Deuterium isotope effects on the ionization of the lower carboxylic acids in water and deuterium oxide

1976 ◽  
Vol 54 (18) ◽  
pp. 2879-2883
Author(s):  
Jan Bron
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Ionization Constants ◽  
Emf Method ◽  
Acidic Group ◽  
A Value ◽  
Alkanoic Acids ◽  
Group A ◽  
Deuterium Isotope Effects

To facilitate the interpretation of isotope effects on the ionization of weak acids in water and deuterium oxide, a comparison of these quantities with that for a standard acid is proposed. Therefore, a quantity Kr has been defined by the equation Kr = (kH/kD)/(kH′/KD′). The equilibrium constants KH and KD refer to the ionization constants in water and deuterium oxide respectively. The equilibrium constant KX′(X = H, D) refers to the acid used as a reference. An equation is derived from which it may be concluded, that for a series of acids closely similar in geometry and force field around the acidic group, a value of Kr close to unity should be obtained. To test this prediction the values of KH/KD for a series of n-alkanoic acids (N = 3–6) are compared experimentally with the value of KH/KD of acetic acid (25 °C). An emf method has been used in these measurements (quinhydrone electrode). In agreement with the theory a value for Kr close to unity has been observed.

Mechanism of initiation in the thermal polymerization of styrene. Kinetic deuterium isotope effects in the initiation step of the thermal polymerization of some deuterated styrenes

1969 ◽  
Vol 47 (21) ◽  
pp. 4049-4058 ◽  
Author(s):  
Karl R. Kopecky ◽  
Syamalarao Evani
Keyword(s):  
Hydrogen Transfer ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Thermal Polymerization ◽  
Convenient Synthesis ◽  
Initiation Step ◽  
Deuterium Isotope Effects

A convenient synthesis of 2,6-dideuteriostyrene starts with N,N-dimethyl-(1-phenylethyl)-amine which is deuterated in the 2 and 6 positions by a series of exchanges using n-butyllithium followed by deuterium oxide. The deuterium isotope effects at 70° on the rates of the thermal polymerization, [Formula: see text], of 2,6-dideuterio-, α-deuterio-, and β,β-dideuteriostyrene are 1.29, 1.00, and 0.78, respectively. The deuterium isotope effects at 70° on the 2,2′-azobis-(2-methylpropionitrile) initiated rates of polymerization,[Formula: see text], are 0.96, 0.86, and 0.81, respectively. From these values the deuterium isotope effects on the rates of initiation of the thermal polymerization, k1H/k1D, are calculated to be 1.80, 1.31, and 0.92, respectively. At 147° the presence of 1.5% potassium t-butoxide decreases the rate of the thermal polymerization of neat styrene by a factor of 17, and results in the formation of 1-phenyltetralin as the greatly predominant dimer. The results support the suggestion that the thermal polymerization of styrene is initiated by hydrogen transfer from 1-phenyl-1,2,3,9-tetrahydronaphthalene, formed by a concerted dimerization of two molecules of styrene, to a third molecule of styrene.

Berechnung kinetischer Isotopeneffekte für die Reaktion von Methyljodid mit Cyanid-Ion

1966 ◽  
Vol 21 (9) ◽  
pp. 1377-1384
Author(s):  
A. V. Willi
Keyword(s):  
Transition State ◽  
Secular Equation ◽  
Isotope Effects ◽  
Force Constants ◽  
Bond Breaking ◽  
Bending Force ◽  
A Value ◽  
Order Of Magnitude ◽  
Deuterium Isotope Effects ◽  
The Difference

Kinetic carbon-13 and deuterium isotope effects are calculated for the SN2 reaction of CH3I with CN-. The normal vibrational frequencies of CH3I, the transition state I · · · CH3 · · · CN, and the corresponding isotope substituted reactants and transition states are evaluated from the force constants by solving the secular equation on an IBM 7094 computer.Values for 7 force constants of the planar CH3 moiety in the transition state (with an sp2 C atom) are obtained by comparison with suitable stable molecules. The stretching force constants related to the bonds being broken or newly formed (fCC, fCC and the interaction between these two stretches, /12) are chosen in such a way that either a zero or imaginary value for νʟ≠ will result. Agreement between calculated and experimental methyl-C13 isotope effects (k12/ k13) can be obtained only in sample calculations with sufficiently large values of f12 which lead to imaginary νʟ≠ values. Furthermore, the difference between fCI and fCC must be small (in the order of 1 mdyn/Å). The bending force constants, fHCI and fHCC, exert relatively little influence on k12/k13. They are important for the D isotope effect, however. As soon as experimental data on kH/kD are available it will be possible to derive a value for fHCC in the transition state if fHCI is kept constant at 0.205 mdynA, and if fCI, fCC and f12 are held in a reasonable order of magnitude. There is no agreement between experimental and calculated cyanide-C13 isotope effects. Possible explanations are discussed. — Since fCI and fCC cannot differ much it must be concluded that the transition state is relatively “symmetric”, with approximately equal amounts of bond making and bond breaking.

scholarly journals Deuterium Isotope Effects on Permeation and Gating of Proton Channels in Rat Alveolar Epithelium

1997 ◽  
Vol 109 (4) ◽  
pp. 415-434 ◽  
Author(s):  
Thomas E. DeCoursey ◽  
Vladimir V. Cherny
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Channel Gating ◽  
Alveolar Epithelium ◽  
Ionic Species ◽  
Alveolar Epithelial Cells ◽  
Proton Channels ◽  
Deuterium Isotope Effects ◽  
Solvent Isotope

