Dipyrrolylquinoxaline-bridged hydrazones: A new class of chemosensors for copper(II)

Article abstract of DOI:10.1007/s10847-011-9941-6

Novel 2,3-bis(1H-pyrrol-2-yl)quinoxaline-fun-ctionalized hydrazones were prepared and characterized as new chemosensors for copper(II) ion. The binding properties of the compounds 4,5, 6 and 7 for cations were examined by UV-vis, fluorescence spectroscopy, and linear sweep vol-tammetric experiments (LSV). The results indicate that a 1:1 stoichiometric complex is formed between compound 4 (or 5, 6, 7) and copper(II) ion, and the association constant is 1.3 × 10⁵ M^-1 for 4, 2.1 × 10⁶M^-1 for 5, 4.1 × 10⁵M^-1 for 6 and 8.0 × 10 M ^-1 for 7, respectively. The recognition mechanism between compound 4 (or 5, 6, 7) and metal ion was discussed based on their electrochemical properties, absorbance changes, and the fluorescence quenching effect when they interact with each other. Control experiments revealed that compound 4 (or 5, 6, 7) has a highly selective response to copper (II) ion.

Full text of DOI:10.1007/s10847-011-9941-6

J Incl Phenom Macrocycl Chem (2012) 72:79–88
DOI 10.1007/s10847-011-9941-6
ORIGINAL ARTICLE
Dipyrrolylquinoxaline-bridged hydrazones: a new class
of chemosensors for copper(II)
•
Qian-ni Guo Cheng Zhong Yun-guo Lu
•
•
•
Chuang Shi Zao-ying Li
Received: 12 November 2010 / Accepted: 19 February 2011 / Published online: 22 March 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Novel 2,3-bis(1H-pyrrol-2-yl)quinoxaline-fun-
ctionalized hydrazones were prepared and characterized as
new chemosensors for copper(II) ion. The binding properties
of the compounds 4, 5, 6 and 7 for cations were examined by
UV–vis, fluorescence spectroscopy, and linear sweep vol-
tammetric experiments (LSV). The results indicate that a 1:1
stoichiometric complex is formed between compound 4 (or
5, 6, 7) and copper(II) ion, and the association constant is
1.3 9 105 M-1 for 4, 2.1 9 106 M-1 for 5, 4.1 9 105 M-1
for 6 and 8.0 9 105 M-1 for 7, respectively. The recognition
mechanism between compound 4 (or 5, 6, 7) and metal ion
was discussed based on their electrochemical properties,
absorbance changes, and the fluorescence quenching effect
when they interact with each other. Control experiments
revealed that compound 4 (or 5, 6, 7) has a highly selective
response to copper (II) ion.
two decades [1–6]. Among the transition metal ions of
interest, divalent copper, Cu2?, is particularly attractive,
because it is not only an environmental pollutant at high
concentrations, [7, 8] but also an essential trace element for
many biological process and systems [9, 10]. Therefore,
many excellent work of Cu2? sensing by synthesized col-
orimetric/fluorescent probes has been reported and investi-
gated [11–16]. However, there is still an intense demand for
new efficient Cu2? chemosensors, especially those that can
work with high selectivity and sensitivity. Work related to
this area is of great challenge and increasing interest.
The Schiff bases (SB) are known to form stable com-
plexes with transition metal ions. Almost all of metals form
1:1 metal complexes with SBs. The feature of SBs gives
geometric and cavity controlof host–guest complexation and
modulation of its lipophilicity, and produces remarkable
selectivity, sensitivity and stability for a specific ion. The
resulting SB complexes have attracted increasing attention
in the area of ionic binding due to their unique properties and
reactivity. Schiff bases with N and O as donor atoms are well
known to form strong complexes with transition metal ions
[17]. Since the structure of hydrazones is similar to the Schiff
bases, they have similar properties of Schiff bases [18].
