Synthesis, spectral and antimicrobial activity of Zn(II) complexes with Schiff bases derived from 2-hydrazino-5-[substituted phenyl]-1,3,4-thiadiazole and benzaldehyde/2-hydroxyacetophenone/indoline-2,3-dione

Article abstract of DOI:10.1016/j.saa.2013.04.045

(Chemical Equation Presented) Zn(II) complexes have been synthesized by reacting zinc acetate with Schiff bases derived from 2-hydrazino- 5-[substituted phenyl]-1,3,4-thiadiazole and 2-hydroxyacetophenone/benzaldehyde/indoline-2, 3-dione. All these comple

Full text of DOI:10.1016/j.saa.2013.04.045

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Synthesis, spectral and antimicrobial activity of Zn(II) complexes with
Schiff bases derived from 2-hydrazino-5-[substituted phenyl]-1,3,
4-thiadiazole and benzaldehyde/2-hydroxyacetophenone/indoline-2,3-
dione
1
⇑
Ajay K. Singh , O.P. Pandey, S.K. Sengupta
Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273 009, 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
ꢀ
ꢀ
ꢀ
ꢀ
Zn(II) complexes with Schiff bases
containing 1,3,4-thiadiazole ring have
been synthesized and characterized.
Schiff bases and their corresponding
Zn(II) complexes are bactericidal in
nature.
Isatin derived compound 10 showed
maximum activities against all
microbes.
MIC value of compound 10 was
comparable to any commercial
synthetic pesticide.
a r t i c l e i n f o
a b s t r a c t
Article history:
Zn(II) complexes have been synthesized by reacting zinc acetate with Schiff bases derived from 2-hydra-
zino-5-[substituted phenyl]-1,3,4-thiadiazole and 2-hydroxyacetophenone/benzaldehyde/indoline-2,
3-dione. All these complexes are soluble in DMF and DMSO; low molar conductance values indicate that
they are non electrolytes. Elemental analyses suggest that the complexes have 1:2 metal to ligands stoichi-
ometry of the types [ZnL2(H2O)2](L = monoanionic Schiff bases derived from 2-hydrazino-5-[substituted
Received 27 November 2012
Received in revised form 5 April 2013
Accepted 10 April 2013
Available online 18 April 2013
phenyl]-1,3,4-thiadiazole and 2-hydroxyacetophenone/indoline-2,3-dione) [ZnL0 (OOCCH3)2(H2O)2]
2
Keywords:
(L0 = neutral Schiff bases derived from 2-hydrazino-5-[substituted phenyl]-1,3,4-thiadiazole and benzalde-
hyde), and they were characterized by IR, 1H NMR, and 13C NMR. Particle sizes of synthesized compounds
were measured with dynamic light scattering (DLS) analyser which indicates that particle diameter are of
the range ca. 100–200 nm. All these Schiff bases and their complexes have also been screened for their anti-
bacterial (Bacillus subtilis (B. subtilis), Escherichia coli (E. coli) and antifungal activities (Colletotrichum falca-
tum (C. falcatum), Aspergillus niger (A. niger), Fusarium oxysporium (F. oxysporium) Curvularia pallescence (C.
pallescence). The antimicrobial activities have shown that upon complexation the activity increases.
Ó 2013 Elsevier B.V. All rights reserved.
Zn(II) complexes
Schiff bases
DLS analysis
Antifungal
Antibacterial
Introduction
antitumor properties [1–4], and other useful application are con-
ducting polymer [5,6], solar cell [7], sensor [8,9], enzymatic appli-
1,3,4-Thiadiazole derivatives are important class of biological
active compounds showing anti-inflammatory, antimicrobial,
cation [10], energy storage [11], electrodes [12], anxiolytic activity
[13], etc. Schiff base ligands are able to coordinate many elements
⇑
Corresponding author. Tel.: +91 551 2203621.
E-mail address: sengupta@hotmail.co.uk (S.K. Sengupta).
Present address: Department of Chemical Engineering, Pohang University of Science and Technology, Hyoja-dong, Nam-gu, Pohang 790-784, Republic of Korea.
