Exchangeable Hydrogen Research Articles

Electrochemical and kinetic performance of amorphous/nanostructured TiNi-based intermetallic compound with Nb substitution synthesized by mechanical alloying

Abstract

The structural and dynamical role of water in natural organic matter: A 2H NMR and XRD study

Natural organic matter (NOM) is an important component in many near-surface geochemical environments, and its properties are greatly affected by the incorporation of water. Because of its importance, the macroscopic behavior and effects of water in NOM and soil organic matter (SOM) have been extensively studied using a wide range of experimental and computational methods. The molecular scale structural and dynamical behavior of water in these materials, however, is less well understood. This paper presents a variable temperature 2H NMR and XRD study of water in Suwannee River NOM and its fulvic acid (FA) and humic acid (HA) fractions that provides new insight into the dynamical behavior of structurally different types of water and exchangeable hydrogen environments in NOM. The results provide a basis for future studies of more complex natural organic materials and the interaction of organic materials with mineral surfaces. Room temperature 2H NMR spectra of samples hydrated in 2H2O and then dehydrated, distinguish 2H2O molecules that are in rapid reorientational motion (correlation times, νc, > 105 Hz), 2H exchanged onto carboxylic sites of the NOM that do not undergo rapid reorientation at frequencies >∼103 Hz, and 2H exchanged onto phenolic and possibly other alcohol sites of the NOM that undergoes rapid, but anisotropic, dynamical reorientation. For samples exposed to water and not dried, the XRD results collected at temperatures from 173 to 298 K show the formation of ice-1h in samples exposed to 100% relative humidity (R.H.) but not in samples exposed to 43% R.H. 2H NMR of those samples collected at temperatures from 313 K to 173 K show the presence of multiple sites. Near room temperature, the spectra contain a narrow resonance for mobile water undergoing rapid isotropic motion, and a broader symmetrical resonance probably due to a combination of more dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups undergoing rapid anisotropic motion. The 43% R.H. samples also yield a broader, quadrupole-dominated, resonance for 2H exchanged onto functional groups of the NOM. With decreasing temperature the resonances for dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups become broader, reflecting a decreasing rate of exchange between the water molecules and functional groups and a decreasing rate of reorientation of the 2H2O molecules. The formation of ice-1h is directly reflected in the 2H spectra of the 100% R.H. samples as a resonance with a quadrupole coupling constant (QCC) of ∼180 kHz. For the 43% R.H. samples, there is also a broad, poorly resolved resonance with typical QCCs of ∼180 kHz for which the relative signal intensity increases with decreasing temperature. This signal represents 2H2O molecules that are not crystallized in ice-1h but have greatly reduced reorientation frequencies at low temperature and a hydrogen bonding network with hydrogen bond strengths similar to, but somewhat weaker than, ice-1h. Such molecules are also likely to be present in the 100% R.H. samples. At both R.H.s, some of the 2H2O molecules do not freeze and retain their isotropic motion down to 173 K, the lowest temperature investigated.

Long-lived 15 N Hyperpolarization and Rapid Relaxation as a Potential Basis for Repeated First Pass Perfusion Imaging - Marked Effects of Deuteration and Temperature.

Deuteration of the exchangeable hydrogens of [15 N2 ]urea was found to prolong the T1 of the 15 N sites to more than 3 min at physiological temperatures. This significant increase in the lifetime of the hyperpolarized state of [15 N2 ]urea, compared to [13 C]urea - a pre-clinically proven perfusion agent, makes [15 N2 ]urea a promising perfusion agent. The molecular parameters that may lead to this profound effect were assessed by investigating small molecules with different molecular structures containing 15 N sites bound to labile protons and determining the hyperpolarized 15 N T1 in H2 O and D2 O. Dissolution in D2 O led to marked prolongation for all of the selected sites. In whole human blood, the T1 of [15 N2 ]urea was shortened. We present a general strategy for exploiting the markedly longer T1 outside the body and the quick decay in blood for performing multiple hyperpolarized perfusion measurements with a single hyperpolarized dose. Improved storage of the generated [15 N2 ]urea polarization prior to the contact with the blood is demonstrated using higher temperatures due to further T1 prolongation.

