Porphyrin-based multi-signal chemosensors for Pb2+ and Cu 2+

Article abstract of DOI:10.1039/c2ob25313e

Two metal-free tetra(aryl)porphyrin derivatives modified by one and four N,N-bis(2-pyridylmethyl)amino group(s), namely porphyrin-1-DPA (1) and porphyrin-4-DPA (2) respectively, have been designed, synthesized, and characterized. Binding with Pb²⁺ induces a significant change in their solution color and in the ratio of two absorption/fluorescence signal peaks, rendering them the first example of porphyrin-based triple-signal optical sensors for Pb²⁺. Their dual-mode Cu²⁺-selective sensing properties via either the porphyrin fluorescence ON-OFF mechanism or metal displacement from the 1-Pb²⁺ complex that results in a triple-signal change clearly reveals their potential application as excellent and versatile sensors.

Full text of DOI:10.1039/c2ob25313e

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PAPER
Porphyrin-based multi-signal chemosensors for Pb2+ and Cu2+†
Yuting Chena,b,c and Jianzhuang Jiang*b,c
Received 12th February 2012, Accepted 25th April 2012
DOI: 10.1039/c2ob25313e
Two metal-free tetra(aryl)porphyrin derivatives modified by one and four N,N-bis(2-pyridylmethyl)amino
group(s), namely porphyrin-1-DPA (1) and porphyrin-4-DPA (2) respectively, have been designed,
synthesized, and characterized. Binding with Pb2+ induces a significant change in their solution color and
in the ratio of two absorption/fluorescence signal peaks, rendering them the first example of porphyrin-
based triple-signal optical sensors for Pb2+. Their dual-mode Cu2+-selective sensing properties via either
the porphyrin fluorescence ON–OFF mechanism or metal displacement from the 1–Pb2+ complex that
results in a triple-signal change clearly reveals their potential application as excellent and versatile
sensors.
for the simultaneous detection of the often co-existing Pb2+ and
Introduction
Cu2+ ions has not been reported thus far. As a result, developing
a versatile molecular optical sensor for synchronously detecting
these two metal ions is highly desirable.
Chemosensors with high sensitivity and simplicity have attracted
increasing interest in recent years. In particular, detecting heavy
and transition metal (HTM) ions is important because of their
extremely toxic impact on the environment and human health.1
Various molecular optical sensors using electronic absorption,
fluorescent emission, and/or colorimetric signals have been syn-
thesized and applied to detect different species of HTM ions
selectively including Pb2+, Cu2+, Hg2+, and Cd2+.2 Most of the
reports, however, focused on single-analyte chemosensors with
few examples for multi-metal ions.3 Quinoline-based fluorescent
sensors able to detect both Zn2+ and Cd2+ simultaneously via
PET and ICT mechanisms, respectively, were developed by
Jiang and co-workers.4 A styryl-Bodipy-based molecular logic
sensor with multi-receptors for Zn2+, Ca2+, and Hg2+ was syn-
thesized by Akkaya et al.5 Suzuki reported a “jewel pendant
ligand” multi-analyte (Fe3+ and Cu2+) chemosensor containing
three chromogenic units.6 A small molecular probe for Zn2+ and
Hg2+ based on self-assembly and a metal ion replacement mech-
anism was prepared by Yang et al.7 Very lately, Jiang and co-
workers reported the first porphyrin-Bodipy FRET ratiometric
sensor for Fe2+ and Hg2+.8 However, a molecular optical sensor
The porphyrin chromophore is one of the most promising sig-
naling units for constructing fluorescent sensors due to its advan-
tageous photophysical characteristics, such as pronounced
photostability, high extinction coefficient, and tunable fluor-
escence emission.9 The central tetrapyrrole moiety of this series
of conjugated macrocyclic ligands is also able to act as a good
functional receptor for various metal ions due to its strong co-
ordinating ability. As a consequence, extensive investigations
have been conducted into porphyrin-based fluorescent sensors.10
However, exploration of versatile molecular sensors with a por-
phyrin moiety acting as both the signal chromophore and a
multi-analyte receptor has not yet been carried out, to the best of
our knowledge.