The dipyrrolylquinoxaline (DPQ) derivatives have been
reported as anion receptors,[19–22] but to the best of our
knowledge, they have only been employed as cation
receptors for mecury(II) [23].
Keywords Chemosensor ꢀ Selectivity ꢀ Sensitivity
Introduction
The design of artificial chemosensors for selective and sen-
sitive quantification of biologically and environmentally
important ion species, especially transition-metal ions, has
attracted wide-spread interests of chemists, biologists, clin-
ical biochemists and environmentalists in recent years.
Because of their advantages of simple instrumentation, high
sensitivity and facile analysis, many efficient chemosensors
for transition-metal ions have been developed during the last
In this article, we wish to develop a new chemosensor by
using dipyrrolylquinoxaline as the basic fluorophore, pyrrole
and the hydrazone as the recognition site. Due to the change
in the electronic density of the chromophore induced by
complexation, when the ionophore moiety is complexed to a
metal ion, remarkable changes in the fluorescence intensity
and the absorption spectra appear [24, 25]. Since the rec-
ognition site is now part of the fluorophore, when it is
Q. Guo ꢀ C. Zhong ꢀ Y. Lu ꢀ C. Shi ꢀ Z. Li (&)
College of Chemistry and Molecular Sciences, Wuhan
University, Wuhan 430072, People’s Republic of China
e-mail: zyliwuc@whu.edu.cn
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
Scheme 1 Synthesis of ligand
4 and complex 4a
CHO
benzene-1,2
-diamine
N
N
N
N
H
N
N
N
Cl
Cl
O
O
DMF,POCl3
CH2ClCH2Cl
O
pyrrole
H
H
o
H
H
-78 C
reflux
AcOH
NH
N
N
O
CH2Cl2
CHO
2
1
3
F
F F
F
F
F
F
F
F
H
N N
N
H
N
N
F
N
N
F
N N
N
.
reflux CH3OH
C6F5NHNH2
Ni(OAc)2 4H2O
CH3OH
H
Ni
F
F
H
N
H
N
H
N
N
F
F
F
N N
F
F
F
F
4a
4
Scheme 2 Synthesis of ligands
5, 6, and 7
O
N N
N N
N
H
N
5
O
H
N
reflux
CH3OH
N
N NH2
O
O
O
CHO
CHO
N N
N N
N NH
N
H
2 reflux CH3OH
N
N
N
N
H
6
H
H
N
N
N
O
O
3
reflux
CH3OH
O
N N
N N
N
H
N
N
N
NH2
7
H
N
O
conjugated with the cation in solution, the analytical poten-
tial of the system should be greatly enhanced. The metal ion
binding affinity is adequately controlled by the cavity size of
the molecular clamp. As expected, synthetic compounds
have the advantage of detecting Cu2? ion. The cation binding
can be visualized by changes in the UV–vis absorption
spectrum, fluorescence spectrum, linear sweep voltammetric
experiments (LSV), and can be observed by naked eyes.
(or 5, 6, 7) was synthesized by refluxing the methanol
solution of 2,3-bis(5-formylpyrrol-2-yl)quinoxaline and an
equivalent molar amount of 1-(perfluoro- phenyl)hydrazine
(or 2-(2-methoxypropan-2-yl)pyrrolidin-1-amine, 2-meth-
oxy pyrro-lidin-1-amine, 3-methoxypiperidin-1-amine) in
the presence of triethylamine. The products were obtained
as an orange (or red) powder in a high yield and charac-
1
terized by IR, H NMR, MALDI-TOF, FAB-MS and ele-
mental analysis.
