Synthesis, characterization, DNA binding, oxidative damage of DNA strand scission, and antimicrobial activities of β-diketone condensed Schiff-base transition metal complexes

Article abstract of DOI:10.1080/00958972.2010.485643

Co(II), Ni(II), Cu(II), Zn(II), and VO(IV) complexes containing a versatile β-diketone Schiff-base ligand (obtained by the condensation of 3-furan-2-ylmethylene-2,4-dione and 2-aminophenol) have been synthesized and characterized. Microanalytical, magnetic, and spectroscopic data reveal that the central metal is coordinated to two oxygens of phenolate and two nitrogens of imine of the ligand. Binding of synthesized complexes with calf thymus DNA has been investigated by spectroscopic and electrochemical methods and viscosity measurements. The complexes are able to form adducts with DNA and to distort the double helix by changing the base stacking. Electrostatic binding of vanadyl complex is observed from the weak hypochromism in electronic absorption spectra and no change in the viscosity with DNA. Oxidative DNA cleavage activities of the complexes are studied with supercoiled pUC19 DNA using gel electrophoresis. The hydroxyl radical (OH?) is likely to be the species responsible for the cleavage of pUC19 DNA by the synthesized complexes. Under our experimental conditions, the vanadyl complex has no significant cleavage of DNA. The compounds have been screened for activity against several bacterial and fungal strains and the results are compared with the activity of standard drugs.

Full text of DOI:10.1080/00958972.2010.485643

This article was downloaded by: [University of Haifa Library]
On: 17 May 2013, At: 05:38
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis, characterization, DNA
binding, oxidative damage of DNA
strand scission, and antimicrobial
activities of β-diketone condensed
Schiff-base transition metal complexes
a
a
a
a
N. Raman , R. Jeyamurugan , R. Usha Rani , T. Baskaran
&
b
L. Mitu
a
Research Department of Chemistry, VHNSN College,
Virudhunagar 626001, Tamil Nadu, India
b
Department of Physics and Chemistry, University of Pitesti,
Pitesti 110040, Romania
Published online: 18 May 2010.
To cite this article: N. Raman , R. Jeyamurugan , R. Usha Rani , T. Baskaran & L. Mitu (2010):
Synthesis, characterization, DNA binding, oxidative damage of DNA strand scission, and
antimicrobial activities of β-diketone condensed Schiff-base transition metal complexes, Journal of
Coordination Chemistry, 63:9, 1629-1644
To link to this article: http://dx.doi.org/10.1080/00958972.2010.485643
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-
conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Journal of Coordination Chemistry
Vol. 63, No. 9, 10 May 2010, 1629–1644
Synthesis, characterization, DNA binding, oxidative damage of
DNA strand scission, and antimicrobial activities of b-diketone
condensed Schiff-base transition metal complexes
N. RAMAN*y, R. JEYAMURUGANy, R. USHA RANIy,
T. BASKARANy and L. MITUz
yResearch Department of Chemistry, VHNSN College,
Virudhunagar 626001, Tamil Nadu, India
zDepartment of Physics and Chemistry, University of Pitesti,
Pitesti 110040, Romania
(
Received 20 November 2009; in final form 3 February 2010)
Co(II), Ni(II), Cu(II), Zn(II), and VO(IV) complexes containing a versatile ꢀ-diketone
Schiff-base ligand (obtained by the condensation of 3-furan-2-ylmethylene-2,4-dione and
2-aminophenol) have been synthesized and characterized. Microanalytical, magnetic, and
spectroscopic data reveal that the central metal is coordinated to two oxygens of phenolate and
two nitrogens of imine of the ligand. Binding of synthesized complexes with calf thymus DNA
has been investigated by spectroscopic and electrochemical methods and viscosity measure-
ments. The complexes are able to form adducts with DNA and to distort the double helix by
changing the base stacking. Electrostatic binding of vanadyl complex is observed from the weak
hypochromism in electronic absorption spectra and no change in the viscosity with DNA.
Oxidative DNA cleavage activities of the complexes are studied with supercoiled pUC19 DNA
.
using gel electrophoresis. The hydroxyl radical (OH ) is likely to be the species responsible for
the cleavage of pUC19 DNA by the synthesized complexes. Under our experimental conditions,
the vanadyl complex has no significant cleavage of DNA. The compounds have been screened
for activity against several bacterial and fungal strains and the results are compared with the
activity of standard drugs.
Keywords: DNA binding; DNA cleavage; Complexes; Schiff base; Antimicrobial
1. Introduction
The interaction of transition metal compounds with DNA has been extensively studied.
Due to the unusual binding properties and general photoactivity, these coordination
compounds were suitable candidates as DNA secondary structure probes, photo-
cleavers, and antitumor drugs [1–3]. Transition metal complexes can bind to DNA by
non-covalent interactions such as external surface binding for cations, groove binding
for large molecules, and intercalating system. Among the factors governing the binding
modes, it appears that the most significant is the molecular shape. Those complexes that
best fit against the DNA helical structure display the highest binding affinity [4, 5].
*
Corresponding author. Email: drn_raman@yahoo.co.in
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.485643

