Fluorescent and chromogenic receptor bearing amine and hydroxyl functionality for iron (III) detection in aqueous solution

Article abstract of DOI:10.1007/s10895-014-1358-3

The noncyclic 2,2′-[ethane-1,2-diylbis (iminomethanediyl)]diphenol (4) fluorescent receptor bearing two amine and hydroxyl groups have been designed and investigated for their binding properties towards various cations. The fluorescent spectral measuremen

Full text of DOI:10.1007/s10895-014-1358-3

J Fluoresc
DOI 10.1007/s10895-014-1358-3
SHORT COMMUNICATION
Fluorescent and Chromogenic Receptor Bearing
Amine and Hydroxyl Functionality for Iron (III) Detection
in Aqueous Solution
Umesh Fegade & Shivaji Tayade & G. Krishna Chaitanya &
Sanjay Attarde & Anil Kuwar
Received: 18 October 2013 /Accepted: 28 January 2014
#
Springer Science+Business Media New York 2014
Abstract The noncyclic 2,2′-[ethane-1,2-diylbis
iminomethanediyl)]diphenol (4) fluorescent receptor bearing
the field of supramolecular chemistry [1–4]. Detection of
heavy metal ions is important due to its involvement in many
biological processes as well as toxic and known as environ-
mental pollutants [5, 6]. Recently, many of cation receptors
has been designed and synthesized. Many signals, such as
redox potential changes [7], UV–Vis spectral changes [8],
color changes [9, 10] and emission fluorescence changes
[11, 12] have been developed in different methods. Among
these methods, much effort has been made in colour changes
and emission fluorescent changes because they can be easily
observed by ‘naked eye’.
(
two amine and hydroxyl groups have been designed and
investigated for their binding properties towards various cat-
ions. The fluorescent spectral measurements revealed that
3
+
receptor 4 is a selective fluorescent sensor for Fe ions but
3
+
2+
2+
2+
2+
2+
not for metal ions such as Cr , Mn , Co , Ni , Cu , Zn ,
2
+
2+
2+
3+
Cd , Hg , Pb and Bi . The binding ability was confirmed
with spectroscopic methods and density functional theory
calculation (DFT). This straightforward and cost effective
receptor provides rapid detection of Fe ions at concentra-
tions as low as 2.5 μM and expected to be useful to design
efficient chemically and biological sensor.
3
+
Transition metal plays an important role in biology and
chemistry. Among various transition metals, iron is the most
abundant essential trace element in the human body which
plays vital roles in many biological processes [13–15]. In
well-cultivated people the total iron content is about 4 g. Iron
is essential in living systems since it is the oxygen carrier in all
tissues in the form of hemoglobin and assists to transport
electrons as cytochromes. Deficiency of iron in primary stages
can cause anemia [16–20], which can harm or even kill by
depriving organs. Encouraged with this interesting report we
.
.
Keywords Fluorescence receptor Cation sensing
.
Association constant DFT
Introduction
In recent year the development of fluorescent probe for the
detection of heavy metal ions is the important research area in
3
+
have tried to propose a Fe sensor using a distinctive reaction.
Herein, we report a convenient and efficient route for the
preparation of noncyclic receptor i.e. 2,2′-[ethane-1,2-
diylbis(iminomethanediyl)]diphenol (4) and its new applica-
tion as a cation sensor. Synthesized receptor 4 provides two
amine and two hydroxyl functional groups for cation binding.
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-014-1358-3) contains supplementary material,
which is available to authorized users.
:
:
U. Fegade S. Tayade A. Kuwar (*)
School of Chemical Sciences, North Maharashtra University,
Jalgaon 425001, MS, India
e-mail: kuwaras@gmail.com
Experimental Detail
:
U. Fegade S. Attarde
School of Environmental & Earth Sciences, North Maharashtra
University, Jalgaon 425001, MS, India
Reagents and Apparatus
All commercial grade chemicals and solvents were used with-
out further purification. H NMR spectra were recorded on a
Varian NMR mercury System 300 spectrometer operating at
G. K. Chaitanya
School of Chemical Sciences, Swami Ramanand Teerth
Marathawada University, Nanded 431 606, MS, India
1

