Synthesis, characterization and superoxide dismutase activity of bi-copper(II)-bisacetato- μ-phthalicacid[bis(benzyloxy)ethyl]ester

Article abstract of DOI:10.1007/s12039-015-0798-x

A new binuclear copper(II) complex, bridged by the ligand phthalicacid[bis(benzyloxy)ethyl]ester, where each copper(II) is coordinated to one carboxylate (from ligand) and one acetate in square planar mode is reported. The ligand synthesized by the reaction of phthalic anhydride and ethylene glycol, has been characterized by FT-IR, ¹HNMR and LCMS. The binuclear Copper(II) complex has been characterized by UV/visible spectra, FTIR spectra, EPR spectra, ESI-MS spectra, magnetic moment measurement and thermogravimetric analysis. DFT calculation has shown a Z type structure for the complex. Excellent superoxide dismutase activity with IC₅₀ value 8.6 ×10^-6 M for the complex has been observed. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-015-0798-x

J. Chem. Sci. Vol. 127, No. 3, March 2015, pp. 455–459. ꢀc Indian Academy of Sciences.
DOI 10.1007/s12039-015-0798-x
Synthesis, characterization and superoxide dismutase activity
of bi-copper(II)-bisacetato-μ−phthalicacid[bis(benzyloxy)ethyl]ester
a
b
a,∗
BABITA SARMA , PRADIP K BHATTACHARYYA and DIGANTA KUMAR DAS
a
Department of Chemistry, Gauhati University, Guwahati, Assam, India 781 014
Department of Chemistry, Arya Vidyapeeth College, Guwahati, Assam, India 781 016
b
e-mail: digantakdas@gmail.com
MS received 10 February 2014; revised 6 August 2014; accepted 19 August 2014
Abstract. A new binuclear copper(II) complex, bridged by the ligand phthalicacid[bis(benzyloxy)ethyl]ester,
where each copper(II) is coordinated to one carboxylate (from ligand) and one acetate in square planar mode is
reported. The ligand synthesized by the reaction of phthalic anhydride and ethylene glycol, has been character-
1
ized by FT-IR, HNMR and LCMS. The binuclear Copper(II) complex has been characterized by UV/visible
spectra, FTIR spectra, EPR spectra, ESI-MS spectra, magnetic moment measurement and thermogravimet-
ric analysis. DFT calculation has shown a Z type structure for the complex. Excellent superoxide dismutase
activity with IC50 value 8.6×10− M for the complex has been observed.
6
Keywords. phthalic anhydride; ethylene glycol; acetate; copper(II); superoxide; IC50; DFT.
1
. Introduction
these enzymes through oral or intraperitonial routes is
severely restricted due to their rapid degradation and
short life time in biological systems. Small metal
complexes having good superoxide scavenging activity
are potential candidates in this regard.
20
Copper(II) is a biologically important metal ion
involved in a number of enzymes such as – superox-
ide dismutase (SOD), tryosinase, galactose oxidase, B
-
hydroxylases, monoaminooxidase, ascorbic acid oxi-
Copper(II) complexes with Schiff base ligands
derived from various aldehydes and ketones have been
1
–3
dase, plastocyanine, azurine, etc. Complexes of cop-
per in oxidation state +2 are also biologically signifi-
cant because of their antioxidant and free radical scav-
enging activity. Binuclear copper (II) complexes are
potential models for a number of important biological
systems containing couple sites and have been studied
extensively.
tidentate Schiff base ligands have played a vital role
in the development of coordination chemistry.
21
reported to mimic SOD activity. Other examples
in this regard include imidazole bridged copper(II)
4
,5
22
complexes, planar copper(II) complex on addition of
23
a base such as N-methyl imidazole or pyridine, cur-
6
24
cumin complexes of copper(II), etc. There is also a
report that the copper(II) complexes with Schiff base
ligands of salicylaldehyde semicarbazone has SOD
activity which could be tuned by heterocyclic bases,
7
–12
Besides, copper (II) complexes of mul-
1
3–15
The
25
bimetallic copper (II) complexes have also attracted
much attention in magneto chemistry due to the spin-
spin interaction between the copper (II) centres.
pyridine and N-methyl imidazole.
