A highly selective and ratiometric fluorescent sensor for relay recognition of zinc(ii) and sulfide ions based on modulation of excited-state intramolecular proton transfer

Article abstract of DOI:10.1039/c3ra42931h

A new fluorescent 2-(2'-aminophenyl)benzimidazole derivatized sensor BMD was designed and synthesized. In CH₃CN/H₂O (2:8, v/v, HEPES 10 mM, pH 7.4) solution, sensor BMD displays two emission bands and exhibits a highly selective and ratiometric response to Zn²⁺ ions with a distinctly longer-wavelength emission blue shifted through the inhibition of the excited-state intramolecular proton transfer (ESIPT) process. BMD can clearly discriminate Zn²⁺ from Cd²⁺ and other metal ions. Moreover, the in situ generated BMD-Zn²⁺ solution exhibits a highly selective and ratiometric response to S^2- among various anions and thiol-containing amino acids via Zn²⁺ displacement approach, which results in a revival of the ESIPT phenomenon of free BMD. These results demonstrate that BMD can serve as a ratiometric sensor for sequential recognition of Zn²⁺ and S^2- in aqueous solution through inhibition and turn-on of ESIPT process. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra42931h

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A highly selective and ratiometric fluorescent sensor for
relay recognition of zinc(II) and sulfide ions based on
modulation of excited-state intramolecular proton
transfer3
Cite this: RSC Advances, 2013, 3,
16802
Lijun Tang,* Mingjun Cai, Pei Zhou, Jia Zhao, Keli Zhong, Shuhua Hou
and Yanjiang Bian
A
new fluorescent 2-(29-aminophenyl)benzimidazole derivatized sensor BMD was designed and
synthesized. In CH3CN/H2O (2 : 8, v/v, HEPES 10 mM, pH 7.4) solution, sensor BMD displays two emission
bands and exhibits a highly selective and ratiometric response to Zn2+ ions with a distinctly longer-
wavelength emission blue shifted through the inhibition of the excited-state intramolecular proton
transfer (ESIPT) process. BMD can clearly discriminate Zn2+ from Cd2+ and other metal ions. Moreover, the
in situ generated BMD-Zn2+ solution exhibits a highly selective and ratiometric response to S22 among
various anions and thiol-containing amino acids via Zn2+ displacement approach, which results in a revival
of the ESIPT phenomenon of free BMD. These results demonstrate that BMD can serve as a ratiometric
sensor for sequential recognition of Zn2+ and S22 in aqueous solution through inhibition and turn-on of
ESIPT process.
Received 13th June 2013,
Accepted 12th July 2013
DOI: 10.1039/c3ra42931h
www.rsc.org/advances
emission collection efficiency, the environment around the
sensor, sensor concentration, bleaching and illumination
1. Introduction
intensity.5 On the other hand, Zn2+ recognition often suffers
from the interference of Cd2+,6 because these two metals are in
the same main group in the Periodic Table and have very
similar chemical properties. Although many successful fluor-
escent probes for Zn2+ and Cd2+ have been reported,7 the
design of single fluorescent probes that can successfully
discriminate Zn2+ from Cd2+ still remains attractive and
challenging.8
The development of chemical probes for highly selective
recognition of biologically and environmentally important
heavy and transition metal (HTM) ions as well as anions has
received increasing attention due to the important roles they
play in chemical, biological and environmental processes.1 As
the second most abundant transition metal ion in human
body, Zn2+ plays critical roles in a variety of biological
processes, such as gene transcription, signal transmission,
and mammalian reproduction.2 The normal Zn2+ content of
blood plasma is 12 to 16 mM in humans,2d however, disruption
of Zn2+ concentration in cells can result in some pathological
processes including Alzheimer’s disease, epilepsy and infantile
diarrhoea.2c,3 In recent years, considerable efforts have been
focused on the development of fluorescent probes for Zn2+ due
to the high sensitivity and easy operability of fluorescence
techniques.4
Sulfide, as a toxic traditional pollutant, has received
increasing attention. Although sulfide has many applicable
utilities in the fields of manufacturing of sulfuric acid, dyes
and cosmetics,9 exposure to high levels of sulfide can lead to
various physiological and biochemical problems including
irritation in mucous membranes, unconsciousness, and
respiratory paralysis.9,10 Therefore, sulfide detection has
received immense interest and a number of S22 ion-selective
fluorescent probes have been developed.11 Sulfide sensing by
using a metal complex via S22-induced metal ion displacement
has been proved to be an effective method.11b–f,12 However,
fluorescent sulfide detection with a Zn2+ complex is still rare.
