A naphthalimide-quinoline based probe for selective, fluorescence ratiometric sensing of trivalent ions

Article abstract of DOI:10.1039/c2ra22624c

A new naphthalimide-quinoline based probe (NAQ) is designed and synthesized and its structure is confirmed through single crystal analysis. It detects the trivalent ions (Fe³⁺ or Al³⁺ or Cr³⁺) selectively among other alkali and transition metal ions studied. NAQ shows a distinct ratiometric fluorescence behavior upon addition of trivalent metal ions in CH₃CN-HEPES buffer solution (40/60, v/v, pH = 7.4). This fluorogenic sensing of NAQ to M³⁺ (M³⁺ = Fe³⁺ or Al³⁺ or Cr³⁺) can be observed by the naked eye, when illuminated under the UV light.

Full text of DOI:10.1039/c2ra22624c

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A naphthalimide-quinoline based probe for selective,
fluorescence ratiometric sensing of trivalent ions
Journal: RSC Advances
Manuscript ID: RA-ART-10-2012-022624.R1
Article Type: Paper
Date Submitted by the Author: 13-Dec-2012
Complete List of Authors: Goswami, Shyamaprosad; Bengal Engineering and Science University,
Shibpur, Dept. of Chemistry

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ARTICLE TYPE
A naphthalimide-quinoline based probe for selective, fluorescence
ratiometric sensing of trivalent ions
*
Shyamaprosad Goswami , Krishnendu Aich, Avijit Kumar Das, Abhishek Manna and Sangita Das
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A new naphthalimideꢀquinoline based probe (NAQ) is designed and synthesized and its structure is confirmed through single crystal
3
+
3+
3+
analysis. It detects the trivalent ions (Fe or Al or Cr ) selectively among other alkali and transition metal ions studied. NAQ shows a
distinct ratiometric fluorescence behavior upon addition of trivalent metal ions in CH CNꢀHEPES buffer solution (40/60, v/v, pH = 7.4).
3
3
+
3+
3+
3+
3+
1
0
This fluorogenic sensing of NAQ to M (M = Fe or Al or Cr ) can be observed in naked eye, when illuminated under the UV light.
55
(
internal charge transfer) mechanism. Experimental studies
Introduction
revealed that NAQ shows a selective fluorescence ratiometric
behavior towards trivalent cations in CH CNꢀHEPES buffer
solution (40/60, v/v, pH = 7.4).
3
In recent decade, the fluorogenic sensing of different metal ions
1
2
2
3
3
4
4
5
5
0
5
0
5
0
5
0
have paid a great attention due to the advantages such as high
1
60
sensitivity, selectivity, rapid response time and versatility.
A
large number of chemosensors for divalent metal ions have been
reported in the literature but only a few chemosensors for
Results and discussion
2
3+
trivalent ions are known. However, trivalent ions such as Fe ,
NAQ was prepared through a high yielding synthetic route
(overall yield = 80%), shown below in scheme 1. The
Iron in its trivalent form is indispensable for most organisms, as it 65 intermediate 2 was prepared from 8ꢀHydroxyquinoline according
3+
3+
Al and Cr play many important roles in the living organism.
9
is involved in both electron transfer and oxygen transport due to
its sufficient redox potential and high affinity towards oxygen.
to the procedure reported in the literature. The molecular
structure and purity of NAQ was established from different
3
+
1
High levels of Fe within the body have been associated with
spectroscopic studies like H NMR and ESI MS. In addition, the
increasing incidence of certain cancers and dysfunction of certain
structure of the receptor (NAQ) has been confirmed through its
3
organs, such as the heart, pancreas, and liver. Aluminum is the 70 single Xꢀray crystallographic analysis.
third most prevalent element and the most abundant metal in the
earth's crust. Intake of excessive amounts of aluminium can be
toxic to humans. Alzheimer’s disease, osteoporosis, colic, rickets,
gastrointestinal problems, interference with the metabolism of
calcium, extreme nervousness, anemia, headaches, decreased
liver and kidney function, memory loss, speech problems,
softening of the bones, and aching muscles can all be caused by
Scheme 1: Synthetic scheme of NAQ.
