Journal articles: 'Isotope kinetic effect'

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Musich, О., A. Zubko, and О. Demyanуuk. "Isotopic effect of macro- and microelements in ecosystems." Balanced nature using, no. 4 (August 18, 2020): 132–38. http://dx.doi.org/10.33730/2310-4678.4.2020.226644.

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Isotopic effects occurring in living organisms due to metabolism are analyzed. The phenomenon of metabolism is considered in the classical sense as a combination of biochemical reactions (mainly enzymatic) that take place in the cells of living beings and provide the cleavage, synthesis and interconversion of complex compounds. The scope of use of natural isotopes is wide and diverse. Isotopes are carriers of information about the birth and transformation of molecules, and isotope fractionation is a chemical characteristic of a substance. Isotope metabolism consists in the intermolecular fractionation of isotopes at separate stages of biochemical reactions, namely the cleavage, synthesis and interconversion of complex compounds caused by differences in the structure and fundamental properties of isotope nuclei. It is proved that the fractionation of isotopes in chemical and biochemical reactions due to isotopic effects is based on two fundamental properties of atomic nuclei — mass and magnetic moment. The kinetic (mass-depen dent) isotopic effect distributes the isotopic nuclei by their masses, and the magnetic one fractionates the nuclei by their magnetic moments. The kinetic isotopic effect depends on the magnitude of the difference in the masses of isotopic molecules, temperature and the difference in the activation energies of isotopic forms. The magnetic isotope effect depends on the reaction rate in a single cell, its projection, magnetic moment and energy of electron-nuclear interaction. It is determined that the fractionation of isotopes in living organisms is that the relative content of one of the isotopes in this compound increases by reducing its content in the other. As a result, there is a fractionation of isotopes within one biological object.

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Xu, Yingkui, Dan Zhu, Xiongyao Li, and Jianzhong Liu. "Why magnesium isotope fractionation is absent from basaltic melts under thermal gradients in natural settings." Geological Magazine 157, no. 7 (November 25, 2019): 1144–48. http://dx.doi.org/10.1017/s0016756819001304.

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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.

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Binder, David A., and Robert Eliason. "Kinetic hydrogen isotope effect." Journal of Chemical Education 63, no. 6 (June 1986): 536. http://dx.doi.org/10.1021/ed063p536.

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Krinkin, David. "Anomalously large kinetic isotope effect." Open Chemistry 5, no. 4 (December 1, 2007): 1019–63. http://dx.doi.org/10.2478/s11532-007-0048-2.

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AbstractActivated diffusion of water between macromolecules in swollen cellulose is accompanied by anomalously high kinetic isotope effects of oxygen. The separation factor of heavy-oxygen water (H218O /H216O) is thousands of permilles instead of tens of permilles according to modern Absolute Rate Theory. This anomalous separation under usual conditions is disguised by the opposing process of very fast equalization to equilibrium through water-filled cellulose pores. This process is quicker by approximately 3 orders of magnitude than diffusion through the cellulose body. As a consequence, this opposition-directed equalization virtually eliminates the results of isotope separation. To reveal this anomaly it is necessary to suppress equalization, which was the primary problem for both discovery of this anomaly and its investigation. The method of investigating the anomalous separation in cellulose was developed with suppression of this negative influence. Discussion of the theoretical nature of the anomalous kinetic isotope effect is presented. This theoretical study would probably permit the discovery and use for isotope separation of the anomalously high isotope effect for other chemical elements, in particular, for those heavier than oxygen.

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Joelsson, L. M. T., J. A. Schmidt, E. J. K. Nilsson, T. Blunier, D. W. T. Griffith, S. Ono, and M. S. Johnson. "Development of a new methane tracer: kinetic isotope effect of 13CH3D + OH from 278 to 313 K." Atmospheric Chemistry and Physics Discussions 15, no. 19 (October 15, 2015): 27853–75. http://dx.doi.org/10.5194/acpd-15-27853-2015.

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Abstract. Methane is the second most important long lived greenhouse gas and impacts the oxidative capacity of the Earth's atmosphere. Nontheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including doubly substituted species (e.g. 13CH3D), offers new constraints on the methane source budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH which accounts for around 90 % of methane removal in the troposphere. Here we present experimentally derived methane + OH kinetic isotope effects and their temperature dependence over the range of 278 to 313 K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D=1.31 ± 0.01 and kCH4/k13CH3D = 1.34 ± 0.03 at room temperature, implying that the methane + OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) = kCH4/k13CH3D to within the experimental uncertainty. In addition the kinetic isotope effect were characterized using transition state theory with tunneling correction. Good agreement between the experimental, quantum chemical and available literature values was obtained. The theoretical calculations show that 13CH3D isotope effects is the product of D- and 13C-isotope effect. Based on the results we conclude that the OH reaction at steady-state can produce an atmospheric clumped isotope signal (Δ(13CH3D) = ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02.

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Röckmann, T., S. Walter, B. Bohn, R. Wegener, H. Spahn, T. Brauers, R. Tillmann, E. Schlosser, R. Koppmann, and F. Rohrer. "Isotope effect in the formation of H2 from H2CO studied at the atmospheric simulation chamber SAPHIR." Atmospheric Chemistry and Physics 10, no. 12 (June 16, 2010): 5343–57. http://dx.doi.org/10.5194/acp-10-5343-2010.

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Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in the SAPHIR atmosphere simulation chamber under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only an indirect effect and cannot be effectively constrained. The molecular channel kinetic isotope effect KIEmol, the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) at surface pressure, is determined to be KIEmol=1.63−0.046+0.038. This is similar to the kinetic isotope effect for the total removal of HCHO from a recent relative rate experiment (KIEtot=1.58±0.03), which indicates that the KIEs in the molecular and radical photolysis channels at surface pressure (≈100 kPa) may not be as different as described previously in the literature.

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7

Away, Kenneth Charles West, and Zhu-Gen Lai. "Solvent effects on SN2 transition state structure. II: The effect of ion pairing on the solvent effect on transition state structure." Canadian Journal of Chemistry 67, no. 2 (February 1, 1989): 345–49. http://dx.doi.org/10.1139/v89-056.

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Identical secondary α-deuterium kinetic isotope effects (transition state structures) in the SN2 reaction between n-butyl chloride and a free thiophenoxide ion in aprotic and protic solvents confirm the validity of the Solvation Rule for SN2 Reactions. These isotope effects also suggest that hydrogen bonding from the solvent to the developing chloride ion in the SN2 transition state does not have a marked effect on the magnitude of the chlorine (leaving group) kinetic isotope effects. Unlike the free ion reactions, the secondary α-deuterium kinetic isotope effect (transition state structure) for the SN2 reaction between n-butyl chloride and the solvent-separated sodium thiophenoxide ion pair complex is strongly solvent dependent. These completely different responses to a change in solvent are rationalized by an extension to the Solvation Rule for SN2 Reactions. Finally, the loosest transition state in the reactions with the solvent-separated ion pair complex is found in the solvent with the smallest dielectric constant. Keywords: ion pairs, transition state, solvent effects, nucleophilic substitution, isotope effects.

