scholarly journals VAPOR PRESSURES OF TRITIUM OXIDE AND DEUTERIUM OXIDE. INTERPRETATION OF THE ISOTOPE EFFECT

1963 ◽  
Author(s):  
W.M. Jones
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Vapor Pressures

Mechanistic Effects of Deuteration on the Aqueous Corrosion of Nuclear Waste Glasses

1990 ◽  
Vol 212 ◽  
Author(s):  
X. Feng ◽  
L. Fu ◽  
T. K. Choudhury ◽  
I. L. Pegg ◽  
P. B. Macedo
Keyword(s):  
Isotope Effect ◽  
Nuclear Waste ◽  
Deuterium Oxide ◽  
Aqueous Media ◽  
Extensive Study ◽  
Dissolution Mechanism ◽  
Deuterated Water ◽  
Aqueous Corrosion ◽  
Rate Determining Step ◽  
Data Yield

ABSTRACTIsotopically labeled water has been utilized by several researchers to help elucidate the glass dissolution mechanism in aqueous media. However, most of the results have been obtained with simple silicate glasses and have utilized low surface-to-volume (S/V) ratios and relatively short time scales. In this paper we report the results of an extensive study of the leach behavior of the preliminary West Valley nuclear waste glass composition, WV205, in deuterium oxide using multiple S/V ratios at both short and long times. The WV205 glass was leached in parallel in both ordinary deionized water and in deuterated water at five S/V ratios (20, 100, 200, 2000 and 6000 m−1) at 90°C under PCT (the SRL-modified MCC3 procedure) conditions with sampling at 1, 3, 7, 28, 56, 120 days, and four times annually thereafter; the tests will continue for several years. Initial rates were determined by measurements at shorter times with polished monoliths. A significant isotope effect, as measured by the ratio of leach rates, RH20/RD20, was found at all S/V ratios and reached values as large as 360%. Our data yield different values for RH20/RD20 in the diffusion, matrix dissolution, and saturation dominated regimes with the largest effect in the middle stage. Large values of RH20/RD20 would be characteristic of a primary kinetic isotope effect suggestive of a bond breakage involving hydrogen in the rate determining step.

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.

Solvent Isotope Effect on the Reaction Catalysed by the Pyruvate Dehydrogenase Complex from Escherichia coli

2003 ◽  
Vol 384 (4) ◽  
pp. 673-679 ◽  
Author(s):  
X. Liu ◽  
H. Bisswanger
Keyword(s):  
Escherichia Coli ◽  
Isotope Effect ◽  
Pyruvate Dehydrogenase ◽  
Deuterium Oxide ◽  
Pyruvate Dehydrogenase Complex ◽  
Pyrimidine Ring ◽  
Ph Profile ◽  
Kinetic Isotope ◽  
Michaelis Constants ◽  
Solvent Isotope

Abstract The pyruvate dehydrogenase from Escherichia coli showed a primary kinetic isotope effect when its overall reaction or the partial reaction of the pyruvate dehydrogenase component were tested in deuterium oxide. The Michaelis constants for pyruvate were nearly unchanged, but the maximum velocities in water and deuterium oxide differed, their ratio being DV = 1.7 for the overall reaction and DV = 2.1 for the E1p reaction. The pH profile and, accordingly, the δpK1 and δpK2 values were shifted by 0.6 units to higher pL values. A linear proton inventory curve was obtained when varying the atom fractions of protons relative to deuterons from 100 to 0%. This is an indication for a single proton transfer. It is proposed that this relatively weak primary isotope effect may be caused by the protonation of the N1 nitrogen at the pyrimidine ring of the cofactor by an adjacent glutamate residue. The proton of its carboxylic group exchanges very fast with deuterons of the solvent.

scholarly journals H/D Isotope Effects on Redox-Switching of DNA Self-Assembled Monolayers Observed by EQCM and Cyclic Voltammetry

2018 ◽  
Author(s):  
Sarasi K. K. Galagedera ◽  
Gerd-Uwe Flechsig
Keyword(s):  
Isotope Effect ◽  
Drug Testing ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Electrochemical Quartz Crystal Microbalance ◽  
Reaction Rate Constant ◽  
Reduction Peak ◽  
Buffer Medium ◽  
Self Assembled ◽  
Redox Switching

An electrochemical quartz crystal microbalance (EQCM) was employed to study the interactions of hexammine ruthenium(III) (RuHex) and hexammine cobalt(III) (CoHex) with a mixed self-assembled monolayer of single-stranded DNA and 6-mercapto-1-hexanol (ssDNA/MCH SAM) immobilized on gold electrodes. When the buffer medium was switched to deuterium oxide (D<sub>2</sub>O) from normal water (H<sub>2</sub>O), we observed a pronounced H/D kinetic isotope effect where a consistent shift of up to 400 mV was seen for the reduction peak potential of CoHex but not with RuHex. This was attributed to a 2400-fold change of the apparent reaction rate constant. Though there was a dramatic increase in the EQCM frequency response at a millisecond time scale in the presence of both redox indicators, compared to the signal observed in a low ionic strength buffer (10 mM tris(hydroxymethyl)aminomethane (Tris)/H<sub>2</sub>SO<sub>4 </sub>at pH 7.5), a 10 Hz decrease in the frequency shift was observed upon switching from H<sub>2</sub>O to D<sub>2</sub>O-based buffer medium. The hydrogen bond network within the ssDNA layer seems to amplify the H/D isotope effect with CoHex. Amplified isotope effects may play a role in living systems. The mechanisms of recently reported H/D isotope effects in medicinal and biochemistry are still widely unclear. Voltammetric and EQCM studies of H/D isotope effects can provide a platform to investigate amplified isotope effects not only with DNA layers, but probably also with proteins and small organic molecules and may be useful for studies of cell proliferation, as well as drug testing.

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