In present day, density functional theory (DFT) has
become an effective tool for determining structure, elec-
tronic properties of molecules, vibrational frequencies,
SOD is an enzyme involved in protecting biological
16
26–29
cells from the toxic effects of superoxides. Based on
the metal ions present in the active sites, SODs have
beendivided into – Cu-Zn-SOD, Mn-SOD and Fe-SOD,
out of which the first one is found in mammals. Defi-
cient level of SOD concentration in human body is
one of the reasons behind diseases and disorders like
diabetes, ischemia, cataract, Parkinson’s disease, can-
atomization energies, ionization energies, etc.
Par-
ticularly when X-ray grade crystals are not obtained,
DFT calculation has been an effective mode of confirm-
ing the structure of metal complexes.
17
In this paper, we report the synthesis of a new ligand
phthalicacid[bis(benzyloxy)ethyl]ester characterized
1
by FTIR, HNMR and mass spectra. This ligand
18,19
cer, etc.
Supplementation of antioxidant enzymes
has been reported to bridge two Copper (II) ions
through its two carboxylates and each Copper (II) is
coordinated to one acetate in square planar fashion.
DFT calculation shows a Z type structure for the
should be a part of the treatment but administration of
∗
For correspondence
455

456
Babita Sarma et al.
+
1
complex. The high superoxide scavenging activity of LCMS: m/e (M ) 357.3, calc. 358.3. HNMR (CDCl ,
3
the complex is also reported.
δ in ppm): 7.72 (2H, t, J = 5.1 Hz); 7.56 (2H, t, J =
5
.7 Hz); 7.44 (4H, d, J = 4.0 Hz); 4.52 (4H, s) (see
Supplementary Information).
2. Experimental
2
.1 Materials and methods
2.3 Synthesis of bi-copper(II)-bisacetato-
μ−phthalicacid[bis(benzyloxy) ethyl]ester
Phthalic anhydride and ethylene glycol were purchased
from Merck and copper(II)acetate monohydrate was
(
(CH COO)Cu(II)LCu(II)(OOCCH )), Cu C H O
3 3 2 22 20 12
purchased from LOBA Chemie. The FTIR spectra Cu(II)acetate monohydrate 1 mmol (0.199 g) was dis-
were recorded in KBr discs on a Perkin Elmer spec- solved in 10 mL methanol. A solution of L, prepared by
1
trum RXI FTIR system. The H NMR spectra were dissolving 1 mmol (0.380 g) into 10 mL of methanol,
recorded in Bruker Ultra shield 300 spectrophotome- was added dropwise with vigorous stirring. The stirring
ter. The electronic spectra in the range of 200–1000 was continued for three hours till dark blue precipitate
nm were obtained in acetonitrile on a UV-1800 SHI- was obtained. The precipitate was washed with diethyl
MADZU spectrophotometer. Thermogravimetric mea- ether and dried in air. The compound was recrystallized
surements were carried out on a PERKIN ELMER 300 from acetonitrile to get blue coloured crystals.
TGA instrument. CHI 600B Electrochemical Analyzer
(
USA) with a three electrode cell assembly was used for
3
. Results and Discussion
electrochemical studies. The electrodes were cleaned as
per reported procedure.30 Electron paramagnetic reso-
nance (EPR) spectra were recorded on a Bruker EMX
spectrometer (centre field 0.4 T, sweep width 0.8 T, res-
olution 1024 points, microwave frequency 9.877×109
Hz, power 0.188 mW). Magnetic susceptibility mea-
surements were performed at ambient temperature by
the Gouy method using a Cambridge magnetic balance
3.1 Electronic and vibrational spectroscopy
of (CH COO)Cu(II)LCu(II)(OOCCH )
3
3
The UV/visible spectra of the complex was recorded
in acetonitrile and a broad band was observed at λmax
7
14 nm (figure 1). The extinction coefficient (ε) was
−1
−1
calculated to be 709.68 L mol cm .
