A derivation of the classical jump rate I' for tracer diffusion aimed at a clear expression for the mass dependence of the frequency factor v is presented. The derivation is effected without using the usual collective normal coordinates which usually combine the masses in a complicated way. v depends explicitly on the mass of the surrounding host atoms (as well as on the tracer-atom mass) if th...

Kinetic isotope effects related to the breaking of chemical bonds drive sulfur isotope fractionation during dissimilatory sulfate reduction (DSR), whereas oxygen isotope fractionation duringDSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explo...

Orotidine-5'-monophosphate decarboxylase (OMP decarboxylase, ODCase) catalyzes the decarboxylation of orotidine-5'-monophosphate (OMP) to uridine-5'-monophosphate (UMP). Despite extensive enzymological, structural, and computational studies, the mechanism of ODCase remains incompletely characterized. Herein, carbon kinetic isotope effects were measured for both the natural abundance substrate a...

A combined experimental and theoretical investigation of the deuterium isotope effects on the bacterial luciferase reaction is described. The experimental studies focus on determining if the unusual aldehydic deuterium isotope effect of approximately 1.5 observed in these reactions is an intrinsic isotope effect resulting from a single rate-limiting step or is a composite of multiple rate-limit...

Literature data on H /D isotope effects on polarizability are reviewed. An argument based on perturbation theory correlates the isotopic differences with electronic transition moments via vibra­ tional averaging. The contribution of the second moment isotope effect is especially important. The approach is first illustrated with a calculation on H 2/D 2 and then employed to correlate differentia...

The D/H ratios of hydrogen gas in equilibrium with aqueous alkali halide solutions were determined at 25 °C, using a hydrophobic platinum catalyst. The hydrogen isotope effect between the solution and pure water changes linearly with the molality of the solution at low concentrations, but deviates from this linearity at higher concentration for all alkali halide solutions. The magnitude of the ...

The diffusional isotope effect of a monatomic Lennard-Jones liquid is calculated by molecular-dynamics simulation. Mass differences of 10-40 % were used. At equilibrium density, with decreasing temperature a strong reduction of the isotope effect is found that indicates a marked increase of the collectivity of motion. Changing the density at constant temperature, the same effect is seen that sh...

Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichlo...

it is very important to determine the stable nitrogen isotope ratio for the nitrogenous substances in aerosols and the geochemistry behavior of stable nitrate ion isotopes in aerosols in order to elucidate the chemical and physical functions of clouds. hence, aerosol field sampling was conducted in the skies offshore from malibu beach and santa barbara, california, u.s.a. on 16 and 18 july 2009...