Synthesis and antibacterial activities of copper(II) with [(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid

Article abstract of DOI:10.1080/00958972.2010.514338

A new tridentate ligand, [(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid (HDBA), has been synthesized from 3,5-diiodosalicylaldehyde and glycine in ethanol. A 1-D coordination polymer has been synthesized by reaction of HDBA with Cu(Ac)₂ · H₂O in ethanol-water. The complex was characterized by UV, IR, ESI-MS, elemental analyses, and X-ray crystallography. The central copper(II) is five-coordinate by one nitrogen and two oxygens from HDBA, one oxygen from water, and one oxygen from another HDBA. The complex was assayed for antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter cloacae) activities by the 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyl tetrazolium bromide method. Complex 1 showed favorable antimicrobial activity with minimum inhibitory concentrations of 6.25, 6.25, 3.125, 6.25, 6.25, and 3.125 μg mL^-1 against B. subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae, respectively.

Full text of DOI:10.1080/00958972.2010.514338

Journal of Coordination Chemistry
Vol. 63, No. 19, 10 October 2010, 3463–3470
Synthesis and antibacterial activities of copper(II) with
[
(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid
SUO-PING XUyz, LEI SHIz, YUAN PEIy, YING YANGz, GUO XUy and
HAI-LIANG ZHU*yz
ySchool of Chemistry and Chemical Engineering, Xuzhou Normal University,
Xuzhou 221116, China
zSchool of Life Sciences, Nanjing University, Nanjing 210093, China
(
Received 1 May 2010; in final form 30 June 2010)
A new tridentate ligand, [(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid (HDBA), has
been synthesized from 3,5-diiodosalicylaldehyde and glycine in ethanol. A 1-D coordination
polymer has been synthesized by reaction of HDBA with Cu(Ac)
2
ꢀ H
2
O in ethanol–water. The
complex was characterized by UV, IR, ESI–MS, elemental analyses, and X-ray crystallography.
The central copper(II) is five-coordinate by one nitrogen and two oxygens from HDBA, one
oxygen from water, and one oxygen from another HDBA. The complex was assayed for
antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas
aeruginosa, Escherichia coli, and Enterobacter cloacae) activities by the 3-(4,5-dimethylthiazol-
2-yl)-2,5-diphenyl tetrazolium bromide method. Complex 1 showed favorable antimicrobial
activity with minimum inhibitory concentrations of 6.25, 6.25, 3.125, 6.25, 6.25, and
ꢁ1
3
.125 mg mL against B. subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae,
respectively.
Keywords: 3,5-Diiodosalicylaldehyde; Glycine; Copper(II) complex; Structure; Antibacterial
1. Introduction
Salicylaldehyde Schiff bases and their metal complexes have a wide range of
antibacterial activities [1–10]. There is much interest shown by researchers in the
synthesis, characterization, and structure–activity relationships (SAR) of Schiff bases
[
11–15]. Salicylaldehyde derivatives, with one or more halogens in the aromatic ring,
showed antibacterial and antifungal activities [16]. Recently, Chohan et al. [17] reported
that some metal complexes of amino acid derived Schiff bases showed favorable
antibacterial activities. In this article, a new complex of 3,5-diiodosalicylaldehyde with
glycine and copper(II) ions has been synthesized. This copper(II) complex was assayed
for antibacterial activities against three Gram-positive bacterial strains (Bacillus subtilis,
Staphylococcus aureus, and Streptococcus faecalis) and three Gram-negative
bacterial strains (Escherichia coli, Pseudomonas aeruginosa, and Enterobacter cloacae)
*
Corresponding author. Email: zhuhl@nju.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.514338

