Metal ion-assisted ring-opening of a quinazoline-based chemosensor: Detection of copper(II) in aqueous media

Article abstract of DOI:10.1039/c4dt03791j

A quinazoline-based fluorescence chemosensor, 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quinazoline (HL), for highly selective recognition of Cu(II) in aqueous media was synthesized. The detection limit was of the order of 10^-6 M. The crystal structures of the Cu(II) and Cd(II) complexes showed that HL changed to a Schiff base when it reacts with metal salts and that the metal ions coordinate with two nitrogen atoms and one hydroxyl oxygen atom from the Schiff base. The theoretical calculations at B3LYP-SCRF/6-31G(d) confirmed that it is the Cu(II) ion that assisted the ring-opening of the quinazoline derivative, forming a Cu(II) Schiff base complex during the detection. LMCT leads to the disappearance of fluorescence. A cell imaging study indicated that HL could be used to detect the intracellular Cu²⁺ ion.

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Metal ion-assisted ring-opening of a quinazoline-
based chemosensor: detection of copper(II) in
aqueous media†
Cite this: DOI: 10.1039/c4dt03791j
Wei Cao, Xiang-Jun Zheng,* De-Cai Fang* and Lin-Pei Jin
A quinazoline-based fluorescence chemosensor, 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quin-
azoline (HL), for highly selective recognition of Cu(II) in aqueous media was synthesized. The detection
limit was of the order of 10−6 M. The crystal structures of the Cu(II) and Cd(II) complexes showed that HL
changed to a Schiff base when it reacts with metal salts and that the metal ions coordinate with two nitro-
gen atoms and one hydroxyl oxygen atom from the Schiff base. The theoretical calculations at
B3LYP-SCRF/6-31G(d) confirmed that it is the Cu(II) ion that assisted the ring-opening of the quinazoline
derivative, forming a Cu(II) Schiff base complex during the detection. LMCT leads to the disappearance of
fluorescence. A cell imaging study indicated that HL could be used to detect the intracellular Cu2+ ion.
Received 11th December 2014,
Accepted 3rd February 2015
DOI: 10.1039/c4dt03791j
www.rsc.org/dalton
tives can act as excellent probes for detection of metal ions. To
increase the aqueous solubility and the coordination ability of
Introduction
Fluorescent chemosensors for biologically important metal the quinazoline derivative, we selected salicylaldehyde with a
ions1 have received considerable attention due to their high hydroxyl group to react with 2-(2-aminophenyl)benzimidazole
selectivity and sensitivity. Cu2+ plays an important role in to prepare the target compound, 6-phenol-2-yl-(5,6-dihydro-
many fundamental physiological processes, but excessive Cu2+ benzimidazo[1,2-c])quinazoline (HL).
will lead to severe neurodegenerative disease.2 The U.S.
Also, during the recognition process, it was reported that a
Environmental Protection Agency (EPA) has set the limit of solvent-assisted [1,5] sigmatropic-type shift of the secondary
copper in drinking water as 1.3 ppm (about 20 μM).3 Also, the N–H proton from the quinazoline derivative probably occurred
average concentration of blood copper in the normal group is to result in a metal Schiff-base complex.5a–c Generally, the
100–150 μg dL−1 (15.7–23.6 μM). Therefore the design and syn- breakage of the C–N bond needs an energy of 60–90 kcal
thesis of chemosensors for detection of Cu2+ ions in aqueous mol−1.6 It is really a challenge for the solvent to break the C–N
media are very important. Quinazoline derivatives play an bond of the quinazoline ring only with the assistance of a
important role in the field of pesticides and pharmaceuticals solvent. The transformation mechanism from quinazoline
due to their extensive biological and pharmaceutical activi- derivatives to Schiff bases to form the metal complexes has not
ties.4 This suggests that quinazoline derivatives generally have yet been solved. In this context, investigating the response
a low hazard to environment and organisms. The quinazoline mechanism of quinazoline derivatives as chemosensors has
derivatives synthesized using different aldehydes and 2-(2- become particularly important. In this paper, the detection of
aminophenyl)benzimidazole could be used as fluorescence Cu(II) by 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quin-
chemosensors for metal ions, such as Pb2+, Hg2+, Cr3+, Zn2+, azoline (HL) was investigated. The response mechanism was
Fe2+, Fe3+, and Al3+,5 indicating that the quinazoline deriva- discussed with a combination of experiments and theoretical
calculations in detail. Also HL can be used to detect the Cu2+
ion in living cells by bioimaging.