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Murata, Yasujiro, Shih-Ching Chuang, Fumiyuki Tanabe, Michihisa Murata, and Koichi Komatsu. "Recognition of hydrogen isotopomers by an open-cage fullerene." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, no. 1998 (September 13, 2013): 20110629. http://dx.doi.org/10.1098/rsta.2011.0629.

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We present our study on the recognition of hydrogen isotopes by an open-cage fullerene through determination of binding affinity of isotopes H 2 /HD/D 2 with the open-cage fullerene and comparison of their relative molecular sizes through kinetic-isotope-release experiments. We took advantage of isotope H 2 /D 2 exchange that generated an equilibrium mixture of H 2 /HD/D 2 in a stainless steel autoclave to conduct high-pressure hydrogen insertion into an open-cage fullerene. The equilibrium constants of three isotopes with the open-cage fullerene were determined at various pressures and temperatures. Our results show a higher equilibrium constant for HD into open-cage fullerene than the other two isotopomers, which is consistent with its dipolar nature. D 2 molecule generally binds stronger than H 2 because of its heavier mass; however, the affinity for H 2 becomes larger than D 2 at lower temperature, when size effect becomes dominant. We further investigated the kinetics of H 2 /HD/D 2 release from open-cage fullerene, proving their relative escaping rates. D 2 was found to be the smallest and H 2 the largest molecule. This notion has not only supported the observed inversion of relative binding affinities between H 2 and D 2 , but also demonstrated that comparison of size difference of single molecules through non-convalent kinetic-isotope effect was applicable.

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9

Tsai, I.-Chun, Wan-Yu Chen, Jen-Ping Chen, and Mao-Chang Liang. "Kinetic mass-transfer calculation of water isotope fractionation due to cloud microphysics in a regional meteorological model." Atmospheric Chemistry and Physics 19, no. 3 (February 8, 2019): 1753–66. http://dx.doi.org/10.5194/acp-19-1753-2019.

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Abstract. In conventional atmospheric models, isotope exchange between liquid, gas, and solid phases is usually assumed to be in equilibrium, and the highly kinetic phase transformation processes inferred in clouds are yet to be fully investigated. In this study, a two-moment microphysical scheme in the National Center for Atmospheric Research (NCAR) Weather Research and Forecasting (WRF) model was modified to allow kinetic calculation of isotope fractionation due to various cloud microphysical phase-change processes. A case of a moving cold front is selected for quantifying the effect of different factors controlling isotopic composition, including water vapor sources, atmospheric transport, phase transition pathways of water in clouds, and kinetic-versus-equilibrium mass transfer. A base-run simulation was able to reproduce the ∼ 50 ‰ decrease in δD that was observed during the frontal passage. Sensitivity tests suggest that all the above factors contributed significantly to the variations in isotope composition. The thermal equilibrium assumption commonly used in earlier studies may cause an overestimate of mean vapor-phase δD by 11 ‰, and the maximum difference can be more than 20 ‰. Using initial vertical distribution and lower boundary conditions of water stable isotopes from satellite data is critical to obtain successful isotope simulations, without which the δD in water vapor can be off by about 34 ‰ and 28 ‰, respectively. Without microphysical fractionation, the δD in water vapor can be off by about 25 ‰.

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10

Uspenskaya, Elena V., Tatyana V. Pleteneva, Anton V. Syroeshkin, Ilaha V. Kazimova, Tatyana E. Elizarova, and Artem I. Odnovorov. "Role of stable hydrogen isotope variations in water for drug dissolution managing." Current Issues in Pharmacy and Medical Sciences 33, no. 2 (June 1, 2020): 94–101. http://dx.doi.org/10.2478/cipms-2020-0017.

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AbstractIn the present work, we provide the results of defining by utilizing Laser diffraction spectroscopy, the kinetic isotopic effect of solvent and constant of dissolution rate κ, s−1 of аn active pharmaceutical ingredient (API) in water with a different content of a stable _2^1{\rm{H}} isotope on the basis of the laws of first-order kinetics. This approach is based on the analysis of the light scattering profile that occurs when the particles of the dispersion phase in the aquatic environment are covered with a collimated laser beam. For the first time, the dependence of the rate of dissolution is demonstrated not only on the properties of the pharmaceutical substance itself (water solubility mg/ml, octanol–water partition coefficient log P oct/water, topological polar surface area, Abraham solvation parameters, the lattice type), but also on the properties of the solvent, depending on the content of stable hydrogen isotope. We show that the rate constant of dissolution of a sparingly hydrophobic substance moxifloxacin hydrochloride (MF · HCl) in the Mili-Q water is: k=1.20±0.14∙10−2 s−1 at 293.15 K, while in deuterium depleted water, it is k=4.24±0.4∙10−2 s−1. Consequently, we have established the development of the normal kinetic isotopic effect (kH/kD >1) of the solvent. This effect can be explained both by the positions of the difference in the vibrational energy of zero levels in the initial and transition states, and from the position of water clusters giving volumetric effects of salvation, depending on the ratio D/H. The study of kinetic isotopic effects is a method that gives an indication of the mechanism of reactions and the nature of the transition state. The effect of increasing the dissolution of the API, as a function of the D/H ratio, we have discovered, can be used in the chemical and pharmaceutical industries in the study of API properties and in the drug production through improvement in soluble and pharmacokinetic characteristics.

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11

Harijan, Rajesh K., Ioanna Zoi, Dimitri Antoniou, Steven D. Schwartz, and Vern L. Schramm. "Catalytic-site design for inverse heavy-enzyme isotope effects in human purine nucleoside phosphorylase." Proceedings of the National Academy of Sciences 114, no. 25 (June 5, 2017): 6456–61. http://dx.doi.org/10.1073/pnas.1704786114.

