Bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)ethylenediamine: A novel cation sensor

Article abstract of DOI:10.1007/s10895-013-1223-9

Novel substituted phenol-based new symmetrical bis(2-hydroxy-3-isopropyl-6- methyl-benzaldehyde)ethylenediamine (1) has been designed and synthesized. The compound 1 fluorometrically recognized Cu²⁺ ion in CH ₃OH/H₂O (90:10, v/v) by exhibiting an increase in emission upon complexation. In addition, Cu²⁺ gave rise to a change in colour of the solution of compound 1, which was clearly visible to the naked eye under UV irradiation. The association constant (K) of compound 1 with Cu²⁺ ion was computed with the Benesi-Hildebrand plot and Scatchard plot at 43,000 M^-1 and 43,011 M^-1 respectively.

Full text of DOI:10.1007/s10895-013-1223-9

J Fluoresc
DOI 10.1007/s10895-013-1223-9
SHORT COMMUNICATION
Bis(2-Hydroxy-3-Isopropyl-6-Methyl-Benzaldehyde)
Ethylenediamine: A Novel Cation Sensor
Anil S. Kuwar & Umesh A. Fegade & Kundan C. Tayade &
Umesh D. Patil & Horst Puschmann & Vikas V. Gite &
Dipak S. Dalal & Ratnamala S. Bendre
Received: 8 January 2013 /Accepted: 30 April 2013
#
Springer Science+Business Media New York 2013
Abstract Novel substituted phenol-based new symmetrical
bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)
ethylenediamine (1) has been designed and synthesized. The
compound 1 fluorometrically recognized Cu2+ ion in
CH3OH/H2O (90:10, v/v) by exhibiting an increase in emis-
sion upon complexation. In addition, Cu2+ gave rise to a
change in colour of the solution of compound 1, which was
clearly visible to the naked eye under UV irradiation. The
association constant (K) of compound 1 with Cu2+ ion was
computed with the Benesi-Hildebrand plot and Scatchard
plot at 43,000 M−1 and 43,011 M−1 respectively.
gained considerable attention recently because of their abil-
ity of complexation towards ionic and/or neutral molecules
[2]. We have so far synthesized non-cyclic compounds with
plural hydroxyl groups and imine function groups have been
proved to serve not only as cation sensors but also as pre-
cursors for constructing supramolecular system, e.g.
metallo-supramolecular complexes [3]. So the precise de-
sign and efficient synthesis of noncyclic compound has
continued to play a very important role in the area of
supramolecular chemistry. Although many kinds of
noncyclic compounds are prepared, development of a cost
effective synthetic route under mild conditions to this type
of compound still remains a smart and demanding subject
for synthetic chemists.
2+
.
.
Keywords Phenol substituted receptors Cu binding
.
Fluorometric sensor Association constant
The discriminating strap of chemical species upon mo-
lecular recognition can express bulky perturbation in the
host environment, particularly when the ionic or neutral
guest is used. Fluoroionophore can offer chemical informa-
tion on the ion concentration, which constituted important
area in metal ion analysis [4]. The development of particular
chemosensor for the recognition, discovery and enhanced
capacity of transition metal ions extraction have drawn
particular interest as these ions play important roles in
nature [5].
Copper, the third most plentiful important trace element
in the human body and commonly founds as Cu2+ ion in
natural water [6]. However, free Cu2+ ions potentially toxic
to aquatic life, both acutely and chronically. For example,
micro-organisms affected by submicromolar concentrations
of Cu+2 ions [7]. Even if a variety of aspects of copper
transportation and metabolism have been investigated in
the last few decades [8] very little is known about the
specifics of intracellular copper transfer. Cloning of the
genes may be liable for the two major genetic disorders of
copper metabolism in human, it has been seen that Menkes
and Wilson diseases were resulted due to excessive intracel-
lular copper transport [9, 10].
Introduction
The design and synthesis of new cation binding agents is an
important area of current research interest due to the grow-
ing awareness of the environmental and clinical importance
of cations. The different size and shapes of cations are
responsible for the fast growth in the development of cation
binding agents as compared to anion binding agents [1].
Noncyclic compounds containing plural bonding sites have
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-013-1223-9) contains supplementary material,
which is available to authorized users.
:
:
:
:
A. S. Kuwar (*) U. A. Fegade K. C. Tayade U. D. Patil
:
:
V. V. Gite D. S. Dalal R. S. Bendre (*)
School of Chemical Sciences, North Maharashtra University,
Jalgaon 425 001 MS, India
e-mail: kuwaras@gmail.com
e-mail: bendrers@rediffmail.com
H. Puschmann
Department of Chemistry,
Durham University, Durham DH1 3LE, UK

