Synthesis, spectral characterization and antibacterial activity of copper(II) complexes of functionalized hydrazones

Article abstract of DOI:10.14233/ajchem.2019.21942

Copper(II) complexes having the formula CuL2 {where, L = 2-acetylthiophene acetoylhydrazone (ATAH), 2-acetylthiophene benzoylhydrazone (ATBH)} have been investigated on the basis of elemental analysis, molar conductivity measurements, magnetic susceptibil

Full text of DOI:10.14233/ajchem.2019.21942

Asian Journal of Chemistry; Vol. 31, No. 6 (2019), 1289-1293
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.21942
Synthesis, Spectral Characterization and Antibacterial Activity of
Copper(II) Complexes of Functionalized Hydrazones
1
1,*,
2,
D. KASIMBI , K. HUSSAIN REDDY
and N. DEVANNA
1Department of Chemistry, Sri Krishnadevaraya University, Ananthapuramu-515003, India
2Department of Chemistry, Jawaharlal Nehru Technological University, Ananthapuramu-515002, India
*Corresponding author: E-mail: khussainreddy@yahoo.co.in
Received: 18 January 2019;
Accepted: 12 February 2019;
Published online: 29 April 2019;
AJC-19370
Copper(II) complexes having the formula CuL2 {where, L = 2-acetylthiophene acetoylhydrazone (ATAH), 2-acetylthiophene
benzoylhydrazone (ATBH)} have been investigated on the basis of elemental analysis, molar conductivity measurements, magnetic
susceptibility, UV-visible, IR and ESR spectral data. Non-electrolytic nature of the complexes are revealed by molar conductance data. IR
spectral data suggested that hydrazones act as tridentate ligands. The spin Hamiltonian, orbital reduction and bonding parameters of
complexes are calculated using ESR spectra of complexes. The compounds are screened for their antibacterial activities against Pseudomonas
aureoginos and Bacillus cereus. Acetoylhydrazones show more antibacterial activity than the corresponding benzoyl hydrazones. Some
of the Cu(II) complexes show more activity than hydrazone ligands.
Keywords: Copper(II) complexes, Trifunctional donor ligands, Octahedral geometry, Antibacterial activity.
[19-22] lanthanide complexes of 2-benzoylpyridine benzoyl-
hydrazone, 2-acetylpyridine acetoylhydrazone, 2-benzoyl-
pyridine acetoylhydrazone and 2-formylpyridine benzoylhydra-
zone. Recently, DNA binding and cleavage activities on Cu(II)
complexes with tetradentate ligands is also reported in the
literature [23]. However, there is no report on antibacterial
property of copper derivatives of hydrazones derived from
2-acetylthiophene. These ligands contain assorted donor (N,
O and S) atoms and expected to form complexes with copper
and to show interesting properties and activities.
INTRODUCTION
Copper proteins have attracted considerable attention
owing to their biological functions such as electron transport,
oxygen transport, copper storage and many oxidase activities
[1]. Copper is biostatic metal and its surface have natural prop-
erties which can destroy a wide range of microorganisms [2].
Current interest in copper complexes springs from their
immense use as pharmacological agents. Tridentate Schiff base
ligands form stable complexes by bonding through potential
donor atoms. However, copper complexes with tridentate ligands
with thiophene moiety and having assorted donor (N,O,S)
atoms are limited [3].
Metal complexes of hydrazones have wide applications
in biological processes [4-15]. A good number of transition
metal complexes with hydrazones have been reported [16]. Our
survey of literature revealed that only few reports are available
on the antibacterial activity of such complexes with hydrazones.
Cu(II) and Zn(II) complexes with 2-benzoylpyridinemethyl-
hydrazone are reported by Beraldo et al. [17]. Koo et al. [18]
reported Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes
of 2-acetylpyridine benzoylhydrazone. Recently, we have studied
Based on the lacuna identified and to renew our research
interests [24-28], herein we reported the current findings on
copper(II) complexes of 2-acetylthiophene acetoylhydrazone
(ATAH) and 2-acetylthiophene benzoylhydrazone (ATBH).
EXPERIMENTAL
The organic precursors (2-acetylthiophene, acetic hydra-
zide and benzhydrazide) were purchased from Sigma-Aldrich
Chemicals Pvt. Ltd. India. The copper salt (CuCl2·2H2O) was
purchased from Merck Company. Only distilled solvents were
used in the preparation of hydrazones and their metal derivatives.
