Biologically active and thermally stable polymeric Schiff base and its metal polychelates: Their synthesis and spectral aspects

Article abstract of DOI:10.1016/j.saa.2015.03.116

New metal polychelates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) obtained by the interaction of metal acetates with polymeric Schiff base containing formaldehyde and piperazine, have been investigated. Structural and spectroscopic properties have been

Full text of DOI:10.1016/j.saa.2015.03.116

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Biologically active and thermally stable polymeric Schiff base and its
metal polychelates: Their synthesis and spectral aspects
⇑
Raza Rasool , Sumaiya Hasnain
Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi 110025, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Results obtained, revealed that the
synthesized polymers exhibited
higher thermal stability than their
corresponding ligands.
ꢀ
ꢀ
Spectral studies confirmed the
proposed structure of the metal
polychelates.
Antimicrobial studies show that
biological activities of the polymers
were enhanced after coordination
with the metal.
ꢀ
Antimicrobial activity and thermal
stability of AGP-Cu(II) was the best
amongst all synthesized metal
polychelates.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 August 2014
Received in revised form 23 March 2015
Accepted 27 March 2015
Available online 13 April 2015
New metal polychelates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) obtained by the interaction of metal acet-
ates with polymeric Schiff base containing formaldehyde and piperazine, have been investigated.
Structural and spectroscopic properties have been evaluated by elemental analysis, FT-IR and 1H-NMR.
Geometry of the chelated polymers was confirmed by magnetic susceptibility measurements, UV–
Visible spectroscopy and Electron Spin Resonance. The molecular weight of the polymer was determined
by gel permeation chromatography (GPC). Thermogravimetric analysis indicated that metal polychelates
were more thermally stable than their corresponding ligand. All compounds were screened for their
antimicrobial activities against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, (bacteria) and
Candida albicans, Microsporum canis, Cryptococcus neoformans (fungi) by agar well diffusion method.
Interestingly, the polymeric Schiff base was found to be antimicrobial in nature but less effective as com-
pared to the metal polychelates. On the basis of thermal and antimicrobial behavior, these polymers hold
potential applications as thermally resistant antimicrobial and antifouling coating materials as well as
antimicrobial packaging materials.
Keywords:
Coordination polymers
Thermogravimetric analysis
Antimicrobial activity
Schiff base
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
to make them durable in the environment. Coordination poly-
mers are usually known for their optical, mechanical and ther-
Continuous efforts have been made to make polymers more
stable, increase their mechanical and chemical strengths and
mal stability [1]. Interest in construction of coordination
polymers by linking transition metal ions with polydentate
ligands has been constantly growing over the past years [2–4].
In addition to the above discussion, coordination polymers,
derived from Schiff base have attractive physicochemical,
⇑
Corresponding author. Tel.: +91 112 682 3254; fax: +91 112 684 0229.
E-mail address: razarasool@gmail.com (R. Rasool).
http://dx.doi.org/10.1016/j.saa.2015.03.116
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

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R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
chemical and biological properties, which make them highly
processable [5]. Polymeric Schiff base are an important class
of coordination polymers with multidentate donor sites, known
to form polychelates with transition metal ions. Basic properties
of polymeric Schiff base are due to the azomethine linkage in
polymeric backbone [6]. They may serve as models in biologi-
cally important species, finding applications in biological, clini-
cal, analytical and thermal activities.
Complexation of a metal ion to functional polymeric Schiff base
changes its activity due to polymeric effect which has led to a vari-
ety of applications. Luminescent properties of polydentate Schiff-
base coordination polymers have also been reported [7]. Various
works on coordination complexes has revealed that the heteroge-
neous systems possess more economical potentials and advantages
over homogeneous systems [8]. Several metallo-polymers contain-
ing metals in the backbone of polymer chain have already been
prepared [9,10]. The preparation of polychelates from a polymeric
ligand involving anthranilic acid and thiosemicarbazide, thiourea
with formaldehyde resin has been reported [11,12]. Salicylidene
anthranilic acid possesses antiulcer activity and complexation
behavior with copper, increases its antiulcer activity [13].
Antimicrobial activity of coordination polymers depends on the
central metal ion as well as nature of the ligand attached along
their spatial relationship. So synthesis and structural studies of
new compounds of this type have much interest as a first step in
search for new Schiff base polymers as potential antimicrobial
agents.