In the present paper, two new porphyrin derivatives, namely
5-[p-N,N-bis(2-pyridylmethyl)amino-phenyl]-10,15,20-tris(4-
tert-butylphenyl)porphyrin
(Porphyrin-1-DPA)
(1)
and
5,10,15,20-tetra[p-N,N-bis(2-pyridylmethyl) amino-phenyl]por-
phyrin(Porphyrin-4-DPA) (2) were designed and synthesized,
Scheme 1. In addition to the optical signaling role, the metal-
free tetrapyrrole moiety in 1 and 2 functions as a versatile recep-
tor for both Pb2+ and Cu2+, along with the peripheral N,N-bis(2-
pyridylmethyl)amine (DPA) unit(s). Interestingly, binding of
these two porphyrin compounds with Pb2+ directly induced a
color change visible to the naked eye and also a remarkable ratio
signal change of two absorption–emission peaks. Thus, 1 and 2
are the first examples of porphyrin-based multi-signal optical
sensors for Pb2+. The dual-mode Cu2+-selective approach was
implemented in these two compounds via a porphyrin fluor-
escence ON–OFF mechanism and triple-signal metal displace-
ment, revealing their versatile sensing nature.
aKey Laboratory of Coordination Chemistry and Functional Materials
in Universities of Shandong, Dezhou University, Dezhou 253023, China
bDepartment of Chemistry, University of Science and Technology
Beijing, Beijing 100083, China
cDepartment of Chemistry, Shandong University, Jinan 250100, China.
E-mail: jianzhuang@ustb.edu.cn
†Electronic supplementary information (ESI) available: 1H NMR and
13C NMR spectra of compounds 1, 1Zn, and 2 in CDCl3, MALDI-TOF
mass spectra of these compounds, the electronic absorption and fluor-
escence emission spectra of 1 and 2, together with 1Zn upon addition of
different metal ions in CH2Cl2–MeOH (1 : 1). See DOI: 10.1039/
c2ob25313e
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Scheme 1 Synthesis of DPA-modified porphyrin derivatives 1, 1Zn, and 2.
Fig. 1 The electronic absorption spectra (A) and emission spectra (B) of 1 at the concentration of 2 μM in CH2Cl2–MeOH (1 : 1) upon addition of
Pb2+ and Cu2+, respectively, with an excitation of 420 nm.
addition of Pb2+. A new peak simultaneously appears around
466 nm, resulting in the I466/I417 ratio increasing from 0 to 1.32.
Results and discussion
Interestingly, the change in the electronic absorption spectrum of
1 upon addition of Pb2+ also induces an obvious solution color
change from baby pink to light green, Fig. 1A. Meanwhile, a
significant change also occurs in the fluorescent emission spec-
trum of 1 after addition of Pb2+. The fluorescent emission inten-
sity of 1 at 650 nm decreases significantly, while a new
fluorescent emission peak appears at 604 nm, Fig. 1B. This
leads to a change in the ratio of F604/F650 from approximately
7576 to 0.26. In addition, the quantitative absorption titration
experiments for 1 (2 μM) in CH2Cl2–MeOH (1 : 1) with increas-
ing amounts of Pb2+ (0–10 equiv.) indicate a 1 : 1.5 binding stoi-
chiometry between 1 and Pb2+. The approximate association
constant (Ka) is 2.1 × 104, which is confirmed by the absorption
Job plot and the fluorescent titration experiments, Fig. 2. This
suggests a possible binding mode between 1 and Pb2+ in 1–Pb2+
system as depicted in Fig. S7A (ESI†). The detection limit for
Pb2+ ions with 1 was determined to be 3.1 × 10−7 M under the
present conditions.13 These results clearly reveal that the metal-
free porphyrin-1-DPA 1 can be used for colorimetric and dual
As shown in Scheme 1, the synthesis of porphyrin sensors 1 and
2 involved the prior generation of 5-(p-carboxylphenyl)-
10,15,20-tris (4-tert-butylphenyl)porphyrin (3) and 5,10,15,20-
tetra(p-carboxylphenyl)porphyrin (5), respectively, in accord-
ance with literature procedures.11–12 The compounds were
refluxed in SOCl2 and treated with DPA in THF. The zinc
complex (1Zn) was obtained by reaction of the metal-free por-
phyrin 1 with zinc acetate in a mixed solvent of CHCl3 and
MeOH. These three compounds were characterized by MALDI-
1
TOF mass and H as well as 13C NMR spectroscopy, Fig. S1–6
(ESI†).
