Synthesis, characterization and biological evaluation of some novel hydrazide Schiff's bases and their metal complexes

Article abstract of DOI:10.14233/ajchem.2013.13619

N'-(4-Hydroxy-3-methoxyphenyl)methylidene]formic hydrazide (L-1), N'-[-(4-hydroxy-3-methoxyphenyl)methylidene]-3'-hydroxynaphthalene-2'- carbohydrazide (L-2) N'-[-(5-methylfuran-2-yl)methylidene]-3'- hydroxynaphthalene-2'-carbohydrazide (L-3), N'-[-1''-(4

Full text of DOI:10.14233/ajchem.2013.13619

Asian Journal of Chemistry; Vol. 25, No. 5 (2013), 2668-2672
http://dx.doi.org/10.14233/ajchem.2013.13619
Synthesis, Characterization and Biological Evaluation of Some Novel
Hydrazide Schiff’s Bases and Their Metal Complexes
*
MAZHAR HUSSAIN, ZAHID SHAFIQ , MIAN HASNAIN NAWAZ, MUHAMMAD ASLAM SHAD,
HAQ NAWAZ, MUHAMMAD YAQUB and HAFIZ BADARUDDIN AHMAD
Department of Chemistry, Bahauddin Zakariya University, Multan, Pakistan
*Corresponding author: Fax: +92 61 9210138; Tel: +92 61 9210085; E-mail: z_shafiq@yahoo.com
(Received: 18 February 2012; Accepted: 19 November 2012)
AJC-12425
N'-(4-Hydroxy-3-methoxyphenyl)methylidene]formic hydrazide (L-1), N'-[-(4-hydroxy-3-methoxyphenyl)methylidene]-3'-
hydroxynaphthalene-2'-carbohydrazide (L-2) N'-[-(5-methylfuran-2-yl)methylidene]-3'-hydroxynaphthalene-2'-carbohydrazide (L-3), N'-
[-1''-(4-fluorophenyl)ethylidene]-3'-hydroxynaphthalene-2'-carbohydrazide (L-4) and N'-[(-1'-(4-chlorophenyl)ethylidene]formic hydrazide
(L-5) were synthesized and tested for their antioxidant activity. All these newly synthesized Schiff’s bases were treated with Cu(II), Co(II)
and Zn(II) chlorides to form their respective complexes. Antioxidant activity of the synthesized ligands (L-1, L-2, L-3, L-4 and L-5), their
corresponding metal(II) complexes, salts of the metal used in the complex formation and Trolox (as standard antioxidant) was measured
in terms of their ability to scavenge the DPPH free radical. Ligand (L-4) was found to be the best antioxidant among all the ligands. As
regards the activity of metal(II) complexes, Zn-L-4 exhibited the best antioxidant activity.
Key Words: Hydrazones, Hydrazides, Schiff’s bases, Antioxidant activity.
in term of antioxidant and cytoprotective effects was found to
be the symmetrical compound bearing two hydrazine scaffolds
while all other ones were much less potent.
INTRODUCTION
Oxidative stress is a well-known mechanism that is
responsible for the development of vascular damage. Different
pathogenic stimuli involved in cardiovascular diseases, such
as activated macrophages, hyperglycaemia, oxidized low-
density lipoprotein (LDL), exert their harmful effects, at least
partially, through an increased local generation of reactive
oxygen species. Reactive oxygen species (ROS) are normally
produced throughout oxygen metabolism and play a major
role in physiological and pathological cell redox signaling1.