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Heavy-enzyme isotope effects (15N-, 13C-, and 2H-labeled protein) explore mass-dependent vibrational modes linked to catalysis. Transition path-sampling (TPS) calculations have predicted femtosecond dynamic coupling at the catalytic site of human purine nucleoside phosphorylase (PNP). Coupling is observed in heavy PNPs, where slowed barrier crossing caused a normal heavy-enzyme isotope effect (kchemlight/kchemheavy > 1.0). We used TPS to design mutant F159Y PNP, predicted to improve barrier crossing for heavy F159Y PNP, an attempt to generate a rare inverse heavy-enzyme isotope effect (kchemlight/kchemheavy < 1.0). Steady-state kinetic comparison of light and heavy native PNPs to light and heavy F159Y PNPs revealed similar kinetic properties. Pre–steady-state chemistry was slowed 32-fold in F159Y PNP. Pre–steady-state chemistry compared heavy and light native and F159Y PNPs and found a normal heavy-enzyme isotope effect of 1.31 for native PNP and an inverse effect of 0.75 for F159Y PNP. Increased isotopic mass in F159Y PNP causes more efficient transition state formation. Independent validation of the inverse isotope effect for heavy F159Y PNP came from commitment to catalysis experiments. Most heavy enzymes demonstrate normal heavy-enzyme isotope effects, and F159Y PNP is a rare example of an inverse effect. Crystal structures and TPS dynamics of native and F159Y PNPs explore the catalytic-site geometry associated with these catalytic changes. Experimental validation of TPS predictions for barrier crossing establishes the connection of rapid protein dynamics and vibrational coupling to enzymatic transition state passage.

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12

Fang, Yao-ren, Zhu-gen Lai, and Kenneth Charles Westaway. "Isotope effects in nucleophilic substitution reactions X. The effect of changing the nucleophilic atom on ion-pairing in an SN2 reaction." Canadian Journal of Chemistry 76, no. 6 (June 1, 1998): 758–64. http://dx.doi.org/10.1139/v98-056.

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The effect of ion-pairing in an SN2 reaction is very different when the nucleophilic atom is changed from sulfur to oxygen, i.e., changing the nucleophile from thiophenoxide ion to phenoxide ion. When the nucleophile is sodium thiophenoxide, ion-pairing markedly alters the secondary α -deuterium kinetic isotope effect (transition state structure) and the substituent effect found by changing the para substituent on the nucleophile. When the nucleophile is sodium phenoxide, ion-pairing does not significantly affect the secondary α -deuterium or the chlorine leaving group kinetic isotope effects (transition state structure) or the substituent effects found by changing a para substituent on the nucleophile or the substrate. The different effects of ion-pairing may occur because the electron density on the hard oxygen atom of the sodium phenoxide is not affected significantly by ion-pairing.Key words: nucleophilic substitution, SN2, kinetic isotope effect, transition state, substituent effects, ion-pair.

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HUANG, Ter-Mei, Hui-Chih HUNG, Tsu-Chung CHANG, and Gu-Gang CHANG. "Solvent kinetic isotope effects of human placental alkaline phosphatase in reverse micelles." Biochemical Journal 330, no. 1 (February 15, 1998): 267–75. http://dx.doi.org/10.1042/bj3300267.

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Human placental alkaline phosphatase was embedded in a reverse micellar system prepared by dissolving the surfactant sodium bis(2-ethylhexyl) sulphosuccinate (Aerosol-OT) in 2,2,4-trimethylpentane. This microemulsion system provides a convenient instrumental tool to study the possible kinetic properties of the membranous enzyme in an immobilized form. The pL (pH/p2H) dependence of hydrolysis of 4-nitrophenyl phosphate has been examined over a pL range of 8.5-12.5 in both aqueous and reverse micellar systems. Profiles of log V versus pL were Ha-bell shaped in the acidic region but reached a plateau in the basic region in which two pKa values of 9.01-9.71 and 9.86-10.48, respectively, were observed in reverse micelles. However, only one pKa value of 9.78-10.27 in aqueous solution was detected. Profiles of log V/K versus pL were bell-shaped in the acidic region. However, they were wave-shaped in the basic region in which a residue of pKa 9.10-9.44 in aqueous solution and 8.07-8.78 in reverse micelles must be dehydronated for the reaction to reach an optimum. The V/K value shifted to a lower value upon dehydronation of a pKa value of 9.80-10.62 in aqueous solution and 11.23-12.17 in reverse micelles. Solvent kinetic isotope effects were measured at three pL values. At pL 9.5, the observed isotope effect was a product of equilibrium isotope effect and a kinetic isotope effect; at pL 10.4, the log V/K value was identical in water and deuterium. The deuterium kinetic isotope effect on V/K was 1.14 in an aqueous solution and 1.16 in reverse micelles. At pL 11.0 at which the log V values reached a plateau in either solvent system, the deuterium kinetic isotope effect on V was 2.08 in an aqueous solution and 0.62 in reverse micelles. Results from a proton inventory experiment suggested that a hydron transfer step is involved in the transition state of the catalytic reaction. The isotopic fractionation factor (ϕ) for deuterium for the transition state (ϕT) increased when the pH of the solution was raised. At pL 11.0, the ϕT was 1.07 in reverse micelles, which corresponds to the inverse-isotope effect of the reaction in this solvent system. Normal viscosity effects on kcat and kcat/Km were observed in aqueous solution, corresponding to a diffusional controlled physical step as the rate-limiting step. We propose that the rate-limiting step of the hydrolytic reaction changes from phosphate releasing in aqueous solution to a covalent phosphorylation or dephosphorylation step in reverse micelles.

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CHANG, RAYMOND. "Primary Kinetic Isotope Effect: A Lecture Demonstration." Chemical Educator 2, no. 3 (August 1997): 1–3. http://dx.doi.org/10.1007/s00897970121a.

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15

Basov, Alexander, Liliya Fedulova, Ekaterina Vasilevskaya, and Stepan Dzhimak. "Possible Mechanisms of Biological Effects Observed in Living Systems during 2H/1H Isotope Fractionation and Deuterium Interactions with Other Biogenic Isotopes." Molecules 24, no. 22 (November 13, 2019): 4101. http://dx.doi.org/10.3390/molecules24224101.

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This article presents the original descriptions of some recent physics mechanisms (based on the thermodynamic, kinetic, and quantum tunnel effects) providing stable 2H/1H isotope fractionation, leading to the accumulation of particular isotopic forms in intra- or intercellular space, including the molecular effects of deuterium interaction with 18O/17O/16O, 15N/14N, 13C/12C, and other stable biogenic isotopes. These effects were observed mainly at the organelle (mitochondria) and cell levels. A new hypothesis for heavy nonradioactive isotope fractionation in living systems via neutron effect realization is discussed. The comparative analysis of some experimental studies results revealed the following observation: “Isotopic shock” is highly probable and is observed mostly when chemical bonds form between atoms with a summary odd number of neutrons (i.e., bonds with a non-compensated neutron, which correspond to the following equation: Nn − Np = 2k + 1, where k ϵ Z, k is the integer, Z is the set of non-negative integers, Nn is number of neutrons, and Np is number of protons of each individual atom, or in pair of isotopes with a chemical bond). Data on the efficacy and metabolic pathways of the therapy also considered 2H-modified drinking and diet for some diseases, such as Alzheimer’s disease, Friedreich’s ataxia, mitochondrial disorders, diabetes, cerebral hypoxia, Parkinson’s disease, and brain cancer.