J Fluoresc
2Ar-H, ortho to isopropyl gr), 7.09 (d, 2H, 2Ar-H ortho to
methyl gr), 8.66 (s, 2H, 2CH=N); 13C NMR (CDCl3, δ
ppm): 17.2, 21.8, 27.3, 66.2, 120.1, 123.3, 126.4, 133.8,
136.9, 156.2, 162.3; MS (ESI): m/z (%): 403 (22), 380
(100); Elemental analysis calculated for C24H32N2O2: C,
75.8; H, 8.48; N, 7.35 %. Found: C, 75.75, H, 8.23; N,
7.15 %.
N
N
O
a
OH
HO
NH2 NH2
OH
1
Scheme 1 Synthetic route to receptor 1 (a=Ethanol, 1 h)
The yellow colour product obtained was purified by
1
As a part of our work in the molecular recognition, we
reported here design and synthesis of novel chemosensor
bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)
ethylenediamine (1) and studied its inclusion phenomenon
with various cations.
recrystallization from ethanol and characterized by IR, H
and 13C NMR, mass spectroscopic techniques and was
confirmed by elemental analysis. The elemental analysis
and spectral data were in good agreement with chemical
structure of compound 1. The assigned structure for 1 was
supported by an X-ray crystallographic structure determina-
tion (Fig. 1). Supplementary crystallographic data for 1 was
shown in CCDC 870837 [11]. The crystal structure of
compound 1 is shown in (Fig. 1). Selected bond lengths
and angles are summarized in Table 1.
Crystal Data for C24H32N2O2 (M =380.53): triclinic,
space group P-1 (no. 2), a=8.4604(4) Å, b=10.4538(5) Å,
c=13.9426(5) Å, α=99.479(3)°, β=107.165(4)°, γ=
108.166(4)°, V=1073.80(9) Å3, Z=2, T=120.0 K, μ(Mo
Kα)=0.075 mm−1, Dcalc=1.1768 g/mm3, 18363 reflections
measured (5.2≤2Θ≤55), 4917 unique (Rint=0.0379) which
were used in all calculations. The final R1 was 0.047732
(I>=2σ(I)) and wR2 was 0.113297 (all data).
Hydrogen bonding of the phenolic –OH shown in
(Fig. 1) was major advantageous feature in host guest
complexation. Invariability, phenolic hydrogen atom
formed an intramolecular hydrogen bond to N atom of
the azomethine group, giving a six membered ring. This
interaction was usually characterized in terms of phenolic
oxygen to ethylenediamine nitrogen separation [12]. This
distance varies little between the two molecules. In all
free ligand structure, the molecular association was via
intramolecular hydrogen bonding. The compound 1 ex-
hibits intramolecular hydrogen bonding (Table 1), where
the H atom of phenolic hydroxyl group formed a strong
O-H….N intramolecular hydrogen bond with O….N dis-
tance 2.55 Å which was in the middle of expected range
of such hydrogen bonds[13].
Experimental
All commercial grade chemicals and solvents were procured
1
and used without further purification. H and 13C NMR
spectra were recorded on a Varian NMR mercury System
300 spectrometer operating at 300 and 75 MHz in CDCl3
with Me4Si as an internal standard, respectively. The Fluo-
rescence and UV-visible spectra of the receptor compound 1
with selected metal ions were recorded in CH3OH/H2O
(90:10, v/v) namely on HORIBA JOBIN YVON
Fluoromax-4 spectrofluorometer and Shimadzu UV-24500
at room temperature using 1 cm pathlength cell.
Bis(2-Hydroxy-3-Isopropyl-6-Methyl-Benzaldehyde)
Ethylenediamine (1)
A solution of 1,2-diamino ethane (0.06 g, 0.001 mol) was
added to a solution of 2-hydroxy-3-isopropyl-6-methyl-
benzaldehyde (0.356 g, 0.002 mol) in ethanol (50 mL) and
mixture was stirred at ambient temperature up to 1 h. There
by deposited yellow crystals at room temperature were
filtered and recrystallized from ethanol, 83 %, mp 112–
115°C. (Refer Scheme 1)
1
IR (KBr, cm−1): 1623, 1340; H NMR (CDCl3, δ ppm):
1.27 (d, J=1.2 Hz, 12H, gem 4CH3), 2.34 (s, 6H, 2Ar-CH3),
3.32 (heptet, 2H, 2CH), 3.91 (s, 4H,CH2-CH2), 6.58 (d, 2H,
Fig. 1 The structure contains
two independent ‘half-
molecules’. The full molecules
are generated by an inversion
centre located in the middle of
the bond between C1A and its
symmetry equivalent atom
C1A1. The geometry of the
molecule that is not shown is
very similar to the geometry
exhibited by the one shown
above