Besides the direct free radical attack of cellular components,
oxidative stress induces a lipid peroxidation of cellular
membranes resulting in the generation of reactive carbonyl
compounds (RCC) that react rapidly with free amino groups
and thiol residues on proteins thereby forming adducts involved
in the carbonyl stress2,3. Both oxidative and carbonyl stress
alter protein function and trigger the accumulation of modified
proteins, which results in inflammation and apoptosis3,4.Anti-
oxidants inhibit the generation of ROS and the subsequent
formation of lipid peroxidation products, thereby preventing
both oxidative and carbonyl stress. Most antioxidants prevent
LDL oxidation in cell-dependent and cell-free systems, and
delay the formation of atherosclerotic lesions in animal models
for atherosclerosis such as apoE-/-mice5. The best compounds
Hydrazones have been found with wide applications in
synthetic chemistry6, to be used as indicators. Hydrazones are
now being used extensively in detection and quantitative
determination of several metals, for the preparation of compounds
having diverse structures, analytical chemistry for the identi-
fication and isolation of carbonyl compounds7,8. However, the
most valuable property of hydrazones is, perhaps, their great
physiological activity. The hydrazones have also been used
for different purposes such as herbicides, insecticides,
nematocides, redenticides and plant growth regulators9. The
hydrazones are also important for their use as plasticizers and
stabilizers for polymers10,11, polymerization initiators and
antioxidants12.A polyphenol antioxidant is a type of antioxidant
containing a polyphenolic substructure. Numbering over 4,000
distinct species, these compounds have antioxidant activity in
vitro but are unlikely to have antioxidant roles in vivo13. Rather,
they may affect cell-to-cell signalling, receptor sensitivity,
inflammatory enzyme activity or gene regulation14.
In order to get insight on the efficiency of the hydrazone
functionality, we report here the synthesis of some hydrazones.
Keeping in view the promising use of potentially metal-based
antimicrobial, antioxidant and antiinflammatory properties,

Vol. 25, No. 5 (2013)
Synthesis of Some Novel Hydrazide Schiff’s Bases and Their Metal Complexes 2669
some metal-based [(Cu(II), Co(II) and Zn(II)] compounds
incorporated with some novel formichydrazides and naphtha-
lene-2-carbohydrazides (L-1-L-5) Schiff’s bases are reported.
(>C=O), 1595 (-HC=N-), 1520 (-OCH3), UV (DMSO) λmax
(nm) 227; non-electrolyte; 1H NMR (DMSO) δ: 3.91 ( s, 3H,
-OCH3), 7.00 (d, J = 8 Hz, 1H, C2-H), 6.83 (d, J = 8 Hz, 1H,
C5-H), 7.26 ( m, 4H, C6,1′,4′,7′-H), 7.42 ( m, 1H, C6′-H), 7.61 (d,
J = 7.6 Hz, 2H, C5',8'-H), 7.75 ( s, 1H, CHN), 8.14 ( s, 1H,
C3'-OH), 8.39 ( s, 1H, NH) ppm. EIMS (m/z) = 336 (M+), 171,
165, 143, 117.
Synthesis of 3'-hydroxy-N'-[(E)-(5-methylfuran-2-yl)-
methylidene]naphthalene-2'-carbohydrazide (L-3): To a hot
stirred solution of 3-hydroxy-2-naphthoic hydrazide (1.5 g,
0.0074 mol) in mixture of ethanol (35 mL) and 1,2-dioxane
(2 mL), 5-methyl furfural (0.736 mL, 0.0074 mol) was added.
The reaction mixture was heated under reflux for 2 h. The
product was purified according to the previous procedure.Yield
87 %, yellow powder; m.p. 206 ºC; IR (KBr, νmax, cm-1): 3230
(OH), 3055 (NH), 1647 (>C=O), 1575 (>C=N-), UV (DMSO)
λmax (nm) 348; non*electrolyte; 1H NMR (DMSO) δ: 7.74 (d,
J = 7.6 Hz, 1H, C4-H), 7.67 (d, J = 8 Hz, 1H, C3-H), 2.36 (s,
3H, CH3), 7.29 (m, 3H, C1',4',7'-H), 7.47 (m, 1H, C6;-H), 7.61
(d, J =7.6 Hz, 2H, C5',8'-H), 8.22 (s, 1H, C3'-OH), 8.39 (s, 1H,
NH), 7.75 ( s, 1H, CHN) ppm. EIMS (m/z) = 294 (M+), 171,
123, 143, 115, 79.
