Kinetics, exchange

During a simple exchange reaction between a gas (e.g., CO, C02,Os) containing excess of IS0 and an oxide whose surface contains the normal concentration, we find experimentally a continuous fall of 180 concentra- 

Other symbols which will be used include 

From the plot of log (a — a ) vs. time, we obtain the experimental rate constant ke, so that 

In many cases (23, 24), in order to get further information about the 

As in the case of the oxygen exchange described above in Section IV (see also Fig. 16), well-behaved first-order kinetics were observed for all the cyanide exchange reactions for which the modified exponential form of the McKay equation (8) was used to determine the observed rate constants. 

Upon addition of the 13C-labeled cyanide to the [WO(OH2)(CN)4]2 complex, there is a rapid trans substitution, (kx = 1 M 1 s-1) (50), followed by the exchange at the equatorial cyano sites as shown in Eq. (29) (also see final spectrum in Fig. 7) 

4 Equatorial cyanide exchange on the dinuclear complex ([Re203(CN)8]4 (Fig. 3) or [Tc203(CN)8]4-). 

The significant reactivity difference for cyanide exchange on the Tc(V) and Re(V) of 4000 is in general agreement with that found in previous complex-formation and oxygen-exchange studies (1, 2, 76, 

A further, more unlikely process occurring to account for this observed accelerated exchange can in principle be attributed to the for- 

It is theoretically possible that equilibrium between liquid and resin will be maintained at all points of contact. Liquid and solid concentrations are then related by the sorption isotherm. It is usual, however, that pellet or film diffusion will dominate or control the rate of exchange. It is also possible that control will be mixed, or will change as the ion exchange proceeds. In the latter case, the initial film-diffusion control will give way to pellet-diffusion control at a later stage. 

Exchange between counter-ions A in beds of resin and counter-ions B in a well-stirred solution may be represented by the Nemst-Planck equation as  

The term in the square bracket is an effective diffusion coefficient DAB. In principle, this may be used together with a material balance to predict changes in concentration within a pellet. Algebraic solutions are more easily obtained when the effective diffusivity is constant. The conservation of counter-ions diffusing into a sphere may be expressed in terms of resin phase concentration Csr, which is a function of radius and time. 

This equation has been solved by Eagle and Scott(11) for conditions of constant concentration outside the sphere and negligible resistance to mass transfer in the boundary film. The solution may be written in terms of a mean concentration through a sphere Cs, which is a function of time only, to give  

When t is large, the summation may be restricted to one term and the equation becomes  

Consider a mixture of AX and BX at chemical equilibrium. When, for example, radioisotopes are used as tracers, they are injected into the equilibrium mixture in the form of a very small amount of B X. At various times, either (BX + B X) or (AX + A X) is separated from the mixture and analyzed. When nmr line broadening is used to monitor the exchange the tracer is already present e.g. H or O (or an additional amount can be added) and the exchange is monitored in situ and assessed from the shape of the nmr signals (Sec. 3.9.6). If the concentration of (AX + A X) is a and the concentration of (BX + B X) is b, and the fraction of exchange at time t is F, it is not difficult to show that the gross or overall rate of X transfer between AX and BX, (M s ) is given by  

The exchange of Mn between MnOj and MnOj has been followed using the Mn radioisotope and quenched-flow methods (Sec. 3.3.2).The results are shown in Table 1.3, from which it is apparent that 

Even complex rate laws may be easily constructed by examining the dependence of F xch on the concentrations of the various species in solution. The rate of exchange of Ni between Ni + and Ni(edta) obeys the rate law 

The five terms simply represent paths through which exchange can occur (Sec. 4.4.3). 

If there is more than one exchanging atom of X in the interacting molecules, for example AX exchanging with BX , the rate expression (1.191) is modified accordingly, with a and b replaced by na and mb respectively. This applies only when the nX or mX atoms are equivalent. In basic solution the vanadium(V) ion, exchanges oxygen with solvent 

---

This assumes that the gas-solid exchange kinetics at the interface is rapid. When this process affects the exchange kinetics significantly dieii analysis of concentrations layer by layer in die diffused sample is necessaty. This can be done by the use of SIMS (secondary ion mass spectrometry) and the equation used by Kihier, Steele and co-workers for this diffusion study employs a surface exchange component. 