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Inaniyan, Yashasvi, Pooja Tak, Pramila Naga, and Priyanka Purohit. "Correlation analysis of reactivity in the oxidation of some vicinal and non-vicinal diols by Tributylammonium chlorochromate: A kinetic and mechanistic approach." Research Journal of Chemistry and Environment 26, no. 9 (August 25, 2022): 26–32. http://dx.doi.org/10.25303/2609rjce026032.

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The kinetics of oxidation of four vicinal, four non-vicinal diols by tributylammonium chlorochromate (TBACC) has been studied in dimethylsulphoxide (DMSO). The main product of oxidation is the corresponding hydroxycarbonyl compound. The reaction is first order each in TBACC. Michaelies-Menten type of kinetics is observed with respect to the diols. The reaction is catalysed by hydrogen ions. The hydrogen ion dependence is taking the form: kobs = a + b[H+]. The oxidation of [1,1,2,2-2H4] ethanediol exhibits a substantial primary kinetic isotope effect (kH/kD = 5.81 at 298 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft's and Swain's multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed.

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Koerner, Terry, Kenneth Charles Westaway, Raymond A. Poirier, and Y. Wang. "An unusually large secondary α-deuterium kinetic isotope effect in hydride ion SN2 reactions." Canadian Journal of Chemistry 78, no. 8 (August 1, 2000): 1067–72. http://dx.doi.org/10.1139/v00-100.

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Theoretical calculations at the HF/6-31+G* level suggest the secondary α-deuterium kinetic isotope effects for hydride ion SN2 reactions are much larger than expected for the structure of the transition state. The secondary α-deuterium kinetic isotope effects for the SN2 reactions between sodium borohydride (hydride ion) and para-methyl- and para-chlorobenzyl chlorides are much larger than expected as the theoretical calculations suggest. It appears the secondary α-deuterium isotope effects are larger than expected for the structure of the SN2 transition state because the hydride ion is too small to affect the CαH(D) out-of-plane bending vibrations in the transition state.Key words: secondary α-deuterium kinetic isotope effects, SN2, nucleophilic substitution, transition state, substituent effects.

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Gromov, S., P. Jöckel, R. Sander, and C. A. M. Brenninkmeijer. "A kinetic chemistry tagging technique and its application to modelling the stable isotopic composition of atmospheric trace gases." Geoscientific Model Development 3, no. 2 (August 10, 2010): 337–64. http://dx.doi.org/10.5194/gmd-3-337-2010.

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Abstract. Isotope composition, in many cases, holds unique information on the sources, chemical modification and sinks of atmospheric trace gases. Vital to the interpretation and use of an increasing number of isotope analyses is appropriate modelling. However, the exact implementation of isotopic information in chemistry-climate models is a challenge, and often studies use simplifications which limit their applicability. Here we implement a thorough isotopic extension in MECCA, a comprehensive kinetic chemistry sub-model. To this end, we devise a generic tagging technique for the kinetic chemistry mechanisms implemented as the sub-submodel MECCA-TAG. The technique is diagnostic and numerically efficient and supports the investigation of various aspects of kinetic chemistry schemes. We focus specifically on the application to the modelling of stable isotopic composition. The results of MECCA-TAG are evaluated against the reference sub-submodel MECCA-DBL, which is implicitly full-detailed, but computationally expensive and thus sub-optimal in practical applications. Furthermore, we evaluate the elaborate carbon and oxygen isotopic mechanism by simulating the multi-isotope composition of CO and other trace gases in the CAABA/MECCA box-model. The mechanism realistically simulates the oxygen isotope composition of key species, as well as the carbon isotope signature transfer. The model adequately reproduces the isotope chemistry features for CO, taking into account the limits of the modelling domain. In particular, the mass-independently fractionated (MIF) composition of CO due to reactions of ozone with unsaturated hydrocarbons (a source effect) versus its intrinsic MIF enrichment induced in the removal reaction via oxidation by OH is assessed. The simulated ozone source effect was up to +1‰ in Δ17O(CO). The versatile modelling framework we employ (the Modular Earth Submodel System, MESSy) opens the way for implementation of the novel detailed isotopic chemistry treatment in the three-dimensional atmospheric-chemistry general circulation model EMAC. We therefore also present estimates of the computational gain obtained by the developed optimisations.

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Wawer, A., and J. Szyd⊚owski. "Kinetic isotope effect in hydrogen isotope exchange between water and phosphines." Journal of Radioanalytical and Nuclear Chemistry 230, no. 1-2 (April 1998): 303–5. http://dx.doi.org/10.1007/bf02387486.

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Joelsson, L. M. T., J. A. Schmidt, E. J. K. Nilsson, T. Blunier, D. W. T. Griffith, S. Ono, and M. S. Johnson. "Kinetic isotope effects of 12CH3D + OH and 13CH3D + OH from 278 to 313 K." Atmospheric Chemistry and Physics 16, no. 7 (April 11, 2016): 4439–49. http://dx.doi.org/10.5194/acp-16-4439-2016.

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Abstract. Methane is the second most important long-lived greenhouse gas and plays a central role in the chemistry of the Earth's atmosphere. Nonetheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including the doubly substituted species 13CH3D, offers new insight into the methane budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH in the troposphere, which accounts for around 84 % of all methane removal. Here we present experimentally derived methane + OH kinetic isotope effects and their temperature dependence over the range of 278 to 313 K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D = 1.31 ± 0.01 and kCH4/k13CH3D = 1.34 ± 0.03 at room temperature, implying that the methane + OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) = kCH4/k13CH3D, within the experimental uncertainty, given the literature value of kCH4/k13CH4 = 1.0039 ± 0.0002. In addition, the kinetic isotope effects were characterized using transition state theory with tunneling corrections. Good agreement between the experimental, quantum chemical, and available literature values was obtained. Based on the results we conclude that the OH reaction (the main sink of methane) at steady state can produce an atmospheric clumped isotope signal (Δ(13CH3D) = ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02. This implies that the bulk tropospheric Δ(13CH3D) reflects the source signal with relatively small adjustment due to the sink signal (i.e., mainly OH oxidation).

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Westaway, Kenneth Charles, and Zhu-Gen Lai. "Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of SN2 reactions." Canadian Journal of Chemistry 66, no. 5 (May 1, 1988): 1263–71. http://dx.doi.org/10.1139/v88-205.

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Spectroscopic and conductivity studies of sodium thiophenoxide solutions in four different solvents and the secondary α-deuterium kinetic isotope effects found in the presence of 15-crown-5 ether demonstrate that the secondary α-deuterium kinetic isotope effect and transition state structure for the SN2 reaction between sodium thiophenoxide and n-butyl chloride are significantly different, depending on whether the ionic reactant is a solvent-separated ion-pair complex or a free ion. In all three solvents in which the form of the ionic reactant changes, a smaller isotope effect and tighter transition state are found for the reaction with the ion-pair complex.