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1290 Kasimbi et al.
Asian J. Chem.
Preparation of 2-acetylthiophene acetoylhydrazone
(ATAH): Acetic hydrazide (3.0 g, 0.03 mol) dissolved in 20
mL methanol was added to a hot methanolic solution (20 mL)
of 2-acetylthiophene (5.03 mL, 0.03 mol) in a 100 mL round
bottom flask. Few drops of glacial CH3COOH was added to
the reaction mixture. The contents were refluxed over water
bath for 2 h and cooled to room temperature. By filtration, the
compound was collected. It was washed 3-4 times with 2 mL
portions of hot water and finally dried in vacuo. The product
was recrystallized from methanol (Scheme-I). Yield: 80 %
m.p.: 176-178 ºC.
Preparation of 2-acetylthiophene benzoylhydrazone
(ATBH): Benzhydrazide (3 g, 0.02 mol) dissolved in 20 mL
methanol was added to a hot methanolic solution (20 mL) of
2-acetylthiophene (2.7 mL, 0.03 mol) in a 100 mL round bottom
flask. Few drops glacial CH3COOH was added to the reaction
mixture.The contents were refluxed over water bath for 2 h
and cooled to room temperature. By filtration, the compound
formed was collected and washed 3-4 times with 2 mL portions
of hot water and finally dried in vacuo. It was recrystallized
from methanol (Scheme-II). Yield: 85 %; m.p. 198-200 ºC.
hexane and dried in vacuo.Yield, 72 %; decomposition point:
> 290 ºC.
Preparation of Cu(ATBH)2: It was prepared by mixing
hot ethanolic solution (20 mL) of 2-acetylthiophene benzoyl-
hydrozone (ATBH) (1 g, 0.410 mmol) and CuCl2·2H2O (0.53
g, 0.410 mmol) dissolved in ethanol (sprit) (20 mL) in 1:1
ratio in a clean 100 mL round bottom flask and the contents
were refluxed on water bath for 3 h. The resulting solution was
allowed to stand at room temperature and after slow evapo-
ration, dark green coloured complex which was separated out
by filtration, washed with methanol followed by hexane and
dried in vacuo. Yield: 70 %; decomposition point: above
290 ºC.
Preparation of sample solution for antimicrobial activity:
With different concentrations of 200, 300 and 500 µg of each
compound was prepared in DMF that had no influence on the
microbial growth.
Test microorganisms and growth media: Bacillus cereus
(MTCC 1305) and Pseudomonas aureoginosa (MTCC 2453)
were targeted in the present study and procured from Department
of Microbiology, Osmania University College, Hyderabad, India.
The bacteria were grown on Mueller-Hinton agar plates at 37 ºC.
The bacterial stock cultures were incubated for 24 h at 37 ºC on
nutrient agar.Antibacterial activities of ligands and complexes
were determined by zone inhibition method. Standard procedures
were used in the preparation of paper discs.
Synthesis of copper complexes
Preparation of Cu(ATAH)2: The complex was prepared
by mixing hot methanolic solution (20 mL) of 2-acetylthiophene
acetoylhydrozone (ATAH) (1 g, 0.55 mmol) and CuCl2·2H2O
(0.63 g, 0.55 mmol) dissolved in methanol (20 mL) in 1:1 ratio
in a clean 100 mL round bottom flask and the contents were
refluxed on water bath for 3 h. The resulting solution was
allowed to stand at room temperature and after slow evaporation,
light green coloured complex which separated out was
collected by filtration, washed with methanol followed by
Antibacterial activity: The agar medium was sterilized
at 121 ºC for 30 min. By pouring about 10 mL of the medium
into petri-dishes (diameter = 10 cm) under aseptic condition
the agar plates were prepared. The plates left undisturbed for
2 h to solidify the medium. About 1 mL aliquot of inoculums
(containing suspension) of bacteria was poured on to the plates
CH3
C
N
S
H+
CH3
H2NHN
CH3
+
C
O
S
NH
C
Reflux, 2 h in methanol
O
O
CH3
Scheme-I: Synthesis of 2-acetylthiophene acetoylhydrozone (ATAH)
CH3
C
N
S
H+
CH3
H2NHN
C6H5
+
C
O
S
NH
C
Reflux, 2 h in methanol
O
O
C6H5
Scheme-II: Synthesis of 2-acetylthiophene benzoyl hydrozone (ATBH)

Vol. 31, No. 6 (2019)
Synthesis and Antibacterial Activity of Copper(II) Complexes of Functionalized Hydrazones 1291
TABLE-1
ANALYTICAL DATA OF COPPER(II) COMPLEXES
m.p.*
(°C)
Elemental analysis (%): Found (Calcd.)
