Isotopic Exchanges

To determine the principal pathway of exchange, isotopic exchange by functional position was examined. The lower halves of Tables II and III show the amounts of incorporation of protium into the spent Tetralin. In E10, 66% was in the position, 23% in the position, and 11% in the Har position. A similar distribution was found in El9. This preferential incorporation in the Hx position of Tetralin strongly suggests that the predominant path-... 

Introducing the masses of exchanging isotopes (m and m°, respectively), the ratio of partition functions for crystalline components can be related to that of the primitive unit cell (Kieffer, 1982), thus defining reduced partition function ratio / (whose formulation is equivalent to that obtained by Bigeleisen and Mayer, 1947, and Urey, 1947, for gaseous molecules) ... 

Cleland introduced the net rate constant method to simplify the treatment of enzyme kinetic mechanisms that do not involve branched pathways. This method can be applied to obtain rate laws for isotope exchange, isotope partitioning, and positional isotope exchange. Since the net-rate constant method allows one to obtain VraaJKra and in terms of the individual rate constants, this method has greatest value for the characterization of isotope effects on and Kj. Because only... 

Molecular modelling of transition metal complexes (TMC), reproducing characteristic features of their stereochemistry and electronic structure, is in high demand in relation with studies and development of various processes of complex formation with an accent on ion extraction, ion exchange, isotope separation, neutralization of nuclear waste, and also when studying structure and reactivity of metal-containing enzymes. Solving these techno-... 

Thermolysis of l,l-difluoro-2,3-diphenylcyclopropane in supercritical CO2 has allowed the rate of geometrical isomerization [i.e. cis-( 109) to /ra/M-(109)] and racemization [i.e. (/< )-( 109) to (S)-( 109)] to be determined from O2 dependence of the trapping rate of the postulated intermediate 1,3-biradical.246 Above 150 °C, the formation of 2,2-difluoroindane and its decomposition products is reported. A similar thermally induced equilibrating series of stereomutations has been observed with the analogous non-fluorinated cyclopropane in which rate constants and deuterium exchange isotope effects are reported.247 Theoretical studies of this isomerization have focused on classical248 and quasi-classical trajectories.249... 

Water samples Bromine Bromide/bromate Ion exchange/isotopic dilution 6jug I"1 bromide 30/tg I"1 bromate Diemer and Heumann (1997)... 

In the standard experiments on the MIF there is extensive isotopic exchange ("isotopic scrambling"), such as Q -I- OO QOO QO -i- O. However, there is also a body of experimental data on ozone formation obtained under very special experimental conditions [18] in which isotopic exchange is minor. In these experiments ratios of recombination rate constants, such as the -F... 

Raushel EM, Cleland WW. Determination of the rate-limiting steps and chemical mechanism of fructokinase by isotope exchange, isotope partitioning, and pH studies. Biochemistry 1977 16 2176-2181. 

At the time that the previous chapter in Volume 11 was written, the method of King and Altman (7) was the method of choice for deriving steady-state rate equations for enzymic reactions, and this is still true for any mechanism involving branched reaction pathways. The best description of this method may be found in Mahler and Cordes (8). A useful advance was made in 1975 with the introduction of the net rate constant method (9), and because it is the simplest method to use for any nonbranched mechanism, as well as for equations for isotopic exchange, positional isotopic exchange, isotope partitioning, etc., we shall present it here. 

A continuous ion-exchange isotope separation process for uranium enrichment has been developed in Japan. Few details of this process have been disclosed. However, it is known that "reflux" is obtained by oxidation and reduction of U " " and U02 . A demonstration plant with a capacity of 2 kSWU/y is in operation at Hyuga. 

After correcting the peak intensities for non-exchanged isotopic contributions such as C, the series of data is fit typically to a system of coupled ordinary differential equations using programs such as KinFit [27] to determine the rate constants. 

Amide-hydrogen isotopic exchange is performed in either the exchange-in or exchange-out format. In the former, the protiated form of the protein is exchanged isotopically with an excess of the deuterated solvent, whereas in the latter format, the fully deuterated protein is back-exchanged with the protiated solvent. 

The principle used for the counter-current ion-exchange isotope separation by electromigration in a column is the balancing of the hydraulic flow of the ions X, the isotopes of which are to be separated, by the opposite flow of ions Y in an electric field. The X ions should be the more strongly sorbed on the ion exchanger and the Y ions should be the more mobile ones in the field. A sharp boimdary between the two kinds of ions is attained at some place in the column and is maintained there by the balancing of the flows. The steady passage of electric current is equivalent to movement of the sorbed band of X (which is actually... 

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