Oxygen Isotope Fractionation and the Structure of Aqueous Alkali Halide Solutions

1977 ◽  
Vol 32 (12) ◽  
pp. 1419-1425 ◽  
Author(s):  
P. Bopp ◽  
K. Heinzinger ◽  
A. Klemm
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effects ◽  
Free Water ◽  
Alkali Halides ◽  
Md Simulations ◽  
Ionic Species ◽  
Bulk Water ◽  
Oxygen Isotope Fractionation ◽  
Plausible Assumption ◽  
The Individual

Abstract The oxygen isotope effects between H2O and D2O solutions of various alkali-halides and the respective pure solvents have been measured by means of the CO2 equilibration technique. In general, the effects for H2O are smaller than those for D2O. With "hydration numbers" estimated from the angular distributions of the water dipoles around the ions obtained from MD-simulations and with the plausible assumption that in highly concentrated LiCl solutions the effect is purely cationic, the measured effects are separated into effects between the hydration shells of the individual ionic species (Li, Na, K, Cs, CI, Br, I) and bulk water. The cationic effects thus obtained are compared with the corresponding effects between free water-cation-pairs and bulk water calculated on the basis of the energy surfaces published by Kistenmacher et al. It is found that, in general, the trends coincide but the former effects are smaller than the latter ones.

scholarly journals Oxygen isotope fractionation during N<sub>2</sub>O production by soil denitrification

2016 ◽  
Vol 13 (4) ◽  
pp. 1129-1144 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jens Dyckmans ◽  
Jan Kaiser ◽  
Alina Marca ◽  
Jürgen Augustin ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Effect ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
N2o Production ◽  
Oxygen Isotope Fractionation ◽  
Oxygen Isotope Exchange ◽  
Incubation Experiments

Abstract. The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O ∕ 16O ratio of soil water and the N2O product of δ18O(N2O ∕ H2O)  =  (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O ∕ H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O ∕ H2O) showed a significant correlation (R2 = 0.70, p <  0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification, isotope exchange occurs prior to isotope branching and that this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰, in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects.

Sauerstoffisotopieeffekte und Hydratstruktur von Alkalihalogenid-Lösungen in H2O und D2O / Oxygen Isotope Effects and Hydrate Structure of Alkali Halide Solutions in H2O and D2O

1973 ◽  
Vol 28 (2) ◽  
pp. 137-141 ◽  
Author(s):  
D. Götz ◽  
K. Heinzinger
Keyword(s):  
Oxygen Isotope ◽  
Oxygen Isotopes ◽  
Alkali Halide ◽  
Isotope Effects ◽  
Bulk Water ◽  
Hydration Water ◽  
Solvent Isotope Effect ◽  
Anion Effect ◽  
Solvent Isotope ◽  
Fractionation Factors

The fractionation of the oxygen isotopes in solutions of LiCl, NaCl. KCl, KBr, KJ and CsCl with H2O and D2O as solvent has been measured at 25 °C by means of the CO2-equilibration technique. As opposed to earlier measurements a slight anion dependence for the potassium halides has been found in H2O. This anion effect is much more pronounced in D2O. It even leads to a change in the directions of the 180 enrichment between cationic hydration water and bulk water for KCl and KBr. The absolute values of the fractionation factors for LiCl and CsCl, which differ in sign in H2O in agreement with positive and negative cationic hydration, respectively, as known from other kinds of measurements, is increased for LiCl and decreased for CsCl in D2O. There is no fractionation of the oxygen isotopes between hydration water and bulk water in both solvents for NaCl.The solvent isotope effect is explained by the stronger anion influence on the structure of the bulk water in D2O as compared with H2O. This stronger influence is expected because of the higher structural order in D2O than in H2O at the same temperature.

Hydrogen Isotope Fractionation in Aqueous Alkali Halide Solutions

1997 ◽  
Vol 52 (11) ◽  
pp. 811-820 ◽  
Author(s):  
Masahisa Kakiuchi
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effect ◽  
Alkali Halide ◽  
Hydrogen Isotope ◽  
Isotope Fractionation ◽  
Free Water ◽  
Aqueous Alkali ◽  
Water Molecules ◽  
Oxygen Isotope Fractionation ◽  
Hydrogen Isotope Effect

Abstract The D/H ratios of hydrogen gas in equilibrium with aqueous alkali halide solutions were deter-mined at 25 °C, using a hydrophobic platinum catalyst. The hydrogen isotope effect between the solution and pure water changes linearly with the molality of the solution at low concentrations, but deviates from this linearity at higher concentration for all alkali halide solutions. The magnitude of the hydrogen isotope effect is in the order; Kl > Nal > KBr > CsCl ≧ NaBr > KCl > NaCl > LiCl, at concentrations up to a molality of 4 m. The sign and trend of the hydrogen isotope effect is different from that of oxygen. In aqueous alkali halide solutions, the hydrogen isotope effect is influenced by both the cation and the anion species, while the oxygen isotope effect is mainly caused by the cation species. This suggests that the mechanism of hydrogen isotope fractionation between the water molecules in the hydration spheres and the free water molecules differs from the mechanism of the oxygen isotope fractionation. The hydrogen and oxygen isotope effects for alkali halides, except LiCl and NaCl, may be influenced by changes in energy of the hydrogen bonding in free water molecules.