3
464
S.-P. Xu et al.
by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl trtrazolium bromide (MTT) method.
This study may be useful to gain in-depth understanding of the antimicrobial activity of
metal(II) complexes with 3,5-diiodosalicylalidene Schiff bases.
2
2
. Experimental
.1. Physical measurement
The 3,5-diiodosalicylalidene was synthesized from salicylaldehyde, KI, and KIO [18].
3
The other chemicals (reagent grade) used were commercially available. UV spectra were
recorded on a U-3000 Spectrophotometer. IR spectra were recorded on a Nexus 870
FT-IR. ESI–MS spectra were recorded on a Mariner System 5304 Mass spectrometer.
Elemental analyses were performed on a CHN-O-Rapid instrument and the results were
within ꢂ0.4% of theoretical values. Melting points were measured on a Boetius
micromelting point apparatus.
2
.2. Synthesis of [(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid
Equimolar quantities (4 mmol) of 3,5-diiodo-salicylaldehyde and glycine were dissolved
in ethanol (10 mL) and stirred at room temperature for 2 h to give yellow Schiff base
(
[(2-hydroxy-3,5-diiodo-benzylidene)-amino]-acetic acid, HDBA). The precipitates were
separated by filtration, washed with ethanol three times, and dried in a vacuum
desiccator containing anhydrous CaCl2.
ꢃ
HDBA is a yellow thin prism crystal, yield 90%, m.p.: 268 C. UV (ꢀ nm): 385.0;
ꢁ1
2
1
6
56.0. Selected IR data (cm , KBr): 3355.2(m); 1629.7(s); 1605.1(s); 1480.4(s);
423.7(s); 1393.5(s); 1310.4(m); 1278.0(m); 1215.0(s); 1134.8(s); 863.8(m); 759.9(m);
þ
þ
56.6(m). ESI–MS: 431.96 (C H I NO , [M þ H] ). Anal. Calcd for C H I NO :
9
8 2
3
9
7 2
3
C, 25.08%; H, 1.64%; N, 3.25%. Found: C, 25.13%; H, 1.60%; N, 3.27%.
2
.3. Synthesis of 1
Equimolar quantities (2 mmol) of HDBA and Cu(Ac) ꢀ H O were dissolved in ethanol
2
2
(10 mL) and water (5 mL). The mixture was stirred for 3 h at room temperature and
then filtered. Upon keeping the filtrate in air for 5 days, green prism crystals of Cu(II)
complex, suitable for X-ray crystal determination, formed at the bottom of vessel on
slow evaporation of the solvent. The crystals were isolated, washed three times with
ethanol, and dried in a vacuum desiccator containing anhydrous CaCl .
2
ꢃ
Complex 1 is a green prism crystal, yield 80%, m.p.: 4290 C. UV (ꢀ nm):
76.5; 255.0. Selected IR data (cm , KBr): 3370.8(m); 1645.2(s); 1585.1(s); 1490.3(s);
ꢁ
1
3
1
6
439.7(s); 1385.3(m); 1369.6(s); 1294.9(m); 1146.0(s); 998.4(m); 869.6(m); 752.1(m);
þ
þ
74.8(m). ESI–MS: 511.49 (C H I NO Cu , [M þ H] ). Anal. Calcd for
9
8 2
4
C H I NO Cu: C, 21.16%; H, 1.37%; N, 2.74%. Found: C, 21.10%; H, 1.39%;
9
7 2
4
N, 2.71%.

