Isotope Effect

isotope effect

[′ī·sə‚tōp i‚fekt]
(physical chemistry)
The effect of difference of mass between isotopes of the same element on nonnuclear physical and chemical properties, such as the rate of reaction or position of equilibrium, of chemical reactions involving the isotopes.
(solid-state physics)
Variation of the transition temperatures of the isotopes of a superconducting element in inverse proportion to the square root of the atomic mass.

Isotope Effect


the variation in the properties of the isotopes of a given element or in the properties of compounds differing in isotopic composition, which is caused by the difference in their atomic masses. The differing properties of isotopes determined not by mass but by other characteristics of the atomic nucleus (as manifested in, for example, radioactive decay) are usually not classified as isotope effects.

The difference in the masses of isotopes is responsible for the difference in the masses of the molecules, their moments of inertia, and the strength of the corresponding chemical bonds. This leads both to nonuniform distribution of the isotopes among chemical compounds on reaching equilibrium of isotopic exchange (thermodynamic isotope effects) and to differing rates of a given chemical reaction that transpires with the participation of various isotopic forms of the reacting compounds (kinetic isotope effects). The higher the atomic number of the element the smaller the relative difference in the masses of isotopes. In isotopes of hydrogen it is 100 percent for deuterium D (2H) and 200 percent for tritium T (3H) in comparison with protium H (’H). Therefore, for hydrogen and helium the isotope effects are expressed more strongly. Among them in particular are the isotopic shift and the effects observed on transition to a superconducting state or to a state of superfluidity.

The difference in the masses of the isotopes of a given element is responsible for their differing properties in the isotopic forms of a chemical compound containing the element (such as density, the index of refraction, viscosity, and diffusion coefficient). As a result of isotope effects such thermodynamic properties as heat capacity, thermal conductivity, evaporation heat, heat of fusion, and saturated vapor pressure at a given temperature, as well as the vibrational frequencies of atoms in molecules and crystal lattices, also change.

The use of isotopes as isotope tracers (tagged atoms) is based on the concept of the identical nature of the physical and chemical properties of the isotopes of a given element. As experience shows, this simplifying assumption is close to reality for many isotopes, and the magnitude of isotope effects (both kinetic and thermodynamic) does not exceed the errors of a chemical experiment. However, for light elements the differences in the chemical properties of isotopes may be significant. This must be taken into account when isotopes of light elements, especially the isotopes of hydrogen—deuterium and tritium—are used as tagged atoms. Isotope effects underlie nearly all known laboratory and industrial methods of isotope separation.


References in periodicals archive ?
When protium (H) is completely replaced by deuterium (D), the 2-3-fold kinetic isotope effect is well known [5].
One of such processes is a carbon isotope effect during sonochemical carbon monoxide disproportionation in water [49].
Some physical properties of two-band hybridized superconductor, that is, critical temperature, zero-temperature order parameter, gap-to-[T.sub.c] ratio, and isotope effect coefficient, were investigated.
Although there are many metabolic pathways which do not involve the cleavage of a C-H bond and therefore would not exhibit a kinetic isotope effect (for example, oxidation of nitrogen (N) to N-oxides), the cleavage of a C-H bond in favor of a more polar atom, such as oxygen (O), is a primary metabolic pathway.
(2006), that there was no unusual isotope effect that would alter the [delta][sup.13]C] 100 % terrestrial end-point from the expected value of -20 [+ or -] 1 [per thousand]
We call this phenomenon an "isotope effect," and if we can measure these isotope effects, we can distinguish the reactions that produce them.
This small degree of isotope fractionation may be attributable to the "isotope effect" and the difference in isotope concentrations in the solution.
The scientists, who formed magnesium diboride wires, observed the isotope effect typical of conventional superconductors.
From earlier work on the "isotope effect" in germanium, it is believed that the occasional carbon-13 atom (which is 8 percent heavier than a carbon-12 atom) in the diamond lattice impedes the transmission of heat by interfering with the passage of phonons, like a speed bump slows traffic on an otherwise smooth highway.
This study demonstrates the relationship between the modification of the mechanical treatment of solid-phase substance and its solubility rates (laser diffraction method) in the waters of different deuterium/protium ratio (kinetic isotope effect), IR spectral properties in the middle and terahertz ranges, and differences in ligand-receptor interactions as a function of the dispersity of pharmaceutical substances samples for the biological model (Spirotox, the Arrhenius interpretation).
The solvent isotope effect was studied in [D.sub.2] O, where k' = 7.95 x [10.sup.-4] [s.sup.-1] in [D.sub.2]O medium and 795 x [10.sup.-4] [s.sup.-1] in water leading to a solvent isotope effect, k' ([H.sub.2]O)/k' ([D.sub.2]O) = 1.07.