Reduction functional model

Collman JP, Fu L, Herrmann PC, Zhang X. 1997. A functional model related to C3ftochrome c oxidase and its electrocatal34ic four-electron reduction of O2. Science 275 949. 

At a molecular scale, a three-function model can be defined with no direct interaction between the so-called reductant and NO. In this case, the apparent contradiction to the global equation (1) can be ruled out, and the F>cNOx reaction by itself occurs owing to the third function of the model (Figure 5.1). 

Figure 5.1. The three-function model for designing DeNOx catalysts in the presence of methane as reductant [12].

The Functional Model. Synthesis of a chemically similar or dissimilar molecule that will mimic the desired function of the enzyme be it dioxygen transport, electron transport, isomerization, or small molecule reduction. 

In closely related experiments it was shown that sp C—H activation takes place reversibly within the coordinahon sphere of the electron-rich Ir(I)-diphosphine complex 58 (Scheme 6.9) to form an alkyl-amino-hydrido derivative 57 reminiscent of the CCM intermediate 24 the solid-state structure of 57 is shown in Figure 6.13 [40]. It appears that C—H activation only takes place after coordination of the amine function to the Ir(I) center (complex 58, NMR characterized). Amine coordination allows to break the chloro bridge of 59 and to augment the electron density of the metal center, thus favoring oxidative addihon of the C—H bond. Most importantly, the microscopic reverse of this C—H activation process (i.e. C—H reductive elimination) models the final step of the CCM cycle (see Scheme 6.1) indeed, the reaction of Scheme 6.10 is cleanly reversible at 373 K. 

A closer look at the functional models developed so far reveals that the aspect of integration plays a more prominent role than the shear miniaturization of the characteristic dimensions involved. This is in contrast to the common misconception that micromechanical fabrication techniques result in a dramatic reduction of the physical size of the devices. Although there exist impressive examples of relatively long separation columns folded on a device of a few cm2 and below, at the present state of development, the outer dimensions are usually dictated by the constraints of interfacing the chip to the outside world (sample, buffer solutions, reagents, etc.). 

The unreacted core shrinking model gives rise to the size reduction function of the following form (13) ... 

A number of studies have been made of the reduction of model enones in buffered aqueous or buffered ethanolic solutions in order to elucidate the sequence of electron transfer, proton transfer, and coupling steps as a function of pH [39-42,91-95]. The experimental methods applied include polarography, CV, LSV, and chronocoulometry. 

A reductant other than hydroxide could in principle have been used so that dioxygen was not produced. This work was performed before the role of HS-HTP had been uncovered, and in any case it would be difficult in model compound work to generate specifically a mixed disulfide. Although it is unlikely that the above scheme is that which occurs in MCR, the fact that in aqueous solution the natural substrate was catalytically converted to methane by a Ni complex represented an excellent example of using small molecules as functional models of enzyme action. 

Thus, great strides have been made in generating structural and crudely functional models for the heme-copper CcO active site. The latter involve either electrocatalytic O2 reductions using heme-copper complexes with superstructured ligands, or 02-reactivity studies aimed at how a proximate copper ion affects heme/02 reactions, or how a heme influences copper/02 reactivity. Such investigations can and will provide fundamental chemical, spectroscopic and mechanistic insights. 

Data reduction for the o = 0 and 02 = 1 state of H2 0 using the generating-function model of the effective Hamiltonian, see [03Mik]. 

Kim (1998b) has given what may seem to be a direct argument for the identity of functional properties with physical properties. Kim presents the functional model of reduction as follows ... 

Ricard, D., B. Andrioletti, B. Boitrel, and M. L Her (1999). Electrocatalytic reduction of dioxygen to water by tren-capped porphyrins, functional models of cytochrome c oxidase. Chem. Commun. 1523-1524. 

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