Molar conductivity
Yield
(%)
Complex
Colour
m.w.
(Ω cm2 mol-1)
C
H
N
M
Cu(ATAH)2
Cu(ATBH)2
Light green 72
Dark green 70
423.6
547.5
290
280
45.10 (45.32)
57.25 (56.98)
4.28 (4.25)
4.40 (4.38)
13.60 (13.22)
10.15 (10.22)
14.70 (15.00)
11.50 (11.60)
4.9
4.1
*Decomposition temperatures
separately containing solidified agar media. The prepared
sterile filter paper discs were dipped into the compound solu-
tions and shaken well and these test plates incubated for a
period of 2 days in BOD at 37 ºC for the development of inhi-
bitory zones. An average of two independent readings for each
organism for different compound solutions was documented.
The inhibition zones were measured after 24 h at 37 ºC. The
diameter of the inhibition zone was measured and recorded
using plastic ruler.
(acetoyl), thiophene and >NH protons. GC-MS spectrum of
ATAH shows a peak at m/z 182 due to the formation of molecular
ion.
The FTIR spectrum of 2-acetylthiophene benzoylhydrazone
(ATBH) shows the peaks at 3327, 1651and 1608 cm-1, which
are assigned to ν(C=N), ν(C=O) and ν(NH) vibrations, respec-
1
tively. The H NMR spectrum of ATBH (recorded in CDCl3
solvent) shows δ (2.34) (singlet 3H), δ (7.03- 8.00) multiplet
8H and δ (8.88) (singlet 1H) respectively assigned to -CH3,
and aromatic (thiophene + phenyl ring) protons and •NH protons.
GC-MS spectrum of ATBH shows a peak at m/z 244 due to
the formation of molecular ion.
RESULTS AND DISCUSSION
The complexes are sparingly soluble in H2O and less soluble
in CH3OH and C2H5OH, but readily soluble in CH3CN, (CH3)2SO
and (CH3)2NC(O)H. Molecular formulae of the Cu(II) comp-
lexes are proposed based on analytical data. The complexes
are non-electrolytes (Table-1). The magnetic moment values of
the complexes are relative to their respective spin-only values.
IR spectral data of acetylthiophene acetoylhydrazone
(ATAH) and 2-acetylthiophene benzoylhydrazone (ATBH) and
their copper(II) complexes and their assignments are given in
Table-2. Data and assignments suggested that the heterocyclic
sulphur atom, azomethine nitrogen atom and oxygen atom
are involved in chelation.
UV-visible spectral data of complexes are given in Table-3.
In the electronic spectra of Cu(ATAH)2 and Cu(ATBH)2, the
bands at 27322 and 27030 cm-1 are related to M−L charge transfer
transitions. The spectra of Cu(ATAH)2 and Cu(ATBH)2
complexes showed symmetrical peaks at 12755 and 12936
cm-1, respectively. These weak Laporte forbidden bands are
2
2
assigned to Eg → T2g electronic transition [1] in favour of
octahedral geometry for the complexes.
TABLE-3
ELECTRONIC SPECTRAL DATA (cm-1) OF
METAL COMPLEXES IN SOLUTION STATE*
Cu(ATAH)2
Cu(ATBH)2
Assignment
Structure
27322 (3100)
27030 (4500)
Charge transfer
transition (M→L)
TABLE-2
IMPORTANT IR SPECTRAL BANDS*
12755 (280)
12936(460)
d-d transition
Octahedral
(cm-1) AND THEIR ASSIGNMENT
(2T2g→2Eg)
*Spectral of complexes were recorded in DMF solvent.
Cu(ATAH)2
Cu(ATTH)2
Assignment
Molar absorptivity (L mol-1 cm-1) values are given in parenthesis.
–
–
ν(N-H)
(3174)
(3327)
–
–
ν(C=O)
ν(C=N)
Table-4 gives ESR spectral data of both Cu(II) complexes.
Well resolved peaks are observed (Fig. 1) at low field and at
high field region and these are related to g|| and g⊥, respectively.
Tetracyanoethylene (TCNE) free radical was used as the g
marker for computing g values.
