Differences In Isotope Effects Research Articles

Application of the Bland-Altman and Receiver Operating Characteristic (ROC) Approaches to Study Isotope Effects in Gas Chromatography-Mass Spectrometry Analysis of Human Plasma, Serum and Urine Samples.

The Bland-Altman approach is one of the most widely used mathematical approaches for method comparison and analytical agreement. This work describes, for the first time, the application of Bland-Altman to study 14N/15N and 1H/2H (D) chromatographic isotope effects of endogenous analytes of the L-arginine/nitric oxide pathway in human plasma, serum and urine samples in GC-MS. The investigated analytes included arginine, asymmetric dimethylarginine, dimethylamine, nitrite, nitrate and creatinine. There was a close correlation between the percentage difference of the retention times of the isotopologs of the Bland-Altman approach and the area under the curve (AUC) values of the receiver operating characteristic (ROC) approach (r = 0.8619, p = 0.0047). The results of the study suggest that the chromatographic isotope effects in GC-MS result from differences in the interaction strengths of H/D isotopes in the derivatives with the hydrophobic stationary phase of the GC column. D atoms attenuate the interaction of the skeleton of the molecules with the lipophilic GC stationary phase. Differences in isotope effects in plasma or serum and urine in GC-MS are suggested to be due to a kind of matrix effect, and this remains to be investigated in forthcoming studies using Bland-Altman and ROC approaches.

Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 80:289-300 (2017) - DOI: https://doi.org/10.3354/ame01859 Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates Juliane Jacob1,2,*, Boris Nowka3, Véronique Merten4, Tina Sanders1, Eva Spieck3, Kirstin Dähnke1 1Helmholtz Center Geesthacht, Institute of Coastal Research, Max-Planck-Str. 1, 21502 Geesthacht, Germany 2Institute of Biogeochemistry and Marine Chemistry, University of Hamburg, Bundesstr. 55, 20146 Hamburg, Germany 3Biozentrum Klein Flottbek, Department of Microbiology and Biotechnology, University of Hamburg, Ohnhorststr. 18, 22609 Hamburg, Germany 4GEOMAR Helmholtz Center for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany *Corresponding author: juliane.jacob@uni-hamburg.de ABSTRACT: Nitrification, the step-wise oxidation of ammonium to nitrite and nitrate, is important in the marine environment because it produces nitrate, the most abundant marine dissolved inorganic nitrogen (DIN) component and N-source for phytoplankton and microbes. This study focused on the second step of nitrification, which is carried out by a distinct group of organisms, nitrite-oxidizing bacteria (NOB). The growth of NOB is characterized by nitrite oxidation kinetics, which we investigated for 4 pure cultures of marine NOB (Nitrospina watsonii 347, Nitrospira sp. Ecomares 2.1, Nitrococcus mobilis 231, and Nitrobacter sp. 311). We further compared the kinetics to those of non-marine species because substrate concentrations in marine environments are comparatively low, which likely influences kinetics and highlights the importance of this study. We also determined the isotope effect during nitrite oxidation of a pure culture of Nitrospina (Nitrospina watsonii 347) belonging to one of the most abundant marine NOB genera, and for a Nitrospira strain (Nitrospira sp. Ecomares 2.1). The enzyme kinetics of nitrite oxidation, described by Michaelis-Menten kinetics, of 4 marine genera are rather narrow and fall in the low end of half-saturation constant (Km) values reported so far, which span over 3 orders of magnitude between 9 and >1000 µM NO2-. Nitrospina has the lowest Km (19 µM NO2-), followed by Nitrobacter (28 µM NO2-), Nitrospira (54 µM NO2-), and Nitrococcus (120 µM NO2-). The isotope effects during nitrite oxidation by Nitrospina watsonii 347 and Nitrospira sp. Ecomares 2.1 were 9.7 ± 0.8 and 10.2 ± 0.9‰, respectively. This confirms the inverse isotope effect of NOB described in other studies; however, it is at the lower end of reported isotope effects. We speculate that differences in isotope effects reflect distinct nitrite oxidoreductase (NXR) enzyme orientations. KEY WORDS: Nitrification · Nitrite-oxidizing bacteria · Isotope effect · Enzyme kinetics · Marine environment Full text in pdf format PreviousCite this article as: Jacob J, Nowka B, Merten V, Sanders T, Spieck E, Dähnke K (2017) Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates. Aquat Microb Ecol 80:289-300. https://doi.org/10.3354/ame01859 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 80, No. 3. Online publication date: December 13, 2017 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2017 Inter-Research.

Carbon and nitrogen isotope systematics in diamond: Different sensitivities to isotopic fractionation or a decoupled origin?

Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon–nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n=94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in δ13C (−28.4 ‰ to −1.1‰, mode at −5.8‰), δ15N (−5.8 to +18.8‰, mode at −3.0‰) and nitrogen contents ([N]; 3800 to less than 1at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low δ13C and [N] to mantle-like δ13C and high [N]. Overall, δ13C appears to be uncorrelated to δ15N and [N] on both the inter- and intra-diamond levels. Co-variations of δ15N–log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive δ15N (about −3 and +2‰, respectively) and variable but overall high [N].Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model.Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low δ13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative δ13C and δ15N). (3.) In waning stages of influx, availability of the mantle-type fluid at the site of diamond growth became limited, leading to Rayleigh fractionation. These fractionation trends are clearly depicted by δ15N–[N] but are not detected when examining co-variation diagrams involving δ13C. Also on the level of individual diamonds, large (≥5‰) variations in δ15N are associated with δ13C values that typically are constant within analytical uncertainty. The much smaller isotope fractionation factor for carbon (considering carbonate- or methane-rich fluids as possible carbon sources) compared to nitrogen leads to an approximately one order of magnitude lower sensitivity of δ13C values to Rayleigh fractionation processes (i.e. during fractionation, a 1‰ change in δ13C is associated with a 10‰ change in δ15N). As a consequence, even minor heterogeneity in the primary isotopic composition of diamond forming carbon (e.g., due to addition of minor subducted carbon) will completely blur any possible co-variations with δ15N or [N]. We suggest this strong difference in isotope effects for C and N to be the likely cause of observations of an apparently decoupled behaviour of carbon and nitrogen isotopes in diamond.

Bioactive Phenylenediamine Derivatives of Dehydroacetic Acid: Synthesis, Structural Characterization and Deuterium Isotope Effects

Several phenylenediamine derivatives of dehydroacetic acid, 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one have been synthesized and their structure elucidated by using NMR and IR spectroscopies and mass spectrometry. Spectral analyses have pointed toward the localized keto-amine form as the predominant tautomeric form in solution and solid-state which was in agreement with X-ray data. The relatively broad N–H stretching bands observed in IR spectra and significant N–H proton down-field and keto C=O up-field shifts in NMR spectra indicated the presence of intra-molecular hydrogen bonds in all studied compounds. In order to gain further insights into nature of these interactions in solution deuterated isotopomers have been prepared and deuterium isotope effects in 13C NMR spectra have been determined and analyzed. The magnitude and sign of isotope effects have confirmed the existence of intra-molecular hydrogen bonds. Observed differences in isotope effects reflected different hydrogen bond structure and dynamics in studied compounds. The results presented in this paper might help in better understanding of biological properties of the related compounds.

Linking Diversity and Stable Isotope Fractionation in Ammonia-Oxidizing Bacteria

The link between similarity in amino acid sequence for ammonia monooxygenase (AMO) and isotopic discrimination for ammonia oxidation ( l AMO ) was investigated in g -subdivision ammonia-oxidizing bacteria. The isotope effects for ammonia oxidation in pure cultures of the nitrifying strains Nitrosomonas marina , Nitrosomonas C-113a, Nitrosospira tenuis , Nitrosomonas europaea , and Nitrosomonas eutropha ranged from 14.2 to 38.2. The differences in isotope effects could not be readily explained by differential rates of ammonia oxidation, transport of NH 4 + , or accumulation of NH 2 OH or N 2 O among the strains. The major similarities and differences observed in l AMO are, however, paralleled by similarities and differences in amino acid sequences for the f -subunit of AMO (AmoA). Robust differences in l AMO among nitrifying bacteria may be expected to influence the stable isotopic signatures of nitrous oxide (N 2 O) produced in various environments.

Kinetic isotope effect in hydrogen isotope exchange between water and phosphines

The kinetic parameters of the tritium exchange between*H2O(*D2O) and (CH3)2PH in the gas phase and between*H2O(*D2O) and (C6H5)2PH in liquid were measured. Both reactions appeared to be heterogeneous ones. The*HH/*DD kinetic isotope effects were estimated and compared with the results of exchange between methanol and phosphines. The differences in isotope effects are explained by the change of the symmetry of the four center cyclic transition complex resulting from the various type of solvation of this complex.

