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L. Shen et al. / Electrochimica Acta 329 (2020) 135142
3) The resulting mixture was filtered to remove NaCl and the sol-
vent ethanol was evaporated under vacuum at 60 ꢁC.
4) The solid product obtained above was dissolved in 100 mL
acetone under stirring, followed by filtration through an organic
filter to remove residual NaCl precipitate. After that, the solvent
acetone was removed under vacuum at 60 ꢁC.
designability and so on. Therefore, they are ideal media for elec-
trosynthesis [23e25]. The use of RTIL as medium for the synthesis
of conducting polymers could result in conductive materials with
both ionic and electronic properties, which is of great significance
for the development of functionalized electrode materials and
electrochemical devices [26e30]. In recent years, RTILs containing
active pharmaceutical ingredients (API-ILs) have aroused interests
in pharmaceuticals and biomedicine areas due to their efficacy in
improving drug solubility and bioavailability [31e37]. There have
been many reports about API-ILs-based drug delivery systems
[38e40]. Yasushi Miwa et al. transformed a poorly water-soluble
drug ꢀ etodolac (a drug for the treatment of arthritis) into a salt
in the form of RTIL, which significantly improved its hydropho-
bicity, hydrophilicity and skin permeability, and therefore
improved the efficiency of transdermal drug delivery [41].
Combining API-ILs with conducting polymers could develop new
strategies for the construction of conducting polymer-based elec-
trochemically controlled drug release systems. Stephanie Car-
quigny et al. used API-ILs as supporting electrolyte to synthesize
conducting polypyrrole films and studied the potential-controlled
release kinetics of active drug anions as dopants. They found that
the drug release rate and the amount released could be controlled
by varying the applied potentials [5]. However, there are few re-
ports in this field. In order to simplify the construction of drug
delivery system, we develop, in the present work, a novel func-
tionalized organic salt ꢀ anilinium saccharinate salt ([HANI][Sac]).
Its cation is protonated aniline, which can act as monomer for the
eletrosynthesis of PANI; its anion is active pharmaceutical ingre-
dient. Using the functionalized organic salt as supporting electro-
lyte, active drug anion ([Sac]-) doped PANI (PANI-[Sac]) was
synthesized by simple electrochemical method. The present strat-
egy can ensure that the aniline electropolymerization goes effec-
tively without an exogenous proton source and that the drug anion
is the only doping anion. The resulting PANI has a hierarchical
porous structure with the doping degree of 33.5% and the
maximum amount of released drug being 3.6 mmol gꢀ1 at ꢀ1.5 V
(vs. SCE).
5) The resulting product was placed in a vacuum oven at 70 ꢁC for
48 h, getting the pure [HANI][Sac].
The characterization of [HANI][Sac] was made using NMR, ESI/
MS and TG/DSC techniques. The 1H NMR and 13C NMR spectra of
[HANI][Sac] (DMSO‑d6 as solvent) were recorded on a Bruker
Avance 300 MHz NMR spectrometer. The mass spectrum of [HANI]
[Sac] (10 mg mLꢀ1 in ethanol) was recorded on an Agilent 6510 Q-
TOF mass spectrometer (ESI source). The thermogravimetric and
differential scanning calorimetry (TG-DSC) analyses were per-
formed on a PerkinElmer STA 8000 thermal analyzer in a temper-
ature range of 30e200 ꢁC (N2 atmosphere) with a heating rate of
10 ꢁC minꢀ1
.
2.3. Electrosynthesis of PANI
At ambient temperature (~25 ꢁC), 4.0 mL of 0.1 M [HANI][Sac] in
acetonitrile was used as a medium (the conductivity is ca.
3.3 ꢂ 10ꢀ4 S cmꢀ1) for the electrosynthesis of PANI. Prior to the
electrosynthesis, the medium was purged with high purity nitro-
gen for 20 min. During the electrosynthesis the nitrogen atmo-
sphere was maintained.
The electrochemical polymerization was performed on
a
CHI660E electrochemical workstation. The three-electrode system
was composed of a working electrode (GC disk electrode, 3 mm in
diameter), a Pt wire counter electrode, and a saturated calomel
electrode (SCE) as reference (all the potentials given in this paper
were vs. SCE). Prior to use, the GC disk electrode was polished to a
mirrorlike surface in the following steps: firstly, polished with
0.5 mm and 0.05 mm Al2O3, respectively, then washed with ultrapure
water and ethanol, and finally sonicated in ultrapure water for
5 min. The electrochemical polymerization was carried out using
cyclic voltammetry. The setting of the parameters for the electro-
chemical polymerization was described in the figure captions. After
the electropolymerization, the obtained PANI/GC electrode was
rinsed with ultrapure water and dried for subsequent use.
2. Experimental section
2.1. Materials
Aniline (ANI, S99.5%), absolute ethyl alcohol, hydrochloric acid
(36%), sulfuric acid (H2SO4, 98%) were purchased from Sinopharm
Chemical Reagent Co., Ltd., China. Acetone was purchased from
Laiyang Kangde Chemical Co., Ltd., China. Acetonitrile was pur-
chased from Yuwang Industrial Co., Ltd., China. Sodium saccha-
rinate (Na [Sac], 99%) and DMSO‑d6 were purchased from Sigma-
Aldrich. All chemical reagents were of analytical grade. Ultrapure
2.4. Characterization of PANI
The PANI for FTIR and SEM characterizations was electro-
polymerized in acetonitrile containing 0.1 M [HANI][Sac] according
to the procedure described in section 2.3. To facilitate the charac-
terization, a detachable GC electrode (3 mm in diameter) was used
as working electrode. After the electropolymerization, the potential
was set at 0.6 V (vs. SCE) for 10 s. The GC electrode with PANI was
rinsed with ultrapure water, and then dried for subsequent char-
acterization. The morphology of PANI was examined using cold
field emission scanning electron microscopy (FESEM, ZEISS Gem-
iniSEM 300, Germany). The FTIR spectrum of the PANI was recorded
on an FTIR spectrometer (Thermo scientific Nexus 670, America) in
an ATR mode. The doping degree of saccharinate anion ([Sac]-) was
characterized by the EDS attachment of a cold field emission
scanning electron microscopy (FESEM, ZEISS GeminiSEM 300,
Germany).
water (18.25 МU$cm) was used throughout the experiments.
2.2. Preparation and characterization of anilinium saccharinate salt
The anilinium saccharinate salt ([HANI][Sac]) was prepared by
ion exchange between anilinium chloride ([HANI]Cl) and sodium
saccharinate (Na [Sac]). The brief steps are as follows:
1) A 27.9 g of aniline (0.3 mol) and an equivalent mole of hydro-
chloric acid was mixed in a single-necked flask and the mixture
was stirred in ice bath for 3 h, followed by drying in a vacuum
oven for 24 h, getting a solid [HANI]Cl.
The PANI for electrochemical characterization was obtained in
the same way as described above. Here, the polymerization charge
was controlled for comparison, and the electropolymerization was
stopped at a potential of ꢀ0.2 V (vs. SCE) for 60 min. The electro-
chemical characterization of PANI was carried out by cyclic
2) The dried Na [Sac] (12.31 g, 60 mmol) (120 ꢁC, 6 h) was mixed
with [HANI]Cl (7.78 g, 60 mmol) in 100 mL absolute ethanol as
solvent under stirring overnight.