Synthesis, thermal, and biological studies of newly synthesized Cu(II) complexes with ciprofloxacin based on bromo-coumarins derivatives

Article abstract of DOI:10.1080/15533174.2012.754763

The authors describe synthesis, characterization, and biological evaluation of Cu(II) complexes. Characterization of ligands has been carried out by elemental analysis, melting point, mass spectra, (¹H & ¹³C) NMR, and FT-IR, while st

Full text of DOI:10.1080/15533174.2012.754763

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:1049–1058, 2013
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.754763
Synthesis, Thermal, and Biological Studies of Newly
Synthesized Cu(II) Complexes With Ciprofloxacin Based
on Bromo-Coumarins Derivatives
Ketan S. Patel, Jiten C. Patel, Hitesh R. Dholariya, and Kanuprasad D. Patel
Chemistry Department, V. P. & R. P. T. P. Science College, Sardar Patel University, Gujarat, India
carboxamide moiety are found to have diuretic, analgesic my-
orelaxant, antifungal,[4] and anthelmintic activities.[5] It is sug-
gested that the compounds having antimicrobial activity may act
either by killing the microbe or blocking their active site.[6] It is
also well known that coumarin derivatives can yield a wide vari-
ety of metal complexes with different coordination modes, spec-
troscopic properties, and potential applications. In particular, the
complexation of coumarin-derived ligands to various d-block
metal ions has been recognized as a promising route toward
development of new therapeutic agents. Ciprofloxacin is a typi-
cal second-generation quinolone (4-quinolone or quinolonecar-
boxylic acid) antibacterial agent used to treat diverse gram-
negative infections.
Metal is key for metalloproteinase to carry out specific physi-
ological functions.[7] Copper complexes of many several ligands
have been prepared and evaluated for anti-inflammatory,[8] an-
tioxidant activity,[9] and irritancy after oral, subcutaneous, and
local administration in rats and guinea pigs. Consequently, com-
pounds with antioxidant properties could be expected to offer
protection in rheumatoid arthritis and inflammation that leads
to potentially effective drugs. Thus, we found it interesting in
the current study to test the antiantioxidant activity of the newly
synthesized complexes.
The authors describe synthesis, characterization, and biologi-
cal evaluation of Cu(II) complexes. Characterization of ligands has
been carried out by elemental analysis, melting point, mass spectra,
(1H & 13C) NMR, and FT-IR, while structure of metal complexes
was confirmed by electronic spectra and FAB-mass spectral stud-
ies. Spectral studies confirm ligands is mono functional bidentate
and octahedral environment around metal ions. Thermal behavior
of Cu(II) complexes were investigated by means of TGA and mag-
netic measurements. The kinetic parameters are reported using
the Freeman-Carroll method. Complexes were found significant
potent antimicrobial and antioxidant activities compared to par-
ent ligands employed for complexation.
Supplemental materials are available for this article. Go to the
publisher’s online edition of Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry to view the supplemen-
tal file.
Keywords antimicrobial, antioxidant, ciprofloxacin
INTRODUCTION
Coumarin (2H-1-benzopyran-2-one) derivatives are oxygen-
containing heterocyclic compounds that are present in a large
number of natural products.[1] The diversity of applications for
coumarin-based compounds has resulted in well established
general methods for their synthesis were still attracts organic as
well as medicinal chemists toward improvements and modifica-
tions of already-existing methods,[2] which are known to have
biological activities.[3] Some coumarin derivatives possessing
Formerly, a series of coumarin derivatives and their transition
complexes was synthesized.[10] In order to have further investi-
gation, the coordination abilities and complexation behaviors of
coumarin-based ligands, we extended the study to the synthesis
of new bromocoumarin derivatives and their transition metal
complexes. The present work describes antimircobacterial and
antioxidant activity of new Cu(II) complexes.
Received 16 June 2012; accepted 28 November 2012.
The authors are grateful to the Principal and management of V. P. &
R. P. T. P. Science College, Vallabh Vidyanagar, for providing infras-
tructures and obligatory facilities for research. They are thankful to the
Director, SICART, Vallabh Vidyanagar, for analytical facilities. The
authors are also grateful to the Director, SAIF-RSIC, Panjab Univer-
sity, Chandigarh, for NMR analysis. They articulate their appreciation
to IIT-Bombay for the TG and DTG scan analysis facility.
Address correspondence to Kanuprasad D. Patel, Chemistry De-
partment, V. P. & R. P. T. P. Science College, Sardar Patel Univer-
sity, Vallabh Vidhyanagar 388 120, Gujarat, India. E-mail: drkdpa-
tel64@yahoo.co.in
EXPERIMENTAL
Materials
All reagents were of analytical reagent (AR) grade purchased
commercially from Spectro Chem. Ltd., Mumbai-India and used
without further purification. Solvents employed were distilled,
purified and dried by standard procedures prior to use.[11] Clio-
quinol was purchased from Agro Chemical Division, Atul Ltd.,
Valsad-India. The metal nitrates used were in hydrated form.