Herein we report the synthesis and ion recognition
behavior of a new di(2-picolyl)amine (DPA) decorated benzi-
midazole derivative (BMD) (Fig. 1). BMD can discriminate Zn2+
from Cd2+ and other metal ions through distinct fluorescence
responses; the in situ generated BMD-Zn2+ complex exhibits
Fluorescent probes that exhibit a ratiometric response to
Zn2+ are more attractive and are still highly desired. This kind
of probe can eliminate the effects of some factors such as
Department of Chemistry, Liaoning Provincial Key Laboratory for the Synthesis and
Application of Functional Compounds, Bohai University, Jinzhou, China.
E-mail: ljtang@bhu.edu.cn; Fax: +86 416 3400158; Tel: +86 416 3400302
Electronic supplementary information (ESI) available: Cif file, 1H NMR, 13C
3
NMR and HRMS of sensor BMD, and other supplementary data. CCDC 919147.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3ra42931h
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ESIPT have been documented for metal cation sensing.17
Although the ESIPT feature of 2-(29-aminophenyl)benzimida-
zole (2-APBI) and its derivatives has been well investigated for
many years, only one study on 2-(29-benzenesulfonamidophe-
nyl)benzimidazole derivatives as Zn2+ sensors based on
inhibition of ESIPT has been reported.17f Unfortunately, those
probes also seriously suffer from the interference of Cd2+.
Early studies demonstrated that 2-(29-acetamidophenyl)benzi-
midazole displays a more active ESIPT process compared with
that of its parent compound 2-APBI,18 because the introduced
electron-withdrawing acetyl group can greatly increase the
acidity of 29-NH, which is favorable to ESIPT. However, metal
ion recognition by using of this kind of probe has not been
reported so far. One can envision that if the ESIPT process can
be inhibited through a metal ion binding process, it is possible
to develop a ratiometric probe for the metal ion. Furthermore,
if the metal ion in the formed metal-fluorophore complex can
be snatched by a certain anion, the inhibited ESIPT will revive,
thus resulting in ratiometric recognition of the anion. Based
on this idea, we designed and synthesized a new DPA-
decorated 2-APBI derivative BMD as a promising fluorescent
sensor.
Fig. 1 Molecular structure of sensor BMD with the atomic numbering scheme.
The solvent molecule (H2O) was omitted for clarity.
highly selective ratiometric recognition to S22 via a Zn2+
displacement approach. As far as we are aware, this is the first
example for ratiometric fluorescent recognition of Zn2+ and
S22 with a simple Zn2+ and Cd2+ discriminable fluorescent
sensor.
