Synthesis, characterization of thiosemicarb?zone metal complexes and their antioxidant activity in different in vitro model systems

Article abstract of DOI:10.2298/JSC120325099K

The synthesis of bimetallic Cu(II), Co(II), Ni(II), Zn(II) and U(VI) complexes with general stoichiometry [H₂L M(X₂)(H ₂O)₂] (where H₂L is the di-deprotanated ligand and X is chloride/sulphate) were o

Full text of DOI:10.2298/JSC120325099K

J. Serb. Chem. Soc. 77 (2) 229–240 (2012)
JSCS–4411
UDC 547.496/.497+546.302+
542.913:615.27:543.4
Original scientific paper
Synthesis, characterization of thiosemicarbаzone metal
complexes and their antioxidant activity in different
in vitro model systems
1
1
DESIREDDY HARIKISHORE KUMAR REDDY , SEUNG-MOK LEE *,
2
3
KALLURU SESHAIAH and K. RAMESH BABU
1
Department of Environmental Engineering, Kwandong University, Gangneung, Republic of
2
Korea, Inorganic and Analytical Chemistry Division, Department of Chemistry, Sri
3
Venkateswara University, Tirupati – 517 502, India and Department of Biochemistry,
Sri Venkateswara University, Tirupati – 517 502, India
(
Received 25 March, revised 12 September 2012)
Abstract: The synthesis of bimetallic Cu(II), Co(II), Ni(II), Zn(II) and U(VI)
complexes with general stoichiometry [H L M(X )(H O) ] (where H L is the
2
2
2
2
2
di-deprotanated ligand and X is chloride/sulphate) were obtained with the li-
gand terephthaladehyde bis(thiosemicarbazone) (H L) and are discussed. The
2
ligand and its binuclear complexes were characterized by micro analysis
1
(
CHNS), H-NMR, FT-IR, UV-vis, TG-DTA and conductance measurements.
The thermal behaviour of these complexes showed that the hydrated complexes
loose water molecules of hydration in the first step, followed immediately by
decomposition of the anions and ligand molecules in the subsequent steps. The
molar conductance measurements of the complexes in DMF correspond to the
non-electrolytic nature of the complexes. Furthermore, the antioxidant activity
of the ligand and its complexes were determined in vitro by the hydroxyl
radical scavenging, DPPH, NO and reducing power methods. The obtained
IC50 value of the DPPH activity for complex 2 (IC50 = 0.254 M) was shown to
be the best.
Keywords: thiosemicarbazone; transition metal complexes; spectral analysis;
bimetallic complexes; antioxidant activity
INTRODUCTION
Thiosemicarbazones (TSCs) have become the subject of intense research in-
terest with coordination chemists as they are simple to prepare, have excellent
complexation ability with both transition and non-transition elements and the
complexes have interesting structural characteristics and possible analytical ap-
plications. This interest and wide range of applications resulted in a large number
*
Corresponding author. E-mail: leesm@kwandong.ac.kr
doi: 10.2298/JSC120325099K
2
29
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REDDY et al.
of papers and several reviews on TSCs.1–4 In addition, TSCs have received con-
siderable attention due to their broad profile of pharmacological activity, as they
5
,6
afford a diverse variety of compounds with different activities. The mechanism
of action of TSCs is due to their ability to inhibit DNA biosynthesis, possibly by
blocking the enzyme ribonucleotide diphosphate reductase; binding to the nitro-
gen bases of DNA, hindering or blocking base replication, or creating lesions in
7,8
the DNA strands by oxidative rupture. The remarkable biological activities of
TSCs have provided real impetus to drive developments in their coordination
chemistry, which subsequently showed that the biological activity of TSCs is
related to their metal complexing ability. In some cases, the highest activity of
TSCs is associated with a metal atom, and the biological properties of TSCs are
often related to their metal ion coordination. The lipophilicity, which controls the
rate of entry of TSCs into the cell, is modified by coordination. Additionally, the
metal complexes can be more active than the free ligands, and some of the side
effects associated with free ligands may decrease upon complexation. In addition,
9
the complexes may exhibit bioactivities which are not exerted by free ligands.