scholarly journals The mechanism of oxygen isotope fractionation during N<sub>2</sub>O production by denitrification

2015 ◽  
Vol 12 (20) ◽  
pp. 17009-17049
Author(s):  
D. Lewicka-Szczebak ◽  
J. Dyckmans ◽  
J. Kaiser ◽  
A. Marca ◽  
J. Augustin ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Effect ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
Nitrite Reduction ◽  
N2o Production ◽  
Oxygen Isotope Fractionation ◽  
Oxygen Isotope Exchange

Abstract. The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. We performed several soil incubation experiments. For the first time, Δ17O isotope tracing was applied to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found bacterial denitrification to be typically associated with almost complete oxygen isotope exchange and a stable difference in δ18O between soil water and the produced N2O of δ18O(N2O / H2O) = (17.5 ± 1.2) ‰. However, some experimental setups yielded oxygen isotope exchange as low as 56 % and a higher δ18O(N2O / H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a very significant correlation (R2 = 0.70, p < 0.00001). We hypothesise that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification the isotope exchange occurs prior to the isotope branching and that the mechanism of this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰; in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects.

Testing different methods for the extraction and purification of leaf and phloem sugars for oxygen isotope analysis

2020 ◽  
Author(s):  
Melanie Egli ◽  
Marco M. Lehmann ◽  
Nadine Brinkmann ◽  
Roland A. Werner ◽  
Matthias Saurer ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Isotope Analysis ◽  
Isotopic Signature ◽  
Phloem Tissue ◽  
Oxygen Isotope Fractionation ◽  
Isotopic Signatures ◽  
Extraction And Purification ◽  
Oxygen Isotopic ◽  
The Individual ◽  
The Impact

&lt;p&gt;Oxygen isotope analysis of plant material, such as sugars in different tissues, provides an important tool to understand how plants function, interact with their environment and also cope with climate change. Knowing how to extract and purify carbohydrates without artificially altering their oxygen isotope ratio (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O) is therefore essential.&lt;/p&gt;&lt;p&gt;We aimed to resolve the impact of different steps on sugars' &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O values during their extraction and purification from leaf and phloem tissue. More precisely, we investigated (1) different drying processes (oven- vs freeze-drying), and (2) how extraction and purification affect leaf sugars. To clearly see fractionation and exchange processes, these experiments were performed using &lt;sup&gt;18&lt;/sup&gt;O-labelled water. We further examined (3) the influence of different EDTA media and immersion times to facilitate sugar exudation and subsequent yield from twig phloem tissue. Finally, we analysed (4) the sugar phloem composition, as well as the individual compounds&amp;#8217; carbon isotopic signatures (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C).&lt;/p&gt;&lt;p&gt;Comparison of freeze- and oven-dried sugars showed lower &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O memory effects and more consistent oxygen isotopic signatures across different sugars, indicating lyophilisation as the more reliable method. The extraction and purification can be conducted without significant oxygen isotope fractionation. However, &lt;sup&gt;18&lt;/sup&gt;O-depletion was observed when sugars were dissolved and dried multiple times. This suggests that additional dissolution and drying steps should best be avoided whenever possible. Different immersion times and exudation media during twig phloem extraction revealed to have a substantial influence on the phloem sugars' overall oxygen isotopic signature, their composition, and the individual compounds' &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C values.&lt;/p&gt;&lt;p&gt;Our research illustrates which precautions during sample preparation &amp;#8211; from drying to extracting and purifying &amp;#8211; need to be taken when plant sugars and their oxygen isotopic signature are of interest. Regarding the preservation of the phloem sugars' original &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O values and stabilising their composition (prevention of sucrose degradation) as much as possible, we recommend a short immersion time of approx. 1 hour. After a thorough initial rinse of the tissue, the sap should be eluted in pure water without any additives (no EDTA). This further reduces the possibility of hexoses to exchange oxygen with that of the surrounding water.&lt;/p&gt;

Calculations of the Oxygen Isotope Fractionation between Hydration Water of Cations and Free Water

1974 ◽  
Vol 29 (11) ◽  
pp. 1608-1613 ◽  
Author(s):  
P. Bopp ◽  
K. Heinzinger ◽  
P. C. Vogel
Keyword(s):  
Water Molecule ◽  
Oxygen Isotope ◽  
Gas Phase ◽  
Isotope Fractionation ◽  
Pure Water ◽  
Free Water ◽  
Oxygen Isotope Fractionation ◽  
Free Water Molecule ◽  
Separation Factors ◽  
Fractionation Factors

The oxygen isotope fractionation factors between the hydration complex of the alkali ions in the gas phase and a free water molecule have been computed on the basis of the energy surfaces calculated by Kistenmacher, Popkie and Clementi for a water molecule in the field of an alkali ion. For comparison with recently measured oxygen isotope fractionation factors in aqueous alkali halide solutions, the gas phase values are multiplied with the corresponding separation factors between water vapor and liquid water thus relating the hydration complex in the gas phase with pure water. Qualitative agreement between computed and observed fractionation factors has been found for H2O and D2O even neglecting the isotope effect connected with the transfer of the hydration complex from the gas phase to the solution. This transfer effect is estimated for H2O by a quantitative comparison of computed and observed oxygen isotope fractionation factors.

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