25 mL EtOH and left for crystallization at room temperature.
Dark brown product was collected, washed with EtOH and dried
in vacuum. Yield was 68%.
Elemental analysis for C16H12N2O4 (296.28 g/mol); Cal.: C,
64.86%; H, 4.08%; N, 9.46%. Obt.: C, 64.27%; H, 4.14%; N, 9.69%.
FTIR (KBr pellet, cmꢂ1): 3352 (OH), 2931 (@CHACH@), 3132
(aromatic CH), 1657 (CH@N), 1717 (C@O).
To this synthesized Schiff base (0.01 mol), formaldehyde
(0.02 mol) was added in presence of 40 mL DMF and 2–3 drops
of conc. HCl. The three necked round bottom flask was equipped
with thermometer, condenser and magnetic stirrer. Schematic rep-
resentation is shown in Scheme 1.
Progress of reaction was monitored by thin layer chromatogra-
phy. The resulting mixture was heated at 70 5 °C for 1 h with
continuous stirring. To this solution 0.86 g (0.01 mol) of piperazine
dissolved in 15 mL of DMF was added. After that the reaction mix-
ture was again stirred at 80–90 °C for 24 h. The obtained solution
was poured into a beaker and made viscous by vaporizing the
excess solvent. Then it was precipitated with an excess amount
of cold water. The resulting light brown colored viscous product
was washed with distilled water, acetone and diethyl ether.
Finally, the product was dried in vacuum desiccators on calcium
chloride. The polymeric Schiff base (AGP) was obtained in 62%
yield.
Synthesis of metal polychelates
Keeping the foregoing facts in mind and in continuation to
our research work in this domain, new Schiff base polymers
containing transition metal ions in the main chain has been
synthesized and their properties have been discussed. Its syn-
thesis represents an attempt to give an organic polymer inor-
ganic functionality.
Metal polychelates of [Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)]
were prepared by using equimolar ratio of polymeric ligand
(AGP) and metal(II) acetates. Typical procedure for preparation of
metal polychelates of manganese(II) was as follows:
This metal polychelate was prepared by mixing a hot solu-
tion of manganese(II) acetate tetrahydrate (2.45 g, 0.01 mol dis-
solved in 25 mL DMF) with a solution of polymeric Schiff base
(0.01 mol dissolved in 25 mL DMF). The reaction mixture was
heated at 80 °C for 12 h, with continuous stirring as it becomes
sticky and viscous. Brownish yellow product was precipitated by
adding ice cooled water. The precipitate was filtered, washed
several times with distilled water and acetone, and then dried
under vacuum over anhydrous calcium chloride, yield 63%.
Same procedure was adopted for the synthesis of other metal
polychelates.
Experimental
Materials and microbial strains
Anthranilic acid (Merck), 40% Glyoxal (S.D. fine), 35%
hydrochloric acid (Merck), Formaldehyde 37–41% (S.D. Fine
Chem), Piperazine (Qualingens), transition metal(II) acetates:
Manganese(II)
acetate
tetrahydrate
[Mn(CH3COO)2ꢁ4H2O],
Cobalt(II) acetate tetrahydrate [Co(CH3COO)2ꢁ4H2O], Nickel(II)
acetate tetrahydrate [Ni(CH3COO)2ꢁ4H2O], Copper(II) acetate
monohydrate [Cu(CH3COO)2ꢁH2O], Zinc(II) acetate dihydrate
[Zn(CH3COO)2ꢁ2H2O] (Merck), were used without further purifica-
tion. Solvents like dimethylformamide (DMF), dimethylsulfoxide
(DMSO), ethanol, methanol and acetone (Qualingens) were dis-
tilled before use. Microorganisms, Escherichia coli, Staphylococcus
aureus, Bacillus subtilis, (bacteria) and Candida albicans,
Microsporum canis, Cryptococcus neoformans (fungi) were provided
by the culture collection of microbiology laboratory, department of
microbiology (A.M.U. Aligarh).
