Self-exchange kinetics

The reader is also referred to the innovative nonphotochemical electron transfer studies of Weaver et al. [147], These authors have been exploring dynamical solvent effects on ground state self-exchange kinetics for or-ganometallic compounds. This work has explored many aspects of solvent control on intermediate barrier electron transfer reactions, including the effect on a distribution of solvation times. The experimental C(t) data on various solvents have been incorporated into the theoretical modeling of the ground state electron transfer reactions studied by Weaver et al. [147]. 

Ion pairs of the type MT +, MXm generally exhibit weak CT absorption bands. When self-exchange kinetic data and reduction potentials are available (or can be estimated) for the MT +/MTjf- (+ and couples, then the thermal parameters can be compared to the spectroscopic based on equation (20). In this Umit, the free energy contribution can be approximated by the difference in the half-wave potentials of the donor and acceptor as in equation (60) AGj)p - FAiii/2 (F = Faraday s constant in this limit, the correction for the difference in the species involved in light absorption and the electrochemical process, proportional to is small). 

However, there are good reasons for treating this type of bond separately. One is that this bond is often reversible, that is there are low energy barriers for bond breaking and bond formation. This is however not always the case, and for some metal ions in certain oxidation states bond forming and breaking is extremely slow, for example the [Ir(H20)6] ion has the slowest self exchange kinetics of any homoleptic mononuclear metal centre with a half-life of coordinated waters of more than 3 years [12]. 

Fu, Z., Santore, M. Effect of layer age and interfacial relaxations on the self-exchange kinetics of poly(ethylene oxide) adsorbed on silica. Macromolecules 32(6), 1939-1948 (1999)... 

In the present case, the electron hopping chemistry in the polymeric porphyrins is an especially rich topic because we can manipulate the axial coordination of the porphyrin, to learn how electron self exchange rates respond to axial coordination, and because we can compare the self exchange rates of the different redox couples of a given metallotetraphenylporphyrin polymer. To measure these chemical effects, and avoid potentially competing kinetic phenomena associated with mobilities of the electroneutrality-required counterions in the polymers, we chose a steady state measurement technique based on the sandwich electrode microstructure (19). 

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... 

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. 

Kinetic Parameters for Fe /Fe Self-Exchange in Water at 298K. 

Kinetic Parameters for PuO + Pu -> PuO +Pu Cross-exchange Calculated from Theoretical Values for Constituent Self-exchange in Aqueous Solution (5, 8)... 

Table II are selective, they are, nevertheless, reasonably representative. Self-exchange parameters obtained from kinetic data reported in the literature are widely scattered (Table II) for both the 02/02 an< M suPerox°/lJ Peroxo couples. Despite...

In the homogeneous case, the derivation of an activation-driving force relationship and of an expression of the intrinsic barrier is less straightforward. It is interesting in this connection to relate the kinetics of crossexchange reactions (31) to those of the two self-exchange reactions (also called identity or isotopic reactions) [(32) and (33)]. 

How might one measure the kinetic parameters for the self-exchange k 10 M s ) of (T -arene)2CrV(Ti -tu ene)2Cr in solution What would be the advantages of such a system for testing outer-sphere electron transfer theories How might the rate constant vary with the optical and static dielectric constants for various solvents ... 

A values have been obtained for oxidation of benzenediols by [Fe(bipy)(CN)4], including the effect of pH, i.e., of protonation of the iron(III) complex, and the kinetics of [Fe(phen)(CN)4] oxidation of catechol and of 4-butylcatechol reported. Redox potentials of [Fe(bipy)2(CFQ7] and of [Fe(bipy)(CN)4] are available. The self-exchange rate constant for [Fe(phen)2(CN)2] has been estimated from kinetic data for electron transfer reactions involving, inter alios, catechol and hydroquinone as 2.8 2.5 x 10 dm moF s (in dimethyl sulfoxide). 

The kinetics of the reduction of perruthenate(VII) by [FefCbOe]" and [W(CN)g]" and the oxidation of ruthenate(VI) by [Mo(CN)g] and [Ru(Cb06] have been studied in aqueous alkaline solutions. The cross-reaction data have been treated according to the Marcus relations and yield a self-exchange rate constant of 10 s at 25.0 °C and 1.0 M ionic strength for the... 

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