The sensor BMD was facilely synthesized by reaction of N-[2-
(1H-benzoimidazol-2-yl)-phenyl]-2-chloroacetamide (2) with
DPA (Scheme 1). The structure of BMD was characterized by
1H NMR, 13C NMR, high resolution mass spectroscopy (HRMS)
(see Electronic Supplementary Information ), and single
3
crystal X-ray structural analysis (Fig. 1). The X-ray crystal-
lographic structure clearly indicates that the introduced DPA
moiety together with the amide and imino nitrogen atoms can
provide coordination sites when BMD binds to a certain metal
ion. The crystal structure also shows that BMD exists in trans
form (the O and H atoms in the amide group point to opposite
sides), and there is an intramolecular hydrogen bond between
the amide NH proton and imino nitrogen atom of benzimi-
dazole (N(2)) with a distance of 2.7348 Å; these structural
features are favorable to the desired ESIPT process.18
2. Results and discussion
2.1 Design and synthesis of sensor BMD
To date a number of conventional sensing mechanisms, such
as photoinduced electron transfer (PET),1a intramolecular
charge transfer (ICT),1a electronic energy transfer (EET),1a
fluorescence resonance energy transfer (FRET),13 and excimer
formation,1a have been developed and applied to the optical
detection of different target species. Recently, a new sensing
mechanism based on the modulation of excited-state intra-
molecular proton transfer (ESIPT)14 has been explored in ion
detection; the commonly used ESIPT fluorophores are focused
on 2-(29-hydroxyphenyl)benzoxazole and 2-(29-hydroxyphenyl)-
benzothiazole, and they are generally applied to anion
recognition through inhibition15 or turn on16 of the ESIPT
process; only very few examples based on the modulation of
2.2 Fluorescence response of BMD to Zn2+
Firstly, the fluorescence spectra of BMD in different solvents
were examined. As shown in Fig. S1 (ESI ), in aprotic solvents
3
such as cyclohexane, dioxane and acetonitrile, BMD displays
similar emission spectrum shape with a longer-wavelength
emission band at around 513 nm accompanied with a large
Stokes shift greater than 180 nm. This longer-wavelength
Scheme 1 Synthesis of sensor BMD.
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emission band centered at 424 nm appeared with 78 nm of
longer-wavelength emission blue-shift. The addition of 1.0
equiv. Cd2+ ions resulted in a 23 nm blue-shift of the longer-
wavelength emission from 502 nm to 479 nm. The distinct
blue-shifts induced by these two metal ions indicate that Zn2+
and Cd2+ coordinate with the BMD fluorophore in different
manners, which elicit intramolecular charge transfer to
different extents. Other HTM ions did not induce any
significant emission wavelength shift. Among them, Hg2+
and Ag+ caused a slight decrease in fluorescence intensity, and
Fe2+ and Pb2+ led to a moderate quenching effect. However,
Cu2+, Co2+ and Ni2+ ions resulted in almost complete
fluorescence quenching owing to their paramagnetic nature.
The presence of metal ions including K+, Na+, Mg2+, Ca2+, Sr2+,
Ba2+, Al3+, Fe3+ and Mn2+ do not induce noticeable fluores-
cence spectra changes. These observations reveal that the
sensor BMD shows specific responses to Zn2+ and Cd2+ over
other metal ions, and BMD can clearly discriminate Zn2+ from
Cd2+ by the distinct longer-wavelength emission blue-shift.
The sensing property of BMD to Zn2+ was further evaluated
by fluorescence titration experiment (Fig. 3). The emission
intensities at 367 nm and 502 nm of BMD solution
progressively decreased on incremental increasing the added
Zn2+ concentration. Meanwhile, the intensity of the newly
formed emission band at 424 nm gradually increased. The
titration reached saturation when 1.0 equiv. of Zn2+ ions was
employed, suggesting the formation of a 1 : 1 complex
between BMD and Zn2+, which was further confirmed by
Scheme 2 Emission mechanism for sensor BMD.
emission is assigned to the ESIPT fluorescence emission band
(tautomer emission). Meanwhile, there are also three adjacent
shorter-wavelength emission bands at around 370 nm (normal
emission bands). When in protic solvents such as methanol
and water, the longer-wavelength emission is slightly blue
shifted to 503 nm and 499 nm, respectively. Interestingly, in
neat water solution, the fine structure of normal emission
bands fused together and only behaves as a single smooth
emission band centered at 373 nm. These observations are
very similar to the ESIPT phenomena of 2-(29-acetamidophe-
nyl)benzimidazole18 and 2-(29-benzamidophenyl)benzimida-
zole.19 The emission mechanism of sensor BMD is
illustrated in Scheme 2. For the sake of good probe solubility
and potential applicability, a cosolvent of CH3CN/H2O (2 : 8, v/
v) was selected in this study.