“Assessing the potential of biochar and aged biochar to alleviate aluminum toxicity in an acid soil for achieving cabbage productivity”

Biochar has a significant effect on alleviating acid soil aluminum (Al) toxicity and promoting plant growth. The potential effects of aged biochar (long-term applied biochar in soil) on soil amendment have attracted increasing attention. Here, the effects of biochar and aged biochar were evaluated through a pot experiment. The seedlings of cabbage were grown in red soil for 45 days with the following four biochar treatments: CK (0% biochar), PB (2% primary biochar), WB (2% water washed biochar) and AB (2% acidulated biochar) to investigate the potential effect of biochar and aged biochar on mitigating red soil aluminum toxicity and improving cabbage growth. Results indicated that biochar increased the content of available potassium, available phosphorus, and organic carbon in red soil and improved cabbage growth. Biochar not only increased the pH of red soil by 0.42 units, but also reduced exchangeable acid and exchangeable hydrogen (H+) content by 52.74% and 2.86% respectively compared with CK. Additionally, the amount of the total active aluminum and exchangeable Al3+ were reduced by 26.74% and 66.09%, respectively. However, water washed biochar and acidulated biochar decreased the effect of relieving the acidity substantially as compared to the primary biochar. Moreover, acidulated biochar treatment increased the Al3+ content by 8.07% and trend of increasing soil available nutrients was declined with aged biochar. Taken together, it is concluded that biochar can reduce aluminum toxicity by increasing pH of acid soil and available nutrients, thus improves cabbage growth. However, aged biochar had a negative effect on aluminum toxicity reduction and acidic soil improvement, thus inhibited plant growth.

Determination of Backbone Amide Hydrogen Exchange Rates of Cytochrome c Using Partially Scrambled Electron Transfer Dissociation Data

The technological goal of hydrogen/deuterium exchange-mass spectrometry (HDX-MS) is to determine backbone amide hydrogen exchange rates. The most critical challenge to achieve this goal is obtaining the deuterium incorporation in single-amide resolution, and gas-phase fragmentation may provide a universal solution. The gas-phase fragmentation may generate the daughter ions which differ by a single amino acid and the difference in deuterium incorporations in the two analogous ions can yield the deuterium incorporation at the sub-localized site. Following the pioneering works by Jørgensen and Rand, several papers utilized the electron transfer dissociation (ETD) to determine the location of deuterium in single-amide resolution. This paper demonstrates further advancement of the strategy by determining backbone amide hydrogen exchange rates, instead of just determining deuterium incorporation at a single time point, in combination with a wide time window monitoring. A method to evaluate the effects of scrambling and to determine the exchange rates from partially scrambled HDX-ETD-MS data is described. All parent ions for ETD fragmentation were regio-selectively scrambled: The deuterium in some regions of a peptide ion was scrambled while that in the other regions was not scrambled. The method determined 31 backbone amide hydrogen exchange rates of cytochrome c in the non-scrambled regions. Good fragmentation of a parent ion, a low degree of scrambling, and a low number of exchangeable hydrogens in the preceding side chain are the important factors to determine the exchange rate. The exchange rates determined by the HDX-MS are in good agreement with those determined by NMR. Graphical Abstract ᅟ.