Fig. 1. Structure of ligands
EXPERIMENTAL
Solvents used were of analytical grade and all metals(II)
were used as their chloride salts. IR spectra were recorded on
8400-FTIR Spectrophotometer using KBr disc method. NMR
spectra were recorded on a Bruker-300 MHz NMR spectro-
photometer. UV-Visible spectra were obtained in DMSO on
IMRECO UV-VIS spectrophotometer, model U-2020. Conduc-
tance of the metal complexes was determined in DMSO on
conductometer, Hitachi (Japan), modelYSI-32. Melting points
were recorded on a Gallenkamp melting point apparatus and
are uncorrected. The complexes were analyzed for their metal
contents by EDTA titrations15. Proton magnetic resonance
spectra were recorded in CDCl3 and DMSO-d6 on Bruker AM
300 and AM 400 spectrometers (Rheinstetten-Forchheim,
Germany) operating at 300 and 400 MHz, respectively.
Tetramethyl-silance was used as an internal standard.
Synthesis of N'-[(1Z)-1''-(4-fluorophenyl)ethylidene]-
3'-hydroxy naphthalene-2'-carbohydrazide (L-4): To a hot
stirred solution of 3-hydroxy-2-naphthoic hydrazide (1.5 g,
0.0074 mol) in ethanol (40 mL), 4-fluroacetophenone (0.9 mL,
0.0074 mol) was added. The reaction mixture was heated
under reflux for 12 h. The product was purified according to
the previous procedure. Yield 87 %, cream coloured powder;
m.p. 270 ºC; IR (KBr, νmax, cm-1): 3593 (OH), 3143 (-NH-),
1639 (>C=O), 1623, (-C=N-), UV (DMSO) λmax (nm) 336;
non-electrolyte; 1H NMR (DMSO) δ: 2.37 (s, 3H, CH3), 7.29
(m, 3H, C1',4',7'-H), 7.47 (m, 1H, C6;-H), 7.61 (d, J = 7.6 Hz,
2H, C5',8'-H), 8.23 (s, 1H, C3'-OH), 8.43 (s, 1H, NH), 8.71 (d,
J = 8.7 Hz, 2H, C3,5-H), 7.90 (d, J = 8.7 Hz, 2H, C2,6-H) ppm.
EIMS (m/z) = 322 (M+), 171, 151, 115, 83.
Preparation of Schiff’s base
Synthesis of N'-[(E)-(4-hydroxy-3-methoxyphenyl)
methylidene] formic hydrazide (L-1): To a hot stirred
solution of formic acid hydrazide (1 g, 0.017 mol) in ethanol
(15 ml), vanillin (2.53 g, 0.017 mol) was added. The reaction
mixture was heated under reflux for 1.5 h. During reflux
precipitates were formed. The reaction was monitored through
TLC. After completion of reaction, the mixture was cooled at
room temperature. The solid material was collected by suction
filtration. The precipitates were washed with hot ethanol,
filtered and dried.Yield 55 %, white powder; m.p. 170 ºC; IR
(KBr, nmax, cm-1): 3320 (OH), 3055 (NH), 1680 (>C=O), 1650
(>C=N), UV (DMSO) λmax (nm) 218; non-electrolyte; 1H NMR
(DMSO) δ: 6.82 (d, J = 8 Hz, 1H, C5-H), 6.95 (m, 2H, C2,6-H),
7.24 (s, 1H, CHN), 3.32 (s, 1H, C4-OH), 3.87 (s 3H, -OCH3),
7.73 (s, 1H, NH), 8.65 ( s, 1H, CHO) ppm. EIMS (m/z) = 194
(M+), 165, 148, 134, 123, 106.
Synthesis of N'-[(1E)-1'-(4-chlorophenyl)ethylidene]-
formic hydrazide (L-5): To a hot stirred solution of formic
hydrazide (1 g, 0.017 mol) in ethanol (15 mL), 4-chloroaceto-
phenone (1.37 g, 0.01 mol) was added. The reaction mixture
was heated under reflux for 5 h. The product was purified
according to the previous procedure.Yield 88 %, white powder;
m.p. 195 ºC; IR (KBr, νmax, cm-1): 3201 (-NH-), 1695 (>C=O),
1615 (>C=N-), 700 (>C-Cl), UV (DMSO) λmax (nm) 272; non-
electrolyte; 1H NMR( DMSO) δ: 2.22 (s, 3H, CH3), 7.46 (d,
J = 8.7 Hz, 2H, C3,5-H), 7.77 (d, J = 8.7 Hz, 2H, C2,6-H), 8.75
(s, 1H, NH), 11.12 (s, 1H, CHO) ppm. EIMS (m/z) = 196
(M+), 181, 167, 153, 137, 102.
