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Topic: Kinetic isotope effect


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In the News (Tue 23 Jul 19)

  
  Kinetic isotope effect Summary
Kinetic isotope effects (KIE) refer to the impact on reaction rate when one of the atoms in a molecule is replaced by its isotope.
The kinetic isotope effect is a variation in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes.
Stable chlorine intramolecular kinetic isotope effects from the abiotic dehydrochlorination of DDT
www.bookrags.com /Kinetic_isotope_effect   (1562 words)

  
  Britain.tv Wikipedia - Isotope
Thus, different isotopes of a given element all have the same number of protons and electrons and the same electronic structure; because the chemical behavior of an atom is largely determined by its electronic structure, isotopes exhibit nearly identical chemical behavior.
The main exception to this is the kinetic isotope effect: due to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element.
Isotopic substitution can be used to determine the mechanism of a reaction via the kinetic isotope effect.
www.britain.tv /wikipedia.php?title=Isotope   (1212 words)

  
 [No title]
Isotopes can be used as markers to determine the nature of intermediates in chemical reactions.
Primary kinetic isotope effect arises when the bond to the isotopic substitution is broken at or before the transition state.
Isotope effects should also exist with heavier atoms, such as C, N, S, Cl etc. However, since the ratio of reduced mass approaches unity as the atomic weight increases, the KIE values become smaller for heavier atoms.
www.orgchem.iisc.ernet.in /faculty/um/cd213/isotope2.html   (1765 words)

  
 ISOTOPE FACTS AND INFORMATION
Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different mass numbers because they contain different numbers of neutrons.
The word ''isotope'', meaning ''at the same place'', comes from the fact that all isotopes of an element are located at the same place on the periodic table.
In scientific nomenclature, isotopes (nuclides) are specified by the name of the particular element by a hyphen and the number of nucleons (protons and neutrons) in the atomic nucleus (e.g., helium-3, carbon-12, carbon-14, iron-57, uranium-238).
www.splammer.com /?req=isotope   (940 words)

  
 Kinetic isotope effect - Wikipedia, the free encyclopedia
In this particular intramolecular KIE study the radical substitution of hydrogen by bromine is examined with mono-deuterated toluene (obtained by organic reduction of benzyl chloride with zinc and deuterated acetic acid) and N-bromosuccinimide.
In this study the KIE is calculated from the reaction rate constants for regular 2,4-dimethyl-3-pentone and its deuterated isomer by optical density measurements.
Stable chlorine intramolecular kinetic isotope effects from the abiotic dehydrochlorination of DDT
en.wikipedia.org /wiki/Kinetic_isotope_effect   (1098 words)

  
 I
The effect on the rate or equilibrium constant of two reactions that differ only in the isotopic composition of one or more of their otherwise chemically identical components is referred to as a kinetic isotope effect (see isotope effect, kinetic) or a thermodynamic (or equilibrium) isotope effect (see isotope effect, thermodynamic), respectively.
A kinetic isotope effect attributable to isotopic substitution of an atom to which a bond is made or broken in the rate-controlling step or in a pre-equilibrium step of a specified reaction is termed a primary isotope effect.
A kinetic isotope effect that is attributable to isotopic substitution of an atom to which bonds are neither made nor broken in the rate-controlling step or in a pre-equilibrium step of a specified reaction, and is therefore not a primary isotope effect, is termed a secondary isotope effect.
www.chem.qmul.ac.uk /iupac/gtpoc/I.html   (3495 words)

  
 [No title]   (Site not responding. Last check: 2007-10-19)
The observed kinetic isotope effect on C-3 is discussed to originate from the formation of the enamine, which comes to equilibrium before the rate determining release of glyceraldehyde 3-P from the ternary complex.
The equilibrium isotope effect is seen as the reason for an earlier-found relative 13C enrichment in position C-3 and C-4 of glucose and for varying enrichments in 13C of carbohydrates from different compartments of cells.
The kinetic isotope effect is suggested to cause 13C discriminations in the C-3 pool in context with the hexose formation in competition with other dihydroxyacetone phosphate turnover reactions.
www.lycoszone.com /info/isotope--positions.html   (315 words)

