Lithium Ion Recognition with Nanofluidic Diodes through Host-Guest Complexation in Confined Geometries

Article abstract of DOI:10.1021/acs.analchem.8b00902

The lithium ion recognition is receiving significant attention because of its application in pharmaceuticals, lubricants and, especially, in energy technology. We present a nanofluidic device for specific lithium ion recognition via host-guest complexatio

Full text of DOI:10.1021/acs.analchem.8b00902

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Article
Lithium ion recognition with nanofluidic diodes through
host-guest complexation in confined geometries
Mubarak Ali, Ishtiaq Ahmed, Patricio Ramirez, Saima Nasir,
Salvador Mafe, Christof M Niemeyer, and Wolfgang Ensinger
Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b00902 • Publication Date (Web): 07 May 2018
Downloaded from http://pubs.acs.org on May 7, 2018
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Lithium ion recognition with nanofluidic diodes through
host-guest complexation in confined geometries
a,b
c
d
a
e
Mubarak Ali, * Ishtiaq Ahmed, Patricio Ramirez, Saima Nasir, Salvador Mafe,
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Christof M. Niemeyer, and Wolfgang Ensinger
a
Technische Universität Darmstadt, Fachbereich Materialꢀ u. Geowissenschaften, Fachgebiet
Materialanalytik, AlarichꢀWeissꢀStr. 2, Dꢀ64287 Darmstadt, Germany
b
GSI Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, Dꢀ64291 Darmstadt, Germany
c
Karlsruhe Institute of Technology (KIT), Institute for Biological Interfaces (IBGꢀ1), Hermannꢀvonꢀ
HelmholtzꢀPlatz, Dꢀ76344 EggensteinꢀLeopoldshafen, Germany
d
Departament de Física Aplicada, Universitat Politécnica de València, Eꢀ46022 València, Spain
e
Departament de Física de la Tierra i Termodinàmica, Universitat de València, Eꢀ46100 Burjassot,
Spain.
*
Corresponding author:
Eꢀmail address: M.Ali@gsi.de
Abstract
The lithium ion recognition is receiving significant attention because of its
application in pharmaceuticals, lubricants, and, especially, in energy technology. We
present a nanofluidic device for specific lithium ion recognition via host–guest
complexation in a confined environment. A lithiumꢀselective receptor molecule, the
2
aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 (BC12C4–NH ) is designed and functionalized on
single conical nanopores in polyethylene terephthalate (PET) membranes. The native
carboxylic acid groups on the pore walls are covalently linked with the crown ether
moieties and the process is monitored from the changes in the current–voltage (I–V)
curves. The B12ꢀcrownꢀ4 moieties are known to specifically bind with lithium ions
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and when the modified pore is exposed to different alkali metal chloride solutions
separately, significant changes in the ion current and rectification are only observed
for lithium chloride. This fact suggests the generation of positively charged B12C4–
+
Li complexes on the pore surface. Furthermore, the nanofluidic diode is able to
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recognize the lithium ion even in the presence of high concentrations of potassium
ions in the external electrolyte solution. Thus, this nanodevice suggests a strategy to
miniaturize nanofluidic porous systems for efficient recognition, extraction and
separation of lithium from raw materials.
Keywords: synthetic nanopores; trackꢀetching; chemical functionalization; host–guest
interactions; crown ethers; electric current rectification.
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1
. Introduction
Ion channel proteins control the trafficking of ions and molecules across the cell
membrane and regulate a variety of biological functions including signal transmission
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ꢀ4
and muscle contraction. The channels have the ability to discriminate between very
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similar ions and exhibit also unique characteristics such as gating and ion current
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,2,5ꢀ8
rectification.
In addition to ion selectivity, protein channels embedded in the
membrane lipid bilayer allow for a variety of applications in nano and biotechnology
9ꢀ11
such as sensing and manipulation of single molecules.
The unique functionality and ionic selectivity of ion channels is partly due to the
asymmetric distribution of amino acid residues. Inspired from nature, artificial
analogues of biological ion channels with similar functionalities have been prepared.
Trackꢀetched conical nanopores have received great interest because of their
mechanical stability, control over pore dimensions (size and geometry), and surface
12ꢀ14
functionalization.