To investigate the selectivity of the metal-free porphyrins for
metal ions, the photophysical properties of 1 (2 μM) upon
addition of different metal ions, such as Pb2+, Fe2+, Co2+, Hg2+,
Mn2+, Cu2+, Zn2+, Ni2+, Cd2+, Ca2+, Ba2+, Mg2+, Li+, Na+, or
K+ (10 equiv.), were studied by UV–vis and fluorescence
measurements in CH2Cl2–MeOH (1 : 1). As shown in Fig. 1A,
the intensity of the strongest absorption peak of metal-free por-
phyrin-1-DPA (1) at 417 nm significantly decreases upon
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Fig. 2 The electronic absorption (A) and fluorescent emission spectra (B) of 1 upon addition of increasing amounts (0, 0.2, 0.4, 0.6, 0.8, 0.9 1, 1.2,
1.4, 1.5, 1.6, 1.8, 2, 4, 6, 8, and 10 equiv.) of Pb2+, with an excitation of 420 nm. The inset in A shows the 1 : 1.5 binding stoichiometry between 1
and Pb2+ in the 1–Pb2+ system at the 466 nm absorption peak.
optical-ratiometric detection of Pb2+. It represents the first triple-
signal molecular optical sensor for this divalent heavy metal
cation.14
Addition of Cu2+ quenches the fluorescent emission of 1 at
650 nm, but without significantly changing its electronic absorp-
tion spectrum, Fig. 1. A quantitative fluorescent titration of 1
with Cu2+ shows that the emission intensity at 650 nm gradually
decreases to be almost quenched when the amount of Cu2+ is
increased from 0 to approximately 2.0 equiv., Fig. 3A. Further
increases in the amount of Cu2+ to 10 equiv. lead to almost no
change in the emission spectrum. These results, together with
the fluorescence emission Job plot (Fig. 3A), indicate a possible
1 : 2 binding model between 1 and Cu2+ with an approximate Ka
of 7.4 × 105, Fig. S7B (ESI†). Interestingly, adding Cu2+ (10
equiv.) into a solution of 1–Pb2+ (Cu2+ : Pb2+ = 1 : 1) leads to a
rapid color change from light green to baby pink as viewed by
the naked eye, Fig. 3B. Electronic absorption spectroscopic
measurements confirmed the change from 1–Pb2+ to 1–Cu2+
with the disappearance of the absorption peak at 466 nm and
appearance of the absorption peak at 414 nm, Fig. 3B. This
suggests the displacement of Pb2+ from the 1–Pb2+ complex by
Cu2+ and the formation of a 1–Cu2+ complex. This hypothesis is
further validated by the disappearance of the 1–Pb2+ fluor-
escence emission peak at 604 nm after addition of Cu2+ ions,
Fig. S8 (ESI†). The replacement of Pb2+with Cu2+ can be attrib-
uted to the difference in the atomic radius between Pb2+ and
Cu2+. Pb2+ has a bigger atomic radius and is located at the per-
iphery of the porphyrin chromophore when binding with the
Fig. 3 The fluorescence emission spectra of 1 (2 μM) in CH2Cl2–
metal-free porphyrin 1, whereas Cu2+ with a smaller atomic
MeOH (1 : 1) upon addition of increasing amounts (0, 0.2, 0.4, 0.6, 0.8,
radius can be embedded into the central porphyrin core and form
1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 3, 4, 6, 8, and 10 equiv.) of Cu2+ (A),
a more stable 1–Cu2+ system than 1–Pb2+, resulting in corre-
and the electronic absorption spectra and solution color change of 1–
Pb2+ upon addition of the same amount of Cu2+ ion in CH2Cl2–MeOH
(1 : 1) (B). The inset in A shows 1 : 2 binding stoichiometry between 1
and Cu2+ in the 1–Cu2+ system using 650 nm fluorescence emission.