1049

1050
K. S. PATEL ET AL.
SCH. 1. General procedure for synthesis of ligands (A) (color figure available online).
mass from 3 to 8 mg were heated in Al2O3 crucible. The elec-
Physical Measurements
tronic spectra were collected using LAMBDA 19 UV/Vis/NIR
spectrophotometer (USA) in the region 200–1200 nm.
All reactions were monitored by thin-layer chromatography
(TLConaluminum plates coatedwithsilica gel 60F254, 0.25 mm
thickness, E. Merck, Mumbai-India) and detection of the com-
ponents were measured under UV light or explore in Iodine
chamber. Carbon, hydrogen, and nitrogen were estimated by
elemental analyzer Perkin-Elmer, USA 2400-II CHN analyzer.
Metal ion analyses was carried out by the dissolution of solid
complex in hot concentrated nitric acid, further diluting with
distilled water and filtered to remove the precipitated organic
ligands. Remaining solution was neutralized with ammonia so-
Synthesis of 3-Acetyl Coumarin
3-acetyl coumarin was prepared according to the reported
method.[13] A mixture of 6-bromo salicylaldehyde (12.2 g, 0.1
mol), ethyl acetoacetate (13.0 g, 0.1 mol) and 3–4 drops piperi-
dine were stirred for 10 min. at room temperature in a 100 mL
round bottom flask. After 10 min. it was heated for 30 min in
water bath. A yellow solid obtained was taken out and washed
with cold ether. It was recrystallized from chloroform-hexane.
Yield: 92%; M.p. 119.5◦C.
1
lution and the metal ions were titrated against EDTA. H and
13C NMR measurements were carried out on Advance-II 400
Bruker NMR spectrometer, SAIF, Chandigarh. The chemical
shifts were measured with respect to TMS, which was used as
internal standard and DMSO-d6 used as solvent. Infrared spec-
Synthesis of Ligands (A1–A5)
The neutral bidentate ligands were synthesized using
tra of solids were recorded in the region 4000–400 cm−1 on a Claisen-Schmidt condensation.[14] General procedure for syn-
Nicolet Impact 400D Fourier-Transform Infrared Spectropho- thesis of the ligands (A) is shown in Scheme 1. The ligands
tometer (USA) using KBr pellets. The FAB mass spectrum of were characterized using elemental analysis, FT-IR, Mass, and
the complex was recorded at SAIF, CDRI, Lucknow, with JEOL NMR (1H and 13C) spectroscopy, while the mass (A2), 1H NMR
SX-102/DA-6000 mass spectrometer. Melting point of the lig- (A2), 13C NMR (A4), and FT-IR (A2) spectra are given in the
ands and metal complexes were measured by open capillary tube supplementary data (S1–S4).
method. Solid state magnetic susceptibility measurements were
carried out at room temperature using a Gouy’s magnetic sus- Synthesis of 6-bromo-3-cinnamoyl-2H-chromen-2-one (A1)
ceptibility balance with mercury tetrathiocyanato cobaltate(II)
being used as a reference standard (g = 16.44 × 10−6 c.g.s.
units). Molar susceptibility was corrected using Pascal’s con-
stant.[12] Thermal decomposition (TG/DTG) analysis was ob-
tained by a model Diamond TG/DTA, Perkin-Elmer, USA. The
experiments were performed in N2 atmosphere at a heating rate
of 20◦C min−1 in the temperature range 30–840◦C. DSC anal-
yses were carried out using a Perkin-Elmer, USA, differential
scanning calorimeter (DSC-PYRIS-1). DSC analyses of com-
plexes were also evaluated from dynamic scanning experiments
In a 100 mL round-bottom flask 6-bromo 3-acetyl coumarin
(0.01 mol, 1.88 g) and benzaldehyde (0.015 mol) were taken
in 15 mL of pyridine. Catalytic amount of piperidine (1.0 mL)
was added and the reaction mixture was stirred for 10 min at
room temperature. After clear solution obtained, the reaction
mixture was refluxed on oil bath. Completion of reaction was
checked by TLC using mobile phase ethyl acetate:hexane (7:3).
After the completion of reaction, subsequently it was allowed
to room temperature. Afterwards it was pour into ice-cold wa-
ter and adjust the pH 4–5 using diluted HCl. A solid product
separated out was filtered off, later on washed with cold ethanol
and dried in air. It was recrystallized from ethanol. Yield 72%,
M.p. 163–165◦C. FTIR (KBr, cm−1): ν(C O, α, β-unsaturated
at multiple heating rates of 2.5, 5, 10, 15, and 20◦C min−1
,
with the best resolution and comparative results achieved at a
scanning rate of 10◦C min−1. The samples sizes were ranged in

MIXED LIGAND CU(II) COMPLEX
1051
TABLE 1
Analytical and physical parameters of complex
Elemental analyses,% found (required)
Compounds/
empirical formula
M.p.
(◦C)
Yield
(%)
Molecular
weight
μeff/
B.M.
