Chemical isotope

Bigeleisen, J. and Ishida, T. Application of finite orthogonal polynomials to the thermal functions of harmonic oscillators. I. Reduced partition function of isotopic molecules, J. Chem. Phys. 48, 1311 (1968). Ishida, T., Spindel, W. and Bigeleisen, J. Theoretical analysis of chemical isotope fractionation by orthogonal polynomial methods, in Spindel, W., ed. Isotope Effects on Chemical Processes. Adv. Chem. Ser. 89, 192 (1969). 

As discussed at length in this review. Mo isotope variations are now known to be pervasive. This finding was not rmexpected. First, the Mo isotope system spans a mass range of 8% (Fig. 1), which compares favorably with many other stable isotope systems. Second, the dynamic redox chemistry of Mo, and the fact that Mo-ligand interactions have strong covalent character, lends itself to chemical isotope effects. Finally, with seven stable isotopes of relative abundance -10-25%, high-precision Mo isotope analyses are analytically tractable. 

The Heisenberg Uncertainty Principle, describing a dispersion in location and momentum of material particles that depends inversely on their mass, gives rise to vibrational zero-point energy differences between molecules that differ only isotopically. These zero-point energy differences are the main origin of equilibrium chemical isotope effects, i.e., non-unit isotopic ratios of equilibrium constants such as K /Kj) for a reaction of molecules bearing a protium (H) atom or a deuterium (D) atom. 

Enzymes, enantoselectivity, 148 Equilibrium chemical isotope effects, 28 for NCMH model, 40-41 ESI-MS analysis... 

Amed with these suggestive prolegomena, we may now turn to the key problem of chemical (isotopic) evolution in galaxies, starting with our own. 

Chemical isotope effects are divided into two classes—those affecting the position of the equilibrium in a chemical reaction and those affecting the rate of a chemical reaction. Equilibrium isotope effects have their origin in the fact that the extent to which any chemical reaction goes is governed by the number of possible ways it can proceed (the phase space available). The more equally probable reaction paths available, the more likely the reaction will go. To illustrate this point, consider the exchange reaction... 

What is the criterion for labelling an element exotic This question could be formulated in another way. How can we be sure that a particular isotope distribution cannot be explained by normal physico-chemical isotope effects, so making it necessary to opt for an abnormal initial isotope distribution It must be clear that as far as we... 

Mazor, E. (1986) Chemical, isotopic and physical data used to check basic (commonly assumed) hydrological interrelations. Proc. Int. Conf. on Groundwater Systems Under Stress, Brisbane, Australia, May 1986, 1-14. 

Mazor, E., Vautax, F.D., and Jaffe, F.C. (1985) Tracing groundwater components by chemical, isotopic and physical parameters, example Schinziach, Switzerland. J. of Hydrology 76, 233-246. 

The variety of physical, chemical, isotopic, and dating methods is systematically presented via the basic observations, stressing the applied aspects, based on the multiparameter-multisampling approach. 

The separation of chemical isotopes is based on small differences in their physical and chemical properties. For the lower-mass isotopes, chemical exchange, distillation, and electrolysis have been used. For the higher-mass isotopes, techniques based on mass have been used, including gaseous diffusion, centrifugation, thermal diffusion, and ion activation.29,30 A newer method uses lasers that produce coherent light tuned to the specific wavelength of a vibration bond related to the desired isotope in an atom or molecule. This technique is still under development but... 

Abstract Planet formation is a very complex process through which initially submicron-sized dust grains evolve into rocky, icy, and giant planets. The physical growth is accompanied by chemical, isotopic, and thermal evolution of the disk material, processes important to understanding how the initial conditions determine the properties of the forming planetary systems. Here we review the principal stages of planet formation and briefly introduce key concepts and evidence types available to constrain these. 

In Section 6.7, the discovery of the magnetic isotope effect (ME) of C was introduced. In this Chapter, a more detailed review of MEs will be given. Because the chemical isotope effects (CEs) of hydrogen is much larger than those of heavier elements, their MEs will be dealt with in this Chapter. Let us consider the following reactions from a starting molecule (A) through a radical pair (RP) ... 

Theoretical Analysis of Chemical Isotope Fractionation by Orthogonal Polynomial Methods... 

Kerrich, R. 1986. Fluid infiltration into fault zones Chemical, isotopic, and mechanical effects. PAGEOPH, 124 225-268. 

The ideal chemical isotopic tag is one that will react with every protein or peptide present in the sample and be reactive enough that the protein/peptide becomes fully labeled. However, the intrinsic reactivity of the compound should not be so high that it degrades upon storage under proper conditions. Also, the ideal tag will be stable upon mass spectrometry and not readily break apart under standard conditions. The ideal chemical tag will either be commercially available or relatively easy to synthesize, and the price should be reasonable. At a minimum, the tag needs to be available in a heavy and light form, but ideally would be available in a range of masses so that multiple replicates can be combined. It is also important that peptides labeled with the heavy and light forms of the tag coelute from HPLC otherwise, the quantitation is less accurate when... 

The differences in the properties of the isotopes of an element are called isotopic effect. The origin of an isotopic effect is always a physical phenomenon which can be attributed to the isotopic masses in chemical isotopic fractionations For example. 

Intrinsic KIEs. The phrase intrinsic KIEs is often used. This refers to the situation where only chemical steps are kinetically signihcant, i.e. irreversible or rate-limiting, depending on the context. As the goal of TS analysis is to understand the chemical mechanisms of catalysis, the goal is always to measure intrinsic KIEs that do not contain contributions from non-chemical, isotopically insensihve steps. 

Simultaneous measurement as iso-absorbance on the sides of optical spectra as seen in Figure 17-30. One species (2) may be measured relative to another (1) considered as a standard and which serves as a reference. Traces of (2) can thus be detected even if species (1) is highly absorbent at the measurement wavelengths A, and A,. This concept was demonstrated in the Chem c process for the chemical isotopic separation of uranium [34, 163]. 

Stable isotopes are chemical isotopes that are not radioactive. Stable isotopes of the same element have the same chemical characteristics and behave chemically almost identically. Mass differences, due to a difference in the number of neutrons, result in partial separation of the light from the heavy isotopes during chemical reactions (isotope fractionation). 

Chemical isotope effects are divided into two types equilibrium and kinetic. The latter are of particular importance in palaeolimnology (and other branches of the sedimentary N cycle) and are typically associated with complex, irreversible, biologically mediated reactions. A characteristic, but not invariable aspect of kinetic isotope fractionation is a marked discrimination against the heavier isotope, snch that the product of the reaction is enriched in N relative to the substrate. 

Recently, we have demonstrated that enrichment up to 6%o can occur during simulated laboratory experiments of sulfur incorporation into OM (Amrani and Aizenshtat, 2003). This finding can explain part of the difference between pyrite and OM to a value that can be explained solely by this fractionation or in combination with chemical isotope mixing discussed previously. The mechanisms controlling this discrimination are under investigation and will be published elsewhere. 

Q./Q ) and useful for the calculation of chemical isotope separation factors. We define... 

Thus the reduced partition function ratio, (s/s )f, Is just the chemical Isotope fractionation factor of the chemical species against the gaseous atom. With the convention prime Is the light Isotope It Is easy to prove that ln(s/s )f Is always positive. This follows from the fact that u. > u.. 

Chemical isotope extraction and purification processing in the Hot Ceil Laboratory ... 

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