(UK), LC-MS data were recorded in Agilent LCMS
Vibrational spectra for the complex synthesized
6
410 Series (USA).
−1
showed peaks at 2966.5 cm (υ
cm & 705 cm (C-H out of plan vibration for C H );
of C H ); 756
C−H
6 5
−1
−1
6
5
−1
−1
−1
−
1631.7 cm (υ ); 1400 cm (υsymm. COO ); 1589.3
C=O
2
.2 Synthesis and characterization of phthalic acid
−1
−
cm (υasymm. COO ); 3441cm (υ ).
O−H
bis(benzyloxy)ethyl ester (L, C H O )
18
14
8
2
0 mmol (2.96 g) phthalic anhydride was taken in a
3
.2 EPR spectroscopy of (CH COO)Cu(II)LCu(II)
3
mortar and grinded. 10 mmol (0.6 mL) of ethylene gly-
col was added dropwise with constant stirring. The
reaction mixture was heated to 60 C and 2–3 drops of
pyridine was added. The mixture was cooled to obtain
an off-white product which was then recrystallized from
methanol. The synthetic path for the ligand (L) is shown
in scheme 1 below.
(OOCCH3)
◦
The X–band EPR spectra of the complex was recorded
as the polycrystalline samples at room temperature
(
figure 2). The g value and geometric parameter G i.e.,
iso
−
1
FTIR (KBr pellet, cm ): 3404 (υ ), 2920.7
O−H
(
υ
), 1627 (υ ), 1289.4 (υ ), 1391.3 (δ
),
C−H
C=O
C−O
−CH2−
756 and 705 (aromatic C-H out of plane bending).
O
O
O
O
2
O
+
HO
O
OH
Wavelength (nm)
OH
HO
O
O
O
3
Figure 1. The UV/visible spectrum of (CH COO)Cu(II)
−3
LCu(II)(OOCCH3) in acetonitrile. (1×10 M, path length
Scheme 1. Synthetic path for the ligand (L).
1.0 cm)

Synthesis, characterization and SOD activity of copper(II) complex
457
Gauss
Scheme 2. Proposed structure of (CH3COO)Cu(II)LCu(II)
OOCCH3), confirmed by DFT calculation (figure 5).
(
Figure 2. The X–band EPR spectra of (CH3COO)Cu(II)
LCu(II)(OOCCH3) recorded as the polycrystalline samples
at room temperature.
◦
function of temperature showed one step at ca. 210 C
◦
with a shoulder at 310 C. It is well known that acetates
◦
◦
the measurement of exchange interaction between the dissociate in the temperature range 200 C to 400 C.
copper centres was evaluated by using the expression:
31
The weight loss profile has been analysed as reported in
34
literature. The total loss in weight is ca. 73.61%. This
weight loss is justified if we assume that the end product
is two equivalent of CuO. This thermogravimetric anal-
ysis supports the structure of the complex as depicted in
scheme 2.
giso = 1/3(g + 2g )
ꢁ
⊥
(
g − 2.0023)
4K 2ꢀE
ꢁ
ꢁ
k ꢀE
xz
G = (
g − 2.0023)
=
2
⊥
⊥
xy
The calculated value of g tensor parameter was g =
ꢁ
2
.06 and g = 2.03. Hence, g g >2.003 which reveals
−
ꢁ −
32
that d
2
2
is the ground state. The value of G was 3.5 ESI-MS of (CH COO)Cu(II)LCu(II)(OOCCH )
x −y
3
3
calculated to be 2.04 which is less than 4 indicating
effective interaction between the copper centres.
33
The ESI-MS spectra were measured in order to con-
firm the composition and purity of the compound under
investigation. The spectra displayed the molecular ion
peak of complex at m/z 602.48. The calculated value of
molecular mass of complex is 603.48.