1
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.04.045

394
A.K. Singh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
Table 1
Physical properties and analytical data of Zn(II) complexes.
Complex Mol. formula
% yield/color
Decomp. Temp.
(°C)/kM
Molecular weight
found(Cal.)
% Analysis found(Cal.)
*
C
H
N
S
Zn
1
2
C
C
34H34N8O6S2Zn
34H32N8O6Cl2
64/Light green
67/Yellow
204/18
270/19
780(780.22)
849(849.11)
52.22(52.34) 4.16(4.39) 14.12(14.36) 8.10(8.22) 8.11(8.38)
47.84(48.09) 3.45(3.80) 13.05(13.20) 7.34(7.55) 7.35(7.70)
S2Zn
3
4
C34H32N8O6Cl2
S2Zn
C34H32N10O10S2Zn
71/Yellow
260/19
240/20
848(849.11)
870(870.21)
47.80(48.09) 3.55(3.80) 13.07(13.20) 7.32(7.55) 7.45(7.70)
46.84(46.93) 3.47(3.71) 16.02(16.10) 7.24(7.37) 7.37(7.52)
74/Greenish-
yellow
5
6
7
8
C32H30N8O4S2Zn
70/White
280/12
220/13
280/13
220/14
719(720.17)
788(789.06)
788(789.06)
810(810.16)
53.24(53.37) 4.12(4.20) 15.24(15.56) 8.45(8.90) 8.65(9.08)
48.44(48.71) 3.33(3.58) 14.04(14.20) 8.01(8.13) 8.11(8.29)
48.52(48.71) 3.48(3.58) 14.01(14.20) 8.07(8.13) 8.09(8.29)
C
C
C
32H28N8O4Cl2S2Zn 72/Yellow
32H28N8O4Cl2S2Zn 68/Yellow
32H28N10O8S2Zn
63/Brown
47.21(47.44) 3.15
(3.48)
17.11(17.29) 7.64(7.92) 7.90(8.07)
9
10
C32H24N10O4S2Zn
C32H22N10O4Cl2
75/Orange
67/Brown
170/7
230/8
742(742.13)
810(811.02)
51.48(51.79) 3.16(3.26) 18.55(18.87) 8.44(8.64) 8.63(8.81)
47.19(47.39) 2.58(2.73) 17.04(17.27) 7.55(7.91) 7.71(8.07)
S2Zn
11
12
C32H22N10O4Cl2
S2Zn
C32H22N12O8S2Zn
62/Chocolate
210/8
810(811.02)
831(832.13)
47.14(47.39) 2.41(2.73) 17.14(17.27) 7.66(7.91) 7.71(8.07)
46.03(46.19) 2.44(2.66) 20.02(20.20) 7.45(7.71) 7.41(7.86)
72/Light
orange
220/10
*
Ohmꢁ1 cmꢁ1 molꢁ1 (in DMSO).
and to stabilize them in various oxidation states. Furthermore,
Schiff bases have been known to be used in the preparation of
many potential drugs, and are known to possess a broad spectrum
of biological activities such as antiviral [14], antifungal [15], anti-
parasitic [16], antibacterial [17], anti-inflammatory [18], antitumor
[19], anti-HIV [20], and anticancer [21]. Schiff bases derived from
1,3,4-thiadiazole have been synthesized and extensively studied
because they have some typical properties such as manifestations
of original structures, thermal stability, significant biological prop-
erties, high synthesis flexibility and therapeutic utility [22]. Previ-
ously, many scientists reported that after complexation of
transition metal complexes to Schiff bases microbial activity was
generally increased [23].
acceptable limits ( 0.5). Molar conductance of 10ꢁ3 M solutions
of the complexes in DMSO was recorded on a Hanna EC 215 con-
ductivity meter by using 0.01 M KCl water solution as calibrant.
The purity of compounds was checked by thin layer chromatogra-
phy on silica gel plate using ether and ethyl acetate as a solvent
system. Iodine chamber was used as a developing chamber.