Characterization
Elemental analysis for the estimation of percentage of C, H and
N present in metal polychelates was carried out by using elemental
analyzer system GmbH Vario ELIII. Metal content of metal poly-
chelates was determined by complexometric titration against
ethylenediamine tetraacetic acid after decomposition of the com-
plexes with concentrated nitric acid. FT-IR spectra were recorded
on a Perkin Elmer IR spectrophotometer (Model 621) using KBr
pellets in the range 4000–400 cmꢂ1. Proton NMR spectra was
obtained from JEOL GXS 300-MHz FX-1000 Fourier transform
NMR spectrometer, taking DMSO-d6 as solvent and tetramethylsi-
lane as an internal standard. Ultra violet–visible (UV–Vis) spectra
were taken on a Perkin Elmer Lambda (EZ-201) spectrophotome-
ter. Magnetic susceptibility was measured on a vibrating sample
magnetometer (model 155). Electron Spin Resonance (ESR) of the
copper complex was recorded on Varian E112 Xband
Spectrometer. The number average (Mn), weight average (Mw),
molecular weights were determined by gel permeation chro-
matography (Shimadzu, Japan) using tetrahydrofuran (THF) as
mobile phase and polystyrene as a stationary phase.
Synthesis
Synthesis of polymeric Schiff base (AGP)
Schiff base of anthranilic acid and glyoxal was synthesized by
slightly modified method as described by Kurtoglu et al. [14].
Anthranilic acid (2.74 g, 0.02 mol) was dissolved in 30 mL ethanol
then glyoxal (0.58 g, 0.01 mol) was added drop wise at 50 °C with
continuous stirring. The reaction mixture was acidified with con-
centrated HCl and was stirred magnetically under reflux for a
day at 60 °C. The formed dark yellow product was dissolved in

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437
O
O
O
O
OH
HO
EtOH
OH
2
+
N
N
NH2
O
Glyoxal
Anthranilic acid
Monomeric Schiff Base
O
O
H
N
OH
HO
N
O
2
+
+
N
CH2
N
H
Monomeric Schiff Base
Piperazine
Formaldehyde
O
O
OH
N
HO
N
N
PolymericSchiff Base (AGP)
N
Scheme 1. Synthetic route to polymeric Schiff base [AGP].
Thermal behavior of synthesized polymers was recorded with
TA Analyzer 2000 at a heating rate of 20 °C/min in nitrogen
atmosphere.
Antimicrobial assessment
Antimicrobial activity of polymeric ligand and its metal poly-
chelates was tested against different microorganisms in DMSO as
a solvent. The sample concentration was 50 l
g mLꢂ1. Bacterial
strains were nourished in a nutrient broth and yeasts in a malt-ex-
tract broth and incubated for 24 and 48 h, respectively at room
temperature (23–27 °C). According to the agar-diffusion method,
bacteria were incubated on Muller-Hinton agar and yeast on
Sabouraud dextrose agar. Wells were dug in media with the help
of a sterile steel borer and then 0.1 mL of each sample was intro-
duced in the corresponding well. Other wells were supplemented
with DMSO for positive control and standard drugs, viz.
Tetracycline (for bacterial strains) and Fluconazole (for antifungal
strains) as negative control. The resulting zones of inhibition on
the plates were measured in millimeters.
Results and discussion
The above synthesized Schiff base was subjected to react with
formaldehyde in the presence of hydrochloric acid and mechanism
for the preparation of polymeric Schiff base (AGP) is given as:
Polymeric Schiff base (AGP) and its metal polychelates were
prepared by the procedure mentioned in experimental section
and as shown in Schemes 1 and 2. The ligand and coordination
polymers were colored compounds, soluble in DMSO and DMF
but insoluble in common organic solvents.
Chemistry of the polymeric Schiff base and its metal polychelates
Nitrogen atom of anthranilic acid act as a nucleophile having a
lone pair of electron, which attacks on carbon atom with positive
charge of glyoxal, to form imine linkage (C@N). Mechanism
involved during the formation of imine is given below:

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R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
O
O
OH
HO
N
N
N
Polymeric Schiff Base (AGP)
O
N
O
Metal Acetate
O
O
M'
N
N
Metal Acetate
N
polymer metal complexes
N
N
N
x
N
N
M
O
O
x
Where,
M=Mn(II)
M'=Co(II), Ni(II), Cu(II), Zn(II)
x=H20
O
O
polymer metal complex
Scheme 2. Synthetic route to metal polychelates [AGP-M(II)].
coordination polymer of Mn(II) was coordinated with two mole-
cules of water which is also corroborated by the FT-IR and TGA
analyses discussed in the proceeding sections.