The g|| values for Cu(ATAH)2 and Cu(ATBH)2 complexes
are respectively found to be 2.415 and 2.253. The g⊥ values
suggest ionic character for former complex and covalent
character for latter complex [30]. The trend, g|| > g⊥ > 2.0023
suggested that the unpaired electron predominantly in the
(1666)
1590
(1606)
476
(1651)
1502
(1508)
472
ν(Cu-O)
ν(Cu-N)
407
393
*Ligands’ bands are given in parenthesis
In FTIR spectrum of acetylthiophene acetoylhydrazone
(ATAH), the bands at 3174, 1666, 1606 cm-1 are assigned to
ν(C=N), ν(C=O) and ν(NH) vibrations, respectively. The 1H
NMR spectra (recorded in CDCl3 solvent) showsδ(2.35) (singlet
3H), δ (2.28) (singlet 3H), δ (7.00-7.30) (multiplet 3H), δ (9.50)
(singlet 1H) are respectively assigned to -CH3 (acetyl), -CH3
2
2
dx -y orbital [31,32] characteristic of octahedral geometry. The
axial symmetry parameter G is defined as:
TABLE-4
HAMILTONIAN AND ORBITAL REDUCTION PARAMETERS OF COPPER(II) COMPLEXES
In DMF at RT
In DMF at LNT
Complex
A||×105
0.00238 0.00018
g⊥
g⊥
λ
K⊥
A⊥×105
g||
gav
G
g||
gav
G
K||
Cu(ATAH)2
Cu(ATBH)2
2.142
2.149
2.028
2.006
2.066
2.054
4.48
3509
2.415
2.225
2.079
2.092
2.181
2.136
5.334
2.478
659
360
0.891
0.656
0.755
0.846
-
-

1292 Kasimbi et al.
Asian J. Chem.
K|| and K⊥ are 0.656 and 0.846, respectively. These values
1000
500
suggested the presence of in-plane π-bonding in the complex.
2
The covalency factor (α ) is evaluated by the following
expression:
2
α = A||/p + (g|| – 2.0023)3/7(g⊥ – 2.0023) + 0.004
0
2
The α value for the complex (0.3085) suggested the covalent
nature of metal ligand bond.
-500
-1000
-1500
-2000
The dipolar term P is estimated from the expression
P = (A|| – A⊥)/(g|| – 2) – 5/4 g⊥ – 2) – 6/7
Giordano and Bereman [33] suggested the identification
of bond on groups from the values of dipolar term "P". The
redu-ction of "P" value from the free ion value (0.036 cm-1)
may be attributed to the presence of covalent character of M−L
bonding.
0
100
200
300
400
500
600
Antibacterial activity studies: The antibacterial activities
of hydrazone ligands and their copper(II) complexes were invest-
igated. The zone inhibition diameters (mm) are given in Table-5.
The compound 2-acetylpyridine acetoylhydrazone (APAH)
shows more activity than 2-acetylpyridine benzoylhydrazone
(APBH). Similarly, 2-acetylthiophene acetoylhydrazone (ATAH)
is more active than 2-acetylthiophene benzoylhydrazone (ATBH).
This trend indicates that acetoylhydrazones are more active
than benzoylhydrazones against Gram-positive and Gram-
negative bacteria. Moreover,APAH is more active thanATAH
and APBH is more active than ATBH. This trend suggested
that pyridine based hydrazones show more activity than thio-
phene based hydrazones against Gram-positive and Gram-
negative bacteria.
The data given in Table-5 also suggested that the ligands
showed more activity against E. coli and Staphylococcus aureus
than the complexes. However, copper(II) complexes exhibited
higher antibacterial activity than the free ligand, in the cases
of Bacillus and P. aureoginosa in analogy with previous observ-
ations [34-36]. Overtone's concept [37] and Tweedy's chelation
theory [38] would explain the enhanced activity of complexes.
According to former concept, the lipid membrane surrounding
the cell support the passage of only lipid-soluble materials,
which means that lipid solubility is an important element for
controlling antimicrobial activity. The polarity of a metal ion
is greatly reduced on chelation. Delocalization of π-electrons
over the whole chelating ring enhances the penetration ability
Field strength
Fig. 1. ESR spectrum of Cu(ATAH)2 complex at LNT
[g|| − 2.0023]
G =
[g⊥ − 2.0023]
The calculated G value for Cu(ATAH)2 and Cu(ATBH)2
complexes are respectively found to be 5.33 and 2.47. The G
value is more than 4 for Cu(ATAH)2 complex which indicates
the absence of exchange coupling and mis-alignment of mole-
cular axes. The G value is less than 4 for Cu(ATBH)2 complex
which indicates the absence of exchange coupling and mis-
alignment of molecular axes.