Beijing Key Laboratory of Energy Conversion and Storage Materials, College of
Chemistry, Beijing Normal University, Beijing, 100875, People’s Republic of China.
E-mail: xjzheng@bnu.edu.cn, dcfang@bnu.edu.cn
†Electronic supplementary information (ESI) available: Optimized Cartesian
Results and discussion
coordinates, total energies, free energies and frequencies for the stationary
points located; ESI-MS, 1H NMR and crystal structure of HL; competition exper-
HL was synthesized via solvothermal conditions and character-
iments of HL with Cu2+ in the presence of various metal ions; changes of absorp-
ized by elemental analyses, IR, 1H NMR, ESI-MS and single-
tion spectra of HL upon addition of Cu2+ ions; Job’s plot and ESI-MS of HL +
Cu2+; fluorescence titration. CCDC 1030199–1030201. For ESI and crystallo-
crystal X-ray diffraction (Fig. S1, ESI†). The single-crystal X-ray
diffraction revealed that it is not a coplanar molecule because
graphic data in CIF or other electronic format see DOI: 10.1039/c4dt03791j
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of the existence of a sp3 carbon.7 All the results showed that
the quinazoline derivative has been successfully prepared.
Table 1 Crystal data and structure refinement parameters of com-
plexes 1, 4 and 5a
Compound
1
4
5
Photophysical properties of HL
Formula
Fw
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
20H14ClN3OCu C44H34N6O6Cd2 C46H42N6O8Cd2
From the fluorescence spectra (Fig. 1), it can be seen that HL
can emit blue light with an emission peak at 437 nm. There
was no remarkable change of fluorescence intensity when Li+,
Na+, K+, Mg2+, Ca2+, Al3+, Cr3+, Mn2+, Fe3+, Ni2+, Zn2+, Cd2+,
Pb2+ or Hg2+ was added, respectively (Fig. 1 and Fig. S2a†). But
addition of Cu2+ to HL quenched the fluorescence completely.
Therefore HL was used to detect Cu2+ in a DMSO–H2O (1 : 9,
v/v, HEPES 20 mM, pH = 7.4) solution. The competition experi-
ments indicated that other metal ions did not interfere with
the selective recognition of HL toward Cu2+ (Fig. S2b†). HL
could act as an efficient chemosensor for the detection of
Cu2+. From UV-vis absorption spectra (Fig. S2c†) we can see
that compared to the absorption of HL, there are no signifi-
cant changes upon addition of metal ions except Cu2+. HL
shows two bands at ca. 300 nm and a broad band at 350 nm.
Upon addition of Cu2+ to HL, the band at 350 nm disappeared,
two bands at ca. 300 nm became one broad band, and a new
band emerged at 404 nm which could be attributed to the
ligand–metal charge transfer (LMCT),8 accompanied by the
411.33
967.59
Monoclinic
P2(1)/c
10.445(7)
21.759(1)
8.695(6)
90
1031.68
Monoclinic
P2(1)/n
11.633(6)
12.346(6)
14.607(7)
90
Triclinic
ˉ
P1
8.064(6)
10.188(8)
10.856(9)
90.52(1)
105.14(1)
94.42(1)
858.2(1)
2
α (°)
β (°)
101.74(1)
90
90.26(1)
90
γ (°)
V (Å3)
1934.9(2)
2
1.661
2097.9(2)
2
1.633
Z
Calculated
1.592
density (Mg
m−3
)
F (000)
418
5244/3812
968
11 656/4449
1040
14 307/4798
Reflections
collected/
unique
Goodness-of-fit
1.123
1.036
1.034
on F2
Final R indices
[I > 2σ(I)]
R indices (all
data)
R1 = 0.0375
wR2 = 0.0961
R1 = 0.0508
wR2 = 0.1182
R1 = 0.0304
wR2 = 0.0721
R1 = 0.0433
wR2 = 0.0778
R1 = 0.0252
wR2 = 0.0520
R1 = 0.0352
wR2 = 0.0558
color change from colorless to yellow. With increasing a R1 = ∑(|Fo| − |Fc|)/|Fo|; wR2 = {∑[(w|Fo2| − |Fc2|)2/∑w(Fo2)2]}1/2
the amount of Cu2+, an isosbestic point could be observed at
388 nm, indicating a clear conversion of HL into the Cu(II)
complex (Fig. S3†).
.
