title: pH-tunable equilibria in azocrown ethers with histidine moieties.
abstract: The crown ethers with electro- and photoactive azo moieties containing substituents with mobile protons such as in the -COOH groups of histidine, show unique effect of pH switched on/off presence of the azo form. The differences observed for the electrochemical behavior of azocrown ethers with N-acetylhistidine and imidazole moieties reveal the interference of a chemical reduction pathway in strongly acidified solutions. This chemical reduction process leads to the formation of a hydrazine derivative which can be detected by its further electroreduction on the electrode surface. The involvement of chemical reduction is seen clearly in the presence of mobile protons of the -COOH group and mercury as the electrode substrate. The behaviour of the N-acetylhistidine azomacrocyle is similar to that of compounds known to exist in quinone-hydrazone tautomeric equilibria.
authors.affiliation: Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02093 Warsaw, Poland.
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Jabłonowska
authors.forename: Barbara
authors.initials: B
authors.lastname: Pałys
authors.forename: Ewa
authors.initials: E
authors.lastname: Wagner-Wysiecka
authors.forename: Marzena
authors.initials: M
authors.lastname: Jamrógiewicz
authors.forename: Jan F
authors.initials: JF
authors.lastname: Biernat
authors.forename: Renata
authors.initials: R
authors.lastname: Bilewicz
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry; D043844:Crown Ethers / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D006639:Histidine / Q000031:analogs & derivatives / Q000737:chemistry*; D006834:Hydrazines / Q000032:analysis*; D006835:Hydrazones / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008628:Mercury / Q000737:chemistry; D010084:Oxidation-Reduction; D011522:Protons; D012996:Solutions / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D001391:Azo Compounds; D016227:Benzoquinones; D002264:Carboxylic Acids; D043844:Crown Ethers; D006834:Hydrazines; D006835:Hydrazones; D007093:Imidazoles; D011522:Protons; D012996:Solutions; C029424:hydrazine; C004532:quinone; D006639:Histidine; C029899:imidazole; D008628:Mercury; C023495:N-acetylhistidine