N-(3-Imidazolyl)propyl dansylamide as a selective Hg2+ sensor in aqueous media through electron transfer

Article abstract of DOI:10.1016/j.saa.2015.03.091

Abstract N-Imidazolylpropyl dansylamide 1 was synthesized for the sensing of metal ions and found to be selective and sensitive toward Hg²⁺ ions in a PBS-EtOH (1:4, pH = 7.4) solution. The sensing ability of probe 1 was examined by UV-Vis, fluorescence, and ¹H NMR spectroscopy. The sensing of Hg²⁺ exhibited a quenching of emission band at λ_max = 515 nm of probe 1, which was associated with quenching of green fluorescence emission under 365 nm illumination. Probe 1 showed a good association constant with Hg²⁺ (K_a = 6.48 × 10⁴ M^-1) with a stoichiometry of 1:1 in PBS-EtOH (1:4, pH = 7.4) having the lowest detection limit of 1 μM for Hg²⁺; on the other hand, probe 2, which has no imidazole moiety, was not able to detect any metal ion. In the case of probe 1, electrons on the imidazole nitrogen are available for electron transfer (ET), which was responsible for its green emission band that was quenched on addition of Hg²⁺; this clearly indicates that these electrons were used for the formation of a coordinate bond with Hg²⁺ and that ET was switched off.

Full text of DOI:10.1016/j.saa.2015.03.091

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 250–254
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
N-(3-Imidazolyl)propyl dansylamide as a selective Hg2+ sensor
in aqueous media through electron transfer
⇑
Ashwani Kumar, Hong-Seok Kim
Department of Applied Chemistry, School of Applied Chemical Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
A highly Hg2+ selective chemosensor
1 was synthesized and investigated.
N-(3-Imidazolyl)propyl dansylamide
acting as a selective Hg2+ sensor in
aqueous media.
ꢀ
ꢀ
The sensor showed high selectivity
for Hg+2 even in the presence of other
interfering metals (Ag+, Cu+2, Zn+2).
The detecting mechanism of Hg2+ was
based on the electron transfer (ET).
a r t i c l e i n f o
a b s t r a c t
Article history:
N-Imidazolylpropyl dansylamide 1 was synthesized for the sensing of metal ions and found to be selec-
tive and sensitive toward Hg2+ ions in a PBS–EtOH (1:4, pH = 7.4) solution. The sensing ability of probe 1
was examined by UV–Vis, fluorescence, and 1H NMR spectroscopy. The sensing of Hg2+ exhibited a
quenching of emission band at kmax = 515 nm of probe 1, which was associated with quenching of green
fluorescence emission under 365 nm illumination. Probe 1 showed a good association constant with Hg2+
(Ka = 6.48 Â 104 MÀ1) with a stoichiometry of 1:1 in PBS–EtOH (1:4, pH = 7.4) having the lowest detection
Received 12 January 2015
Received in revised form 26 February 2015
Accepted 21 March 2015
Available online 28 March 2015
Keywords:
limit of 1 l
M for Hg2+; on the other hand, probe 2, which has no imidazole moiety, was not able to detect
Fluorogenic probe
Dansylamide
Hg2+ ion sensor
Quenching
ET
any metal ion. In the case of probe 1, electrons on the imidazole nitrogen are available for electron trans-
fer (ET), which was responsible for its green emission band that was quenched on addition of Hg2+; this
clearly indicates that these electrons were used for the formation of a coordinate bond with Hg2+ and that
ET was switched off.
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
are very toxic to organisms, including human [6–8]. The high affin-
ity of mercury and its derivatives for thiol groups in proteins and
Metal ions play an essential role in about one third of the known
enzymes; in particular, they can modify the electron flow in a sub-
strate or enzyme, thus effectively controlling an enzyme-catalyzed
reaction [1–5]. Without the appropriate metal ion, a biochemical
reaction catalyzed by a particular metalloenzyme may proceed, if
at all, very slowly. Some of the metal ions, such as mercury and lead,
enzymes causes dysfunction of cells, leading to health problems.