FT-IR analysis
IR spectra provide valuable information regarding the nature of
functional groups attached to the metal atom. The polymeric Schiff
base and its metal polychelates were characterized and their
assignments are given in Table 2 and Fig. 1. Spectral band for
m
(C@N) appeared at 1622 cmꢂ1 in metal free Schiff base (AGP)
while in metal polychelates, AGP-M(II), this bands shifted towards
lower frequency by 15–22 cmꢂ1. Shifting of this band to lower
energy on complex formation indicated the coordination of nitro-
gen atom of azomethine moiety [15,16]. Bands responsible for
symmetric stretching vibration of carboxylate ion appeared at
1419–1375 cmꢂ1 while for asymmetric stretching it appeared at
1608–1555 cmꢂ1
,
D
m
(COOꢂ) ꢃ230 cmꢂ1 for AGP polymers, indicat-
ing unidenticity of carboxylate group [17]. Spectra of AGP-Mn(II)
exhibited a broad band at 3345 cmꢂ1 suggesting the presence of
water molecule [11,12] which was further confirmed by the
appearance of band at 855 cmꢂ1 assigned to rocking and wagging
modes of water [18]. The presence of coordinated water was also
confirmed by TG analyses. Spectra of other metal polychelates,
AGP-M(II), showed bands in the range of 496–535 cmꢂ1 and
Analytical data of polymeric Schiff base (AGP) with its metal
polychelates are given in Table 1, and are in good agreement with
1:1 metal to polymeric ligand molar ratio. It also revealed that
416–460 cmꢂ1 assigned to
tively [19–20].
m(MAO) and m(MAN) vibrations respec-

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439
Table 1
Elemental analysis data for polymeric Schiff base and its metal polychelates.
Abbreviation
Empirical formula
(Yield %)
Calculated (observed)a (%)
C
H
N
M
AGP
[C22H22N4O4]n
62
63
65
70
68
67
65.01
(64.35)
5.46
(5.55)
13.78
(13.89)
–
–
AGP-Mn(II)
AGP-Co(II)
AGP-Ni(II)
AGP-Cu(II)
AGP-Zn(II)
[C22H24N4O6Mn]n
[C22H20N4O4Co]n
[C22H20N4O4Ni]n
[C22H20N4O4Cu]n
[C22H20N4O4Zn]n
53.34
(54.10)
4.88
(4.96)
11.31
(11.44)
11.09
(11.02)
57.03
(56.88)
4.35
(4.40)
12.09
(12.15)
12.72
(12.76)
57.06
(56.98)
4.35
(4.37)
12.10
(12.13)
12.67
(12.64)
56.46
(56.71)
4.31
(4.35)
11.97
(12.10)
13.58
(13.46)
56.24
4.29
11.92
13.92
(56.31)
(4.33)
(12.02)
(14.04)
a: Calculated value (observed).
n: number of repeating units of polymeric chain.
Table 2
FT-IR spectral bands and assignments of polymeric Schiff base and its metal polychelates.
Compounds
Assignments
m
(H2O)
(HOH)
m
(COOꢂ) (asym–sym)
-CH2 (sym–asym)
m
(C@N)
m
(MAO)
m(MAN)
(q&x)
AGP
–
–
1608–1419
1570–1406
1586–1401
1555–1391
1588–1375
1595–1387
2852–2926(m)
2852–2926(m)
2852–2926(m)
2852–2926(m)
2852–2926(m)
2852–2926(m)
1622
–
–
AGP-Mn(II)
AGP-Co(II)
AGP-Ni(II)
AGP-Cu(II)
AGP-Zn(II)
3345
855(s)
1607(s)
1605(s)
1605(s)
1603(s)
1600(s)
528(s)
535(m)
517(s)
496(s)
520(m)
460(s)
453(s)
416(s)
437(m)
445(s)
–
–
–
–
–
–
–
–
s, strong; b, broad; m, medium; w, weak; sym, symmetric; asym, asymmetric;
q
, rocking;
x
, wagging.
1H NMR spectra
crystal field parameters, viz. ligand field splitting parameter (Dq),
Racah interelectronic repulsion parameter (B), ligand field splitting
energy (10 Dq), covalency and ionic character (b and b°) were cal-
culated and the results revealed that the formed coordination poly-
mers are stable and have good covalent character.