Synthesis of metal(II) complexes
Synthesis of 3'-hydroxy-N'-[(Z)-(4-hydroxy-3-
methoxyphenyl)methylidene]naphthalene-2'-carbo-
hydrazide (L-2): To a hot stirred solution of 3-hydroxy-2-
naphthoic hydrazide (1.5 g, 0.0074 mol) in a mixture of
ethanol (50 mL) and 1,2-dioxane (2 mL), vanillin (1.13 g,
0.0074 mol) was added. The reaction mixture was heated
under reflux for 10 h. The product was purified according to
the previous procedure. Yield 95 %, yellow powder; m.p. 152
ºC; IR (KBr, nmax, cm-1): 3307, 3307 (-OH), 3145 (NH), 1660
Synthesis of copper(II) complex (Cu-L-1): Copper(II)
chloride dihydrate (1.3 mmol 0.218 g) was added to a
magnetically stirred solution of L-1 (2.6 mmol, 0.5 g) in 1,4-
dioxane (20 mL). The mixture was refluxed for 1 h. Precipi-
tates were formed during reflux. The product was filtered,
washed with ethanol and dried. The dried precipitates were
kept in desicator.All other Cu(II), Co(II) and Zn(II) complexes
of ligands (L-1 to L-5) were synthesized according to the same
method.

2670 Hussain et al.
Asian J. Chem.
with vanillin and 4-chloroacetophenone were refluxed to
synthesize Schiff bases (L-1) and (L-5) respectively. Similarly
to get Schiff's bases (L-2), (L-3) and (L-4), 3-hydoxy-2-
naphthoic acid hydrazide separately was refluxed with vanillin,
5-methyl-2-furfural and 4-fluroacetophenone. The structures
of these Schiff's bases formed were elucidated by IR, NMR,
mass spectrometry and micro analytical data. These Schiff's
bases were further used for the complexation reaction with
Cu(II), Co(II) and Zn(II) metal ions.All of the newly synthesized
metal complexes were found to be stable in air and moisture.
They were prepared by the stoichiometric reaction with the
corresponding metal(II) chlorides and the Schiff's bases (L-1
to L-5) in the molar ratios (M:L) 1:2. The complexes are
amorphous solids, which are decomposed above 100 ºC. These
are insoluble in common organic solvents (chloroform,
acetone, ethanol and methanol), but soluble in DMSO and
DMF. All the complexes exhibited high values of molar
conductance (31-116 Ω-1 cm2 mol-1) determined in DMSO
which show their ionic and electrolyte nature.
Fig. 2. Structures of metal(II) complexes
Antioxidant analysis
Method for antioxidant activity: The antioxidant activity
of the ligands (L-1, L-2, L-3, L-4 and L-5) and their metal(II)
complexes, salts of corresponding metals and Trolox (as
standard antioxidant) was determined by 1,1-diphenyl-2-
picrylhydrazyl (DPPH) radical scavenging method of Brand-
Williams et al.16. The methanolic solutions (0.1 mL) of the
ligands, metal complexes, salts and Trolox were mixed with
40 µM methanolic DPPH• solution (2.9 mL) and absorbance
was recorded after 0.5 h at 517 nm using a UV-Visible spectro-
photometer. The antioxidant ability was calculated in terms of
DPPH• inhibition by a linear regression equation obtained from
a calibration curve (R2 = 0.9902) of DPPH•:
In the IR spectra of ligands the disappearance of absor-
ption band at 1735 and 3420 cm-1 due to carbonyl ν(C=O)
and ν(NH2) stretching vibrations and a new band appeared at
ca. 1607 cm-1 assigned17 to the azomethine ν(HC=N) linkage
indicate that amino and aldehyde moieties of the starting
reagents have been converted into their corresponding Schiff's
bases. The ν(NH)-amide, ν(C=O)-amide and ν(NNH)-imino
stretching frequencies were present at 3440, 1679 and 1607
cm-1, respectively. A comparison18 of the IR spectra of the
Schiff's bases to their metal(II) complexes (Table-1) indicated
that the Schiff's bases are coordinated to the metal atom mainly
in two ways, thus the ligands are acting in a bidentate manner.