Moreover, it can accumulate in plants, thereby reducing the rate
of photosynthesis and transpiration, and in the human body, result-
ing in a variety of damaging health effects such as prenatal-brain
damage, cognitive disorders, and immune system dysfunction, even
at relatively low concentrations. Methyl-mercurial species are
readily absorbed by the human gastrointestinal (GI) tract; they
can cross the blood–brain barrier and target the central nervous
system [9–15]. A noteworthy epidemic occurred in Iraq following
⇑
Corresponding author. Tel.: +82 53 9505588; fax: +82 53 9506594.
E-mail address: kimhs@knu.ac.kr (H.-S. Kim).
http://dx.doi.org/10.1016/j.saa.2015.03.091
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

A. Kumar, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 250–254
251
the use of methyl mercury-tainted seed grain for bread. The United
States Environmental Protection Agency (EPA) has mandated an
upper limit of 2 ppb (10 nM) for Hg2+ in drinking water [16]. The
health concerns over exposure to mercury have motivated the
exploration of selective and efficient methods for the monitoring
of mercury in biological and environmental samples. Fluorescent
molecules appended with different types of architectures, such as
thioether containing crown ethers/acetals [17–19], thioureas
[20–23], podands [24–27], amines/amides [28–33], spirolactones
[34–35], and heterocycle-based moieties [36–40], are used for
Hg2+ sensing. Most of these are chemodosimeters, i.e., irreversibly
selective Hg2+ sensors. Others are chemosensors, i.e., they can
mass spectrum (HRMS) of probe 1 clearly showed a molecular ion
peak for [M+H]+ at m/z = 359.1543 (see ESI). Similarly, probe 2 was
synthesized in a single step from dansyl chloride and characterized
by 1H and 13C NMR as well as HRMS.
The UV–Vis absorption spectrum of probe 1 (20
lM, PBS–EtOH
(1:4), pH = 7.4) exhibited absorption maxima at kmax = 338 nm.
Upon addition of different metal ions, such as Na+, K+, Mg2+, Ca2+
,
Ba2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Pb2+, Ga3+, In3+, and
Hg2+, only Hg2+ showed a significant red shift (kmax = 370 nm);
the other metal ions did not show any significant changes in the
UV–Vis spectra of probe 1 (Fig. SI 1).
Excitation of probe 1 (3 lM, PBS–EtOH (1:4), pH = 7.4) at
338 nm (kmax in the UV–Vis spectra of probe 1) resulted in fluores-
cence emission maxima at 515 nm with high quantum yield
reversibly detect Hg2+
,
albeit non-selectively, showing some
interference from either Cu2+/Ag+ [41–45]. In continuation of our
research efforts on metal ion sensing [46–52], in this study we focus
on Hg2+ sensing in aqueous media.
(
U
= 0.31). Upon addition of different metal ions, such as Na+, K+,
Mg2+, Ca2+, Ba2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Pb2+, Ga3+
,
Dansyl, which is a good fluorescent tag used extensively in
research, has a variety of binding sites for metal ion sensing
In3+, and Hg2+, only Hg2+ caused quenching of the green emission
band at kmax = 515 nm; other metal ions did not show any signifi-
cant changes in the fluorescence emission band of probe 1
(Figs. 1 and SI 2).
[53–57]. Thus, we synthesized
a dansyl-appended amide of
3-aminopropylimidazole/n-butylamine, i.e., probes 1 and 2, respec-
tively, for metal ion sensing in aqueous media. These probes were
easily synthesized in a single step by the reaction of dansyl chloride
with the corresponding amine, e.g., 3-aminopropylimidazole/
n-butylamine in good yield.