C
H
N
Cu(II)
C1 C35H31BrCuFN3O8
C2 C36H35BrCuFN3O9
C3 C36H39BrCuFN3O12
C4 C35H34BrCuFN4O12
C5 C35H32BrCuFN4O11
53.42(53.61)
52.76(52.98)
49.63(49.81)
48.46(48.59)
49.36(49.63)
3.72(3.99)
4.24(4.32)
4.42(4.53)
3.82(3.96)
3.65(3.81)
5.16(5.36)
5.02(5.15)
4.59(4.84)
6.32(6.48)
6.48(6.61)
7.70(8.10)
7.53(7.79)
7.06(7.32)
7.18(7.35)
7.27(7.50)
350
350
300
350
300
67
75
64
72
70
784.08
816.13
868.16
865.11
847.10
1.82
1.86
1.78
1.82
1.84
ketone) 1615, ν(C O, lactone carbonyl of coumarin) 1738. 1H
NMR (DMSO-d6,400 MHz): δ = 6.84 (1H, d, J = 16, CH CH-
protons), 7.19–8.04 (8H, m, eight aromatic protons), 8.24 (1H, d,
J = 16, CH CH- protons), 8.58 (1H, s, C4-H). 13C NMR
(100 MHz, DMSO-d6): 118.2, 119.7, 124.4, 125.2, 126.9, 128.7,
129.6, 130.6, 134.9, 135.4, 135.8, 142.9 (12 different types of
aromatic carbons), 147.9(C-4), 152.7(C-9), 159.8 (C O, lac-
tone carbonyl of coumarin), 183.9 (C O, α, β-unsaturated ke-
tone). MS (ESI) m/z 355.0 [M+H]+, 357.0 [M+H]+2; Anal.
Calcd. for C18H11BrO3 (355.18): C 60.72 (60.87); H 2.98
(3.12).
Synthesis of 6-bromo-3-(3-p-tolylacryloyl)-2H-chromen-2-one
(A2)
A2 was synthesized by same method used for A1 by using
4-methyl benzaldehyde instead of benzaldehyde. Yield 73%,
M.p. 165–167◦C FTIR (KBr, cm−1): ν(C O, α, β-unsaturated
ketone), 1618, ν(C O, lactone carbonyl of coumarin) 1742.
1HNMR (DMSO-d6, 400 MHz) δ = 6.87 (1H, d, J = 16,
CH CH- protons), 7.15–8.09 (7H, m, Ar-H), 8.22 (1H, d,
J = 16, CH CH- protons); 2.28 (3H, s, -CH3); 8.55 (1H,
s, C4-H). 13C NMR (100 MHz, DMSO-d6): δ 21.2 (C-18,
CH3), 118.5, 119.5, 124.7, 125.2, 128.4, 128.7, 130.1, 132.9,
134.4, 134.8, 137.6, 142.5 (12 different types of aromatic
carbons), 147.6(C-4), 152.8(C-9), 159.6 (C O, lactone car-
bonyl of coumarin), 183.4 (C O, α, β-unsaturated ketone).
MS (ESI) m/z 368.0 [M+H]+, 370.0 [M+H]+2; Anal. Calcd.
for C19H13BrO3 (369.21): C 61.67 (61.81); H, 3.36 (3.55)
SCH. 2. General synthetic route of complexes (C) (color figure available
online).
(C-4), 148.7(C-16, carbon attach to phenolic NO2), 154.4(C-9),
159.2 (C O, lactone carbonyl of coumarin), 160.4(C-16), 189.5
(C O, α, β-unsaturated ketone). MS (ESI) m/z 384.0 [M+H]+,
386.0[M+H]+2; Anal. Calcd. for C19H13BrO4 (385.21): C 59.08
(59.24), H 3.24 (3.40).
Synthesis of 6-bromo-3-(3-(3-nitrophenyl)acryloyl)-2H-
chromen-2-one (A4)
A5 was synthesized by same method used for A1 by us-
ing 3-nitro benzaldehyde instead of benzaldehyde. Yield 74%,
M.p. 158–160◦C FTIR (KBr, cm−1): ν(C O, α, β-unsaturated
ketone) 1622, ν(C O, lactone carbonyl of coumarin) 1745,
Synthesis of 6-bromo-3-(3-(3-methoxyphenyl)acryloyl)-2H-
chromen-2-one (A3)
1
ν(O-H) 3426,. HNMR (DMSO-d6, 400 MHz) δ = 6.82 (1H,
A4 was synthesized by same method used for A1 by using
3-methoxybenzaldehyde instead of benzaldehyde. Yield 76%,
M.p. 168–169◦C FTIR (KBr, cm−1): ν(C O, α, β-unsaturated
ketone) 1621, ν(C O, lactone carbonyl of coumarin) 1743.