Then, the fluorescence response of BMD (10 mM) in CH3CN/
H2O (2 : 8, v/v, pH 7.4) to various metal ions was examined
(Fig. 2). Free BMD solution exhibits a strong emission band at
502 nm (tautomer emission) and a weak emission band at 367
nm (normal emission) upon being excited at 315 nm. Upon
addition of 1.0 equiv. of Zn2+, the emission intensities at 502
nm and 367 nm were greatly decreased, concomitantly a new
Job’s plot (Fig. S2, ESI ). HRMS analysis of the BMD solution in
3
the presence of Zn2+ exhibited a prominent peak at m/z
511.1219, which is assignable to the species of [BMD + Zn2+
2
H+]+ (Fig. S3, ESI ). This result presented solid evidence for the
3
1 : 1 interaction between BMD and Zn2+. The well-defined
isoemissive points appearing at 379 nm and 458 nm indicate
the existence of an equilibrium between free BMD and a BMD-
Zn2+ complex. Thus, sensor BMD displays a ratiometric
response output to Zn2+. Based on the titration profile, the
binding constant was evaluated to be 1.63 6 105 M21 (Fig. S4,
ESI ) by using the Hill plot method,20 and the detection limit
3
Fig. 2 Fluorescence spectra changes of BMD (10 mM) in CH3CN/H2O (2 : 8, v/v,
HEPES 10 mM, pH 7.4) in the presence of 1.0 equiv. of different metal ions. Inset:
The naked eye fluorescence changes of BMD before and after addition of Zn2+
and Cd2+ ions under the portable UV lamp at 254 nm.
Fig. 3 Fluorescence spectra changes of BMD (10 mM) solution upon the
addition of different amounts of Zn2+
.
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Fig. 5 1H NMR spectrum of BMD in DMSO-d6 without (a) and with (b) 1.0 equiv.
Fig. 4 Changes in the fluorescence intensity ratios (F424nm/F502nm) of BMD
solution (10 mM) in CH3CN/H2O (2 : 8, v/v, HEPES 10 mM, pH 7.4). The gray bars
represent the intensity ratio F424nm/F502nm of BMD solution in the presence of
1.0 equiv. of different metal ions. The red bands represent the intensity ratio
(F424nm/F502nm) of BMD for 1.0 equiv. of Zn2+ in the presence of different metal
ions.
of Zn2+ and the proposed binding mode of BMD with Zn2+
.
addition of Zn2+ this signal shifted upfield to about 8.0 ppm
(Fig. 5b), indicating the coordination of the amide O atom with
Zn2+, which weakened the hydrogen bonding. The signal of
protons He neighbouring pyridine N atom at 8.47 ppm are
shifted downfield to 8.68 ppm upon addition of Zn2+. In
addition, the methylene protons (Hc) adjacent to the amide
group signal at 3.44 ppm (Fig. 5a) shifted downfield to 4.12
ppm after the addition of Zn2+ (Fig. 5b). Meanwhile, the singlet
peak of the methylene protons (Hd) in the DPA moiety at 4.0
ppm (Fig. 5a) is shifted downfield and divided into two
nonequivalent groups (appearing at 4.64 ppm and 4.42 ppm,
respectively) with a large coupling constant of 16 Hz (Fig. 5b),
which indicates that the free rotation of s bonds in DPA is
suppressed after coordination with Zn2+. Thus the 1H NMR
studies demonstrate that BMD binds with Zn2+ through an
imidic acid form, and the amide oxygen and DPA nitrogen
atoms are involved in coordination with Zn2+. The proposed
binding mode of BMD with Zn2+ is depicted in Fig. 5.
Similarly, we explored the fluorescence titration of the BMD
solution with different concentrations of Cd2+ ions (Fig. 6).
