Synthesis, characterization, antimicrobial activity of first row transition metal(ii) complexes of novel Schiff base derived from Sulfapyridine, pyridine-2-aldehyde

Article abstract of DOI:10.14233/ajchem.2013.13596

A new Schiff base ligand (N-pyridin-2-yl-4-[(pyridin-2-yl)methyl amino]benzene sulfonamide) (L) was prepared by the reaction between sulfapyridine and pyridine-2-aldehyde. The ligand is bidentate by coordinating through pyridinyl nitrogen and azomethine nitrogen atom with Co(II), Ni(II), Cu(II), Zn(II) and Mn(II) chlorides. The complexes were synthesized and characterized by elemental analysis, molar conductance, magnetic moment, IR, H1 NMR and electronic spectral data. These complexes were screened in vitro antibacterial activity against the test microorganisms Staphylococcus aureus, Pseudomonas aeruginosa and fungi Candida albicans and Aspergillus niger. The results of these studies revealed that all complexes exhibit significant to moderate antimicrobial activity.

Full text of DOI:10.14233/ajchem.2013.13596

Asian Journal of Chemistry; Vol. 25, No. 6 (2013), 3225-3228
http://dx.doi.org/10.14233/ajchem.2013.13596
Synthesis, Characterization and Antimicrobial Activity of First Row Transition Metal(II)
Complexes of Novel Schiff Base Derived from Sulfapyridine and Pyridine-2-Aldehyde
*
I. RAMA and V. USHA
Post Graduate and Research Department of Chemistry, Seethalakshmi Ramaswami College, Tiruchirappalli-620 002, India
*Corresponding author: E-mail: rama14jai@yahoo.co.in
(Received: 15 February 2012;
Accepted: 14 December 2012)
AJC-12553
A new Schiff base ligand (N-pyridin-2-yl-4-[(pyridin-2-yl)methyl amino]benzene sulfonamide) (L) was prepared by the reaction between
sulfapyridine and pyridine-2-aldehyde. The ligand is bidentate by coordinating through pyridinyl nitrogen and azomethine nitrogen atom
with Co(II), Ni(II), Cu(II), Zn(II) and Mn(II) chlorides. The complexes were synthesized and characterized by elemental analysis, molar
conductance, magnetic moment, IR, H1 NMR and electronic spectral data. These complexes were screened in vitro antibacterial activity
against the test microorganisms Staphylococcus aureus, Pseudomonas aeruginosa and fungi Candida albicans and Aspergillus niger. The
results of these studies revealed that all complexes exhibit significant to moderate antimicrobial activity.
Key Words: Sulfapyridine, Transition metal complexes, Antibacterial, Schiff base.
aldehydes like indole-2-aldehyde and pyrrole-2-aldehyde are
coupled with sulfa drugs the resulting compound sulfadrug-
imine can act as an effective antibacterial agent10. In the present
investigation an attempt has been made to synthesize Schiff
base by coupling pyridine-2-aldehyde and sulfapyridine and also
its complexes with various first row transition metal chlorides.
INTRODUCTION
The application of inorganic chemistry to medicine is
rapidly developing field and novel therapeutic and diagnostic
metal complexes are now having an impact on medical
practice. Advances in bio-coordination chemistry are vital for
improving the design of compounds to reduce toxic side-
effects and understand their mechanisms of action. Most of
the pharmaceutical agents contain metal compounds which
are in current clinical use1,2 and new areas of applications are
rapidly emerging. The prominent biological activity of the
metal complexes of Schiff bases derived from sulfa drugs has
led to considerable interest in their coordination chemistry.
The condensation products of sulfa drugs with aldehydes and
ketones are biologically active and also form complex with
metal ions3-5. Many chemotherapeutically important sulfa
drugs like sulfadiazine, sulfapyridine, sulfamerazine possess
-SO2NH- moiety which is an important toxophoric functional
group. Schiff base derived from sulfanethioxazole and salicy-
laldehyde or thiophene-2-aldehyde and also the complexes
derived from these Schiff bases show toxicity against insects6.
Among the metal complexes it is well known that transi-
tion metal complexes inhibit DNA and RNA polymerase
activities and induce strand scission of DNA in presence of
H2O27. First row transition metal complexes of copper, zinc,
cobalt etc., have attracted much attention due to their biological
importance8. Many heterocyclic aldehydes9 are known to
be potential inhibitors for DNA synthesis. If heterocyclic
EXPERIMENTAL
All the reagents and solvents used were of analar grade.
All the metal(II) complexes were prepared by using corres-
ponding metal chlorides. Microanalyses of carbon, hydrogen
and nitrogen were carried out at SAIF, IIT, Madras, India. IR
spectra were recorded as KBr pellets on a Shimadzu 8000
1
FTIR spectrophotometer in the range of 4000-400 cm-1. H
NMR spectra of compounds were recorded with a Bruker
SpectrospinAvance DPX-400 using TMS as internal standard
and DMSO-d6 as solvent. UV-visible spectra were obtained in
DMF on a Perkin Elmer Lambda 35 spectrophotometer in the
range of 190-1100 nm. Magnetic susceptibility measurements
were carried out on solid compounds at National Institute of
Technology, Trichy, India. Conductance measurements were
studied using Elico conductivity bridge and dip type conduc-
tivity cell. Melting points were determined by using Elico
melting point apparatus. In vitro antibacterial and antifungal
screening were studied at Periyar Maniammai Pharmaceutical
College, Trichy, India.
Synthesis of Schiff-base ligand (L): A hot ethanolic
solution of pyridine-2-aldehyde (0.0125 mol) was added to a