Copper(II) salicylaldehyde
3465
2.4. X-ray crystallography
The crystal structure of 1 was determined using a SMART 1000 CCD diffractometer.
3
A single crystal of 1 with dimensions 0.30 ꢄ 0.18 ꢄ 0.10 mm was chosen for X-ray
diffraction study. The data were collected with graphite-monochromated Mo-Kꢁ
˚
radiation (ꢀ ¼ 071073 A) using !–2ꢂ scan technique. A total of 10,299 reflections were
collected and 2129 were independent (R ¼ 0.0735), of which 1749 were observed
int
reflections with I 4 2ꢃ(I). The structure was solved using direct methods and refined by
full-matrix least-squares techniques. All non-hydrogen atoms were assigned anisotropic
displacement parameters in the refinement. All hydrogens were added at calculated
2
positions and refined using a riding model. The structures were refined on F using
SHELXTL-97. The crystal used for the diffraction study showed no decomposition
during data collection. Crystal data and refinement data are listed in table 1. Selected
bond lengths and angles are given in table 2.
2
.5. Antibacterial activity
Antibacterial activity of the synthesized complex was tested against B. subtilis,
S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae using an MTT medium. The
minimum inhibitory concentrations (MICs) were determined by a colorimetric method
ꢁ
1
using the MTT dye [19]. A stock solution of the synthesized complex (50 mg mL ) in
DMSO was prepared and graded quantities of the test complex were incorporated in a
specified quantity of sterilized liquid medium. A specified quantity of the medium
Table 1. Crystallographic and experimental data for 1.
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
9 7 2 4
C H I NO Cu
510.50
298(2)
Orthorhombic
Pbca
˚
ꢃ
)
Unit cell dimensions (A,
a
b
c
ꢁ
ꢄ
ꢅ
7.1487(12)
7.1487(12)
22.760(2)
90
90
90
2446.9(6), 8
2.772
6.832
3
˚
Volume (A ), Z
Calculated density (g cm
ꢆ (mm
F(0 0 0)
ꢂ range for data collection ( )
Maximum and minimum transmission
Data/restraints/parameters
Index ranges (h, k, l )
ꢁ
3
)
ꢁ
1
)
1880
ꢃ
1.79–25.01
0.5482 and 0.2337
2129/0/158
ꢁ8 ꢅ h ꢅ 8;
ꢁ
17 ꢅ k ꢅ 10;
27 ꢅ l ꢅ 27
ꢁ
Reflections collected/unique
R
Final R indices [I 4 2ꢃ(I )]
10,299/2129
0.0735
int
a
b
R ¼ 0.0764, wR ¼ 0.1849
ꢁ
3
˚
(
Dꢇ)max, (Dꢇ)min (e A
)
5.815 and ꢁ1.432
P
P
a
R ¼ ||F
o
|ꢁ|F
c
|/ |F
2
o
|.
P
P
b
2
o
2
2
2 1/2
wR ¼ [ [w(F ꢁ F ) ]/ [w(F ) ]]
.
c
o