Synthesis of 5-[substituted phenyl] 2- mercapto-1,3,4-thiadiazole
5-[Substituted phenyl]-2-mercapto-1,3,4-thiadiazoles were
prepared according to the method of Mishra et al. [24].
Because of interesting observations on synthetic routes and
applicability of zinc(II) complexes and Schiff bases, it was thought
be of interesting to study the coordination behaviour of Schiff
bases containing thiadiazole ring and to study their antimicrobial
properties.
Preparation of 5-(substituted phenyl)-2-hydrazino-1,3,4-thiadiazole
A mixture of 5-[substituted phenyl]-2-mercapto-1,3,4-thiadia-
zole and hydrazine hydrate in 1:1 molar ratio in ethanol was re-
fluxed for about 4–5 h on water bath. The reaction mixture was
cooled to room temperature; within an hour the compound precip-
itated from the clear solution. It was filtered off, washed and
recrystallized in ethanol.
Experimental
Materials and reagents
The solvents and used chemicals were purchased from Merck
and used without further purification. Zinc acetate dihydrate was
purchased from Sigma–Aldrich.
Synthesis of Schiff bases (L1–L12H)
A mixture of 5-[substituted phenyl]-2-hydrazino-1,3,4-thiadia-
zole
and
benzaldehyde/2-hydroxyacetophenone/indoline-2,
3-dione in 1:1 molar ratio was refluxed in ethanol (25 cm3)
containing few drops of conc. HCl for 5–6 h. The product was sep-
arated out on evaporation of the ethanol which was recrystallized
in ethanol/ether (1:1).
Instruments
Melting points/decomposition temperature were determined
on a Buchi 530 apparatus in open capillary tubes. FAB mass spectra
were obtained on a JEOL SX-120/DA6000 spectrometer using argon
(6 kV, 10 mA) as the FAB gas. FT-IR spectra were recorded on a
Shimadzu 8201 PC model FT-IR spectrophotometer as KBr disks.
1H and 13C NMR spectra were recorded on a Bruker DRX-300 spec-
trometer using DMSO-d6 as solvent. Chemical shifts (d) are
reported in parts per million (ppm) relative to an internal standard
of Me4Si. Elemental Analyses were recorded by Elementar Vario EL
III Carlo Erba 1108 models. Dynamic radiuses of synthesized com-
plexes were measured with help of Nano BioChem DLS analyser.
Powdered XRD were scanned by Philips Xpert X-ray diffractometer
Synthesis of zinc(II) complexes
Zn(II) complexes with ligands L1–L4
An ethanolic solution (30 cm3) of Zn(II) acetate dihydrate
(0.01 mol) was added to a refluxing solution of appropriate Schiff
base (L1–L4) (0.02 mol) in ethanol (30 cm3). The reaction mixture
was refluxed for about 8–11 h. The colored complex was obtained.
The complex was filtered off, washed thoroughly with ethanol and
dried under vacuo at room temperature. The complexes were
obtained as powdered material.
with CuK
a (1.54056) radiation. Elemental analysis (C, H, N, Zn)
indicates that the found and calculated values were within

A.K. Singh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
395
N
N
SH
R
R
S
NH2NH2.H2O
N
N
NHNH2
S
Isatin
Benzaldehyde
2-Hydroxyacetophenone
N
N
N
N
N
N
R'
R
NH
N
R''
NH
NH
N
S
S
S
CH3
R'=C6H5(L5H);
R'=2-ClC6H4(L6H);
R'=4-ClC6H4(L7H);
N
C
R''=C6H5(L9H);
R=C6H5 (L1);
R=2-ClC6H4 (L2);
R=4-ClC6H4 (L3);
CH
OH R''=2-ClC6H4(L10H);
R''=4-ClC6H4(L11H);
R''=4-O2C6H4(L12H)
NH
O
R'=4-NO2C6H4(L8H)
R=4-NO2C6H4 (L4)
Zn(OAc)2.2H2O
CH3COONa
Zn(OAc)2.2H2O
CH3COONa
Zn(OAc)2.2H2O
NH
N
N
N
N
N
N
R''
R'
S
S
NH
N
R
NH
S
H2O
H2O
CH3
O
N
H2O
AcO
N
N
C
O
N
Zn
H2O
Zn
H2O
CH
Zn
O
N
N
O
C
N
HC
OAc
R
N
H3C
H2O
HN
HN
S
S
S
R''
HN
R'
N
N
N
N
N
Fig. 1. Reaction scheme for the preparation of Schiff base and their Zn(II) complexes (R = C6H5 (1); R = 2-ClC6H4 (2); R = 4-ClC6H4 (3); R = 4-NO2C6H4 (4); R0 = C6H5 (5);
R0 = 2-ClC6H4 (6); R0 = 4-ClC6H4 (7); R0 = 4-NO2C6H4 (8); R00 = C6H5 (9); R00 = 2-ClC6H4 (10); R00 = 4-ClC6H4 (11); R00 = 4-NO2C6H4 (12).