Towards speciation of organically bound tritium and deuterium: Quantification of non-exchangeable forms in carbohydrate molecules

An original methodology to quantitatively explore exchangeability of hydrogen isotopes in carbohydrate molecules is proposed. To access the speciation of organically bound hydrogen isotopes, isotopic exchanges were carried out under a soft path regime in the vapor phase at 20 °C with set (D,T/H) vapor pressure ratios. When steady states were reached, the fraction of exchangeable hydrogen of microcrystalline cellulose, alpha-cellulose and wheat grains were obtained and ranged from 13 to 31% (versus a theoretical value of 30%). In cellulose, and more specifically in microcrystalline cellulose, the molecular hydrogen bonds as well as the different conformations of the network seemed to decrease the hydroxyl groups of glucose units available for isotopic exchange. On the contrary, the assumed enzymatic hydrolysis of the constitutive molecules of wheat starch into low-molecular weight carbohydrate molecules enhanced the exchangeable pool. An average value of the activity between non-exchangeable organically bound tritium (NE-OBT) and non-exchangeable organically bound hydrogen was calculated for wheat grains, (TH)NE = 0.55 ± 0.03 Bq.g−1 of hydrogen atoms.

Methanogenic fermentation of lignite with carbon-bearing additives, inferred from stable carbon and hydrogen isotopes

Lignite from the Konin area (Poland) was used as a substrate for incubation experiments to evaluate its potential for simulation of biogenic methane production. Lignite was incubated with a bacterial inoculum enriched from lake sediments, mineral media, and various supplemental components for microbial life. Additives, such as acetate, methanol, glucose, nutrient broth, and yeast extract, can significantly increase methane production. At the same time, biodegradation of these additional carbon sources leads to overestimation of methane yield. In this paper, selected geochemical properties (total organic carbon content; stable isotopic composition of carbon δ13C) were analyzed in order to evaluate changes in the organic matter of fermented lignite. Stable isotope analysis of carbon and hydrogen was applied in order to identify sources of methane and carbon dioxide formation. TOC decreased in range from 1.4 to 9.6% in lignite after fermentation. The δ13C value of lignite used in the experiments (−25.2‰) decreased after incubation to values in range from −27.1 to −26.2‰. Methane yield per g of TOC (lignite + organic carbon in nutrients) ranged from 0.47 to 2.60mM/g. Glucose, acetate, and methanol significantly increased biogas production. Nutrient broth and yeast extract were not a source of organic carbon for methane formation, but their presence enhanced biogas production. Values of δ13C(CH4) and δ2H(CH4) across incubation conditions ranged from −70.2 to −24.2‰ and from −396.6 to −290.5‰, respectively. Values of δ13C(CO2) ranged from –55.2 to 45.0‰. The high level of variation of δ13C(CH4) and δ13C(CO2) suggests mixing of gases from different carbon sources during incubation, but can also be caused by mixing of metabolic modes by the microbial community. Understanding the δ2H(CH4) variation is even more difficult than the δ13C(CH4) and δ13C(CO2), since many substrates often contain exchangeable hydrogen (e.g. in water, lignite, and elements of nutrients). The combined values of δ13C(CH4) and δ13C(CO2) suggests that the dominant methanogenesis pathway in our experiments may be acetate fermentation. In biodegraded lignite, high relative concentrations of p-cresol (one of the most abundant in the sample) and n-(2-acetylphenyl)formamide were identified. These compounds are most probably lignin decomposition products, or, in the case of the latter, bacterial by-products or remnants. Organic compounds with low molecular weights, n-alkanes, and biomolecules including ferruginol, sugiol, and 6,7-dehydroferruginol, as well as amyrins and tocopherols, were preferentially degraded. The potential for methane production from lignite spiked with carbon-bearing additives is at least one magnitude lower than that from agricultural wastes. The lignite utilization as the single substrate for methanogenic fermentation is economically unprofitable. Mixing of lignite with the external substrate as biomass may be an alternative for consideration and future research.