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22

Röckmann, T., S. Walter, B. Bohn, R. Wegener, H. Spahn, T. Brauers, R. Tillmann, E. Schlosser, R. Koppmann, and F. Rohrer. "Isotope effect in the formation of H2 from H2CO studied at the atmospheric simulation chamber SAPHIR." Atmospheric Chemistry and Physics Discussions 9, no. 6 (November 25, 2009): 25187–212. http://dx.doi.org/10.5194/acpd-9-25187-2009.

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Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in a large photochemical reactor under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only a second order effect and can thus not be derived with high precision. The molecular channel kinetic isotope effect (KIEmol), the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) under tropospheric conditions is determined to be KIEmol=1.63±0.03. Combining this result with the total KIE from a recent relative rate experiment, it is likely that KIEmol and KIErad are not as different as described previously in the literature.

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Pham, T. V., and K. C. Westaway. "Solvent effects on nucleophilic substitution reactions. III. The effect of adding an inert salt on the structure of the SN2 transition state." Canadian Journal of Chemistry 74, no. 12 (December 1, 1996): 2528–30. http://dx.doi.org/10.1139/v96-283.

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The nitrogen and secondary α-hydrogen–deuterium kinetic isotope effects found for the SN2 reaction between thiophenoxide ion and benzyldimethylphenylammonium ion at different ionic strengths in DMF at 0 °C indicate that the structure of the transition state changes markedly with the ionic strength of the reaction mixture. In fact, a more reactant-like, more ionic, transition state is found at the higher ionic strength. This presumably occurs because a more ionic transition state is more stable in the more ionic solvent. Key words: transition state, ionic strength, secondary α deuterium kinetic isotope effects, nitrogen isotope effects, SN2.

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Pająk, Małgorzata. "Kinetic and solvent isotope effects in oxidation of halogen derivatives of tyramine catalyzed by monoamine oxidase A." Journal of Biochemistry 167, no. 1 (October 24, 2019): 49–54. http://dx.doi.org/10.1093/jb/mvz089.

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Abstract The isotope effects approach was used to elucidate the mechanism of oxidative deamination of 3′-halotyramines, catalyzed by monoamine oxidase A (EC 1.4.3.4). The numerical values of kinetic isotope effect (KIE) and solvent isotope effect (SIE) were established using a non-competitive spectrophotometric technique. Based upon KIE and SIE values, some of the mechanistic details of investigated reaction were discussed.

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Pham, Thuy Van, and Robert A. McClelland. "The nature of the transition state in diarylmethyl cation nucleophile combination reactions as probed by secondary α-deuterium isotope effects." Canadian Journal of Chemistry 79, no. 12 (December 1, 2001): 1887–97. http://dx.doi.org/10.1139/v01-182.

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Transition-state structures for the carbocationnucleophile combination reactions of (4-substituted-4'- methoxydiphenyl)methyl cations with water, chloride, and bromide ions in acetonitrilewater mixtures have been investigated by measuring the secondary α-deuterium kinetic and equilibrium isotope effects. Rate constants in the combination direction were measured with laser flash photolysis. Equilibrium constants were measured for the water reaction by a comparison method in moderately concentrated sulfuric acid solutions, for the bromide reaction via the observation of reversible combination, and for the chloride reaction from the ratio of the combination rate constant and the rate constant for the ionization of the diarylmethyl chloride product. The fraction of bond making in the transition state has been calculated as the ratio log (kinetic isotope effect):log (equilibrium isotope effect). For the water reaction, there is 5065% bond making in the transition state; this is also true for cations that are many orders of magnitude less reactive. The same conclusions, 5065% bond formation in the transition state independent of reactivity, have previously been made in correlations of log kw vs. log KR. Thus, two quite different measures of transition structure provide the same result. The kH:kD values for the halide combinations in 100% acetonitrile are within experimental error of unity. This is consistent with suggestions that these reactions are occurring with diffusional encounter as the rate-limiting step. Addition of water has a dramatic retarding effect on the halide reactions, with rate constants decreasing steadily with increased water content. Small inverse kinetic isotope effects are observed (in 20% acetonitrile:80% water) indicating that carbonhalogen bond formation is rate-limiting. Comparison of the kinetic and equilibrium isotope effects shows ~25 and ~40% bond formation in the transition states for the reactions with bromide and chloride, respectively.Key words: carbocation, isotope effect, transition state, halide.

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Gromov, S., P. Jöckel, R. Sander, and C. A. M. Brenninkmeijer. "A kinetic chemistry tagging technique and its application to modelling the stable isotopic composition of atmospheric trace gases." Geoscientific Model Development Discussions 3, no. 1 (February 23, 2010): 201–72. http://dx.doi.org/10.5194/gmdd-3-201-2010.

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Abstract. Isotope composition, in many cases, holds unique information on sources, chemical modification and sinks of atmospheric trace gases. Vital to the interpretation and use of an increasing number of isotope analyses is appropriate modelling. However, the exact implementation of isotopic information is a challenge, and often studies use simplifications which limit their applicability. Here we confer a thorough isotopic extension to MECCA, a comprehensive kinetic chemistry sub-model. To this end, we devise a generic tagging technique for the kinetic chemistry mechanisms implemented as the sub-submodel MECCA-TAG. The technique constitutes a diagnostic tool that can benefit the investigation of various aspects of kinetic chemistry schemes; at the same time, the designed numerical optimisation reduces the computational effort while keeping important details unaffected. We further focus specifically on the modelling of stable isotopic composition, including the required extensions of the approach. The results of MECCA-TAG are evaluated against the reference sub-submodel MECCA-DBL, which is implicitly full-detailed, but necessarily is sub-optimal in practical applications due to its high computational demands. Furthermore, we evaluate the elaborate carbon and oxygen isotopic mechanism by simulating the multi-isotope composition of CO and other trace gases in the CAABA/MECCA box-model. The mechanism realistically simulates the oxygen isotope composition of key species resulting from the interchange with ozone and main atmospheric reservoirs, as well as the carbon isotope signature transfer. The model adequately reproduces the isotope chemistry features for CO under the limitation of the modelling domain. In particular, the mass-independently fractionated (MIF) composition of CO due to reactions of ozone with unsaturated hydrocarbons (a source effect) versus its intrinsic MIF enrichment induced in the removal reaction via oxidation by OH is assessed. As for the simulated conditions, the ozone source effect was found to be up to +1‰ in Δ17O(CO). The versatile modelling framework we employ (the Modular Earth Submodel System, MESSy) opens the way for implementation of the novel detailed isotopic chemistry treatment in the three-dimensional atmospheric-chemistry general circulation model EMAC. We therefore also present estimates of the computational gain obtained by the developed optimisations.