Table 2
The important IR frequencies (cmꢁ1) of Zn(II) complexes.
Complexes
IR frequency (cmꢁ1
(OAH) (NAH)
)
t
t
t
(ArAH)
t
(ACOO)
t(C@N)
t(C@C)
t
(ANO2)
Phenolic
t(CAO)
t
(NAN)
t(CACl)
t(ZnAO)
t(ZnAN)
1
2
3
4
5
6
7
8
9
3432s
3436s
3345s
3440s
3430s
3434s
3430s
3440s
3420s
3436s
3437s
3446s
3180m
3195m
3182m
3190m
3200m
3195m
3205m
3202m
3190m
3195m
3186m
3195m
3050w
3070w
3075w
3080w
3065w
3078w
3087w
3088w
3110w
3121w
3112w
3125w
1730m
1745m
1755m
1740m
–
–
–
–
–
–
–
–
1590s
1585s
1610s
1595s
1585s
1605s
1600s
1615s
1590s
1596s
1595s
1615s
1575w
1580w
1610w
1585w
1570w
1578w
1595w
1598w
1576w
1585w
1592w
1580w
–
–
–
–
–
–
–
1195m
1200m
1210m
1215m
1217m
1220m
1223m
1227m
1225m
1222m
1224m
1221m
–
415m
410m
420m
414m
445m
460m
465m
466m
464m
470m
475m
480m
420m
430m
435m
432m
440m
445m
450m
442m
455m
450m
440m
452m
775w
765w
–
1535m
–
–
–
1540m
–
–
–
1375s
1350s
1343s
1380s
1355s
1350s
1310s
1340s
–
769w
774w
–
–
10
11
12
780w
775w
–
1545m
Zn(II) complexes with ligands L5H–L12
H
mixture was refluxed for ca.10–11 h on a water bath. Light yellow
or brown precipitate obtained was filtered, washed with ethanol
and hot water and dried in vacuo at room temperature. The
complexes were obtained as powdered material.
The procedure involves the addition of the appropriate Schiff
base (L5H–L12H) (0.04 mol) to an aq. ethanol (ꢂ30 cm3) of zinc ace-
tate dihydrate (0.02 mol) and sodium acetate (0.04 mol). The

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A.K. Singh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
Table 3
1H NMR and 13C NMR spectral bands Zn(II) complexes.