  
 Atmospheric Chemistry: Saueressig 2001
Measurements of the C-13 and D kinetic isotope effects (KIE) in methane, (KIE)-K-13C = k((CH4)-C-12)/k((CH4)-C-13) and (KIE)-K- D = k((CH4)-C-12)/k((CH3D)-C-12), in the reactions of these atmospherically important methane isotopomers; with O(D-1) and OH have been undertaken using mass spectrometry and tunable diode laser absorption spectroscopy to determine isotopic composition.
For the carbon kinetic isotope effect in the reaction with the OH radical, (KIEOH)-K-13C = 1.0039 (+/- 0.0004, 2 sigma) was determined at 296 K, which is significantly smaller than the presently accepted value of 1.0054 (+/-0.0009, 2 sigma).
The carbon kinetic isotope effect in the reaction with O(D-1), (KIEO(1D))-K-13C, was determined to be 1.013, whereas the deuterium kinetic isotope effect is given by (KIEO(1D))-K-D = 1.06.
www.atmosphere.mpg.de /enid/fe.html   (249 words)

  
 kinetic isotope effect   (Site not responding. Last check: 2007-10-19)
Carbon kinetic isotope effect in the reaction of CH4 with Cl atoms...
Kinetic isotope effects as probes for hydrogen tunneling in enzyme catalysis...
JCE 2000 (77) 1042 [Aug] Kinetic Isotope Effect in the Chromic Acid Oxidation of...
www.scienceoxygen.com /chem/172.html   (263 words)

  
 Take a BrainSip
An isotopic substitution will greatly modify the measured reaction rate when the isotopic replacement is in a chemical bond that is broken or formed in the rate-determining step.
Isotopic rate changes are most pronounced when the relative mass change is greatest.
To see why it is the relative mass difference (and not absolute mass difference) that matters for the Kinetic isotope effect, note that the fundamental vibrational frequency (''ν'') of a chemical bond between atom A and B is, when approximated by a harmonic oscillator:
kinetic-isotope-effect.brainsip.com   (500 words)

  
 Metabolite Pools and Metabolic Branching as Factors...
Inter- and intra-molecular non-statistical isotope distributions do not only require the existence of a kinetic isotope effect on a defined enzyme catalyzed reaction, but also the prerequisite that this reaction is located at a metabolic branching point.
C pattern of natural malic acid is discussed as a consequence of isotope effects on the carboxylation of pyruvate and PEP and on the pyruvate dehydrogenase reaction.
An isotope effect on the reduction of "active formaldehyde" to "active methyl" and the existence of corresponding pools is responsible for
www.ufz.de /index.php?en=2402   (215 words)

  
 Carbon Isotope Effects on the Fructose-1,6-bisphosphate Aldolase Reaction, Origin for Non-statistical 13C Distributions ...
by the carbon isotope effect on the reaction.
isotope effect on the reaction was determined by incubation of
isotope effects for the conversion of the substrate with
www.jbc.org /cgi/content/full/272/9/5382   (3703 words)

  
 Kinetic isotope effect   (Site not responding. Last check: 2007-10-19)
The kinetic isotope effect is a difference in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes.
In many cases, the rate difference can be rationalized by noting that the mass of an atom affects the vibration frequency of the chemical bond that it forms, even if the electron configuration is nearly identical.
To see why it is the relative mass difference (and not absolute mass difference) that matters for the Kinetic isotope effect, note that the fundamental vibrational frequency (''ν'') of a chemical bond between atom A and B is, when approximated by a harmonic oscillator: :
kinetic-isotope-effect.borgfind.com   (513 words)