3
(
.3 Magnetic moment of (CH COO)Cu(II)LCu(II)
3
OOCCH3)
The magnetic moment value was measured to be 1.65
BM which is a little lower than the single electron value 3.6 Electrochemistry of (CH COO)Cu(II)LCu(II)
3
of 1.74 BM. This low value of magnetic moment may (OOCCH3)
be due to anti-ferromagnetic coupling of the individual
magnetic moments of the copper (II) centres.
Cyclic voltammogram of 1.0 mM solution of the com-
plex in acetonitrile was done on Pt disc electrode. A
very sharp irreversible reduction peak was observed
3
.4 Thermogravimetric studies of (CH COO)Cu(II)
−1
3
at −0.005 V versus Ag-AgCl (Scan rate 0.1 Vs ).
LCu(II)(OOCCH3)
This observation is obvious because in the complex,
the Cu(II) ion is bound to four hard oxygen donor sites
which makes the co-ordination very stable. On reduc-
tion of Cu(II) into Cu(I), which is relatively soft, the
four oxygen donors are no longer suitable and the com-
plex is expected to break down. Hence, the irreversible
reduction peak without any oxidation counterpart was
observed.
Thermogravimetric weight loss curve for the complex
is shown in figure 3. The weight loss profile as a
3.7 DFT optimization of the complex
o
Temperature ( C)
The complex has been optimized using 6-31+G(d)
Figure 3. TGA curve of (CH3COO)Cu(II)LCu(II)(OOC basis set, with Becke three-parameter exchange and
35
CH3).
Lee, Yang and Parr correlation functional, B3LYP; the

458
Babita Sarma et al.
Figure 5. DFT optimized structures of (CH3COO)Cu(II)
LCu(II)(OOCCH3). Pink = Cu(II); Red = O; Gray = C;
Figure 4. Plot of the percentage inhibition of superoxide White = H.
formation against the (CH3COO)Cu(II)LCu(II)(OOCCH3)
concentration.
4
. Conclusion
optimized structure is shown in figure 4. The DFT opti-
mised structure shows that each of the two carboxylates
A new binuclear copper(II) complex, (CH COO)Cu(II)
3
LCu(II)(OOCCH ), where L is phthalic acid bis(benzy-
3
of L binds one Cu2 ion. Each of the Cu ion is bound
to one acetate in a planar mode. The final structure of
the complex resembles the alphabet Z.
+
2+
loxy)ethyl ester, has been synthesized and characterized
by various spectroscopic methods. DFT calculation
showed a Z-type structure for the complex. Good
superoxide scavenging behaviour was observed for the
complex.
3
.8 SOD activity of (CH COO)Cu(II)LCu(II)
3
(OOCCH3)
Supplementary Information
The SOD activity of copper (II) phthalicacid[bis(ben-
zyloxy)ethyl]ester has been studied by the method of
nitrobluetetrazolium (NBT, Structure included in SI)
1
LC-MS and HNMR spectra of the ligand L, FTIR and
LC-LS spectra of (CH COO)Cu(II)LCu(II)(OOCCH ),
3
3
−.
reduction using KO as the source of superoxide
2
structure of NBT (Nitrobluetetrazolium) are available at
www.ias.ac.in/chemsci.
36
radical. The blue colour developed due to the for-
mation of formazon dye was measured immediately
at 560 nm against an appropriate blank. One unit of
SOD activity (IC50 value) was defined as the amount
of test substance required for 50% inhibition of NBT
Acknowledgement
reduction by the superoxide anion.25 A linear relation
We thank UGC, New Delhi and DST, New Delhi for
financial assistance. BS thanks UGC for fellowship
under RFSMS. We thank IIT-Guwahati for ESR and
LC-MS spectra.
was obtained between the concentration of the cop-
per complex and the inhibition of the superoxide ion.
The 100% of superoxide activity corresponds to an
assay performed in the absence of complex. In order
to determine the concentration of the complex required
to yield 50% inhibition of the reaction, we plotted the
percentage of inhibition against the metal concentration
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