Isotopic exchange kinetics

Figure 11. Determination of ferrous-ferric isotope exchange kinetics in dilute aqueous solutions using Fe-enriched tracer solutions. Measured 5 Fe values for ferrous (squares) and ferric (circles) Fe in solution versus time. Initial 5 Fe values for Fe(II), 0%o and Fe(III),q 331%o. The rapid convergence in Fe/ Fe ratios for the ferric and ferrous species indicates that isotopic equilibrium is attained within minutes. Adapted from Welch et al. (2003).

Gregory, R.T., et al. 1989. Oxygen isotope exchange kinetics of mineral pairs in closed and open systems application to problems of hydrothermal alteration of igneous rocks and Precambrian iron formations. Chemical Geology, 75, 1-42. 

A measure of the amount of a stable isotopic label that exceeds its natural abundance in unlabeled tracee. This is most directly accomplished using an ion ratio mass spectrometer to measure the ratio of ion currents for isotopomers such as C02 at mass 44 and 2 at mass 45. From the difference between the ion current ratio for a sample (Zsampie) and the ion current ratio for a reference gas (Zreference), the atom percent excess (APE) can be estimated. See Tracer/Tracee Ratio Compart-mental Analysis Isotope Exchange Kinetics... 

ASPARTATE CARBAMOYLTRANSFERASE ATMOSPHERE ATOM PERCENT EXCESS TRACER/TRACEE RATIO COMPARTMENTAL ANALYSIS ISOTOPE EXCHANGE KINETICS ATOMIC MASS UNIT ATOMIC ORBITAL ATOMIZATION ATP... 

ATOM PERCENT EXCESS OXYGEN ISOTOPE EXCHANGE COMPARTMENTAL ANALYSIS ISOTOPE EXCHANGE KINETICS GRAPHICAL METHODS... 

NATURAL ABUNDANCE ISOTOPE EXCHANGE KINETICS COMPARTMENTAL ANALYSIS ISOTOPE DILUTION Isotope effects,... 

Isotope incorporation 489 Isotope exchange kinetics 47, 235, 236,240,563-569 Isozyme 461 -465... 

Owing to the emphasis in our treatment on criteria rather than on individual reactions, the various arguments that a specific reaction series followed the addition-elimination route were spread among the different sections. It is worthwhile to summarize that the use of stereochemical, isotope exchange, kinetics and element effects show that the a-arylsulphonyl-j8-haloethylenes (Modena et al.), the j3-halo-a-nitro-styrenes (Modena et al.,) the a-aroyl-/ -haloethylenes (Montanari et al.) and the /3-halocrotonic esters and nitriles (Theron, 1967) systems react with thioanions via this route. Use of some of these criteria together show its operation for other reaction systems. 

Comparison of the computerized results obtained for the kinetic curves (Fig. 2a) reveals a very interesting feature of the IE process under discussion. Kinetic curves F (Fo) for variants I and III, resolved when a favorable isotherm of the B ion and the relation D >Dg apply, are described by the kinetic equation of diffusion into a spherical bead with constant diffiisivity D. In other words the kinetic curves F(Fo) coincide with the isotope exchange kinetic curves if a sharp profile appears in the bead and do not coincide if the exchange zone is greatly spread. The remaining kinetic curves in Fig. 2 formally correspond to the exchange process where varies in value. This is especially evident when comparing kinetic curves II and I.e (Fig. 2a). 

The kinetics of deprotonation leading to the enamine had been investigated by several groups using isotope exchange kinetics " as well as triiodide trapping of the... 

As in the case of hydrolysis, there has been a good deal of study of substituent effects, solvent effects, isotopic exchange, kinetics, and the catalysis of these processes. In contrast to hydrolysis, the alcoholysis reaction is reversible in both acidic and basic solutions. The key intermediate is the tetrahedral adduct. Its fate is determined mainly by the relative basicity of the two alkoxy groups. A tetrahedral intermediate generated by addition of methoxide ion to a p-nitrophenyl ester, for example, breaks down exclusively by elimination of the much less basic /j-nitrophenoxide ion. 

Evaluation of the experimental data has shown the molecular oxygen-zeolite isotopic exchange kinetics to obey first order equations. For example, Figure 1 presents some kinetic data on the exchange between 02 and sodium forms of zeolites studied at 620° and 700°C. These are treated according to the equation... 

Frossard, E. and Sinaj, S. (1997) The isotopic exchange kinetic technique a method to describe the availability of inorganic nutrients. Applications to K, P, S and Zn. Isotopes in Environmental and hlealth Studies 33, 51 -77. 

Felipe MA, Kubicki JD, Rye DM (2001) Hydrogen isotope exchange kinetics between water and dissolved silica from ab initio cdculations. Geochim Cosmochim Acta, snbmitted Fermann JT, Blanco C, Auerbach S (2000) Modeling proton mobility in acidic zeolite clnsters. I. 

FIGURE 6.25 Isotopic exchange kinetics as a function of pH of CdClj solution. (Source Dobrowolski, R., Jaroniec, M., and Kosmulski, M., Carbon, 24, 15, 1986. With permission.)... 

The isotopic exchange kinetics of Zn + ions in hydrated Zn-A zeolite of composition Zn5.55Nao.9o(A102)i2(Si02)i2 aq were investigated by measuring the fractional attainment of isotopic equilibrium between a ZnCl2 solution and a Zn-labelled Zn-... 

C. K. Woodward and B. D. Hilton, Biophys., 32, 561 (1980). Hydrogen Isotope Exchange Kinetics of Single Protons in Bovine Pancreatic Trypsin Inhibitor. 

Transport properties (separate determination of electronic and ionic conductivity, oxygen tracer diffusion and chemical diffusion) and surface stages (rate/constant of exchange) parameters of dense ceramics can be studied by several methods, such as electronic blocking polarization methods [32-34], O tracer profile analysis by SIMS [26, 27, 29, 35], study of the isotope exchange kinetics by gas-phase analysis of the isotope composition [27,... 

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