N,N,N,N-tetradentate macrocyclic ligand based selective fluorescent sensor for zinc (II)

Article abstract of DOI:10.1007/s10895-012-1046-0

N,N,N,N-tetradentate macrocyclic ligand (L) has been synthesized by the condensation of benzil and semi-carbazide and characterized. On excitation by light of wavelength 350 nm, L exhibited a fluorescent peak at λ_max= 454 nm, which showed ca 6

Full text of DOI:10.1007/s10895-012-1046-0

J Fluoresc (2012) 22:1081–1085
DOI 10.1007/s10895-012-1046-0
ORIGINAL PAPER
N,N,N,N-tetradentate Macrocyclic Ligand Based Selective
Fluorescent Sensor for Zinc (II)
Priyanka Goswami & Diganta Kumar Das
Received: 21 November 2011 /Accepted: 8 March 2012 /Published online: 28 March 2012
#
Springer Science+Business Media, LLC 2012
Abstract N,N,N,N-tetradentate macrocyclic ligand (L) has
been synthesized by the condensation of benzil and semi-
carbazide and characterized. On excitation by light of wave-
human body such as –influencing DNA synthesis, gene
expression, enzyme catalysis [4], apotosis [5], immune sys-
tem function, and neuronal signal transmission [6]. However,
in spite of its physiological importance, zinc ion is a metal
pollutant and presence of a large amount of zinc in the envi-
ronment may reduce the soil microbial activity causing phy-
totoxic effects [7] and also it is a common contaminant in
agricultural and food wastes [8]. Moreover, zinc ion is also a
contributory factor in neurological disorders such as Parkin-
son’s disease, epilepsy and Alzheimer’s disease [9].
length 350 nm, L exhibited a fluorescent peak at λmax
0
4
54 nm, which showed ca 6 times enhancement in intensity
2
+
with a blue shift on interaction with Zn . L has been found
to act as a selective fluorescent sensor for zinc ion over a
host of other metal ions such as- Cd , Pb , Hg , Ca , Fe ,
Na , Co , Mn , Cu and Ni , in 1:1 CH OH:H O. A 1:1
complex formation between L and Zn was proved. The
enhancement in the fluorescence could be explained on the
basis of Photo induced electron transfer (PET) mechanism
with log β01.86.
2
+
2
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
3
2
2
+
So far, several analytical methods have been reported for
the determination of zinc, such as UV/visible spectrsocopy
[10–12], electrochemical [13, 14], fluorescent [15, 16] etc.
However, owing to its simplicity and sensitivity, fluorescent
detection of zinc ions has been widely preferred. Moreover,
.
.
.
.
Keywords Benzil Salicyldehyde Fluorescence Sensor
2
+
2+
.
Binding constant Photo induced electron transfer (PET)
Zn and Cd have similar chemical properties, due to
which they cause similar spectral changes, when coordinated
with fluorescent sensors [17–19]. Therefore, there is a need for
2
+
developing such sensors which can distinguish Zn
from Cd and other transition metal ions.
Introduction
2
+
Recent years have seen increasing interest in the devel-
opment of zinc sensors. A quinoline carboxaldehyde and
phenylenediamine based ratiometric fluorescent sensor for
zinc was developed by Chen and coworkers [20]. A novel
fluorescent zinc sensor based on bis (pyroll-2-yl-methylene-
amine) ligand has been reported by J.S Ma et al. [21].
Further, a novel water soluble compound, 8-pyridyl
methyloxy-2-methyl-quinoline, was found to act as a highly
sensitive fluorescent sensor for zinc [22]. P. Banerjee et al.
also reported the selective fluorescent zinc sensing property
by certain Schiff base compounds [23]. A coumarin based
Fluorescent sensors are widely used for real-time monitor-
ing and detection of metal ions at a molecular level without
any special instrumentation, and are applicable in many
fields such as medical, environmental monitoring, living
cells and electronics [1]. Recently, there has been a signif-
icant interest in the design and synthesis of fluorescent
sensors for detection of physiologically important ions and
molecules [2] and for monitoring harmful pollutants in the
environment [3]. Zinc ion is the second most abundant metal
ion and is well known to play a number of roles in the
2
+
fluorescent sensor is also known for the detection of Zn ,
:
P. Goswami D. K. Das (*)
2+
2+
Cd and Pb [24]. We have also previously reported 2,7-
dichlorofluorescein as a selective fluorescent sensor [25] for
Department of Chemistry, Gauhati University,
Guwahati 781 014 Assam, India
e-mail: digkdas@yahoo.com
2
+
2+
distinguishing Zn , Cd and certain other metal ions. We

1
082
J Fluoresc (2012) 22:1081–1085
have recently reported that the condensation product of
2
+
salicylaldehyde and semicarbazide can detect Cd [26].