Upon gradual aliquot additions of Hg(ClO4)2 to probe 1 (3 lM,
PBS–EtOH (1:4), pH = 7.4), the emission intensity at 515 nm slowly
decreased until saturation. The fitting of these fluorescence titra-
tion data shows the formation of a 1:1 complex with a good
association constant (Ka = 6.48 Â 104 MÀ1) (Fig. 2). Probe 1 can
detect Hg2+ in the range of 1–11
lM: that was determined from
Results and discussion
the linear relationship between fluorescence emission intensity
at kmax = 515 nm i.e., I515 vs [Hg2+] having R = 0.9969 on titration
of probe 1 with Hg2+ (Fig. SI 3). The formation of the 1:1 complex
of probe 1 with Hg2+ ion was also observed from Job’s plot (Fig. 3).
In order to check their interference, 10 equiv of other metal ions
were added to the solution of 1 + [Hg2+] (1:1)-complex; it was
found that probe 1 could detect Hg2+ ions even in the presence
of other metal ions (Fig. 4).
Probe 1 was easily synthesized by the reaction of dansyl chlo-
ride with 1(3-aminopropyl)-imidazole in dichloromethane in good
yield (Scheme 1). The 1H NMR spectrum of probe 1 in DMSO-d6
showed three CH2 propyl-chain groups: two as multiplet at d
1.67–1.74, 2.69–2.74, and one as
a triplet at d 3.86 for
SO2NHCH2; one singlet at d 2.82 for six protons of –N(CH3)2; and
three imidazole protons as singlet at d 6.88, 6.97, and 7.53 for
the H-b, -c, and, -a protons, respectively. In the 13C NMR spectrum
of probe 1, imidazole C-2 appears at d 151.83. The high-resolution
In the case of probe 2 (3
lM, PBS–EtOH (1:4), pH = 7.4), excita-
tion at 338 nm (kmax in the UV–Vis spectra of probe 2) resulted in
Scheme 1. Synthesis of probes 1 and 2.
Fig. 1. Fluorescence relative intensity of probe 1 (3
figure, visual fluorescence color change of probe 1 (3
figure legend, the reader is referred to the web version of this article.)
l
l
M, PBS–EtOH (1:4), pH = 7.4) on addition of 10 equiv of different metal ions (kex = 338 nm, kem = 515 nm); also in the
M) with Hg2+ (10 equiv) under illumination at 365 nm is shown. (For interpretation of the references to color in this

252
A. Kumar, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 250–254
Fig. 2. Fluorescence titration of probe 1 (3 lM, PBS–EtOH (1:4), pH = 7.4) with
Hg(ClO4)2, kex = 338 nm. The inset shows the curve fitting; points show the
experimental values and line shows the curve fit at I515 vs [Hg2+], respectively.
Fig. 5. Fluorescence study of probe
2 (3 lM, PBS–EtOH (1:4), pH = 7.4) upon
addition of different metal ions; kex = 338 nm, kem = 515 nm.
Hg2+ ions. In order to further investigate the mode of complexation
and binding nature of Hg2+ ions with probe 1, the 1H NMR titration
of probe 1 with Hg2 ions in DMSO-d6 was carried out (Figs. 6 and SI
3); DMSO-d6 was used because precipitation was observed in
CD3OD.
The addition of 1 equiv of Hg(ClO4)2 to the solution of probe 1 in
DMSO-d6 led to a significant downfield shift of the imidazole pro-
tons labeled as Ha, Hb, and Hc from d 7.530 to 8.365, d 6.880 to
7.340 and d 6.966 to 7.616 respectively; while Hg of the dansyl unit
also shifted downfield from d 8.458 to 8.479; whereas protons Hl
shifted upfield from d 8.283 to 8.266. Because of the active nature
of sulfonamide N-H signal (Hn), however, disappeared, probably
due to the deprotonation induced by Hg2+, which was also sup-
ported by the significant upfield shift of the Hl proton. Similarly,
the aliphatic signals of the propyl-chain i.e., protons d, e and f
are shifted downfield from d 2.710 to 2.745, d 1.710 to 1.870 and
d 3.860 to 4.210 respectively; this effect was more pronounced in
the case of CH2 (f-protons). No changes were observed in the
methyl signals (m-protons) of N,N-dimethyl (Fig. SI 4). Upon a fur-
ther addition of 1 equiv of Hg(ClO4)2, no further shift of the proton
signals was observed, indicating the formation of the 1:1 complex
between probe 1 and Hg2+. In this case, the electrons on the
nitrogen of the imidazole ring were available for electron transfer
Fig. 3. Job’s plot for the complex of probe 1 (3
Hg(ClO4)2, kex = 338 nm, kem = 515 nm.