3
466
S.-P. Xu et al.
˚
Table 2. Selected bond lengths (A) and angles ( ) of 1.
ꢃ
Bond
Distance
Bond
Distance
Bond
Distance
Cu(1)–N(1)
Cu(1)–O(4)
I(2)–C(8)
O(1)–C(1)
O(3)–C(5)
1.926(11)
1.982(9)
2.092(14)
1.251(17)
1.303(17)
Cu(1)–O(3)#1
Cu(1)–O(2)
N(1)–C(3)
1.928(9)
Cu(1)–O(1)
I(1)–C(6)
N(1)–C(2)
O(2)–Cu(1)
1.973(10)
2.102(15)
1.482(16)
2.288(11)
2.288(11)
1.233(18)
1.248(16)
#
2
O(2)–C(1)
ꢃ
ꢃ
ꢃ
Angle
( )
Angle
( )
83.3(4)
92.1(4)
Angle
( )
168.8(5)
88.7(4)
N(1)–Cu(1)–O(3)
N(1)–Cu(1)–O(4)
N(1)–Cu(1)–O(2)
O(3)–Cu(1)–O(2)
O(1)–Cu(1)–O(2)
O(4)–Cu(1)–O(2)
93.1(4)
164.5(5)
103.8(4)
90.1(4)
101.1(5)
90.7(4)
127.3(10)
N(1)–Cu(1)–O(1)
O(3)–Cu(1)–O(4)
C(3)–N(1)–C(2)
C(2)–N(1)–Cu(1)
C(5)–O(3)–Cu(1)
O(2)–C(1)–C(2)
N(1)–C(2)–C(1)
O(3)–Cu(1)–O(1)
O(1)–Cu(1)–O(4)
C(3)–N(1)–Cu(1)
C(1)–O(1)–Cu(1)
O(2)–C(1)–O(1)
O(1)–C(1)–C(2)
N(1)–C(3)–C(4)
#
1
1
1
1
121.1(12)
111.2(9)
123.1(8)
117.7(12)
108.4(11)
126.8(9)
116.0(10)
125.8(15)
116.3(12)
125.5(12)
#
#
#
#
2
C(1)–O(2)–Cu(1)
#
1
#2
Symmetry transformation: x ꢁ 1/2, ꢁy þ 3/2, ꢁz; x þ 1/2, ꢁy þ 3/2, ꢁz.
Table 3. MICs of 1.
ꢁ1
Microorganisms MICs (mg mL
)
Gram-positive
Gram-negative
Compound
B. subtilis
S. aureus
S. faecalis
P. aeruginosa
E. coli
E. cloacae
1
HDBA
Cu(Ac)
Penicillin
6.25
6.25
12.5
1.562
0.39
6.25
12.5
25
1.562
1.562
3.125
6.25
25
1.562
3.125
6.25
12.5
12.5
6.25
3.125
6.25
12.5
25
6.25
3.125
3.125
6.25
25
3.125
1.562
2
ꢀ H
2
O
Kanamycin
containing the complex was poured into microtitration plates. Suspension of the
ꢁ1
5
microorganism was prepared to contain approximately 10 cfu mL and applied to
microtitration plates with serially diluted complex in DMSO to be tested and incubated
ꢃ
at 37 C for 24 h. After the MICs were visually determined on each of the microtitration
plates, 50 mL of phosphate buffered saline (PBS 0.01 mol L
ꢁ1
,
pH 7.4:
Na HPO ꢀ 12H O 2.9 g, KH PO 0.2 g, NaCl 8.0 g, KCl 0.2 g, distilled water
2
4
2
2
ꢁ
4
1
000 mL) containing 2 mg mL of MTT was added to each well. Incubation was
1
continued at room temperature for 4–5 h. The content of each well was removed and
ꢁ
1
100 mL of isopropanol containing 5% 1 mol L HCl was added to extract the dye.
After 12 h of incubation at room temperature, the optical density (OD) was measured
with a microplate reader at 570 nm. The observed MICs are given in table 3.
3
. Results and discussion
The HDBA was synthesized with 3,5-diiodosalicylaldehyde and glycine. The reaction of
the Schiff base with Cu(Ac) ꢀ H O in ethanol–water led to the formation of a new 1-D
2
2

