Supramolecular chemosensor for selective detection of iron in aqueous medium

Article abstract of DOI:10.1080/10610278.2013.804186

We have successfully developed a 'turn-on' colorimetric chemosensor for Fe³⁺ based on 1,10-phenanthroline. An amide derivative of 1,10-phenanthroline 4 was developed for the selective recognition of Fe ³⁺ over Co²⁺, Cr³⁺, Cu²⁺, Mn ²⁺, Ni²⁺, Ag⁺ and Zn²⁺ and could measure Fe³⁺ concentration in the range of 15-210 μM by UV-vis spectroscopy. Moreover, the addition of Fe³⁺ to a colourless solution of 4 turned its colour to light pink, indicating that 4 is capable of detecting Fe³⁺ by the naked eye. Compound 4 exhibits a major absorption band centred at 268 which shifted to 278 nm after addition of Fe³⁺, and a shoulder band around 514 nm was also observed. The complexation of Fe ³⁺ with 4 was analysed at a different pH and favourable binding was observed at pH 6.2.

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Supramolecular Chemistry
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Supramolecular chemosensor for selective detection of
iron in aqueous medium
Said Nadeemab, Muhammad Raza Shaha, Burhan Khana, Numan Hodab & Önder Topelb
a H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological
Sciences, University of Karachi, Karachi-75270, Pakistan
b Department of Chemistry, Akdeniz University, 07058, Antalya, Turkey
Published online: 19 Jun 2013.
To cite this article: Said Nadeem, Muhammad Raza Shah, Burhan Khan, Numan Hoda & Önder Topel (2013) Supramolecular
chemosensor for selective detection of iron in aqueous medium, Supramolecular Chemistry, 25:12, 798-805, DOI:
10.1080/10610278.2013.804186
To link to this article: http://dx.doi.org/10.1080/10610278.2013.804186
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Supramolecular Chemistry, 2013
Vol. 25, No. 12, 798–805, http://dx.doi.org/10.1080/10610278.2013.804186
Supramolecular chemosensor for selective detection of iron in aqueous medium
a
a
b
b
Said Nadeema,b, Muhammad Raza Shah *, Burhan Khan , Numan Hoda and Onder Topel
¨
aH.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-
75270, Pakistan; Department of Chemistry, Akdeniz University, 07058 Antalya, Turkey
b
(Received 11 April 2013; final version received 6 May 2013)
We have successfully developed a ‘turn-on’ colorimetric chemosensor for Fe3þ based on 1,10-phenanthroline. An amide
derivative of 1,10-phenanthroline 4 was developed for the selective recognition of Fe3þ over Co2þ, Cr3þ, Cu2þ, Mn2þ, Ni2þ
,
Agþ and Zn2þ and could measure Fe3þ concentration in the range of 15–210 mM by UV–vis spectroscopy. Moreover, the
addition of Fe3þ to a colourless solution of 4 turned its colour to light pink, indicating that 4 is capable of detecting Fe3þ by
the naked eye. Compound 4 exhibits a major absorption band centred at 268 which shifted to 278 nm after addition of Fe3þ
and a shoulder band around 514 nm was also observed. The complexation of Fe3þ with 4 was analysed at a different pH and
favourable binding was observed at pH 6.2.
,
Keywords: chemosensor; 1,10-phenanthroline; Fe3þ complex
Introduction
quenching (16–19). The Fe3+ induces quenching of
fluorescence in most chemosensors, which is believed to
be associated to its paramagnetic properties, so the design
of colorimetric sensor for detection of Fe3+ remains an
attractive area to add further additions to the field of
chemosensors. Here, we present 1,10-phenanthroline-
based colorimetric sensors which can provide a practical
solution to this problem. The receptor 4 selectively binds
Fe3þ by changing from colourless to yellow in ethanol and
in the mixture of 1:1 (v/v) ethanol/water.
The simplest definition of a sensor is that ‘a substance
which sense something’, i.e. receives information and
transforms it into a form compatible with our perception,
knowledge and understanding. Supramolecular sensors are
promising candidates for the realisation of innovative
materials for information technology (1).
The design and synthesis of supramolecules for the
detection of biologically important metal ions, such as
Fe3þ, is an important subject in the field of supramolecular
chemistry. Iron is the most abundant metal ion found in
the human body and is critically important for various
biochemical processes such as oxygen transport (2),
electron transport (3) and oxidoreductase catalysis (4). It
is a well-established fact that the deficiency of iron in the
human body can lead to anaemia (5), liver and kidney
damages (6), diabetes (7) and heart diseases (8). Similarly,
excessive presence of iron in the body can also cause
oxidative damage to tissue and fibrosis in various organs
(9). So the detection, monitoring and regulation of iron
are of pivotal importance. A number of sophisticated
techniques including atomic absorption spectrometry,
inductively coupled plasma mass spectroscopy (10),
inductively coupled plasma-atomic emission spectrometry
(11) and voltammetry (12) have been developed for the
detection of iron, but these techniques require expensive
equipments and are not easily employed in on-site analysis.
The development of selective and sensitive sensors for the
detection of iron has attracted the attention of scientists
recently (13–15). Most of the reported fluorescent Fe3þ
chemosensors operate on the principle of fluorescence
Results and discussion
Synthesis
Amine 2 was synthesised according to the literature
procedure (20) and reacted with 2,2-diphenylacetyl
chloride 3 in the presence of triethylamine in dichlor-
omethane (DCM), and the reaction mixture was stirred at
room temperature for 3 h as shown in Scheme 1.
The structure of ligand 4 was established on the basis
of NMR and EI-MS. The fragmentation pattern in the EI-
MS was well defined and the calculated molecular weight
was in good correlation with the experimentally obtained
molecular weight, i.e. 389.15.
UV–vis studies
The UV–vis spectra of compound 4 N-(1,10-Phenanthro-
lin-5-yl)-2,2-diphenylacetamide (PHMD) were obtained
in ethanol and in ethanol þ water 1:1 mixture with a
concentration of 30 mM. In both cases, a lmax of 268 nm
*Corresponding author. Email: raza.shah@iccs.edu
q 2013 Taylor & Francis

