We report the iron (Fe) isotope effect on the transition temperature (T(c)) in oxygen-deficient SmFeAsO(1-y), a 50-K-class, Fe-based superconductor. For the optimally doped samples with T(c) = 54  K, a change of the average atomic mass of Fe (M(Fe)) causes a negligibly small shift in T(c), with the Fe isotope coefficient (α(Fe)) as small as -0.024 ± 0.015 (where α(Fe)=-d lnT(c)/dlnM(Fe)). This ...

Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditi...

Abstract Hydrogen isotope exchange in China low activation martensitic (CLAM) steel was investigated by plasma-driven permeation (PDP) measurements the temperature range of ∼670–920 K. It found that as H introduced into D plasma, flux HD increased while 2 decreased. The total flux, however, remained almost unchanged. Such a result allowed analysis replacement and showed reduction is balanced ri...

Reactions occurring at a carbon atom through the Walden inversion mechanism are one of the most important and useful classes of reactions in chemistry. Here we report an accurate theoretical study of the simplest reaction of that type: the H+CH4 substitution reaction and its isotope analogues. It is found that the reaction threshold versus collision energy is considerably higher than the barrie...

The kinetic mechanism of the reaction of D-amino acid oxidase (EC 1.4.3.3) from Trigonopsis variabilis with [alpha-1H]- and [alpha-2H]phenylglycine has been determined. The pH dependence of Vmax is compatible with pKa values of approximately 8.1 and >9.5, the former of which is attributed to a base which should be deprotonated for efficient catalysis. The deuterium isotope effect on turnover is...

Oxygen isotope effect studies of the ferromagnetic Curie temperature Tc of La1AxCaxMnO3 are presented. The isotope exponent α0G−∆ ln Tcy∆ ln m0 changes from 0.4 to 0.14 in the range 0.2FxF0.43. The isotope exponent decreases strongly with increasing tolerance factor, or decreasing lattice distortion. Above Tc the conductivity is characteristic of small polarons. Raman scattering shows a promine...

Oxygen-isotope effect has been investigated in a recently discovered superconductor Sr0.4K0.6BiO3. This compound has a distorted perovskite structure and becomes superconducting at about 12 K. Upon replacing 16O with 18O by 60-80%, the Tc of the sample is shifted down by 0.32-0.50 K, corresponding to an isotope exponent of αO = 0.40(5). This isotope exponent is very close to that for a similar ...

Accurate path integral Monte Carlo or molecular dynamics calculations of isotope effects have until recently been expensive because of the necessity to reduce three types of errors present in such calculations: statistical errors due to sampling, path integral discretization errors, and thermodynamic integration errors. While the statistical errors can be reduced with virial estimators and path...

The isotope effect at C-1 on the H2O2-catalysed decarboxylation of pyruvate (used as a model reaction for the enzymic reaction) increases between pH 3 and 10 from 1.0007 +/- 0.0004 to 1.0283 +/- 0.0014 (25 degrees C). This result indicates a change in the rate-determining step from formation of the tetrahedral intermediate to decarboxylation of this intermediate. Practically no isotope fraction...

Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K(-1) mol(-1)) and in deuterium oxide (-35.7 J K(-1) mol(-1)). This difference suggests a role for distinct protein ...