The semiquantal time-dependent Hartree (SQTDH) theory is applied to the coupled Morse and modified Lippincott-Schroeder (LS) model potentials of hydrogen bond. The structural correlation between the heavy atoms distance and the proton position, the geometric isotope effect, the energy of hydrogen bond formation, and the proton vibrational frequency shift are examined in a broad range of structu...

The D/H ratio of hydrogen gas in equilibrium with water vapor over aqueous lithium chloride solutions was measured at 25 °C, using a hydrophobic platinum catalyst. Experimental details are described. The hydrogen isotope effect between the solution and pure water depends linearly on the LiCl concentration up to ca. 12 m, and at higher concentrations a marked deviation from linearity takes place...

The uranium isotope effect in the exchange system uranyl(VI)-malate ligand at 288–343 K has been studied by ion exchange displacement chromatography. At all temperatures 235U is enriched at the front of the uranium band. The single stage separation coefficient, (e =a – 1), increased from (0.9 ± 0.1)× 10 at 288 K to (2.9 ± 0.3)× 10–4 at 343 K. The equilibrium constant of the isotope exchange rea...

Three-dimensional, triple resonance NMR techniques are described for measurement of two-bond (intraresidual) and three-bond (sequential) amide deuterium isotope effects on 13CR chemical shifts. Measurements were carried out for uniformly 15N and 13C labeled human ubiquitin equilibrated in a 50% H2O/50% D2O mixed solvent. The three-bond isotope shift, 3∆CR(ND), ranges from about 10-50 ppb, and, ...

Application of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has led to big breakthrough of analytical methods for metal stable isotopes, resulting in rapid progresses in non-traditional stable isotope geochemistry. As a new geological tracer, Mg isotopes have been widely applied in studies of almost all important disciplines of geochemistry. High precision Mg isotope...

We have investigated Mo and W isotope compositions in acid leachates and an insoluble residue from the Murchison carbonaceous chondrite. The new data reveal variable enrichments of sand r-process isotopes and demonstrate that several isotopically diverse presolar components are present in Murchison. The insoluble residue is enriched in s-process Mo and W, evidently due to the enrichment s-proce...

Intramolecular isotope effects were determined for the N-demethylation of N-methyl-N-trideuteriomethylaniline catalyzed by two isozymes of cytochrome P-450 and several peroxidases in order to differentiate between deprotonation and hydrogen atom abstraction steps. Lactoperoxidase, hemoglobin, myoglobin, and two isozymes of horseradish peroxidase catalyzed the hydroperoxide-dependent N-demethyla...

We investigated the influence of organic substrates and phosphate concentration on the rates of dissimilatory microbial sulfate reduction and the 34S/32S isotopic fractionation produced by several Desulfovibrio species. Our experiments corroborate the previously reported species-specific correlation between sulfur isotope fractionation and cell-specific sulfate reduction rates. We also identify...

The isotope effect and excitation-energy dependence have been measured in the oxygen K-edge x-ray emission spectrum (XES). The use of XES to monitor core decay processes provides information about molecular dynamics (MD) on an ultrafast time scale through the O1s lifetime of a few femtoseconds. Different nuclear masses give rise to differences in the dynamics and the observed isotope effect in ...