Synthesis, characterization and biocidal activities of Schiff base polychelates containing polyurethane links in the main chain

Article abstract of DOI:10.1016/j.saa.2012.04.018

The concept of combining metallo-polymers with urethanes offers a versatile approach for the synthesis of new polymeric materials. Polyurethane containing transition metals was synthesized by the reaction of Schiff base metal complex with toluene 2,4 diisocyanate. The proposed structures were confirmed by elemental analysis, ¹H NMR, ¹³C NMR and FT-IR. The geometry is determined by UV-Visible spectra and magnetic moment measurements, which reveals that the Mn(II), Co(II) and Ni(II) complexes have octahedral geometry while square planer geometry is reported for Cu(II) and tetrahedral for Zn(II) complex. The antimicrobial activities are determined using the agar well diffusion method with Staphylococcus aureus, Escherichia coli, Bacillus subtilis (bacteria), Aspergillus niger, Candida albicans and Aspergillus flavus (yeast). All the polymeric metal complexes show comparatively good biocidal activity, which is further enhanced after polymerization.

Full text of DOI:10.1016/j.saa.2012.04.018

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 452–457
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and biocidal activities of Schiff base polychelates
containing polyurethane links in the main chain
⇑
Sumaiya Hasnain, Nahid Nishat
Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi 110 025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The concept of combining metallo-polymers with urethanes offers a versatile approach for the synthesis
of new polymeric materials. Polyurethane containing transition metals was synthesized by the reaction
of Schiff base metal complex with toluene 2,4 diisocyanate. The proposed structures were confirmed by
elemental analysis, 1H NMR, 13C NMR and FT-IR. The geometry is determined by UV–Visible spectra and
magnetic moment measurements, which reveals that the Mn(II), Co(II) and Ni(II) complexes have octa-
hedral geometry while square planer geometry is reported for Cu(II) and tetrahedral for Zn(II) complex.
The antimicrobial activities are determined using the agar well diffusion method with Staphylococcus
aureus, Escherichia coli, Bacillus subtilis (bacteria), Aspergillus niger, Candida albicans and Aspergillus flavus
(yeast). All the polymeric metal complexes show comparatively good biocidal activity, which is further
enhanced after polymerization.
Received 3 December 2011
Received in revised form 20 March 2012
Accepted 5 April 2012
Available online 23 April 2012
Keywords:
Antimicrobial activity
Metal containing polyurethanes
Schiff base
Toluene 2,4 diisocyanate
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
heart, blood pumps and valves. Several metallo-polymers contain-
ing metals in the backbone of the polymer chain have already been
In polymer science, there is continuous requirement for the
development of materials that are stronger, durable and inhibit
microbes. From the last few years, extensive efforts have been
made, both in academics and in industry to develop the Schiff base
polymers, as they possess high thermal stability, complex forming
ability and semiconducting properties. The incorporation of transi-
tion metals into polymeric Schiff bases not only affects their
physical characteristics, but also their chemical activity [1].
Complexation of a metal ion to functional polymeric ligand
changes its activity due to polymeric effect, which has led to a vari-
ety of applications such as aqueous thickeners, impregnates, textile
seizers, adhesives, additives, resins and catalysts [2–4]. Their cata-
lytic actions in a variety of organic reactions have been known for a
long time [5,6]. Polyurethanes are the most versatile family of
polymeric materials due to the fact that they are used in many
forms and find their way into many applications [7,8]. Polyure-
thane coatings mainly moisture-cured are applied on products to
improve their appearance, lifespan, scratch and corrosion resis-
tance [9,10]. Modification of polyurethanes by incorporating metal
and functional groups are used extensively to improve various
typically desired properties of materials, such as enhanced thermal
stability, fire redundancy, flexibility and solubility [11]. These are
also extensively used in biological applications such as artificial
prepared [12,13]. So the synthesis and structural studies of new
compounds of this type have much interest as a first step in the
search for new Schiff base polymers as potential antimicrobial
agents. Keeping the foregoing facts in mind and in continuation
to our research work in this domain [14–17], novel Schiff base
polyurethane containing transition metal ions in the main chain
has been synthesized, and their spectral, magnetic and antimicro-
bial properties have been discussed.
Experimental
Materials
Semicarbazide and toluene-2,4-diisocyanate, salicylaldehyde,
formaldehyde (37–41%) and dimethylsulfoxide were obtained
from S.D. fine chemicals and Merck India, while Manganese(II) ace-
tate tetrahydrate, cobalt(II) acetate tetrahydrate, nickel(II) acetate
tetrahydrate, copper(II) acetate monohydrate and zinc(II) acetate
dihydrate were purchased from Qualigens fine chemicals, India.