Results and discussion
Absorbance change of 4, 5, 6 and 7 with copper(II)
and other metal ions
Synthesis and characterization of the compounds
As shown in Figs. 1, 2, 3 and 4, an obvious absorption of
ligands 4, 5, 6 and 7 appeared at 396, 408, 418 and 422 nm,
respectively, in acetonitrile solution, and their absorption
The synthetic routes for compounds 4, 5, 6, 7 and 4a were
depicted in Schemes 1 and 2. The new fluorescent sensor 4
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
81
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.75
1.2
0.70
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.65
1.0
0.60
0.55
0.8
0.50
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
-5
2+/10
M
C
-5
M
Cu
C
/10
2+
0.6
0.4
0.2
0.0
Cu
250 300 350 400 450 500 550 600 650
250
300
350
400
450
500
550
600 650
Wavelength (nm)
Wavelength (nm)
Fig. 3 UV absorbance spectra of 6 (3.3 9 10-5 mol/L) upon the
addition of various amounts of Cu2?. The inset shows the absorbance
intensity at kmax = 418 nm as a function of copper concentration
Fig. 1 UV absorbance spectra of 4 (3.0 9 10-5 mol/L) upon the
addition of various amounts of Cu2?. The inset shows the absorbance
intensity at kmax = 396 nm as a function of copper concentration
The selectivity experiments
0.75
0.70
0.65
To explore the utility of 4, 5, 6 and 7 as an ion-selective
chemosensor for Cu2?, the control experiments were con-
ducted with Co2?, Ni2?, Zn2?, at increase concentration
(about 10-6–10-5M). As shown in Fig. 5, there was vir-
tually no obvious change of the absorbance intensity and
no remarkable isosbestic point can be observed when other
cations (e.g. Co2?, Ni2?, Zn2?) were used instead of Cu2?
with ligand 4. Ligand 5, 6 and 7 showed similar properties
in this context. Because cations Co2?, Ni2?, Cu2? and
Zn2? were near each other in the same periods of the
elements periodic table, the sizes of them were different.
The phenomenon suggested that only the size of copper (II)
could fit with the ligands’ cave, which indicated their
1.2
0.60
0.55
1.0
0.50
0.45
0.8
0.6
0.4
0.2
0.0
0.40
0
1
2
3
4
5
6
7
-5
C
/10
M
2+
Cu
250
300
350
400
450
500
550
600 650
prominent selectivity towards Cu2?
.
Wavelength (nm)
Fig. 2 UV absorbance spectra of 5 (3.0 9 10-5 mol/L) upon the
addition of various amounts of Cu2?. The inset shows the absorbance
intensity at kmax = 408 nm as a function of copper concentration
Determination of the association constants (Kass
of complexes
)
intensity also decreased gradually with an increase in Cu2?
ion concentration (about 10-6–10-5M, linearly dependent
coefficient R2 = 0.9896, 0.9679, 0.9890 and 0.9742 for 4,
For a metal complex of 1:1 stoichiometry, the association
constant (Kass) can be estimated according to the following
relation: [26, 27]
ꢀ
5,
6 and 7
respectively). With Cu2?/ligand mole
X ¼ X0 þ ðXlim ꢁ X0Þ=2c0 cH þ cG þ 1=Kass
ratio [ 1:1, a clear red shift (up to 20 nm) was observed.
Isosbestic points were observed at 442, 466, 465 and
484 nm respectively for ligands 4, 5, 6 and 7. As more and
more Cu2? solution was added to the ligand solution, the
absorbance intensity got a minimum and did not change
obviously any more. When considered the value of R2 of 4,
5, 6 and 7, we can find all of them were more than 0.9500,
which were so closed to 1. The results showed the for-
mation of a complex with a 1:1 stoichiometry for 4 (or 5, 6,
ꢁ
h
i
1=2
2
ꢁ ðcH þ cG þ 1=KassÞ ꢁ4cHcG
where X represents the absorbance intensity, cH and cG are
the corresponding concentration of the host and guest. The
association constants obtained by a non-linear least-square
analysis of X vs. cH and cG are listed in Table 1. The data
shows that receptors 4, 5 6 and 7 have an excellent
selectivity for Cu2? ion.
7) and Cu2?
.