Species formed in the solution
Table 2 Selected bond distances (Å) and angles (°) for 1, 4 and 5
To identify the species formed in the response system, three
methods were adopted to obtain the Cu2+ complex. First, a
1
one-pot reaction of CuCl2 with salicylaldehyde and 2-(2-amino-
phenyl) benzimidazole under solvothermal conditions gave
the single crystal of 1. Crystallographic data and selected bond
distances and angles are summarized in Tables 1 and 2,
respectively. The result of single-crystal X-ray diffraction shows
that it is a Cu(II)–Schiff base (L1) complex. The Cu2+ ion is four-
coordinated with a hydroxyl oxygen atom, an imine nitrogen
and a benzimidazole nitrogen atom from L1 and one Cl− in a
square geometry (Fig. 2a). In addition, the mixed solution of
CuCl2 and HL gave red crystals either under solvothermal
Cu(1)–Cl(1)
Cu(1)–O(1)
O(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
2.237(8)
1.904(2)
147.06(11)
94.21(9)
90.72(10)
Cu(1)–N(2)
Cu(1)–N(3)
O(1)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
N(3)–Cu(1)–Cl(1)
1.954(2)
1.976(2)
91.76(7)
99.02(8)
151.88(8)
4
Cd(1)–O(3)
Cd(1)–O(1)
Cd(1)–N(2)
2.241(2)
2.241(2)
2.251(2)
99.74(7)
147.59(7)
109.70(8)
96.24(8)
79.11(6)
102.25(7)
94.91(8)
81.05(7)
Cd(1)–O(1)#1
Cd(1)–N(3)
Cd(1)–O(2)
N(2)–Cd(1)–N(3)
O(1)#1–Cd(1)–N(3)
O(3)–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
N(2)–Cd(1)–O(2)
O(1)#1–Cd(1)–O(2)
N(3)–Cd(1)–O(2)
2.278(2)
2.317(2)
2.535(2)
77.07(8)
158.61(8)
53.80(7)
151.45(7)
94.42(7)
111.25(7)
90.05(7)
O(3)–Cd(1)–O(1)
O(3)–Cd(1)–N(2)
O(1)–Cd(1)–N(2)
O(3)–Cd(1)–O(1)#1
O(1)–Cd(1)–O(1)#1
N(2)–Cd(1)–O(1)#1
O(3)–Cd(1)–N(3)
O(1)–Cd(1)–N(3)
Symmetry code: #1 −x + 1, −y + 1, −z + 1
5
Cd(1)–N(1)
Cd(1)–O(3)
Cd(1)–O(1)
2.250(2)
2.280(2)
2.290(1)
117.52(6)
153.27(6)
84.32(5)
114.71(6)
82.81(5)
81.41(5)
79.90(6)
98.65(6)
Cd(1)–O(1)#2
Cd(1)–N(3)
Cd(1)–O(2)
O(1)–Cd(1)–N(3)
O(1)#2–Cd(1)–N(3)
N(1)–Cd(1)–O(2)
O(3)–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
O(1)#2–Cd(1)–O(2)
N(3)–Cd(1)–O(2)
2.303(1)
2.318(2)
2.452(2)
81.75(5)
162.86(5)
80.14(6)
159.27(6)
82.29(6)
79.60(6)
95.02(6)
N(1)–Cd(1)–O(3)
N(1)–Cd(1)–O(1)
O(3)–Cd(1)–O(1)
N(1)–Cd(1)–O(1)#2
O(3)–Cd(1)–O(1)#2
O(1)–Cd(1)–O(1)#2
N(1)–Cd(1)–N(3)
O(3)–Cd(1)–N(3)
Fig. 1 Fluorescence spectra of HL (10 µM) upon the addition of 1 equiv.
metal ions in DMSO–H2O (1 : 9, v/v, HEPES 20 mM, pH = 7.4) (λex
=
Symmetry code: #2 −x + 1, −y, −z
352 nm).
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Fig. 2 (a) Crystal structure of the complex 1 with an atom labelling; (b)
powder X-ray diffraction patterns of 1, 2 and 3; (c) the absorption
spectra of complex 1, HL+ 1 equiv. Cu2+ (HL + Cu2+) and HL.
Fig. 3 (a) Crystal structure with an atom labelling for 4, symmetry
code: A: −x + 1, −y +1, −z + 1; (b) crystal structure with an atom labelling
for 5, symmetry code: A: −x + 1, −y, −z.
be [CdL1(Ac)]2 (4) and [CdL1(Ac)(CH3OH)]2 (5), respectively.