lM, PBS–EtOH (1:4), pH = 7.4) with
fluorescence emission maxima at 515 nm. Upon addition of differ-
ent metal ions, such as Na+, K+, Mg2+, Ca2+, Fe2+, Co2+, Ni2+, Cu2+
,
Zn2+, Ag+, Cd2+, Pb2+, Ga3+, In3+, and Hg2+, no significant changes
in the fluorescence emission intensity of probe 2 were observed
(Fig. 5).
The fluorescence study of probe 2 clearly showed the relevance
of the imidazole ring in probe 1, which provides the appropriate
binding site for the electron transfer (ET) for the detection of
Fig. 4. Interference study of probe 1 (3
kem = 515 nm.
l
M, PBS–EtOH (1:4), pH = 7.4) upon addition of different metal ions to the solution of 1 + [Hg2+](1:1)-complex, kex = 338 nm,

A. Kumar, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 250–254
253
(iii)
a
(ii)
(i)
c
b
b
c
g
l
n
j
i
a
h,k
Fig. 6. (i) Partial 1H NMR spectra of probe 1; (ii) upon addition of 1 equiv of Hg(ClO4)2; (iii) 2 equiv of Hg(ClO4)2 in DMSO-d6.
ET ON
ET OFF
Fig. 7. The proposed scheme for complexation of probe 1 with Hg2+ ion.
(ET), which was responsible for the green emission band at
kmax = 515 nm that was quenched upon addition of Hg2+; this
clearly indicates that these electrons were used for the formation
of the coordinate bond with Hg2+ and that ET was switched off.
Thus, based on the results obtained from fluorescence experi-
ments, 1H NMR titrations, and job’s plot, we proposed a binding
model of Hg2+ ion detection by probe 1 as shown in Fig. 7.
measurements were performed at 298 K. Analytical grade ethanol
was purchased from Merck. All other materials for synthesis were
purchased from Aldrich Chemical Co. and used as received. The
quantum yield (U) was calculated using the procedure reported
in the literature [58].
Synthesis of probes 1 and 2
Conclusions
Probe 1
To a solution of dansyl chloride (134 mg, 0.5 mmol) in dichlor-
omethane (10 mL), which was stirred at 0–10 °C under argon
atmosphere, 1(3-aminopropyl)imidazole (125 mg, 1.0 mmol) was
added dropwise. Triethylamine (202 mg, 2.0 mmol) was then
added for neutralization of the generated acid; the reaction mix-
ture was stirred at room temperature for 3 h. After completion of
the reaction, the reaction mixture was concentrated and purified
by silica gel column chromatography with CH2Cl2: CH3OH (9:1)
as eluent (Rf = 0.6) to obtain yellow solid 1 (90 mg, 50%). mp.
72 °C (CH2Cl2-hexane); 1H NMR (400 MHz, DMSO-d6) d 1.67–1.74
(m, 2H, CH2), 2.69–2.74 (m, 2H, CH2), 2.82 (s, 6H, 2 x CH3), 3.86
(t, J = 6.8 Hz, 2H, CH2), 6.88 (s, 1H, ImHb), 6.97 (s, 1H, ImHc), 7.26
(d, J = 6.8 Hz, 1H, ArH), 7.53 (s, 1H, ImHa), 7.61 (t, J = 8.0 Hz, 2H, 2
x ArH), 8.02 (t, J = 6.0 Hz, 1H, SO2NH), 8.07 (d, J = 8.0 Hz, 1H,
ArH), 8.28 (d, J = 8.8 Hz, 1H, ArH), 8.46 (d, J = 8.8 Hz, 1H, ArH);
13C NMR (100 MHz, DMSO-d6) d 31.12 (CH2), 39.80 (CH2), 43.42
(CH2), 45.43 (2 x CH3), 115.55, 119.32, 119.42, 124.01, 128.30,
128.68, 128.81, 129.38, 129.45, 129.90, 136.12, 137.40, 151.83;
HR-FAB mass calcd for: C18H23N4O2S (M + H)+: 359.1542; Found:
m/z 359.1543.