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Wiktorowicz, Justyna, and Stefan Jankowski. "13C Kinetic Isotope Effect of the Pudovik Reaction." Phosphorus, Sulfur, and Silicon and the Related Elements 189, no. 7-8 (August 3, 2014): 1144–48. http://dx.doi.org/10.1080/10426507.2014.905780.

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Taatjes, Craig A. "Kinetic Isotope Effect in the CH[2Π] + O2Reaction." Journal of Physical Chemistry 100, no. 45 (January 1996): 17840–45. http://dx.doi.org/10.1021/jp961685l.

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Krishtalik, Lev I. "Kinetic isotope effect in the hydrogen evolution reaction." Electrochimica Acta 46, no. 19 (June 2001): 2949–60. http://dx.doi.org/10.1016/s0013-4686(01)00526-6.

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Singleton, Daniel A., Chao Hang, Michael J. Szymanski, and Erin E. Greenwald. "A New Form of Kinetic Isotope Effect. Dynamic Effects on Isotopic Selectivity and Regioselectivity." Journal of the American Chemical Society 125, no. 5 (February 2003): 1176–77. http://dx.doi.org/10.1021/ja027221k.

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Poulin, Myles B., Jessica L. Schneck, Rosalie E. Matico, Patrick J. McDevitt, Michael J. Huddleston, Wangfang Hou, Neil W. Johnson, Sara H. Thrall, Thomas D. Meek, and Vern L. Schramm. "Transition state for the NSD2-catalyzed methylation of histone H3 lysine 36." Proceedings of the National Academy of Sciences 113, no. 5 (January 19, 2016): 1197–201. http://dx.doi.org/10.1073/pnas.1521036113.

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Nuclear receptor SET domain containing protein 2 (NSD2) catalyzes the methylation of histone H3 lysine 36 (H3K36). It is a determinant in Wolf–Hirschhorn syndrome and is overexpressed in human multiple myeloma. Despite the relevance of NSD2 to cancer, there are no potent, selective inhibitors of this enzyme reported. Here, a combination of kinetic isotope effect measurements and quantum chemical modeling was used to provide subangstrom details of the transition state structure for NSD2 enzymatic activity. Kinetic isotope effects were measured for the methylation of isolated HeLa cell nucleosomes by NSD2. NSD2 preferentially catalyzes the dimethylation of H3K36 along with a reduced preference for H3K36 monomethylation. Primary Me-14C and 36S and secondary Me-3H3, Me-2H3, 5′-14C, and 5′-3H2 kinetic isotope effects were measured for the methylation of H3K36 using specifically labeled S-adenosyl-l-methionine. The intrinsic kinetic isotope effects were used as boundary constraints for quantum mechanical calculations for the NSD2 transition state. The experimental and calculated kinetic isotope effects are consistent with an SN2 chemical mechanism with methyl transfer as the first irreversible chemical step in the reaction mechanism. The transition state is a late, asymmetric nucleophilic displacement with bond separation from the leaving group at (2.53 Å) and bond making to the attacking nucleophile (2.10 Å) advanced at the transition state. The transition state structure can be represented in a molecular electrostatic potential map to guide the design of inhibitors that mimic the transition state geometry and charge.

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de Petris, Giulia, and Anna Troiani. "Isotope Effects in Isotope-Exchange Reactions: Evidence for a Large12C/13C Kinetic Isotope Effect in the Gas Phase." Journal of Physical Chemistry A 112, no. 12 (March 2008): 2507–10. http://dx.doi.org/10.1021/jp710634p.

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Qi, Yanying, Jia Yang, Anders Holmen, and De Chen. "Investigation of C1 + C1 Coupling Reactions in Cobalt-Catalyzed Fischer-Tropsch Synthesis by a Combined DFT and Kinetic Isotope Study." Catalysts 9, no. 6 (June 19, 2019): 551. http://dx.doi.org/10.3390/catal9060551.

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Understanding the chain growth mechanism is of vital importance for the development of catalysts with enhanced selectivity towards long-chain products in cobalt-catalyzed Fischer-Tropsch synthesis. Herein, we discriminate various C1 + C1 coupling reactions by theoretical calculations and kinetic isotope experiments. CHx(x=0−3), CO, HCO, COH, and HCOH are considered as the chain growth monomer respectively, and 24 possible coupling reactions are first investigated by theoretical calculations. Eight possible C1 + C1 coupling reactions are suggested to be energetically favorable because of the relative low reaction barriers. Moreover, five pathways are excluded where the C1 monomers show low thermodynamic stability. Effective chain propagation rates are calculated by deconvoluting from reaction rates of products, and an inverse kinetic isotope effect of the C1 + C1 coupling reaction is observed. The theoretical kinetic isotope effect of CO + CH2 is inverse, which is consistent with the experimental observation. Thus, the CO + CH2 pathway, owing to the relatively lower barrier, the high thermodynamic stability, and the inverse kinetic isotope effect, is suggested to be a favorable pathway.

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Guo, X., and M. L. Sinnott. "A kinetic-isotope-effect study of catalysis by Vibrio cholerae neuraminidase." Biochemical Journal 294, no. 3 (September 15, 1993): 653–56. http://dx.doi.org/10.1042/bj2940653.

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Michaelis-Menten parameters for hydrolysis of seven aryl N-acetyl alpha-D-neuraminides by Vibrio cholerae neuraminidase at pH 5.0 correlate well with the leaving-group pKa (delta pK 3.0; beta 1g (V/K) = -0.73, r = -0.93; beta 1g (V) = -0.25; r = -0.95). The beta-deuterium kinetic-isotope effect, beta D2(V), for the p-nitrophenyl glycoside is the same at the optimum pH of 5.0 (1.059 +/- 0.010) as at pH 8.0 (1.053 +/- 0.010), suggesting that isotope effects are fully expressed with this substrate at the optimum pH. For this substrate at pH 5.0, leaving group 18O effects are 18(V) = 1.040 +/- 0.016 and 18(V/K) = 1.046 +/- 0.015, and individual secondary deuterium effects are beta proRD(V) = 1.037 +/- 0.014, beta proSD(V) = 1.018 +/- 0.015, beta proRD(V/K) = 1.030 +/- 0.017, beta proSD(V/K) = 1.030 +/- 0.017. All isotope effects, and the beta 1g(V/K) value are in accord with the first chemical step being both the first irreversible and the rate-determining step in enzyme turnover, with a transition state in which there is little proton donation to the leaving group, the C-O bond is largely cleaved, there is significant nucleophilic participation, and the sugar ring is in a conformation derived from the ground-state 2C5 chair. The apparent conflict between the beta 1g (V) value of -0.25 with all the kinetic-isotope-effect data can be resolved by the postulation of an interaction between the pi system of the aglycone ring and an anionic or nucleophilic group on the enzyme.