Copper(II) salicylaldehyde
3467
I
I
O
O
Ethanol-water
N
+
NH CH COOH
2
2
OH
OH
OH
I
I
I
O
N
I
O
CH CH OH/H O
N
OH
3
2
2
+
Cu(Ac)2
OH
O
Cu
O
O
I
I
H
H
Scheme 1. Synthesis of 1.
coordination polymer (scheme 1). The complex gave satisfactory results for chemical
analyses (ꢂ0.4%) and UV, IR, and ESI–MS spectra were consistent with the assigned
structure.
Complex 1 (C H I NO Cu) was prepared from HDBA and Cu(Ac) ꢀ H O in
9
7 2
4
2
2
ethanol–water, as described in section 2. Infrared spectra of the complex (KBr pellets)
. This
band shifts by 15 cm to higher wavenumbers compared to 1630 cm , which is
ꢁ
1
display an intense absorption band at 1645 cm attributable to the ꢈ(
C¼N)imine
ꢁ1
ꢁ1
ꢁ
1
attributable to ꢈ(
This band is shifted 20 cm to lower wavenumbers compared to 1585 cm , which is
of HDBA. The 1605 cm is attributable to ꢈ
.
C¼N)imine
(C¼O)carbonyl
ꢁ1
ꢁ1
ꢁ
1
of HDBA. The absorption at 3355 cm attributed to
attributable to ꢈ(
C¼O)carbonyl
of the ligand disappeared in 1. The absorption at 3371 cm is attributed
ꢁ1
ꢈ(
to ꢈ(–OH)water of 1. UV spectra of the complex display an intense absorption at 255 nm
ꢁOH)carbonyl
(
ꢉ ! ꢉ*) and 376 nm (n ! ꢉ*).
The molecular structure of 1 crystallizes in orthorhombic with space group Pbca.
A perspective view of the crystal structure and packing diagram is shown in figure 1.
The Cu(II) adopts a distorted pyramidal geometry coordinated by one nitrogen and two
oxygens from HDBA, and one water and one oxygen from another HDBA. The Cu(1)–
N(1), Cu(1)–O(3), Cu(1)–O(1), Cu(1)–O(4), and Cu(1)–O(2A) bond lengths are
˚
1
.926(1), 1.928(9), 1.973(1), 1.982(9), and 2.288(1) A, respectively. The dihedral angle
ꢃ
between phenyl ring plane A (C4–C9) and plane B (N1/Cu1/O3/C5/C4/C3) is 8.3 . The
dihedral angle between B (N1/Cu1/O3/C5/C4/C3) and C (N1/C2/C1/O1/Cu1) planes is
1
ꢃ
ꢃ
6.3 . Some important torsion angles of 1 are: O(1)–C(1)–C(2)–N(1) ¼ 18 , O(2)–C(1)–
ꢃ
ꢃ
C(2)–N(1) ¼ ꢁ157.0 ,
O(3)–Cu(1)–N(1)–C(3) ¼ 18.2 ,
O(1)–Cu(1)–N(1)–C(3) ¼
ꢃ
ꢃ
ꢃ
ꢁ
151.1 , O(3)–Cu(1)–O(1)–C(1) ¼ ꢁ80 , and O(4)–Cu(1)–O(1)–C(1) ¼ ꢁ174.9 . The
ꢃ
bond angles of trans O(3)–Cu(1)–O(1) and N(1)–Cu(1)–O(4) are 168.8(5) and 164.5(5) ,
respectively, while bond angles of cis N(1)–Cu(1)–O(3), O(3)–Cu(1)–O(2A), O(1)–
ꢃ
Cu(1)–O(2A), and O(4)–Cu(1)–O(2A) are in the range 90.1(4)–101.1(5) . A 1-D chain
structure is formed by the Cu–O coordination bond (figure 2). These chains are stacked
to furnish a 3-D supramolecular network (figure 3). There are three intramolecular
hydrogen bonds in 1 (table 4).
The complex was screened for antibacterial activity against three Gram-positive
bacterial strains (B. subtilis, S. aureus, and S. faecalis) and three Gram-negative
bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by the MTT method. The MICs

3
468
S.-P. Xu et al.
Figure 1. Crystal structure of 1 showing 30% probability displacement ellipsoids (arbitrary spheres for
hydrogens).
Figure 2. The 1-D chain structure of 1.
of the complex against the bacteria are shown in table 3. Also included was the activity
of reference compounds, penicillin (North China Pharmaceutical Co. Ltd, D0211107,
Hebei 050015, China) and kanamycin (Nanjing Zhuyan Biotechnology Co. Ltd,
Amresco 060D0504, Nanjing 210002, China). Compared with other copper complexes

Copper(II) salicylaldehyde
3469
Figure 3. The packing structure of 1 along the a-axis.
˚
Table 4. Hydrogen bonds for 1 [(A) and ( )].
ꢃ
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
d(D ꢀ ꢀ ꢀ A)
ff(DHA)
O(4)–H(4C) ꢀ ꢀ ꢀ O(2)
O(4)–H(4D) ꢀ ꢀ ꢀ O(3)
C(2)–H(2B) ꢀ ꢀ ꢀ O(1)
0.85
0.85
0.97
1.87
2.12
2.52
2.64(3)
2.88(7)
3.19(6)
150
150
126
recently reported [20–23], 1 showed higher activity against S. faecalis and E. cloacae
ꢁ
1
(
(
MICs: 3.125 mg mL ) than against B. subtilis, S. aureus, P. aeruginosa, and E. coli
ꢁ
1
MICs: 6.25 mg mL ). HDBA showed high antimicrobial activity against B. subtilis,
S. faecalis, P. aeruginosa, E. coli, and E. cloacae (MICs: 6.25–12.5 mg mL ).
ꢁ
1