Dynamic diversity of synthetic supramolecular polymers in water as revealed by hydrogen/deuterium exchange

Numerous self-assembling molecules have been synthesized aiming at mimicking both the structural and dynamic properties found in living systems. Here we show the application of hydrogen/deuterium exchange (HDX) mass spectrometry (MS) to unravel the nanoscale organization and the structural dynamics of synthetic supramolecular polymers in water. We select benzene-1,3,5-tricarboxamide (BTA) derivatives that self-assemble in H2O to illustrate the strength of this technique for supramolecular polymers. The BTA structure has six exchangeable hydrogen atoms and we follow their exchange as a function of time after diluting the H2O solution with a 100-fold excess of D2O. The kinetic H/D exchange profiles reveal that these supramolecular polymers in water are dynamically diverse; a notion that has previously not been observed using other techniques. In addition, we report that small changes in the molecular structure can be used to control the dynamics of synthetic supramolecular polymers in water.

Mobility of copper and zinc in near-surface groundwater as a function of the hypergenic zone lithology at the Kampinos National Park (Central Poland)

In the paper, we assess the mobility of copper and zinc in two sections, Granica and Kampinos, of the glacial and post-glacial sediments in the Kampinos National Park (Poland) and its buffer zone. The Granica section is practically devoid of carbonates and clay fraction, and the environment is markedly acidic. The other section, Kampinos, is characterized by a considerable content of carbonates (up to 20%) and clay fraction (up to 34%) with high sorption potential. The bonds of Zn2+ and Cu2+ cations with the solid phase occur mainly through adsorption and formation of salts, and through creation of chelated and complex connections. We found that, while sorption of Cu2+ within the shallow groundwater zone under typical natural environment equilibrium conditions depends mainly on the content of the sorbing solid phase (i.e. organic matter and metal oxides and hydroxides), sorption of Zn2+ within the shallow groundwater zone depends mainly on the fluctuating acidity and ionic strength of the groundwater, and to a lesser extent on the content and nature of the solid phase. The sorption process within the Kampinos section occurred predominantly on to three sorption media: clay fraction, organic matter and amorphous forms of Fe, Al and Mn. In the Granica section, because of the absence of clay fraction, sorption of the two metals occurred mainly with the organic matter and amorphous forms of Fe, Al and Mn. In addition, the sorption potential of the two metals in this section was low, because of the acidic pH of the environment, i.e. high availability of exchangeable hydrogen in the sorption complex. The concentrations of copper and zinc in the soil (So) were examined using both: the Lindsay and Norvell’s and aqua regia methods. The methods of variable extraction capacity yielded very similar results for copper. In addition, the study found that the amounts of extracted zinc depended on the type of solution. The highest concentrations of zinc and copper were observed using the extraction with aqua regia. The results from determining zinc and copper concentrations (So) in the soil and rocks and the results of hydrochemical modelling show that the mobility of these two elements is highly limited by sorption processes; moreover, zinc is less effectively adsorbed than copper in these sections.

Insights into the Catalytic Mechanism and Transition State Stabilization of 5′‐Methylthioadenosine Nucleosidase using Neutron Crystallography

5′‐Methylthioadenosine nucleosidase (MTAN) is an obligatory homodimeric protein that catalyzes the hydrolysis of the N‐ribosidic bond of a variety of adenosine‐containing metabolites. The proposed catalytic mechanism of MTAN is initiated by D198 protonating the N7 position of the adenyl moiety, which consequently causes elongation and ultimate breaking of the N‐ribosidic bond, resulting in the formation of an oxocarbenium ion intermediate. Of particular interest is the pKa elevation of D198 that was proposed to have a value of 8.2, which is significantly higher than the theoretical pKa for an aspartic acid side chain. In this study we present the first joint X‐ray/neutron crystal structures of Helicobacter pylori MTAN (HpMTAN) in complex with a substrate (S‐adenosylhomocysteine), early (Formycin A) and late (p‐ClPh‐Thio‐DADMe‐ImmA) dissociative transition state analogues, as well as with the catalytic products (adenine and S‐ribosylhomocysteine). The solved X‐ray/neutron crystal structures provide the positions of exchangeable hydrogen atoms and protonation states of ionizable groups that further our understanding of the catalytic mechanism as well as the stabilization of the transition state for HpMTAN. These results confirm that the catalytic reaction is initiated by D198 functioning as a general acid through the observation of a shared deuterium atom with unconventional hydrogen bond geometry between the carboxylate group of D198 and the N7 position of adenine. Additionally, the transition state analogues neutron structures illustrate the minor differences in the hydrogen bond interactions resulting in the DADMe‐ImmA analogues being extremely potent inhibitors with Kd values in the picomolar range, despite HpMTAN shown to contain an early dissociative transition state structure.Support or Funding InformationThis work was supported by the Center for the Advancement of Science in Space via a cooperative agreement with National Aeronautics and Space Administration Grant N‐123528‐01 (to D.R.R) and by National Institute of Allergy and Infectious Disease/NIH Grant AI105084 (to D.R.R.).