In this paper, we report the fluorescence zinc (II) sensing
property of a compound (L), synthesized by the condensa-
tion of benzil and ethylene diamine. In 1:1 CH OH: H O, L
3
2
was found to exhibit a fluorescent peak at λmax value
54 nm on excitation by 350 nm wavelength photons. It
has been observed that the fluorescent intensity peak at
54 nm increases significantly to ca 6 times on interaction
4
4
2
+
with Zn . However no such remarkable enhancement in
2
+
2+
intensity has been observed for the metal ions - Cd , Pb ,
2
+
2+
2+
2+
2+
2+
2+
2+
Hg , Ca , Fe , Na , Co , Mn , Cu and Ni .
Experimental
Benzil was purchased from Loba Chemie and ethylenedi-
amine was obtained from Merck. All the metal salts (sul-
phate) and methanol were purchased from Merck. All
chemicals were of analytical grade and used without further
purification. The metal salts were recrystallized from water
Scheme 1 Structure of L
(
Millipore). Fluorescence spectra were recorded in a Hitachi
−
5
2
500 spectrophotometer using quartz cuvette. A 10
M
solution of L in 1:1 (v/v) CH OH: H O (phosphate buffer
crystalline solid was obtained. This was washed with etha-
nol and dried Scheme 1.
3
2
solution, pH 7.0) was used in the experiments. Metal salt
solutions (10− M) were prepared in PBS, pH 7.0. Time
resolved fluorescence spectra was recorded in Life Spec II
5
(
Edinbergh Instrument) using light source EPL – 375, pico-
Results and Discussion
second pulsed diod laser.
Electrochemical measurements were carried out in a CHI
The fluorescence property of L was examined in 1:1
6
00B Electrochemical Analyser (USA), consisting of a
CH OH: H O at room temperature. The emission spectrum
3
2
three-electrode assembly with a platinum disc as the work-
ing electrode, Ag-AgCl (3 M NaCl) as the reference elec-
trode and tetrabutylammonium perchlorate (TBAP, 0.1 M)
as the supporting electrolyte. The working electrode was
cleaned as reported [27] by polishing with 0.1 μm alumina
slurry using a polishing kit (CHI), followed by sonication in
distilled water for 5 min.
of L was obtained in the range 370–600 nm, on excitation
by light of wavelength 350 nm. The maximum intensity
fluorescent peak was observed at 454 nm. The effect on
the fluorescent intensity of L on interaction with a number
2
+
2+
2+
2+
2+
+
2+
of metal ions - Cd , Pb , Hg , Ca , Fe , Na , Co ,
UV/Visible spectra were recorded in a Shimadzu UV
1
13
1
800 spectrophotometer. H NMR and C NMR spectra
were recorded in a Bruker Ultrashield 300 spectrometer. All
NMR spectra were obtained in CDCl at room temperature
3
and the chemical shifts are reported in δ values (ppm)
relative to TMS. FTIR spectra were recorded for L in KBr
−
1
pellet which shows peaks at 2835 and 2943 cm (ν C-H),
−
1
−1
1
1
593 and 1508 cm (ν C-N), 991 cm (ν
bending),
C-H
−1
438 cm (ν C-C).
Synthesis of L was carried out as per reported procedure
27]. 0.210 mg (1 mol) of benzil was dissolved in 10 mL
[
2+
Fig. 1 Fluorescence emission spectra of L on addition of Zn in 1:1
ethanol and an equimolar proportion of 0.05 mL ethylenedi-
amine was added. 6 mL of conc. HCl was added dropwise to
the resulting mixture and refluxed for 4 h till a yellow
-5
3 2
CH OH:H O {[0, 0.99, 1.9, 2.9, 3.8, 4.7, 6.5, 7.4, 8.2 and 9.0 (X 10 M)
(
in order of increasing intensity); λex0350 nm; λemi0370–600 nm; Inset:
2+
plot of I/Io as a function of Zn ion concentration

J Fluoresc (2012) 22:1081–1085
1083
Fig. 2 Bar diagram showing effect of 1 equivalent of different metal
ions (9.0 X 10− M) on the fluorescent intensity of L, in 1:1 CH
5
3
OH:
2
H O
2
+
2+
2+
Mn , Cu and Ni was investigated in 1:1 CH OH: H O.