These chemicals were all used as received.
Synthesis
Synthesis of monomeric ligand
Semicarbazide (0.01 mol, 1.11 g) was dissolved in minimum
amount of distilled water in 250-mL three-necked round-bottom
flask and was attached to the ice-cooled reflux condenser fitted
⇑
Corresponding author.
E-mail addresses: hasnain.sumaiya@gmail.com (S. Hasnain), nishat.nch
em2010@gmail.com (N. Nishat).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.04.018

S. Hasnain, N. Nishat / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 452–457
453
[C17H19N3O7Ni(II)]: C% = 46.72 (44.98), H% = 4.39 (3.61),
N% = 9.63 (8.24), Ni(II)% = 13.46 (12.90); Cal.(Found).
IR (KBr): 1162 cmꢀ1 (w, CAO), 1722 cmꢀ1 (m, C@O), 1548 cmꢀ1
(m, CH@N), 3375 cmꢀ1 (m, NH), 1626 cmꢀ1 (w, dNH), 521 cmꢀ1
t
(m, MAO), 448 cmꢀ1 (m, MAN), MAH2O(rocking)=981 cmꢀ1
MAH2O(wagging)=749 cmꢀ1
,
.
[C17H15N3O5Cu(II)]: C% = 50.41 (51.21), H% = 3.73 (3.06),
N% = 10.37 (11.71), Cu(II)% = 15.69 (14.98); Calc. (Found).
IR (KBr): 1159 cmꢀ1 (w, CAO), 1720 cmꢀ1 (m, C@O), 1548 cmꢀ1
Fig. 1. Monomeric ligand [SSF].
(m, CH@N), 3382 cmꢀ1 (m, NH), 1620 cmꢀ1 (w, dNH), 525 cmꢀ1
t
over the magnetic stirrer and maintained at 50 °C. Salicylaldehyde
(0.02 mol, 2.44 mL) was dissolved in 20 mL ethanol and added drop
wise by a burette to the semicarbazide solution, and the reaction
mixture was stirred continuously for about 2 h. Solvent was re-
moved by filtration, washed with distilled H2O and diethyl ether
several times and finally dried at 30–40 °C in vacuum oven for
8 h to give Schiff base semicarbazone (2.15 g, 76.2% yield). Its melt-
ing point is 110 °C.
(m, MAO), 452 cmꢀ1 (m, MAN).
(m = medium, w = weak).
[C17H15N3O5Zn(II)]: C% = 50.20 (48.96), H% = 3.71 (3.01),
N% = 10.33 (9.27), Zn(II)% = 16.07 (15.11); Cal.(Found).
IR (KBr): 1161 cmꢀ1 (w, CAO), 1720 cmꢀ1 (m, C@O), 1552 cmꢀ1
(m, CH@N), 3377 cmꢀ1 (m, NH), 1626 cmꢀ1 (w, dNH), 516 cmꢀ1
t
(m, MAO), 450 cmꢀ1 (m, MAN).
(m = medium, w = weak).
The dried Schiff base (2.15 g, 0.01 mol) was further dissolved in
DMSO and heated at 60 °C. Formaldehyde (37–40%) (0.15 mL,
0.02 mol) was added to this hot solution of Schiff base in the
three-necked round-bottom flask attached to a water condenser,
the reaction mixture was further heated at this temperature for
2 h. Monomeric ligand [SSF] was obtained after washing it with
distilled water, diethyl ether and drying at 40 °C. Its melting point
was approx. 115 °C. Proposed structure of monomeric ligand is
represented in Fig. 1.
Elemental analysis and FT-IR spectral data suggest that the
disappearance of phenolic OH peak and shifting of azomethine
and hydroxyl carbon peak to lower frequency is due to the coordi-
nation of metal to the hydroxyl oxygen and azomethine nitrogen.
Proposed structure for monomeric metal complexes has been
provided in Fig. 2.
Synthesis of metal containing polyurethane [SPU-M(II)]
Above prepared monomeric metal complex, as for Mn(II), 2.87 g,
0.01 mol, was dissolved in DMSO and taken in a three-necked
round-bottom flask. The temperature of the flask was set up to
80 °C and stirred magnetically. Then, toluene 2,4-diisocyanate
(TDI) (0.01 mol, 1.74 mL) was added to this solution in the presence
of 2–3 drops of di-n-butyltindilaurate (DBTDL) as catalyst. The
reaction mixture was stirred at this temperature for 6 h. It was pre-
cipitated and washed with distilled water, then with diethyl ether
and dried at room temperature for 24 h to give metal-chelated
polyurethane [SPU-Mn(II)] in 68.9% yield. Synthetic route to metal
containing polyurethane is represented in Scheme 1.