In this work, probe 1 was found to act as a good sensor for Hg2+
ions in aqueous solution. The probe enabled the visual detection of
Hg2+ through a color change under 365 nm illumination accompa-
nied with the quenching of green emission band at kmax = 515 nm
through ET having lowest detection limit of 1 l .
M for Hg2+
Experimental section
General
The melting points were determined using a Thomas-Hoover
capillary melting-point apparatus and were uncorrected. The 1H
and 13C NMR spectra were recorded on a Bruker AM-400 spec-
trometer using Me4Si as the internal standard. The HR-FAB mass
was determined at the KBSI Daegu branch. The UV–Vis absorption
spectra were obtained with a Shimadzu UV-1650PC spectropho-
tometer. The fluorescence spectra were measured on a Shimadzu
RF-5301 fluorescence spectrometer equipped with a xenon dis-
charge lamp using 1 cm quartz cells with slit width 5 nm. All the

254
A. Kumar, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 250–254
[16] Guidelines for drinking water quality, 3rd ed.; World Health Organization:
Probe 2
Geneva 2004, 188.
The procedure for the preparation of probe 2 is similar to that of
[17] S. Voutsadaki, G.K. Tsikalas, E. Klontzas, G.K. Froudakis, H.E. Katerinopoulos,
Chem. Commun. 46 (2010) 3292–3294.
probe 1; dansyl chloride (134 mg, 0.5 mmol), n-butylamine
(87 mg, 1.0 mmol), and triethylamine (202 mg, 2.0 mmol) were
used. The crude product was purified by silica gel column chro-
matography with CH2Cl2 as eluent (Rf = 0.8) to obtain a light-green
thick liquid 2 (135 mg, 88%). liquid at room temperature; 1H NMR
(400 MHz, CDCl3) d 0.74 (t, J = 7.2 Hz, 3H, CH3), 1.14–1.23 (m, 2H,
CH2), 1.32–1.39 (m, 2H, CH2), 2.87 (m, 2H, CH2), 2.92 (s, 6H, 2 x
CH3), 4.70 (bs, 1H, SO2NH), 7.23 (d, J = 7.2 Hz, 1H, ArH), 7.52–7.59
(m, 2H, 2 Â ArH), 8.25 (d, J = 7.6 Hz, 1H, ArH), 8.33 (d, J = 8.4 Hz,
1H, ArH), 8.59 (d, J = 8.4 Hz, 1H, ArH); 13C NMR (100 MHz, CDCl3)
[18] X. Cheng, Q. Li, C. Li, J. Qin, Z. Li, Chem. Eur. J. 17 (2011) 7276–7281.
[19] S.-H. Gao, M.-S. Xie, H.-X. Wang, H.-Y. Niu, G.-R. Qu, H.-M. Guo, Tetrahedron 70
(2014) 4929–4933.
[20] J.V. Mello, N.S. Finney, J. Am. Chem. Soc. 127 (2005) 10124–10125.
[21] Z. Guo, W. Zhu, M. Zhu, X. Wu, H. Tian, Chem. Eur. J. 16 (2010) 14424–14432.
[22] C. Wang, D. Zhang, X. Huang, P. Ding, Z. Wang, Y. Zhao, Y. Ye, Sens. Actuators, B
198 (2014) 33–40.
[23] G.K. Wang, Q.L. Mi, L.Y. Zhao, J.J. Hu, L.E. Guo, X.J. Zou, B. Liu, X.G. Xie, J.F.