  
 K and L
A kinetic electrolyte effect ascribable solely to the influence of the ionic strength on activity coefficients of ionic reactants and transition states is called a "primary kinetic electrolyte effect".
A kinetic electrolyte effect arising from the influence of the ionic strength of the solution upon the pre-equilibrium concentration of an ionic species that is involved in a subsequent rate-limiting step of a reaction is called a "secondary kinetic electrolyte effect".
A common case encountered in practice is the effect on the concentration of hydrogen ion (acting as catalyst) produced from the ionization of a weak acid in a buffer solution.
www.chem.qmul.ac.uk /iupac/gtpoc/KL.html   (1857 words)

  
 Glossary - K   (Site not responding. Last check: 2007-10-19)
Kinetic Control: A reaction under kinetic control will produce products in a ratio related to the difference in the energy of the transition states of the products.
Kinetic Isotope Effect: For example, reaction in which a C-H bond must be broken will proceed more slowly if the H atom is replaced with a deuterium.
Clearly, in principle, it occurs for all elements and their isotopes, however, the effect is greatest for hydrogen, because this has the largest percentage increase.
www.everyscience.com /Chemistry/Glossary/K.php   (258 words)

  
 L20. Deuterium Kinetic Isotope Effects in the Reactions of CH [2?] with Methane and Acetylene and C2H [2S ] with O2
The observed temperature and pressure dependences are in accordance with a barrierless addition of the methylidyne radical to methane or acetylene with rapid decomposition of the adduct, consistent with an interpretation of these reactions as capture-limited.
Such an isotope effect, although relatively small, is larger than would be predicted by a simple transition-state theory which assumes that the conserved modes are unchanged from reactants to transition state.
kinetic isotope effect suggests that any rearrangement of the intermediate complex is rapid and facile, and that the total reaction rate is governed by the initial complex formation.
www.cstl.nist.gov /div838/kinet_conf/agenda/l_session/l20.html   (302 words)

  
 Stable Isotope Fractionation of Tetrachloroethene during Reductive Dechlorination by Sulfurospirillum multivorans and ...
corresponding to a reduction of the isotope effect of 33 to
Equilibrium carbon isotope effect on a decarboxylation reaction.
Carbon isotope effects on the enzyme-catalyzed carboxylation of ribulose bisphosphate.
aem.asm.org /cgi/content/full/71/7/3413   (4207 words)

  
 Olle Matsson
Matsson, O. Primary and Secondary andbeta;-Deuterium Kinetic Isotope Effects in the 1,3-Prototropic rearrangement of 1-Methylindene using Tertiary Amines as Catalysts in the Solvents Toluene and Dimethyl Sulphoxide.
C Kinetic Isotope Effect in the Base-Catalyzed Prototropic Rearrangement of 1- to 3-Methylindene.
C Kinetic Isotope Effect of the Tyrosine Phenol-Lyase Catalyzed andalpha;,andbeta-Elimination of L-Tyrosine.
www.org.kemi.uu.se /Forskning/OlleM/OMfulllist.shtm   (1153 words)

  
 IGAC | Biogenic aerosol formation in the boreal forest (BIOFOR)
This isotope effect is thus directly related to the isotopic composition of an important source of the gas.
The isotopic depletion of water vapor in contact with liquid water is a good example of a classic equilibrium isotope effect, which is purely mass dependent.
The mass dependence of isotope fractionation in chemical reactions according to transition state calculations and equilibrium calculations is mainly the result of differences in the normal vibrational frequencies for the individual isotopic species [Kaye, 1987].
www.igac.noaa.gov /newsletter/16/mass-new.php   (3604 words)