Compound
NMR data
13C NMR
ANH (s)
ACH3 (s)
Aromatic ring (m)
AHC@N (s)
ACOO
ACH3
AC@N
Aromatic ring
1
2
3
4
5
6
7
8
9
12.24
12.58
12.23
12.48
12.60
12.66
12.67
12.64
12.10
12.23
2.16
2.26
2.31
2.41
1.25
1.27
1.21
1.31
–
7.00–8.71
7.10–8.82
7.15–8.70
7.03–8.65
7.17–8.45
7.07–8.53
7.09–8.37
7.15–8.42
7.13–8.51
7.17–8.46
8.21
8.23
8.27
8.29
–
–
–
–
–
182.4
182.7
182.8
182.6
–
–
–
–
–
–
23.4
23.8
23.7
23.5
12.4
12.6
12.7
12.5
–
155.4
155.8
155.6
155.7
158.4
158.3
158.5
158.3
143.4
143.1
135.4, 131.1, 130.8, 130.2, 129.3, 128.7, 128.3, 127.4
137.4, 133.4, 130.7, 130.5, 129.7, 129.4, 128.9, 128.4, 127.7
135.4, 132.2, 131.2, 130.6, 129.4, 128.7, 127.4
148.6, 140.5, 131.2, 129.5, 128.9, 125.4
152.4, 134.3, 131.4, 130.5, 129.7, 129.1, 122.4, 115.5, 114.6
152.7, 138.8, 132.5, 131.1, 129.4, 128.7, 121.7, 115.4, 114.8
152.6, 135.6, 131.6, 129.6, 128.9, 122.2, 115.9, 114.4
153.0, 149.4, 139.8, 130.4, 129.3, 124.5, 121.7, 115.4, 114.9
155.5, 133.6, 131.3, 130.1, 129.7, 128.9, 127.7, 126.4, 122.8
155.3, 137.5, 133.6, 131.2, 130.4, 129.7, 129.1, 127.5, 127.3,
126.9, 122.2
10
–
–
–
11
12
12.20
12.30
–
–
7.21–8.57
7.22–8.51
–
–
–
–
–
–
143.2
143.5
155.7, 135.4, 131.9, 130.4, 129.5, 128.8, 127.6, 126.5, 122.7
155.6, 148.4, 138.3, 130.6, 129.8, 128.3, 127.1, 126.4, 122.2
The details of the reactions along with the analytical data of the
products are given in Table 1. The general reaction scheme is given
in Fig. 1.
at 765–780 cmꢁ1 assigned for the CACl stretching modes [27]. The
spectra of Schiff bases show a medium band at 3175–3200 cmꢁ1
due to t(NAH) which remains almost at the same position in com-
plex indicating the non involvement of NAH group in bond forma-
tion. The ligands show one medium intensity band at ca.
Biological activity study
1630 cmꢁ1 assignable [26,28] to
t(C@N) which shifts to 1590–
1615 cmꢁ1 in the complexes. This shifting indicates that the coor-
dination of azomethine nitrogen to metal ion [29–32]. The bands at
All newly prepared Schiff bases and Zn(II) complexes were
screened for their activity against four fungal organisms Colletotri-
chum falcatum, Aspergillus niger, Fusarium oxysporium and Curvular-
ia pallescence and two bacteria namely Bacillus subtilis, and
Escherichia coli by disc-diffusion method [25]. Antifungal and anti-
bacterial activity of each compound was evaluated at three differ-
ent concentrations, i.e., 1000, 100, 10
mL, respectively.
Bacterial zone of inhibition was measured by well forming
method. E. coli and B. subtilis were grown at 37 °C and 32 °C main-
tained on LB plates (Luria base Hi-media). Well are formed in LB
ca. 420–455 cmꢁ1 were assigned [32] to
t(ZnAN). L5H–L12H Schiff
bases show broad band at ca. 2640 cmꢁ1 due to intramolecular H-
bonded OH group. This band disappear in their corresponding
Zn(II) complexes indicating the coordination of phenolic oxygen
to zinc metal ion through deprotonation. This is further supported
lg/mL and 200, 100, 10 lg/
by shift in phenolic t
(CAO) band from 1285 to 1300 cmꢁ1 (in the
free ligand) to ca. 1310–1380 cmꢁ1 in the complexes. The coordi-
nation through phenolic oxygen has been further confirmed by
the appearance of band at ca. 445–480 cmꢁ1 assignable to
t(ZnAO)
[33]. The presence of coordinated water in the complexes is indi-
cated by a broad trough band in the region ca. 3420–3446 cmꢁ1
and two weaker bands in the region 750–810 and 700–730 cmꢁ1
plates with the help of sterilized plastic tips. 10 lg/mL concentra-
tion Zn(II) complexes (2, 6 and10) were added in separate well and
further temperatures were maintained for 24 h, zone of inhibition
was measured with help of barmier callipers. Fluconazole was used
as standard drug for antifungal and gentamycine was used as stan-
dard drugs for antibacterial activity.