In the particular case of polyethylene terephthalate (PET) membranes, the
carboxylic acids groups generated on the pore surface can be easily functionalized
with different molecules, leading to the modulation of the ionic transport and
15ꢀ23
rectification characteristics.
Moreover, the surface charge regulated phenomena
can be implemented in miniaturized sensing devices by decorating the pore surface
24ꢀ33
30,33ꢀ39
with recognition elements for the detection of biomolecules,
anions
Among the various metal cations, alkali metal ions are involved
in a variety of essential biological processes. Jiang and coꢀworkers have recognized
and
16,40ꢀ47
metal cations.
+
47
potassium cation (K ) with DNAꢀmodified nanopores.
The crown ether
functionalized nanopores have the ability to bind specifically to potassium and sodium
+
43,44
cations (Na ), leading to significant changes in the electronic readout of the pore.
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+
We have recently demonstrated the detection of cesium cation (Cs ) by using
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calixcrown ether functionalized nanopores. However, the design and development of
+
a nanofluidic device which specifically recognize lithium cation (Li ) has not been
explored.
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Lithium is the lightest and less abundant alkali metal. It is the 25th most abundant
element in the Earth's crust. Recently, much attention has been paid towards the
recognition and extraction of lithium because of its extensive use in pharmaceuticals,
48,49
heatꢀresistant ceramics, lubricants, energy technology, and nuclear power plants.
Regarding the biomedical application, lithium compounds are successfully used for
the treatment of bipolar disorder and may reduce the risk of suicide attempt in
50
patients. On the other hand, excessive ingestion of lithium can adversely affect the
5
1
kidneys and nervous system. Because of the high use of rechargeable lithium ion
batteries, especially in portable biomedical devices and mobile phones, the leakage of
lithium to environment and its adverse effect cannot be neglected. Hence, techniques
52ꢀ55
and methods are being developed for lithium recognition.
However, the
coexistence of lithium with other alkali cations in liquid solutions makes it difficult to
selectively recognize it.
We design and miniaturize a functional nanofluidic device exhibiting selectivity to
lithium ion in the presence of other alkali cations. To this end, single conical
nanopores in polymers membranes are fabricated and chemically modified with
lithiumꢀselective receptor moieties, the aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 (BC12C4–
2
NH ). The modified pore is evaluated with different alkali metal chloride solutions
and exhibits current rectification only for the case of the lithium chloride solution.
+
Because B12C4 moieties on the pore surface generate B12C4–Li complexes, the
pore surface charge changes from neutral to positive, becoming anion selective as
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revealed from the inversion observed in the ion current rectification. The experimental
results show that the nanofluidic device can recognise lithium ion at lower
concentrations, even in the presence of other metal cations in the electrolyte solution.
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2. Materials and methods
2.1 Materials
Polyethylene terephthalate (PET, Hostaphan RN 12, Hoechst, 12 µm thick) foils,
Nꢀ(3ꢀdimethylaminopropyl)ꢀN'ꢀethylcarbodiimide·hydrochloride
pentafluorophenol (PFP), dopamine hydrochloride (DA), triethylamine, diꢀtertꢀbutyl
dicarbonate (Boc )O), triethylene glycol, pꢀtoluenesulfonyl chloride, potassium tꢀ
(EDC·HCl),
2
butoxide (tꢀBuOK), potassium carbonate (K
chloride (LiCl), sodium chloride, (NaCl), potassium chloride (KCl), rubidium chloride
RbCl) and cesium chloride (CsCl) were used in this study. All the chemical and
2 3
CO ), trifluoroacetic acid (TFA), lithium
(
solvent were purchased from SigmaꢀAldrich, Taufkirchen, Germany, and used
without further purification.
1
13
3
H and C NMR spectra were recorded at 500 and 125 MHz in CDCl ,
respectively. Highꢀresolution mass spectra were measured using a Finnigan MAT90
mass spectrometer. Analytical TLC (silica gel, 60Fꢀ54, Merck) and spots were
visualized under UV light and/or phosphomolybdic acidꢀethanol. Flash column
chromatography was performed with silica gel 60 (70ꢀ230 mesh, Merck) and basic
aluminum oxide (activated, basic, ~150 mesh, 58 Å, Aldrich).