Zhang, Q.H. Zhao, Y. Zhou, Chem. Asian J. 9 (2014) 744–748.
[24] J.S. Kim, M.G. Choi, K.C. Song, K.T. No, S. Ahn, S.- K. Chang, Org. Lett. 9 (2007)
1129–1132.
[25] M.-H. Ha-Thi, M. Penhoat, V. Michelet, I. Leray, Org. Biomol. Chem. 7 (2009)
1665–1673.
d
14.03, 20.08, 30.10, 34.40, 45.91, 115.73, 120.60, 123.73,
[26] Y.-B. Chen, Y.-J. Wanga, Y.-J. Lin, C.-H. Hu, S.-J. Chen, J.-L. Chir, A.-T. Wu,
Carbohydr. Res. 345 (2010) 956–959.
[27] K.-H. Chen, C.-Y. Lu, H.-J. Cheng, S.-J. Chen, C.-H. Hu, A.-T. Wu, Carbohydr. Res.
345 (2010) 2557–2561.
128.23, 130.16, 130.29, 130.49, 130.71, 134.87, 151.53; HR-FAB
mass calcd for: C16H22N2O2S (M)+: 306.1402; Found: m/z 306.1404.
[28] Y. Wan, W. Niu, W.J. Behof, Y. Wang, P. Boyle, C.B. Gorman, Tetrahedron 65
(2009) 4293–4297.
Acknowledgements
[29] J. Wang, X. Qian, J. Cui, J. Org. Chem. 71 (2006) 4308–4311.
[30] C.R. Lohani, J.M. Kim, K.-H. Lee, Tetrahedron 67 (2011) 4130–4136.
[31] P. Srivastava, S.S. Razi, R. Ali, R.C. Gupta, S.S. Yadav, G. Narayan, A. Misra, Anal.
Chem. 86 (2014) 8693–8699.
[32] S. Maiti, C. Pezzato, S.G. Martin, L.J. Prins, J. Am. Chem. Soc. 136 (2014) 11288–
11291.
This research was supported by the Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Science, ICT and Future Planning
– Republic of Korea (2013R1A1A2006777).
[33] J. Choi, S.K. Lee, J. Bae, S.-K. Chang, Tetrahedron Lett. 55 (2014) 5294–5297.
[34] C. Kaewtong, N. Niamsa, B. Wanno, N. Morakot, B. Pulpoka, T. Tuntulani, New J.
Chem. 38 (2014) 3831–3839.
Appendix A. Supplementary data
[35] N. Kumari, N. Deya, S. Bhattacharya, RSC Adv. 4 (2014) 4230–4238.
[36] X. Liu, X. Yang, Y. Fu, C. Zhu, Y. Cheng, Tetrahedron 67 (2011) 3181–3186.
[37] A. Han, X. Liu, G.D. Prestwich, L. Zang, Sens. Actuators, B 198 (2014) 274–277.
[38] A. Kumar, S. Kumar, Tetrahedron Lett. 53 (2012) 2030–2034.
[39] K. Bera, A.K. Das, M. Nag, S. Basak, Anal. Chem. 86 (2014) 2740–2746.
[40] X.-L. Ni, Y. Wu, C. Redshaw, T. Yamato, Dalton Trans. 43 (2014) 12633–12638.
[41] E. Karakus, M. Ucuncu, M. Emrullahoglu, Chem. Commun. 50 (2014) 1119–
1121.
[42] M. Tian, L. Liu, Y. Li, R. Hu, T. Liu, H. Liu, S. Wang, Y. Li, Chem. Commun. 50
(2014) 2055–2057.
[43] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Chem. Soc. Rev. 41 (2012) 3210–3244.
[44] S. Areti, D.S. Yarramala, K. Samanta, V.K. Hinge, J. Khedkar, C.P. Rao, RSC Adv. 4
(2014) 16290–16297.
[45] J. Park, B. In, L.K. Neupane, K.-H. Lee, Analyst 140 (2015) 744–749.
[46] A. Helal, H.-S. Kim, Tetrahedron Lett. 50 (2009) 5510–5515.
