Quinonedi-imine

A special kind of condensation reaction occurs as a side reaction during the reduction of o-nitroaniline [120,137] A phenazine derivative is formed. In the reaction (Chapter 18), a double Michael addition of o-phenylenediamine to the intermediate o-quinonedi-imine takes place other nucleophiles might under suitable conditions attack the diimine. 

CA[Mn] efficiently catalyzed the oxidation of o-dianisidine to the red quinonedi-imine with hydrogen peroxide (Scheme 2). This o-dianisidine oxidation is a common assay for peroxidase [47-50] or for peroxidase-based detection of hydrogen peroxide [51]. As control reactions, native zinc carbonic anhydrase showed <1% of the activity of CA[Mn], while the same concentrations of manganese(ll) chloride and bicarbonate alone showed only 5% of the activity of CA[Mn]. Unlike other peroxidases [47-50], the CA[Mn]-catalyzed oxidation of o-dianisidine required bicarbonate and showed only 1.5% of the activity in the absence of bicarbonate. 

A typical photometric reaction is, for example, the interaction between hydrogen peroxide and 2-phe-nylenediamine, leading to the colored quinonedi-imine with an absorption maximum at 492 nm. This reaction is catalyzed by the above-mentioned peroxidase enzyme and, hence, the absorbance is proportional to the concentration of the unbound enzyme steroid complex in the equilibrium mixture. 

The kinetics of redox reactions of oxidized p-phenylenediamine derivatives (ppd) have been investigated. The photolysis of p-azidoaniline in water rapidly yields quinonedi-imine (qd) and the reaction... 

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