The band absorption at 1607 cm-1 corresponding to azomethine
group was shifted to lower frequencies by ca. 20 cm-1, indi-
cating participation of the azomethine nitrogen is coordinated19.
A new medium strong band appearing at 540-533 cm-1 is
assigned to ν(M-O)20. This demonstrated that oxygen of the
C=O-amide has formed a coordinate bond with the metal ions
in an enolic form. A weak band at 420, 440 cm-1 is assigned to
ν(M-N). This further confirms that the nitrogen of the HN-imino
group bonds to the metal atom. All of the data establishes that
a conjugate chelate ring formed by ligand enolization exists
in the complexes.
Abs517 nm = 0.2533 × [DPPH•](µg)
The % DPPH• remaining was calculated as:
[DPPH•]R (%) = 100 × [DPPH•]T ÷ [DPPH•]T=0
where, [DPPH•]T is the remaining concentration of DPPH• at
0.5 h time while [DPPH•]T=0 is the initial concentration of
DPPH•.
A kinetic study was also conducted to evaluate the free
radical scavenging properties of the ligands, their complexes
with metals(II), salts of corresponding metals and Trolox at
varying time intervals. The percentage of remaining DPPH• at
every 5 min interval up to 30 min was plotted against time to
obtain the initial time at which the samples inhibit the
maximum concentration of DPPH•.
RESULTS AND DISCUSSION
Chemistry of Schiff's base ligands (L-1-L-5) and their
metal complexes: Ethanolic solutions of formic acid hydrazide
NMR spectrum of the ligand was determined in DMSO.
1H NMR spectral data are reported along with possible
TABLE-1
MELTING/DECOMPOSITION POINTS AND UV-VISIBLE, IR SPECTRAL DATA OF THE SYNTHESIZED COMPLEXES
No.
Metal complexes / m.f.
m.p. / d.p. (ºC)
IR (cm-1)
λmax (nm)
1
2
[Cu(L-1)2Cl2] / C16H18N4O6CuCl2 [522]
[Co(L-1)2Cl2] / C16H18N4O6CoCl2 [518]
[Zn(L-1)2Cl2] / C16H18N4O6ZnCl2 [524]
[Cu(L-2)2Cl2] / C38H26N4O8CuCl2 [806]
[Co(L-2)2Cl2] / C38H26N4O8CoCl2 [802]
[Zn(L-2)2Cl2] / C38H26N4O8ZnCl2 [808]
[Cu(L-3)2Cl2] / C34H28N4O6CuCl2 [722]
[Co(L-3)2Cl2] / C34H28N4O6CoCl2 [718]
[Zn(L-3)2Cl2] / C34H28N4O6ZnCl2 [724]
[Cu(L-4)2Cl2] / C38H30N4O4CuCl2 [778]
[Co(L-4)2Cl2] / C38H30N4O4CoCl2 [774]
[Zn(L-4)2Cl2] / C38H30N4O4ZnCl2 [780]
[Cu(L-5)2Cl2] / C18H18N4O2Cl2CuCl2 [526]
170
300
115
155
220
280
200
230
125
300
242
220
170
381
415
399
364
331
438
445
437
468
409
458
474
431
1650 (CO), 1585 (C=N), 510 (M-O), 435 (M-N)
1630 (CO), 1610 (C=N), 545 (M-O), 440 (M-N)
1650 (CO), 1600 (C=N), 532 (M-O), 430 (M-N)
1637 (CO), 1593 (C=N), 535 (M-O), 415 (M-N)
1625 (CO), 1595 (C=N), 525 (M-O), 455 (M-N)
1632 (CO), 1601 (C=N), 533 (M-O), 435 (M-N)
1635 (CO), 1602 (C=N), 530 (M-O), 425 (M-N)
1635 (CO), 1560 (C=N), 535 (M-O), 455 (M-N)
1632 (CO), 1595 (C=N), 505 (M-O), 435 (M-N)
1638 (CO), 1550 (C=N), 520 (M-O), 442 (M-N)
1639 (CO), 1600 (C=N), 525 (M-O), 445 (M-N)
1630 (CO), 1610 (C=N), 520 (M-O), 433 (M-N)
1670 (CO), 1510 (C=N), 560 (M-O), 455 (M-N)
3
4
5
6
7
8
9
10
11
12
13

Vol. 25, No. 5 (2013)
Synthesis of Some Novel Hydrazide Schiff’s Bases and Their Metal Complexes 2671
100
assignments.All the protons were found to be in their expected
regions21,22
Control
L-1
.