They have binuclear molecular structures (Fig. 3a and 3b). For
Cd2+ ions, similarly to Cu2+, after one-pot reaction of the tri-
component or direct reaction of Cd2+ ions with HL, a Schiff
base complex was formed. The Schiff base L1 adopts a tetra-
dentate coordination mode to link two Cd2+ ions. Cd2+ ions in
4 and 5 are both six-coordinated in a distorted octahedral geo-
metry. The structures of 1–5 directly support the ring-opening
of the quinazoline compound HL to become the Schiff-base in
the Cu(II) and Cd(II) complexes. The results indicated that ring-
opening of HL is assisted by the binding of HL with metal
ions.
conditions (2) or after slow evaporation at room temperature
(3). Crystals of 2 and 3 were characterized by elemental ana-
lyses, IR, and powder X-ray diffraction (Fig. 2b). The results
show that 2 and 3 are the same complex as 1, which implies
that the C–N bond in HL was broken to become a benzimid-
azole-based Schiff base (HL1) with more chelating sites to bind
Cu2+, resulting in the formation of complex 1.
Furthermore, it was observed that the absorption spectrum
of the system HL + Cu2+ was different from that of HL, but the
same as that of complex 1 (Fig. 2c), indicating that complex 1
was formed in the system. The Job’s plot indicated that HL
binds Cu(II) to form a 1 : 1 Cu–L1 complex (Fig. S4†). To gain
an insight into the stoichiometry of the Cu–L1 complex, the
electrospray ionization mass spectrum was recorded (Fig. S5†).
A peak appearing at m/z 375.02 was attributed to Cu–L1 with a
1 : 1 binding mode (calculated [CuL1]+ m/z is 374.90), while the
peak at m/z 453.03 can be ascribed to [CuL1DMSO]+ (calcd.
453.03). All the above results indicated that upon the addition
of Cu2+ to the solution of HL, HL changed to HL1, and that the
formation of 1 resulted in fluorescence quenching of HL.
Based on the fluorescence titrations, the detection limit for
Cu2+ was 7.1 µM and the association constant (log Ka) deduced
for 1 : 1 stoichiometry was 4.7 (Fig. S6†).9 The detection limit
was lower than the limit of copper in drinking water defined
by the U.S. EPA limit (∼20 µM).3
Ring-opening and fluorescence quenching of HL by Cu2+
To explore the probable reaction of HL + CuCl2 → [CuL1Cl] +
HCl, the B3LYP-SCRF/6-31G(d) method has been employed to
characterize the energies, structures and frequencies. The
probable reaction pathway and relative energy are schemati-
cally described in Fig. 4, from which one can see that the for-
mation of COM1 would release free energy of 29.7 kcal mol−1
.
After that one of the Cl atoms in CuCl2 would take a hydrogen
atom in the OH group to form an HCl molecule, and then the
hydrogen atom in the HCl molecule could be easily transferred
into an N atom in the imidazole ring to form INT2 without any
transition state, releasing the free energy of 9.3 kcal mol−1
.
Considering copper has a changeable valence in complexes,
we selected a d10 metal ion, Cd2+, to investigate its corres-
ponding complexes, the preparation of which is similar to
those of complexes 1 and 2. Orange and yellow crystals were
obtained and characterized by single-crystal X-ray diffraction to
Breaking the C–N bond is the rate-controlling step in this reac-
tion, with the free energy barrier being 21.8 kcal mol−1, which
is easy to overcome under experimental conditions. As we
know, the bond energy of the C–N bond in HL has been calcu-
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Fig. 5 The frontier orbitals and their orbital energies for [CuL1Cl].
Fig. 4 The relative energy (kcal mol−1) at B3LYP-SCRF/6-31G(d) for the
stationary points during the reaction of HL + CuCl2 → [CuL1Cl] + HCl.
lated to be 69.3 kcal mol−1, which is hard to overcome without
the assistance of CuCl2. In INT2, TS2 and INT3, the Cl atom
bonded to a hydrogen atom holds a charge of ca. −0.85e, and
thus it is in fact Cl−, which is only loosely bonded to NH and
probably could be freely moved in solution. Therefore, the
formation of INT3a is also a favorable process, releasing a free
energy of 3.8 kcal mol−1, and then the release of an HCl mole-
cule would further lower the free energy by 21.2 kcal mol−1
indicating that this is an automatic process.
