Biology Reference
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The superstructure acts as
π
-acceptor receptor for complexation
of
-donor substrates, such as dialkoxybenzene, as was found
for molecular square
π
19
in the solution. Binding of analytes
such as
-hydroquinone to the receptor units increases the local
concentration at the electrode surface and allows its electrochemical
sensing by the three-dimensional conductive Au. Therefore, the
Au-nanoparticle/square
p
assembled superstructure acts as a
functional interface to concentrate
19
-donor analytes and enable
their electrochemical sensing. It was found that the electrochemical
response was enhanced upon increasing the number of layers.
Another approach for the electrochemical sensing of substrates
by molecular square sensory layers on the basis of size selectivity
was introduced by Hupp and coworkers [67]. A thin film of neutral
rhenium molecular squares (such as
π
) was prepared on inert
conductive platforms, which was subsequently used as working
electrodes in electrochemical cells. When the film-coated electrodes
were exposed to solutions containing redox-active substances of
various sizes, the electrochemical responses could be observed only
for the species capable of permeating through the film depending on
the cavity size of the metallacyclic supramolecule.
The sensing properties in the presence of volatile organic
compounds (VOCs) of the self-assembled rectangle
3b
in the solid
state were also studied [47]. The emission of thin films containing
the complex were quenched upon exposure to
5b
-toluidine vapor
(which is a known reductant), but the emission was enhanced and
shifted to higher energy when the film of rectangle
p
was exposed
to THF vapor. The THF exposure also increased the luminescence
lifetime from 620 to 950 ns. Both film-based emission study and
crystal structure analysis suggested that rectangle
5b
might behave
as a high internal surface area mesoporous host material. The
guest molecules were taken up into the film voids in the rectangle
aggregate. The selectivity of this film-based mesoporous material
5b
5b
can be assessed by quantitative quartz crystal microgravimetry
(QCM) measurements. The results showed that (a) the binding
affinity increased with the film thickness as expected if the guest
uptake is based on the permeation into the voids rather than simple
physical adsorption, (b) the host
guest ratio exceeded 1:1 with
high concentration of guest implying both intra- and intermolecular
−
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