The voltage-activated H+ selective conductance of rat alveolar epithelial cells was studied using whole-cell and excised-patch voltage-clamp techniques. The effects of substituting deuterium oxide, D2O, for water, H2O, on both the conductance and the pH dependence of gating were explored. D+ was able to permeate proton channels, but with a conductance only about 50% that of H+. The conductance in D2O was reduced more than could be accounted for by bulk solvent isotope effects (i.e., the lower mobility of D+ than H+), suggesting that D+ interacts specifically with the channel during permeation. Evidently the H+ or D+ current is not diffusion limited, and the H+ channel does not behave like a water-filled pore. This result indirectly strengthens the hypothesis that H+ (or D+) and not OH− is the ionic species carrying current. The voltage dependence of H+ channel gating characteristically is sensitive to pHo and pHi and was regulated by pDo and pDi in an analogous manner, shifting 40 mV/U change in the pD gradient. The time constant of H+ current activation was about three times slower (τact was larger) in D2O than in H2O. The size of the isotope effect is consistent with deuterium isotope effects for proton abstraction reactions, suggesting that H+ channel activation requires deprotonation of the channel. In contrast, deactivation (τtail) was slowed only by a factor ≤1.5 in D2O. The results are interpreted within the context of a model for the regulation of H+ channel gating by mutually exclusive protonation at internal and external sites (Cherny, V.V., V.S. Markin, and T.E. DeCoursey. 1995. J. Gen. Physiol. 105:861–896). Most of the kinetic effects of D2O can be explained if the pKa of the external regulatory site is ∼0.5 pH U higher in D2O.

Third dissociation constant of phosphoric acid in H2O and D2O from 75 to 300 °C at p = 20.4 MPa using Raman spectroscopy and a titanium-sapphire flow cell

2021 ◽  
Author(s):  
Jacy Conrad ◽  
Peter R. Tremaine
Keyword(s):  
Raman Spectroscopy ◽  
Phosphoric Acid ◽  
Dissociation Constant ◽  
Raman Spectra ◽  
Isotope Effects ◽  
Flow Cell ◽  
Ionization Constants ◽  
Hydrothermal Conditions ◽  
Phosphate Ion ◽  
Deuterium Isotope Effects

The first reported Raman spectra and ionization constants for the phosphate ion in H2O and D2O above 50 °C quantify deuterium isotope effects under hydrothermal conditions.

DEUTERIUM ISOTOPE EFFECTS ON HYDROGEN BONDING

1966 ◽  
Vol 44 (22) ◽  
pp. 2611-2615 ◽  
Author(s):  
Surjit Singh ◽  
C. N. R. Rao
Keyword(s):  
Hydrogen Bonding ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Zero Point ◽  
Deuterium Isotope Effects

The interaction of phenol and phenol-d with a number of donors of varying basicity has been studied in terms of the equilibrium constants, ΔS0, ΔH0, ΔvOH, and ΔvOD and various aspects of deuterium isotope effects on hydrogen bonding have been discussed. The deuterium isotope effects are found to vary markedly with the basicity of the donor and the results are discussed in terms of the zero point contributions to the KH/KD.

High Levels of Circulating Thrombomodulin in Human Foetuses and Children

1999 ◽  
Vol 81 (06) ◽  
pp. 906-909 ◽  
Author(s):  
Marie-Hélène Aurousseau ◽  
Danielle Gozin ◽  
Fernand Daffos ◽  
Armando D’Angelo ◽  
François Forestier ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Endothelial Cell ◽  
Protein C ◽  
Endothelial Cell Surface ◽  
A Value ◽  
Median Level ◽  
Group A ◽  
Anticoagulant Function ◽  
Cell Surface Proteoglycan ◽  
Human Foetuses

SummaryThrombomodulin (TM) is an endothelial cell surface proteoglycan with anticoagulant functions, also implicated in cell proliferation, cell-cell adhesion and differentiation. In this study we determined circulating plasma TM (pTM) levels in human foetuses at different stages of pregnancy, at birth and in childhood. TM levels increased with gestational age, the median level reaching a peak of approximately 165 ng/ml between the 23rd and 26th week, thereafter decreasing gradually, reaching a value of 108 ng/ml at birth. pTM continues to decrease progressively during childhood, reaching in the 5-15 years group a median of 56 ng/ml which approaches the adult value. The pTM peak was statistically significant and represents a specific foetal phenomenon as it was independent of the corresponding maternal values. As a whole, the pTM pattern during foetal maturation appears totally different from that of protein C, prothrombin and other coagulation activators and inhibitors and thus, TM may play in the foetus another role in addition to its well-known anticoagulant function.

Mechanism of hydration and isomerisation of 4-ethylidene-2,6-di-tert-butyl-2,5-cyclohexadien-1-one. Kinetics, acid-base catalysis and solvent deuterium isotope effects

1979 ◽  
Vol 44 (1) ◽  
pp. 110-122 ◽  
Author(s):  
Jiří Velek ◽  
Bohumír Koutek ◽  
Milan Souček
Keyword(s):  
Aqueous Medium ◽  
Rate Equation ◽  
Kinetic Data ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Quinone Methide ◽  
Reaction Products ◽  
Acid Base ◽  
Deuterium Isotope Effects ◽  
Hydroxybenzyl Alcohol

Competitive hydration and isomerisation of the quinone methide I at 25 °C in an aqueous medium in the region of pH 2.4-13.0 was studied spectrophotometrically. The only reaction products in the studied range of pH are 4-hydroxybenzyl alcohol (II) and 4-hydroxystyrene (III). The form of the overall rate equation corresponds to a general acid-base catalysis. The mechanism of both reactions for three markedly separated pH regions is discussed on the basis of kinetic data and solvent deuterium effect.

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