2+
3
2
Fig. 4 Change in U/V visible spectra of L when concentration of Zn
−
5
It was found that the intensity of the fluorescent peak of L
ion was changed from 0 to 9.0 x 10 M. Inset: Plot of log[(Ao – As)/
2
+
2+
increases with gradual addition of Zn ion into the solution
and attains the maximum (5.5 times to the original intensity)
(As – Aα)] versus log[Zn ]
at 9.9×10− M concentration of Zn . The intensity en-
5
2+
the fluorescence spectra of L. The bar diagram clearly
indicates that L acts as a selective fluorescent sensor for
hancement was accompanied by a blue shift in the λmax
2
+
from 454 nm to 420 nm. Figure 1 portrays the fluorescence
Zn over all the other metal ions.
2
+
spectra of L at zero and at various added concentration of
Determination of the number of Zn ions bound to L and
the binding constant was done by plotting log [(I - Io)/(Imax -
I)] against log[Zn ] (Fig. 3) [26]. The plot obtained was linear
R 00.984) with the slope and the X-axis intercept represent-
ing the number of Zn ions bound and the log of binding
constant (β) respectively. The slope was calculated to be
.092, indicating the binding of one Zn ion to L and the
2+
−5
−5
Zn (0.99X 10 to 10.71 X 10 M). Inset of Fig. 1 shows
2
+
2
+
the plot of I/I as a function of Zn ion concentration,
0
2
where I refers to the intensity at a given concentration of
(
2+
2+
2
+
Zn ion and I is the intensity at zero concentration of Zn .
0
2
The I/I value increased linearly (R 00.9561) to 5.5 till the
concentration of Zn became 9.9 X 10 M and remained
constant thereafter. The detection limit of L for Zn was
calculated to be 2.754 x 10 M.
Ca , Cd and Pb ions induced about two times en-
hancement in the fluorescent peak of L but unlike Zn no
shift in the λmax value of the fluorescent emission peak was
0
2
+
−5
2
+
1
2
+
log β value was 1.86.
−5
The UV/Visible spectra of L in 1:1 (v/v) CH OH:H O
showed two absorption peaks with λmax values at 284 nm
and 354 nm. On increasing the concentration of Zn ion
M to 9.0 X10 M) in the solution, the
absorbance of both the peaks were found to increase
3
2
2
+
2+
2+
2
+
2
+
−
5
−5
(0.99 X 10
+
2+
observed. On the other hand, the metal ions – Na , Mn ,
2
+
2+
2+
2+
Fe , Co , Ni and Cu were found to quench the inten-
sity of the fluorescent peak of L to a remarkable extent. The
2
+
maximum quenching effect was seen for Co ion. The
metal ion selectivity profile of L is shown by a bar diagram
(
Fig. 2), which depicts the effect of different metal ions on
2
+
Fig. 5 Square Wave Voltammogram of L in 1:1 CH
3
OH:H
2
O at Zn
2
+
−5
−5
−5
Fig. 3 Plot of log [Zn ] as a function of log [(I-I
o
)/(Imax -I)] for
ion concentration 0 (a), 1.9×10 M (b), 2.9×10 M (c), 3.8×10 M
2
+
−5
titration of L against Zn in 1:1 CH
3 2
OH:H O
(d) and 4.7×10 M

1
084
J Fluoresc (2012) 22:1081–1085
2
+
2+
(
Fig. 4). In order to confirm the number of Zn ions bound
blue shift on interaction with Zn . Interaction with the
2
+
2+
2+
to L, log [(Ao-As)/(As-A∞)] value was plotted against log
Zn ] (Fig. 4, inset) for the absorbance values of 354 nm
peak. Here, Ao, As and A∞ are the absorbances of L at zero,
at an intermediate and at infinite concentration of Zn
metal ions - Cd , Pb and Ca enhances the fluorescent
intensity by a small amount without any blue shift. On the
2
+
[
2
+
+
2+
2+
2+
2+
other hand metal ions Fe , Na , Co , Mn , Cu and Ni
2
+
quenches the fluorescence intensity of L. A 1:1 complexation
between L and Zn ion is proved to be formed which snaps
2
2+
respectively. The plot was found to be linear (R 00.987)
with slope 1.12 indicating and thus further confirming the
the PET process in L leading to fluorescent enhancement.