3226 Rama et al.
Asian J. Chem.
hot ethanolic solution of sulfapyridine (0.0125 mol). The
mixture solution was then refluxed on a water bath for 4-5 h.
A coloured solid mass separated out on cooling which was
filtered, washed several times and subsequently dried over
anhydrous CaCl2 in a desiccator and recrystallised from ethanol
(m.p. 134 ºC, yield 78 %).
(M:L) stoichiometry. The physical characteristics, micro
analytical data, conductance and magnetic moment values of
the metal complexes and the ligand are given in the Table-1.
Conductance and magnetic susceptibility measure-
ments: The molar conductance values fell within the range of
6.18-39.32 ohm-1 cm2 mol-1 for all complexes showing the
non-electrolytic12 nature. This suggested that the chloride ions
are coordinated with the metal ions. The observed magnetic
moment value for Co(II) and Ni(II) complex (4.64 and 3.24
BM) suggest octahedral geometry for these complexes13. The
observed magnetic moment value for copper(II) complex (1.77
BM) lie in the range as expected for a d9 system, which contains
one unpaired electron with octahedral geometry14. The zinc(II)
complex was found to be diamagnetic15 as expected. The
manganese(II) complex has a magnetic moment value of 5.85
BM indicating high spin octahedral environment16 around
manganese.
Synthesis of metal(II) complexes: To a hot magnetically
stirred dioxane solution of Schiff base ligand (0.003 mol), an
aqueous solution of the corresponding metal(II) chloride
(0.0015 mol) was added. The mixture was refluxed for 6 h in
a heating mantle. The bright coloured complex separated out on
cooling, was filtered by suction, washed and dried in vacuo over
anhydrous CaCl2. The yields of the complexes were 50-80 %.
Antimicrobial activity: The synthesized ligand and the
metal complexes were screened in vitro for antimicrobial
activity against pathogenic bacterial species (Staphylococcus
aureus and P. aeruginosa) and fungi (Candida albicans and
A. niger ) by diffusion plate method11. The results were
recorded and compared with standard drug.
Infrared spectra: The important IR spectral bands of the
ligand and its metal complexes are given in the Table-2.
Potential electron pair donor sites of the synthesized ligand
are the pyridinyl nitrogen, the azomethine nitrogen, the
sulfonamide oxygens and the sulfonamide nitrogen. In the IR
spectra of the ligand a sharp band observed in the region 1632