J Fluoresc
H
Scheme 1 Synthesis of
,2′-[ethane-1,2-diylbis
iminomethanediyl)]diphenol (4);
a CH OH, 30 min and b NaBH4,
THF/CH OH 70:30 v/v, 0–5 °C,
and 90 min
2
(
O
N
N
3
a
2
3
H N
2
NH2
OH
OH
HO
1
2
3
4
b
NH
HN
OH
HO
3
00 MHz in CDCl with Me Si (TMS) as an internal standard.
with CH OH/H O (60:40, v/v) solution and the corresponding
3 2
3
4
−3
The Fluorescence and UV-Visible spectra were recorded on
Fluoromax-4 Spectrofluorometer and Shimadzu UV-24500
with 5 nm slit of fluorescence. The metal nitrate salts used
for cations binding study. Ultrapure water with a Millipore
Purification System (Milli-Q water) was used throughout the
analytical experiments.
working solutions (c=1×10 M) were simply prepared by
diluting with CH OH/H O (60:40, v/v).
3
2
Fluorescence Study
The fluorescence titration experiments were carried out with a
Fluoromax-4 spectrofluorometer in CH OH/H O solvent sys-
3
2
Sample Preparation
tem at room temperatures (298 K) with the aim of determining
the association constant (K) for receptor 4–cation in this
solvent system. These titration experiments were accom-
plished through a stepwise addition of metal salt solutions
A stock solution of probe 4 (c=1×10−3 M) in CH OH/H O
3
2
(
60:40,v/v) solution was prepared (probe 4 is freely soluble in
−3
CH OH at 25 °C), and the corresponding working solutions(c
(0.03 ml, 1×10 M, guest) to a solution of receptor 4 (2 ml,
3
−4
−4
=
1×10 M) were simply prepared by diluting with CH OH/
1×10 M) in CH OH/H O (60:40, v/v) in the cell. The
3
3
2
H O (60:40,v/v). All stock and working solution were pre-
2
fluorescence intensity was recorded at λ /λem=272/307 nm
ex
pared in ultrapure water and spectroscopic grade methanol.
Stock solution of all cations (c=1×10 M) were prepared
alongside a reagent blank. The excitation and emission slits
were both set to 5 nm. This was followed by a 5 min interval
−2
Fig. 1 Fluorescent intensity (λex
272 nm) of probe 4 upon the
addition of a particular metal salt
in CH OH/H O (60:40, v/v)
9.00E+06
8.00E+06
Host
Cr(III)
Fe(III)
Ni(II)
Zn(II)
Hg(II)
Bi(III)
K(I)
=
Mn(II)
Co(II)
Cu(II)
Cd(II)
Pb(II)
Na(I)
Ca(II)
3
2
7
6
5
4
3
2
1
0
.00E+06
.00E+06
.00E+06
.00E+06
.00E+06
.00E+06
.00E+06
.00E+00
Fe (II)
2
80
300
320
340
360
380
400
Wavelength (nm)

