A novel Cr3+ turn-on probe based on naphthalimide and BINOL framework

Article abstract of DOI:10.1016/j.tetlet.2013.11.024

Naphthalimide and BINOL framework based fluorescent probe NP-B was rationally designed and synthesized. NP-B exhibited 'turn-on' fluorescence for Cr³⁺ and high selectivity over other metal ions. 1:1 binding mode between NP-B and Cr³⁺ was proposed and the mode was verified through MALDI-TOF mass spectrum. The detection limit was calculated to be 0.20 μM, which indicated the good sensitivity for Cr³⁺.

Full text of DOI:10.1016/j.tetlet.2013.11.024

Tetrahedron Letters 55 (2014) 351–353
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A novel Cr3+ turn-on probe based on naphthalimide and BINOL
framework
⇑
Shengying Wu, Kewei Zhang, Yefeng Wang, Dan Mao, Xin Liu, Jianjun Yu, Limin Wang
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Naphthalimide and BINOL framework based fluorescent probe NP-B was rationally designed and synthe-
sized. NP-B exhibited ‘turn-on’ fluorescence for Cr3+ and high selectivity over other metal ions. 1:1 bind-
ing mode between NP-B and Cr3+ was proposed and the mode was verified through MALDI-TOF mass
Received 1 August 2013
Revised 1 November 2013
Accepted 7 November 2013
Available online 15 November 2013
spectrum. The detection limit was calculated to be 0.20
l
M, which indicated the good sensitivity for Cr3+
Ó 2013 Elsevier Ltd. All rights reserved.
.
Keywords:
Naphthalimide
BINOL
Trivalent chromium probe
Turn-on
High selectivity
Trivalent chromium (Cr3+) is an essential nutrient for humans
and plays an important role in the metabolism of carbohydrates,
lipids, proteins, and nucleic acids.1 Insufficient intake of Cr3+ in-
creases the risk for diabetes2 and cardiovascular diseases,3 whereas
excessive intake causes genotoxic effects.4 Accurate and rapid
determination of Cr3+ amount in the environment is therefore nec-
essary. Traditional analytical methods for Cr3+ employ expensive
instruments such as atomic absorption spectrometry5 and induc-
tively-coupled plasma atomic emission spectrometry.6 Although
these methods enable accurate and specific detection of Cr3+, they
are usually time-consuming and require complicated and tedious
sample preparation.7
its derivatives are widely employed in the construction of chemo-
sensors.13 So far, few fluorescent probes for Cr3+ based on the
naphthalimide and BINOL derivatives are reported. Herein, we
designed and synthesized a new highly selective and turn-on fluo-
rescent probe for detection of Cr3+ based on naphthalimide
derivative.
The synthesis of NP-B was started from [1,10-binaphthalene]-
2,20-diol (BINOL) and 4-bromo-1,8-naphthalic anhydride, as shown
in Scheme 1. A414 and B315 have been synthesized from [1,10-
binaphthalene]-2,20-diol (BINOL) or 4-bromo-1,8-naphthalic anhy-
dride according to literature procedures, respectively. A4 and B3
were condensed to furnish the desired Schiff base NP-B as a yellow
solid in 96% yield. Metal ions are readily avaliable from
corresponding chloride, nitrate, sulfate, or perchlorate salts.
The interaction of probe NP-B with the cations was investigated
through fluorescence spectra. All the fluorescence behavior of
probe NP-B was studied in THF/H2O solutions (85/15, v/v).
Fluorescence titration of NP-B with Cr3+ was performed and the
responding spectra are shown in Figure 1. Free NP-B exhibited a
The fluorescence method has more advantages over above-
mentioned methods such as facile operation, high selectivity, en-
hanced sensitivity, rapid and high frequency sample detection,
nondestructive methodology, enhanced sensitivity, high sampling
frequency and low cost of equipment, and direct visual percep-
tion.8 For example, an efficient fluorescent sensor in a recent report
has shown high selectivity toward the target ion with a significant
fluorescent intensity change observed.9
slight fluorescence response with
a maximum at 491 nm
Thus, the detection and estimation of Cr3+ always constitute an
active area of research.10 Although a lot of chemosensors for Cr3+
have been developed, most of them are turn-off chemosensors
(U = 0.08), due to efficient photoinduced electron transfer (PET)
process from the electro-rich receptor to the excited NP-B fluoro-
phore. Upon addition of Cr3+, fluorescence enhancement and a
red-shift of emission band centered at 498 nm could be observed
(U = 0.27). The fluorescence enhancement was attributed to the
formation of a NP-B/Cr3+ complex and PET mechanism was
quenched, while the red-shift to 498 nm was caused by a change
for Cr3+ due to the paramagnetic nature of Cr3+ 11
Turn-off sensors
.
showed poor sensitivity and selectivity for the cations,12 compar-
ing with turn-on chemosensors. Furthermore, naphthalimide and
of the internal charge transfer process (ICT).
enhancement of fluorescence intensity could be observed along
A continuous
⇑
Corresponding author. Tel./fax: +86 21 64253881.
E-mail address: wanglimin@ecust.edu.cn (L. Wang).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.11.024