H
N
O
NH
2
O
OEt
75
O
OH
O
N
N
N
4
(i)
(ii)
aluminium toxicity. Trivalent chromium is one of the most
important heavy metal elements. It is an essential nutrient for
humans and plays an important role in the metabolism of
2
1
5
carbohydrates, lipids, proteins, and nucleic acids. Insufficient
H
N
O
NH
2
3+
intake of Cr increases the risk for diabetes and cardiovascular
80
6
diseases, whereas excessive intake causes genotoxic effects. So,
O
O
O
O
O
N
there is a great need to develop a chemosensor which can detect
the presence of trivalent cations in environmental and biological
samples.
Recently, the development of fluorescence ratiometric probes for
metal ions has attracted much attention since they allow the
measurement of emission intensities at two different wavelengths.
It is still a challenging task to design a ratiometric probe that
N
(
iii)
N
O
NH
O
+
2
O
NAQ
Reagents and conditions: (i) Ethyl chloroacetate, K CO , TBAB
(tetra butyl ammonium bromide), Acetone, reflux, 4 h. (ii)
selectively interacts with metal ions and show high ratiometric 85 Hydrazine hydrate, EtOH, reflux, 2 h. (iii) EtOH, reflux, 14 h.
2
3
signals. Though many ratiometric chemosensors are reported for
7
monovalent and divalent cations , surprisingly only a few are
The fluorometric behavior of NAQ is investigated upon addition
2
(b, c, e), 7(b, f)
+
+
2+
2+
2+
2+
known for detection of trivalent ions.
In continuation of our research work to develop fluorescence
of several metal ions such as Na , K , Mg , Ba , Ca , Zn ,
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
Cd , Hg , Pb , Co , Ni , Mn , Fe , Fe , Al and Cr in
sensor for biologically important substrates, herein we report a 90 CH CNꢀHEPES buffer solution (40/60, v/v, pH = 7.4). The
8
3
new naphthalimideꢀquinoline based probe (NAQ) for selective
detection of trivalent cations (Fe , Al and Cr ) based on ICT
emission spectrum of free NAQ (20 ꢁM) showed a strong band
with emission maxima positioned at 390 nm, upon excitation at
3
+
3+
3+
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obvious isoꢀemission point at 432 nm. This indicates a clear
3
42 nm. There was no other emission band at any wavelength
3
+
which indicates the absence of dual channel emission due to two
different fluorophores (Fig. 1).
ratiometric fluorescence response of the probe towards Fe . The
65 fluorescence intensity ratios of the receptor at 484 nm and 432
2
nm (I484/I432) increased linearly (R = 0.9822) with the amount of
3+
Fe in the range of 0 – 60 ꢁM (Fig. 3, Inset). From the
fluorescence titration experiments, the detection limit of the
5
+
+
2+
2+
2+
NAQ Na , K ,Ca ,Mg ,Ba
500
400
300
200
100
0
2+
2+
2+
2+
Fe , Co , Ni , Mn
3+
2
+
2+
2+
probe for Fe was evaluated and determined to be 20 ꢁM, using
Hg ,Pb ,Cd
7
0
the equation DL = K × Sb /S, where K = 3, Sb is the standard
1
1
3
+
deviation of the blank solution and S is the slope of the
Fe
11
calibration curve (see ESI).
10
2
+
3+
Zn
Al
600
500
2.5
75
R2 = 0.9822
2
Cu
+
2.0
1.5
1.0
0.5
3+
Cr
15
4
00
00
00
00
4
00 450 500 550 600 650
Wavelength (nm)
0.0
80
0
20
40
+] /
60
80
3
µM
3
[Fe
Fig. 1 Changes of emission spectra of NAQ (20 ꢁM) upon addition of
different metal ions (8 equivalents) in (CH CNꢀHEPES buffer, 40/ 60,
3
v/v) solution at pH = 7.4.
20
2
1
85
As shown in Fig. 1, the binding of trivalent ions to NAQ caused a
large redꢀshift (~94 nm) of emission spectra from 390 nm to 484
nm. Interestingly, the introduction of other common metal ions,
no obvious red shift was observed in the emission spectra,
revealed that this change was specific for trivalent cations only
0
25
30
35
400 450 500 550 600 650
Wavelength (nm)
9
9
0
5
(Fig. 1).
