アミノ基を末端に有するチオール単分子膜電極を用いたインジゴイオンの酸化還元挙動

抄録

The influences of thiol monolayers having terminal amino groups on the electron transfer rate for indigotetrasulfonate have been examined by cyclic voltammetry and ac impedance spectroscopy. The electron transfer rate for indigotetrasulfonate decrease with increasing pH at a bare Au electrode. The adsorption of indigotetrasulfonate ion onto 4-aminothiophenol monolayer, at low pH values, resulted primarily from an electrostatic attraction between the protonated terminal amino groups and the anions. An increase in solution pH, however, 4-aminothiophenol, cystamine, and 4-mercaptopyridine monolayer-modified electrode showed a increase in electrochemical reversibility with deprotonation of the terminal amino groups. Whereas 11-amino-1-undecanethiol, which is longchain thiol having terminal amino groups impedes the electrode reaction of [Co (phen)₃]³⁺, this monolayer raised the apparent rate constant for indigotetrasulfonate to twice that observed at a bare Au in pH 6. Furthermore, in the presence of ethylenediamine or triethylenetetramine at pH 8, indigotetrasulfonate was obtained the reversible wave using at a bare Au. We propose a chemical interaction between the amine groups of the thiol monolayer and the carbonyl groups of indigotetrasulfonate. We postulate that protons transfer from the reduced indigo ion to the unprotonated terminal amino groups of thiols.