1HNMR (DMSO-d6, 400 MHz,) δ = 6.83(1H, d, J = 16,
CH CH- protons), 7.07–8.05 (7H, m, Ar-H), 8.25 (1H, d, J
= 16, CH CH- protons); 3.79 (3H, s, -OCH3); 8.58(1H, s, C4-
H). 13C NMR (100 MHz, DMSO-d6): δ 55.7 (C-17, OCH3), δ
114.1, 116.3, 118.5, 124.9, 125.7, 126.9, 127.1, 129.5, 130.6,
134.8, 146.8, (11 different types of aromatic carbons), 147.8
d, J = 16, CH CH- protons), 7.10–8.03 (8H, m, Ar-H), 8.24
(1H, d, J = 16, CH CH- protons); 8.56(1H, s, C4-H). 13C
NMR (100 MHz, DMSO-d6): δ 114.1, 116.3, 118.5, 124.9,
125.7, 126.9, 127.1, 128.7, 129.5, 130.6, 134.8, 146.8, (12 dif-
ferent types of aromatic carbons), 147.2 (C-4), 148.7(C-16, car-
bon attach to phenolic NO2), 154.7(C-9), 159.6 (C O, lac-
tone carbonyl of coumarin), 189.7 (C O, α, β-unsaturated
ketone). MS (ESI) m/z 399.0 [M+H]+, 401.0 [M+H]+2
;
Anal. Calcd. for C18H10BrNO5 (400.18): C 53.82 (54.02),
H 2.38(2.52).

1052
K. S. PATEL ET AL.
FIG. 1. Freeman-Carroll plot for thermal dehydration of [Cu(A2)(CF)(H2O)OH]•H2O.
Complexes C2-C5 was prepared according to same method
and their physicochemical parameters are summarized in Ta-
ble 1. The synthetic protocol of complexes is shown in Scheme 2,
while FT-IR spectrum of C2 is given in the supplementary data
(S5).
Synthesis of 6-bromo-3-(3-(4-nitrophenyl)acryloyl)-2H-
chromen-2-one (A5)
A6 was synthesized by same method used for A1 by us-
ing 4-nitro benzaldehyde instead of benzaldehyde. Yield 75%,
M.p. 158–160◦C FTIR (KBr, cm–1): ν(C O, α, β-unsaturated
ketone) 1625, ν(C O, lactone carbonyl of coumarin) 1740.
1HNMR (DMSO-d6, 400 MHz) δ = 6.86 (1H, d, J = 16,
CH CH- protons), 7.10–8.05 (7H, m, Ar-H), 8.26 (1H, d, J =
16, CH CH- protons); 8.57(1H, s, C4-H). 13C NMR (100 MHz,
DMSO-d6): δ 114.2, 116.5, 118.7, 124.4, 125.9, 126.5, 127.7,
129.8, 130.9, 134.2, 146.4, (11 different types of aromatic car-
bons), 147.6 (C-4), 148.9(C-16, carbon attach to phenolic NO2),
154.6(C-9), 159.8 (C O, lactone carbonyl of coumarin), 189.5
(C O, α, β-unsaturated ketone). MS (ESI) m/z 399.0 [M+H]+,
401.0 [M+H]+2; Anal. Calcd. for C18H10BrNO5 (400.18): C
53.82(54.02), H 2.38(2.52).
Antimicrobial Activity
Peptone (5 g), sodium chloride (5 g), and beef extract (1.5 g)
were suspended in 1000 mL distilled water. The solution was
boiled to dissolve all the ingredients completely. The pH of
the solution at 25◦C was adjusted to 7.4 0.2 and sterilized
by autoclaving at 15 lb pressure (121◦C) for 15 min. One day
prior to the test, bacterial and fungal strains were made in the
sterile nutrient broth and incubated at 37◦C overnight. Sam-
ple solutions were prepared by dissolving 1 mg of sample in
10 mL of 2% DMSO to give the concentration 100 μg/mL.
The standard solutions of streptomycin (antibacterial drug) and
fluconazole (antifungal drug) were prepared in 2% DMSO to
give concentration of 100 μg/mL. Serial broth microdilution
was adopted as a reference method. Serial dilutions of test
Synthesis of Metal Complexes
[Cu(A1)(CF) (H2O)OH] (C1)
An aqueous solution of Cu(NO3)2•3H2O salt (10 mmol) compounds were made in broth, after which a standardized
was added into ethanolic solution of ligand (A1) (10 mmol) and microorganism suspension was added. Quantities of test com-
subsequently an ethanolic solution of ciprofloxacin (10 mmol) pounds were serially diluted to attain the final concentrations
was added with continuous stirring. Then the pH was ad- of 100, 50, 25, 12.5, 6.25, and 3.125 μg/mL. One of the test
justed in between 4.5–6.0 by addition of diluted NH4OH so- tubes was kept as control. Each of the 10 test tubes was in-
lution. The resulting solution was refluxed for 5 h and then oculated with a suspension of microorganism to be tested and
heated over a steam bath to evaporate up to half of the vol- incubated at 35◦C for 18 h. At the end of the incubation period,
ume. The reaction mixture was kept overnight at room tem- the tubes were visually examined for the turbidity. Cloudiness
perature. A fine colored crystalline product was obtained. The in the test tubes indicated that microorganism growth has not
obtained product was washed with ether and dried over vacuum inhibited by the antibiotic contained in the medium at the test
desiccators.
concentration.