1
630
N. Raman et al.
Applications of these complexes require that the complex bind to DNA through
an intercalative mode with the ligand intercalating into the adjacent base pairs of DNA.
In fact, some of these complexes also exhibit interesting properties upon binding
to DNA [6–8].
In this article, we synthesized Co(II), Ni(II), Cu(II), Zn(II), and VO(IV) complexes
containing a ꢀ-diketone ligand with phenolic oxygen and azomethine nitrogen and
studied their binding properties to calf thymus DNA (CT DNA) using absorption
spectroscopy, cyclic DPV (differential pulse voltammogram), and viscosity measure-
ments. Their oxidative cleavage behavior toward pUC19 DNA and the mechanism
for cleavage were also investigated. The result should be of value in understanding
the binding of complex to DNA as well as laying the foundation for the design of DNA
molecular light switch and DNA cleaving agents [9].
2
2
. Experimental
.1. Chemicals
All reagents were procured from Merck. The solvents used for electrochemical and
spectroscopic studies were purified by standard procedures [10]. Supercoiled (SC)
pUC19 (cesium chloride purified) DNA was purchased from Bangalore Genei (India).
DNA solution in 5 mmol Tris–HCl/50 mmol NaCl (pH 7.2) buffer medium gave a ratio
of UV absorbance at 260–280 nm of ca 1.8–1.9, indicating that the DNA was
sufficiently free from protein [11]. The DNA concentration per nucleotide was
determined by absorption spectroscopy using the molar absorption coefficient
ꢀ
1
ꢀ1
ꢁ
(
4
6600 mol cm ) at 260 nm [12]. Stock solutions were stored at 4 C and used within
days. Agarose (molecular biology grade), ethidium bromide (EB), and tetrabutyl-
ammonium perchlorate were obtained from Sigma (USA). Tris–HCl buffer solution
was prepared using deionized, sonicated triply-distilled water.
2
.2. Physical measurements
Elemental analyses (C, H, N, and S) were carried out with a Carlo Erba 1108 analyzer.
ꢀ1
Infrared (IR) spectra of the samples were recorded in the region 4000–400 cm using
KBr pellets and a Perkin Elmer 783 spectrophotometer. Proton nuclear magnetic
1
resonance ( H-NMR) spectra (300 MHz) of the samples were recorded in CDCl and
3
DMSO-d with TMS as internal standard on a Bruker Avance DRX 300 FT-NMR
6
(
(
FT, Fourier transform) spectrometer. Fast atom bombardment mass spectra
FAB-MS) were obtained using a VGZAB-HS spectrometer in a 3-nitrobenzyl alcohol
matrix. The X-band electron spin resonance (ESR) spectra of the complexes were
recorded at 300 and 77 K using tetracyanoethylene (TCNE) as the g-marker. Electronic
absorption spectra were recorded using a Shimadzu UV-1601 spectrophotometer.
Magnetic susceptibility measurements of the complexes were carried out by Gouy
balance using copper sulfate as the calibrant. The purity of the ligand and its complexes
was evaluated by column chromatography and thin layer chromatography.
Antimicrobial activity was carried out in the Research Department of Chemistry,