cm-1 and a medium sharp band at 1387 cm-1 were assigned17 to
the ν(-HC=N-) mode of azomethine and ν(C-N) stretching of
pyridinyl ring, respectively. Evidence of the nitrogen bonding
of azomethine (-HC=N-) group to the central metal atom stems
from the shift of the ν(-HC=N-) band to lower frequency by
21-42 cm-1 in all the complexes. The coordination through the
pyridinyl ring nitrogen was revealed by shifting of the ν(C-N)
RESULTS AND DISCUSSION
The Schiff base ligand was synthesized by refluxing an
equimolar ratio of sulfapyridine and pyrindine-2-aldehyde in
hot ethanolic medium. The composition of the ligand is consis-
tent with its micro analytical data. The structure of the synthe-
sized ligand was established with the help of IR, NMR and
micro analytical data. The complexes are microcrystalline
coloured powders having melting points higher than the ligand.
They are stable in air and non-hygroscopic in nature. All com-
plexes gave satisfactory elemental analysis suggesting 1:2
TABLE-1
PHYSICAL CHARACTERISTICS AND MICRO ANALYTICAL
DATA OF SCHIFF BASE LIGAND AND ITS METAL COMPLEXES
Elemental analysis (%) calcd.
(observed)
Λm
(ohm-1 cm2
mol-1)
m.p.
(ºC)
Yield
(%)
Compound
Colour
Geometry
µEff
C
H
N
[C17H14N4SO2]
Yellow
Orange
134
240
78
54
52
59
63
81
60.30
(60.21)
50.60
4.20
(3.81)
3.50
16.60
(16.31)
13.90
–
–
–
(L)
[Co(C17H14N4SO2)2Cl2]/[Co(L)2Cl2]
(LA)
Octahedral
Octahedral
Octahedral
Octahedral
Octahedral
4.64
3.24
1.77
Dia
31.85
30.96
39.32
11.6
(50.33)
(3.42)
(13.43)
[Ni(C17H14N4SO2)2]Cl2/[Ni(L)2 Cl2]
(LB)
Greenish 250
yellow
50.63
(50.55)
3.50
(3.25)
13.90
(13.17)
[Cu(C17H14N4SO2)2Cl2]/[Cu(L)2Cl2]
Dark
green
195
157
170
50.30
(50.04)
50.20
3.50
(3.43)
3.50
13.80
(13.45)
13.80
(LC)
[Zn(C17H14N4SO2)2Cl2]/[Zn(L)2Cl2]
Dark
brown
(50.03)
50.90
(50.61)
(3.06)
3.50
(3.21)
(12.96)
13.97
(13.88)
(LD)
[Mn(C17H14N4SO2)2Cl2]/[Mn(L)2Cl2]
(LE)
Grey
5.85
6.78
TABLE-2
IMPORTANT ELECTRONIC AND IR SPECTRAL BANDS IN SCHIFF BASE LIGAND AND ITS METAL COMPLEXES
IR Spectral bands (cm-1)
Electronic spectral bands (λmax) (cm-1)
Comp.
νa(SO2),
νs(SO2)
ν(-CH=N-)
Azomethine
ν(C-N) Pyridynyl
nitrogen
ν(N-H)
ν(S-N)
ν(M-N)
L
28333, 32424
36498, 37320
32884
3413
3415
3418
3413
3407
3413
1632
1597
1611
1598
1609
1590
1387
1358
1373
1363
1366
1368
1276, 1138
1275, 1134
1272, 1130
1279, 1134
1273, 1139
1260, 1134
957
957
961
960
953
946
–
M → L
M → L
M → L
M → L
LA
LB
LC
LD
LE
492
483
494
460
490
36000
32232, 33919, 35039, 35869
29412
M
→
L
6 A1g → 4Eg (D)