  
 The Kinetic Deuterium Isotope Effect as a Probe of a Proton Coupled Electron Transfer Mechanism in the Oxidation of ...
Panel B: Deuterium isotope effect on the kinetics of the transient absorption at 310 nm induced by a laser pulse excitation of 2APr (0.1 mM) and dGMP (1.2 mM) in oxygenated H
The kinetic isotope effect on the electron-transfer equilibrium between 2APr and dGMP may be interpreted in terms of Scheme 1.
We have recently shown, using deuterium isotope effects, that the quenching of the fluorescence of a pyrene derivative by the nucleobases dG, dC, and dT occurs via a proton-coupled electron transfer mechanism.
pubs.acs.org /cgi-bin/jtextd?jpcbfk/104/i01/html/jp993239e   (1763 words)

  
 RNA Center - Faculty Pages - Michael E. Harris
Effects of deprotonation and direct coordination by Mg2+ on the observed solvent nucleophile isotope effect (18knuc) provide information about reaction mechanism.
Magnesium will also perturb the equilibrium isotope effect on deprotonation of water to form hydroxide (18KOH), resulting in a similar inverse shift in the observed effect.
It is also possible that metal ion interactions can alter the intrinsic kinetic isotope effect for bond formation (18kbond); however, metal ion coordination does not appear to alter the transition state for monoester hydrolysis.
www.rnaresearch.org /harris_res.htm   (487 words)

  
 Research   (Site not responding. Last check: 2007-10-19)
This value is very large compared to ~3, which is considered the "normal" kinetic isotope effect for an enzyme.
Because the KIE is large, it is believed that hydrogen tunneling plays a major role in this enzymatic step.
We were able to reproduce the temperature dependence of the KIE of soybean lipoxygenase with two different models.
www.personal.psu.edu /users/e/r/erh119/research_pcet.htm   (580 words)

  
 Carbon 13 and D kinetic isotope effects in the reactions of CH4 with O(1D) and OH: New laboratory measurements and ...
Carbon 13 and D kinetic isotope effects in the reactions of CH4 with O(1D) and OH: New laboratory measurements and their implications for the isotopic composition of stratospheric methane
Carbon 13 and D kinetic isotope effects in the reactions of CH
For the carbon kinetic isotope effect in the reaction with the OH radical,
www.agu.org /pubs/crossref/2001/2000JD000120.shtml   (404 words)

  
 Isotope - Enpsychlopedia
Isotopes are forms of an element whose nuclei have the same atomic number - the number of protons in the nucleus - but different mass numbers because they contain different numbers of neutrons.
In scientific nomenclature, isotopes (nuclides) are specified by the name of the particular element by a hyphen and the number of nucleons (protons and neutrons) in the atomic nucleus (e.g., helium-3, carbon-12, carbon-14, iodine-131, uranium-238).
Exploring the Table of the Isotopes at the LBNLaf:Isotoop
enpsychlopedia.org /psypsych/Isotope   (1000 words)

  
 [No title]   (Site not responding. Last check: 2007-10-19)
Besides the various methods known in the literature for the synthesis of isotopically labeled compounds, the use of metallorganic methylene equivalents such as the Simmons-Smith and the Tebbe-Grubbs reactions, are investigated.
The kinetic isotope effects obtained by these experiments can be interpreted if the vibronic force constants are known.
Alternatively, the potential use of electrochemical techniques for the determination of the kinetic isotope effects is explored.
www.nd.edu /~owiest/experimental.html   (283 words)

  
 [No title]   (Site not responding. Last check: 2007-10-19)
Title : Symmetry Induced Kinetic Isotope Effects Abstract : In this project in the Physical Chemistry program of the Chemistry Division, Professor Gregory Gellene of the Chemistry Department of Texas Tech University will pursue investigations on the symmetry- induced kinetic isotope effect, a new mechanism in ion-molcule reactions.
The symmetry-induced kinetic isotope effect is a sofar little recognized effect in physical chemistry.
This effect appears to play a significant role in the ozone chemistry of the earth's atmosphere, as well as in laboratory situations.
www.cs.utexas.edu /users/yguan/NSFAbstracts/Abstracts/MPS/CHE.MPS.a9521008.txt   (203 words)

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