Studies related to new developments in metal-based drugs are both promising
1
0,12
and of great interest in the development of therapeutic agents.
Atherosclerosis and its associated complications are currently the major
causes of cardiovascular morbidity and mortality worldwide. Elevated levels of
cholesterol, especially low-density lipoprotein (LDL) and triglycerides, along
with free radical oxidative stress are recognized as the leading causes of ather-
•
osclerosis and coronary heart disease. Hydroxyl radicals (OH ) are generated by
the metal ions present in serum, and changes in their oxidation states result in
oxidative damage of LDL and other lipoproteins in plasma, which is responsible
for the initiation and progression of atherosclerosis in hyperlipidemic subjects.
Free radicals also interact with proteins in other normal metabolic processes,
1
3–17
which can lead to many types of pathologic changes.
To protect biomole-
cules against the attack of free radicals and/or to suppress the resultant damage,
numerous natural and synthetic free radical scavengers and antioxidants have been
1
8,19
developed and studied
Among them, thiosemicarabazones and their metal
2
0,21
complexes have been evaluated for their free radical scavenger activity.
The synthesis and characterization of copper(II), cobalt(II) and nickel(II)
complexes with terephthalaldehyde bis(thiosemicarbazone) was described by
2
2
Minghao et al. In addition, the coordination polymerization (polycoordination)
of terephthalaldehyde bis(thiosemicarbazone) with mercury(II) and cadmium(II)
2
3
complexes was studied by Marcu et al. However, the biological activity of tere-
phthalaldehyde bis(thiosemicarbazone)–metal complexes has not been reported.
Given the potential biological activity of thiosemicarbazone and the involvement
of metal ions in cell metabolism, a systematic study was undertaken to explore
this chemistry, with the development of new biologically active pharmaceuticals
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THIOSEMICARBАZONE METAL COMPLEXES
231
as the final goal. Herein, the preparation and spectroscopic characterization of
five metal complexes derived from terepthaladehyde bis(thiosemicarbazone) are
reported. The ligand and metal complexes were evaluated for their antioxidant
activity. It was envisaged that the thiosemicarbazone could be useful in control-
ling metabolic disorders by scavenging free radicals.
EXPERIMENTAL
Physical measurements
Melting points were determined by the open capillary method and are uncorrected. The
metal content of the complexes was estimated using standard methods. The analysis of
CHNS/O contents of ligand and metal complexes were realized on a Euro elemental analyzer.
The IR spectra were recorded as KBr pellets using a Perkin–Elmer Fourier-Transform Spec-
-
1
trum RX1 spectrophotometer in the region 4500–450 cm . The TG/DTA curves for the
complexes were recorded on a Nietzsche thermobalance (model-STA 40g) with a P V P 10
t
s
t
%
Rh thermocouple under dynamic air conditions between room temperature (≈20 °C) and
-
1
1
020 °C (gradient 10 K min ).
Synthesis of the ligand (1)
The synthesis of terepthaladehyde bis(thiosemicarbazone) (1) was based on the follow-
ing method: an ethanolic solution (50 mL) of terepthaladehyde (0.2 g) and thiosemicarbazide
(
0.270 g) in an ethanol–water mixture (50 mL) were mixed and refluxed for 2 h. After cooling
to room temperature, the formed yellow solid was isolated and dried under vacuum.
Synthesis of metal complexes (2–6)
In a representative preparation, the complexes were synthesized by refluxing DMF–etha-
nol (1:1, 20 mL) solution of ligand (5 mmol) with an ethanolic solution (20 mL) of corres-
ponding metal salt (10 mmol) for 12 h at 70 °C. On cooling overnight, the collared complex
precipitated out. The precipitate was filtered, washed with cold DMF–ethanol and dried under
vacuum. The metal salts used in this study were CuSO ·5H O, CoCl ·6H O, NiCl ·6H O,
4
2
2
2
2
2
ZnSO ·7H O and UO (CH COO) ·2H O.