2.2 Fabrication of single asymmetric nanopores
Single conical nanopores in PET membranes were fabricated through asymmetric
15
chemical etching of latent ion tracks. For this purpose, PET foils were first irradiated
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with single swift heavy ions (Au) of kinetic energy 11.4 MeV/nucleon at the linear
accelerator UNILAC (GSI Helmholtz Centre for Heavy Ion Research, Darmstadt,
Germany). Then, the latent ion tracks in polymer membranes were sensitized with soft
UV light. The chemical trackꢀetching process was performed in a customꢀmade
conductivity cell having three chambers. The chemical asymmetric trackꢀetching
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process can be found elsewhere . Briefly, an etching solution (9 M NaOH) was filled
in the middle compartment and the stopping solution (1 M KCl + 1 M HCOOH) was
filled on the side chambers. The etching process was carried out at room temperature
and monitored by applying a potential of –1 V across the membrane. After the
breakthrough, the etching process was stopped when the current reached a certain
defined value. Then, the etched membrane was washed with stopping solution,
followed by deionized water. The etched sample was dipped in deionized water
overnight in order to remove the residual salts. The chemical etching process resulted
in the generation of carboxylic groups (COOH) on the inner pore walls due to the
hydrolysis of ester bonds in the backꢀbone of polymer chains.
2
.3 Synthesis of aminoethyl-benzo-12-crown-4 (B12C4–NH
Figure 1 depicts the preparation of the different crown ether derivatives involved in
the synthesis of aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 (4) following previously reported
2
)
56ꢀ58
reaction procedures with slight modifications.
Details of the synthesis are given in
the Electronic Supplementary Information (ESI) file.
2
We have synthesised aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 (B12C4–NH ) to modulate the
nanopore surface chemistry and transport properties in response to lithium cation. The
reaction scheme for the synthesis of B12C4–NH is shown in Figure 1. The first step
2
5
6
was the protection of amine group of dopamine hydrochloride (DA). For this
purpose, Nꢀtertꢀbutoxycarbonylꢀ3,4ꢀdihydroxyphenylethylamine (1) was prepared by
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treating commercially available DA with diꢀtertꢀbutyl dicarbonate in the presence of
triethylamine. The second step was the synthesis of triethylene glycol ditosylate (2) by
reacting triethylene glycol and pꢀtoluenesulfonyl chloride in sodium hydroxide and
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THF mixture. Protected crown ether 3 was obtained by refluxing compound (1) and
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compound (2) with potassium carbonate in dried acetonitrile. Finally, the
deprotection of Nꢀboc group was carried out using trifluoroacetice acid to afford
2
B12C4–NH (4). The chemical structures of synthetic crown ether derivatives were
characterized through 1H NMR, 13C NMR and HRMSꢀFAB techniques.
2.4 Chemical functionalization of nanopore surface
The carboxylic acid groups on the pore surface were first activated by exposing the
trackꢀetched singleꢀpore membrane to an ethanol solution containing EDC (100 mM)
and PFP (200 mM) at room temperature for 1 h. After washing with ethanol several
2
times, the activated pore was treated with B12C4–NH (35 mM) solution for 24 h.
During this reaction period, amineꢀreactive PFPꢀesters were covalently coupled with
the amine group of the B12C4–NH . Subsequently, the modified pore was washed
2
thoroughly with ethanol followed by careful rinsing with deionized water.
2.5 Currentꢀvoltage measurements
The unmodified and modified pores were characterized by measuring the current–
voltage (I–V) curves before and after functionalization. The electrolyte solutions were
prepared in 10 mM trisꢀbuffer. The measurement of I–V curve was performed using a
picoammeter/voltage source (Keithley 6487, Keithley Instruments, Cleveland, Ohio,
USA) and the LabVIEW 6.1 software (National Instruments). For this purpose, the
singleꢀpore asꢀprepared membrane was fixed between the two compartments of the
conductivity cell. An aqueous electrolyte was filled in both halves of the cell. The
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electrodes consisting of a Ag wire coated with AgCl were inserted into each halfꢀcell
solution to establish a transmembrane potential difference (voltage V) and the ionic
current I through the pore was then measured. In the present case, the ground was
placed on the big opening side and the electrodes facing the tip side of the conical
nanopore. Then a scanning triangle voltage signal was applied from −1 to +1 V across
the membrane to record the I–V curves.