2
+
binding of one Zn ion to L. The log β01.97 value found
to be in conformity to that obtained from fluorescent intensity
calculation.
Acknowledgement UGC, New Delhi is thanked for financial sup-
port to the department under SAP and RFSMS to PG. DST, New Delhi
is thanked for FIST to the department. SIF, IIT – Guwahati is thanked
for time resolved fluorescence spectroscopy.
The enhancement of the fluorescence intensity of L on
2
+
interaction with Zn is due to the efficient Photoinduced
2
+
electron Transfer Mechanism (PET) between L and Zn .
Initially, the fluorescence of L is quenched due the transfer
of electron density from the N-atoms of the receptor part
References
(
(
ethylene diamine) to the LUMO of the fluorophore part
benzil). Both fluorescence and UV spectral titration indi-
1. Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM, Mc
Coy CP, Rademacher JT, Rich TE (1997) Signalling recognition
event with fluorescent sensors and switches. Coord Chem Rev
2
+
2+
cate that one Zn binds to L. The Zn preferably coordi-
nates to L via the four N-atoms of the two ethylene diamine
groups. Due to the binding of Zn to L the energy of the
electrons originating at the N atoms are lowered and the
PET process is hindered, as a result of which the fluores-
cence intensity is enhanced.
We have carried out fluorescence lifetime studies to con-
firm the involvement of PET process in the fluorescence
signalling action. A multiexponential fluorescence behav-
iour was observed for L yielding decay parameters :
9
7:1515–1566
2
+
2
3
4
. Spichiger-Keller YE (1998) US-sensors and biosensors for medi-
cal and biological applications. Wiley-VCH, New York
. Mason CF (2002) Biology of freshwater pollution, 2nd edn.
Longman, New York
. Lippard SJ, Berg JM (1994) Principles of bioinorganic chemistry.
University Science, Mill Valley, Ca, USA
5. Kimura E, Aoki S, Kikuta E, Koike T (2003) A macrocyclic zinc
II) fluorophore as a detector of apoptosis. Proc Natl Acad Sci
(
USA 100:3731–3736
6
. Czarnik AW (1993) Fluorescent chemosensors for ion and mole-
cule detection. American Chemical Society, Washington DC
τ 00.204 ns (57.39 %), τ 01.236 ns (32.33 %) and
1
2
τ304.457 ns (10.28 %). The complex nature of the fluores-
cence decay behaviour is a reflection of the flexibility of the
7. Voegelin A, Poster S, Scheinost AC, Marcus MA, Kretzschmar
2005) Changes in zinc speciation in field soil after contamination
with zinc oxide. Environ Sci Technol 39:6616–6623
(
molecule [28]. The components with life time τ 00.204 ns
1
8
9
. Callender E (2000) The Urban environmental gradient:anthropo-
genic influences on the spatial and temporal distributions of lead
and zinc in sediments. Environ Sci Technol 34:232–238
and τ 01.236 ns favours PET process in 89.42 % of the
2
2
+
total molecules. Addition of Zn ion results in the disap-
pearance of the shorter lifetime component with the forma-
2
+
. Weiss JH, Sensi SL, Koh JY (2000) Zn : a novel ionic mediator
of neutral injury in brain disease. Trends Pharmacol Sci 21:395–
tion of a new component at τ 04.75 ns. Disappearance of
1
4
01
the shorter life time components confirm the suppression of
the PET process [29].
1
0. Whitlock BJ, Whitlock HW (1990) Concave functionality: design
criteria for nonaqueous binding sites. J Am Chem Soc 112:3910–
3
915
The Osteryoung Square Wave Voltammetric response of
L in 1:1 (v/v) CH OH:H O was investigated. The experi-
1
1. Benesi HA, Hildebrand JH (1949) A spectrophotometric investi-
gation of the interaction of iodine with aromatic hydrocarbons. J
Am Chem Soc 71:2703–2707
12. Hanna MW, Ashbaugh AL (1964) Nuclear magnetic resonance
study of molecular complexes of 7,7,8,8-tetracyanoquinodime-
thane and aromatic donors. J Phys Chem 68:811–816
3. De Voogt P, van Hattum B, Feenstra JF, Peereboom JWC (1990)
Toxicol Environ Chem Rev 3:89
3
2
ments were carried out by using Glassy carbon disc as the
working electrode and Ag-AgCl as the reference electrode.
The redox peak potential value was obtained at - 0.272 V.