IR (KBr): 3424 cmꢀ1(sb, OH), 1173 cmꢀ1(m, CAO), 1720 cmꢀ1(s,
C@O), 1566 cmꢀ1(m, CH@N), 3389 cmꢀ1(mb, NH), 1626 cmꢀ1(w,
NH).
(sb = strong and broad, m = medium, mb = medium and broad,
w = weak).
1H-NMR:
7.89 ppm(2H,
CH@N),
2.7 ppm(4H,
CH2),
10.06 ppm(4H, OH), 7.02 ppm(1H, NH), 6.12–6.70 ppm(6H, C6H3)
for the azomethine linkage, methylene, hydroxyl, NH and phenyl
groups, respectively.
Synthesis of monomeric metal complexes
A series of transition metal complexes of Mn(II), Co(II), Ni(II),
Cu(II) and Zn(II) were prepared from the monomeric ligand [SSF].
A typical procedure for the preparation of manganese monomeric
complex is as follows:
Preparation of microbial culture
The antimicrobial activities of the metal containing polyure-
thanes were tested against various microorganisms in DMSO as
The monomeric Schiff base [SSF] was dissolved in 20 mL DMSO
and heated at 70 °C in a round-bottom flask fitted to an ice-cooled
condenser. Manganese(II) acetate tetrahydrate (1.27 g, 0.01 mol)
dissolved in DMSO was added to this hot solution and refluxed
for 6–7 h, slight change in color appears. It was precipitated in dis-
tilled H2O, filtered and washed several times with distilled H2O and
diethyl ether. It was oven-dried at 45 °C for 8–10 h to obtain the
monomeric metal complex of manganese [SSF-Mn(II)] of light yel-
low color.
the solvent. The sample concentration was 50
lg/mL for antibacte-
rial studies and 100 g/mL for antifungal studies. The antibacterial
l
activity was screened against Staphylococcus aureus, Bacillus subtilis
(Gram-positive) and Escherichia coli (Gram-negative), while anti-
fungal screening was done against Aspergillus niger, Candida
albicans and Aspergillus flavus.
Bacterial strains were nourished in a nutrient broth (Difco) and
yeasts in malt extract broth (Difco) and incubated for 24 and 48 h,
respectively. According to the agar-diffusion method [18,19], bacte-
ria were incubated on Mueller–Hinton agar and yeast on Sabouraud
dextrose agar. The wells were dug in the media with the help of a
sterile steel borer, and then 0.1 mL of each sample was introduced
in the corresponding well. Standard drugs, kanamycin and
Similar procedure was used to isolate the Co(II), Ni(II), Cu(II)
and Zn(II) complexes. Analytical data of these complexes are given
below:
[C17H19N3O7Mn(II)]: C% = 47.23 (46.21), H% = 4.43 (3.98),
N% = 9.72 (9.01), Mn(II)% = 12.70 (13.11); Cal.(Found).
IR (KBr): 1161 cmꢀ1 (w, CAO), 1720 cmꢀ1 (m, C@O), 1551 cmꢀ1
(m, CH@N), 3376 cmꢀ1 (m, NH), 1628 cmꢀ1 (w, dNH), 515 cmꢀ1
t
(m, MAO), 447 cmꢀ1 (m, MAN), MAH2O(rocking)=980 cmꢀ1
MAH2O(wagging)=742 cmꢀ1
,
.
[C17H19N3O7Co(II)]: C% = 46.80 (45.10), H% = 4.39 (3.11),
N% = 9.63 (8.52), Co(II)% = 13.50 (12.72); Cal.(Found).
IR (KBr): 1160 cmꢀ1 (w, CAO), 1721 cmꢀ1 (m, C@O), 1550 cmꢀ1
(m, CH@N), 3380 cmꢀ1 (m, NH), 1625 cmꢀ1 (w, dNH), 520 cmꢀ1
t
(m, MAO), 449 cmꢀ1 (m, MAN), MAH2O(rocking)=981 cmꢀ1
MAH2O(wagging)=746 cmꢀ1
,
.
Fig. 2. Proposed structure of monomeric metal complexes [SSF-M(II)].