J Fluoresc
Table 1 Distances and angles around the hydrogen bonded D- A atoms. The X-ray distances were derived from the model where the O-H distance
was fixed to 0.840Å and the values adjusted for the neutron-corrected hydrogen position used a restrained distance of 0.983Å
O1A-N1A/Å
H1A-N1A/Å
O1A-H1A-N1A
O1B- N1B/Å
H1B-N1B/Å
O1B-H1B-N1B
X-Ray
2.55627(10)
1.801(10)
1.638(8)
148.6(9)
2.53326(13)
1.776(7)
1.629(9)
148.8(5)
Neutron
–
153.9(17)
–
150.5(16)
Determination of the Binding Constant
by Spectroflourometric Titration
salt solution for which the receptor was selective, accompa-
nied by the emission peak height enhancement. It was well
understood from (Fig. 2) that receptors were highly sensitive
and selective towards Cu2+ ion by exhibiting a distinct mode
of emission. It was well known that copper compound have
paramagnetic nature with +2 oxidation state and the great
stability [14]. In our precise analysis, the enhancement of
compound 1 after binding with Cu2+ ions was fairly remark-
able and mentionable along with other few related accessi-
ble systems.
The binding mode of compound 1 exposed the impor-
tance of the hydroxyl group in Cu2+ binding. Generally
hydroxyl group acts as a good binding site and also plays
an effective role in binding of transition metal ions such
as Cu2+ metal ion. Therefore, it was appeared that the
core functionality required for compound 1 to efficiently
bind with Cu2+ ion were imine association and hydroxyl
groups. However, due to binding of Cu2+ ion in the gap,
the metal–fluorophore interaction was modulated [15] and
the excitation energy transfer from the receptor to the
metal d orbital and/or receptor to metal charge transfer
was inhibited. Fluorescence ratiometric response of recep-
tor compound 1 and interference toward the surveyed
metal ions are displayed in (Fig. 3a, b). The results
showed a highly selective response of compound 1 to-
wards Cu2+ ions as compared to the other metal ions.
Although Zn2+, Cr3+, Mn2+ and Ni2+ gives fluorescence
enhancement but in the presence of Cu2+ ion, there inten-
sity is negligible. The data presented here will be helpful
for the researcher to expand the new function of com-
pound 1 in analytical and environmental science.
The fluorescence titration experiments were carried out with
a HOSHIBA JOBIN YVON Fluoromax-4 spectrofluorom-
eter in CH3OH/H2O (90:10, v/v, mole fraction≈0.8) at room
temperature (298 K) and then the association constant (Ka)
was computed for receptor compound 1–cation complexa-
tion. The selectivity of various metal ions towards receptor 1
was studied. The titration of the selective metal ion was
talented through addition of changeable amount of metal
salt solution (0.005 ml, 1×10−3 M) to a fixed amount of
receptor compound 1 solution (2 ml, 1×10−4 M) in
CH3OH/H2O (90:10, v/v) in the cell. This was followed
by a 5 min interval (in which the reaction cell was left under
continuous stirring to ensure mixing). Then the fluorescence
data was collected and processed to calculate the association
constant (Ka) of the appropriate cation and receptor 1
complex.
Result and Discussion
The response of receptor 1 towards various metal ions was
recorded in CH3OH/H2O (90:10, v/v) using fluorescence
spectroscopy. The change in fluorescence of compound 1
was observed upon addition of selected metal salts solution
prepared in CH3OH/H2O (90:10, v/v). As can be seen from
(Fig. 2), the broad emission peak centered at 600 nm for
compound 1 in CH3OH/H2O (90:10, v/v), progressively
increase with the addition of increasing amount of metal
Fig. 2 Changes in fluorescence
intensity of compound 1 (1×
10−4 M) upon the addition of
fixed amount of metal ion
solution (1×10−3 M) in
CH3OH/H2O (90:10, v/v)