3+
Fig. 3 Fluorescence spectra of NAQ (20 ꢁM) upon titration with Fe (0
to 8 equivalents) in CH CNꢀHEPES buffer (40/ 60, v/v, pH = 7.4)
solution. λex = 342 nm. Inset: fluorescence intensity ratio (I484 / I432) as
3
4
3
2
1
0
3+
function of [Fe ].
3+
On increasing the concentration of Al (0 to 8 equivalents) to
solution of NAQ (20 ꢁM), we observed that the similar
quenching of fluorescence intensity at 390 nm and enhancement
3+
(
~12 fold) at 484 nm has occurred (Fig. 4). In case of Cr , the
1
00 quenching (at 390 nm) and enhancement (at 484 nm, ~4 fold) of
emission intensity was both minor, in the same experimental
3
+
condition (Fig. 5). Further increasing of the concentration of Fe
3+
3+
or Al or Cr did not lead to any enhancement of emission
intensity at 484 nm. The limit of detection of NAQ for Al and
05 Cr was determined from fluorescence titration data (23 ꢁM and
3
+
40
3+
1
2
5 ꢁM respectively) (see ESI).
Fig. 2 The plot of the sensing indexes (I484/I390) of NAQ (20 ꢁM) upon
addition of different metal ions (8 equivalents) in (CH
40/ 60, v/v) solution at pH = 7.4.
3
CNꢀHEPES buffer,
600
500
45
1
10
2
+
2+
Upon addition of Cu and Zn , the maximum quenching of
fluorescence intensity of NAQ has occurred. Other cations
showed a little effect (quenching emission intensity) on the
fluorescence spectra of NAQ. Severe quenching of the emission
of NAQ was due to the chelation enhanced fluorescence
4
00
00
3
50
55
60
1
0
115
200
quenching (CHEQ). The values of the sensing index (I484/I390
)
3+
3+
3+
for NAQ to Fe , Al and Cr are 3.8, 0.8 and 0.2 respectively,
whereas it is less than 0.05 for other metal ions (Fig. 2). It
indicates the receptor is highly sensitive toward trivalent ions
over other competing metal ions.
100
0
400 450 500 550 600 650
Wavelength (nm)
In order to better understand the sensing mechanism, absorption
and fluorescence experiments of NAQ (20 µM) were conducted
1
1
20
3
+
3+
3+
3+
with different concentrations of Fe , Al and Cr (0 – 8
Fig. 4 Fluorescence spectra of NAQ (20 ꢁM) upon titration with Al (0
to 8 equivalents) in CH CNꢀHEPES buffer (40/ 60, v/v, pH = 7.4)
solution. λex = 342 nm. Inset: Emission color changes of NAQ (20 ꢁM)
3+
equivalents) (Fig. 3). As shown in Fig. 2, the addition of Fe
elicited a gradual decrease at 390 nm and a simultaneous increase
~22 fold) in a new red shifted emission band at 484 nm with an
3
3
+
25 after addition of Al (80 ꢁM) under UV light.
(
2
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also by the naked eye experiment. In absence of trivalent cations,
600
500
400
300
200
3+
3+
3+
NAQ (20 ꢂM) showed blue emission, but M (Fe or Al or
3+
Cr ) (80 ꢂM) change its original blue emission to a bluishꢀgreen
emission under UV light, that facilitates its quick naked eye
detection (Scheme 2).
65
5
3+
Scheme 2: Probable binding mode of the receptor (NAQ) with Fe
1
0
100
0
400 450 500 550 600 650
Wavelength (nm)
UVꢀvis spectrum of the free receptor (20 ꢁM) is characterized by
1
2
5
0
7
7
8
0
5
0
a clear band centred at 338 nm in CH CNꢀHEPES buffer (40/ 60,
v/v, pH= 7.4) solution. Upon titration of NAQ (20 ꢁM) with Fe
3
3
+
Fig. 5 Fluorescence spectra of NAQ (20 ꢁM) upon titration with Cr (0
to 8 equivalents) in CH CNꢀHEPES buffer (40/ 60, v/v, pH = 7.4)
solution. λex = 342 nm. Inset: Emission color changes of NAQ (20 ꢁM)
3+
3
(0ꢀ 10 equivalents), the absorption maxima increase slightly with
3+
an isosbestic point at 240 nm which indicates formation of a new
after addition of Cr (80 ꢁM) under UV light
.
