Isotope Effects in Deuterium Oxide Solution. I. Acid-Base Equilibria

1961 ◽  
Vol 83 (1) ◽  
pp. 42-47 ◽  
Author(s):  
C. A. Bunton ◽  
V. J. Shiner
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Acid Base

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.

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.

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.

The Hydrolysis of Disubstituted Alkyl Phosphorochloridates and N,N,N′,N′-Tetra-stibstituted Phosphorodiamidic Chlorides in Water and Deuterium Oxide: Heat Capacity of Activation and Kinetic Solvent Isotope Effects

1973 ◽  
Vol 51 (4) ◽  
pp. 597-603 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Thermodynamic Parameters ◽  
Alkyl Group ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Potential Relationship ◽  
Mechanism Of Reaction ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The pseudo-thermodynamic parameters, ΔH≠, ΔS≠, and ΔCp≠ and the kinetic solvent isotope effects have been determined for the three alkyl-phosphorochloridates, where the alkyl group is ethylisopropyl and n-propyl; for tetra-methyl and tetra-ethyl phosphorodiamidic chlorides; the di-n-propyl and di-isopropyl analog, the di(isopropylmethylcarbinyl)phosphorochloridate and the tetra-ethylthiophosphorodiamidic chloride. These compounds have a potential relationship to compounds used as insecticides and as polymers. The mechanism of reaction is discussed on the basis of these data.

The hydrogen isotope effect in the bromination of 2-carbethoxy cyclo pentanone

1956 ◽  
Vol 235 (1203) ◽  
pp. 453-468 ◽  
Keyword(s):  
Isotope Effect ◽  
Hydrogen Isotope ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Activation Energies ◽  
Tunnel Effect ◽  
Fluoride Ion ◽  
Energy Barriers ◽  
Hydrogen Isotope Effect ◽  
Kinetics Of

Measurements are reported on the kinetics of the base-catalyzed bromination of 2-car-bethoxycyclopentanone, with either hydrogen or deuterium in the active position. The solvent throughout was deuterium oxide, the catalysts employed were the solvent, monochloroacetate ion and fluoride ion, and measurements were made at 5° intervals over the range 10 to 70°C. The observed activation energies are all greater for the deutero- than for the proto-ester, but the differences are greater than would be expected on current theories of isotope effects. The observed collision factors are in every case greater for deuterium than for hydrogen, especially for catalysis by fluoride ion, where the ratio of these factors is A D / A H = 24 ± 4. These observations can only be accounted for by invoking the tunnel effect, i. e. by supposing that the motion of the proton is markedly non-classical in nature. It is shown that this hypothesis leads to reasonable dimensions for the energy barriers involved, and some if its general consequences are discussed.

Solvent isotope effects in the oxidation of dipeptides by aqueous chlorine

1999 ◽  
Vol 77 (5-6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Armesto ◽  
M Canle L. ◽  
V García ◽  
J A Santaballa
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Second Step ◽  
Solvent Isotope Effect ◽  
General Base ◽  
Peptide Oxidation ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

A kinetic study of the mechanism of oxidation of Ala-Gly and Pro-Gly by aqueous chlorine has been carried out. Among other experimental facts, the deuterium solvent isotope effects were used to clarify the mechanisms involved. In a first stage, N-chlorination takes place, and then the (N-Cl)-dipeptide decomposes through two possible mechanisms, depending on the acidity of the medium. The initial chlorination step shows a small isotope effect. In alkaline medium, two consecutive processes take place: first, the general base-catalyzed formation of an azomethine (β ca. 0.27), which has an inverse deuterium solvent isotope effect (kOH-/kOD- ~ 0.8). In a second step, the hydrolysis of the azomethine intermediate takes place, which is also general base-catalyzed, without deuterium solvent isotope effect, the corresponding uncatalyzed process having a normal deuterium solvent isotope effect (kH2O/kD2O ~ 2). In acid medium, the (N-Cl)-dipeptide undergoes disproportionation to a (N,N)-di-Cl-dipeptide, the very fast decomposition of the latter in deuterium oxide preventing a reliable estimation of the solvent isotope effect.Key words: chlorination, deuterium isotope effects, fractionation factors, peptide oxidation, water treatment.

Determination of isotope effects on acid–base equilibria by 13C NMR spectroscopy

1997 ◽  
pp. 445-450 ◽  
Author(s):  
Tonis Pehk ◽  
Ene Kiirend ◽  
Endel Lippmaa ◽  
Ulf Ragnarsson ◽  
Leif Grehn
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Isotope Effects ◽  
13C Nmr Spectroscopy ◽  
Acid Base
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