TABLE 2
FT-IR data of synthesized compounds
ν(O–H) br
υ
υ
α, β-unsaturated ν lactone carbonyl ν ν (Cu–O)carbo ν (Cu–O)keto ν (C–F) w ν (C–N) w
Comp
cm–1
(COO)sy (COO)asy
(C O) s cm–1
(C O) s cm–1
cm–1
cm–1
cm–1
cm—1
C1
C2
C3
C4
C5
3435
3432
3428
3445
3447
1371
1373
1375
1372
1376
1590
1586
1582
1587
1585
1605
1613
1606
1608
1612
1722
1732
1730
1725
1737
428
425
423
422
427
545
542
550
548
541
1275
1272
1277
1274
1270
1354
1355
1349
1352
1357
s
= strong, w = weak, br = broa.

MIXED LIGAND CU(II) COMPLEX
1053
TABLE 3
Thermoanalytical results (TG and DTG) of metal complexes
Complex
C1
TG range/◦C
60–380
DTGmax/◦C
Mass loss% obsvd. (calcd.)
49.34(49.76)
Assignment
231
342
553
>650
84
218
300
540
>650
95
245
354
562
>650
98
232
354
568
>650
93
Loss of one –OH & H2O molecules
Removal of A1 ligand
Removal of Ciprofloxacin ligand
Leaving CuO residue
Loss of one lattice water molecules
Loss of one –OH & H2O molecules
Removal of A2 ligand
Removal of Ciprofloxacin ligand
Leaving CuO residue
Loss of three lattice water molecules
Loss of one –OH & H2O molecules
Removal of A3 ligand
Removal of Ciprofloxacin ligand
Leaving CuO residue
Loss of two lattice water molecules
Loss of one –OH & H2O molecules
Removal of A4 ligand
Removal of Ciprofloxacin ligand
Leaving CuO residue
380–800
70–380
42.25
8.12
51.75(51.92)
C2
C3
C4
C5
380–800
80–380
40.59
7.45
54.35(54.62)
380–800
80–375
38.16
7.33
54.28(54.46)
375–800
70–370
38.30
7.30
53.15(53.49)
Loss of one lattice water molecules
Loss of one –OH & H2O molecules
Removal of A5 ligand
Removal of Ciprofloxacin ligand
Leaving CuO residue
247
355
545
>650
370–800
39.11
7.49
10 mM TPTZ solution in 40 mM HCl, 20 mM FeCl3.6H2O and
25 mL, 0.3 M acetate buffer at pH 3.6. A mixture of 40.0 mL,
0.5 mM sample solution, and 1.2 mL FRAP reagent was incu-
bated at 37◦C for 15 min. Absorbance of intensive blue color
[Fe(II)–TPTZ] complex was measured at 593 nm. The ascorbic
acid was used as a standard antioxidant compound. The re-
sults are expressed as ascorbic equivalent (mmol/100 g of dried
Antioxidant Activity
Ferric reducing antioxidant power (FRAP) was measured by
a modified method of Benzie and Strain.[15] The antioxidant
potentials of the compounds were estimated as their power
to reduce the TPTZ–Fe(III) complex to TPTZ–Fe(II) com-
plex (FRAP assay), which is simple, fast, and reproducible.
FRAP working solution was prepared by mixing a 25.0 mL,
TABLE 4
Thermodynamic data of the thermal decomposition of metal complexes
Compound
C1
TG range/◦C
Ea/kJ mol–1
n
A/s–1
S∗/J K –1 mol–1
H∗/kJ mol–1
G∗/kJ mol–1
60–380
380–800
70–380
380–800
80–380
380–800
80–380
380–800
70–380
380–800
3.37
8.0
3.20
8.7
3.82
10.02
3.76
3.47
3.33
10.05
0.99
1.31
1.15
1.25
1.09
1.21
1.35
1.31
0.97
1.18
0.142
0.059
0.102
0.082
0.181
0.025
0.168
0.073
0.152
0.061
–104.45
–101.14
–103.23
–101.21
–101.09
–98.12
–109.86
–95.56
–104.76
–103.43
0.588
0.020
0.226
0.030
0.756
0.89
0.843
0.076
0.587
0.061
32.12
44.37
37.03
45.68
38.70
43.10
35.05
53.11
32.97
48.58
C2
C3
C4
C5

1054
K. S. PATEL ET AL.
FIG. 2. TG curve of the complex [Cu(A2)(CF)(H2O)OH]•H2O.
compound). All the tests were run in triplicate and are expressed RESULTS AND DISCUSSION
as the mean and standard deviation (SD)
The synthesized Cu(II) complexes were characterized by ele-
mental analysis, FTIR, and mass (ESI-MS & FAB) spectra, The
metal ion in their complexes were determined after mineraliza-
tion. The metal content in chemical analysis was estimated by
complexometrically,[18] while geometry of the complexes was
confirmed from electronic spectra, magnetic moment, thermal
properties, and kinetic measurements. However, ligands and its
complexes have been screened for their in vitro antioxidant and
antimicrobial activities.