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2.6
Modeling
The theoretical I – V curves were calculated using the Poisson and Nernstꢀ
Planck (PNP) equations
2
F
∇
φ
= −
z c
,
(1)
(2)
∑
i i
ε
i
ꢉ
ꢁ
∙ ꢀꢂ =ꢃ−∇ ∙ ꢄꢅ ꢇ∇ꢈ + ꢌ ꢈ ∇∅ꢍꢎꢃ
ꢆ ꢆꢃ ꢆ ꢆ
ꢊꢋ
∇
where R is the gas constant, F is the Faraday constant, and T is the absolute
temperature. In these equations,
φ is the electric potential and ε is the electrical
r
J
permittivity of the solution.
, D , z , c , and are, respectively, the flux, the diffusion
i
i
i
i
coefficient, the charge number, and the local concentration of the ionic species i. The
boundary condition for the electric potential is the Gauss law
1
∂
θ
φ
σ
ε
=
,
(3)
r ∂
pore
surface
where r and
θ
are spherical coordinates with the origin in the cone apex and
σ
is the
surface concentration of fixed charges. The boundary conditions for the ionic
concentrations are based on the Donnan equilibrium conditions for the external and
pore solution concentrations. Solving Equations (1)ꢀ(2) at a given applied voltage V,
allows for the calculation of the ionic fluxes, the axial profiles of electric potential and
ionic concentrations, and the electric current
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I = ziF
π
a Ji
(4)
∑
i
through a pore section of radius a. Additional equations for the boundary conditions
and numerical details can be found in References 59ꢀ62.
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. Results and discussion
Figure 2A shows the chemical modification of the COOH groups with amineꢀ
2
terminated benzoꢀ12ꢀcrownꢀ4 (B12C4–NH ) molecules through carbodiimide
coupling chemistry. The crown ethers are known to selectively bind a metal cation,
depending on their cavity size (Figure 2B). The lithium cation is captured by the 12ꢀ
+
crownꢀ4 moieties because the metal cation (Li ) diameter (140 pm) is comparable to
the cavity size (120 to 150 pm) of the macrocycle.
The nanopores are characterized by measuring the asymmetric I–V curves which
are sensitive to the pore surface charges. Indeed, these charges interact with the ions
passing through the nanopore and then oppositely charged pores show different
rectifications. Thus, the pore functionalization can be confirmed by measuring the I–V
characteristics before and after modification of the nanopore.
Figures 3A (experiment) and 3B (model) illustrate the characterization of the
unmodified (asꢀprepared) nanopore in symmetric 100 mM KCl solutions. Assuming
infinite dilution values for the diffusion coefficients of the ionic species and a conical
geometry for the pore, the only unknown model parameters are the pore tip (d) and
base (D) diameters, and the surface concentration of fixed charges,
diameter determined from the etching time is D = 400 nm. At pH = 3.5, the carboxylic
acid groups attached on the pore walls are protonated ( = 0), leading to a quasiꢀlinear
σ. The pore base
σ
I–V curve. Fitting the theoretical model to the experimental data gives then the pore
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tip diameter d = 10 nm. At close to neutral pH values, the pore shows rectification
because of the asymmetric distribution of the fixed charges and the electric potential
along the axis. High currents are obtained at positive voltages and low currents at
59ꢀ64
negative voltages, as shown in Figure 3A.
This fact leads to the preferential
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transport of cations from the tip to the base opening of the conical nanopore. The only
unknown model parameter
σ
is then calculated by fitting the theoretical model to the
2
experimental data of Figure 3A at pH = 6.5, giving
σ
= −0.25 e/nm , where e is the
elementary charge. In this estimation, we assume that the COO¯ groups are
homogeneously distributed on the pore walls.
Figure 3C shows the I–V curves of the asꢀprepared single conical nanopore
measured in 100 mM alkali salt solutions. On exposure to various alkali cations, the
unmodified nanopore exhibits similar current rectifications and the currents measured
for different cations can be described using the values of the diffusion coefficients of
the different cations at infinite dilution. Figure 3D shows the theoretical results
obtained with the same model parameters as in Figure 3B. The good agreement
between theory and experiment supports the assumptions concerning the conical pore
geometry and the fixed charge distribution.
