Chemistry Reference
In-Depth Information
1
H NMR changes in the chemical shifts of the amide protons of compound
17
in acetone-d
6
(a) alone, (b) in the presence of 2 equiv. (1 equiv. per aza-crown ether) of TBAF,
(c) in the presence of 2 equiv. of KPF
6
, and (d) in the presence of 2 equiv. of KPF
6
and 2 equiv. of
TBAF. Adapted from Gonzalez et al. [36].
FIGURE 8.10
weakens the hydrogen bonding between the fluoride anion and the amide groups in
17
probably due to the ion-pairing interaction K
รพ
-F
.
The condensation reaction of octamethylferrocenyl aldehyde with DAB-based
poly(propyleneimine) dendrimers and further reduction of the imine groups affords
up to the fourth generation of the octamethylferrocenylmethylamine dendrimers
21-24
(Scheme 8.3) [40]. These dendrimers represent another type of receptor
systems capable of electrochemically recognizing anionic guest species. Solution
voltammetric studies are characteristic of reversible oxidation processes with formal
potentials considerably more negative than those corresponding to nonmethylated
analogs as the result of the strong electron donating effect of the eight methyl groups
on the ferrocene rings. The dendrimers exhibit a tendency to adsorb on electrode
surfaces. Pt or GC electrodes modified with these dendritic molecules containing
redox-active octamethylferrocenyl moieties and amine NH-CH
2
hydrogen-bonding
functionalities exhibit a well-defined and persistent electrochemical response that is
sensitive to the presence of H
2
PO
4
anion. A shift of the anodic peak to less positive
potentials of about 195 mV for the fourth generation
24
(Scheme 8.3) in the presence
of [n-Bu
4
N][H
2
PO
4
]2
10
5
M is reported.
The development of surface immobilized conducting polymers bearing function-
alities capable of recognizing and detecting a particular target analyte, constitutes a
very active field of research in continuous growth. At this respect, the anodic
electropolymerization of pyrrole-substituted ferrocenyl derivatives is a well-estab-
lished route to fabricate conducting polymer-coated electrodes [57,75-79] with a high
potential for the electrochemical sensing of analytes. Likewise, in the field of
molecular recognition, designing receptors that can bind and sense anions in water