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
Fluorescence titration of 4, 5, 6 and 7 with copper(II)
concentration, the fluorescence intensity of 7 at 496 nm
was gradually reduced. Meanwhile, a blue shift was dis-
tinctly observed. The fluorescence intensity decreased lin-
early (0.7-7.0 9 10-5 M, linearly dependent coefficient
R2 = 0.9646 for 7) with an increase in Cu2? ion concen-
tration. Ligands 4, 5, and 6 showed similar properties in
this context. When the hydrazone group (the electron
donor) interacts with Cu2? ion, the latter reduces the
electron-donating character of this group due to the
reduction of conjugation, and a decrease of the extinction
coefficient was expected [28, 29]. Careful analysis of the
evolution of the emission spectra revealed that a 1:1
complex was formed between Cu2? and compound 4 (or 5,
6, 7). The sensors exhibited fluorescence quenching
according to the concentration of Cu2?, with a dynamic
working arrange of 0.7-7.0 9 10-5 M, respectively. In
other words, the ligands 4, 5, 6 and 7 have remarkable
The sensitive signal response of compounds 4, 5, 6 and 7
toward Cu2? were carried out in acetonitrile solution. As
shown in Fig. 6, with a gradual increase of Cu2? ion
0.60
0.58
1.0
0.56
0.54
0.52
0.50
0.8
0.48
0.46
0.44
0.6
0.4
0.2
0.0
0.42
0
1
2
3
4
5
6
7
-5
/10
C
M
2+
Cu
sensitive fluorescence responses to Cu2?
.
500 550 600 650
250 300 350 400 450
Figure 7 showed the Job’s plot of compound 5 with
Cu2?. The total concentration of the host and guest was
constant (3.0 9 10-5 molꢀL-1) in acetnitrile, with a con-
tinuously variable molar fraction of the guest
([G]/([H] ? [G])). When the molar fraction of the guest
Wavelength (nm)
Fig. 4 UV absorbance spectra of 7 (3.4 9 10-5 mol/L) upon the
addition of various amounts of Cu2?. The inset shows the absorbance
intensity at kmax = 422 nm as a function of copper concentration
Fig. 5 a UV absorbance
spectra of 4 (3.0 9 10-5 mol/L)
upon the addition of various
(b)
(a)
1.2
1.0
1.0
amounts of Co2?, b UV
absorbance spectra of 4
0.8
0.6
0.4
0.2
0.0
0.8
(3.0 9 10-5 mol/L) upon the
addition of various amounts of
0.6
Ni2?, c UV absorbance spectra
0.4
of 4 (3.0 9 10-5 mol/L) upon
the addition of various amounts
0.2
0.0
of Zn2?, d UV absorbance
intensity of compound 4
300
400
500
600
300
400
500
600
(3.0 9 10-5 mol/L) at
Wavelength (nm)
Wavelength (nm)
kmax = 396 nm as a function of
cobalt (filled square), nickel
(filled circle), copper (filled
triangle) and zinc (filled
(c)
(d)
1.0
0.8
0.6
0.4
0.2
0.0
0.9
0.8
0.7
0.6
0.5
inverted triangle) concentration
0
5
10
15
20
25
30
35
300
400
500
600
-5
Wavelength (nm)
C
/10
2+
M
M
Table 1 Association constants Kass of receptors 4, 5, 6 and 7 with guest cations
Ligand
4
5
6
7
R2
0.9896
1.3 9 105M-1
0.9679
7.2 9 106M-1
0.9890
4.1 9 105M-1
0.9742
8.0 9 105M-1
Kass
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
83
600
50% (v/v) acetonitrile/(0.1 M KNO3 aqueous solution as
supporting electrolyte) with a modified glassy carbon
(3 mm in diameter) working electrode, and the auxiliary
and reference electrodes were platinum wire and saturated
calomel electrode (SCE), respectively. Deoxygenation of
the solutions was achieved by bubbling nitrogen gas for at
least 5 min and the working electrode was cleaned after
each run. The linear sweep voltammograms were recorded
with a scan rate of 100 mV S-1. The Cu2? was added at an
increase concentration (1.05–15.75 lM). The Fig. 8
exhibited an irreversible oxidation wave at ca. ? 0.43 V
which may be assigned to the oxidation of the pyrryl-
hydrazone group of compound 6, since the compound 3
had no signal toward it. The addition of Ni2? and Zn2?