Design of combined system of helium charge exchange spectroscopy and hydrogen beam emission spectroscopy in VEST

A 468.6-nm HeII charge exchange spectroscopy (CES) system combined with 656.3-nm H beam emission spectroscopy (BES) system is designed to measure helium impurity density as well as toroidal rotation and ion temperature in Versatile Experiment Spherical Torus (VEST). A dichroic beam splitter is used to measure CES and BES spectra simultaneously with sharing the same observation and transmission components which include the line of sight, lenses, and fiber bundles. In the combined system, we employ the transmission gratings with high diffraction efficiency for CES and BES in order to obtain high throughput and spectral resolution. Spectra simulation results show that the signal to noise ratio (SNR) of this diagnostic system is no less than 10 with the injection of a diagnostic neutral hydrogen (beam energy and current are 40keV and 0.4A, respectively).

Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation.

Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation. Graphical Abstract ᅟ.

VARIATION OF EUTRIC CAMBISOLS CHEMICAL PROPERTIES BASED ON ALTITUDINAL AND GEOMORPHOLOGIC ZONING

This study of the variation process of the chemical properties of eutric Cambisols on altitudinal levels, forest station subclasses and geomorphologic units, was based on soil analyses from 847 soil horizons gathered from 379 profiles. These profiles were distributed on Romania s entire forest area. The average values of the eutric Cambisol s chemical properties fit were within the known limits for this type of soil, but there were slight variations based on altitude, forest station subclass and geomorphologic units. As expected, the most chemical properties decrease according to the altitudinal levels, from altitudes of over 900 metres to altitudes of under 300 metres. At the level of the Ao horizon, the pH has a value of 5.78 (the soils are slightly acid) at altitudes lower than 300 m and of 5.03 (the soils are mildly acid) at altitudes higher than 900 m.The saturation degree basis is 72% (the soils are mezobasic towards eubasic) at altitudes lower than 300 m, and 56.7% (the soils are mezobasic towards oligomezobasic) at altitudes higher than 900 m. The exchangeable hydrogen decreases from 16.95 me/100 g soil at altitudes higher than 900 m to 9.01 me/100 g soil at altitudes lower than 300 m.

Method development for separating organic carbonates by ion-moderated high-performance liquid chromatography.

An ion-moderated partition high-performance liquid chromatography method was developed for the separation and identification of common organic carbonates. The separation of organic carbonates was achieved on an ion exclusion column with an exchangeable hydrogen ion. An isocratic, aqueous mobile phase was used for elution and detection was performed with a refractive index detector. The developed method was validated for specificity, linearity, limits of detection and quantification, precision and accuracy. All calibration curves showed excellent linear regression (R2 > 0.9990) within the testing range. The limits of detection were 3.8-30.8 ppm for the analyzed carbonates. Improvements in the peak resolution of the chromatograms were achieved by decreasing the column temperature. Addition of the organic modifier, acetonitrile, to the eluent was found to have insignificant effects on the peak resolution. The developed method was demonstrated for analyzing organic carbonate components in the electrolyte system of a commercial lithium ion battery.