J Fluoresc
Fig. 2 a Fluorescence ratiometric
a 0.9
0.8
response (I-I
4
0
/I
0
) of probe
(c=1×10− M) upon the
addition of a particular metal salt
4
0
0
.7
.6
-3
(
c=1×10 M) in CH
3 2
OH/H O
(
60:40, v/v). b Recognition of
3+
0.5
0.4
Fe ion by receptor 4 in the
presence of other metal ion
0
0
0
0
.3
.2
.1
.0
Metal Ions
b 7.00E+06
Competing Ion
Competing Ion + Fe Ion
6
5
4
3
2
1
0
.00E+06
.00E+06
.00E+06
.00E+06
.00E+06
.00E+06
.00E+00
Metal Ions
(
in which the reaction cell was left under continuous stirring to
benzaldehyde (0.24 g, 2 mM) in ethanol (50 mL) with stirring
for 30 min [21]. Compound 3 was obtained with good yield
and appears as a yellow crystalline powder with 88 % yield,
mp >250 °C. Further receptor 4 was obtained from compound
ensure mixing). Then, the fluorescence data were collected
and processed using the Hyper quad program to calculate the
association constant (K) of the appropriate cation complexes.
3
by reduction under NaBH in CH OH with good yield. 85 %,
4 3
1
Sysnthesis of Receptor 4
m.p. 124–126 °C, H NMR (300 MHz, CDCl
, ppm) : δ=2.83
3
(
s, 4H, 2CH ), 3.99 (s, 4H, 2Ar, CH ), 6.76–6.84 (m, 4H, 2Ar-
2
2
Compound 3 was synthesized by stirring one mole 1,2-di-
amine ethane (0.06 g, 1 mM) with two moles of 2-hydroxy
H), 6.96–6.98 (d, J=6.6 Hz, 2H, 2Ar-H),7.15–7.20 (m, 2H,
2ArH); IR (KBr): υ=620, 722, 760,795, 859, 964, 1,100,
Fig. 3 Fluorescence spectrum of
7.00E+06
6.00E+06
5.00E+06
−4
probe 4 (c=1×103 M) after
+
the addition of Fe salt of
3
(
(
c=1×10− M) in CH
3 2
OH/H O
60:40, v/v)
4
3
2
1
0
.00E+06
.00E+06
.00E+06
.00E+06
.00E+00
2
80
300
320
340
360
380
400
Wavelength (nm)

J Fluoresc
Fig. 4 Normalized response of
y = 0.6908x - 2E+06
R² = 0.982
-
1.69E+06
fluorescence signal to changing
3+
-1.69E+06
-1.69E+06
Fe concentrations in the
CH OH/H O (60:40, v/v)
3
2
solution.(receptor 4,
-
-
-
-
-
-
1.69E+06
1.69E+06
1.69E+06
1.69E+06
1.69E+06
1.69E+06
c=1×10− M and Fe salt
4
3+
of c=1×10− M)
3
-
5.00
-4.80
-4.60
-4.40
-4.20
-4.00
-3.80
Log G
Fig. 5 1:1 Stoichiometry of the
host guest relationship realised
from the Job’s plot between
0.00016
0
0
0
0
0
0
0
0
.00014
.00012
.00010
.00008
.00006
.00004
.00002
.00000
3+
receptor 4 and Fe
0
0.2
0.4
0.6
0.8
1
[H]/[H]+[G]
Fig. 6 Benesi-Hildebrand
1.00E-05
Plot (adjusted equation:
1
/F-F
0
=−1.0E-10x+1E-06 1/[G],
R=0.982) and the K value for
Fe at 10,000 M
0
.00E+00
1.00E-05
2.00E-05
3.00E-05
3+
−1
-
-
-
0.00E+00
5.00E+04
1.00E+05
1.50E+05
2.00E+05
2.50E+05
1/G