3
+
species (see ESI). UVꢀvis titration experiment of NAQ with Al
3+
and Cr were also performed. The absorption spectra were
characterized by two isosbestic points at 243 nm and 263 nm
respectively in each case, indicating the complex formation of
To utilize NAQ as a selective sensor for trivalent ions, the effect
3+
of competing metal ions was studied using 3 equivalents of Fe
and 10 equivalents of the interfering metal ions. As shown in Fig.
, no significant variation in the emission spectra at 484 nm was
observed by the addition of interfering metal ions, i.e. Fe can be
easily detected in presence of all of the competing metal ions by
means of its ratiometric response to NAQ. The competition
3+
3+
NAQ with Al and Cr (see ESI).
6
3+
Single crystals of the sensor (NAQ) suitable for Xꢀray
diffractometry were obtained by dissolving powder of the pure
2
5
compound in CHCl / MeOH (1:1) and slow evaporation of the
3
3
+
3+
solution free from vibrations. The perspective view of the
receptor (NAQ) with atom numbering scheme is shown in Fig.7.
experiments were also performed using Al and Cr and the
3
+
results were similar as Fe (see ESI). Thus it is concluded that
NAQ can be used as a selective fluorescence ratiometric sensor
for trivalent cations. Job’s plot of emission spectra obtained for
NAQꢀM (M = Fe , Al and Cr ) system clearly indicates the
formation of a 1:1 stoichiometry (see ESI).
3
0
3
+
3+
3+
3
4
4
5
0
5
85
Fig.7 A molecular view of NAQ in solid state with atom numbering
scheme.
Fig. 6 Metal ion selectivity profile of the receptor (20 ꢁM): (black bars)
n+
5
0
change of emission intensity of receptor + 10 equiv M ; (blue bars)
n+
change of emission intensity of receptor + 10 equiv M , followed by 3
3
+
equiv Fe at 484 nm.
Upon binding with trivalent ions, NAQ showed a new emission
3
+
5
5
band at 484 nm. The complex formation of NAQ with Fe or
90
3+
3+
Al or Cr modulated the ICT efficiency of the fluorophore and
thereby result the ratiometric change in fluorescence. The
Fig. 8 Crystal packing diagram of the receptor (NAQ).
3+
probable hostꢀguest complex formation of NAQ with Fe is
shown in scheme 2. Noteworthy, the ratiometric sensing process
Selected metrical parameters are given in Table 1 (see ESI). The
6
0
can readily be detected not only by fluorescence spectroscopy but 95 lattice is orthrhombic in nature with Pbca symmetry and the unit
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cell consists of eight molecules. The crystal packing diagram is
shown in Fig. 8. The plane containing three rings of
naphthalimide moiety makes a dihedral angle with quinoline
moiety of 78.56°. In NAQ, O1 and O2 atoms are in ‘trans’
position with respect to C10ꢀC11 bond whereas N3 and O2 atoms
are in ‘cis’ position with respect to N2ꢀC11 bond. The torsion
containing sensor and increasing concentrations of cations were
prepared separately. The spectra of these solutions were recorded
by means of fluorescence methods.