1H NMR spectra of the synthesized polymers was recorded in
DMSO-d6 solvent, using tetramethylsilane (TMS) as an internal
standard. Spectra of polymeric Schiff base AGP and AGP-Zn(II),
are shown in Figs. 2 and 3 respectively. Aromatic protons show
multiple resonance signals between 6.80 to 7.95 ppm for AGP
and AGP-Zn(II). The peak of aromatic protons became broad due
to intermolecular interaction towards metal ion and variation in
the pi-electron density around protons. Peak observed at
11.10 ppm and 11.30 ppm was assigned to proton of ACOOH group
of AGP [21] while in the spectra of AGP-Zn(II), this signal disap-
peared, suggesting the participation of acidic proton to metal cen-
tre forming COO–M linkage. Azomethine linkage appeared at
8.30 ppm [22] in polymeric Schiff base, which showed downfield
shifting in metal polychelate interpreting the participation of
nitrogen of azomethine in the MAN bond formation. In AGP, reso-
nance signal at 2.51 ppm indicated the presence of ACH2ACH2A
groups of piperazine moiety. Appearance of signal at 3.3 ppm
was due to proton of benzylic methylene group in AGP. Results
of 1H-NMR spectra reveal that piperazine moiety was attached to
anthranilic acid with methylene group of formaldehyde.
Significant shifting of all peaks of AGP-Zn(II) were observed, which
confirmed the formation of polymer metal complex.
Electronic spectra of synthesized metal polychelates were
recorded in DMSO. Various crystal field parameters, 10 Dq, B, b
and b° were calculated and tabulated in Table 3. Magnetic moment
of AGP-Mn(II) was 5.67 B.M., which suggested the presence of five
unpaired electrons. The electronic spectrum exhibited bands at
21,252 cmꢂ1, 18,500 cmꢂ1, 14,450 cmꢂ1 which were assigned to
4
4
4A1g(G) 6A1g(F), T2g(G) 6A1g(F), T1g(G) 6A1g(F) transitions
respectively, suggesting an octahedral geometry [23]. Polymer com-
plex of Co(II) had a magnetic moment of 4.54 B.M. [24] and the tran-
sitions appeared at 9213 cmꢂ1 and 16,598 cmꢂ1 corresponding to
4T1 4A2 and 4T1 4A2 respectively while t3 was not visible due
to broadness, which indicated tetrahedral geometry [25].
AGP-Ni(II) exhibited magnetic moment of 2.63 B.M. and three
absorption bands were observed at 3994 cmꢂ1, 9497 cmꢂ1 and
16,465 cmꢂ1 corresponding to 3T1(P) 3T1, 3A2 3T1 and 3T2 3T1
transitions, respectively; suggesting tetrahedral geometry of the
polychelate [26]. Magnetic moment for AGP-Cu(II) was 1.69 B.M.
and the electronic spectrum showed spectral bands at
15,890 cmꢂ1 and 25,432 cmꢂ1 which were assigned to
2A1g 2B1g(F) and a charge-transfer band respectively, indicating
square planar geometry [27]. Thus, electronic spectral study fur-
ther supports the structure proposed for metal polychelates.
Electron Spin Resonance (ESR) method is employed to under-
stand the symmetry of surroundings of the paramagnetic ion and
nature of its bonding to the neighboring ligands. ESR of Cu(II)
Electronic spectra, magnetic property and Electron Spin Resonance
UV–Visible spectral analysis provides an accurate method for
the determination of geometry of metal polychelates. The actual
position of band maxima observed in electronic spectra is a func-
tion of geometry and strength of coordinating ligand. Various

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R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
Fig. 1. FT-IR spectra of AGP and its metal polychelates.
Fig. 2. 1H-NMR spectrum of AGP.
chelated polymer was recorded in DMF at room temperature,
which showed anisotropy with resolved hyperfine structure, with
the following values: gII = 2.326, g\ = 2.062, in which gII > g\.
These values indicate that the ground state of Cu(II) is dx2 ꢂ y2,

R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
441
Fig. 3. 1H-NMR spectrum of AGP- Zn(II).
Table 3
Magnetic susceptibility, electronic spectra and ligand field parameters.
Compounds
Magnetic moment
(B.M.)
