Nj. Simmons et al., Synthesis and characterization of a catechol-terminated alkanethiolate monolayer adsorbed on gold, J ELEC CHEM, 482(2), 2000, pp. 178-187
Structural, redox, and metal ion binding characterizations of the monolayer
formed by the chemisorption of 3,4-dihydroxyphenethyl mercaptan (DHPM) on
gold are described. This system was explored as a model for investigations
of surface-immobilized molecules that contain redox-transformable coordinat
ion sites for binding metal ions from solution. The characterizations were
carried out using infrared reflection spectroscopy, X-ray photoelectron spe
ctroscopy, cyclic voltammetry, and long optical pathlength thin-layer spect
roscopy. The XPS data show that this monolayer adsorbs as a thiolate, and t
he IRS results indicate that the average orientation of the aromatic ring p
lane is close to the surface normal. Cyclic voltammetry reveals that the pe
ndant catechol/quinone undergoes the expected two-electron, two-proton redo
x transformation; however, the oxidized form of the couple is unstable, par
ticularly in alkaline aqueous solutions. A determination of Cu(II) binding
ability to the surface-immobilized catechol moieties, using a long optical
pathlength thin-layer cell to follow the depletion of Cu(II) from solution,
indicated that the complexation of the metal was not substantially differe
nt from that for the solution form of catechol. The instability of the oxid
ized form of the ligand, nevertheless, precluded an assessment of its metal
ion binding ability. An approach using these data for estimating the condi
tional formation constant for the surface complexation reaction is also dev
eloped. (C) 2000 Elsevier Science S.A. All rights reserved.