When the Cd2+/BMD ratio is smaller than 0.6, the fluorescence
intensity was enhanced gradually and blue-shifted from 502
nm to 486 nm (Fig. 6a). Upon further addition of Cd2+ ions
(0.7–1.5 eq.), however, the emission intensity at 486 nm
gradually decreased and further blue-shifted to 479 nm
(Fig. 6b). These results indicate the formation of two different
metal complexes between BMD and Cd2+, the metal/ligand
ratios of which may 1 : 2 and 1 : 1, respectively.23 This
speculation was confirmed by HRMS analysis of BMD solution
in the presence of 0.5 equiv. and 1.0 equiv. of Cd2+ ions,
of BMD to Zn2+ was evaluated to be 6.21 6 1027 M (Fig. S5,
ESI ). Fluorescence changes of the BMD solution with 1.0
3
equiv. of Zn2+ at different pH values were examined. The
results demonstrate that the intensity ratios (F424nm/F502nm
)
are almost stable between pH 6 and 9 (Fig. S6, ESI ). Both
3
strong acidic and basic conditions can induce a decrease in
the intensity ratio (F424nm/F502nm). These results indicate the
potential practical applicability of BMD for Zn2+ detection in
real water samples.
To further confirm the high selectivity of BMD to Zn2+,
fluorescence competition experiments were then conducted
(Fig. 4). The emission intensity ratios (F424nm/F502nm) of BMD
solution in the presence of miscellaneous metal ions did not
show significant changes. Upon further addition of Zn2+ to
metal ion containing BMD solution, the ratios of F424nm/F502nm
significantly increased. These results further corroborate the
high selectivity of BMD to Zn2+ without significant interference
from other metal ions.
To get further insight into the binding mode of BMD and
Zn2+, the 1H NMR spectrum of BMD in DMSO-d6 in the
presence of 1.0 equiv. of Zn2+ was determined and the result
was shown in Fig. 5. The amide NH (Ha) signal appeared at
13.26 ppm in free BMD (Fig. 5a), which disappeared upon the
addition of 1.0 equiv. of Zn2+ (Fig. 5b). However, the imidazole
NH (Hb) signal at 13.16 ppm became broadened with a small
downfield shift. The Zn2+-induced disappearance of the amide
NH proton may be attributed to the transformation of the
amide group to imidic acid upon binding with Zn2+ 7i,8g,21
which also implies that the negatively charged oxygen atom in
deprotonated imidic acid may coordinate with Zn2+ 22
This
,
respectively (Fig. S7 and S8, ESI ). These complicated binding
3
modes retarded the quantitative detection of Cd2+ with BMD.
.
2.3 Fluorescence recognition of BMD-Zn2+ for sulfide
Zn2+ binding event suppressed the ESIPT process of BMD and
led to the ratiometric fluorescence changes. The signal
appearing at 8.77 ppm (Fig. 5 a) can be assigned to the Hf
(C(12) proton, see Fig. 1) due to the existence of hydrogen
bonding between Hf and the amide O atom (2.8503 Å). Upon
Considering the high affinity of sulfide to Zn2+, the in situ
formed BMD-Zn2+ complex (1 : 1 mixing of BMD and Zn2+) was
explored as a promising S22 sensor. Fig. 7 shows the
fluorescence spectra changes of BMD-Zn2+ solution (10 mM)
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in the presence of 20 equiv. of different anions including F2,
2
Cl2, Br2, I2, CN2, SCN2, PO432, S2O322, S2O822, H2PO4
,
,
HPO422, NO22, NO32, SO422, P2O742, HSO42, CO322, HCO3
2
AcO2, ClO42, C2O422, and some thiol-containing amino acids
such as L-cysteine (L-Cys), L-homocysteine (L-Hcys) and
reduced glutathion (GSH). Obviously, only the addition of
S22 anions resulted in significant fluorescence spectrum
changes. The emission at 424 nm was greatly quenched,
meanwhile two new emission bands at 367 nm and 502 nm
were developed. Other anions and thiol-containing amino
acids induced almost negligible fluorescence changes. These
results demonstrate that the sensor BMD-Zn2+ has an excellent
selectivity toward the S22 ion.