J Fluoresc
Fig. 3 a Fluorescence
ratiometric response (I0-I/I0) of
compound 1 (1×10−4 M) upon
the addition of a particular
metal salt (1×10−3 M) in
CH3OH/H2O (90:10, v/v). b
Respective interference of
metals at the time of detection
of Cu2+ ion
When receptor 1 was titrated with Cu2+ in CH3OH/H2O
(90:10, v/v), a progressive fluorescence enhancement was
observed with Cu2+ ion and the development reached up to
saturation as seen in (Fig. 4) observed change may be due
to the chelation followed by prevention of the photoelec-
tron transfer. Normalized response of fluorescence signal
to change Cu2+ ion concentration in the CH3OH/H2O
(90:10, v/v) solution is shown by (Fig. S2 in Supplement
data).
The fluorescence intensity was gradually increased
(Fig. S2 in Supplement data) with increasing the guest
concentration. To determine the binding stoichiometry be-
tween receptor 1 and Cu2+, the continuous variation method
was used [16]. (Fig. S3 in Supplement data) shows the Job
plot of the fluorescence intensity of free receptor 1 and the
intensity of the system with the molar fraction of the host
{[H]/([H]+[G])} for a series of solutions, in which the total
concentration of host and guest was constant, with the molar
Fig. 4 Changes in fluorescence
spectrum of receptor 1 (1×10−4
M) upon the addition of Cu2+
salt of (1×10−3 M) in CH3OH/
H2O (90:10, v/v)