454
S. Hasnain, N. Nishat / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 452–457
Scheme 1. Synthetic route to metal containing polyurethane [SPU-M(II)].
miconazole, were taken as control for bacteria and fungi, respec-
tively. After incubation, the zone of inhibition was measured, and
according to the zone of inhibition and clarity of the zone, results
are represented as inactive, mildly active, moderately active and
highly active.
DMF, while these are insoluble in THF and other common organic
solvents such as benzene, toluene, ethanol, methanol and water.
FT-IR analysis
The IR spectrum of Schiff base [SSF] shows a characteristic
absorption peak at 1566 cmꢀ1 for the formed azomethine linkage,
while a very broad absorption peak is observed at 3424 cmꢀ1 for
the OH group with a small shoulder which is for the overlapping
of NAH peak with OH peak. Thereafter, Mn(II), Co(II), Ni(II), Cu(II)
and Zn(II) complexes are prepared. The IR spectra of the metal
complex show two additional peaks in the range of 447–452 and
515–525 cmꢀ1 due to MAN and MAO bond formation while azo-
methine band shifts slightly to lower frequency (15–20 cmꢀ1),
revealing the complexation of metal ion to ligand. Coordinated
Measurements
Elemental analysis of C, H and N was carried out on an elemental
analyzer system GmbH Vario ELIII, while the percentage of metal
was obtained by complexometric titration with EDTA after
digestion with conc. HNO3 at room temperature. The magnetic sus-
ceptibility measurements are recorded on a vibrating sample mag-
netometer model 155 at room temperature. FT-IR spectra are
obtained on a Perkins Elmer IR spectrophotometer model 621 using
KBr pellets. Proton and carbon nuclear magnetic resonance spectra
(1H NMR and 13C NMR) are recorded on a JEOL-GSX 300 MHz FX
1000 FT NMR spectrometer using DMSO as a solvent and Tetra-
methylsilane (TMS) as an internal standard. The UV–Visible spectra
are carried on a Perkins Elmer Lambda EZ-201 spectrophotometer
using DMSO as a solvent.
water peaks appear at 980–982 cmꢀ1 and 742–747 cmꢀ1
.
IR absorption bands for SPU-M(II) are illustrated in Table 2. The
IR spectrum show peaks at 1720 cmꢀ1 due to carbonyl stretching
(AC@O) [22] and the absorption band at 1159–1161 cmꢀ1 due to
phenolic (CAO). The peak at 3374–3382 cmꢀ1 is due to ANH
stretching and at 1628–1620 cmꢀ1 due to NH bending. Carboxylate
ions (ACOO) give two broad peaks in the range of 1552–1559 cmꢀ1
and 1462–1466 cmꢀ1. The characteristic C@O peak is observed at
1720 cmꢀ1 while and CH@N peaks observed at 1566 cmꢀ1 [23] is
shifted to 15–25 cmꢀ1 to lower frequency after chelation, indicating
that nitrogen is involved in bond formation with the metal. The
coordination of metal ion to the polymeric ligand is supported by
the appearance of MAN, MAO and MAH2O stretching vibrations
Results and discussion
The monomeric ligand and its metal polychelates are synthe-
sized by the reaction of semicarbazide with salicylaldehyde, and
then formaldehyde is attached to the formed Schiff base. Here,
one thing is to be taken care of that the ratio of formaldehyde to
Schiff base must be 1:1 in order to avoid polymerization [20].
The ligand formed is tetradentate, with oxygen of salicylaldehyde
and nitrogen of semicarbazide being involved in coordination. All
the metal complexes are hydrated with the exceptions of the Cu(II)
and Zn(II) complexes. Polyaddition of toluene 2,4-diisocyanate
(TDI) with metal-chelated Schiff base [SSF-M(II)] is done in the
presence of DBTDL to obtain metal-chelated polyurethane [SPU-
M(II)]. Reaction between diols and diisocyanates is catalyzed by
DBTDL, and it takes place via the formation of a ternary complex
between the reagents and the catalyst [21]. To avoid cross-linking
of the polymers, the mole ratio of mixtures of diols and diisocya-
nates is taken as 1:1. The elemental analysis data of all the poly-
mers show that the experimentally determined percentage
values of C, H, N and M are within the calculated values, results
being depicted in Table 1.
at 447–452 cmꢀ1
,
515–525 cmꢀ1 and 980–982 cmꢀ1(rocking),
742–747 cmꢀ1(wagging) for coordinated water, respectively [24].