Post-column hydrogen–deuterium exchange technique to assist in the identification of small organic molecules by mass spectrometry

To improve the certainty that a specific small organic molecule has been detected in a given sample by high-resolution mass spectrometry, other techniques that give conclusive evidence about the chemical structure of a compound like nuclear magnetic resonance or complementary information on its composition such as hydrogen–deuterium exchange (HDX) are often necessary. This study presents a systematic investigation that aims to improve the applicability of post-column HDX for those purposes. Key parameters like mobile-phase flow rates, volume percentage of H2O in the mobile phase, and D2O addition flow rates were optimized to provide an isotopic pattern that allows the accurate determination of the number of exchangeable hydrogen atoms in small organic molecules. A loop injection setup was used to emulate chromatographic conditions in the optimization process, and trimethoprim, a widely used anti-infective, was used as test compounds for the experiments. As expected, results showed that deuteration percentage decreased with a higher mobile-phase flow rate and increased with higher D2O flow rate. The post-column HDX technique was then validated with extracts of samples of river water and plants separated by liquid chromatography in hydrophilic interaction or reversed-phase modes. Mass spectra showed a completely visible isotopic pattern that allowed assessing correctly and unambiguously the number of exchangeable hydrogens in the compounds of interest. This study shows that post-column HDX can be used as a complementary technique to identify unknown small organic molecules in complex matrices. The current paper proposes an efficient, cost-effective, versatile technique of HDX that is helpful to assign a unique structure to a given high-resolution mass spectrometry signal.

Structural phase transformation and electrochemical features of La–Mg–Ni-based AB4-type alloys

In this work, we studied the structural phase transformation and electrochemical characteristics of AB4-type La–Mg–Ni-based alloys through zoning annealing of La0.78Mg0.22Ni3.90 polymorphic alloy. The as-cast La0.78Mg0.22Ni3.90 alloy contained two phases of LaNi5 (50.8wt.%) and (La,Mg)2Ni7 (49.2wt.%). When annealed at 1173K, solid LaNi5 phase reacted with a liquid phase from (La,Mg)2Ni7 converting into the (La,Mg)5Ni19 phase. Increasing temperature to 1223K, the residual LaNi5 phase continued to react with a liquid phase from (La,Mg)5Ni19 forming a new (La,Mg)6Ni24 phase in the alloy. Field-emission scanning electron microscope (FE-SEM) analysis found that the (La,Mg)6Ni24 phase showed diffuse distributing in the alloys and this particular morphology provided plenty of phase boundaries which offered more hydrogen diffusion routes. The high rate dischargeability (HRD) of the alloy electrodes increased with higher (La,Mg)6Ni24 phase abundance. When the abundance of (La,Mg)6Ni24 phase raised to 62.0wt.%, the HRD of the alloy electrode at a discharge current density of 1500mAg−1(HRD1500) reached 68.0%. Meanwhile, the surface exchange current density (I0) and hydrogen diffusion coefficient (D) increased to 360.35mAg−1 and 2.450×10−11cm2s−1, respectively.

Dynamical aspects of water-poly(ethylene glycol) solutions studied by 1H NMR

This paper describes the results of a detailed investigation on the dynamic behavior of poly(ethylene glycol), PEG, with low molar mass (200, 300, 400 and 600gmol−1) and water in all ranges of concentrations. The study is based on spin–spin (T2), spin–lattice (T1) relaxation times and on the variations of the proton chemical shift. The relaxations of the exchangeable and non-exchangeable hydrogen atoms depend on the mobility of the molecules of the solutions. Therefore, the results of T1 and T2 allow one to determine the transitions between the dilute, semi-dilute and concentrate polymeric regimes, and they were well correlated with the kinematic viscosity of the solutions. The distribution of water molecules between the ethylene oxide and the terminal hydroxyl groups of PEG in the entire regime was investigated by using high-field NMR, and the characteristic average number of water molecules belonging to the hydration layer of PEG was also determined.