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McNevin, Dennis B., Murray R. Badger, Heather J. Kane, and Graham D. Farquhar. "Measurement of (carbon) kinetic isotope effect by Rayleigh fractionation using membrane inlet mass spectrometry for CO2-consuming reactions." Functional Plant Biology 33, no. 12 (2006): 1115. http://dx.doi.org/10.1071/fp06201.

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Methods for determining carbon isotope discrimination, Δ, or kinetic isotope effects, α, for CO2-consuming enzymes have traditionally been cumbersome and time-consuming, requiring careful isolation of substrates and products and conversion of these to CO2 for measurement of isotope ratio by mass spectrometry (MS). An equation originally derived by Rayleigh in 1896 has been used more recently to good effect as it only requires measurement of substrate concentrations and isotope ratios. For carboxylation reactions such as those catalysed by d-ribulose-1,5-bisphosphate carboxylase / oxygenase (RuBisCO, EC 4.1.1.39) and PEP carboxylase (PEPC, EC 4.1.1.31), this has still required sampling of reactions at various states of completion and conversion of all inorganic carbon to CO2, as well as determining the amount of substrate consumed. We introduce a new method of membrane inlet MS which can be used to continuously monitor individual CO2 isotope concentrations, rather than isotope ratio. This enables the use of a simplified, new formula for calculating kinetic isotope effects, based on the assumptions underlying the original Rayleigh fractionation equation and given by: --> The combination of inlet membrane MS and this formula yields measurements of discrimination in less than 1 h. We validate our method against previously measured values of discrimination for PEP carboxylase and RuBisCO from several species.

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Chan, Jefferson, Ariel Tang, and Andrew J. Bennet. "Transition-state structure for the hydronium-ion-promoted hydrolysis of α-d-glucopyranosyl fluoride." Canadian Journal of Chemistry 93, no. 4 (April 2015): 463–67. http://dx.doi.org/10.1139/cjc-2014-0451.

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The transition state for the hydronium-ion-promoted hydrolysis of α-d-glucopyranosyl fluoride in water has been characterized by combining multiple kinetic isotope effect measurements with theoretical modelling. The measured kinetic isotope effects for the C1-deuterium, C2-deuterium, C5-deuterium, anomeric carbon-13, and ring oxygen-18 are 1.219 ± 0.021, 1.099 ± 0.024, 0.976 ± 0.014, 1.014 ± 0.005, and 0.991 ± 0.013, respectively. The transition state for the hydronium ion reaction is late with respect to both C–F bond cleavage and proton transfer.

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Bahlmann, Enno, Frank Keppler, Julian Wittmer, Markus Greule, Heinz Friedrich Schöler, Richard Seifert, and Cornelius Zetzsch. "Evidence for a major missing source in the global chloromethane budget from stable carbon isotopes." Atmospheric Chemistry and Physics 19, no. 3 (February 8, 2019): 1703–19. http://dx.doi.org/10.5194/acp-19-1703-2019.

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Abstract. Chloromethane (CH3Cl) is the most important natural input of reactive chlorine to the stratosphere, contributing about 16 % to stratospheric ozone depletion. Due to the phase-out of anthropogenic emissions of chlorofluorocarbons, CH3Cl will largely control future levels of stratospheric chlorine. The tropical rainforest is commonly assumed to be the strongest single CH3Cl source, contributing over half of the global annual emissions of about 4000 to 5000 Gg (1 Gg = 109 g). This source shows a characteristic carbon isotope fingerprint, making isotopic investigations a promising tool for improving its atmospheric budget. Applying carbon isotopes to better constrain the atmospheric budget of CH3Cl requires sound information on the kinetic isotope effects for the main sink processes: the reaction with OH and Cl in the troposphere. We conducted photochemical CH3Cl degradation experiments in a 3500 dm3 smog chamber to determine the carbon isotope effect (ε=k13C/k12C-1) for the reaction of CH3Cl with OH and Cl. For the reaction of CH3Cl with OH, we determined an ε value of (-11.2±0.8) ‰ (n=3) and for the reaction with Cl we found an ε value of (-10.2±0.5) ‰ (n=1), which is 5 to 6 times smaller than previously reported. Our smaller isotope effects are strongly supported by the lack of any significant seasonal covariation in previously reported tropospheric δ13C(CH3Cl) values with the OH-driven seasonal cycle in tropospheric mixing ratios. Applying these new values for the carbon isotope effect to the global CH3Cl budget using a simple two hemispheric box model, we derive a tropical rainforest CH3Cl source of (670±200) Gg a−1, which is considerably smaller than previous estimates. A revision of previous bottom-up estimates, using above-ground biomass instead of rainforest area, strongly supports this lower estimate. Finally, our results suggest a large unknown CH3Cl source of (1530±200) Gg a−1.

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Wolfe, Saul, Chan-Kyung Kim, Kiyull Yang, Noham Weinberg, and Zheng Shi. "Transverse compression and the secondary H/D isotope effects in intramolecular SN2 methyl-transfer reactions." Canadian Journal of Chemistry 76, no. 1 (January 1, 1998): 102–13. http://dx.doi.org/10.1139/v97-215.

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Using ab initio molecular orbital theory mainly at the 3-21 + G level, intramolecular SN2 methyl transfer between two oxygens confined within a rigid template is found to proceed exclusively by a high energy retention mechanism when the oxygens are separated by three or four bonds, and by a high energy inversion mechanism when the oxygens are separated by six bonds. Both mechanisms exist when the oxygens are separated by five bonds. The CH3/CD3 kinetic isotope effects are normal (1.21-1.34) in the retention processes and inverse (0.66-0.81) in the inversion reactions. In the case of inversion, compression of C-H bonds of the transition state by structural effects in the plane perpendicular to the O-C-O plane increases the inverse isotope effect. The retention barriers are high because retention is inherently unfavorable, even when pericyclic stabilization of the transition state is possible. The inversion barriers are high because a rigid template cannot accommodate a linear O-CH3-O structure, and the O-C-O bending vibration is stiff (the Eschenmoser effect). Using a novel design strategy, a nonrigid template has been found in which the barrier and the CH3/CD3 kinetic isotope effect are the same as in an intermolecular reaction.Key words: Eschenmoser effect, isotope effect, compression, SN2, sigmatropic rearrangement.

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Wolfe, Saul, Chan-Kyung Kim, Kiyull Yang, Noham Weinberg, and Zheng Shi. "Additions and corrections: Transverse compression and the secondary H/D isotope effects in intramolecular SN2 methyl-transfer reactions." Canadian Journal of Chemistry 76, no. 3 (March 1, 1998): 359–70. http://dx.doi.org/10.1139/v98-090.