NMR analysis
1H NMR spectrum of SPU-Zn(II) is shown in Fig. 3. The spectrum
shows signals for NH proton of the urethane group (ANHAC@
OAOA) at around 9.05 ppm. Resonance signals in the range of
6.40–7.96 ppm appeared due to the aromatic protons of TDI and
benzene ring. The peak at 8.14 is for the proton linked to the carbon
of salicylaldehyde (ACH@NA) [25]. NHA protons of semicarbazide
appear at 7.05 ppm. Methyl and methylene protons appear at 2.3
and 2.9 ppm, respectively.
13C-NMR spectrum of SPU-Zn(II) is shown in Fig. 4. The aro-
matic carbons of urethane group show peaks at 137.93, 119.06
and 115.99 ppm [26]. Methyl and methylene carbons show peaks
at 17.32 ppm and 19.20 ppm. Carbonyl carbon of urethane group
(NHCOOA) show peak at 152.68 ppm. Five carbons of benzene ring
show peaks in the range of 120.11–130.02 ppm [27], while the
Solubility data
The synthesized Schiff base polychelates [SSF-M(II)] and poly-
urethanes containing metal [SPU-M(II)] are soluble in DMSO and

S. Hasnain, N. Nishat / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 452–457
455
Table 1
Elemental analysis data.
Compound abbreviation
Empirical formula
Elemental analysisa (%)
Carbon
Hydrogen
Nitrogen
Metal
Semicarbazone Schiff base
SSF
SPU-Mn(II)
SPU-Co(II)
SPU-Ni(II)
SPU-Cu(II)
C
C
C
C
C
C
C
15H13N3O3
17H17N3O5
66.44 (65.19)
59.46 (58.21)
51.49 (50.24)
51.15 (50.26)
51.17 (50.54)
53.93 (53.22)
53.76 (53.15)
4.26 (3.11)
4.99 (3.56)
4.15 (4.05)
4.12 (3.22)
4.12 (4.00)
3.65 (3.45)
3.64 (3.04)
13.67 (12.54)
12.23 (11.71)
11.54 (10.98)
11.47 (10.11)
11.47 (11.09)
12.09 (11.85)
12.05 (11.74)
–
–
26H21N5O7-Mn(II)-(H2O)2
26H21N5O7-Co(II)-(H2O)2
26H21N5O7-Ni(II)-(H2O)2
26H21N5O7-Cu(II)
26H21N5O7-Zn(II)
9.05 (8.83)
9.65 (9.11)
9.61 (9.17)
10.97 (10.61)
11.25 (10.93)
SPU-Zn(II)
(Observed) value.
a
Calculated value.
Table 2
Important FT-IR spectral bands of metal containing polyurethane with their assignments.
Assignments
SPU-Mn(II)
SPU-Co(II)
SPU-Ni(II)
SPU-Cu(II)
SPU-Zn(II)
C@O (urethane) stretching Bending
NAH (stretching) bending
C@O (carbonyl)
CH@N (azomethine)
CAO (phenolic)
MAO
MAN
MAH2O (rocking)
(wagging)
1556(s) 1462(m)
3376(s) 1628(w)
1720(s)
1551(s)
1161(w)
515(s)
452(s)
980
742
1559(s) 1465(m)
3374(s) 1622(w)
1720(s)
1546 (s)
1160(w)
518(s)
450(s)
982
745
1552(s) 1466(m)
3374(s) 1625(w)
1720(s)
1549 (s)
1160(w)
522(s)
447(s)
982
747
1558(s) 1462(m)
1552(s) 1466(m)
3380(s) 1626(w)
3382(s) 1620(w)
1720(s)
1541 (s)
1159(w)
525(s)
452(s)
–
–
1720(s)
1546(s)
1159(w)
520(s)
452(s)
–
–
(s) Strong, (m) medium, (b) broad, (w) weak.
Fig. 3. 1H NMR OF SPU-Zn(II).
characteristic peak of phenolic carbon is observed at 155.76 ppm.
The azomethine carbon (ACH@NA) show peak at 137.64 ppm.
compound. The polymer metal complex of Co(II) had the magnetic
moment of 4.80 B.M. due to four unpaired electrons and electronic
transitions at 9580, 17,586 and 19,960 cmꢀ1 corresponds to
4T2g 4T1g, 4A2g 4T1g and 4T1g(P) 4T1g transitions, respectively
[29]. The spectral parameters 10Dq = 7742.7 cmꢀ1, B = 860.3 cmꢀ1
,
UV–Visible analysis
b = 0.88 and b° = 0.12 suggest the covalent nature of the compound.