Supramolecular Chemistry
799
N
N
N
N
N
H2SO4, HNO3
reflux, 3h
Pd/C, hydrazine
Ethanol, 10h
70˚C
O2N
N
H2N
2
1
N
N
2
O
dichloromethane
N
H
Cl
triethylamine
rt, 3h
O
3
4
Scheme 1. Synthesis of ligand 4 from 1,10-phenanthroline.
was observed and the region between 800 and 350 nm was
blank as shown in Figure 1.
A broad peak was observed in the UV–vis spectrum at
514 nm of ligand 4 in the presence of Fe3þ while no such
kind of additional peak was found in case of the reaction
mixture of 4 with the rest of the metals. The baseline for
the absorption spectrum recorded in the presence of Ag(II)
is a bit high, which was probably the consequence of the
turbidity observed in solution during the mixing of Ag(II).
Similarly, the spectrum recorded in the presence of Cu(II)
shows a broad absorption band which might also be
associated with slight turbidity that occurred while mixing
Cu(II) in reaction mixture.
Ligand PHMD was screened with different metals, i.e.
Co2þ, Cr3þ, Cu2þ, Fe3þ, Mn2þ, Ni2þ, Agþ and Zn2þ with
the help of UV–vis spectroscopy. The 30 mM solutions of
metals were mixed with ligand 4 in a 1:1 ratio and stirred
for 30 min. The reaction mixture of 4 with Fe3þ became
pinkish while the reaction mixture of 4 with other metals
remained colourless as shown in Figure 2.
All the metal solutions with ligand 4 were analysed
through UV–vis spectroscopy as shown in Figure 3.
Figure 1. UV–vis spectra of ligand PHMD in ethanol and ethanol þ H2O mixture (1:1).