352
S. Wu et al. / Tetrahedron Letters 55 (2014) 351–353
O
O
600
H
H
OH
OH
OMOM n-BuLi/THF
OMOM
NaH/THF
HCl/THF
OMOM
OMOM
OH
OH
MOMCl, 0oC
90% yield
DMF/-78oC
0 o
C
y = 165.2441 + 34.9645*x
525
450
375
300
225
70%yield
95% yield
2
R
= 0.9979
A1
A2
A3
A4
O
N
O
O
O
O
O
N
O
NH2
O
N
O
H2N
NH2
A4
EtOH, reflux
NH
Reflux
83% yield
AcOH, reflux
85% yield
N
Br
HN
Br
H2N
B3
OH
OH
B1
B2
2
4
6
8
10
12
2 equiv. to 12 equiv.
NP-B
Figure 2. Curve of fluorescence intensity at 498 nm of NP-B (1 ꢁ 10ꢀ5 M) versus
Scheme 1. The synthetic route of NP-B.
increasing concentrations of Cr3+ (2–12 equiv).
with the increasing of the Cr3+ concentration (Fig. 1) and this
enhancement was saturated upon the addition of 14 equiv of Cr3+
(a)600
.
3+
Figure 2 shows there was a good linearity between the emission
probe + Cr
at 498 nm and concentrations of Cr3+ in the range from 20 to
500
120 lM, indicating that sensor NP-B can detect nearly quantita-
400
tively relevant concentrations of Cr3+. The linear equation was
found to be y = 34.9645x + 165.2441 (R2 = 0.9979), where y was
the emission at 498 nm measured at a given Cr3+ concentration
and x represented the concentration (10ꢀ5 mol/L) of Cr3+ added.
According to IUPAC, the detection limit was determined from three
probe + other metal ions
300
probe
2+
200
100
0
probe + Cu
times the standard deviation of the blank signal (3s) as 0.20
lM.
The result indicated that NP-B was sensitive to Cr3+
.
In order to further understand the coordination of NP-B with
Cr3+, MALDI-TOF-MS was carried out (Fig. S4). The unique signal
at m/z = 679.1392 corresponding to [probe + Cr-3H + Na]+ was
clearly observed when 14 equivalents of Cr3+ was added to NP-B,
whereas NP-B without Cr3+ exhibited a different signal at m/
z = 608.2547 (calcd for 608.2549) (Fig. S3).
450
500
550
600
650
Wavelength (nm)
Figure 3 shows the fluorescence spectra (kex = 420 nm) of NP-B
(1 ꢁ 10ꢀ5 M) measured in THF/H2O (85/15, v/v) with a buffer solu-
tion of 3-(N-morpholino) propanesulfonic acid (MOPS, 10 mM,
Figure 3. (a) Fluorescent response of NP-B (1 ꢁ 10ꢀ5 M) to various metal ions at
14 equiv concentration in THF/H2O (85/15, v/v) with a buffer solution of 3-(N-
morpholino) propanesulfonic acid (MOPS, 10 mM, pH = 7.0). (b)
A photograph
showing the color change of NP-B (1 ꢁ 10ꢀ5 M) at 365 nm in THF/H2O (85/15, v/v)
pH = 7.0), with 14 equiv of respective metal cations such as Ca2+
Cu2+, Ag+, Zn2+, Co2+, Ni2+, Mg2+, Ba2+, Cd2+, Mn2+, Pb2+, Hg2+, Fe3+
,
,
upon addition of 14 equiv of various metal ions.
Fe2+, Na+, K+, Al3+, and Cr3+. Without cations, NP-B showed weak
fluorescence due to efficient photoinduced electron transfer (PET)
process from the electron-rich receptor to the excited NP-B
fluorophore. After addition of Cr3+, the PET mechanism was
quenched. Thus, a strong fluorescence emission enhancement with
a red-shift was observed. As shown in Figure 3b, green fluores-
cence was observed upon Cr3+ addition. In contrast, addition of
other metal cations could not cause a significant enhancement in
fluorescence emission, especially, the copper ions could even
quench the fluorescence. We suspected the quench was caused
Cr3+/equiv.
600
600
14
13
500
by the magnetic properties of copper ions and p–p stacking. p–p
12
11
10
9
500
400
300
200
100
0
Stacking was induced by the dimer which was formed by copper
ions and probe.16 With Cr3+, the enhancement factor is determined
to be 600. In contrast, other metal ions quenched fluorescence of
NP-B or had little influence on NP-B, which suggested that the fac-
tor of Cr3+ was more than 3.5 times greater than that of other metal
cations, as shown in Figure 4. The above-mentioned findings
clearly indicated that NP-B behaved as a highly selective turn-on
fluorescent probe for Cr3+. In addition, the fluorescence enhance-
ment took place immediately after Cr3+ addition (within 10 s), indi-
cating that NP-B enabled rapid detection of Cr3+. As for the high
selectivity for Cr3+, we reasoned that the following two factors
might play critical roles. On one hand, avoiding the use of sulfur
atom in our scaffold could prevent interference from other metal
ions especially from mercury.17 On the other hand, the receptor
of NP-B was relatively rigid and cavity-like, which could specifi-
cally fit for Cr3+ but not metal ions.
400
300
200
8
7
0
3
6
9
12
15
6
0 quiv. to 14 equiv.
5
4
3
2
1
0
450
500
550
600
650
Wavelength (nm)
Figure 1. Fluorescence spectra of NP-B (1 ꢁ 10ꢀ5 M) in THF/H2O (85/15, v/v) with a
buffer solution of 3-(N-morpholino) propanesulfonic acid (MOPS, 10 mM, pH = 7.0)
in the presence of different concentrations of Cr3+ (0–14 equiv), kex = 420 nm. Inset:
fluorescence intensity at 498 nm of NP-B as a function of Cr3+ concentration.