J Fluoresc
Fig. 7 Absorbance spectrum of
1
.4
−4
probe 4 (c=1×103 M) upon
Host
+
1.2
1
the addition of Fe metal
Host + Fe
3
(
(
c=1×10− M) in CH
3 2
OH/H O
60:40, v/v)
0
0
0
0
.8
.6
.4
.2
0
2
50
270
290
310
330
350
370
390
410
430
450
Wavelength (nm)
−
1
+
1
,589, 1,615, 2,923, 3,275, 3,439 cm ; MS (M+H ):
Fluorescence Studies of Receptors 4
C H N O requires 272.152 found 273.30.
16 20 2 2
The responses of receptor 4 towards various cations were
monitored in CH OH/H O (60:40, v/v) using fluorescence
3
+
3
2
Synthesis of 4.Fe Complex
spectroscopic response. Figure 1 illustrates the change in
fluorescence of 4 after addition of cation salts containing
CH OH/H O (60:40, v/v). It exhibit emission with the emis-
3
+
Fe complex of receptor 4 was synthesized by reaction of one
mole of receptor 4 (0.54 g, 2 mM) with one mole of FeCl3
0.32 g, 2 mM) in CH OH (50 mL) stirring for 3 h. The
3
precipitation was collected at room temperature and dried in
vacuum. Further it was washed with water then ethanol
followed by petroleum ether. Yield- 88 %, IR (KBr, cm ) υ
3
2
sion maximum at 307 nm when they are excited at 272 nm. It
is well understood from Fig. 1 that receptor are highly sensi-
(
3
+
tive and selective towards Fe ion by exhibiting different
−1
modes of emission. The fluorescence emission of receptor 4
3
+
−1
was quenched effectively upon addition of 1 equiv. Fe ions
Fig. 1). To account for such fluorescence quenching, the PET
=
662, 767, 846, 1,111, 1,598, 2,924, 3,163 cm . MS (ESI):
m/z requires C H FeN O : 326.17, found 327.30.
(
1
6
18
2 2
mechanism was exploited. As we all knew, the fluorescence of
the cations PET chemosensor generally was ‘switches off’
rather than ‘switch on’ upon ion sensing unlike most PET
sensors for anions. In the case of the receptor 4, the excited
state of the fluorophore was not, or only to a small amount,
quenched by electron transfer (ET) from the receptor 4 to the
fluorophore prior to the sensor-cation interactions. However,
upon interaction with cations, the reduction potential of the
receptor 4 was increased and in other words, the electron
transfer from the electron rich amine and hydroxyl moiety
Result and Discussion
Synthesis of Receptor 4
Compound 3 was synthesized by reacting one mole of 1,2-
diamine ethane with two moles of 2-hydroxy benzaldehyde in
methanol by stirring for 30 min. Ligand 3 was obtained with
good yield and having yellow crystals. Receptor 4 was ob-
tained from compound 3 by reduction with NaBH with good
yield (Scheme 1). The colorless compound 4 obtained was
3
+
bonded with cation (Fe ion) became more realistic. Upon
3
+
4
further addition of Fe ion, it appeared that the deprotonated
species of receptor 4 (NH and OH functional group), being
more electron rich compared to the coordination complex with
purified by recrystallization from methanol and characterized
1
3
+
by IR, H NMR and mass spectroscopy (S1-2, Supporting
Fe ion, activated the PET process more efficiently and
showed up a greater quenching.
Information). The spectral data found to be consistent with its
structure.
Table 1 An optimized energy value calculated at B3LYP/6-31G(d)/
LanL2DZ level, bond lengths and bond angles related to noncovalent
3
+
bonds between 4 and 4.Fe ion based on optimized geometries
3+
Bond angle/length
4.Fe
Fe-O1
Fe-O2
Fe-N1
Fe-N2
1.881 Å
1.954 Å
1.978 Å
1.979 Å
3+
Fig. 8 The DFT optimized geometrical parameters of 4.Fe complex