Electronic transitions
(cmꢂ1
Assignment
Geometry
B
10 Dq
(cmꢂ1
b
b°
)
)
AGP-Mn(II)
5.67
21,252
18,500
14,450
4A1g(G) 6A1g(F)
4T2g(G) 6A1g(F)
4T1g(G) 6A1g(F)
Octahedral
768
3838
0.79
0.21
AGP-Co(II)
AGP-Ni(II)
4.54
2.63
9213
16,598
4T1(F) 4A2
Tetrahedral
Tetrahedral
664
823
5975
5763
0.59
0.76
0.41
0.24
4T1(P) 4A2
3994
9497
16,465
3T1(P) 3T1
3A2
3T2
2A1g
3T1
3T1
2B1g(F)
AGP-Cu(II)
1.69
15,890
25,432
Square
Planar
–
–
–
–
Charge transfer
which supports square planar structure [28]. The g-values can be
used to calculate G-value, which indicate weak field or strong field
ligand. The equation used is:
Molecular weight measurements
The average molecular weight of the AGP polymer was deter-
mined by gel permeation chromatography. The number average
(Mn) and weight average (Mw) molecular weight were found
2998 and 3860 respectively. The polydispersity index (Mw/Mn)
was found to be 1.28. The polydispersity index indicates the nar-
row distribution of molecular weights.
G ¼ ðgII ꢂ 2:002Þ=g ? ꢂ2:002
If G is less than 4.0, the ligand forming Cu2+ complex is regarded
as a strong field [29]. Since, G-value for AGP-Cu(II) is 5.4, therefore
the ligand forms a weak field complex.
Fig. 4. Thermogram of AGP and its metal polychelates.

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R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
Thermal analysis
ligand was compared to the polymers containing metal. For AGP,
the initial weight loss was 8%, corresponds to the loss of moisture
and other solvents. This loss was up to 11% due to loss of coordi-
nated water in AGP-Mn(II) but no appreciable loss was observed
for Ni(II), Co(II), Cu(II) and Zn(II) metal polychelates, thus favoring
four coordinated geometry for these metal polychelates and as
depicted from other data analysis. For AGP-M(II), up to 400 °C,
40–29% rapid weight loss was observed which shows the decom-
position of organic part while slow and steady decomposition
above 400 °C was due to the decomposition of inorganic part,
finally resulting in the formation of char at 800 °C.
The results reveal that metal polychelate of Cu(II) was compar-
atively more thermally stable than other metal polychelates. Order
of stability on the basis of thermal residual weight at 800 °C
appeared to be AGP-Cu(II) > AGP-Zn(II) > AGP-Co(II) > AGP-
Mn(II) > AGP-Ni(II). Data presented in the study clearly indicated
that improved thermal stability was due to the presence of transi-
tion metal in the polymeric chain.
Thermal stability of the metal polychelates strongly depends on
the structure of polymeric Schiff base and on the mode of complex-
ation [30–31]. Fig. 4 shows TGA thermograms of all of the synthe-
sized polymers. Degradation study was carried out at a linear
heating rate of 20 °C/min. in nitrogen atmosphere to the maximum
temperature of 800 °C. Thermal stability data (Table 4) of synthe-
sized polymeric Schiff base and its metal polychelates is important
to confirm the presence of metal ions, either as inclusion com-
plexes or as absorbed species. Metal ions present in the ligand
are expected to impart greater effect on thermal properties of the
chelating polymer [32–33]. Thus thermal degradation behavior of
Table 4
Thermal properties of polymeric Schiff base (AGP) and its metal polychelates.
Compounds Weight left (%) at the indicated
Characteristic
weight left (%) at
800 °C
temperature (°C)
Antimicrobial evaluation
100 200 300 400 500 600 700
AGP
93
94
93
94
96
95
79
86
89
91
92
91
60
72
75
73
80
77
48
60
68
65
71
68
35
55
57
55
62
56
23
43
48
43
48
42
12
32
33
31
35
30
2
9
11
7
14
12
Agar well diffusion method was used for the assessment of
antimicrobial action against some bacteria (E. coli, S. aureus, B. sub-
tilis) and fungi (C. albicans, M. canis, C. neoformans). Tetracycline
and Fluconazole were used as standard drugs for bacteria and fungi
respectively. Results of the activity showed that polychelates are
AGP-Mn(II)
AGP-Co(II)
AGP-Ni(II)
AGP-Cu(II)
AGP-Zn(II)
Table 5
Antimicrobial activity of polymeric Schiff base (AGP) and its metal polychelates.