65
5
Methods for the preparation of the receptor
NAQ: A mixture of 1, 8ꢀnaphthalic anhydride (270 mg, 1.36
mmol) and 2 (300 mg, 1.38 mmol) in dry ethanol was stirred for
14 h at reflux. After evaporation of the solvent the residue was
angle between the O1ꢀC10ꢀC11 plane and C10ꢀC11ꢀO2 is
0
1
73.51(15) . The distance between H9 and O1 is 2.1Å, which
confirms the existence of intramolecular Hꢀbonding between H9 70 poured into ice water. Resulting precipitate was filtered and
10
and O1 in NAQ.
purified through silica gel column chromatography using 4%
methanol in chloroform (v/v) as eluent. (400 mg, 72%)
0
-1
[
1
m.p = >300 C (decomposed)]. IR (cm ): 822, 887, 1118, 1187,
Conclusions
1
234, 1377, 1497, 1589, 1687, 1728. H NMR (400 MHz,
In summary, we report here a new probe for selective recognition 75 CDCl ): δ 5.005 (s, 2H), 7.193 (d, 1H), 7.551 (m, 4H), 7.768 (t, J
3
of trivalent cations. It shows distinct ratiometric fluorescence
response towards trivalent cations only over other alkali and
HTM ions studied. This ratiometric fluorescence change can be
observed by naked eye also after illumination under the UV light.
It worked nicely in mixed solvent media and at a physiological
pH range.
= 7.64 Hz, 4H), 8.254 (d, J = 6.08 Hz, 2H), 8.645 (d, J = 7.32
Hz, 1H), 8.822 (s,1H). TOF MS (ESI, positive): calcd. for
+
15
C H N O [M ] (m/z): 397.38; found: 397.98.
2
3
15
3
4
80
Acknowledgements
Authors thank the CSIR and DST, Govt. of India for financial
supports. K.A, A.K.D, A.M and S.D acknowledge CSIR for
providing them fellowships.
20
25
30
35
40
Experimental
General methods
8
5
Notes and references
Chemicals and solvents used for the synthesis of the receptor
were purchased from SigmaꢀAldrich chemicals Private Limited
and used without further purification. Silica gel (100ꢀ200 mesh,
Merck) was used for column chromatography. Melting points
were determined on a hotꢀplate melting point apparatus in an
Department of Chemistry, Bengal Engg. and Science University, Shibpur,
Howrah-711 103, INDIA. Fax: +91 33 2668 2916; Tel:+91 33 2668
2961-3; E-mail: spgoswamical@yahoo.com
1
†Electronic Supplementary Information (ESI) available: [Job plot,
association constant determination, detection limit determination,metal
ion selectivity profile of NAQ, 1H NMR, ESI MS spectroscopy,
fluorescence titration spectra of the receptor with different metal ions,
openꢀmouth capillary and are uncorrected. HꢀNMR spectra was
recorded on JEOL, 400 MHz instrument. For NMR spectra,
90
CDCl was used as solvent using TMS as an internal standard.
3
1
1
1
3
+
3+
3+
Chemical shifts are expressed in δ units and H– H and H–C
coupling constants in Hz. UVꢀvis titration experiments was
performed on a JASCO UVꢀV530 spectrophotometer and
fluorescence experiment was done using PerkinElmer LS 55
fluorescence spectrophotometer using a fluorescence cell of 10
mm path. IR spectra were recorded on a JASCO FT/IRꢀ460 plus
spectrometer, using KBr discs. The Xꢀray data were collected
using a BrukerꢀAPEX II SMART CCD diffractometer with the
graphite monochromated MoꢀKα radiation (λ = 0.71073) at a
detector distance of 5 cm and with APEX2 software.
UV-vis titration spectra of NAQ with Fe , Al and Cr , X-ray data].
See DOI: 10.1039/b000000x/
95
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00 2. (a) A. BarbaꢀBon, A. M. Costero, S. Gil, M. Parra, J. Soto, R.
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General method of UV-vis and fluorescence titration:
By UV-vis method
105
4
5
For UVꢀvis titrations, stock solution of the receptor (20 ꢂM) was
prepared in [(acetonitrile / water), 40/60, v/v] (at 25°C) in HEPES
buffered solution. The solution of the guest cations using their
1
1
1
10
15
20
ꢀ
50
chloride and nitrate [Al (NO ) .9H O] salts in the order of 4 x 10
3
3
2
4
M, were prepared in deionized water using HEPES buffer at pH
7.4. Solutions of various concentrations containing sensor and
=
increasing concentrations of cations were prepared separately.
The spectra of these solutions were recorded by means of UVꢀvis
methods.
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in deionized water. Solutions of various concentrations
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