,
In order to elucidate the fluorescence quenching of HL
upon the addition of Cu2+, the LMCT mechanism for the
complex [CuL1Cl] was calculated. The frontier orbitals and
energy levels are depicted in Fig. 5, from which one can realize
that HOMO is mainly on a phenyl ring of ligand (L1) and
LUMO is an empty d orbital; therefore, the overlap of HOMO
and LUMO is almost zero, i.e., the excitation of HOMO to
LUMO is not allowed. Although the overlap between HOMO
and LUMO+1 is not very big, excitation between HOMO and
LUMO+1 seems possible. Once one electron is excited to
LUMO+1, the electron could be transferred into LUMO orbital
(d orbital of Cu) from LUMO+1 (on L1). Then the electron
could not return to HOMO, leading to the disappearance of
fluorescence.
Fig. 6 Live-cell imaging of HeLa cells treated with HL before (A) and
after (B) incubation with CuCl2. (a) and (d) represent the bright-field
images, (b) and (e) represent the fluorescence images, and (c) and (f)
represent the overlay images (λex = 405 nm).
fluorescence was observed when HeLa cells were exposed to
HL, while the bright fluorescence can be quenched completely
by further incubation of the cells with Cu2+. These results
demonstrated that HL is cell-permeable and can respond to
copper(II) ions within living cells.
Conclusions
In summary, a quinazoline derivative, 6-phenol-2-yl-(5,6-di-
hydrobenzimidazo[1,2-c])quinazoline (HL), was synthesized and
characterized. HL showed highly selective and sensitive fluo-
Cell imaging studies
Owning to the encouraging selectivity and sensitivity of HL rescence ‘on–off’ behaviour toward Cu2+, and it can be used to
toward Cu2+ ions, bioimaging experiments were conducted to detect the Cu2+ ion in living cells by bioimaging. The fluo-
prove the ability of HL to detect Cu2+ in living cells. HeLa cells rescence quenching of HL upon the addition of Cu2+ ions was
were first incubated with 20 µM HL for 2 h, and then treated due to LMCT in 1. The combination of experimental obser-
with 10 µM CuCl2 for 15 min. As shown in Fig. 6, intensive vations and theoretical calculations indicated that it is the
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binding of HL with metal ions that leads to the ring-opening ation of the solvents at room temperature, deep red crystals
of HL.
were obtained over a period of 4 days in 29.2% yield. Anal.
Calcd for C20H14ClN3OCu (%): C, 58.39; H, 3.43; N, 10.21.
Found: C, 57.91; H, 3.54; N, 9.98. IR (KBr pellet, cm−1): 3445w,
3182w, 3064w, 1609s, 1590w, 1531s, 1489s, 1463s, 1441s,
1385s, 1322m, 1184s, 1143m, 760s.
Experimental section
General information and materials
All solvents and reagents (analytical grade) were used as One-pot synthesis of [CdL1(Ac)]2 (4)
received. Elemental analyses were conducted using a Vario EL
4 was synthesized as complex 1 except that CuCl2·2H2O was
elemental analyzer. Fourier transform infrared (FT-IR) spectra
were recorded on an Avatar 360 FI-IR spectrometer using KBr
pellets. UV-Vis absorption spectra were recorded using a
spectrophotometer UV-2450, and fluorescence spectra were
recorded on a Cary Eclipse fluorescence spectrophotometer,
with a quartz cuvette (path length = 1 cm). 1H NMR spectra
were obtained using a Bruker Avance III 400 MHz spectro-
meter. Mass spectra (ESI) were recorded on an LCT Premier XE
time-of-flight (TOF) mass spectrometer.
replaced by Cd(Ac)2·2H2O. Orange crystals suitable for X-ray
crystallography were obtained (yield 30.0%). Anal. Calcd for
C22H17N3O3Cd (%): C, 54.62; H, 3.54; N, 8.68. Found: C, 54.52;
H, 3.47; N, 8.63. IR (KBr pellet, cm−1): 3395w, 3058w, 2900w,
1605s, 1573s, 1531s, 1438m, 1301s, 1176m, 1159s, 1044m,
817m, 754s.
Synthesis of [CdL1(Ac)(CH3OH)]2 (5)
5 was synthesized as complex 2 except that 0.1 mmol
CuCl2·2H2O was replaced by 0.05 mmol Cd(Ac)2·2H2O. Yellow
crystals suitable for X-ray crystallography were obtained (yield
40.2%). Anal. Calcd for C23H21N3O4Cd (%): C, 53.55; H, 4.10;
N, 8.15. Found: C, 53.67; H, 4.14; N, 8.08. IR (KBr pellet,
cm−1): 3418w, 3071w, 2900w, 1603s, 1531s, 1436s, 1306m,
1175m, 1158s, 1044m, 818m, 759s.
