This paper describes the results of an electrochemical
and spectroscopic (infrared reflection and X-ray
photoelectron spectroscopies) investigation of the modified gold
electrode surfaces prepared from dilute
ethanolic solutions of 4-mercaptopyridine (PySH) and 4,4‘-dipyridyl
disulfide (PySS). Both precursors
have been used extensively as facilitators for the electron transfer of
redox proteins like cytochrome c (cyt
c). During the course of an investigation of the interfacial
architectures formed from the two different
precursors, a previously unreported structural instability in the
adlayers was discovered. This instability
manifests itself as a decrease in the ability of the modified surfaces
to facilitate the electron transfer of
cyt c that correlates with an increase of the immersion time in the
precursor solutions. Results are presented
that delineate the decrease in facilitator performance and probe the
structural changes resulting in the
decrease in performance. Together, the electrochemical and surface
spectroscopic findings reveal that the
modified surfaces spontaneously decompose to yield an adlayer composed
largely of adsorbed atomic and
oligomeric sulfur, an adlayer that we found to be ineffective in the
facilitation of the electron transfer
reaction of cyt c. The implications of these findings on the use
of this type of modifier to studies of electron
transfer reactions of redox proteins and to issues of the general
structural stability of organosulfur-based
monolayers are briefly discussed.
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