Mass spectra were determined by the instrument JEOL
MS Route and MAT 312 that gives us different fragments of
the Schiff bases. Molecular ion peaks were appeared at same
value of the molecular weight of Schiff's bases.
80
60
40
20
0
Cu-L-1
Co-L-1
Zn-L-1
CuCl2
CoCl2
ZnCl2
Trolox
The conclusions drawn from these studies further support
to the mode of bonding discussed in their IR spectra. It was
also observed that DMSO did not have any coordinating effect
on the spectra of ligands or their metal complexes.
Antioxidant activity: The antioxidant activity of the
synthesized ligands (L-1, L-2, L-3, L-4 and L-5), their corres-
ponding metal(II) complexes, salts of the metal used in complex
formation and Trolox (as standard antioxidant) was measured
in terms of their ability to scavenge the DPPH free radical.
Among the ligands, L-4 was found to be a good antioxidant
followed by L-2 and L-1 while L-5 showed comparatively
lowest antioxidant activity. Among the metal(II) complexes
of these ligands, the salts of Zn(II) with each ligand showed
good response regarding the inhibition of DPPH•. Zn-L-4 was
found to be the best antioxidant followed by Co-L-2, Co-L-4
Zn-L-2 and Zn-L-5 which also showed more than 50 %
inhibition of DPPH•. The Cu (II) complexes of each of the
ligands were found to be poor antioxidants as compared to
the respective ligand. The salts of all of the three metals also
showed low antioxidant activities as compared to the ligands
and their corresponding complexes. However, the antioxidant
activity of all of the ligands, metal complexes and the salts
were found to be low as compared to Trolox (Fig. 3).
00
5
10
15
20
25
30
Time (min)
Control
L-2
100
80
60
40
20
0
Cu-L-2
Co-L-2
Zn-L-2
CuCl2
CoCl2
ZnCl2
Trolox
00
5
10
15
20
25
30
Time (min)
Control
L-3
100
80
60
40
20
0
100
90
80
70
60
50
40
30
20
10
0
Cu-L-3
Co-L-3
Zn-L-3
CuCl2
CoCl2
ZnCl2
Trolox
00
5
10
15
20
25
30
Time (min)
Fig. 3. Comparative antioxidant activity (% inhibition of DPPH•) of
synthesized ligands, their metal complexes, salts of respective metals
and a standard antioxidant (Trolox)
100
80
60
40
20
0
Control
L-4
Cu-L-4
Co-L-4
Zn-L-4
CuCl2
CoCl2
ZnCl2
Trolox
The kinetic behavior of DPPH• inhibition by the ligands,
their metal complexes and salts of metals showed that these
ligands and their complexes with cobalt(II) and Zn(II) cause a
sharp decrease in DPPH• concentration within first 5 min
(Fig. 4A,C). After 5 min a slow decrease in the remaining
DPPH• concentration was observed to be continued for 0.5 h
in each case. The salts of each metal and the complexes of
the ligands with Cu(II) showed no further decrease in DPPH•
concentration after 5 minutes. However, each of the ligands
and complex showed low rate of DPPH• inhibition as compared
to Trolox (Fig. 4).