Thermal Studies
From decomposition process, the thermodynamic activation
parameters of the complexes such as energy of activation (Ea)
and order of reaction (n) were evaluated graphically by employ-
ing the Freeman–Carroll[16] method using the following relation:
[( − Ea/2.303R)ꢀ(1/T)]ꢀ log wr = −n + [ꢀlog(dw/dt)/
ꢀ log wr]
Elemental Analysis
The analytical and physiochemical data of the complexes
are summarized in Table 1. The experimental data were in very
good agreement with the calculated ones. The complexes were
colored, insoluble in water, and commonly organic solvents
while soluble in DMSO as well as stable in air. The structure of
the complexes is assumed according to the chemical reaction as
shown in the following:
where R is gas constant, T is the temperature in K, wr = wc–w;
wc is the mass loss at the completion of the reaction, and w
is the total mass loss up to time t. Ea and n are the energy of
activation and order of reaction, respectively. A typical plots
of [ꢀlog(dw/dt)/ꢀlogwr] versus [ꢀ(1/T)/ꢀlogwr] were linear
for all of the decomposition steps. The energy of activation
Ea was calculated from the slopes of these plots for all stages
and the order of reactions (n) determined from the intercept,
which shows first order reaction over the whole range of de-
composition for all complexes. A typical plot for the thermal
degradation of [Cu(A2)(CF)(H2O)(H2O)OH]•H2O is shown in
Figure 1. The thermodynamic activation parameters of the de-
composition process of dehydrated complexes such as entropy
(S∗), pre-exponential factor (A), enthalpy (H∗) and free energy
of the decomposition (G∗), were calculated using the following
relations:[17]
Cu(NO3)2 • 3H2O + A + CF →
[Cu(A)(CF)(H2O)OH] • xH2O + 2HNO3+nH2O
where A = A1, A2, A3, A4, A5; x = 0, 1, 3, 2, 1; and n = 3, 2,
0, 1, 2.
FT-IR Spectra
The coordination sites of ligand are elucidated using IR. The
ν(C−O) stretching vibration band appears at ∼1706 cm−1 in
the spectra of ciprofloxacin, while in mixed-ligand complexes
this band shifted toward lower energy at ∼1619–1675 cm−1
(Table 2), suggests that coordination occurs through pyridone
oxygen atom.[19] The absorption bands observed at ∼1614 and
∼1345 cm−1 in ciprofloxacin are assigned to be ν(COO)asy
and ν(COO)sym, respectively, while in mixed-ligand complexes
Ea/RTs2 = A/Ф exp (−Ea/RTs).
S∗ = 2.303(log Ah/KTs)R,
H∗ = Ea − RTs∗
G∗ = H∗−Ts S∗
these bands observed at ∼1582–1588 and ∼1372–1375 cm−1
.
The frequency separation (ꢀν = ν(COO)asy – ν(COO)sym) in
where h is the plank constant, Ф is the heating rate, K is the investigated mixed-ligand complexes is greater than 200 cm−1
,
Boltzmann constant, and Ts is the temperature of peak from suggesting that the carboxyl to group posses unidentate na-
DTG curve.
ture[20]. The absorption bands observed at ∼425–429 cm−1

MIXED LIGAND CU(II) COMPLEX
1055
SCH. 3. Thermal fragmentation of complex [Cu(A2)(CF)(H2O)OH]•H2O.

1056
K. S. PATEL ET AL.
FIG. 3. DTG curve of the complex [Cu(A2)(CF)(H2O)OH]•H2O.
and ∼512–523 cm−1 are attributed to υ(Cu–O)(carbo) and
υ(Cu–O)(keto), respectively, while in case of complex the ob-
served band at ∼470 cm−1 is due to the υ(Cu–O)(phenolic).
The sharp band in ciprofloxacin at ∼3520 cm−1[21] is due to
hydrogen bonding, which is attributed to ionic resonance struc-
ture and peak observed because of stretching vibration of free
hydroxyl group. This band absolutely vanished in the spectra of
mixed ligand complexes indicates deprotonation of carboxylic
proton. The metal-terminal oxygen (Cu Ot) band observed at
∼1000 cm−1 region suggesting the anti conformers and copper
has a distorted octahedral structure.[22] Some prominent IR band
frequencies of compounds are provided in Table 2.
of metal complexes. The electronic spectra of complexes were
recorded in DMF solution with scan range 200–1200 nm. Usu-
ally octahedral geometry was found for Cu(II) complexes,[23]
then again, several copper compounds show temperature de-
pendent geometric distortions and single copper ions in a host
lattice of regular symmetry may reveal interesting spectroscopic
properties.[24]
The electronic spectra of hexa-coordinate Cu(II) complexes
were either D4h or C4v symmetry, the Eg and T2g level of 2D free
ion term will split into B1g, A1g, B2g, and Eg levels, respectively,
under the influence of the distortion, which causes the two tran-
2
2
sitions such as 2B1g→ B2g and 2B1g→ A1g. This promotes the
distorted octahedral Cu(II) complex which was usual in the d9
system.[25] The electronic spectra of Cu(II) complexes (C1-C5)
display three prominent bands. Low intensity broad band in the
16,800–17,500 cm−1 region was assigned as 10 Dq band cor-
Electronic Spectra and Magnetic Measurement
Electronic spectral data along with magnetic susceptibility
measurements gave sufficient support to determine the geometry
2
responding to 2Eg→ T2g transition.[26] In addition, there was a
TABLE 5
Antimicrobial and antioxidant results of compounds
Minimal inhibition concentrationa of microorganisms (μg/mL)
Bacteria
Fungi
Antioxidant activityb
Compound
S.P.