4
2
2
3
2
2
Antioxidant activity
The scavenging effects of compounds 2–6 on the DPPH radical were evaluated using the
•
24
stable DPPH as the reagent. In the H O scavenging activity experiments, the hydroxyl
2
2
•
25
radical (OH ) in aqueous media was generated through the Fenton Reaction. For deter-
mining the nitric oxide (NO) scavenging activity, the absorbance of the chromophore formed
during diazotization of nitrite with sulphanilamide and subsequent N-naphthylethylenediamine
dihydrochloride was measured at 546 nm.
pounds was determined according to the method of Oyaizu.
2
6,27
The reducing power of the synthesized com-
2
8
RESULTS AND DISCUSSION
Terepthaladehyde was treated with thiosemicarbazide in refluxing methanol
to afford terepthaladehyde bis(thiosemicarbazone) (H L). The synthetic route to
2
1
the ligand is shown in Scheme 1. The synthesized ligand was confirmed by H-
-
NMR spectra recorded in d -dimethylsulphoxide (DMSO-d ) solution using tet-
6 6
2
ramethylsilane (TMS) as an internal standard. The hydrazinic proton (–N H) of
the free ligand appeared as a broad single peak at 11.46 ppm. The amino group
2
9
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REDDY et al.
1
(
–N H ) showed a signal in the region 8.05 ppm. A singlet in the region 7.99–
2
–
8.01 ppm was observed which was assigned to the azomethine proton (–HC=N).
In the region 7.8 ppm, the signals were assigned to chemical shifts of hydrogens
on the symmetric aromatic ring of the ligand. Further the metal complexes were
prepared with the ligand as described in experimental section. All the synthesized
complexes were binuclear with an M:L ratio of 2:1. The molar conductance va-
2
–1
lues in DMF were in the expected range (17–24 S cm mol ) of non-electro-
3
0
lytes, indicating bonding of chloride and sulphate anions to the metal ions. The
complexes were analyzed for carbon, hydrogen, nitrogen, oxygen, sulphur and
metals. The analytical results are given in Table I, while the physical, UV/Vis
and molar conductance data are listed in Table II. The metal complexes were
stable under atmospheric conditions for extended periods, and were easily so-
luble in dimethylsulphoxide (DMSO) and N,N-dimethylformamide (DMF); how-
ever, they were insoluble in most common solvents. The composition and coordi-
nation geometry of these complexes were established based on the following ex-
perimental observations.
Scheme. 1 Synthesis of the ligand H L.
2
TABLE I. Analytical data of the compounds
Elemental analysis, Calcd. (found), %
Cmpd.
Molecular formula
C H N S
FW
C
H
N
S
O
–
M
–
1
280.4 42.84
4.31 29.97 22.87
42.74) (4.28) (29.88) (22.86)
1
0 12 6 2
(
2
3
4
5
6
Cu C H N O S
10 14 6 4 5
537.54 22.34
2.63 15.63 17.90 17.86 23.64
2
(
22.01) (2.34) (15.17) (17.24) (17.25) (23.25)
Co C H Cl N O S 503.16 23.87
2.80 16.70 12.75 6.36 23.43
2
10 14
2 6 2 2
(
23.56) (2.78) (16.64) (12.29) (6.33) (23.33)
Ni C H Cl N O S 499.87 23.89
2.81 14.11 12.76 6.37 23.35
2
10 14
2 6 2 2
(
23.80) (2.20) (14.01) (12.32) (6.34) (23.26)
Zn C H N O S
10 14 6 4 5
541.27 22.19
22.13) (2.36) (15.22) (17.32) (17.43) (24.02)
890.47 13.49 2.04 9.44 7.20 14.37 53.46
13.41) (2.01) (9.47) (7.56) (14.22) (53.54)
2.61 15.53 17.77 17.74 24.17
2
(
U C H N O S
10 18 6 8 2
2
(
FT-IR spectra
The spectra of the free thiosemicarabzone ligand showed peaks of concern at
–
1
3
395–3265 (two peaks), 3192 and 1593 cm , attributed to the symmetric and
asymmetric stretching of NH , ν(NH) and ν(C=N), respectively. Additionally, no
2
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THIOSEMICARBАZONE METAL COMPLEXES
233
–
1
band due to an SH group was observed between 2600 and 2500 cm , which is in
3
1
agreement with the deprotonated thiolate form of the ligand in the complexes.