800
S. Nadeem et al.
Figure 2. Optical detection of compound 4 with different metals.
pH study
formation of iron hydroxide seems to be higher than the
interaction of 4 with Fe3þ, which consequently causes a
decrease in the absorption.
The effect of pH on the interaction of receptor 4 with Fe3þ
ions is investigated. The pH values were adjusted by the
addition of diluted NaOH or HCl. The mixtures were stirred
at room temperature in 1:1 (v/v) water and ethanol mixture
for 30 min. Different intensities of pink colour were
observed in the acidic conditions, whereas the mixtures
remained colourless in the basic pH, as shown in Figure 4.
It is evident from Figure 5 that when the pH was
increased from 3 to 6, the value of absorbance increases,
but at pH values above than 6.2, the response decreases. In
acidic pH, the proton is absorbed from the acidic media by
a lone pair of electrons of nitrogen, hence decreasing the
probability of interaction. In pH . 6, the possibility of
Concentration study and limit of detection
Spectral titrations of 4 with Fe3þ were carried out to get
further insight into the interactions at different concen-
trations by keeping the concentration of 4 constant and
Fe3þ variable and vice versa in 2-(N-morpholino)
ethanesulfonic acid (MES) buffer.
For this purpose, 30 mM solution of ligand 4 was
titrated against nine different concentrations of Fe3þ (i.e.
0.72, 1.45, 2.89, 6, 12, 18, 24, 30 and 60 mM) at room
0.2
0.175
0.15
0.125
0.1
PHMD
Ag(II)
Co(II)
Cr(III)
Cu(II)
Fe(III)
Mn(II)
Ni(II)
Zn(II)
0.075
0.05
0.025
0
250
300
350
400
450
500
550
600
Wavelength (nm)
Figure 3. UV–vis spectra of different metals in the presence of phenamide-1 (30 mM, 1:1 equiv.).

Supramolecular Chemistry
801
Figure 4. Fe3þ with ligand 4 complex formation at different pH values.
concentration of ligand 4 was varied from 15 to 210 mM.
After stirring the reaction mixture of ligand 4 and Fe3þ at
room temperature for 10 min, the UV–vis spectra were
recorded in the range of 800–200 nm as shown in Figure 8.
Characteristic lmax values at 207 and 268 nm in the UV–
vis spectrawereobserved for Fe3þ and ligand4, respectively,
while the area between 350 and 800 nm remained blank.
After mixing with 15mM (half concentration of the metal) of
ligand 4, the lmax of ligand shifted from 268 to 278 nm and
another small peak at 252 nm was observed while the peak of
complex at 514 nm was also observed.
Concentration study of ligand 4 and calculation of
The UV–vis spectra of ligand 4 at different concentrations
were obtained in the range of 15–210 mM as shown in
Figure 9.
Figure 5. Fe3þ with 4 complex formation at different pH values
(A recorded at 514 nm).
Beer–Lambert law as shown in Equation (1) was used
to calculate the molar absorptivity (i.e. 1) for different
concentrations of metal ions and ligand (Table 1):
temperature and constant pH (i.e. 6.2) for 10 min. The
UV–vis spectrum at a range of 800–200 nm of compound
4 (blank) at pH 6.2 was plotted against the UV–vis spectra
of mixture of 4 with Fe3þ, which was obtained at different
concentrations of Fe3þ as shown in Figure 6.
A ¼ 1bc:
ð1Þ
The straight line equation was used to plot absorbance
(A) against concentration and a straight line was obtained
as shown in Figure 10.
The region at 400–600 nm in the spectrum of ligand 4
was blank, but a new peak at 514 nm appeared in the
spectrum when compound 4 was titrated against different
concentrations of Fe3þ. In the presence of various
concentrations of Fe3þ ranging from 0.72 to 60 mM,
significant changes in the absorption spectrum were
observed. The peak at 514 nm was highest at 18 mM and
started to decrease at 24, 30 and 60 mM concentrations as
shown in Figure 7.
The limit of detection of Fe3þ with 30 mM ligand was
found to be at a concentration of 0.72 mM by revealing a
slight upward peak at 514 nm in the UV–vis spectrum.
In another approach, the concentration and pH of Fe3þ
were kept constant (30 mM; 6.2) during the titration and the
Experimental
Preparation of solutions
One millimolar stock solution of ligand 4 and of nitrates of
Co2þ, Cr3þ, Cu2þ, Fe3þ, Mn2þ, Ni2þ, Agþ and Zn2þ were
prepared in ethanol. Thirty micromolar dilute solution of
metal ions and ligand from the stock solution was prepared
with ethanol or ethanol þ water 1:1 (v/v) mixture.
UV–vis study
UV–vis spectra were obtained by using PerkinElmer’s
LAMBDA 35 UV/Vis Systems spectrophotometer in the