We functionalize the carboxylic acid groups on the pore surface with crown ether
(host) moieties to selectively capture the lithium cation (guest). For this purpose
2
B12C4–NH is immobilized on the pore surface as described in Figure 2A. The
modified pore I–V characteristics of Figure 3E show that derivatization of carboxylic
acid groups with uncharged B12C4 moieties results in the loss of the pore negative
charges. This fact leads to a significant decrease of the pore rectification for the case
+
+
+
+
of Na , K , Rb and Cs , suggesting no complexation of these cations with the B12C4
moieties. In this case, the metal cation diameters do not match the cavity size of the
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immobilized crown ether groups. On the contrary, Figure 3E shows that upon
exposure to LiCl solution, the modified pore exhibits a reversal in the current
rectification which is attributed to the switching of the pore charge from negative to
+
positive due the specific binding of Li cation with the crown ether moieties. The
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rectification ratios for the alkali cations on the left ordinate axis are obtained by
dividing the average value of the negative current to the positive currents (red
columns). In the case of the right ordinate axis, we consider the ratio of the positive to
the negative currents (blue columns), as shown in the inset of Figure 3E. The clear
difference observed between the rectification ratio for lithium and the other cations
+
further confirm the formation of positively charged B12C4–Li complexes on the pore
+
surface for the electrolyte solution having Li cations.
+
Because of the positively charged B12C4–Li chelates, the nanopore preferentially
–
+
attracts the anions (Cl ) and excludes the cations (Li ), thus reversing the current
17
rectifcation of I–V curve (Figure 3E). Note the different rectification ratios shown in
the inset of Figure 3E. Figure 3F shows the theoretical curves obtained using the
model parameters given in the figure. In order to reproduce the measured currents, the
pore diameters must be decreased by 5 nm because of the functionalization of the
+
+
functional crown ether moieties on the surface. The curves corresponding to Na , K ,
+
+
2
+
Rb and Cs are calculated by assuming
σ = −0.02 e/nm , while the curve for Li is
2
reproduced using
σ
= +0.22 e/nm in the model. The fact that the pore surface charge
+
+
+
+
remains slightly negative for Na , K , Rb and Cs after chemical modification. This
suggests that the immobilization of crown ether moieties of Figure 2A is not 100%
efficient, leaving unmodified COO¯ groups on the pore surface. These carboxylate
groups are responsible for the partial negative pore surface change after chemical
reaction as evidenced from the I–V behaviour of the pore shown in Figure 3E.
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Figures 4A and 4B show the lithiumꢀcrown ether complexation and the I–V
characteristics of the modifed pore at different lithium concentrations. The
background electrolyte (10 mM tris buffer, pH 6.5) gives an essentially
nonconducting pore with very low currents (~ 4 pA).
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The experiments in Figure 4B show that when the modified pore is exposed to
+
solutions of 1 µM and 10 µM Li concentrations, the modified pore starts
rectification with an increase of ion current at −1 V from 4 pA to 20 pA and 60
+
pA, respectively, because of the formation of positively charged B12C4–Li
+
complex (Figure 4A) on the pore surface. Further increasing of the Li ion
concentration from 10 µM to 100 mM, gives gradual increases of the rectified
current from 60 pA to 700 pA measured at −1 V. On te contrary, only small
+
changes in the current at +1 V occur when exposing the pore to different Li ion
+
+
concentrations. These facts clearly show that B12C4–Li complexes allow Li
sensing over a wide range of concentrations. The theoretical calculations of Figure
+
4
B reproduce well the experimental data at concentrations of Li higher than that
+
of the tris buffer (10 mM), suggesting that for Li concentrations lower than 10
mM most of the current is transported by the buffer electrolyte.
To study the reproducibility of the data, we have modified a second conical
nanopore under the same set of experimental conditions. In this case, the
2
characteristic pore parameters are D = 500 nm, d = 22 nm, and
σ
= −0.5e/nm . The
experiments of Figure 5A show the small changes obtained in the I–V curves for
solutions of NaCl, KCl, RbCl and CsCl at 100 mM after pore modification. This is
not the case of the LiCl 100 mM solution, where a significant current rectification
+
is obtained again because of the positively charged B12C4–Li complex. Figure
5
B shows the theoretical curves obtained using the model parameters given in the
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figure, revealing that the immobilization of crown ether groups on COO¯ is now
much more efficient than in the case of the sample of Figures 3 and 4.
