scholarly journals H2 Kinetic Isotope Fractionation Superimposed by Equilibrium Isotope Fractionation During Hydrogenase Activity of D. vulgaris Strain Miyazaki

2019 ◽  
Vol 10 ◽  
Author(s):  
Michaela Löffler ◽  
Steffen Kümmel ◽  
Carsten Vogt ◽  
Hans-Hermann Richnow
Keyword(s):  
Isotope Fractionation ◽  
Hydrogenase Activity ◽  
Kinetic Isotope

Correction of Pre-Steady-State KIEs for Isotopic Impurities and the Consequences of Kinetic Isotope Fractionation†

2008 ◽  
Vol 112 (50) ◽  
pp. 13109-13115 ◽  
Author(s):  
Sam Hay ◽  
Christopher R. Pudney ◽  
Parvinder Hothi ◽  
Nigel S. Scrutton
Keyword(s):  
Steady State ◽  
Isotope Fractionation ◽  
Kinetic Isotope

Why magnesium isotope fractionation is absent from basaltic melts under thermal gradients in natural settings

2019 ◽  
Vol 157 (7) ◽  
pp. 1144-1148
Author(s):  
Yingkui Xu ◽  
Dan Zhu ◽  
Xiongyao Li ◽  
Jianzhong Liu
Keyword(s):  
Isotope Fractionation ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Chemical Diffusion ◽  
Kinetic Isotope Effects ◽  
Thermal Gradients ◽  
Magnesium Isotopes ◽  
Magnesium Isotope ◽  
Natural Systems ◽  
Kinetic Isotope

AbstractLaboratory experiments have shown that thermal gradients in silicate melts can lead to isotopic fractionation; this is known as the Richter effect. However, it is perplexing that the Richter effect has not been documented in natural samples as thermal gradients commonly exist within natural igneous systems. To resolve this discrepancy, theoretical analysis and calculations were undertaken. We found that the Richter effect, commonly seen in experiments with wholly molten silicates, cannot be applied to natural systems because natural igneous samples are more likely to be formed out of partially molten magma and the presence of minerals adds complexity to the behaviour of the isotope. In this study, we consider two related diffusion-rate kinetic isotope effects that originate from chemical diffusion, which are absent from experiments with wholly molten samples. We performed detailed calculations for magnesium isotopes, and the results indicated that the Richter effect for magnesium isotopes is buffered by kinetic isotope effects and the total value of magnesium isotope fractionation can be zero or even undetectable. Our study provides a new understanding of isotopic behaviour during the processes of cooling and solidification in natural magmatic systems.

Assessing the Blank Carbon Contribution, Isotope Mass Balance, and Kinetic Isotope Fractionation of the Ramped Pyrolysis/Oxidation Instrument at NOSAMS

Radiocarbon ◽  
2017 ◽  
Vol 59 (1) ◽  
pp. 179-193 ◽  
Author(s):  
Jordon D Hemingway ◽  
Valier V Galy ◽  
Alan R Gagnon ◽  
Katherine E Grant ◽  
Sarah Z Rosengard ◽  
...  
Keyword(s):  
Mass Balance ◽  
Isotope Fractionation ◽  
Standard Reference Materials ◽  
Weighted Mean ◽  
Kinetic Isotope ◽  
Carbon Mass ◽  
C Value ◽  
Ramped Pyrolysis ◽  
Minimal Mass ◽  
Mass Dependent

AbstractWe estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n=36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12∆E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1–2‰.

Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

2011 ◽  
Vol 75 (10) ◽  
pp. 2696-2707 ◽  
Author(s):  
Yunyan Ni ◽  
Qisheng Ma ◽  
Geoffrey S. Ellis ◽  
Jinxing Dai ◽  
Barry Katz ◽  
...  
Keyword(s):  
Natural Gas ◽  
Isotope Effect ◽  
Hydrogen Isotope ◽  
Isotope Fractionation ◽  
Kinetic Isotope Effect ◽  
Kinetic Isotope

High-Temperature Processes: Is it Time for Lithium Isotopes?

Elements ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 247-252
Author(s):  
Horst R. Marschall ◽  
Ming Tang
Keyword(s):  
High Temperature ◽  
Isotope Fractionation ◽  
Isotope Geochemistry ◽  
Kinetic Isotope ◽  
High Temperature Processes ◽  
Li Isotope ◽  
Isotope Studies ◽  
Short Time ◽  
Diffusion Profiles ◽  
Geologic Processes

The field of high-temperature Li isotope geochemistry has been rattled by major paradigm changes. The idea that Li isotopes could be used to trace the sources of fluids, rocks, and magmas had to be largely abandoned, because Li diffusion causes its isotopes to fractionate at metamorphic and magmatic temperatures. However, diffusive fractionation of Li isotopes can be used to determine timescales of geologic processes using arrested diffusion profiles. High diffusivity and strong kinetic isotope fractionation favors Li isotopes as a tool to constrain the durations of fast processes in the crust and mantle, where other geochronometers fall short. Time may be the parameter that high-temperature Li isotope studies will be able to shed much light on.