[47] A. Helal, S.H. Lee, S.H. Kim, H.-S. Kim, Tetrahedron Lett. 51 (2010) 3531–3535.
[48] A. Helal, S.H. Kim, H.-S. Kim, Tetrahedron 66 (2010) 9925–9932.
[49] A. Helal, M.H. Rashid, C.-H. Choi, H.-S. Kim, Tetrahedron 67 (2011) 2794–2802.
[50] A. Helal, M.H. Rashid, C.-H. Choi, H.-S. Kim, Tetrahedron 68 (2012) 647–653.
[51] A. Helal, H.G. Kim, M.K. Ghosh, C.-H. Choi, S.-H. Kim, H.-S. Kim, Tetrahedron 69
(2013) 9600–9608.
[52] B.-Y. Kim, H.-S. Kim, A. Helal, Sens. Actuators, B 206 (2015) 430–434.
[53] Y. Zhao, Z. Zhong, J. Am. Chem. Soc. 128 (2006) 9988–9989.
[54] D. Maity, T. Govindaraju, Chem. Commun. 46 (2010) 4499–4501.
[55] V. Tharmaraj, K. Pitchumani, Anal. Chim. Acta 751 (2012) 171–175.
[56] J. Piao, J. Lv, X. Zhou, T. Zhao, X. Wu, Spectrochim. Acta, Mol. Biomol. Spectrosc.
128 (2014) 475–480.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.03.091.
References
[1] J.J.R.F.D. Silva, R.J.P. Williams, The Biological Chemistry of the Elements,
Clarendon Press, Oxford, 1991.
[2] K.P. Carter, A.M. Young, A.E. Palmer, Chem. Rev. 114 (2014) 4564–4601.
[3] S.J. Lippard, J.M. Berg, Principles of Bioinorganic Chemistry, University Science
Books, Mill Valley, CA, 1994.
[4] E. Beutler, Blood Cells Mol. Dis. 39 (2007) 140–147.
[5] J.M. Berg, Y. Shi, Science 271 (1996) 1081–1085.
[6] T. Gunnlaugsson, M. Glynn, G.M. Tocci, P.E. Kruger, F.M. Pfeffer, Coord. Chem.
Rev. 250 (2006) 3094–3117.
[7] H.N. Kim, M.H. Lee, H.J. Kim, J.S. Kim, J. Yoon, Chem. Soc. Rev. 37 (2008) 1465–
1472.
[8] J.H. Jung, J.H. Lee, S. Shinkai, Chem. Soc. Rev. 40 (2011) 4464–4474.
[9] J. Gutknecht, J. Membr. Biol. 61 (1981) 61–66.
[10] T.W. Clarkson, L. Magos, Crit. Rev. Toxicol. 36 (2006) 609–662.
[11] T. Takeuchi, N. Morikawa, H. Matsumoto, Y. Shiraishi, Acta Neuropathol. 2
(1962) 40–57.
[12] H. Akagi, P. Grandjean, Y. Takizawa, P. Weihe, Environ. Res. Sect. A 77 (1998)
98–103.
[13] K. Eto, H. Tokunaga, K. Nagashima, T. Takeuchi, Toxicol. Pathol. 30 (2002)
714–722.
[57] P. Xie, F. Guo, R. Xia, Y. Wang, D. Yao, G. Yang, L. Xie, J. Lumin. 145 (2014) 849–
854.
[58] A. Kumar, H.-S. Kim, New J. Chem. 39 (2015) 2935–2942.
[14] P.W. Davidson, G.J. Myers, C. Cox, C.F. Shamlaye, D.O. Marsh, M.A. Tanner, M.
Berlin, J. Sloane-Reeves, E. Cernichiari, O. Choisy, A. Choi, T.W. Clarkson,
Neurotoxicology 16 (1995) 677–688.
[15] G. Shanker, L.A. Mutkus, S.J. Walker, M. Aschner, Mol. Brain Res. 106 (2002) 1–11.