Fluorescence titration experiments were subsequently con-
ducted to examine the sensing property of BMD-Zn2+ to S22
(Fig. 8). Upon gradually increasing the S22 concentration (0–20
equiv.), the emission band at 424 nm progressively decreased,
and simultaneously the emission peak at 502 nm was
gradually enhanced. When 20 equiv. of S22 anions was
employed, the fluorescence spectrum became stable and was
restored to the original emission pattern of free BMD. The
almost complete fluorescence emission recovery of BMD-Zn2+
to the original state of free BMD strongly indicates an S22
-
-
induced Zn2+ removal process. Solid evidence for this S22
induced Zn2+ sequestering came from the HRMS spectrum of
BMD-Zn2+ solution in the presence of S22 anions (Fig. S9,
ESI ). The peak for the BMD-Zn2+ complex disappeared and a
3
peak at m/z 471.1914 assignable to [BMD + Na+]+ was observed,
indicative of the S22-induced Zn2+ sequestering from BMD-
Zn2+, which is responsible for the ESIPT restoration of BMD.
The detection limit of BMD-Zn2+ to S22 was evaluated to be
3.46 6 1026 M (Fig. S10, ESI ).
3
The excellent selectivity of BMD-Zn2+ to S22 was further
validated by competition experiments (Fig. 9). In the absence
of S22, the emission intensity ratios (F424nm/F502nm) of BMD-
Zn2+ solution upon the addition different anions and thiol-
containing amino acids (20 equiv. of each) were similar and
scarcely fluctuated. Upon further addition of 20 equiv. of S22
to the solution containing other tested species, the emission
Fig. 6 Fluorescence spectra changes of BMD solution (10 mM) upon addition of
0–0.6 equiv. (a) and 0.6–1.5 equiv. (b) of Cd2+ in CH3CN/H2O (2 : 8, v/v, HEPES
10 mM, pH 7.4).
Fig. 7 Fluorescence spectra changes of BMD-Zn2+ (10 mM) in CH3CN/H2O (2 : 8,
v/v, HEPES 10 mM, pH 7.4) in the presence of 20 equiv. of different anions and
thiol-containing amino acids. Inset: The naked eye fluorescence changes of
BMD-Zn2+ before and after addition of S22 ions under the portable UV lamp at
254 nm.
Fig. 8 Fluorescence spectra changes of BMD-Zn2+ solution (10 mM) upon
addition of different amounts of S22
.
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4. Experimental section
4.1 Materials and instruments
Unless otherwise stated, solvents and reagents were of
analytical grade from commercial suppliers and were used
without further purification. Compound 2 was prepared by the
literature method.25 1H NMR and 13C NMR spectra were
recorded on Agilent 400-MR spectrometer. Chemical shifts (d)
were expressed in ppm and coupling constants (J) in Hertz.
HRMS was measured on an Agilent 1200 time-of-flight mass
spectrometer (Bruker, micrOTOF-Q). Fluorescence measure-
ments were performed on a Sanco 970-CRT spectrofluorometer
(Shanghai, China). The pH measurements were made with a
Model PHS-25B meter (Shanghai, China).