802
S. Nadeem et al.
Figure 6. Concentration study of Fe3þ against ligand PHMD.
range 800–200 nm. Thirty micromolar solution of ligand 4
was stirred with different metal ions (30mM) for 10min
(otherwise stated in the discussion) and spectra were
obtained. Differentconcentrations ofFe3þ (6–500 mM)with
30mM of 4 and different concentrations of 4 (15–180 mM)
with 30mM of Fe3þ were stirred and analysed through UV–
vis spectroscopy. Similarly UV–vis spectra of 4 were
obtained at different concentrations (15–210 mM) which
were then compared with the mixture spectra of Fe3þ with
different concentrations of compound 4.
Synthesis
5-Nitro-1,10-phenanthroline
In an ice-cooled solution of 5.0 g (27.8 mmol) 1,10-
phenanthroline, 30 ml concentrated sulphuric acid was
added. Fifteen millilitres of fuming nitric acid were then
added dropwise while keeping the temperature at 08C. The
reaction mixture was then stirred at 1508C for 3 h and
subsequently poured into 200-ml ice-cold distilled water.
Subsequently the pH was brought to 3 by the slow addition
of the concentrated solution of NaOH. The precipitate of
5-nitro-1,10-phenanthroline was filtered off, washed with
water and brownish precipitates were formed, which were
filtered and dried in vacuum. The filtrate was further
extracted with chloroform to extract the residual traces of
compound. The compound was obtained in 6.12 g, 90%
1
yield. H NMR (400 MHz, CDCl3) d (ppm) 9.37 (d, 1H,
J ¼ 4.0 Hz), 9.31 (d, 1H, J ¼ 4.0 Hz), 9.05 (d, 1H,
J ¼ 8.8 Hz), 8.70 (s, 1H), 8.45 (d, 1H, J ¼ 8.4 Hz), 7.79–
7.85 (m, 2H); 13C NMR (100 MHz, CDCl3): d 153.7,
151.8, 147.3, 145.9, 143.9, 137.9, 132.7, 125.6, 125.5,
124.5, 124.4, 121.1. ESI-MS: [(M þ H)þ] Calcd
m/z ¼ 226.0611; found m/z ¼ 226.0058.
5-Amino-1,10-phenanthroline
Five grams (22.2 mmol) of 5-nitro-1,10-phenanthroline
were dissolved in 100 ml of absolute ethanol. Ten mole
per cent of Pd/C, i.e. 1 g, was added as a catalyst. The
reaction assembly was purged with argon, and then 13 ml
Figure 7. Absorbance at 514 nm with changing concentration of
Fe3þ(0.72–60 mM) against ligand 4 (30 mM).

Supramolecular Chemistry
803
Figure 8. Concentration study of ligand 4 (15–180 mM) with 30 mM of Fe3þ
.
(26.7 mmol) hydrazine monohydrate was added dropwise
over a period of 30 min. The mixture was stirred for 10 h at
708C. After the completion of reaction, the mixture was hot
filtered to remove the catalyst, and the filtrate was dried
over Na2SO4 and concentrated by using rotary evaporator
and then dried. A 2.1 g of yellow solid was obtained with
47% yield. ESI-MS: [M þ H]þ Calcd m/z ¼ 196.0869;
found m/z ¼ 196.1309. m.p.: 256–2588C. 1H NMR
Figure 9. Concentration study of phenamide-1 (15–210 mM).