caused no significant influence in the oxidation potential
(? 0.43 V) compared to the free receptor. Additionally, the
oxidation wave of pyrryl-hydrazone group is anodically
shifted with respect to the free receptor after the addition of
Cu2?. Further, the current intensity of the oxidation wave
increased linearly with an increase in Cu2? ion concen-
tration. Ligands 5, and 7 showed similar properties in this
context. However, no obvious signal can be detected for
ligand 4, the possible explanation can be speculated
because of the presence of the F, which made the com-
pound difficult to be oxidated and deoxidated. Both prop-
erties above might support the formation of the complexed
species and the selectivity of the ligands for Cu2?. By the
way, in the case of Cu2? an additional redox process was
observed, which was quasi-reversible. Since this was not
observed in the case of Ni2? and Zn2?, it seemed to be
metal based. However, the electrochemical instrument was
not as sensitive as spectroscopic analysis, the properties of
the ligands can be detected by linear sweep voltammetric
experiments (LSV), which additionally supported the sen-
sitivity of the ligands we synthesized.
500
700
400
600
300
200
500
100
400
300
200
100
0
0
1
2
3
4
5
6
7
8
-5
C
/10
M
2+
Cu
438.6 478.6 518.6 558.6 598.6
Wavelength (nm)
Fig. 6 Fluorescence spectra of 7 (3.4 9 10-5 mol/L) upon the
addition of various amounts of Cu2?, kex = 310 nm. The inset shows
the fluorescence intensity at kmax
= 503 nm as a function of
(em)
Cu2? ion concentration
650
600
550
500
-I
0
I
450
400
350
0.0
0.2
0.4
0.6
0.8
1.0
[G] / ( [H] + [G] )
Fig. 7 Job plot of compound 5 with Cu2?. The total concentration of
the host and guest is 3.0 9 10-5 mol L-1 in acetnitrle solution. I0:
fluorescence intensity of the host; I: fluorescence intensity of host in
the presence of the guest
Binding characteristics of computational explanation
To shed light on the binding model between various hosts
(4, 5, 6 and 7) and guests (Co2?, Ni2?, Cu2? and Zn2?),
their corresponding binding structures were optimized by
quantum theory method, based on the crystal structure of
compound 3 (CCDC 782078) we made. Worthy of note
here, the optimized structures shown in Fig. 9(a–d) repre-
sented only one of the possible canonical forms for 4, 5 6
and 7, respectively, and the detailed resonance structures
for them are depicted in Chart 1.
was 0.50, the difference of fluorescence intensity between
the host and the guest reached a maximum, which dem-
onstrated that compound 5 formed a 1:1 complex with
Cu2?, respectively. Ligands 4, 6, and 7 showed similar
properties in this context.
Linear sweep voltammetric experiments (LSV)
Further, linear sweep voltammetric experiments (LSV)
In each optimized structure of the complex between the
host and the guest, the metal atom was bound to four
nitrogen atoms, two from the deprotonated pyrroles and
two from the adjacent imines, and was almost coplanar to
the respective N4 plane. The geometry at each metal centre
was square planar. When interact with Cu2?, the bond length
with compounds 3, 4, 5, 6 and 7 in the presence of Ni2?
,
Cu2? and Zn2? respectively were performed to ascertain
the interaction between the ligands and Cu2?, while com-
pound 3 was used as control. These experiments were
carried out in a solution which contained 10-5 M ligands in
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Fig. 8 a LSV of 6 (3.3 9 10-5
mol/L) upon the addition of
(a)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(b) 1.2
1.0
various amounts of Cu2?
