Chemoselective detection of Ag+ in purely aqueous solution using fluorescence ‘turn-on’ probe based on crown-containing 4-methoxy-1,8-naphthalimide

Article abstract of DOI:10.1016/j.mencom.2019.03.012

A novel derivative of 4-methoxy-1,8-naphthalimide bearing N-phenylazadithia-15-crown-5 ether receptor has been demonstrated as the selective and sensitive fluorescent probe for the detection of silver(I) ions in purely aqueous solution at neutral pH.

Full text of DOI:10.1016/j.mencom.2019.03.012

Mendeleev
Communications
Mendeleev Commun., 2019, 29, 155–157
+
Chemoselective detection of Ag in purely aqueous
solution using fluorescence ‘turn-on’ probe based
on crown-containing 4-methoxy-1,8-naphthalimide
Pavel A. Panchenko,*a,b Anna S. Polyakova, Yurii V. Fedorov and Olga A. Fedorova
b
a
a,b
a
b
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 499 135 5085; e-mail: pavel@ineos.ac.ru
D. I. Mendeleev University of Chemical Technology of Russia, 125047 Moscow, Russian Federation
DOI: 10.1016/j.mencom.2019.03.012
Ag+ (1 equiv.)
2
.5
2.0
.5
1.0
.5
0.0
Free ligand, 1 equiv.
A novel derivative of 4-methoxy-1,8-naphthalimide bearing
N-phenylazadithia-15-crown-5 ether receptor has been
demonstrated as the selective and sensitive fluorescent probe
for the detection of silver(i) ions in purely aqueous solution
at neutral pH.
O
N
O
2+
2+
2+
of Hg , Cu , Ca
,
S
O
O
OMe
1
Mg2+, Zn2+, Ni2+
,
2+ 2+ 2+
Ag+
N
Fe , Pb , Cd
S
0
PET
4
00 450 500 550 600 650
l/nm
Determination of transition and heavy metals in aqueous media,
which exert hazardous effects on the environment, is of significant
importance. Silver(i) is one among metals frequently used in
various fields such as imaging, electronics, pharmacy, photo­
graphy as well jewellery, table cutlery, and filters for water
This led to an increased electron­releasing character of the
receptor (as compared to crown ethers without an aromatic
substituent) and, consequently, to a high optical response due to
switching of photoinduced electron transfer (PET) from N­aryl
moiety to naphthalimide chromophore upon binding to metal
ions. The fluorescence enhancement by more than two orders of
magnitude was observed, which was eventually anticipated, but
not very often revealed for the majority of fluorescent PET sensors.
Regardless of the achieved results, the prepared compounds
could hardly be good candidates for the sensing of metal ions in
aqueous environment since the water molecules may efficiently
compete with the crown ethers, wherein only the oxygen and
aniline nitrogen atoms are involved in the complex formation.
The aim of the present work was to extend a pronounced PET
switching effect in the emission spectra discovered for pre­
1
purifiers. However, superabundance of silver can cause a strong
2
poisoning to organisms. Once it was absorbed in the human body,
2
+
silver ions can displace essential metal ions such as Ca and
2+
Zn in hydroxyl apatite in bones. Moreover, the bioaccumulation
and toxicity of silver ions through binding with various metabolites
such as amine, carboxyl groups, and inactivating sulfhydryl
3
enzymes have also been reported. The high concentration of
+
Ag ion can lead to a variety of adverse health effects, brain
damage, nerve damage, and disorders in immune system.
Some of the traditional methods such as spectrophotometry,
atomic absorption spectrometry, stripping voltammetry, potentio­
metry, and inductively coupled plasma atomic emission spec­
trometry have been employed for the detection of silver ions. How­
ever, these methods are labor­intensive and expensive. In contrast,
a fluorescence­based sensing provides significant advantages of
simplicity, high sensitivity and selectivity, easy operation, and
+
viously studied naphthalimides to selective sensing of Ag in
water.
For this purpose, a novel derivative of 4­methoxy­1,8­naph­
thalimide bearing N­phenylazadithia­15­crown­5 ether receptor
(compound 9), which incorporates two sulfur atoms (known as
the soft donors suitable for binding of cations with diffuse electron
shell) in the structure of aza­15­crown­5 macrocycle, was prepared
4
instant responses. The majority of sensors developed for heavy
†
metal ions are based on the conventional fluorescence emission
(Scheme 1). In its structure, the 4­methoxynaphthalimide chromo­
technique via quenching (‘on–off’ or ‘turn off’ switching) of the
phore has been chosen as a fluorescent unit due to its high emission
quantum yield in protic solvents such as water and alcohols. For
5
fluorescence intensity. In particular, a decrease in the emission
+
6
fl
signal upon coordination with Ag was observed quite often.
instance, the emission quantum yield (j ) of 4­methoxy­N­ethyl­
Although the fluorescence quenching can be used for analytical
measurements, ‘off–on’ intensity change is a more preferable
case. In addition, the fluorescent chemosensors reported for the
1,8­naphthalimide is 0.64 in water and 0.71 in MeCN.10 This
makes 4­methoxy­1,8­naphthalimide moiety quite attractive for
the sensory applications as compared to commonly used 4­amino­
naphthalimides, which usually demonstrate lower fluorescence
+
detection of Ag ions were mostly designed for organic solvents
6(b),7
fl
or mixed aqueous solutions.
efficiencies in polar protic environment, e.g., the j values of
8
In our previous work, we prepared fluorescent sensors
containing benzo­15­crown­5 and N­phenylaza­15­crown­5 ether
receptors as N­aryl substituents attached to N­imide atom of
the well­known naphthalimide fluorophore. A distinct feature
of those designed molecules is that the donor atoms (N or O) of
receptor are conjugated with the p­system of N­phenyl moiety.
4­amino­N­phenyl­1,8­naphthalimide in MeCN and water are
†
Compounds 2,9(b) 4,9(c),(d) 59(c) and 69(e) were previously reported,
however, methods used for the preparation of 4 and 6 were different from
those reported herein. See Online Supplementary Materials for synthetic
procedures.
©
2019 Mendeleev Communications. Published by ELSEVIER B.V.
–
155 –
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.