804
S. Nadeem et al.
Table 1. Calculation of 1 value for ligand 4.
DMSO-d6) ppm: 10.72 (s, 1H), 9.10 (dd, 1H, 4J ¼ 1.51 Hz,
3J ¼ 4.27 Hz), 9.02 (dd, 1H, 4J ¼ 1.76 Hz, 3J ¼ 4.27 Hz),
8.54 (dd, 1H, 4J ¼ 1.51 Hz, 3J ¼ 8.53 Hz), 8.56 (dd, 1H,
4J ¼ 1.63 Hz, 3J ¼ 8.16 Hz), 8.25 (s, 1H), 7.77 (dd, 1H,
4J ¼ 4.27 Hz, 3J ¼ 8.28 Hz), 7.72 (dd, 1H, 4J ¼ 4.27 Hz,
3J ¼ 8.28 Hz), 7.44–7.60 (m, 4H), 7.34–7.44 (m, 4H),
7.24–7.34 (m, 2H), 5.56 (s, 1H); 13C NMR (400 MHz
DMSO-d6 ppm): 171.15, 149.84, 149.39, 145.76, 143.92,
139.92, 135.91, 131.32, 131.26, 128.58, 128.41, 126.69,
124.58, 123.57, 122.82, 120.43, 56.85. Fluorescent data
(nm): Ex max ¼ 347.24, Em max ¼ 471.28.
Serial no.
C (M)
A
1ort. (cm21 M21
)
1
2
3
4
5
6
7
8
15
30
60
90
120
150
180
210
0.25
0.51
1.01
1.47
1.93
2.34
16,667
17,000
16,833
16,333
16,083
15,600
15,000
14,238
15,969
2.70
2.99
1
ort./cm21 M21
Conclusion
(400 MHz, CDCl3) d (ppm) ¼ 9.21 (d, 1H, J ¼ 4.0 Hz),
8.96 (d, 1H, J ¼ 4.0 Hz), 8.29 (d, 1H, J ¼ 8.0 Hz), 7.99 (d,
1H, J ¼ 8.0 Hz), 7.63 (dd, 1H), 7.48 (dd, 1H), 6.94 (s, 1H),
3.63 (s, 2H); 13C NMR (100 MHz, CDCl3/d-DMSO): d
149.3, 146.1, 145.8, 141.3, 140.7, 132.8, 129.9, 129.8,
122.7, 121.8, 121.7, 103.9; UV CDCl3 280 nm; FTIR (KBr;
cm21): 3418 (nas, NH2), 3324 (ns, NH2), 1638 (d, NH2).
We have successfully developed a ‘turn-on’ colorimetric
chemosensor for Fe3þ based on 1,10-phenanthroline. The
chemosensor is accessible via simple synthesis which
shows high sensitivity and selectivity for Fe3þ. The
chemosensor exhibits high selectivity to discriminate
between Fe3þ and chemically close ions (i.e. Co2þ, Cr3þ
,
Cu2þ, Mn2þ, Ni2þ, Agþ and Zn2þ) in conjunction with a
visible colorimetric change from colourless to light pink,
leading to the production of visual detection of Fe3þ. The
interaction of sensor 4 with Fe3þ was investigated in the
presence of MES buffer solution. The UV–vis spectra of
sensor 4 revealed an absorption maximum at 268 nm
which shifted to 278 nm upon addition of Fe3þ ions in the
solution. It is worth noting that a new band appears at
514 nm, which increased with an increase in the
N-(1,10-phenanthrolin-5-yl)-2,2-diphenylacetamide
(ligand 4 or PHMD)
One hundred milligrams (0.513 mmol) of 1,10-phenan-
throline-5-amine and 200 mg of dry KHCO3 in 3 ml of dry
DCM were added in a 25 ml Schlenk tube and stirred for
10 min to dissolve the amine. One hundred and thirty
milligrams (1.11 equiv.) of 2,2-diphenylacetyl chloride
was dissolved in 2 ml DCM and added dropwise to the
Schlenk tube and stirred for 1 h at room temperature. The
solvent was evaporated and the reaction mixture was
poured in 20 ml distilled water and extracted with DCM
thrice (10 ml). The crude reaction mixture was purified
with column chromatography by using 20% ethanol and
concentration of Fe3þ
.
Acknowledgements
We are thankful to TUBITAK (The Scientific and Technological
Research Council of Turkey) for financial support (Program
2216) and the Chemistry Department of Akdeniz University,
Antalya, Turkey.
1
80% hexane; ESI-MS: m/z 389.15; H NMR (400 MHz,
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