sponding metal replacement as detailed above. As a conse-
quence, metal-free porphyrin 1 can operate as a dual-mode
Cu2+-selective sensor via the porphyrin fluorescence ON–OFF
mechanism as well as the triple-signal (colorimetric, ratio of
A
414/A466, and fluorescence ON–OFF) metal displacement from
the 1–Pb2+ complex. Thus, this porphyrin represents a new
example of rare dual-mode multi-signal systems for cation recog-
nition,15 in particular for Cu2+ due to its usual paramagnetic flu-
orescence quenching property.16
In contrast, upon addition of other metal ions, such as Fe2+,
Co2+, Hg2+, Mn2+, Zn2+, Ni2+, Cd2+, Ca2+, Ba2+, Mg2+, Li+,
Na+, or K+, the electronic absorption and fluorescent emission
spectra of the metal-free porphyrin-1-DPA 1 remained almost
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unchanged, Fig. S9–11 (ESI†). Moreover, addition of these
metal ions to the 1–Pb2+ system induces almost no change in
either the electron absorption and fluorescent emission spectra,
Fig. S8 (ESI†). This is also true for the 1–Cu2+ system, Fig. S12
(ESI†). These results clearly indicate the excellent selectivity of
metal-free porphyrin-1-DPA 1 for Pb2+ and Cu2+ ions over all
the tested metal ions.
peripheral DPAs on the detection properties of porphyrin deriva-
tives towards Pb2+ and Cu2+ cations.
To further understand the sensing properties of these two
metal-free porphyrins for Pb2+ and Cu2+, control experiments
with the reference 1Zn were also carried out under the same
experimental conditions. As seen in Fig. S16 (ESI†), addition of
For the purpose of comparative studies, the electronic absorp-
tion and fluorescent emission properties of porphyrin-4-DPA 2
have been investigated in the same manner as for porphyrin 1.
As expected, very similar selectivity and detection properties for
Pb2+ and Cu2+ ions based on the same sensing mechanisms were
revealed, Fig. 4A and B and S13–14 (ESI†). However, the quan-
titative titration experiments for 2 with Pb2+ and Cu2+ show a
binding stoichiometry of 1 : 3 for 2–Pb2+ and of 1 : 5 for 2–Cu2+
due to the increase in the number of peripheral DPA units from
one for 1 and four for 2, Fig. 4C and D and S15 (ESI†). This
suggests that the complexes formed with porphyrin 2 have a
different binding mode than the complexes formed with por-
phyrin 1, as depicted in Fig. 5. Moreover, the observed changes
to the optical properties of porphyrin 2 with increasing amounts
of Pb2+ and Cu2+ are smaller in comparison to porphyrin 1.
These results clearly indicate the effect of the number of
Fig. 5 The proposed coordinating modes of 2 with Pb2+ and Cu2+
respectively.
,
Fig. 4 The electronic absorption spectra (A) and emission spectra (B) of 2 (2 μM) in CH2Cl2–MeOH (1 : 1) upon addition of K+, Li+, Cd2+, Ni2+
,
Pb2+, Cu2+, Mn2+, Ba2+, Fe2+, Co2+, Mg2+, Ca2+, Na+, Hg2+, or Zn2+ (10 equiv.), respectively. The electronic absorption spectra (C) and fluorescent
emission spectra (D) of 2 upon addition of increasing amounts of Pb2+ and Cu2+ (0, 0.2, 0.4, 0.6, 0.8, 0.9 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 4, 6, 8 and 10
equiv.), respectively. The insets of C and D show the 1 : 3 and 1 : 5 binding stoichiometry of 2–Pb2+ and 2–Cu2+, respectively, at an excitation of
420 nm.