00
5
10
15
20
25
30
Time (min)

2672 Hussain et al.
Asian J. Chem.
Control
L-5
100
3. K. Uchida, Free Radic. Biol. Med., 28, 1685 (2000).
4. G. Leonarduzzi, M.C. Arkan, H. Basaga, E. Chiarpotto, A. Sevanian
and G. Poli, Free Radic. Biol. Med., 28, 1370 (2000).
5. R. Stocker, Curr. Opin. Lipidol, 10, 589 (1999).
6. Y.P. Kitaev, B. I. Buzykin and T.V. Troepolskaya, Russ. Chem. Rev.,
39, 441 (1970).
80
60
40
20
0
Cu-L-5
Co-L-5
Zn-L-5
CuCl2
CoCl2
ZnCl2
Trolox
7. N.P. Buu-Hoi, N.D. Xuong, N.H. Ham, F. Binon and R. Royer, J. Chem.
Soc., 1358 (1953).
8. M. Fabin and G. Palmer, Biochemistry, 40, 1867 (2001).
9. T.S. Ma and T.M. Tian, Antibiot. Chemother., 3, 491(1953); I. Pozdnyakova
and P.W. Stafshede, Biochemistry, 40, 13728 (2001).
10. U. Kuehn, S. Warzeska, H. Pritzkow and R. Kraemer, J. Am. Chem. Soc.,
123, 6125 (2001).
11. J.M. Price, Fed. Proc., 20, 223 (1961); K.D. Karlin and J. Zubieta,
Biochemical and Inorganic Perspectives, Adenine Press Guilderland,
New York, p. 457 (1983).
00
5
10
15
20
25
30
Time (min)
12. A.G. Mauk, R.A. Scott and H.B. Gray, J. Am. Chem. Soc., 102, 4360 (1980).
13. R.J. Williams, J.P. Spencer and C. Rice-Evans, Free Radic. Biol. Med.,
36, 838 (2004).
Fig. 4. Kinetic behavior of DPPH• inhibition by synthesized ligands, their
metal complexes, salts of respective metals and a standard
antioxidant (Trolox). A: L-1, B: L-2, C: L-3, D: L-4, E: L-5
14. F. Virgili and M. Marino, Free Radic. Biol. Med., 45, 1205 (2008).
15. Viswanath, A. Urooj and N.G. Malleshi, Food Chem., 114, 340 (2009).
16. W. Brand-Williams, M.E. Cuvelier and C. Berset, Lebensm. Wiss.
Technol., 28, 25 (1995).
Conclusion
17. A.I. Vogel, A Textbook of Quantitative Inorganic Analysis, ELBS and
Longman: London, edn. 3, p. 827 (1978).
All these newly synthesized Schiff's bases were charac-
terized by UV-VIS, IR and 1H NMR spectral data. The mass
spectrometric data of these ligands was also in close resem-
18. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley Interscience: New York, edn. 3, p. 448 (1978).
19. R.K. Agarwal, J. Indian Chem. Soc., 65, 448 (1988).
20. L.J. Bellamy, Infrared Spectra of Complex Molecules, John Wiley:
New York, p. 380 (1975).
1
blance with the structures supported by UV-VIS, IR and H
NMR spectroscopic tools. To determine antioxidant activity
of the ligands (L-1, L-2, L-3, L-4 and L-5), their corresponding
metal(II) complexes and metal chlorides, Trolox was used as
standard antioxidant. Ligand (L-4) was found to be the best
antioxidant among all the ligands while among the metal(II)
complexes; Zn-L-4 exhibited the best antioxidant activity.
21. W.W. Simmons, The Sadler Handbook of Protons NMR Spectra, Sadler
Research Laboratories Inc: Philadelphia, p. 80 (1978).
22. D.J. Pasto, Organic Structure Determination, Prentice Hall International:
London, p. 451 (1969).
REFERENCES
1. H. Sies, Am. J. Med., 91, 31S (1991).
2. H. Esterbauer, R.J. Schaur and H. Zollner, Free Radic. Biol. Med., 11,
81 (1991).