Mendeleev Commun., 2019, 29, 155–157
OH
Cl
O
S
O
S
S
S
O
O
HS
O
O
SH
N
POCl3
N
3
N
NaNO2, HCl
H2O
N
OH
Cl
Cs2CO3, EtOH, H2O,
ON
1
2, 77%
4, 49%
5, 78%
O
O
S
O
S
S
O
S
O
O
O
N
N
O
N
O
O
O
S
O2N
AcOH, H2O,
S
N2H4, Raney Ni
EtOH, H2O,
7
MeOH, KOH
O
N
N
O
H N
2
O N
2
MeO
6
8, 76%
Scheme 1
9, 84%
0
.52 and 0.091, respectively.11 Moreover, the contribution of
coefficient of 0.99 (Figure S6). From the slope of that calibration
non­fluorescent twisted intramolecular charge transfer states
plot (r) and standard deviation of the blank solution (S ), the
Y
2+
in the case of 4­(N,N­dialkylamino)naphthalimides and similar
detection limit for Hg (CDL) was found to be 0.38 mm according
1
2
14
compounds could also affect the spectral characteristics.
The signaling behavior of sensor 9 was investigated towards
to equation (1):
CDL = 3S /r.
(1)
+
2+
2+
2+
2+
2+
2+
2+
Y
various metal ions (Ag , Hg , Cu , Ca , Pb , Cd , Ni , Zn ,
2
+
2+
Mg , and Fe ). First, its spectral characteristics were studied.
Note that the obtained value of CDL is quite close to the
secondary maximum contaminant level of silver(i) in drinking
13
Similarly to other 4­methoxy­1,8­naphthalimides, compound
exhibited the broad­band charge transfer absorption and fluore­
scence in aqueous solution with maxima positions at 374 and
58 nm, respectively (Figure S1, Online Supplementary Materials).
However, the emission quantum yield was found to be very low
–3
9
water (0.1 mg dm or 0.93 mm) established by the US Environ­
1
5
mental Protection Agency.
4
To evaluate the selectivity of probe of 9 in aqueous solution,
the fluorescence responses to various metal ions were investigated.
fl
8(c),(d),(f)
+
(
j = 0.0002). According to our previous results,
such
Figure 2(a) shows that the addition of Ag (1 equiv.) induced
behavior can be explained by the occurrence of PET between the
N­aryl group and naphthalimide moiety in the excited state.
Classical fluorophore–space–receptor architecture of molecule 9
was also confirmed by the optimized ground state geometry
significant spectral changes, while no distinct fluorescence
enhancements were observed in the presence of other metal ions
‡
(
a)
2
.0
1.5
.0
2
1
1
.0
.5
.0
(Figure S2) showing nearly orthogonal orientation of the naphthal­
[Ag+]
imide and phenyl ring planes and thus the lack of conjugation
between the receptor and chromophore.
1
Next, the influence of pH on the fluorescence of compound
0.5
0.0
9
was examined (Figure S3). An obvious increase of intensity in
the emission spectrum was observed with decreasing pH below
.0, which could be attributed to the inhibition of PET process.
0
2
4
6
8 10
+
0.5
Equiv. Ag
4
0
.0
No change in the fluorescence intensity occurred at pH higher
than 6.0, which makes compound 9 attractive for its application
by both physiological and environmental criteria. Based on these
results, we have selected pH 7.3 media buffered with 10 mm
HEPES for the measurements of sensing properties.
4
00
450
500
550
600
l/nm
(
b)
1
.2
1.0
0.8
Figure 1(a) shows that the emission at 460 nm was dramatically
+
enhanced with raising concentration of Ag added to the 5 mm
0
0
0
0
.6
.4
.2
.0
solution of compound 9, while the changes in the absorption
spectrum were negligible (Figure S4). The fluorescence enhance­
+
ment was assigned to the formation of complex with the Ag to
0.501
ligand 9 ratio of 1:1 and applied for the calculation of its stability
+
0.0
0.2
0.4
0.6
0.8
1.0
constant (Kassoc). The evidence of formation of 9·Ag complex
+
+
[
Ag ]/([Ag ] + [9])
was approved by the Job’s plot, which shows the maximum
fluorescence intensity of the mixed solution containing ligand
Figure 1 (a) Fluorescence emission spectra of compound 9 (5 mm) upon
+
+
9
and silver(i) perchlorate at ca. 0.5 molar fraction of Ag
addition ofAg (0–50 mm) and (b) Job’s plot showing the difference between
+
fluorescence intensity before (I ) and after (I) addition of Ag vs. molar
[Figure 1(b)].
0
+
+
fraction of Ag at the constant [Ag ] + [9] value (5 mm) in water at pH 7.3
10 mm HEPES buffer). Excitation wavelength was 375 nm. The inset
The ESI MS analysis of the acetonitrile solution of compound
(
9
in the presence of 1 equiv. of AgClO revealed the major
4
shows the fluorescence intensity at 460 nm as a function of added equivalents
+
signal at m/z 661.13 (calc., m/z: 661.09) corresponding to cation
of Ag .
+
[
9+Ag] (Figure S5). Based on the titration data, the value of
logKassoc was estimated as 6.39±0.07. Moreover, the increase in
fluorescence intensity of 9 with increasing amount of Ag added
‡
The value of fluorescence enhancement was calculated as the ratio
+
between the emission intensity at 460 nm measured after the addition of
metal ion and that measured before the addition.
(0.5–3.5 mm) demonstrated a good linearity with the correlation
–
156 –