–
1
The strong absorption bands near 3480 and 3440 cm in the IR spectra of both
the ligand and the complexes were due to N–H stretching vibrations. The intense
band at 1680 may be assigned to C=N stretching vibration in the free ligand. It
showed a positive shift towards higher frequencies in the spectra of the metal
complexes (an additional band was observed near 1700 cm ). The shifting of the
band towards higher frequency region indicates an increase in bond order of the
coordinated C=N group due to back donation of π-electrons by the metals. The
spectrum of the ligand shows bands at 1358 and 1465 cm , which were assigned
to C=S and N–C–N stretching, respectively. These bands were shifted to higher
values in the complexes, indicates coordination of a thiosemicarbazone to the
metal centre. These bands were absent in the spectra of the complexes due to
likely changes of C=S to C–S and N–C–N to N–C=N on complexation. It is evi-
dent that ligand acts as a binucleating chelating agent coordinating through the
thiol sulphur and nitrogen of the (C=N) group of the Schiff base. The complexes
also display bands due to coordinated water molecules. The bands in the ranges
–
1
–
1
–
1
–1
7
49–849 cm and 609–633 cm appeared in the spectra of the complexes,
3
3
which may be assigned to ρr(H O) and ρw(H O).
2
2
TABLE II. Physical, UV/Vis and molar conductance data for the compounds
2
-1
Cmpd.
Yield, %
Colour
M.p., °C
UV/Vis (DMF), λ / nm
Λ / S cm mol
1
2
3
4
5
6
92
66
58
68
65
54
Yellow
Dark blue
Brown
Green
Black
Yellow
153–156
>280
>280
>280
>280
–
–
224, 265, 363, 413
242, 265, 366, 383
265, 366, 383
265, 383, 365
265, 382, 365
19
21
24
21
17
>280
Electronic spectra
With aim to obtain information about the type of the electronic transition and
interaction liable to exist in solutions, the electronic spectra of ligand and their
complexes were measured in DMF solvent. The recorded spectra of ligand dis-
played two main absorption bands. The first band was observed in the 260−265
nm range as a broad and/or a shoulder band. This band could be ascribed to π–π*
transitions of the benzenoid system of the compounds strongly overlapped with
n–π* electronic transitions involving the nonbonding electrons of the azomethine
nitrogen atom. The longer wavelength band(s) in the recorded spectra of the li-
gands observed in the range 316–355 nm can be ascribed to the transition within
the whole molecule, essentially as intramolecular charge transfer (CT) interac-
tions. The CT bands seem to originate from the aryl moiety, whereas the positive
charged azomethine carbon atom was the acceptor centre. This behaviour sug-
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REDDY et al.
gests an instantaneous complex formation in solution from the reaction of the li-
gand with each of the employed metal ions. Bands due to the n–π* transition of
the C=N chromophores occurred between 260−265 nm as the ligand shifts to
3
3
lower energy upon complexation. In the ultraviolet region, the bands observed
in the range 267–299 nm in spectra of metal complexes can be ascribed to an
intraligand electronic transition, because bands in these regions were sensitive
enough to the type of metal ion used.
The longer wavelength band(s) of the free ligand at 363–366 nm acquired a
red shift on complex formation with a metal ion. A new band was observed at
longer wavelengths (in the range of 382–413 nm) in case of the complex solu-
tions. This behaviour can be explained as follows. The longer wavelength band
observed in the spectrum of the free ligands can be assigned to an intramolecular
CT transition liable to take place within the solute molecule. Thus the red shift
observed in the λmax of this band on complex formation with the divalent tran-
sition metal ions Mn(II), Co(II), Cu(II) and Zn(II) can be interpreted based on the
principle of an expected easier CT transition within the complexed Schiff bases
rather than within the free ligand. This is due to the positive charge of the coor-
dinating metal ions. On the other hand, these bands strongly overlap with an
intermolecular transition from the ligand molecule to the vacant orbitals localized
on the coordinated metal ions, i.e., LMCT.