2
+
On addition of Zn ion the peak potential of L shifted
gradually in negative direction till it became −0.328 V at
1
2
+
−5
Zn ion concentration 4.7×10 M (Fig. 5). However, no
14. Burdette SC, Walkup GK, Spingler B, Tsien RY, Lippard SJ (2001)
2
+
2
+
2+
Fluorescent sensors for Zn based on a fluorescein platform:
synthesis, properties and intracellular distribution. J Am Chem
Soc 123:7831–7841
significant change was observed when metal ions- Cd , Pb ,
2
+
2+
2+
2+
2+
2+
2+
2+
Hg , Ca , Fe , Na , Co , Mn , Cu and Ni were
added to the electrolytic medium alone or together. This elec-
trochemical result further confirmed the selective interaction
1
1
5. Swaile DF, Sepaniak MJ (1991) Determination of metal ions by
capillary zone electrophoresis acid. Anal Chem 63:179–185
6. Fabbrizzi L, Licchelli G, Rabaioli A, Taglietti A (2000) The design
of lumininiscent sensors for anions and ionisable analytes. Coord
Chem Rev 205:85
2+
between L and Zn ion.
In summary, we have shown that the sensor L, synthe-
sized by condensation of benzil and semicarbazide, showed
remarkable enhancement in the fluorescence intensity with
1
7. Nolan EM, Ryu JW, Jaworski J, Feazell RP, Sheng M, Lippard SJ
(2006) Zinspy sensors with enhanced dynamic range for imaging

J Fluoresc (2012) 22:1081–1085
1085
neuronal cell zinc uptake and mobilization. J Am Chem Soc
24. Kulatilleke CP, Silva SA, Eliav Y (2006) A coumarin based fluores-
cent photoinduced electron transfer cation sensor. Polyhedron
25:2593–2596
1
28:15517–15528
1
8. Komatsu K, Kikuchi K, Kojima H, Urano Y, Nagano T (2005)
Selective zinc sensor molecules with various affinities for Zn2+,
revealing dynamics and regional distribution of synaptically released
Zn2+ in hippocampal slices. J Am Chem Soc 127:10197–10204
9. Henary MM, Wu YG, Fahrni CJ (2004) Zinc(II)-selective ratio-
metric fluorecsent sensors based on inhibition of excited-state
intramolecular proton transfer. Chem Eur J 10:3015–3025
0. Chen H, Wu Y, Cheng Y, Yang H, Li F, Yang P, Huang C (2007) A
ratiometric fluorescent sensor for zinc(II) with high selectivity.
Inorg Chem Commun 10:1413–1415
1. Wu Z, Chen Q, Yang G, Xiao C, Liu J, Yang S, Ma JS (2004)
Novel fluorescent sensor for Zn(II) based on bis(pyroll-2-yl-meth-
yleneamine) ligands. Sensors and Actuators B 99:511–515
2. Weng Y, Chen Z, Wang F, Xue L, Jiang H (2009) High sensitive
determination of zinc with novel water-soluble small molecular
fluorescent sensor. Anal Chim Acta 647:215–218
25. Goswami P, Das DK (2010) 2, 7-Dichlorofluorescein, a fluorescent
2
+
+
+
2+
2+
2+
2+
sensor to detect Cd over Na , K , Ca , Cu , Ni and Zn
Indian. J Chem 49A:1617–1620
1
2
2
2
2
26. Dong X, Yang Y, Sun J, Liu Z, Liu Bi-F (2009) Two -photon
excited fluorescent probes for calcium based on internal charge
transfer. Chem Commun 3883–3885
27. Chandra S, Raizada S, Rani S (2008) Structural and spectral
studies of palladium(II) and platinum(II) complexes derived from
N, N, N, N-tetradentate macrocyclic ligands. Spectrochimica Acta
A 71:720–724
28. Sarkar M, Banthia S, Samanta A (2006) A highly selective ‘off-on’
fluorescence chemosensor for Cr(III). Tetrahedron Letters
47:7575–7578
29. Ashokkumar P, Ramakrishnan VT, Ramamurthy P (2011)
2
+
Photoinduced Electron Transfer (PET) Based Zn Fluorescent
Probe: transformation of turn-on sensors into ratiometric ones
with dual emission in Acetonitrile. J Phys Chem A 2011:14292–
14299
3. Roy P, Dhara K, Manassero M, Banerjee P (2009) Synthesis,
characterization and selective fluorescent zinc(II) sensing property
of three Schiff-base compounds. Inorg Chim Acta 362:2927–2932