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the various metal ions, including Pb2+ and Cu2+, into the 1Zn
solution does not induce a remarkable spectroscopic response.
This suggests the important role of the coordinating ability of the
metal-free porphyrin moiety in determining the excellent sensing
properties for Pb2+–Cu2+. This is further proved by the titration
of a N-bis(2-pyridylmethyl)amine (DPA) unit with Pb2+ and
Cu2+, which did not show absorption and fluorescence emission
in the corresponding optical range. It is worth noting that
changes in the optical properties of metal-free 5,10,15,20-tetra-
(4-tert-butylphenyl)porphyrin upon addition of Pb2+ and
Cu2+were similar to those of 1, Fig. S17–18 (ESI†). This clearly
indicates that the first binding site of the metal-free porphyrin 1
is the central moiety instead of the DPA side group when coordi-
nating with these two metals. Due to the different characteristic
outermost electronic structures of Pb2+ and Cu2+, binding of
Pb2+ with the central four pyrrole nitrogen atoms in 1 induces a
corresponding optical-shift, whereas coordinating with Cu2+
results in fluorescent quenching of the porphyrin choromophore.
This should also be true for 2.
Vario El #xX_CYR_HEX_428;. Electronic absorption spectra
were recorded on a U-4100 spectrophotometer. Steady-state flu-
orescence spectroscopic studies were performed on an F 4500
(Hitachi). The slit width was 5 nm for emission. The photon
multiplier voltage was 700 V.
Preparation of 5-[p-N,N-bis(2-pyridylmethyl)amino-phenyl]-
10,15,20-tris (4-tert-butylphenyl)porphyrin (1)
A mixture of compound 3 (83 mg, 0.1 mmol) and thionyl chlor-
ide (10 mL) was refluxed for 5 h under N2 atmosphere and evap-
orated by atmospheric distillation. The residue obtained was
dissolved in THF (8 mL) and then added into a solution of DPA
(100 mg, 0.5 mmol) in THF (5 mL), followed by adding two
drops of TEA. After stirring for another 4 h at 50 °C, the result-
ing black–green mixture was evaporated under reduced pressure.
The residue was chromatographed on a silica gel column using
CHCl3–MeOH (98 : 2) as the eluent, where the second fraction
was collected and evaporated. Repeated chromatography fol-
lowed by recrystallization from CHCl3 and MeOH gave com-
pound 1, 47 mg in the yield of 46%. 1H NMR (CDCl3,
400 MHz) δ 8.88 (d, 6H, J = 8 Hz), 8.78 (d, 2H J = 4 Hz), 8.69
(d, 1H, J = 4 Hz), 8.62 (br, 1H), 8.23 (d, 2H J = 8 Hz), 8.15 (m,
6H, J = 8 Hz), 7.99 (d, 2H, J = 8 Hz), 7.77 (d, 8H J = 8 Hz),
7.62 (d, 1H, J = 8 Hz), 7.42 (d, 1H, J = 12 Hz), 7.26 (2H
obscured by the strong residual CHCl3 signal), 5.08 (d, 4H, J =
4 Hz), 1.61(s, 27H), −2.80 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ 172.7, 156.8, 150.5, 150.1, 145.5, 144.1, 139.1, 136.9,
135.1, 125.6, 123.7, 122.7, 122.5, 121.6, 120.6, 120.4, 118.5,
54.9, 50.9, 34.9, 31.7; MS (MALDI-TOF): an isotopic cluster
peaking at m/z 1008.49, [Calcd For M+ 1008.53]; Anal. Calcd
(%) for C69H65N7O: C, 82.19; H, 6.50; N, 9.72. Found: C,
82.46; H, 6.60; N, 9.34.