ꢀ
-Diketone condensed Schiff base
1631
VHNSN College, Virudhunagar, in association with the Department of Microbiology
of the same institute.
2.3. Preparation of Schiff-base ligand
The non-enolizable diketone was prepared by using the modified procedure reported
earlier [13]. Acetylacetone (10 mmol) was mixed with furfuraldehyde (10 mmol) and
piperidine, and the reaction mixture was stirred thoroughly for ca 5 h with occasional
cooling. Gradually, a dark brown precipitate separated in small amounts. The reaction
mixture was set aside to evaporate to dryness and the residual solid was washed with an
excess of petroleum ether to remove the unreacted reagents. The obtained solid product
was recrystallized from CHCl –petroleum ether to give a pure brown Knoevenagel
3
condensate (3-furan-2-ylmethylene-2,4-dione) that was used as the starting material for
the preparation of Schiff base.
3-Furan-2-ylmethylene-2,4-dione (10 mmol) in 50 mL of ethanol was refluxed with
-aminophenol (20 mmol) for 6 h after the addition of potassium carbonate. The
2
potassium carbonate was filtered off from the reaction mixture and the solvent was
evaporated to dryness. The residual solid was washed with an excess of petroleum ether
to remove any unreacted reagents and the dark brown powder was filtered and dried
in vacuo. Yield: 68%. IR (KBr): 3100–3000, (–OH); 1634, (–C¼N); 2928, (–C–CH )
3
ꢀ
1 1
cm . H-NMR (CDCl ): ꢁ(–OH), 10.1 (s); (phenyl multiplet), 6.6–7.2 ꢁ(m); ꢁ(–CH ),
3
3
þ
þ
2
[
.0 (s); ꢁ(–CH¼C–), 5.8 (s). MS m/z: 361, (M þ 1); 145, [C H N ] ; 93, [C H O] ; 77,
þ þ þ
6 5 4 4 3 22 20 2 3
9
9
2
6
5
C H ] ; 68, [C H O] ; 41, [CH CN] . Anal. Calcd for C H N O (%): C, 73.3;
ꢀ
1
H, 5.6; N, 7.7; Found (%): C, 73.1; H, 5.6; N, 7.6. ꢂmax (EtOH, cm ): 34,482, 30,864.
The outline of the synthesis of ligand is shown in scheme 1.
2
.4. Synthesis of metal complexes
A solution of the metal chloride (5 mmol) in absolute ethanol (20 mL) was added to a
solution of the ligand (5 mmol) in absolute ethanol (25 mL) and the mixture was
refluxed for 3–4 h. The end of the reaction was determined by thin-layer chromatog-
raphy; the precipitate was filtered off, washed with ethanol and diethyl ether, and dried
in vacuo.
ꢀ
1
CoL(H O) ]: Yield: 49%. IR (KBr, cm ): 3432, (–OH of H O), 2922 (–C–CH ), 1600
[
2
2
2
3
þ
(
[
[
C¼N), 450 (M–N), and 480 (M–O). MS m/z: 454, (M þ 1); 418, [CoL] ; 358,
þ
þ
þ
þ
þ
C H N O ] ; 145, [C H N ] ; 93, [C H O] ; 77, [C H ] ; 68, [C H O] ; 41,
2
2
18
2
þ
3
9
9
2
6
5
6
5
4
4
CH CN] . Anal. Calcd for [CoC H N O ] (%): Co, 13.0; C, 58.3; H, 4.9; N, 6.2;
5
3
22 22
2
ꢀ
1
2
ꢀ1
ꢀ3
Found (%): Co, 12.8; C, 58.0; H, 4.8; and N, 6.0. Ã (Ohm cm mol ), 1.6 ꢂ 10
M
;
ꢀ
1
ꢃeff (B.M.), 3.75. ꢂmax (DMF, cm ): 37,652; 29,239; 15,408.
ꢀ
1
[
(
[
NiL]: Yield: 43%. IR (KBr, cm ): 2925, (–C–CH ); 1603, (C¼N); 452, (M–N); 476,
3
þ þ þ þ
M–O). MS m/z: 417, (M ); 358, [C H N O ] ; 145, [C H N ] ; 93, [C H O] ; 77,
22 18 2 3 9 9 2 6 5
þ þ þ
C H ] ; 68, [C H O] ; 41, [CH CN] . H-NMR (DMSO-d ): (phenyl multiplet),
6 5 4 4 3 6
1
6
Ni, 14.1; C, 63.4; H, 4.4; N, 6.7; Found (%): Ni, 13.8; C, 63.1; H, 4.3; N, 6.6.
.8–7.1 ꢁ(m); ꢁ(CH ), 2.3 (s); ꢁ(–CH¼C–), 5.4 (s). Anal. Calcd for [NiC H N O ] (%):
3
22 18
2
3
ꢀ1
2
ꢀ1
ꢀ3
ꢀ1
ÃM (Ohm cm mol ), 1.8 ꢂ 10 ; ꢃeff (B.M.), diamagnetic. ꢂmax (DMF, cm ):
3,256; 36,214; 14,184; 19,417.
2

