorescent product formed, 7-hydroxy coumarin, shows a dependence on oxygen. The yield in the presence of oxygen is three times that in the nitrogen saturated condition. The effect of cysteine, dimethyl sulfoxide, thymine and sodium nitrite on the gamma response of coumarin suggests the involvement of hydroxyl radicals in the formation of the fluorescent product. The hydroxyl rate constant for coumarin was determined using isopropanol as the co-competitor. The G (coumarin) in the aerated and nitrogen saturated conditions was also determined.