Electron transfer with self-assembled copper ions at Au-deposited biomimetic films : mechanistic "anomalies" disclosed by temperature- and pressure-assisted fast-scan voltammetry
It has been suggested that electron transfer (ET) processes occurring in complex
environments capable of glass transitions, specifically in biomolecules, under certain
conditions may experience the medium
’
s nonlinear response and nonergodic kinetic
patterns. The interiors of self-assembled organic films (SAMs) deposited on solid
conducting platforms (electrodes) are known to undergo glassy dynamics as well, hence
they may also exhibit the abovementioned
‘
irregularities
’
. We took advantage of Cu
2+
ions as redox-active probes trapped in the Au-deposited
−
COOH-terminated SAMs,
either L-cysteine, or 3-mercaptopropionic acid diluted by the inert 2-mercaptoethanol, to
systematically study the impact of glassy dynamics on ET using the fast-scan voltammetry
technique and its temperature and high-pressure extensions. We found that respective
kinetic data can be rationalized within the extended Marcus theory, taking into account the
frictionally controlled (adiabatic) mechanism for short-range ET, and complications due
to the medium
’
s nonlinear response and broken ergodicity. This combination shows up
in essential deviations from the conventional energy gap (overpotential) dependence and
in essentially nonlinear temperature (Arrhenius) and high-pressure patterns, respectively.
Biomimetic aspects for these systems are also discussed in the context of recently published
results for interfacial ET involving self-assembled blue copper protein (azurin) placed in
contact with a glassy environment