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Using ab initio molecular orbital theory mainly at the 3-21+G level, intramolecular SN2 methyl transfer between two oxygens confined within a rigid template is found to proceed exclusively by a high energy retention mechanism when the oxygens are separated by three or four bonds, and by a high energy inversion mechanism when the oxygens are separated by six bonds. Both mechanisms exist when the oxygens are separated by five bonds. The CH3/CD3 kinetic isotope effects are normal (1.21-1.34) in the retention processes and inverse (0.66-0.81) in the inversion reactions. In the case of inversion, compression of C-H bonds of the transition state by structural effects in the plane perpendicular to the O-C-O plane increases the inverse isotope effect. The retention barriers are high because retention is inherently unfavorable, even when pericyclic stabilization of the transition state is possible. The inversion barriers are high because a rigid template cannot accommodate a linear O-CH3 -O structure, and the O-C-O bending vibration is stiff (the Eschenmoser effect). Using a novel design strategy, a nonrigid template has been found in which the barrier and the CH3/CD3 kinetic isotope effect are the same as in an intermolecular reaction.Key words: Eschenmoser effect, isotope effect, compression, SN2, sigmatropic rearrangement.

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40

Galezowski, Wlodzimierz, and Arnold Jarczewski. "Kinetics, isotope effects of the reaction of 1-(4-nitrophenyl)-1-nitroalkanes with DBU in tetrahydrofuran and chlorobenzene solvents." Canadian Journal of Chemistry 68, no. 12 (December 1, 1990): 2242–48. http://dx.doi.org/10.1139/v90-345.

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The kinetics of the reaction of[Formula: see text](R = Me, Et, i-Pr; NPNE, NPNP, MNPNP respectively; L is H or D) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) base in tetrahydrofuran (THF) and chlorobenzene (CB) solvents are reported. The products of these proton transfer reactions are ion pairs absorbing at λmax = 460–480 nm. The equilibrium constants in THF were [Formula: see text]and in CB [Formula: see text]for NPNE, NPNP, MNPNP respectively. The thermodynamic parameters of the reactions are also quoted. The substrate reacts with DBU in both THF and CB solvents in a normal second-order proton transfer reaction. In the case of deuteron transfer, isotopic D/H exchange is much faster than internal return. The reactions show low values of enthalpy of activation ΔH* = 14.3, 18.1, 24.2 and 13.0, 15.1, 18.6 kJmol−1 for NPNE, NPNP, and MNPNP in THF and CB respectively, and large negative entropies of activation −ΔS* = 141, 139, 146; 140, 146, 160 J mol−1 deg−1 for the same sequence of substrates and solvents. The kinetic isotope effects are large, (kH/kD)20°c = 12.2, 13.0, 10.1; 12.9, 12.0, 10.2 for the above sequence of substrates and solvents, and show no difference with changes in either steric hindrance of the C-acids or polarity of the solvents. Keywords: proton transfer, kinetic isotope effect.

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41

Cheng, Liang, Charles Doubleday, and Ronald Breslow. "Evidence for tunneling in base-catalyzed isomerization of glyceraldehyde to dihydroxyacetone by hydride shift under formose conditions." Proceedings of the National Academy of Sciences 112, no. 14 (March 23, 2015): 4218–20. http://dx.doi.org/10.1073/pnas.1503739112.

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Hydrogen atom transfer reactions between the aldose and ketose are key mechanistic features in formose chemistry by which formaldehyde is converted to higher sugars under credible prebiotic conditions. For one of these transformations, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the deuterium kinetic isotope effect associated with the hydrogen transfer during the isomerization of glyceraldehyde to the corresponding dihydroxyacetone. To do this, we developed a quantitative HPLC assay that allowed us to measure the apparent large intrinsic kinetic isotope effect. From the Arrhenius plot of the kinetic isotope effect, the ratio of the preexponential factors AH/AD was 0.28 and the difference in activation energies Ea(D) − Ea(H) was 9.1 kJ·mol−1. All these results imply a significant quantum-mechanical tunneling component in the isomerization mechanism. This is supported by multidimensional tunneling calculations using POLYRATE with small curvature tunneling.

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42

Maksay, Gábor, Zsuzsanna Tegyey, and László Ötvös. "Kinetic isotope effect in the metabolic demethylation of temazepam." J. Chem. Soc., Perkin Trans. 2, no. 1 (1988): 57–59. http://dx.doi.org/10.1039/p29880000057.

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43

Eckhardt, André K., Dennis Gerbig, and Peter R. Schreiner. "Heavy Atom Secondary Kinetic Isotope Effect on H-Tunneling." Journal of Physical Chemistry A 122, no. 5 (January 30, 2018): 1488–95. http://dx.doi.org/10.1021/acs.jpca.7b12118.

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44

Moss, Robert A., Guo-Jie Ho, Weiguo Liu, and Claudia Sierakowski. "The kinetic isotope effect in the rearrangement of neopentylchlorocarbene." Tetrahedron Letters 34, no. 6 (February 1993): 927–30. http://dx.doi.org/10.1016/s0040-4039(00)77456-9.

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Lewandowicz, Andrzej, Daria Sicinska, Juliusz Rudzinski, Susumu Ichiyama, Tatsuo Kurihara, Nobuyoshi Esaki, and Piotr Paneth. "Chlorine Kinetic Isotope Effect on the Fluoroacetate Dehalogenase Reaction." Journal of the American Chemical Society 123, no. 37 (September 2001): 9192–93. http://dx.doi.org/10.1021/ja0160400.

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46

Umemoto, Hironobu, Kunikazu Tanaka, Shigeki Oguro, Ryoji Ozeki, and Masashi Ueda. "14N/15N kinetic isotope effect in the association reaction ()++→+." Chemical Physics Letters 345, no. 1-2 (September 2001): 44–50. http://dx.doi.org/10.1016/s0009-2614(01)00838-7.

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Anastasis, Panayiotis, Raymond Duffin, Christopher Gilmore, and Karl Overton. "Partial kinetic ‘resolution’ resulting from a deuterium isotope effect." J. Chem. Soc., Chem. Commun., no. 12 (1991): 801–2. http://dx.doi.org/10.1039/c39910000801.

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48

Durán, R. P., V. T. Amorebieta, and A. J. Colussi. "Lack of kinetic hydrogen isotope effect in acetylene pyrolysis." International Journal of Chemical Kinetics 21, no. 9 (September 1989): 847–58. http://dx.doi.org/10.1002/kin.550210909.

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Cho, Byong K. "Elucidation of Lean-NOxReduction Mechanism Using Kinetic Isotope Effect." Journal of Catalysis 178, no. 2 (September 1998): 395–407. http://dx.doi.org/10.1006/jcat.1998.2169.

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Nikitenko, S. I., M. V. Nikonov, and A. Yu Garnov. "Kinetics and kinetic isotope effect in pentavalent plutonium disproportionation activated by power ultrasound." Journal of Radioanalytical and Nuclear Chemistry Articles 191, no. 2 (April 1995): 361–67. http://dx.doi.org/10.1007/bf02038232.

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Journal articles on the topic 'Isotope kinetic effect'

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