We consider now the case of electrolyte mixtures in Figure 5C. By increasing
the concentration of LiCl from zero to 20 mM in the mixture at constant total
electrolyte concentration (100 mM), the nanopore starts rectifying the current,
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+
suggesting the binding of the Li ion with the crown ether moieties even in the
+
presence of a high K concentration (80 mM). Increasing further the fraction of
lithium over potassium gives relatively low rectification changes indicating the
+
saturation of positive charges (B12C4–Li ) at 40 mM LiCl approximately.
We have also examined the reversibility of lithium ion recognition. Potassium ion
does not fit to the cavity size of B12C4 moieties and can then be used as a control
electrolyte to check this reversibility. To this end, the modified pore is exposed
alternatively to KCl and LiCl solutions and the ion currents are measured at −1 V.
+
Figure 5D shows the results obtained over different cycles of reversible Li binding
and unbinding. The reversible changes observed suggest that it is the surface charge
density that dictates the pore properties from a nonꢀconducting state with B12C4
+
moieties to a conducting state with B12C4–Li chelates.
Finally, we have considered the modified pore under acidic conditions (pH 3.5).
The I–V curves of Figure 6 were obtained using a third functionalized pore sample.
The modified pore shows anion selectivity to all alkali metal cation solutions,
suggesting the loss of specific binding to lithium due to the protonation of crown ether
65
moieties.
4. Conclusions
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In summary, we have demonstrated the miniaturization of a nanofluidic device
based on a single conical nanopore for lithium ion specific recognition. On exposure
to LiCl solutions, hostꢀguest ion recognition occurs in the confined geometry, leading
+
to the switching of the nanopore charges from neutral to positive because of the Li –
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crown ether complexes formed on the surface. This process leads to significant
changes in the pore rectification characteristics, which depend on the asymmetrical
distribution of positively charged groups along the pore axis. On the contrary, other
alkali metal cations do not give significant changes because they are unable to bind
with the immobilized crown ether groups. The experimental data are well described
by a theoretical model based on the Poisson and NernstꢀPlanck equations and show
that the electrical characteristics of the singleꢀpore membrane change significantly
over a wide range of lithium ion concentrations in the solution. Moreover, the
nanodevice can detect lithium ions even in the presence of other metal cations in
mixtures of electrolyte solutions. In summary, we believe that this study can
contribute significantly to the design and development of nanostructured materials for
the recognition, separation, and extraction of lithium ions.
Supporting Information
The Supporting Information is available free of charge on the ACS Publications
website at DOI:
Supporting information contains scheme and detailed synthesis of aminoethylꢀbenzoꢀ
2
12ꢀcrownꢀ4 (B12C4–NH ).
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Acknowledgements
M.A., S.N. and W.E. acknowledge the funding from the Hessen State Ministry of
Higher Education, Research and the Arts, Germany, under the LOEWE project
iNAPO. P.R. and S.M. acknowledge financial support by the Spanish Ministry of
Economic Affairs and Competitiveness (MAT2015ꢀ65011ꢀP), and FEDER. I.A. and
C.M.N. acknowledge financial support through the Helmholtz programme
BioInterfaces in Technology and Medicine. The authors are thankful to Prof. Christina
Trautmann from GSI (Department of Material Research) for support with the heavy
ion irradiation experiments.
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(40) Ali, M.; Ahmed, I.; Ramirez, P.; Nasir, S.; Niemeyer, C. M.; Mafe, S.;
Ensinger, W. LabelꢀFree Pyrophosphate Recognition with Functionalized Asymmetric
Nanopores. Small 2016, 12, 2014ꢀ2021.
(41) Ali, M.; Nasir, S.; Nguyen, Q. H.; Sahoo, J. K.; Tahir, M. N.; Tremel,
W.; Ensinger, W. Metal Ion Affinityꢀbased Biomolecular Recognition and
Conjugation inside Synthetic Polymer Nanopores Modified with IronꢀTerpyridine
Complexes. J. Am. Chem. Soc. 2011, 133, 17307ꢀ17314.