due to
t(AOH) rocking and wagging mode of vibrations, respec-
tively [34,35]. The complexes with ligand L1–L4 show strong bands
in the region 1730–1755 cmꢁ1 which are assigned to
t(OOCCH3). In
complexes Zn–O band appears at 410–420 cmꢁ1, which indicates
that the acetate molecules are bonded to zinc [36]. Further, the
absorption at 1616 and 1410 cmꢁ1, confirm the monodentate nat-
ure of the acetate ion in complexes with ligand L1–L4 [37].
Results and discussion
Zn(II) complexes are sparingly soluble in common solvents;
however, these complexes are soluble in DMF and DMSO. The con-
ductivity measured in DMSO, showed that the complexes are non-
electrolytes. Magnetic susceptibility measurement showed that
they are diamagnetic nature. The presence of water molecules in
the complexes has been confirmed by TG studies which show
weight loss at ca. 165–180 °C, corresponding to two water
molecules.
1H NMR spectra
The proton magnetic resonance spectra of these complexes
have been recorded in DMSO-d6. Chemical shifts for protons in dif-
ferent environments have been given in Table 3. The intensities of
all the resonance lines were determined by planimetric integra-
tion. The following conclusions can be derived by comparing the
spectra of ligands with their corresponding complexes. The spectra
of Schiff bases (L1–L4) exhibit signals at ca. 12.10 and 8.00 ppm due
to NH and azomethine protons, respectively. In zinc(II) complexes
(1–4), the first signal remains almost at the same position but the
second signal shifts to downfield. The downfield shift indicates the
deshielding effect due to the coordination of azomethine nitrogen
to central metal ion. Complexes of type (1–4) show signal at 2.16–
2.41 ppm due to methyl protons of acetate [32]. Schiff base and
their corresponding Zn(II) complexes show multiplet at 7.00–
8.82 ppm due to aromatic protons. Zn(II) complexes (1–4) show
new signal at ca. 5.5 ppm due to the water protons.
Infrared spectra
The characteristic IR spectral bands of Zn(II) derivatives are gi-
ven in Table 2. The IR spectra provide valuable information regard-
ing the coordination behaviour of Schiff bases. Schiff bases derived
from indoline-2,3-dione appear to exist in both keto and enol tau-
tomeric forms (Fig. 2) suggested by a broad band (solution spectra)
at ca. 2600 cmꢁ1, due to intramolecular H-bonded OH group. All
the ligands and complexes show band ca. 3050–3125 cmꢁ1 as-
signed for the t(ArAH). The bands in the IR spectra of complexes
4, 8 and 12 at ca. 1535–1545 cmꢁ1 can be assigned to the NO2
Schiff bases derived from 2-hydroxyacetophenone (L5H–L8H)
exhibit signals at 12.60–12.65 and 10.45 ppm due to hydrazino
group [26]. The IR spectra of complexes 2, 3, 6, 7, 10 and 11 shows

A.K. Singh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
397
N
N
N
N
NHN
R"
NHN
R"
N
NH
S
S
O
HO
Enol form
Keto form
Fig. 2. Tautomeric forms of Schiff bases (L9H–L12H).
complexes indoline-2,3-dione NH signal disappears. Multiplet is
observed at 7.13–8.57 ppm due to aromatic protons in the Schiff
base and their corresponding Zn(II) complexes. Complexes (9–12)
also show new signal at ca. 5.4 ppm due to the water protons.
1.0
0.8
0.6
0.4
0.2
0.0
6
10
13C NMR
The 13C NMR spectra were recorded (Table 3) in DMSO-d6. Schiff
bases derived from benzaldehyde (L1–L4) show signals at ca. d
175 ppm for their azomethine carbon which shift downfield in
their corresponding Zn(II) complexes (d 155 ppm) due to coordina-
tion through the azomethine nitrogen. The complexes of type (1–4)
show signals at ca. d 23 ppm (CH3) and ca. d 182 ppm (ACOO) due
to the presence of coordinated acetate molecules.