The following equations are used in the calculation of orbital
reduction parameters (K||, K⊥):
2
8K|| λ
∆E(d − d)
g|| = ge −
2
2K⊥ λ
g⊥ = ge −
∆E(d − d)
Hathaway pointed that that for pure sigma bonding K|| =
K⊥ = 0.77 and for in-plane pi bonding K|| < K⊥, while for out-
plane pi bonding K|| > K⊥.
For Cu(ATAH)2 complex, K|| and K⊥ are found to be 0.891
and 0.755, respectively. These values suggested the presence
of out-plane π-bonding in the complex. For Cu(ATBH)2 complex
TABLE-5
ANTIBACTERIAL ACTIVITY OF THIOPHENE BASED HYDRAZONES AND ITS COPPER(II) COMPLEXES
Zone of inhibition (mm)
Gram-negative
Gram-positive
Compound
E. coli
P. aureoginosa
B. cereus
S. aureus
200 µg
4.2
300 µg
5.6
500 µg
6.6
200 µg
7.0
300 µg
8.0
500 µg
8.5
200 µg
5.0
300 µg
6.0
500 µg
6.5
200 µg
7.0
300 µg
8.0
500 µg
9.0
APAH
Cu(APAH)2
APBH
Cu(APBH)2
ATAH
Cu(ATAH)2
ATBH
Cu(ATBH)2
2.5
2.0
1.5
4.0
2.2
3.5
2.4
2.7
4.0
1.7
6.0
2.5
4.5
2.8
3.0
6.0
2.4
6.5
3.4
5.5
3.6
2.5
6.0
4.5
5.0
6.2
5.0
8.3
2.5
7.0
6.6
6.0
7.3
5.0
8.5
3.3
7.5
8.4
7.0
8.4
6.0
9.2
4.0
5.0
6.0
5.0
4.0
4.0
5.0
5.0
5.5
6.5
6.0
4.2
5.0
5.5
7.0
6.0
7.0
7.0
5.0
6.0
6.0
4.0
4.0
2.5
6.0
4.0
4.0
3.0
5.0
6.0
4.0
8.0
5.0
6.0
5.0
5.5
8.0
6.0
9.0
5.5
7.0
7.0
APAH = 2-Acetyl pyridine acetoylhydrazone; APBH = 2-Acetylpyridine benzoylhydrazone; ATAH = 2-Acetyl thiophene acetoylhydrazone;
ATBH = 2-Acetyl thiophene benzoylhydrazone

Vol. 31, No. 6 (2019)
Synthesis and Antibacterial Activity of Copper(II) Complexes of Functionalized Hydrazones 1293
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In the present study two ligands viz. 2-acetylthiophene
acetoylhydrazone (ATAH) and 2-acetylthiophene benzoylhydra-
zone (ATBH) were synthesized and characterized based on
spectral data. Copper(II) complexes of these functionalized
hydrazones were investigated. Current studies revealed that the
complexes have general formula ML2 (where, L = ATAH and
ATBH) and acted as monoanioninc tridentate ligands. Copper
complexes are six coordinated and have octahedral structure.
Copper(II) complexes showed more activity than the correspon-
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ACKNOWLEDGEMENTS
One of the authors, KHR is thankful to UGC, New Delhi
for the sanction of one-time grant (sanction Lr. No. F. 19-106/
2013 (BSR) as financial support. The authors are also thankful
to the authorities of SAIF Centers of IIT-Madras and IIT-
Bombay, India for providing the spectral analysis. The authors
thank UGC and DST, New Delhi, for providing the equipment
facilities under UGC-SAP and DST-FIST programs, respec-
tively.
CONFLICT OF INTEREST
27. P. Haribabu, Y.P. Patil, K.H. Reddy and M. Nethaji, Transition Met.
Chem., 39, 167 (2014);
The authors declare that there is no conflict of interests
regarding the publication of this article.
https://doi.org/10.1007/s11243-013-9786-5.
28. H. Pagonda, P.P. Yogesh, H.R. Katreddi and N. Munirathinam, Inorg.
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