Synthesis of C20H15N3O (HL)
A methanol (3 mL) solution of salicylaldehyde (0.2 mmol,
0.020 mL) and 2-(2-aminophenyl)benzimidazole (0.2 mmol,
0.042 g) was sealed in a Teflon-lined stainless steel autoclave
and heated at 80 °C for 3 days, and then cooled to room temp-
erature. Yellow crystals suitable for X-ray crystallography were
obtained (yield 71.9%). Anal. Calcd for C20H15N3O (%): C,
76.66; H, 4.83; N, 13.41. Found: C, 76.54; H, 4.65; N, 13.00. IR
(KBr pellet, cm−1): 3417s, 3051w, 2699w, 1618s, 1535s, 1499s,
1401s, 1322m, 1288s, 1242s, 1159m, 1111m, 863w, 738s.
X-ray crystallography
Single-crystal X-ray diffraction data of HL, 1, 4 and 5 were col-
lected on a Bruker APEX II CCD diffractometer with graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 293 K. The
structures were solved by direct methods and refined by full
matrix least squares based on F2 using the SHELX 97
program.10 All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were placed in calculated positions.
CCDC no. 1030199–1030201 contains the supplementary crys-
tallographic data for this paper.
One-pot synthesis of [CuL1Cl] (1)
A methanol (5 mL) solution of CuCl2·2H2O (0.1 mmol,
0.017 g), 2-(2-aminophenyl)benzimidazole (0.2 mmol, 0.042 g)
and salicylaldehyde (0.2 mmol, 0.020 mL) was sealed in a
Teflon-lined stainless steel autoclave and heated at 80 °C for
3 days, and then cooled to room temperature. Deep red crystals
suitable for X-ray crystallography were obtained (yield 78.3%).
Anal. Calcd for C20H14ClN3OCu (%): C, 58.39; H, 3.43; N,
10.21. Found: C, 58.02; H, 3.62; N, 10.00. IR (KBr pellet, cm−1):
3443w, 3184w, 3067w, 1609s, 1590w, 1531s, 1487m, 1463m,
1442s, 1385m, 1322m, 1184s, 1143m, 760s.
Methods for cell imaging
The HeLa cell line was cultured in DMEM (Dulbecco’s modi-
fied Eagle medium). Cells were incubated with 20 µM of HL at
37 °C for 2 h. After washing with PBS three times to remove
the remaining HL, the cells were then incubated with 7.5 µM
CuCl2·2H2O for 15 min at room temperature. The incubated
cells were washed with PBS and mounted onto a glass slide.
The fluorescent images of the mounted cells were obtained
using a confocal laser scanning microscope with 405 nm
excitation.
Synthesis of [CuL1Cl] (2)
A methanol (3 mL) solution of CuCl2·2H2O (0.1 mmol, 0.017 g)
and HL (0.1 mmol, 0.031 g) was sealed in a Teflon-lined stain-
less steel autoclave and heated at 80 °C for 3 days, and then
cooled to room temperature. Deep red crystals were obtained
in 54.9% yield. Anal. Calcd for C20H14ClN3OCu (%): C, 58.39;
H, 3.43; N, 10.21. Found: C, 58.18; H, 3.47; N, 10.14. IR (KBr
pellet, cm−1): 3445w, 3184w, 3065w, 1609s, 1590w, 1531s,
1489s, 1463s, 1442s, 1386s, 1323m, 1184s, 1143m, 760s.
Calculation methods
In this work, quantum chemical calculations were carried out
using the Gaussian 09 program package.11 The possible
ground state structures have been optimized with density func-
Synthesis of [CuL1Cl] (3)
HL (0.1 mmol, 0.031 g) was dissolved in DMSO (1 mL), and tional theory (DFT) at the B3LYP/6-31G(d) level,12 in which the
then a methanol (3 mL) solution of CuCl2·2H2O (0.1 mmol, effect of the solvent has been considered using the polarized
0.017 g) was added into the solution of HL. Upon slow evapor- continuum model (PCM)13 with the corresponding solvent,
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such as methanol, DMF and DMSO. On the basis of the
optimized configuration for the ground state, TD-DFT14
calculations were performed using the B3LYP functional
(TD-B3LYP-SCRF) within the adiabatic approximation to
predict the excitation energies, which will provide information
on the fluorescence properties of the studied species.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (20971015) and the Fundamental
Research Funds for the Central Universities.
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