,
b LSV of 6 (3.3 9 10-5 mol/L)
upon the addition of various
amounts of Ni2?, c LSV of 6
(3.3 9 10-5 mol/L) upon the
addition of various amounts of
Zn2?
0.8
0.6
0.4
0.2
0.0
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Potential / V
Potential / V
(c)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Potential / V
is the shorter than other three metal ions (Co2?, Ni2?, Zn2?).
This result was based on the optimized structure, which
demonstrated the metal ions binding affinity of the ligands
was molecular clamp cavity size related.
addition of excess of the Cu2?. However, the discoloration
of ligand 4 is not as obvious as others, which can be
ascribed to the electron withdraw effect of F. In contrast,
other cations could not trigger any color changes of the
above four receptors under the same experimental condi-
tions. The dramatic color changes made ligands 5, 6 and 7
to be efficient colorimetric sensors for the detection of
At the B3LYP/6-31 ? G(d) level, the binding energy
between Cu2? and hosts 4, 5, 6 and 7 ranged from 83 to
3635 kJ/mol. This binding energy, included with zero-
point correction and thermal correction at 298 K, was
calculated as the electronic energy of the binding structures
relative to free host and guest molecules. The binding
energies obtained in the theoretical predictions are in line
with the significantly large binding constants measured for
Cu2? and hosts 4, 5, 6 and 7.
Cu2?
.
Conclusion
In summary, four novel chemosensors for Co2?, Ni2?
,
In contrast, the molecular modelling revealed that the
two oxygen atoms in host 5 can serve as electrostatic force
Cu2? and Zn2? metal ions including dipyrrolylquinoxaline
as chromophore 4, 5, 6 and 7 were successfully designed
and synthesized. Compound 4, 5, 6 and 7 exhibited high
selectivity and sensitivity for Cu2? at the concentration of
10-5 M. A 1:1 stoichiometry was obtained from non-linear
fitting of the UV–visible titration curves. The photophysi-
cal studies also revealed interesting properties of this new
family when interact with Cu2?: an intense absorption
change around 410 nm and an obvious fluorescence
quenching around 500 nm. The binding properties of the
ligands can be detected by linear sweep voltammetric
(LSV) titration experiments supported the sensitivity of the
ligands we synthesized additionally. Meanwhile, the com-
putational explanation demonstrated the binding charac-
teristics from the quantum theory by bond length and
binding energy. On the other hand, since the acetonitrile
system can be dissolved with water, our findings will help
donators to interact with Cu2? (bond length was 2.6 A) as
˚
shown in Fig. 10(b) while 4 didn’t have any oxygen atom
and the distance between the atoms in 6 and 7 was too long
˚
([ 3.2 A), as shown in Fig 10(a, c, d), leading to the for-
mation of the most stable complex. As reflected in its
binding constant, this additional electrostatic force inter-
action was comparable to that of the normal binding.
Discoloration experiments
We studied the color changes of ligands 4, 5, 6 and 7 in
acetonitrile upon addition of various cations (Co2?, Ni2?