Mendeleev Commun., 2019, 29, 155–157
(
a)
+
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2
2
1
1
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.5
.0
.5
.0
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of Ag , Hg , Fe , Cu , Zn , Pb , Cd , Ni , Ca , and Mg (1 equiv.)
in water at pH 7.3 (10 mm HEPES buffer); (b) selectivity of 9 for Ag .
Excitation wavelength was 375 nm.
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
+
5
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(
[
1 equiv.). The competition experiments were also conducted
Figure 2(b)]. In a typical procedure, the emission spectrum was
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measured before and after the addition of other ions (5 equiv.) to
the solution of 9 (5 mm) containing Ag (1 equiv.). As one can
see, the presence of Cu , Ca , Pb , Mg , Zn , Ni , or Cd
+
2+
2+
2+
2+
2+
2+
2+
did not cause any pronounced signal interference, while there
9
was a small effect in the cases of Hg2 and Fe . Noteworthy,
such a low response of sensor 9 to mercury(ii) cations was first
seemed quite surprising, since azadithia­15­crown­5 ether is the
+
2+
2+ 16
known ionophore for Hg . The analysis of conditions under
which this receptor was capable to bind Hg effectively has
shown that mostly pure organic solvents (acetonitrile,
chloroform,
the similar high selectivity to Ag over Hg was observed in
aqueous 50 vol% ethanol at pH 7.2. This is consistent with the
fact that mercury(ii) ion is completely hydrolyzed at neutral
pH and exists in the form of Hg(OH) , while Ag is much less
2+
1
6(a),(b)
1
6(c)
16(d)
or THF
) were used as the media. However,
+
2+
10 A. Pardo, J. M. L. Poyato, E. Martin, J. J. Camacho, D. Reyman, M. F.
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6(b)
17
+
2
1
6(e)
subjected to the hydrolysis. In our recent work,
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bearing the same azadithia­15­crown­5 receptor and 4­amino­
we also
1
2
+
1
,8­naphthalimide chromophore to Hg in acidic methanol–
water solution (pH 4.7) or in acetonitrile was fairly high.
In summary, the novel crown­containing 4­methoxy­1,8­naph­
thalimide derivative 9 has been synthesized and evaluated with
respect to its ability to serve as the fluorescent PET chemosensor
for silver(i) ion. The fluorescence intensity of compound 9 is
enhanced in the presence of Ag due to the formation of highly
emissive complex 9·Ag , where the PET process is hampered.
A good selectivity of the new sensor for the quantification of
silver(i) content in purely aqueous solutions at the micromolar
level has been demonstrated.
2
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7
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The work was supported by the Russian Science Foundation
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Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.03.012.
Received: 17th September 2018; Com. 18/5691
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