Conclusion
Two metal-free DPA-modified porphyrin derivatives that use the
central tetrapyrrole moiety as both the signaling fluorophore and
a metal ion receptor have been developed. Significant changes
were observed in the solution color, ratio signal of two absorp-
tion/fluorescence peaks, and fluorescence intensity of these por-
phyrin compounds upon their binding with Pb2+ and Cu2+.
When combined with the optical properties associated with Cu2+
displacement from 1/2–Pb2+ complex, this compound emerges
as the first example of a versatile porphyrin-based optical sensor
with triple-signal sensing properties for Pb2+ and dual-mode
fourfold-signaling for Cu2+.
Experimental
Preparation of 5-[p-N,N-bis(2-pyridylmethyl)amino-phenyl]-
10,15,20-tris (4-tert-butylphenyl)porphyrinato Zinc complex
(1Zn)
Chemicals
Column chromatography was carried out on silica gel (Merck,
Kieselgel 60, 70–230 mesh) with the indicated eluents. THF was
freshly distilled from CaH2 under nitrogen. The CH2Cl2 and
methanol used as solvents for the spectral experiments were
purified via standard methods. Other reagents and solvents were
used as received. The compounds of 5-(4-carboxylphenyl)-
10,15,20-tris(4-tert-butylphenyl)porphyrin (3) 5,10,15,20-tetra-
(4-cyanophenyl)porphyrin (4) and 5,10,15,20-tetra(4-carboxyl-
phenyl) porphyrin (5) were prepared according to literature
procedures.11–12
Zn(OAc)2·2H2O (33 mg, 0.15 mmol) in MeOH (5 mL) was
added into a mixed solution of 5-[p-N,N-bis (2-pyridylmethyl)
amino-phenyl]-10,15,20-tris(4-tert-butylphenyl) porphyrin (1)
(100 mg, 0.1 mmol) in CHCl3–MeOH (3 : 1) (30 mL). The reac-
tion mixture was refluxed for 3 h under N2 atmosphere and then
diluted with CH2Cl2 (50 mL). After washing the resulting
mixture with an aqueous solution (100 mL) containing EDTA
(1 g) and Na2CO3 (8 g), the organic phase was dried over anhy-
drous MgSO4, filtered, and evaporated. The residue was chro-
matographed on a silica gel column using CHCl3–MeOH (98 : 2)
as the eluent. Repeated chromatography followed by recrystalli-
zation from CHCl3 and MeOH gave compound 1Zn, 41 mg in
the yield of 38%. 1H NMR (CDCl3–[D5]pyridine(9 : 1),
400 MHz) δ 8.77 (d, 5H, J = 8 Hz), 8.65 (d, 2H J = 4 Hz), 8.48
(br, 1H), 8.43 (d, 1H, J = 4 Hz), 8.03 (d, 2H J = 8 Hz), 7.96 (d,
5H, J = 8 Hz), 7.80 (d, 2H, J = 8 Hz), 7.56 (d, 8H J = 8 Hz),
7.44 (d, 1H, J = 4 Hz), 7.26 (1H obscured by the strong residual
CHCl3 signal), 7.19 (d, 2H, J = 8 Hz), 7.06 (2H, partly over-
lapped), 4.92 (d, 4H, J = 8 Hz), 1.41(s, 27H); 13C NMR
(100 MHz, CDCl3–[D5]pyridine(9 : 1) δ 172.4, 149.8, 149.7,
General instruments
1H and 13C NMR spectra (1H-400 MHz and 13C-100 MHz) were
recorded on a Bruker DPX 400 MHz spectrometer in CDCl3
with shifts referenced to SiMe4 (0.00 ppm). MALDI-TOF mass
spectra were measured on a Bruker BIFLEX III ultra-high resol-
ution Fourier transform ion cyclotron resonance (FT-ICR) mass
spectrometer with alpha-cyano-4-hydroxycinnamic acid as the
matrix. Elemental analyses were performed on an Elementar
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149.4, 144.9, 139.9, 136.4, 134.1, 131.5, 131.3, 130.7, 124.8,
123.2, 122.1, 121.9, 121.2, 120.6, 120.3, 118.5, 54.4, 50.3, 34.3,
31.2, 29.2; MS (MALDI-TOF): an isotopic cluster peaking at
m/z 1070.31, [Calcd For M+ 1070.44]; Anal. Calcd (%) for
C69H63N7OZn: C, 78.52; H, 6.02; N, 7.85. Found: C, 78.46; H,
6.36; N, 7.34.
