ChemComm
Communication
¨
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Fig. 2 Evolution of the anodic peak current measured at +0.47 V when the
potential is cyclized between 0 and +1 V for transforming the hydroxylamine into
the radical nitroxyl or from +0.7 to À0.5 V to reduce the radical nitroxyl to the
hydroxylamine. Inset OFF state: the EPR signal after cycling between 0.7 and
À0.5 V. Inset ON state: the EPR signal after cycling between 0 and 1 V.
21 Synthesis of N-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-4-
aminobenzamide (AbzTEMPO). The synthesis consists of peptide
coupling between 4-aminoTEMPO and 4-aminobenzoic acid
achieved in three steps: protection, coupling and deprotection.
First, 4-aminobenzoic acid is protected by fluorenylmethyloxy-
carbonyl chloride, according to the procedure described previously
by Carpino and co-workers.25 Then the protected acid is coupled
with 4-aminoTEMPO in the presence of dicyclohexylcarbodiimide/
N-hydroxybenzotriazole, and finally, deprotection is carried out
by piperidine to obtain AbzTEMPO (47%). See ESI† for detailed
synthesis and characterization.
22 Characterization of the modified surfaces. XPS experiments were
performed on gold surfaces prepared by physical vapor deposition
of an adhesion layer of chromium on glass covered with a 100 nm
layer of gold. EPR characterizations were carried out on a BRUKER
EMX spectrophotometer operating at room temperature and at a
frequency of 9.524124 GHz with a modulation amplitude of 2.5 G
and 20 mW. Experiments were performed at room temperature
using a modified 0.5 mm diameter gold (99.99%) wire inserted into
a quartz cell. Cyclic voltammetric measurements were performed in
a three-electrode cell. The working electrode consists of a glassy
carbon or gold disk purchased from Bioanalytical Systems (models
MF-2012 and MF-2014, respectively). A platinum wire was used as a
counter electrode and potential values were reported versus an
Ag|AgCl (saturated KCl) reference electrode. A potentiostat/galvano-
stat model VMP3 (from Bio-Logic) monitored using ECLab software
was used for the electrochemical experiments.
in the nitroxyl/hydroxylamine potential window. The decrease
in the peak current after 2 switches corresponds to 20% of the
total activity recorded after the first switch ‘‘on’’.
In the first place, the reversible redox system can serve as a
switching function between the positively charged oxoammonium
cation and stable nitroxyl radical. In the second place, the com-
bined use of the two kinetically slow redox couples >N+QO/>N–OH
and >N–O/>N–OH allows easy access to the stable nitroxyl radical
or neutral hydroxylamine form capable to be maintained for an
extended period even in the absence of applied potential. This
kind of electro-switchable magnetic surface presents interesting
potentialities for storage and memory applications.
Notes and references
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´ ˆ
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P. Dabrowski, P. J. Kowalczyk, K. Gwozdzinski and G. Grabowski,
Appl. Surf. Sci., 2008, 255, 1921.
25 L. Carpino and G. Y. Han, J. Org. Chem., 1972, 37, 3404.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 4555--4557 4557