3
470
S.-P. Xu et al.
Supplementary material
Crystallographic data for 1 have been deposited with the Cambridge Crystallographic
Data Centre (CCDC 779843).
Acknowledgments
This study was co-financed by grants (Projects 30772627) from National Natural
Science Foundation of China and (Projects 09KJD150005) from Province Natural
Science Foundation of Jiang Su.
References
[1] S.-P. Xu, L. Shi, P.-C. Lv, R.-Q. Fang, H.-L. Zhu. J. Coord. Chem., 62, 2048 (2009).
[2] S.-P. Xu, P.-C. Lv, L. Shi, X.-L. Li, H.-L. Zhu. J. Coord. Chem., 62, 3198 (2009).
[3] L. Shi, H.-M. Ge, S.-H. Tan, H.-Q. Li, Y.-C. Song, H.-L. Zhu, R.-X. Tan. Eur. J. Med. Chem.,
42, 558 (2007).
[
[
4] A. Roth, E.T. Spielberg, W. Plass. Inorg. Chem., 46, 4362 (2007).
5] L.-M. Wu, H.-B. Teng, X.-C. Feng, X.-B. Ke, Q.-F. Zhu, J.-T. Su, W.-J. Xu, X.-M. Hu. Cryst. Growth
Des., 7, 1337 (2007).
[6] J.D. Ranford, J.J. Vittal, Y.M. Wang. Inorg. Chem., 37, 1226 (1998).
[7] S.-P. Xu, P.-C. Lv, R.-Q. Fang, L. Shi, H.-L. Zhu. J. Chem. Cryst., 39, 931 (2009).
[8] M. Chauhan, K. Banerjee, F. Arjmand. Inorg. Chem., 46, 3072 (2007).
[9] C.T. Yang, B. Moubaraki, K.S. Murray, J.J. Vittal. Dalton Trans., 880 (2003).
[10] O. Yamauchi, A. Odani, M. Takani. J. Chem. Soc., Dalton Trans., 18, 3411 (2002).
[11] E.F. Elslager, J. Battaglia, A.A. Phillips, L.M. Werbel. J. Med. Chem., 13, 587 (1970).
[12] S. Ren, R. Wang, K. Komatsu, P.B. Krause, Y. Zyrianov, C.E. McKenna, C. Csipke, Z.A. Tokes,
E.J. Lien. J. Med. Chem., 45, 410 (2002).
[
13] P. Prusis, M. Dambrova, V. Andrianov, E. Rozhkov, V. Semenikhina, I. Piskunova, E. Ongwae,
T. Lundstedt, I. Kalvinsh, J.E.S. Wikberg. J. Med. Chem., 47, 3105 (2004).
14] S. Ren, R. Wang, K. Komatsu, P.B. Krause, Y. Zyrianov, C.E. McKenna, C. Csipke, Z.A. Tokes,
E.J. Lien. J. Med. Chem., 45, 410 (2002).
[
[
[
[
[
[
[
[
[
15] P.H. Wang, J.G. Keck, E.J. Lien, M.M.C. Lai. J. Med. Chem., 33, 608 (1990).
16] L.C. Felton, J.H. Brewer. Science, 105, 409 (1947).
17] Z.H. Chohan, M. Arif, M. Sarfraz. Appl. Organomet. Chem., 21, 294 (2007).
18] S.-P. Xu, G.-Z. Zhu, R.-Q. Fang, X.-L. Li, H.-L. Zhu. Chin. J. Struct. Chem., 28, 87 (2009).
19] E.M. Kosower, T. Miyadera. J. Med. Chem., 15, 307 (1972).
20] N. Nishat, M. Zulfequar, S.H. Asma. J. Coord. Chem., 63, 1273 (2010).
21] N.E.A. El-Gamel. J. Coord. Chem., 63, 534 (2010).
22] M. Rajasekar, S. Sreedaran, R. Prabu, V. Narayanan, R. Jegadeesh, N. Raaman, A. Kalilur. J. Coord.
Chem., 63, 136 (2010).
[
23] S. Budagumpi, U.N. Shetti, N.V. Kulkarni, V.K. Revankar. J. Coord. Chem., 62, 3961 (2009).

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