Exchange, of solvent

It is an empirical fact that in the absence of a significant exchange Of solvent flux with the vapor phase the position of the solvent front with respect to time is adequately represented by... 

A proper D mechanism requires that kx be identical to the rate constant for the exchange of solvent (due account being taken of any statistical correction when more than one solvent molecule is present) and the value of k2 (in reality the term fc2/fc i[S] is used because the constants cannot be separated) should be sensitive to the chemical nature of L rather than its size and charge (factors that control Kos in an interchange mechanism). The most convincing demonstration of a D mechanism would be found in cases where k2/k-1[S] is much larger than any value expected for an outer-sphere complex formation constant, but this is not a necessary requirement for the mechanism. 

Intermolecular interactions between an electron and a nuclear dipole usually contribute to line-widths unless the solvent has no magnetic nuclei. If exchange of solvent molecules is rapid these will be largely... 

Thermal desorption enables the exchange of solvent into a more environmentally friendly stream of gas at the stage where analytes are being released into a suitable trap (sorption tube, denuder, and passive dosimeter). Figure 19.8 illustrates the basic mechanisms of the thermal desorber. 

If the exchange of solvent molecules is fast (r < 10 sec) the dependence of the chemical shift 6 on electrolyte concentration, solvent composition and temperature is interpreted in terms of ion solvation. The chemical shift difference 6 of the solvent protons in the presence and absence of an electrolyte is, generally, assumed to be the sum of three contributions ... 

The solvation of chromium(llI) ion in certain mixed-solvent systems has been studied in experiments which are relatively free of ambiguity. The exchange of solvent molecules between the mixed solvent and the solvated species Cr(OH2)w (So)n3+ (So = organic solvent component) is a very slow process. The species with solvation shells having different compositions can be separated from one another by column ion-exchange procedures. Analytical procedures based upon such separations allow evaluation of equilibrium constants for reactions involving replacement of coordinated water by the polar organic component. These equilibrium constants are reviewed in this chapter with attention focused upon the dependence of the equilibrium constants upon solvent composition, and the relationship of relative values of the equilibrium constants to the statistically expected values. 

Formation of the enediol(ate) of RuBP is readily assayed on the basis of exchange of solvent protons with the C3 proton of substrate (20-22). The six-carbon intermediate of the carboxylation pathway (II in Fig. 1) can be prepared by rapid quench after mixing equimolar amounts of RuBP and the carboxylase in the presence of 14CO2 (23). Availability of this labeled intermediate allows determination of an enzyme s commitment to forward processing in the carboxylation step. Decomposition, via decarboxylation, is observed as a decrease in radioactivity that can be stabilized by borohydride, whereas forward catalysis is equated with an increase in acid-stable radioactivity. 

Operating conditions agitation intensity volume of solvent exchange of solvent... 

In this group there is a variability in coordination numbers brought about by the rapidity of exchanges of solvent H20 between inner and outer spheres, giving a range of different M—O distances. Coordination numbers are sensitive to extraneous factors, e.g., anions present, in a way not observed elsewhere in the periodic table. 

S) —> (R) direction exhibits a much smaller overshoot than the (R) —> (S) direction, and shows significant exchange of solvent deuteron into the substrate pool even when the extent of racemization is low. The (R) —> (S) direction shows much less exchange of deuterium into the substrate pool. 

This mechanistic use of AV X was first proposed in 1958 by Taube,55 who found AV X = +1.2 cm3/mol for the exchange of solvent water on Co(NH3)5OH23+ consistent with an Id mechanism as expected from other information. Taube, in conversation with the present author in 1966, conceded that the smallness of this pressure effect had discouraged him from pursuing the idea further, but agreed that it... 

Figure 6 The chemical mechanism of the C5-mannuronan epimerase reaction. The exchange of solvent deuterium into the product is indicated. Note the conformation change in the polymeric substrate that is induced by the epimerization reaction.

On the basis that a water proton in different electronic environments experiences different magnetic field strengths and therefore exhibits different chemical shifts, two distinct proton resonances should occur corresponding to bound and unbound water molecules provided that the exchange of solvent is not too rapid. Direct comparison of the integrated areas under the respective peaks will give the solvation number of the metal ion. The resonance signal from solvent molecules in the outer-sphere... 

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