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Analysis of Bioremediation in Organic Soils
Published in Subhas K. Sikdar, Robert L. Irvine, Fundamentals and Applications, 2017
Daniel M. White, Robert L. Irvine
In a reaction where more than one product is formed, the carbon isotope ratio in each product will not necessarily equal the isotope ratio in the reactant. The relative concentration of isotopes in reaction products compared to reactants is called fractionation (Hoefs, 1987). The fractionation of isotopes during a reaction is caused by an isotope effect. Although an isotope effect is not directly observable (i.e., it is a physical phenomenon), its existence is inferred to describe readily observed fractionation. Two isotope effects have been described: the isotope exchange effect and the kinetic isotope effect (Hayes, 1992). With the isotope exchange effect, carbon-carbon (C—C) bond strength controls the distribution of 13C between molecules. The heavy isotope generally resides in the compound where it is most strongly bound (Biegleson, 1965). Bond strength differences arise because the heavy isotope, 13C, has a smaller reserve of free energy than 13C and forms bonds of lower minimum free energy. The isotope exchange effect drives the redistribution of 13C between oceanic carbonates and dissolved and gaseous carbon dioxide (i.e., during the hydration of CO2 gas) (Degens, 1969).
Deuterated Liquid Crystals - design and synthesis of deuterium labelled 4,4ʺ-dialkyl-2′,3′-difluoro-[1,1′:4′,1ʺ]terphenyls using batch and continuous flow systems
Published in Liquid Crystals, 2023
Marta Zak, Jakub Herman, Michał Czerwiński, Yuki Arakawa, Hideto Tsuji, Przemysław Kula
Figure 9(a) shows the juxtaposition of a molecular ion (blue line, m/z = 336) with two daughter ions (yellow line m/z = 307; pink line m/z = 292) resulting from ionisation and fragmentation in the collision chamber of a non-deuterated molecule 2T3 H. The intensity of the non-deuterated precursor ion (m/z = 336) is twice that of the deuterated precursor ion (m/z = 345) (Figure 9(b)). On the other hand, in the case of the daughter ions, the intensities of non-deuterated ions (m/z = 307 and m/z = 292) are more than twice as high as their deuterated counterparts (m/z = 314 and m/z = 296) (Figure 9(c,d)). For each pair of precursor and daughter ions the maximum ionisation value is the same. The maximum ionisation of 5 eV is for the precursor ions m/z = 336 and m/z = 345, 15 eV for the daughter ions m/z = 307 and m/z = 314 and 32 eV for the daughter ions m/z = 292 and m/z = 296. Comparing the signal intensity expressed in arbitrary units [a.u.] for molecular ions of the two terphenyl structures 2T3 H and 2T3-d9 and their fragmentation ions it can be concluded that the intensity of the ions formed (at a given value of the ionisation energy in the ionisation chamber) is lower for the deuterated structure than for the non-deuterated analogues. The kinetic isotope effect is clearly noticeable here. The greater stability of the C‒C bonds, at which hydrogen atoms were replaced with deuterium atoms, was indicated. The structures containing a such C‒D system are less labile and more difficult to decompose in the electron beam.
Insertion products in the reaction of carbonyl oxide Criegee intermediates with acids: Chloro(hydroperoxy)methane formation from reaction of CH2OO with HCl and DCl
Published in Molecular Physics, 2021
Craig A. Taatjes, Rebecca L. Caravan, Frank A. F. Winiberg, Kristen Zuraski, Kendrew Au, Leonid Sheps, David L. Osborn, Luc Vereecken, Carl J. Percival
The reaction of the smallest carbonyl oxide Criegee intermediate, CH2OO, with HCl and DCl has been confirmed to produce chloro(hydroperoxy)methane, and the product has been characterised by time-resolved photoionisation mass spectrometry. The photoionisation of chloro(hydroperoxy)methane forms a fragment ion at m/z = 47 (CH2OOH+) above about 10.8 eV, similar to other hydroperoxide insertion products from reactions of CH2OO with halogenated acids. Experiment and theory agree that the overall reaction rate coefficient has at most a small normal kinetic isotope effect; however, the isotope ratio in the stabilisation product is larger, ∼1.6, suggesting a more substantial kinetic isotope effect that is difficult to reconcile with the theory, which predicts a κprod < 1.
Metal isotope complexation with environmentally relevant surfaces: Opening the isotope fractionation black box
Published in Critical Reviews in Environmental Science and Technology, 2021
Michael Komárek, Gildas Ratié, Zuzana Vaňková, Adéla Šípková, Vladislav Chrastný
At seawater ionic strength (∼0.7 M), Cd mainly occurs as CdCl2, CdCl+, while at freshwater ionic strengths, as Cd(H2O)62+ (Bethke & Yeakel, 2005; Parkhurst & Appelo, 1999). In the case of Cd adsorption onto birnessite, Cd isotopic fractionation was only observed at high ionic strengths (seawater), suggesting that the salinity may induce the changes in Cd aqueous speciation affecting the extent of isotope fractionation (Wasylenki et al., 2014). Moreover, a kinetic isotope effect seems to be observed at an early stage of adsorption. Then, sorbed Cd and dissolved Cd are exchanged slowly, being associated with equilibrium fractionation, decreasing the extent of Cd isotopic fractionation during Cd adsorption onto birnessite (Wasylenki et al., 2014).