S. Wu et al. / Tetrahedron Letters 55 (2014) 351–353
353
3.5
3.0
2.5
2.0
1.5
1.0
0.5
naphthalimide ring was involved in Cr3+ chelation. According to
this factor and the MALDI-TOF-MS spectrum, we proposed a plau-
sible binding mode of the probe NP-B with Cr3+ as shown in
Scheme 2, and the association constant between NP-B and Cr3+
was determined to be 2.4 ꢁ 104 Mꢀ1 in THF/H2O (85/15, v/v) by
using nonlinear least-square analysis.
In conclusion, Naphthalimide and BINOL framework based
‘‘turn-on’’ fluorescence probe NP-B was successfully developed.
NP-B displayed a fluorescence enhancement and a little red-shift
response to Cr3+ via a 1:1 binding mode. Fluorescence intensity
was linear with the concentration of Cr3+ cation in a range from
20 to 140 lM. As a probe, NP-B exhibited high selectivity and sen-
sitivity for Cr3+. The detection limit was calculated to be 0.20
lM.
Acknowledgments
Figure 4. Fluorescent emission changes of NP-B (1 ꢁ 10ꢀ5 M) upon addition of
14 equiv of each relevant analyte (Ca2+, Cu2+, Ag+, Zn2+, Co2+, Ni2+, Mg2+, Ba2+, Cd2+
,
The work was supported by the National Nature Science
Foundation of China (NSFC, 21272069, 20672035), the
Fundamental Research Funds for the Central Universities and Key
Laboratory of Organofluorine Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences.
Mn2+, Pb2+, Hg2+, Fe3+, Fe2+, Na+, K+, Al3+, Cr3+) in THF/H2O (85/15, v/v) with a buffer
solution of 3-(N-morpholino) propanesulfonic acid (MOPS, 10 mM, pH = 7.0).
kex = 420 nm.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Supplementary data
Supplementary data (these data include copies of 1H NMR, 13C
NMR spectra, and mass spectra of compounds described in this
Letter) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.tetlet.2013.11.024.
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PET
O
O
O
Cr3+
NH
N
OHOH
O
N
O
N
O
N
N
PET
NP-B
Turn-on Fluorescence
3+
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Scheme 2. Proposed binding mode of NP-B with Cr3+
.
To examine whether probe NP-B still retains sensitivity to Cr3+
under the potential competition from relevant analytes, the probe
was treated with Cr3+ in the presence of other metal ions. As
displayed in Figure 5, all the relevant analytes tested had virtually
little influence on the detection of Cr3+. Thus, probe NP-B could be
particularly applicable to Cr3+, even in the presence of these
relevant analytes.
As observed from the fluorescence titration spectra, the Cr3+ in-
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when the nitrogen, which was also the donor of the push-pull sys-
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