5616289 Substance and/or heat exchanging tower

Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon–nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n = 94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in δ13C (− 28.4 ‰ to − 1.1‰, mode at − 5.8‰), δ15N (− 5.8 to + 18.8‰, mode at − 3.0‰) and nitrogen contents ([N]; 3800 to less than 1 at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low δ13C and [N] to mantle-like δ13C and high [N]. Overall, δ13C appears to be uncorrelated to δ15N and [N] on both the inter- and intra-diamond levels. Co-variations of δ15N–log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive δ15N (about − 3 and + 2‰, respectively) and variable but overall high [N].Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model.Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low δ13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative δ13C and δ15N). (3.) In waning stages of influx, availability of the mantle-type fluid at the site of diamond growth became limited, leading to Rayleigh fractionation. These fractionation trends are clearly depicted by δ15N–[N] but are not detected when examining co-variation diagrams involving δ13C. Also on the level of individual diamonds, large (≥ 5‰) variations in δ15N are associated with δ13C values that typically are constant within analytical uncertainty. The much smaller isotope fractionation factor for carbon (considering carbonate- or methane-rich fluids as possible carbon sources) compared to nitrogen leads to an approximately one order of magnitude lower sensitivity of δ13C values to Rayleigh fractionation processes (i.e. during fractionation, a 1‰ change in δ13C is associated with a 10‰ change in δ15N). As a consequence, even minor heterogeneity in the primary isotopic composition of diamond forming carbon (e.g., due to addition of minor subducted carbon) will completely blur any possible co-variations with δ15N or [N]. We suggest this strong difference in isotope effects for C and N to be the likely cause of observations of an apparently decoupled behaviour of carbon and nitrogen isotopes in diamond.

ChemInform Abstract: Isotope Effects in Arene C‐H Bond Activation by ((C5Me5)Rh(PMe3)).

AbstractThe activation of arene C‐H bonds by (C5Me5)Rh(PMe3) is definitely found to proceed through an intermediate complex, described by the formulation [(C5H5)Rh(PMe3)‐(n2‐ C6H6)] on the basis of the difference in isotope effects observed during the activation of 1,3,5‐C6H3D3 vs. a 1 :1 mixture of C6H6 / C6D6.

Radiometric analysis of oxidative reactions in aromatization by placental microsomes. Presence of differential isotope effects.

In order to study the initial as well as the final steps in the aromatization of androgens to estrogens, high-specific activity [19-C3H3]androstenedione and testosterone were synthesized. Incubations of [19-C3H3]androstenedione with human placental microsomes resulted in the generation of [3H]water, as a result of the dual hydroxylation at C-19, and [3H]formic acid reflecting final aromatization. After an initial lag in the production of [3H]formic acid, the two radiolabeled products were formed linearly with time at a ratio of 2 to 1 under subsaturating conditions and 2.2 to 1 when saturating levels of substrate were present. Incubation of a mixture of [19-C3H3]- and [4-14C]androstenedione with human placental microsomes yielded 19-hydroxy- and 19-oxoandrostenedione, respectively, products of one and two hydroxylations at C-19. The isotope ratios of these derivatives revealed the presence of a tritium isotope effect in the first but not in the second hydroxylation at that site. When [19-C3H2]- and [4-14C]19-hydroxyandrostenedione were used as the substrate, the isotope ratio of the isolated 19-oxoandrostenedione showed no evidence of any isotope effect in its formation. Thus, the second hydroxylation at C-19 exhibits no isotope effect irrespective of whether androstenedione or 19-hydroxyandrostenedione are the substrates, and therefore, a concerted process and catalytic commitment are not responsible for the difference in isotope effects between the first and second C-19 hydroxylation by the placental aromatase complex. Radiometric kinetic analysis employing [19-C3H3]- and [1 beta,2 beta-3H]androstenedione as the comparative substrates provided evidence that the isotope effect is exerted solely through the Vmax component of the reaction. The distinction between the successive hydroxylations at C-19 in the aromatization sequence suggests, but does not prove, that different mechanisms, and hence different catalytic sites, may be involved in these steps.

Influence of sedimentary environments on sulfur isotope ratios in clastic rocks: a review

Strata-bound sulfide deposits associated with clastic, marine sedimentary rocks, and not associated with volcanic rocks, display distributions of δS34 values gradational between two extreme types: 1. a flat distribution ranging from δS34 of seawater sulfate to values about 25‰ lower; and 2. a narrow distribution around value δS34 (sulfide)=δS34 (seawater sulfate) −50‰, and skewed to heavier values. δS34 (seawater sulfate) is estimated from contemporaneous evaporites. There is a systematic relation between the type of δS34 distribution and the type of depositional environment. Type 1 occurs in shallow marine or brackish-water environments; type 2 occurs characteristically in deep, euxinic basins. These distributions can be accounted for by a model involving bacterial reduction of seawater sulfate in systems which range from fully-closed “batches” of sulfate (type 1) to fully open systems in which fresh sulfate is introduced as reduction proceeds (type 2). The difference in the characteristic distributions requires that the magnitude of the sulfate-sulfide kinetic isotope effect on reduction be different in the two cases. This difference has already been suggested by the conflict between δS34 data for modern marine sediments and laboratory experiments. The difference in isotope effects can be accounted for by Rees' (1973) model of steady-state sulfate reduction: low nutrient supply and undisturbed, stationary bacterial populations in the open system settings tend to generate larger fractionations.