Notes and references
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Preparation of 5,10,15,20-tetra[p-N,N-bis(2-pyridylmethyl)-
amino-phenyl] porphyrin (2)
The above procedure was used to prepare compound 2 by substi-
tuting 5,10,15,20-tetra(4-carboxylphenyl)porphyrin (5) (79 mg,
0.1 mmol) for 5-(4-carboxylphenyl)-10,15,20-tris(4-tert-butyl-
phenyl)porphyrin (3) as the starting material. Compound 2
1
(42 mg) was obtained with the yield of 27%. H NMR (CDCl3,
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5 O. A. Bozdemir, R. Guliyev, O. Buyukcakir, S. Selcuk, S. Kolemen,
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Soc., 2010, 132, 8029–8036.
400 MHz) δ 8.79 (s, 8H), 8.69 (d, 4H, J = 4 Hz), 8.63 (d, 4H, J
= 4 Hz), 8.19 (d, 8H, J = 8 Hz), 7.99 (d, 8H J = 8 Hz), 7.79 (t,
8H, J = 16 Hz), 7.61 (d, 4H, J = 8 Hz), 7.42 (d, 4H J = 8 Hz),
7.28 (4H, obscured by the strong residual CHCl3 signal), 5.07
(s, 16H), −2.92 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 172.5,
157.1, 156.7, 150.1, 149.4, 143.5, 136.9, 135.3, 134.4, 125.7,
122.6, 122.4, 121.7, 119.4, 54.9, 50.9; MS (MALDI-TOF): an
isotopic cluster peaking at m/z 1517.12, [Calcd For M+
1517.61]; Anal. Calcd for C96H74N16O4: C, 76.07; H, 4.92; N,
14.79. Found: C, 76.35; H, 5.20; N, 14.52.
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13 Detection limit (DL) is defined as the concentration corresponding to a
signal 3 times the noise level of the background. DL = (0.03 × RSDB)/
(xA/c0), where RSDB is both the relative standard deviation of the back-
ground expressed as a percent and the sensitivity (the slope of the cali-
bration curve of intensity versus composition), xA is the net analyte signal
(i.e., the signal above background), and c0 is the composition of the
element in the sample.
Spectroscopic response experiments
Stock methanol solutions (1 mM) of Hg2+, Mn2+, Cd2+, Ca2+,
Ba2+, Mg2+, Li+, Na+, and K+ were prepared from their chloride
salts, solutions of Co2+, Cu2+, Zn2+, and Ni2+ from their acetate
salts, the solution of Pb2+ from the nitrate salt, and the solution
of Fe2+ from ferrous ammonium sulfate and used immediately.
Solutions of 1, 2 or 1Zn (0.2 mM) in CH2Cl2 were prepared.
Test solutions were prepared by placing 0.1 ml of the probe’s
stock solutions into a test tube, adding an appropriate aliquot of
each metal stock solution and then vaporizing the solvents off,
followed by diluting the obtained mixture with CH2Cl2–MeOH
(1 : 1, 10 ml) to give the final concentration. After complete
mixing for 5 h, UV–vis absorption and fluorescent emission
measurements were carried out with a 1 cm standard quartz cell.
Acknowledgements
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Financial support from the Natural Science Foundation of China,
Ministry of Education of China, and the Fundamental Research
Funds for the Central Universities, the Beijing Municipal Com-
mission of Education, the Fundamental Research Funds for the
Central Universities, and the University of Science and Techno-
logy Beijing is gratefully acknowledged.
16 X. Ni, S. Wang, X. Zeng, Z. Tao and T. Yamato, Org. Lett., 2011, 13,
552–555.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 4782–4787 | 4787