The crown ethers with electro- and photoactive azo moieties containing -OH, or COOH groups show unique effect of pH switched on/off presence of the azo form. It is well known that electrode processes of azocompounds are pH dependent but we show here that they are also strongly influenced by substituents containing mobile protons such as in -COOH groups. Azocrown ether with N-acetyl-histidine moiety in the molecule gave different Raman spectra compared to those of the imidazole azocrown ether, however, only in acidified solutions. . In alkaline medium the spectra were similar.

The differences in the electrochemical reduction of the imidazole and histidine derivatives in strongly acidified solutions reflect the interference of chemical reduction. It is catalyzed by mobile protons of the -COOH group present in the histidine derivative, leading further to the formation of the hydrazine form. Thus, for the N-acetylhistidine azomacrocyle similar behaviour is revealed to that of azophenol compounds which are known to exist in quinone-hydrazone tautomeric equilibria.

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