Citation:
Stuart D. Collyer, Frank Davis, Andrew Lucke, Charles J. M. Stirling and Séamus P. J. Higson, The electrochemistry of the ferri/ferrocyanide couple at a calix[4]resorcinarenetetrathiol-modified gold electrode as a study of novel electrode modifying coatings for use within electro-analytical sensors, Journal of Electroanalytical Chemistry, Volume 549, 5 June 2003, Pages 119-127
Abstract:
The electrochemistry of the ferri/ferrocyanide redox couple has been studied at
Au electrodes modified with calix[4]resorcinarenetetrathiol. Cyclic voltammetry
in Fe(CN)63- solutions yields three separate pairs of faradaic peaks. Evidence
is given for these redox couples corresponding to the reduction of Fe(CN)63- and
the subsequent re-oxidation of Fe(CN)64- in three differing steric arrangements.
One pair of peaks suggest that when the Fe(CN)63- ion resides within the calix
[4]resorcinarene bowl, electron transport is facilitated by the calix
[4]resorcinarene acting as a charge transfer mediator; in this arrangement the
activation energy is found to be lowered by ~24kJmol-1. Another pair of peaks is
thought to correspond to the reduction of Fe(CN)63- as it approaches the Au
electrode by packing itself in-between adjacent calix[4]resorcinarene molecules.
The third pair of redox peaks is attributed to the reduction and subsequent re-
oxidation of Fe(CN)63-/Fe(CN)64- when the ion resides above a saturated calix
[4]resorcinarene coating; in this case the activation energy was raised by
~45kJmol-1. FTIR spectroscopy of calix[4]resorcinarene-coated Au electrodes and
calix[4]resorcinarene-coated Au electrodes exposed to Fe(CN)63- lends further
support to this argument, by demonstrating that the Fe(CN)63- ion resides within
at least two and possibly three differing environments. Calix[4]resorcinarene
modified electrodes previously exposed to ferricyanide lose the calix
[4]resorcinarene coating together with a surface layer of gold when subsequently
scanned in a phosphate buffer. It therefore appears that the calix
[4]resorcinarene/Fe(CN)63- association is stronger than the Au binding to the
underlying glass material.