Compound
Zones diameter showing complete growth inhibition (mm)
E. coli S. aureus B. subtilis
C. albicans
M. canis
C. neoformans
AGP
08
14
20
14
22
16
15
–
2
10
14
18
15
20
16
16
–
1
1
1
2
1
2
2
11
15
18
13
20
18
18
–
1
1
2
1
2
2
2
08
14
16
16
18
17
–
2
1
1
1
3
1
9
1
11
16
18
15
19
17
–
1
2
1
3
1
1
AGP-Mn(II)
AGP-Co(II)
AGP-Ni(II)
AGP-Cu(II)
AGP-Zn(II)
Tetracyclinea
Fluconazoleb
2
1
1
1
1
1
15
13
12
16
18
–
2
1
1
2
1
17
2
15
1
19
1
a
Standard drug (antibacterial activity).
Standard drug (antifungal activity).
b
Fig. 5. Inhibition growth of AGP and AGP-M(II).

R. Rasool, S. Hasnain / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 435–443
443
more biocidal in nature as compared to the ligand on some of the
microorganisms as summarized in Table 5 and shown in Fig. 5.
AGP-Cu(II) show high activity against E. coli, S. aureus, B. Subtilis,
C. albicans and C. neoformans (22, 20, 20, 18 and 19 mm) respec-
tively, while for M. canis AGP-Zn(II) shows high antifungal activity
(18 mm).
applications requiring thermal sterilization due to stable nature
at high temperatures.
Acknowledgments
Raza Rasool is thankful to University Grants Commission (New
Delhi, India) for providing financial support in the form of the Basic
Scientific Research Fellowship. The authors express their sincere
thanks to ‘‘The Third World Academy of Sciences, Italy’’ for UV–
Visible spectrophotometer EZ-201 (Perkin–Elmer) through
research grant scheme No. 00-047 RG/CHE/AS.
AGP-Co(II) and AGP-Zn(II) polychelates display promising
antibacterial activity (20, 18, 18 mm) and (16, 16, 18 mm) against
E. coli, S. aureus, B. Subtilis while promising antifungal activity was
also shown by AGP-Zn(II) 17 mm for C. albicans, AGP-Cu(II) 16 mm
for M. canis, AGP-Co(II) 18 mm for C. neoformans. Lowest antibacte-
rial activity was shown by AGP-Ni(II) (14, 13 mm) for E. coli, B.
Subtilis and AGP-Mn(II) 14 mm against S. aureus, and lowest anti-
fungal activity was shown by AGP-Ni(II) (12, 15 mm) for M. canis,
C. neoformans and 14 mm for AGP-Co(II) against M. canis.
Results reveal that antimicrobial activity of these metal-che-
lated polymers is due to the presence of nitrogen and oxygen donor
groups. Enhanced biological activity can be rationalized to the
structures possessing additional C@N bond and chelation. It has
been suggested that the compound with N and O donor system
inhibit enzyme production because enzymes that require a free
hydroxyl group for their activity appear to be especially suscepti-
ble to deactivation by the ions of the complexes [34].
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Polymeric ligand (AGP) and its metal polychelates with M(II)
acetates were synthesized in good yield. The identities of com-
plexes were established by microanalytical, magnetic, spectro-
scopic and thermal analysis. All polymeric compounds were
soluble in DMF and DMSO but insoluble in common organic sol-
vents. Because of their insoluble nature, the synthesized metal
polychelates can be used as solvent resistant coating materials. It
was observed that the attachment of metal ions in the polymeric
backbone enhanced thermal and anti-microbial activities. AGP-
Cu(II) showed best antibacterial as well as antifungal activity
whereas better inhibitory effects were observed in case of AGP-
Co(II) and AGP-Zn(II) for antibacterial and antifungal activity
respectively. Functional moieties such as azomethine group exhibit
potential biological activities that may be responsible for the
enhanced hydrophobic and lipophilic character of the molecule
to cross-link the cell membrane of the microorganism and increase
the biocidal activity of the polychelate. Being biologically active
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