Thermogravimetric analysis
Thermogravimetric (TG) and differential thermal (DTA) analyses were em-
ployed to describe the thermal behaviour of the prepared complexes 2–6. The TG
curve of complex 2 showed three mass loss steps. The first mass loss step occur-
red in the temperature range 160–300 °C, the second one in the temperature range
3
00–620 °C and the third step between 620–770 °C. The DTA curve showed two
exothermic peaks, one at 290 °C and the other at 620 °C. The TG curve of com-
plex 3 showed four mass loss steps. The first step occurred in the temperature
range between 260–300 °C. In this temperature range, one small endo effect was
observed at 280 °C. The second mass loss step occurred in the temperature range
3
3
–
00–580 °C. In this temperature range, two exothermic peaks were observed at
70 and 520 °C. The third mass loss step occurred in the temperature range 580–
750 °C. The fourth decomposition step occurred between 750–880 °C. This
range was accompanied by one small endo effect at 870 °C. The TG and DTA
study for complex 4 presented two regions of decomposition. In the TG study,
the first mass loss step occurred in the temperature range between 260 and 320
°
C. In this temp range (260–320 °C), one endothermic peak at 270 °C was ob-
served. The second mass loss step occurred in the temperature range 320–710 °C.
In this temperature range, two exothermic peaks were observed, one at 360 °C
and the other at 700 °C. The TG and DTA study for complex 5 showed a two-
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THIOSEMICARBАZONE METAL COMPLEXES
235
-
2
step decomposition. The first mass loss step occurred in the temperature range
70–530 °C, while the second decomposition step occurred between 530–650 °C.
In the temperature range of the first stage of mass loss, one small endo and one
small exo effect can be seen on the DTA curve at 280 and 370 °C, respectively.
The second mass loss step was accompanied by two exo effects with maxima at
5
30 and 630 °C, respectively.
The thermal behaviour of these complexes showed that the hydrated com-
plexes lost water molecules of hydration in the first step followed immediately by
decomposition of the anions and ligand molecules in the subsequent steps. The
final decomposition steps of the complexes are attributed to complete decom-
position of the complexes leaving M residues (M = Cu, Co, Ni, Zn and U).
Antioxidant activities of the ligand and complexes
The antioxidant activities of terepthaladehyde bis(thiosemicarabzone) (1)
and its metal complexes 2–6 were evaluated by several in vitro methods in order
to compare the results and to establish some structure–antioxidant–activity rela-
tionships for each method. The evaluation study was performed at various con-
centrations and comparative studies were realised with standard antioxidants.
DPPH radical scavenging activity. The percentage activity of DMF solu-
tions of compounds 1–6 were examined and compared. The activities of the com-
plexes as a function of concentration are shown in Fig. 1. All the complexes 2–5
Fig. 1. Scavenging activity of compounds 1–6 for DPPH.
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REDDY et al.
showed comparable or slightly lower activity than the standard, butylated hyd-
roxytoluene (BHT). The copper complex 2, containing an electron donating
group showed the dominate DPPH scavenging activity. Nickel complex 3 exhi-
bited slightly lower activity than that of compound 2. At low concentrations,
compound 6 showed negligible DPPH activity The IC50 values for all the com-
pounds were calculated.
Reducing power. The reducing power of compounds 2–6 as a function of
their concentration are shown in Fig. 2. The reducing power of the standard BHT
at various concentrations showed a higher absorbance value to those of the newly
synthesized compounds. The reducing power of newly synthesized compound
solutions in DMF increased with increasing concentration. All the analogues 2–6
showed high absorbance values which were comparable or slightly lower than
those of the standards. The presence of the lone pair electron in complex 2 re-
sulted in a higher reducing power. The absorbance values for compound 6 were
very low, showing the low reducing power of this complex, while compounds 2–5
showed higher values indicating their higher reducing power but lower than that
of the standards.
Fig. 2. Reducing power scavenging activity of compounds 1–6.
•
H O scavenging activity. The data of the suppression ratio for OH are
2
2
•
shown in Fig. 3. The inhibitory effect of the compounds tested on OH were con-
centrate dependent and the suppression ratio increased with increasing sample
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THIOSEMICARBАZONE METAL COMPLEXES
237
concentrations in the range tested. The average suppression ratio of the uranium
•
complex (IC50 = 144.09 µM) for OH was the lowest of all the compounds. The
copper(II) complex (IC50 = 66.72 µM) was the most effective among all the
tested complexes. The order of the suppression ratio of the tested compounds for
•
OH was 2 > 4 > 1 > 5 > 3 > 6.