(42) Han, C.; Su, H.; Sun, Z.; Wen, L.; Tian, D.; Xu, K.; Hu, J.; Wang, A.;
Li, H.; Jiang, L. Biomimetic Ion Nanochannels as a Highly Selective Sequential
Sensor for Zinc Ions Followed by Phosphate Anions. Chem. Eur. J. 2013, 19, 9388ꢀ
9395.
(43) Liu, Q.; Xiao, K.; Wen, L.; Lu, H.; Liu, Y.; Kong, X.ꢀY.; Xie, G.;
Zhang, Z.; Bo, Z.; Jiang, L. Engineered Ionic Gates for Ion Conduction Based on
Sodium and Potassium Activated Nanochannels. J. Am. Chem. Soc. 2015, 137, 11976ꢀ
11983.
(44) PerezꢀMitta, G.; Albesa, A. G.; Knoll, W.; Trautmann, C.; Toimilꢀ
Molares, M. E.; Azzaroni, O. Hostꢀguest supramolecular chemistry in solidꢀstate
nanopores: potassiumꢀdriven modulation of ionic transport in nanofluidic diodes.
Nanoscale 2015, 7, 15594ꢀ15598.
(45) Tian, Y.; Hou, X.; Wen, L. P.; Guo, W.; Song, Y. L.; Sun, H. Z.;
Wang, Y. G.; Jiang, L.; Zhu, D. B. A biomimetic zinc activated ion channel. Chem.
Commun. 2010, 46, 1682ꢀ1684.
(46) Ali, M.; Ahmed, I.; Ramirez, P.; Nasir, S.; Cervera, J.; Mafe, S.;
Niemeyer, C. M.; Ensinger, W. CesiumꢀInduced Ionic Conduction through a Single
Nanofluidic Pore Modified with Calixcrown Moieties. Langmuir 2017, 33, 9170ꢀ
9177.
(47) Hou, X.; Guo, W.; Xia, F.; Nie, F. Q.; Dong, H.; Tian, Y.; Wen, L. P.;
Wang, L.; Cao, L. X.; Yang, Y.; Xue, J. M.; Song, Y. L.; Wang, Y. G.; Liu, D. S.;
Jiang, L. A Biomimetic Potassium Responsive Nanochannel: GꢀQuadruplex DNA
Conformational Switching in a Synthetic Nanopore. J. Am. Chem. Soc. 2009, 131,
7800ꢀ7805.
(48) Aral, H.; VecchioꢀSadus, A. Toxicity of lithium to humans and the
environment—A literature review. Ecotoxicol. Environ. Saf. 2008, 70, 349ꢀ356.
(49) Hartley, J. N.; Gore, B. F.; Young, J. R.: Potential Lithium
Requirments for Fusion Power Plants A2 ꢀ PENNER, S.S. In Lithium Needs and
Resources; Pergamon, 1978; pp 337ꢀ346.
(50) Baldessarini, R. J.; Tondo, L.; Davis, P.; Pompili, M.; Goodwin, F. K.;
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treatment: a metaꢀanalytic review. Bipolar Disord. 2006, 8, 625ꢀ639.
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Birch, N. J. Instant lithium monitoring. Psychiatr. Bull. 2018, 15, 138ꢀ139.
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(52) Kamenica, M.; Kothur, R.; Willows, A.; Patel, B.; Cragg, P. Lithium
Ion Sensors. Sensors 2017, 17, 2430.
(53) Obare, S. O.; Hollowell, R. E.; Murphy, C. J. Sensing Strategy for
Lithium Ion Based on Gold Nanoparticles. Langmuir 2002, 18, 10407ꢀ10410.
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assembled columnar liquid crystals based on a lithium receptor. Chem. Sci. 2018,
DOI: 10.1039/C1037SC03652C.
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electrodes based on crown ethers for serum lithium assay. Anal. Chem. 1987, 59,
331ꢀ2334.
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Jierry, L.; Boulmedais, F. Morphogen Electrochemically Triggered SelfꢀConstruction
of Polymeric Films Based on MusselꢀInspired Chemistry. Langmuir 2015, 31, 13385ꢀ
13393.