The magnetic moment of SPU-Ni(II) complex is 2.86 B.M. Three
bands are observed at 8580, 12,650 and 23,380 cmꢀ1 corresponding
The electronic spectra of all the synthesized polymers are re-
corded in DMSO solution. Various crystal field parameters 10Dq, B,
b and b° have been calculated. The magnetic moment of SPU-Mn(II)
is 5.6 B.M. corresponding to five unpaired electrons. The electronic
spectrum of this complex exhibits three absorption bands at
3
3
to T2g 3A2g
,
3T1g 3A2g and T1g(P) 3A2g transitions, respec-
tively. Spectral parameters 10Dq = 8904.0 cmꢀ1, B = 742.2 cmꢀ1
,
b = 0.68 and b° = 0.32 are suggestive of the octahedral structure of
the complex [30]. SPU-Cu(II) has magnetic moment of 2.18 B.M.
and shows bands at 15,570 and 25,365 cmꢀ1 assigned to
2A1g 2B1g(F) and charge transfer band, respectively, indicative of
square planer geometry. The SPU-Zn(II) is diamagnetic and no d–d
transition being observed.
14,380, 19,760 and 24,650 cmꢀ1, which are assigned to 4T1g 6A1g
,
4T2g 6A1g and 4Eg 6A1g transitions, respectively, suggesting the
octahedral geometry [28]. The 10Dq and
B are 3944.3 and
788.8 cmꢀ1, respectively, while b and b° values are 0.82 and 0.18,
respectively. These values indicate the covalent nature of the

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S. Hasnain, N. Nishat / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 452–457
Fig. 4. 13C NMR OF SPU-Zn(II).
Antimicrobial activity
the metal ion mainly because of the partial sharing of its positive
charge with the donor groups and possibly the -electron delocal-
p
Polymeric ligand [SSF] and its polymeric metal complexes
[SPU-M(II)] are screened for their antibacterial activity against
S. aureus, E. coli and B. subtilis and antifungal activity against A. niger,
C. albicans andA. flavus, and the results are presented in Fig. 5. A gen-
eral trend can be seen that the Cu(II) and Zn(II)-chelated polymer
complexes are more active than other metal-containing polymers.
SPU-Cu(II) and SPU-Zn(II) show high activity against all the tested
bacteria. SPU-Cu(II) is highly active against A. niger and moderately
active against C. albicans, and A. flavus. SPU-Zn(II) is highly active
against C. albicans and A. flavus, but SPU-Co(II) show moderate activ-
ity against these fungi while other polychelates show mild activity.
SPU-Co(II) is highly active against E. coli, while other polychelates
are mildly to moderately active.
It is also evident that all the polymer metal complexes are more
active than the polymeric ligand. This enhancement in the activity
is rationalized on the basis of the structures by possessing an addi-
tional azomethine (C@N) linkage, which imparts in elucidating the
mechanism of transamination and resamination reactions in bio-
logical system [31]. It has also been suggested that the ligands with
nitrogen and oxygen donor systems might inhibit enzyme produc-
tion, since the enzymes that require these groups for their activity
appear to be especially more susceptible to deactivation by the
metal ions upon chelation. Chelation reduces the polarity [32] of
ization within the whole chelate ring system thus formed during
coordination. This process of chelation thus increases the lipophilic
nature of the central metal atom, which in turn favors its perme-
ation through the lipoid layer of the membrane. This in turn is
responsible for increasing the hydrophobic character and lipo-
solubility of the molecule in crossing cell membrane of the micro-
organism, and hence enhances the biological utilization ratio and
activity of the testing drug/compound.
Conclusion
Polyurethanes containing Schiff base and metal in the main
chain underwent addition polymerization giving metal containing
polyurethanes in good yield. Both the ligand and metal complexes
are insoluble in benzene, toluene, ethanol, methanol and H2O but
soluble in DMSO and DMF. Besides chelation, other factors such
as solubility, stability influenced by metal ion may be responsible
for enhanced antibacterial activity of the polychelates. Functional
moieties such as the azomethine group and urethane group exhibit
potential biological activities that may be responsible for the en-
hanced hydrophobic and lipophilic character of the molecule to
cross-link the cell membrane of the microorganism and increase
the biocidal activity of the polychelate.
Acknowledgements
S. Hasnain wishes to thank the Council of Scientific and Indus-
trial Research (C.S.I.R), New Delhi for financial support in the form
of the Senior Research Fellowship.
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