B.S.
E.C.
P.A.
C. A.
A. N.
FRAP value (mmol/100 g)
L1
100
25
50
50
100
50
12.5
6.25
12.5
25
0.025
NT
NT
50
50
25
25
50
100
25
25
100
50
100
6.25
3.125
12.5
12.5
0.020
NT
100
50
50
50
100
50
25
6.25
25
50
25
50
100
50
25
12.5
6.25
25
12.5
NT
0.05
NT
100
50
25
50
25
NT
NT
NT
NT
NT
L2
L3
L4
L5
C1
50
25
50
25
311.7021
337.234
427.7447
367.0213
309.4468
NT
C2
C3
3.25
25
12.5
0.025
NT
NT
3.125
12.5
6.25
NT
0.05
NT
C4
C5
25
Streptomycin
Fluconazole
Ascorbic acid
0.020
NT
NT
NT
500
NT
aAverage value of triplicate results. bFRAP results expressed in mM of ascorbic acid per 100 g of sample (i.e., mmol/100 g). NT = Not Tested

MIXED LIGAND CU(II) COMPLEX
1057
high intensity band in the 22,500–27,000 cm−1 region. This band
was due to symmetry forbidden ligand → metal charge trans-
fer transition.[27] The band above 27,000 cm−1 was assigned
as ligand band. Therefore the distorted octahedral geometry
around Cu(II) ion was suggested on the basis of electronic spec-
tra,[28] which was further revealed by its magnetic moment of
1.79–1.87 BM falls within the range generally observed for oc-
tahedral Cu(II) complexes.[29] Therefore the electronic spectral
data and magnetic moment data support the octahedral geome-
try of the all complexes, while the electronic spectra of C2 given
in supplementary material (S6).
m/z of all the fragments of complex with the relative intensity
confirms the stoichiometry of the complex.
Antimicrobial Bioassay
All the prepared compounds were screened for the inhibi-
tion of microbial growth under standard conditions. The an-
tibacterial and antifungal tests were carried out using the serial
broth dilution method. The in vitro antimicrobial activities of
the investigated compounds were screened against the bacte-
rial and fungal species. The free ligand and its transition metal
complexes are tested at different concentrations and minimum
inhibitory concentration is determined.
Thermal Studies of Synthesized Complexes
Antibacterial activity
Thermal data and kinetic parameters of the complexes
are given in Tables 3 and 4, respectively. The typical TG
curves of the complexes [Cu(A2)(CF)(H2O)OH]•H2O are char-
acterized in Figure 2. Thermal fragmentation for complexes
[Cu(A2)(CF)(H2O)OH]•H2O is shown in Scheme 3. The anhy-
drous complexes show enormous thermal stability up to 250◦C.
Next two steps were occurring exothermic and endothermic
related with removal of coordinated ligand (coumarins) and
ciprofloxacin, respectively. In the third subsequent stage, the
decomposition and combustion of ligand (loss 45.23%) occurs
at 260–430◦C. Where in fourth subsequent stage for complex
show the decomposition and combustion of ciprofloxacin (loss
40.59%) occurs at 500–780◦C. The removal of ciprofloxacin un-
dergoes decomposition forming CuO as the final residue. The
thermodynamic activation parameters of the decomposition pro-
cess of dehydrated complexes, such as activation entropy (ꢀS#),
pre-exponential factor (A), activation enthalpy (ꢀH#), and free
energy of activation (ꢀG#), were calculated using the reported
equations[30] and are tabulated in Table 4. According to the
kinetic data obtained from DTG curves corresponding to the
complex (C2) is represented in Figure 3, all the complexes have
negative entropy, which indicates that the studied complexes
have more ordered systems than reactants.[31] The kinetic pa-
rameters, mainly energy of activation (Ea), was useful in con-
veying the strength of the bonding of ligand moieties with the
metal ion. The calculated Ea values of the investigated com-
plexes for the dehydration stage of ligand (An) were in the range
3.20–3.82 kJ mol−1. The relatively high Ea value indicates that
the ligand (An) is strongly bonded the metal ion. The final solid
product of decomposition was CuO (7.45%) accompanied by
broad exothermic effect on above 800◦C.