J Fluoresc
Fig. 9 The frontier molecular
orbitals HOMO and LUMO of
3+
4
.Fe
HOMO= -4.52 eV
LUMO= -0.74 eV
3
+
To study the influence of other metal ions on Fe binding
with receptor 4, we performed competitive experiments with
UV–Vis Absorption Spectral Studies
3
+
3+
other metal ions in the presence of Fe (Fig. 2a and b). The
observed fluorescence enhancement for mixtures of Fe with
most metal ions was similar to that seen for Fe alone. No
other metal ions appeared to interfere with the fluorescence of
the receptor 4 and Fe . The interference studies have shown
that the interference of other metal ions in Fe detection was
moderately low. Available data may be helpful for the re-
searcher to develop the new applications of receptor 4 in
separation science, biological and analytical chemistry.
Figure 3 shows the emission fluorescence spectra of recep-
The absorption spectrum of receptor 4 with Fe is shown in
Fig. 7. Receptor 4 exhibit max peak at 240 and 272 nm in
CH OH/H O (60:40, v/v) solution together with a swelling at
3
+
3
+
3
2
240 nm and a shoulder at 260 nm. The longer wavelength
band at 272 nm and shoulder at 310 nm may be assigned to
transitions associated with phenol ring. Figure 7 clearly show
3
+
3
+
3
+
new peak appear at 335 nm after addition Fe .
Proposed Binding Mode and Mechanism of Sensing
3
+
tor 4 on addition of Fe ion on the various concentrations.
When exciting at 272 nm the emission fluorescence intensity
of probe 4 at 307 nm quench more than 7 fold for cation Fe . A
The density functional theory (DFT) study was conducted by
using Gaussian 09 program in an attempt to better understand
the nature of receptor 4 and its interaction with Fe ion. The
3
3+
satisfactory linear relationship between concentrations was
observed with the fluorescence intensity and correlation coef-
ficient is high. Normalized response of fluorescence signal to
changing concentrations cation in the CH OH/H O (60:40,
hybrid level exchange correlation functional B3LYP was
employed with 6-31G (d) basis set on main group elements
and LanL2DZ for metal ions [24–26]. The optimized geom-
etry has been further used for analytical frequencies to ensure
that the optimized geometry is global minima on the potential
energy surface. In order to reduce the stress from steric
crowding, two arms held in different direction as are shown
in Fig. 8 it was observed that the oxygen and nitrogen atoms of
hydroxyl and amine groups constitute the pseudo cavity for
3
2
v/v) solution shown in Fig. 4. Under optimal conditions, the
3
+
limit of detection for Fe ion is 2.5 μM.
Stoichiometry and Binding Constant of Receptor 4
3
+
metal ion coordination. On coordination of Fe ion, there is
increase in the stability of the whole system which was con-
firmed from geometry parameters depicted in Table 1. Further
from the frontier molecular orbital pictures (Fig. 9) HOMO
and LUMO it is found that the strong interaction between
metal and ligand and LUMO is main contributor in electronic
transition.
3
+
The binding stoichiometry between receptor 4 and Fe ion
was determined by the continuous variation method [22]. The
results indicate the formation of a 1:1 adduct (Fig. 5). IR
spectrum of free receptor 4 exhibits a broad band at
1
3
,439 cm− which can be assigned for OH group on the ring.
On complexation two deprotonation of OH group took place
and OH functional group was disappeared (Figure S3-4, SI).
Similarly, furthermore, we have confirmed these trends by
mass spectroscopic data. MALDI/TOF–MS data showed the
formation 1:1 complex between two deprotonated ligand (re-
Conclusion
3
+
ceptor 4) and Fe ion [(MS (ESI): m/z requires (Calculated)
C H FeN O : 326.17, found 327.30 (Figure S5, SI). All
In conclusion, we have synthesized the selective and sensitive
fluorescent chemical sensor i.e. 2,2′-[ethane-1,2-
diylbis(iminomethanediyl)]diphenol (4) for the detection of
1
6
18
2 2
attempts was failed to grow the single crystal of receptor
3
+
3+
3+
4
.Fe ion complex. The association constant of Fe ion
Fe in CH OH/H O (60:40, v/v) medium. The detection of
3
2
3
+
was calculated from fluorescence titration experiments by
Fe gave rise to major colorimetric colour change, which can
be easily detected by the naked eye. Furthermore, our sensor is
not affected by the common interference of other ions like
−
1
Benesi– Hildebrand plot [23] and found as 10,000 M for
3
+
Fe (Fig. 6).

J Fluoresc
3
+
2+
2+
2+
2+
2+
2+
2+
3+
1
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