4.2 Synthesis of sensor BMD
To a solution of N-[2-(1H-benzoimidazol-2-yl)-phenyl]-2-chlor-
oacetamide (2) (0.51 g, 1.8 mmol) in 8 mL of DMF, DPA (1.39 g,
7.2 mmol) was added. The reaction mixture was stirred at
room temperature for 8 h, and then poured into 150 mL of
distilled water and adjusted to pH 7. The resulting precipitates
was collected by filtration and washed with H2O, dried and
recrystallized from acetonitrile to give 0.45 g of BMD as brown
solid. Yield: 56%. M.p. 177–179 uC. 1H NMR (400 MHz, DMSO-
d6) d 13.26 (s, 1H), 13.16 (s, 1H), 8.77 (d, J = 8.8 Hz, 1H), 8.47 (d,
J = 4.0 Hz, 2H), 8.09 (d, J = 7.6 Hz, 1H), 7.81 (d, J = 8.0 Hz, 2H),
7.63 (d, J = 6.4 Hz, 2H), 7.49 (t, J = 8.0 Hz, 1H), 7.43 (t, J = 8.0
Hz, 2H), 7.37–7.22 (m, 3H), 7.20–7.17 (m, 2H), 4.00 (s, 4H), 3.44
(s, 2H). 13C NMR (100 MHz, DMSO-d6). d 170.47, 158.25,
150.95, 149.24, 138.09, 136.74, 130.89, 128.22, 123.51, 123.43,
122.74, 120.74, 116.90, 60.53, 58.79. HRMS (ESI+) calcd for
Fig. 9 Changes of intensity ratios (F424nm/F502nm) of BMD-Zn2+ solution (10 mM)
in CH3CN/H2O (2 : 8, v/v, HEPES 10 mM, pH 7.4). The gray bars represent the
intensity ratio (F424nm/F502nm) of BMD-Zn2+ solution in the presence of 20 equiv.
of different anions. The red bards represent the intensity ratio (F424nm/F502nm) of
BMD-Zn2+ to S22 in the presence of others anions.
ratios of the tested solutions were all greatly decreased and
reached the similar level. These facts further demonstrate the
high selectivity of BMD-Zn2+ to S22
.
To evaluate the practical applicability, the potential utilities
of BMD were checked by proof-of-concept experiments.24 Tap,
lake and river water were collected from laboratory, Tinglin
lake (in Bohai University), and Xiaoling river (Linghe district,
Jinzhou), respectively. Different concentrations of Zn2+ or S22
were spiked into these samples before BMD (10 mM) was
added. The intensity ratios (F424nm/F502nm) were proportional
to the concentrations of Zn2+ in the range of 0 to 6 mM (Fig.
C
27H24N6ONa [M + Na]+, 471.1909; Found 471.1908.
4.3 General procedure for spectroscopic analysis
Doubly distilled water was used for all experiments.
Compound BMD was dissolved in CH3CN/H2O (2 : 8, v/v,
HEPES 10 mM, pH 7.4) to afford the test solution (10 mM).
Titration experiments were carried out in 10-mm quartz
cuvettes at 25 uC. Metal ions (as chloride or nitrate salts, 10
mM) and anions (as sodium salts, 10 mM and 100 mM) in
CH3CN/H2O (2 : 8, v/v, HEPES 10 mM, pH 7.4) were added to
the host solution and used for the titration experiment.
BMD-Zn2+ solution for sulfide anion detection was prepared
by addition of 1.0 equiv. of Zn2+ to compound BMD solution
(10 mM) in CH3CN/H2O (2 : 8, v/v, HEPES 10 mM, pH 7.4).
S11, ESI ). Similarly, when this method was applied to sulfide
3
detection with BMD-Zn2+ system, good linear dependence of
fluorescence intensity on S22 concentration were also obtained
in the range of 10 to 50 mM (Fig. S12, ESI ). Therefore, the
3
presented sensors BMD and BMD-Zn2+ could be used for trace
Zn2+ and S22 analyses in these three complicated environ-
mental systems, respectively.
3. Conclusions
In conclusion, we have developed a simple fluorescent sensor,
BMD. It behaves a ratiometric response to Zn2+ with good
discrimination from Cd2+ and other metal ions. The in situ
formed BMD-Zn2+ shows a ratiometric response to sulfide
anion with excellent selectivity and sensitivity. Proof-of-
concept experiments also provided the potential applicability
of BMD in real water sample analysis. Thus, BMD can be used
as a fluorescent sensor for sequential detection of Zn2+ and
S22 in water.
Acknowledgements
We are grateful to the NSFC (No. 21176029), the Natural
Science Foundation of Liaoning Province (No. 20102004) and
the Program for Liaoning Excellent Talents in University (No.
LJQ2012096) for financial support.
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