,
Cu2? and Zn2? added as their acetate salts). Significantly,
as shown in Fig. 11, the yellow solutions of ligands 5, 6
and 7 in acetonitrile all changed to red-brown upon
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
85
N
N
R
R
N
N
R
R
N
N
N
N
N
N
N
N
Ha
Ha
Hb
Hb
N
R
N
R
R
N
N
N
N
N
N
Hb
Ha
Hb
Ha
N
N
N
R
N
N
H
R
N
R
R
N
N
N
N
N
N
H
N
H
H
N
N
N
R
O
F
F
F
H
compound 5 R=
compound 7 R=
N
compound 4 R=
compound 6 R=
F
N
F
O
O
N
N
Chart 1 Resonance structures of compound 4, 5, 6, and 7
activated molecular sieves prior to use. Pyridine was distilled
from NaOH and stored over activated molecular sieves prior
to use. Methanol and dichloromethane were distilled from
CaH2. The 1-(perfluorophenyl)hydrazine, ( )2-(2-methoxy-
propan-2-yl)-pyrrolidin-1-amine, ( )2-methoxypyrrolidin-1-
amine, and ( )3-methoxypiperidin-1-amine were bought
from UniPharm Ltd. The infrared spectra were measured on a
Fig. 9 The computational optimised structures of compounds 4(a),
5(b), 6(c) and 7(d)
1
Shimadzu FT-IR 3000 spectrometer. H NMR spectra was
recorded on a Varian Mercury-VX 300 spectrometer, high-
resolution mass spectra on a API-Qstar-LCMS/MS in
MALDI-TOF mode, and low-resolution mass spectra on a
Finnigan MAT SSQ-710 in FAB (positive) mode. Fluores-
cence spectra were obtained on a Hitachi Model F-4500 FL
Spectrophotometer. UV–vis spectra were taken on a TU-
1901 spectrometer. Linear sweep voltammetric experiments
(LSV) were performed with a CHI 660B electrochemical
workstation (CH Instrument Co. (Shanghai, China)).
to improve the direct detection of Cu2? ion in the envi-
ronment. Exploration along this direction in chemsensor
development is in progress.
Experimental
General information
Syntheses
Unless otherwise indicated, all commercially available start-
ing materials were used directly without further purification.
Pyrrole was dehydrated and distilled prior to use. DMF and
1,2-dichloroethane were distilled from CaH2 and stored over
1,2-Bis(1H-pyrrole-2-yl)ethane-1,2-dione(1): This com-
pound was prepared according to the published procedure
[19].
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J Incl Phenom Macrocycl Chem (2012) 72:79–88
Fig. 11 a The colour changes of ligand 4 (3.0 9 10-5 mol/L in
acetonitrile) after addition of various cations. b The colour changes of
ligand 5 (3.0 9 10-5 mol/L in acetonitrile) after addition of various
cations. c The colour changes of ligand 6 (3.3 9 10-5 mol/L in
acetonitrile) after addition of various cations. d The colour changes of
ligand 7 (3.4 9 10-5 mol/L in acetonitrile) after addition of various
cations. (From left to right: free, Co2?, 1 equiv, 5 equiv; Ni2?, 1
equiv, 5 equiv; Cu2?, 1 equiv; Zn2?, 1equiv, 5 equiv.)
2,3-Bis(1H-pyrrol-2-yl)quinoxaline (2): It was prepared
by the literature method.[20].
2,3-Bis(5_-formylpyrrol-2_-yl)quinoxaline (3): It was
23.
synthesized under the guiding of the literature.
Compound 4: A solution of 2,3-bis(5-formylpyrrol-2-
yl)-quinoxaline (3) (50.4 mg, 0.16 mmol) and triethyl-
amine (80 lL) in dry methanol (50 mL) was stirred at
Fig. 10 The computational optimised structures of complexes 4(a),
5(b), 6(c) and 7(d) with Cu2?
123

J Incl Phenom Macrocycl Chem (2012) 72:79–88
87
reflux for 30 min. After that, 1-(perfluorophenyl)hydrazine
(63.1 mg, 0.32 mmol) in dry methanol (2 mL) was added
dropwise to the solution. The resulting mixture when
refluxed over night, the color of which was changed to
orange from yellow. Evaporated the resulting solution to
dryness, and recrystallized from CH2Cl2/hexane to furnish
an orange solid (91 mg, 84%). 1H NMR(300 MHz; CDCl3)
d: 10.05 (br, 2H, NH), 8.00-7.97 (dd, J = 3.6 Hz, 2H,
quinoxaline), 7.76 (br, 2H, = N–NH), 7.67-7.64 (dd,
J = 3.6 Hz, 2H, quinoxaline), 7.19 (s, 2H, -CH = N), 6.91
(br, 2H, pyrrole), 6.41 (br, 2H, pyrrole). IR (KBr, cm-1):
3433(b), 2825(w), 2359(w), 1632(s), 1602(s), 1384(vs),
1115(b), 611(b). HR-MS (MALDI-TOF): (M ? 1)?
