JOURNAL OF CHEMICAL RESEARCH 2010
RESEARCH PAPER 619
NOVEMBER, 619–621
Mercapto thiadiazole-based sensors with high selectivity and sensitivity
for Hg2+ in aqueous solution
You-Ming Zhang, Ming-Xia Liu, Qi Lin, Qiao Li and Tai-Bao Wei*
Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University,
Lanzhou 730070, Gansu, P. R. China
Two simple mercapto thiadiazole-based sensors have been synthesised by a convenient method and exhibit excel-
lent sensitivity and selectivity for Hg2+ in DMSO/H2O (1:1, v/v) aqueous solution. The sensors react with Hg2+ to form
stable complexes and the association constants, Ka, are 4.4 × 104 M−1 and 1.0 × 103 M−1, respectively. Furthermore, the
detection limit of one sensor towards Hg2+ is 8.0 × 10−7 M.
Keywords: mercury ion sensors, mercapto thiadiazole, cation recognition
1: Yield: 89%, m.p. 235–236 °C (lit. 234–235 °C), 1H NMR
(DMSO-d6, 400MHz) δ 13.21 (s, 1H, S–H), 7.13 (s, 2H, N–H),
IR (KBr, cm−1) v: 3334 (N–H), 2925 (S–H), 1059 (C–N);
2: Yield: 60%, m.p. 219–221 °C (lit. 219–221 °C), 1H NMR
(DMSO-d6, 400MHz) δ 8.81 (s, 1H, CH=N), 7.64 (S, 1H,
N–H), 7.99–8.51 (m, 4H, PhH), IR (KBr, cm−1) v: 1561 (C=N),
3400–3250 (N–H).
The sensing abilities both 1 and 2 toward various metal cat-
ions, such as Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Fe3+, Hg2+, Ag+, Ca2+
and Cu2+, were primarily investigated by UV-Vis spectroscopy.
Upon adding 2 equiv. of Hg2+ to DMSO solutions of sensor 1,
the absorption at 322 nm in the corresponding UV-Vis spec-
trum decreased sharply, accompanied by a blue shift of 42 nm.
To validate the selectivity of 1, the same tests were applied
to other cations; no obvious changes were observed (Fig. 1).
The binding of sensor 2 with metal cations in DMSO was also
studied and a similar result was observed.
The selective response of 1 was investigated by adding vari-
ous cations to its H2O/DMSO (1:1, v/v) solution. Upon addi-
tion of 2 equiv. of Hg2+, sensor 1 showed obvious changes in its
UV-Vis spectrum (Fig. 2, in Electronic Supplementary Infor-
mation, ESI). Other cations did not cause such a change. With
the aim of excluding the possibility of these results being due
to pH changes, we carried out the same experiments in DMSO/
H2O (9.5:0.5, v/v), HEPES (10 mM) buffered solutions at pH
7.20 for sensor 1. A similar spectroscopic variation of the
absorption band was found as above for aqueous solutions.
Note also that the pH of the solution did not change during
these experiments, clearly excluding any pH effects.
To explore further the utility of sensor 1 as an ion-selective
chemosensor for Hg2+, competitive experiments were carried
out in the presence of 2.0 equiv. of Hg2+ and 2.0 equiv. of
various metal ions in a HEPES-buffered solution of sensor 1.
The optical absorbance of sensor 1 with Hg2+ at 283 nm
(Fig. 3 in ESI) was not influenced by the subsequent addition
The development of selective chemosensors for the detection
of mercury ion is of particular interest, because mercury is
considered one of the most toxic and dangerous heavy metal
elements.1–4 The design and synthesis of efficient sensors to
selectively recognise Hg2+ is a fundamental goal for organic
and analytical chemists.5,6 Much effort has gone into the devel-
opment of sensing devices for Hg2+, involving chromogenic7,8
and fluorescent chemosensors9,10, and sensors based on elec-
trochemical devices.11 However, several significant challenges
remain in these systems for practical application, such as
cross-sensitivities toward other metal ions, low water solubil-
ity, and especially complicated and expensive synthesis. In
view of this, and as a part of our research interest in molecular
recognition,12–14 we have attempted to obtain some easy-to-
synthesise, highly selective and sensitive Hg2+ sensors. Our
strategy for the design of Hg2+ sensors has been as follows.
First, in order to obtain an optimum response towards Hg2+, we
have introduced S–H and thiadiazole groups into the same
sensor molecule to strengthen the Hg2+ coordination capacity.15
Second, the receptors were designed to be easily synthesised.
The results showed that compounds 1 and 2 (see Scheme 1)
displayed a highly selective and sensitive response toward
Hg2+ in neutral aqueous solution.
Results and discussion
Compounds 1 and 2 were synthesised according to literature
methods.16 Compound 1 was prepared by mixing thiosemicar-
bazide (6.37 g, 0.06 mol) and CS2 (7.61 g, 0.10 mol) in DMF
solution under reflux conditions for 6 h. Then compound 1
(0.67 g, 0.005 mol) and p-nitrobenzaldehyde (0.76 g,
0.005 mol) were mixed in absolute ethanol, the solution was
refluxed with stirring for 2–3 h, then cooled to room tempera-
ture and the solvent was removed by evaporation. Finally, the
crude product was purified by recrystallisation from ethanol to
give compound 2.
Scheme 1 The synthesis of sensors 1 and 2.
* Correspondent. E-mail: weitaibao@126.com