Fig. 3. Scavenging activity of compounds 1–6 for H O .
2
2
Nitric oxide (NO) scavenging activity. Nitric oxide undergoes a facile radi-
•
–
–
cal–radical reaction with O2 to yield ONOO , a reaction that is three times
•–
•–
faster than the SOD-catalyzed dismutation of O . This diversion of O2 through
ONOO oxidation and decomposition pathways would also limit H O accumu-
lation and subsequent reactions of H O by decreasing the amount of O avail-
2
–
2
2
•–
2
2
2
able for spontaneous or SOD-catalyzed dismutation. It was find that the inhibi-
•
tory effects of the compounds tested on NO were concentration dependent and
the suppression ratio increased with increasing sample concentrations in the
range tested (Fig. 4). The average suppression ratio of the uranium complex
•
(
IC50 = 233.64 µM) for NO was the lowest of all the tested compounds. The
copper(II) complex (IC50 = 134.87 µM) was the most effective among all the
•
complexes. The order of the suppression ratio of the tested compounds for NO is
2
> 4 > 1 >5 > 3 > 6.
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REDDY et al.
Fig. 4. Scavenging activity of compounds 1–6 for NO.
CONCLUSIONS
Based on the above results, the structures of metal complexes shown in Fig. 5
are proposed. The antioxidant properties of the ligand and complexes obtained
were evaluated by several methods. Compounds 2–5 had enhanced antioxidant
activities, which were comparable but slightly lower than that of the standard.
The copper complex 2 revealed high DPPH scavenging, reducing power, H O
2
2
inhibition and nitrous oxide inhibition values. As a result, this study provides evi-
dence that the chelation of different copper complexes with terepthaladehyde bis-
(
thiosemicarbazone) had significant influence on the antioxidant activities in dif-
ferent in vitro model systems.
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THIOSEMICARBАZONE METAL COMPLEXES
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Fig. 5. The proposed structure of metal complexes with H L ligand.
2
И З В О Д
СИНТЕЗА, КАРАКТЕРИЗАЦИЈА КОМПЛЕКСА МЕТАЛА СА
ТИОСЕМИКАРБАЗОНСКИМ ЛИГАНДИМА И ЊИХОВА АНТИОКСИДАТИВНА
АКТИВНОСТ У РАЗЛИЧИТИМ IN VITRO УСЛОВИМА
1
1
2
3
DESIREDDY HARIKISHORE KUMAR REDDY , SEUNG-MOK LEE , KALLURU SESHAIAH и K. RAMESH BABU
1
2
Department of Environmental Engineering, Kwandong University, Gangneung, Republic of Korea, In-or-
ganic and analytical Chemistry Division, Department of Chemistry, Sri Venkateswara University, Tirupati –
5
3
17 502, India и Department of Biochemistry, Sri Venkateswara University, Tirupati – 517 502, India
Полазећи од терефталалдехидbis(тиосемикарбазона) синтетисани су динуклеарни
Cu(II), Co(II), Ni(II), Zn(II) и U(VI) комплекси опште формуле [H LM(X )(H O) ] (где је
2
2
2
2
H L двоструко депротоновани лиганд и X је хлорид/сулфат). Лиганд (H L) и одговара-
2
2
јући комплекси су окарактерисани, поред термалне анализе и методе мерења проводљи-
1
вости, применом H-NMR, FT-IR и UV–Vis спектроскопских метода. Термална анализа
ових комплекса је показала да, у првој фази, хидратисани комплекси губе молекуле
воде, док у наредној фази долази до разлагања хлоридног и сулфатног анјона, као и мо-
лекула лиганда. На основу мерења моларне проводљивости у DMF растварачу закљу-
чено је да су испитивани комплекси неелектолити. Поред тога, одређена је in vitro анти-
оксидативна активност лиганда и одговарајућих комплекса.
(
Примљено 30. априла, ревидирано 3. јула 2012)
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