Assessing the Utility of Hydrogen, Carbon and Nitrogen Stable Isotopes in Estimating Consumer Allochthony in Two Shallow Eutrophic Lakes

Hydrogen stable isotopes (δ2H) have recently been used to complement δ13C and δ15N in food web studies due to their potentially greater power to separate sources of organic matter in aquatic food webs. However, uncertainties remain regarding the use of δ2H, since little is known about the potential variation in the amount of exchangeable hydrogen (Hex) among common sample materials or the patterns of δ2H when entire food webs are considered. We assessed differences in Hex among the typical sample materials in freshwater studies and used δ2H, δ13C and δ15N to compare their effectiveness in tracing allochthonous matter in food webs of two small temperate lakes. Our results showed higher average amounts of Hex in animal tissues (27% in fish and macroinvertebrates, 19% in zooplankton) compared to most plant material (15% in terrestrial plants and 8% in seston/periphyton), with the exception of aquatic vascular plants (23%, referred to as macrophytes). The amount of Hex correlated strongly with sample lipid content (inferred from C:N ratios) in fish and zooplankton samples. Overall, the three isotopes provided good separation of sources (seston, periphyton, macrophytes and allochthonous organic matter), particularly the δ2H followed by δ13C. Aquatic macrophytes revealed unexpectedly high δ2H values, having more elevated δ2H values than terrestrial organic matter with direct implications for estimating consumer allochthony. Organic matter from macrophytes significantly contributed to the food webs in both lakes highlighting the need to include macrophytes as a potential source when using stable isotopes to estimate trophic structures and contributions from allochthonous sources.

Removal of Congo Red and Methylene Blue from Aqueous Solutions by Vermicompost-Derived Biochars.

Biochars, produced by pyrolyzing vermicompost at 300, 500, and 700°C were characterized and their ability to adsorb the dyes Congo red (CR) and Methylene blue (MB) in an aqueous solution was investigated. The physical and chemical properties of biochars varied significantly based on the pyrolysis temperatures. Analysis of the data revealed that the aromaticity, polarity, specific surface area, pH, and ash content of the biochars increased gradually with the increase in pyrolysis temperature, while the cation exchange capacity, and carbon, hydrogen, nitrogen and oxygen contents decreased. The adsorption kinetics of CR and MB were described by pseudo-second-order kinetic models. Both of Langmuir and Temkin model could be employed to describe the adsorption behaviors of CR and MB by these biochars. The biochars generated at higher pyrolysis temperature displayed higher CR adsorption capacities and lower MB adsorption capacities than those compared with the biochars generated at lower pyrolysis temperatures. The biochar generated at the higher pyrolytic temperature displayed the higher ability to adsorb CR owing to its promoted aromaticity, and the cation exchange is the key factor that positively affects adsorption of MB.

Electrochemical performances of Mg45M5Co50 (M=Pd, Zr) ternary hydrogen storage electrodes

In order to improve the discharge capacity and cyclic life of Mg–Co-based alloy, ternary Mg45M5Co50 (M=Pd, Zr) alloys were synthesized via mechanical alloying. TEM analysis demonstrates that these alloys all possess body-centered cubic (BCC) phase in nano-crystalline. Electrochemical experiments show that Mg45Zr5Co50 electrode exhibits the highest capacity (425 mA·h/g) among the Mg45M5Co50 (M=Mg, Pd, Zr) alloys. And Mg45Pd5Co50 electrode lifts not only the initial discharge capacity (379 mA·h/g), but also the discharge kinetics, e.g., exchange current density and hydrogen diffusion ability from that of Mg50Co50. It could be concluded that the electrochemical performances were enhanced by substituting Zr and Pd for Mg in Mg–Co-based alloy.