Another means is available for studying the exchange kinetics of second-order reactions—we can adjust a reactant concentration. This may permit the study of reactions having very large second-order rate constants. Suppose the rate equation is V = A caCb = kobs A = t Ca, soAtcb = t For the experimental measurement let us say that we wish t to be about 10 s. We can achieve this by adjusting Cb so that the product kc 10 s for example, if A = 10 M s , we require Cb = 10 M. This method is possible, because there is no net reaction in the NMR study of chemical exchange. 

Mass-Exchange Kinetics of Organic Ions on Crosslinked Polyelectrolytes... 

Water exchange kinetics in labile aquo and substituted aquo transition metal ions by means of 170 n.m.r. studies. J. P. Hunt, Coord. Chem. Rev., 1971, 7,1-10 (29). 

Reaction scheme, defined, 9 Reactions back, 26 branching, 189 chain, 181-182, 187-189 competition, 105. 106 concurrent, 58-64 consecutive, 70, 130 diffusion-controlled, 199-202 elementary, 2, 4, 5, 12, 55 exchange, kinetics of, 55-58, 176 induced, 102 opposing, 49-55 oscillating, 190-192 parallel, 58-64, 129 product-catalyzed, 36-37 reversible, 46-55 termination, 182 trapping, 2, 102, 126 Reactivity, 112 Reactivity pattern, 106 Reactivity-selectivity principle, 238 Relaxation kinetics, 52, 257 -260 Relaxation time, 257 Reorganization energy, 241 Reversible reactions, 46-55 concentration-jump technique for, 52-55... 

Bonner and Goishi have reviewed the complex exchange kinetics and the... 

Heinen M, Chen Y-X, Jusys Z, Behm RJ. 2006. Room temperature COad desorption/exchange kinetics on Pt electrodes—A combined in-situ IR and mass spectrometry study. ChemPhysChem 8 2484. 

The ligand exchange kinetics between free and coordinated ligands were studied more thoroughly for the ligands trimethylphosphite and triphenylphosphine. The kinetics were analyzed using conventional NMR line shape technique 140). 

The water exchange rate is hardly affected by substituents which do not directly interfere in the inner coordination sphere. Different bisamide DTPA derivatives have similar exchange rates.28-30 Substituents on the carbon backbone of DTPA also have little influence on the water-exchange kinetics.31 38 39... 

As an extension of the intermolecular self-exchange described above, the solvent-induced intramolecular electron exchange kinetics in radical anions of 1,3-dinitrobenzene [47] and benzene 1,3-dicarbaldehyde [48] have been studied by several authors (Freed and Fraenkel, 1964 Grampp et al., 1989, 1990b Shohoji et al, 1987). The advantage of [47] and [48] is their structural simplicity and their high stability, which allows measurements even in protic... 

Ultimately, for Pt(IV) anticancer drugs, a combination of incorporation of bioactive ligands that specifically target cancer cells, control over ligand-exchange kinetics, and selective activation by light would allow for temporal and spatial control of drug delivery and activation. 

Nuclear magnetic resonance (NMR) experiments are used to study the exchange kinetics of chemical systems in equilibrium.28,68,69 As is the case for fluorescence correlation spectroscopy no perturbation of the chemical system in equilibrium is required to obtain kinetic information from NMR experiments. However, NMR is not very sensitive to concentration changes. 

The kinetic information for NMR experiments is contained in the line broadening observed for a nucleus that resides in two different magnetic environments, and values for rate constants can be obtained using line-shape analysis.28,68,69 Line broadening experiments obtained using ID NMR is the method of choice when analyzing the kinetics of a molecule in two sites. 2D NMR techniques, such as 2D EXYS are employed when the kinetics are sequential, i.e. more than one step, or multiple sites are analyzed.69 For example in the case of supramolecular systems this technique was employed to measure the exchange kinetics in capsules.70... 

If the metals bound in complexes exchange with biological ligands, the dissociation kinetics of these complexes, the ligand-exchange kinetics and the association kinetics with the biological ligands must be considered. Simple dissociation kinetics of complexes are related to their thermodynamic stability constants by the relationship ... 

---