requies 677.1182, found 677.1228. Anal. calcd for
C30H14F10N8: C, 53.26; H, 2.09; N, 16.56. Found: C, 53.29;
H, 2.02; N, 16.59.
6.93 (br, 2H, pyrrole), 6.26 (br, 2H, pyrrole), 4.22 (br, 2H,
piperidine), 3.67 (d, J = 11.7 Hz, 4H, piperidine), 3.50 (br,
4H, piperidine), 3.46 (s, 6H, –O–CH3), 3.39-3.35 (m, 4H,
piperidine), 2.89-2.78 (m, 4H, piperidine). IR (KBr, cm-1):
3452(s), 2969(w), 2360(w), 1632(s), 1384(vs), 1351(w),
1139(w). FAB-MS: m/z 540.3 M?. Anal. calcd for
C30H36N8O2: C, 66.64; H, 6.71; N, 20.73. Found: C, 66.67;
H, 6.70; N, 20.70.
Compound 4:. Compound 4 (30 mg, 0.044 mmol) was
dissolved in dry methanol (30 mL) and a solution of
(CH3CO2)2Niꢀ4H2O (11.03 mg, 0.044 mmol) in dry meth-
anol (15 mL) was added. The mixture was stirred for
30 min at refluxing temperature. The mixture was evapo-
rated to dryness. The residue was recrystallized from
CH2Cl2/CH3OH to give an orange solid (31.9 mg, 98%). IR
(KBr, cm-1): 3434(b), 2927(w), 2359(w), 1631(s), 1605(s),
1384(vs), 1094(w), 1050(w), 613(b). HR-MS (MALDI-
TOF): (M ? 1)? requies 733.0379, found 732.9702. Anal.
calcd for C30H12F10N8Ni: C, 49.15; H, 1.65; N, 15.28.
Found: C, 49.19; H, 1.60; N, 15.22.
Compound 5: This compound was prepared similarly as
for 4 except that 2-(2-methoxypropan-2-yl)pyrrolidin-1-
amine (50.3 mg, 0.32 mmol) was used in place of 1-(per-
fluorophenyl)hydrazine to give a red powder (75.9 mg,
79.8%). 1H NMR(300 MHz, CDCl3) d: 9.90 (br, 2H, NH),
7.89–7.86 (dd, J = 3.6 Hz, 2H, quinoxaline), 7.57–7.53
(dd, J = 3.6 Hz, 2H, quinoxaline), 7.19 (s, 2H, –CH = N),
6.97 (br, 2H, pyrrole), 6.18 (br, 2H, pyrrole), 3.55 (t,
J = 7.5 Hz, 2H, pyrrolidine), 3.32 (s, 6H, -OCH3), 3.25
(t, J = 6.0 Hz, 4H, pyrrolidine), 3.01-2.95 (m, 4H, pyr-
rolidine), 2.03-1.93 (m, 4H, pyrrolidine), 1.62 (s, 12H,
-CH3). IR (KBr, cm-1): 3449(b), 2924(w), 2853(w),
1631(s), 1490(w), 1384(vs), 1351(w), 997(w), 762(w). HR-
MS (MALDI-TOF): (M ? 1)? requies 597.3587, found
597.3646. Anal. calcd for C34H44N8O2: C, 68.43; H, 7.43;
N, 18.78. Found: C, 68.47; H, 7.40; N, 18.75.
Acknowledgments The authors gratefully acknowledge financial
support from the National Natural Science Foundation of China (No.
20672082 and No. 90813031).
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