Schiff bases derived from 2-hydroxyacetophenone (L5H–L8H)
show signal at ca. d 173 ppm for azomethine carbon and which
shift downfield in zinc metal complexes (ca. d 158 ppm) due to
coordination through the azomethine nitrogen. For ACH3 carbon,
a signal appears at ca. d 12.0 ppm in ligands and their correspond-
ing complexes of type (5–8).
0
200
400
600
800
1000 1200 1400
Dynamic radius (nm)
Fig. 3. DLS analysed results of compounds 6 and 10.
Schiff bases (L9H–L12H) show signals at ca. d 148 ppm due to
azomethine carbon which shift downfield in their corresponding
Zn(II) complexes (ca. d 143 ppm) due to the coordination through
azomethine nitrogen. Schiff bases of type L1–L4, L5H–L12H and their
corresponding Zn(II) complexes show signals at ca. 172 ppm and
ca. 167 ppm assignable for thiadiazole ring carbons. For aromatic
ring, a number of signals appear these are given in Table 3.
NH and phenolic AOH protons, respectively. The signal due to phe-
nolic AOH at ca. 10.45 ppm disappears in the spectra of complexes
(5–8); this confirms that the hydroxyl group reacted with metal
ion via deprotonation. Multiplet is observed at ca. 7.07–8.53 ppm
due to aromatic protons in the Schiff bases and their corresponding
Zn(II) complexes. Schiff bases (L5H–L8H) and their corresponding
Zn(II) complexes also exhibit a signal at ca. 1.21–1.31 ppm due to
methyl protons. Zn(II) complexes (5–8) show new signal at ca.
5.6 ppm due to the water protons.
Dynamic light scattering (DLS), powdered XRD
Schiff bases derived from indoline-2,3-dione of type (L9H–L12H)
exhibit signals at 12.16 and 5.55 ppm due to hydrazino NH proton
and indoline-2,3-dione NH proton, respectively. In Zn(II)
For the compounds 6 and 10, hydrodynamic radiuses were
measured by DLS analysis and obtained data presented in Fig. 3.
The average dynamic radius of compounds 6 and 10 are 109 and
Table 4
Antifungal screening data of Zn(II) complexes at concentration (lg/mL).
Compound
% Fungal inhibition*
C .falcatum
A. niger
F. oxysporium
C. pallescence
1000
100
10
1000
100
10
1000
100
10
1000
100
10
1
2
3
4
5
6
7
8
9
10
11
12
13
75.9
81.0
78.2
76.0
73.2
82.6
75.5
79.0
75.6
84.2
78.6
81.4
100
63.7
69.2
63.9
65.1
64.0
74.1
67.7
68.4
68.8
76.9
70.5
66.1
100
41.9
55.5
48.9
51.0
47.6
55.2
49.4
53.9
48.9
61.4
58.3
59.1
100
76.6
82.8
80.0
81.7
78.6
84.7
81.2
82.6
80.7
88.6
83.8
84.0
100
65.5
70.9
66.7
68.2
63.3
77.8
71.1
69.5
71.6
68.0
69.3
71.1
100
43.8
54.6
49.0
52.6
47.0
57.4
52.3
55.2
58.8
55.6
57.0
58.2
100
71.4
80.2
72.6
78.5
72.6
83.5
80.7
81.3
72.9
87.6
82.4
81.3
100
61.6
69.4
64.5
67.8
63.6
72.4
65.1
66.9
64.0
66.4
67.6
70.5
100
40.9
52.6
45.8
49.4
44.3
55.5
49.6
51.2
45.3
56.8
53.7
54.5
100
70.2
78.6
74.4
74.8
73.4
80.5
75.6
74.4
69.2
85.4
79.3
77.2
100
59.2
66.5
63.7
65.4
62.3
68.8
63.5
65.1
63.1
65.7
61.3
62.8
100
39.4
50.2
46.6
47.4
42.4
53.3
47.3
49.4
44.2
52.0
49.9
50.1
100
*
Each value observed is within the error limits of 0.1%.