High-resolution carbon and oxygen isotope record in modern brachiopod Pictothyris picta collected off Okinoshima, Japan

2021 ◽  
Author(s):  
Kazuma Oikawa ◽  
Hideko Takayanagi ◽  
Kazuyoshi Endo ◽  
Masa-aki Yoshida ◽  
Yasufumi Iryu
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Growth Stage ◽  
Cold Season ◽  
Strong Positive Correlation ◽  
Isotopic Equilibrium ◽  
Ambient Seawater ◽  
Kinetic Isotope ◽  
Carbon And Oxygen Isotope ◽  
Fractionation Effect

<p>Carbon (δ<sup>13</sup>C) and oxygen (δ<sup>18</sup>O) isotope composition of Rhynchonelliformea brachiopods (hereafter, called ‘brachiopods’) have been regarded as useful paleoenvironmental indicators throughout the Phanerozoic. However, recent studies have revealed that the isotopic composition in modern brachiopod shells records not only environmental changes in ambient seawater but also is influenced by biological controls such as the chemical/isotopic composition of calcifying fluids and physiological processes (e.g., growth rates, metabolism). The latter is known as biological isotope fractionation effects, such as kinetic, metabolic, and pH effects. Recently, a new calcification mechanism in brachiopod shell formation, ion transport mechanism, was proposed. In this study, we measured δ<sup>13</sup>C and δ<sup>18</sup>O values of the primary (PL) and secondary (SL) shell layers of three <em>Pictothyris picta</em> (one male and two female specimens) collected at a water depth of~61 m off Okinoshima to improve our understanding of biological isotope fractionation effects during their shell secretion. We obtained ontogenetic-series δ<sup>13</sup>C and δ<sup>18</sup>O profiles from the PL (PL-Ont) and the uppermost SL (SL-Ont) at the sampling resolution of 3 days to 8 months per sample. We obtained inner-series δ<sup>13</sup>C and δ<sup>18</sup>O profiles from the innermost SL (SL-In) as well. The variations in the δ<sup>13</sup>C and δ<sup>18</sup>O profiles of the PL-Ont showed similar trends to those of the SL-Ont. However, the PL-Ont values mostly exhibited relatively lower δ<sup>18</sup>O values than those of the SL-Ont. Cross plots between the δ<sup>13</sup>C and δ<sup>18</sup>O values of the PL-Ont indicated a strong positive correlation and were lower than those of calcite precipitated in isotopic equilibrium with ambient seawater at the fast growth stage, suggesting the significant influence of the kinetic isotope fractionation effect. The SL was precipitated in oxygen isotopic equilibrium with ambient seawater regardless of the growth stage and/or the seasonal changes in living environments. Furthermore, the PL-Ont, SL-Ont, and SL-Inshowed similar δ<sup>18</sup>O values during the cold season, indicating negligible influences of the kinetic, pH, and magnesium effects on δ<sup>18</sup>O composition. The δ<sup>13</sup>C values of the PL-Ont formed at the cold season (= micro-portion formed under the least kinetic isotope fractionation effect) were lower than those of the SL, indicating the stronger metabolic effect on the PL secretion. Our isotopic data showed that the time lag of the PL and the SL formation varies among specimens.</p>

scholarly journals Evidence of Substantial Carbon Isotope Fractionation among Substrate, Inorganic Carbon, and Biomass during Aerobic Mineralization of 1,2-Dichloroethane byXanthobacter autotrophicus

2000 ◽  
Vol 66 (11) ◽  
pp. 4870-4876 ◽  
Author(s):  
D. Hunkeler ◽  
R. Aravena
Keyword(s):  
Carbon Isotope ◽  
Isotope Effect ◽  
Isotope Fractionation ◽  
Kinetic Isotope Effect ◽  
Inorganic Carbon ◽  
Mechanistic Model ◽  
Fractionation Factor ◽  
Carbon Isotope Fractionation ◽  
Kinetic Isotope ◽  
Factor Α

ABSTRACT Carbon isotope fractionation during aerobic mineralization of 1,2-dichloroethane (1,2-DCA) by Xanthobacter autotrophicusGJ10 was investigated. A strong enrichment of 13C in residual 1,2-DCA was observed, with a mean fractionation factor α ± standard deviation of 0.968 ± 0.0013 to 0.973 ± 0.0015. In addition, a large carbon isotope fractionation between biomass and inorganic carbon occurred. A mechanistic model that links the fractionation factor α to the rate constants of the first catabolic enzyme was developed. Based on the model, it was concluded that the strong enrichment of 13C in 1,2-DCA arises because the first irreversible step of the initial enzymatic transformation of 1,2-DCA consists of an SN2 nucleophilic substitution. SN2 reactions are accompanied by a large kinetic isotope effect. The substantial carbon isotope fractionation between biomass and inorganic carbon could be explained by the kinetic isotope effect associated with the initial 1,2-DCA transformation and by the metabolic pathway of 1,2-DCA degradation. Carbon isotope fractionation during 1,2-DCA mineralization leads to 1,2-DCA, inorganic carbon, and biomass with characteristic carbon isotope compositions, which may be used to trace the process in contaminated environments.

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