Redox-neutral radical pathway

However, the drawback of this reaction is the need of a stoichiometric PhI(OAc)2 to maintain the catalytic turnover and it needs two-electron oxidation to realize the aliphatic C-H amination. They reported that the amidoximes such as readily available A/ -alkylamidoximes could be used as a precursor of the amidinyl radical to realize this C(sp )-H amination. A redox-neutral radical pathway including a Cu(I)-Cu(II) redox catalytic cycle is proposed for this reaction [86] (Scheme 8.47). 

Fig. 3.5 Two substrate oxidation sites in VP left, Oxidation site for high redox-potential substrates (such as VA, RB5, and lignin) by a LRET pathway (dotted arrow) from a tryptophan residue forming a catalytic neutral radical (W164-) to a heme methyl group via a leucine residue [57-59] right, Oxidation site for Mn2+, at the internal propionate of heme, involving three acidic amino acid residues [10]. Axial view of the heme region (a water molecule, represented as van der Waals spheres, is seen at the top position on the heme iron)...

At the molecular level, the buffering capacity of the cellular solution may block the pollutant in its course. Pollutants that generate acids or bases may be neutralized by acid-base buffers. Excess calcium or other cations may complex fluoride, and redox systems may buffer S02, 03, or PAN, or the free radicals they generate. On another level, enzyme structure determines whether the pollutant will penetrate and react with an active site, and the functioning of an enzyme, apparently through effects on its structure, also modifies its susceptibility to the pollutant (6). Moreover, inhibition of a susceptible enzyme may not affect a pathway the enzyme affected may not be rate-limiting in a particular pathway, and considerably greater inhibition must occur before it is. 

---