J Fluoresc
Fig. 5 Changes in absorbance
spectrum of receptor 1 (1×10−4
M) upon the addition of metals
(1×10-3 M) in CH3OH/H2O
(90:10, v/v)
fraction of host continuously varying. The results indicate
the formation of a 1:1 (Host: Guest) complex. Using the
equation: [G]tot=a/2K11(1-a)2[H]tot+a[H]tot/2, where [G]tot
is total concentration of guest, [H]tot is the total concentra-
tion of host, a=(I- I0)/(Ii- I0) with I being the fluorescent
intensity at a particular Cu2+ concentration while I0 and Ii
are the intensities at zero and infinite Cu2+ concentrations,
respectively, the association constant Ka was determined as
4.3×104 0.1 M−1.
fluorometric change. Visual detection studies of receptor com-
pound 1 (1×10−4 M) were conducted with all cations such as
metal chlorides of Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and
Zn2+. The receptor compound 1 in mixed solutions of
CH3OH/H2O (90:10, v/v) was appeared to be almost
colourless at room temperature. With the addition of these
cations (10.0 equivalents) to receptor compound 1, only Cu2+
ion shown spectacular colour change from colourless to fluo-
rescent green colour, which was noticeable in the presence of
UV light compared to other cations (Fig. S1 in Supplement
data). In general, the cations such as Fe3+, Ni2+ and Co2+
interfere in Cu2+ ion detection. However, in our study, we
did not find any significant colour change to the solution of
compound 1 even after the addition of these interfering an-
ions. The probable reason for the colour change in presence of
Cu2+ ion over other cations may probably be attributed to the
fact that the copper have +2 oxidation state and the observable
bathochromic shift. All the attempts failed to grow a single
crystal of Copper complex of compound 1.
Using the Benesi-Hildebrand [17] (Eq.1) and the
Scatchard [18, 19] (Eq.2) methodologies and we made the
calculation of association constant (Ka).
.
.
.
1
F−F ¼ 1 ðF∞−F0ÞK½Gꢀ þ 1 ðF∞−F0Þ
.
ð1Þ
ð2Þ
0
F−F0 ½Gꢀ ¼ ðF∞−F0ÞK−ðF−F0ÞK
Applying both equations two lines were obtained in the
plot of 1/(F-F0) verses 1/[G] for Benesi-Hildebrand equation
and in the plot of (F-F0)/[G]versus(F-F0) for Scatchard
equation, as illustrated in (Fig. S4 in Supplement data) and
(Fig. S5 in Supplement data). Where F∞ was the fluores-
cence intensity in the absence of Cu2+ ions, F was the
fluorescence intensity in presence of Cu2+ ions and [G]
was the concentration of guest. The association value (Ka)
obtained from Benesi-Hildebrand plot and Scatchard plot
was found to be in good agreement and were 43,000 M−1
and 43,011 M−1 respectively.
The absorption spectrum of receptor compound 1 with
various metal salts was shown in (Fig. 5) Receptor exhibited
λmax at 273, 328 and 428 nm in CH3OH/H2O (90:10, v/v)
solution together with a swelling at 273 nm and a shoulder
at 310 nm. The longer wavelength band at 428 nm and
shoulder at 478 nm may be assigned to transitions associat-
ed with phenol substituted ring (Fig. 5). This observation
clearly indicated towards a charge transfer from nitrogen
(donor) of imine to Cu2+ (acceptor) metal ion.
Conclusion
In summary, we have designed and developed a selective
and sensitive fluorescent chemical sensor compound 1 for
the detection of Cu2+ ion in organic and aqueous medium.
The detection of Cu2+ ion gave rise to major colour change
from colourless to fluorescent, which can easily be detected
by the naked eye under UV irradiation. The selective detec-
tion of Cu2+ ion in water was generally complicated in the
presence of other metal ions. But we successfully detected
Cu2+ ion in aqueous environment. The 1:1 stoichiometry of
the host guest complexes in methanol containing 10 % water
was confirmed from job plot. The association constant (Ka)
of compound 1 with Cu2+ ion was calculated with the
Benesi-Hildebrand plot and Scatchard plot and were found
to be 43,000 M−1 and 43,011 M−1 respectively.
In addition, the selective recognition of compound 1 by
Cu2+ ion was visualized by the naked eye owing to the
Most of the reported sensors for these metal cations are
often structurally complicated and required tedious synthetic

J Fluoresc
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procedures. Herein, this reported sensor which was easy-to-
make. We believe that this sensor, with sensitive and selec-
tive naked eye responses can be used for many practical
applications in chemical, environmental and biological
systems.
9. Chelly J, Tumer Z, Tonnesen T, Petterson A, Ishikawa-Brush Y,
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11. These data can be obtained free of charge from The Cambridge
crystallographic data centre via www.ccdc.cam.ac.uk/data_request/
cif
Acknowledgments ASK gratefully acknowledges financial support
from the Department of Science and Technology (DST, under Fast
Track Scheme, File No. SR/FT/CS-160/2011), Government of India,
New Delhi.
12. Butcher RJ, Bendre RS, Kuwar AS (2005) Acta Crystallogrphy
E61:o3511–o3514
13. Butcher RJ, Bendre RS, Kuwar AS (2007) Acta Crystallogrphy
E63:o3360
14. Lee DH, Kim SY, Hong JI (2004) Angew Chem Int Ed 43:4777–
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