The antibacterial activity of synthesized compounds was
tested against skin disease causing bacteria like Streptococ-
cus pyogenes (ATCC12384), Bacillus subtilis (ATCC11774),
Escherichia coli (ATCC25922), and Pseudomonas aerugi-
nosa (ATCC25619). The ligand and its metal complexes were
screened for their antibacterial activities according to the re-
spective literature protocol[32] and the results obtained are pre-
sented in Table 5. The results were compared with those of
the standard drug. All the metal complexes were more po-
tent bactericides than the ligand. C1 complex was much less
microbially active than the other complexes. From Table 5,
it can be seen that the highest inhibition of growth occurred
on C3 complex against the microorganism, while C2, C4, and
C5 shows enhance activity than C1 but less potent than C3.
There was a marked increase in the bacterial activities of the
Cu(II) complex as compared with the free ligand under test,
which is in agreement with antibacterial properties of a range
of Cu(II) complexes evaluated against several pathogenic bac-
teria.[33] This enhancement of metal complexes in the activity
can be explained on the basis of chelation theory.[34] Chelation
reduces the polarity of the metal atom mainly because of partial
sharing of its positive charge with the donor groups and pos-
sible π-electron delocalization within the whole chelate ring.
Such Chelation also enhances the lipophililic character of the
central metal atom, which subsequently favors its permeation
through the lipid layers of cell membrane and the blocking
of the metal binding sites on enzymes of microorganism. The
variation in the effectiveness of different compound against dif-
ferent organisms depends either on the impermeability of the
cell of the microbes or differences in the ribosomes of microbial
cells.
FAB Mass Spectra
Antifungal activity
Fast atom bombardment (FAB) mass spectra and its frag-
The fungal strains used to demonstrate the antifungal po-
mentation scheme of the C1 complex are given in supplemen- tency of the synthesized compounds were Candida albicans
tary material (S7-S8). This spectrum reveals that isotropic peak (ATCC 66027) and Aspergillus niger (ATCC 64958). The re-
at m/z 798 (molecular ion peak) of complex (without water of sults of inhibition are compared with standard antifungal drug
crystallization), whereas several peaks observed at 788.07, 752, fluconazole (Table 5). The complexes exhibit stronger activity
673, 588, 498, 457, 388, 336, and 292 m/z values. Thus the with lower MIC value as compared to free ligand except C1

1058
K. S. PATEL ET AL.
complex whose activity is nearly same as that of the ligand.
Among all the complexes, C3 complex is found to be highly
active against A.n. with a MIC of 3.125 μg/mL. Thus, activity
of ligand has enhanced on complexation. However, activity ex-
hibited by the ligand as well as the corresponding complexes
is less compared with the standard antifungal drug used in the
study.
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10. Patel, K.S.; Patel, J.C.; Dholariya, H.R.; Patel, K.D. Spec. Chim. Acta, Part
A 2012, 96, 468. Panchani, S.C.; Kharadi, G.J.; Patel, K.D. Int. J. Polym.
Mater. 2010, 59, 60; Kharadi, G.J.; Patel, K.D. Appl. Organomet. Chem.
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19. Kharadi, G.J.; Patel, J.A.; Dholakiya, B.Z. Appl. Organomet. Chem. 2010,
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1051.
Antioxidant Studies
A capacity to transfer a single electron i.e. the antioxidant
power of all compounds was determined by a FRAP assay. The
FRAP value was expressed as an equivalent of standard antiox-
idant ascorbic acid (mmol/100 g of dried compound). FRAP
values indicate that all the compounds have a ferric reducing
antioxidant power. The compounds C3 and C4 showed relatively
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poor antioxidant power (Table 5).
In conclusion, the antimicrobial testing results reveal that
complexes possess higher activity at lower concentration com-
pared with the parent ligand. It is known that chelation tends to
make the Schiff bases more powerful and potent bacteriostatic
agents.[35]
CONCLUSIONS
Here elucidate the synthesis of biological active coumarin
derivatives (A1-A5) and their Cu(II) complexes (C1-C5). The
structures of the ligands were investigated and confirmed by
1
the elemental analysis, FT-IR, H-NMR, 13C-NMR, and mass
spectral studies. Octahedral geometry were allocated for Cu(II)
complexes on the basis of electronic, magnetic moment, and TG
analysis. Complexes shows momentous effective antioxidant ac-
tivities compared to their ligands employed for complexation. In
vitro antimicrobial activity of all synthesized compounds show
good results with an enhancement of activity on complexation
with metal ions. This enhancement in the activity may be at-
tributed to increased lipophilicity of the complexes. In review,
the antimicrobial testing results reveal that complexes possess
higher activity compared to the parent ligand. The kinetic pa-
rameters, especially energy of activation (Ea), are helpful in
assigning the strength of the complexes. The calculated Ea val-
ues of the investigated complexes for the first dehydration step
were in the range 3.20–3.82 kJ mol−1 (Table 4). Based on the
activation energy values the thermal stabilities of complexes in
the decreasing order are C3 C4 C1 C5 > C2.
28. Parmar, N.J.; Teraiya, S.B.; Patel, R.A. J. Coord. Chem. 2010, 63,
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2001.
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33. Chohan, Z.H.; Supuran, C.T.; Scozzafava, A. J. Enz. Inhib. Med. Chem.
2004, 19, 79.
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