398
A.K. Singh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 393–399
Table 5
(indoline-2,3-dione). In antifungal strain we observed that all li-
gands and Zn(II) complexes are more active against C. falcatum.
All Schiff bases and Zn(II) complexes are more active against B. sub-
tilis. It is found that substitution in the ligands increases the activ-
ity against bacteria and fungi. Minimum inhibitory measurements
(MIC) showed that synthesized compound 10 has lowest concen-
Antibacterial screening data of Zn(II) complexes at concentration (
lg/mL).
% Bacterial inhibitiona
Compound E. coli
B. subtilis
200 100
MICb
E. coli B. subtilis
200
100
10
10
1
2
3
4
5
6
7
8
9
60.4 47.3 32.1 62.7 49.8 34.5 >500
67.6 55.0 36.7 69.4 57.7 38.2 >410
65.4 51.5 35.1 67.6 53.4 36.5 >445
66.3 48.8 33.4 67.9 55.6 34.7 >430
>450
>385
>405
>410
>425
>340
>360
>350
>340
>290
>315
>325
tration (325
lg/mL for E. coli and 290 lg/mL for B. subtilis) needed
for complete inhibition.
Standard method was used to established whether the Schiff
base and their Zn(II) complexes were bacteriostatic or bactericidal
[27], different weighted amount of Schiff base and Zn(II) com-
61.7 50.2
68.4 57.6 42.6 70.4
64.2 53.0 40.5 65.6 54.3 41.1 >405
66.7 55.8 38.3 67.4 58.6 40.5 >380
62.2 52.0 40.1 63.3 55.7 42.5 >350
70.9 59.1 45.4 71.7 61.1 45.3 >325
67.6 54.0 43.3 68.4 56.7 44.8 >330
69.5 57.2 41.4 67.8 60.1 40.6 >340
36.1 64.5 53.8 37.9 >455
59.7 44.5 >370
plexes 10–200
lg/mL, were incubated with bacteria (B. subtilis
and E. coli) in LB broth for 24 h and then 100-
lL aliquots were
10
11
12
taken from the incubated LB broth and were placed on nutrient soft
agar plates and then incubated at for 24 h, colony were counted,
the results established that all the Schiff bases and Zn(II) com-
plexes have bactericidal properties. The indoline-2,3-dione derived
Schiff base (L6H) and their Zn(II) complexes (10) have excellent
bactericidal properties. B. subtilis zone of inhibition measurement
showed that complex (10) have nearly same zone (19 mm) of the
standard drug streptomycin (20 mm).
a
Maximum error 0.1%.
Maximum error 5 (lg/mL).
b
20
Conclusions
E. coli
B. subtilis
Schiff bases (L1–L4) act as monodentate ligand coordinating
through azomethine nitrogen, while Schiff bases (L5H–L12H) are
monobasic bidentate ligands coordinating through azomethine
nitrogen and phenolic oxygen through deprotonation. The octahe-
dral geometry of the complexes has been established by elemental
analysis, molecular weight and spectral studies. DLS analysis indi-
cated that compounds are fine particles. Antifungal and antibacte-
rial activities of the ligands and corresponding complexes have also
been evaluated, which show that the activities increase on chela-
tion and all Schiff base and Zn(II) complexes are bactericidal in
nature.
16
12
8
2
6
10
13
Compound / antibiotics
Fig. 4. Bacterial zone of inhibition (mm) by 2-chloro derived Zn(II) complex at
concentration 10 g/mL.
Acknowledgement
l
Authors are thankful to the Department of Biotechnology,
D.D.U. Gorakhpur University, Gorakhpur, for help in evaluating
antimicrobial activities.
164 nm, respectively indicating the fine particle nature of the com-
pounds. Absence of appropriate peak in powdered XRD measure-
ments indicates that compounds are amorphous in nature.
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