(57) Balamurugan, A.; Reddy, M. L. P.; Jayakannan, M. [small pi]ꢀ
Conjugated polymerꢀEu3+ complexes: versatile luminescent molecular probes for
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58) Ghidini, E.; Ugozzoli, F.; Ungaro, R.; Harkema, S.; Abu ElꢀFadl, A.;
Reinhoudt, D. N. Complexation of alkali metal cations by conformationally rigid,
stereoisomeric calix[4]arene crown ethers: quantitative evaluation of
preorganization. J. Am. Chem. Soc. 1990, 112, 6979ꢀ6985.
59) Cervera, J.; Ramirez, P.; Mafe, S.; Stroeve, P. Asymmetric nanopore
a
(
rectification for ion pumping, electrical power generation, and information processing
applications. Electrochim. Acta 2011, 56, 4504ꢀ4511.
(60) Cervera, J.; Schiedt, B.; Neumann, R.; Mafe, S.; Ramirez, P. Ionic
Conduction, Rectification, and Selectivity in Single Conical Nanopores. J. Chem.
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(61) Cervera, J.; Schiedt, B.; Ramirez, P. A Poisson/NernstꢀPlanck model
for ionic transport through synthetic conical nanopores. Europhys. Lett. 2005, 71, 35ꢀ
41.
(62) Ramirez, P.; Apel, P. Y.; Cervera, J.; Mafe, S. Pore Structure and
Function of Synthetic Nanopores with Fixed Charges: Tip Shape and Rectification
Properties. Nanotechnology 2008, 19, 315707.
(63) Ramirez, P.; Gomez, V.; Cervera, J.; Schiedt, B.; Mafe, S. Ion transport
and selectivity in nanopores with spatially inhomogeneous fixed charge distributions.
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(64) Siwy, Z. S. IonꢀCurrent Rectification in Nanopores and Nanotubes with
Broken Symmetry. Adv. Funct. Mater. 2006, 16, 735ꢀ746.
(65) Luo, X.; Guo, B.; Luo, J.; Deng, F.; Zhang, S.; Luo, S.; Crittenden, J.
Recovery of Lithium from Wastewater Using Development of Li IonꢀImprinted
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Figures and Legends
K CO , MeCN
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+
24 h, reflux
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Figure 1. Synthesis of the aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 (B12C4–NH2).
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Figure 2. (A) Chemical modification of the carboxylic acid groups on the surface of
an asymmetric nanopore with aminoethylꢀbenzoꢀ12ꢀcrownꢀ4 via carbodiimide
+
coupling chemistry. (B) Specific Li ion complexation with the B12C4 moieties
immobilized on the pore surface.
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Figure 3. (A) Experimental I–V characteristics of the unmodified pore in 100 mM
KCl solutions at two pH values. (B) Model calculations corresponding to the
experimental data. (C) Experimental I–V characteristics of the unmodified pore
exposed to different alkali cation solutions (100 mM, pH 6.5). (D) Model calculations
corresponding to the experimental data. (E) Experimental I–V characteristics of the
B12C4ꢀmodified pore exposed to different alkali cation solutions (100 mM, pH 6.5).
The inset shows the rectification ratio versus alkali cation at potential 1 V. (F) Model
calculations corresponding to the experimental data.
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Figure 4. Schematic representation of the lithium–crown ether complexation on the
nanopore surface (A). Experimental and theoretical I–V characteristics of the modified
pore of Figure 3 exposed to different lithium ion concentrations in the solution (B).
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.5
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NaCl
KCl
RbCl
CsCl
σ (e/nm )
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.5
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-2.5
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Voltage (V)
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.5
.0
(
C)
(D)
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(mM) (mM)
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+ 80
+ 100
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1.0
2
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Voltage (V)
Cycles
Figure 5. (A) I–V characteristics of a second modified pore exposed to different alkali
cation (100 mM, pH 6.5) solutions separately. (B) Model calculations corresponding
to the experimental data. (C) I–V characteristics of the this pore exposed to different
fractions of KCl and LiCl solutions keeping the ionic strength (100 mM) constant
of the electrolyte. (D) The conductance obtained at V =
−1 V after several
measuring cycles on exposing the modified pore to KCl and LiCl solutions,
alternatively.
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Figure 6. I–V curves of the modified pore exposed to different alkali metal chloride
100 mM, pH 3.5) solutions.
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