Vol. 25, No. 6 (2013)
Synthesis of First Row Transition Metal(II) Complexes of Novel Schiff Base 3227
TABLE-3
band to lower frequencies by 14-29 cm-1 in all the complexes
as compared with that of the ligand. This is further confirmed
by the appearance of the new bands at 490-460 cm-1 due to the
ν(M-N) bands18 in metal complexes. The bands in the ligand
due to νa(SO2) and νs(SO2) appeared at 1275-1235 and 1140-
1125 cm-1, respectively19. These bands remain almost un-
changed in the complexes indicating that this group does not
participate in coordination. This is supported by the unchanged
ν(S-N) mode20 appearing at 965-945 cm-1 in the ligand even
after complexation.
1H NMR spectra: 1H NMR spectra of the free ligand and
its complexes were recorded in DMSO-d6. The proton nmr
signal observed at δ = 8.5 ppm in the spectra of the ligand is
due to azomethine (-HC=N-) proton. The azomethine proton
shifts upfield upon complexation due to the increased conju-
gation and coordination. This also confirms the coordination
by azomethine nitrogen21, which has already been shown by
IR spectral data.
ANTIMICROBIAL ACTIVITY OF
THE LIGAND AND COMPLEXES
Bacteria
Fungi
Sample
Staphylococcus
aureus
P.
aeruginosa
Candida
albicans
A.
niger
12
15
30
12
14
–
14
18
18
20
18
9
14
–
12
13
12
14
15
13
35
L
LA
16
15
16
12
25
LB
LC
LD
LE
Standard
35
35
Standard: Ciprofloxacin 5 µg/disc for bacteria; Nystatin 100 units/disc
for fungi.
Antibacterial activity
40
30
20
10
0
Electronic spectra: The electronic spectra of the comp-
lexes were taken in DMF solution and presented in the Table-
2. The Co(II) complex exhibited well-resolved, two high
energy bands at 36,498 and 37,320 cm-1 which are assigned22
to the metal to ligand charge transfer. The Ni(II) and Cu(II) )
complexes also exhibited strong high energy bands at 32,884
and 36,000 cm-1 in turn, assigned to metal to ligand charge
transfer. The electronic spectra of the Zn(II) complex exhibited
four high-intensity bands at 32232, 33919, 35039 and 35869
cm-1 and are assigned to metal to ligand charge transfer. The
electronic spectra of Mn(II) complex show only one band at
29,412 cm-1 assigned23 to the transition 6A1g → 4Eg (D) consis-
tent with octahedral configuration.
L
LA
LB
LC
LD
LE
Std
Staphylococcus aureus
P. aeruginosa
Antifungal activity
Antimicrobial activity: Disc diffusion technique has been
used for determining the activity of Schiff base ligand and
complexes against bacterial species and fungi. It is clear from
the biological data that the ligand and complexes has signi-
ficant antimicrobial activities against the pathogenic bacteria.
The results compared with standard drug (ciprofloxacin 5 µg/
disc for bacteria; Nystatin 100 units/ disc for fungi) have
indicated that compounds were active but activity was lesser
than the standard drugs. The results thus obtained are explained
on the basis of Overtone's concept and chelation theory24.
Comparisons of the biological activity of the synthesized
compounds and standard are presented in Table-3 shows the
free Schiff base ligand and some of its complexes exhibit
better activity. The activity decreases in the case of manga-
nese complexes when compared to ligand. In specific the
Nickel and copper complexes of the ligand show very high
activity against the bacteria Staphylococcus aureus, which
indicates the remarkable antibacterial activity when compared
to the rest of the complexes which is shown in the Fig. 1. In
overall the activity of the ligand is enhanced after chelation
with metal and thus the biological activity increases on comp-
lexation.
40
30
20
10
0
L
LA
LB
LC
LD
LE
Std
Candida albicans
A. niger
Fig. 1
neutral bidentate ligand and its structrure is shown in the
Fig. 2. The metal chelates of ligand have been structurally
characterised. The metal ligand stoichiometry in all these
complexes is 1:2. It is tentatively proposed that the Schiff base
ligand coordinates through the nitrogen of the azomethine
group and the nitrogen of the pyridinyl ring, forming a stable
chelate ring structure. On the basis of the above discussions, it
is concluded that all the complexes exhibit six-coordinated
octahedral geometry as shown in the Fig. 3. Biological studies
of the complexes reveal that these complexes show better
activity compared to that of the ligand.
Conclusion
In this paper the preparation and characterization of a new
Schiff base derived from 2-pyridine carbaldehyde and sulfapy-
ridine has been reported. From the satisfactory micro analytical
and various spectral data, it is concluded that ligand acts as

3228 Rama et al.
Asian J. Chem.
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