Series-parallel reaction mechanism detailed

Catalytic reactions involve a series of chemical transformations resulting from substrate-catalyst interactions, which taken together are referred to as the mechanism of the catalytic reaction. Frequently mentioned in textbooks and research papers alike as catalytic cycles, they should be more appropriately referred to as catalytic reaction networks comprising multiple bifurcation points and parallel reaction pathways. Detailed knowledge of the mechanism is a prerequisite for a rational approach in catalyst development, and a great deal of effort goes into their systematic investigation. 

A recent study,209 in which previous results on the complexation of a series of non-centrosymmetrical guests with CDs were re-evaluated, suggested that the two observed relaxation processes could possibly be interpreted as a mechanism involving two parallel reactions inclusion of the guest through either the wide or narrow rim of the cyclodextrin. This mechanism was shown to lead to the same dependence of observed rate constants on concentration of cyclodextrin as the consecutive mechanism. This study showed that even for seemingly simple host systems the mechanistic details for complexation can be quite complex and still controversial. 

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

The examination of these experimental data, expanded details are reported in Chapter V, illustrates the basic parallel-series mechanism for photocatalytic reactions including the possible influence of the distribution of photocatalytic site activity. 

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