1
632
N. Raman et al.
Scheme 1. Outline of the synthesis of ligand.
ꢀ
1
[
(
[
CuL]: Yield: 54%. IR (KBr, cm ): 2930, (–C–CH ); 1598, (C¼N); 446, (M–N); 482,
3
þ
þ
þ
2
M–O). MS m/z: 422, (M ); 424, (M þ 2); 358, [C H N O ] ; 145, [C H N ] ; 93,
2
2
18
2
3
9
9
þ
þ
þ
þ
C H O] ; 77, [C H ] ; 68, [C H O] ; 41, [CH CN] . Anal. Calcd for [CuC H N O ]
3
6
5
6
5
4
4
22 18
2
3
(
%): Cu, 15.1; C, 62.6; H, 4.3; N, 6.6; Found (%): Cu, 14.9; C, 62.3; H, 4.3; N, 6.5.
ꢀ1
ꢀ
1
2
ꢀ1
ꢀ3
ꢀ1
ÃM (Ohm cm mol ), 3.3 ꢂ 10 ; ꢃeff (B.M.), 1.8. ꢂmax (DMF, mol cm ): 22,988;
5,714; 16,391.
3
ꢀ
1
[
ZnL]: Yield: 38%. IR (KBr, cm ): 2924, (–C–CH ); 1593, (C¼N); 453, (M–N);
3
þ þ þ þ
70, (M–O). MS m/z: 424, (M ); 358, [C H N O ] ; 145, [C H N ] ; 93, [C H O] ;
22 18 2 3 9 9 2 6 5
4
7
6
þ
þ
þ
1
7, [C H ] ; 68, [C H O] ; 41, [CH CN] . H-NMR (DMSO-d ): (phenyl multiplet),
6
5
4
4
3
6
.5–7.0 ꢁ(m); ꢁ(CH ), 2.1 (s); ꢁ(–CH¼C–), 5.6 (s). Anal. Calcd for [ZnC H N O ] (%):
3
22 18
2
3
Zn, 15.4; C, 62.4; H, 4.3; N, 6.6; Found (%): Zn, 15.0; C, 62.1; H, 4.3; N, 6.6.
ꢀ1
2
ꢀ1
ꢀ3
ꢀ1
ÃM (Ohm cm mol ), 0.8 ꢂ 10 ; ꢃeff (B.M.), diamagnetic. ꢂmax (DMF, cm ):
1,259; 33,658.
2
[
(
VOL]: Yield: 40%. IR (KBr): 2924, (–C–CH ); 1596, (C¼N); 450, (M–N); 478,
3
þ
þ
þ
M–O). MS m/z: 426, (M þ 1); 360, [C H N O ] ; 41, [CH CN] ; 68, [C H O] ;
2
2
18
2
3
3
4
4
þ
þ
þ
7
V, 12.0; C, 62.1; H, 4.3; N, 6.6; Found (%): V, 11.8; C, 61.8; H, 4.2; N, 6.4%.
7, [C H ] ; 93, [C H O] ; 109, [C H N ] . Anal. Calcd for [VC H N O ] (%):
6
5
6
5
9
9
2
22 18
2
4

ꢀ
-Diketone condensed Schiff base
1633
ÃM (Ohm cm molꢀ1), 2 ꢂ 10ꢀ3; ꢃeff (B.M.), 1.79. ꢂmax (DMF, cm ): 22,547; 36,982;
ꢀ
1
2
ꢀ1
1
2,165; 19,157.
2
.5. DNA binding and cleavage experiments
Electronic absorption spectra were measured on a Shimadzu UV-1601 spectro-
ꢀ
1
photometer in 5 mmol L Tris–HCl buffer (pH 7.1) containing 50 mmol L NaCl
ꢀ1
at room temperature. Synthesized complexes were dissolved in DMF at 2.5 ꢂ
ꢀ ꢀ1
3
1
0
mol L . Working solutions were prepared by the dilution of the synthesized
ꢀ
1
ꢀ1
.
complexes in 5 mmol L Tris–HCl buffer to 25 mmol L
Absorption titration experiments were performed by maintaining the metal complex
concentration at 25 mmol L , while varying the concentration of the CT DNA from 0
ꢀ
1
ꢀ
1
to 400 mmol L . While measuring the absorption spectra, equal quantity of CT DNA
was added to both the complex solution and the reference solution to eliminate the
absorbance of CT DNA itself. From the absorption data, the intrinsic binding constant
K was determined from a plot of [DNA]/(" ꢀ" ) versus [DNA] using equation (1):
b
a
f
DNAꢃ=ð"a ꢀ "f Þ ¼ ½DNAꢃ=ð"b ꢀ "f Þ þ ½Kbð"b ꢀ "f Þꢃꢀ
1
ð1Þ
½
where [DNA] is the concentration of CT DNA in base pairs. The apparent absorption
coefficients " , " , and " correspond to Aobsd/[M], the extinction coefficient for the free
a
f
b
metal(II) complex, and extinction coefficient for the metal(II) complex in the fully
bound form, respectively [14]. K is given by the ratio of slope to intercept.
b
Cyclic voltammetric and DPV studies were performed on a CHI 620C electrochem-
ical analyzer with a three electrode system of glassy carbon (GC) as the working
electrode, a platinum wire as auxiliary electrode, and Ag/AgCl as the reference
electrode. All the voltammetric experiments were carried out in single-compartment
cells of 5–15 mL. Solutions were deoxygenated by purging with N2 prior to
measurements. Increasing amounts of CT DNA were added directly into the cell
containing the solution (2.5 ꢂ 10ꢀ mol L , 5 mmol L Tris–HCl/50 mmol L NaCl
3
ꢀ1
ꢀ1
ꢀ1
ꢀ
1
buffer, pH 7.1). The concentration ranged from 0 to 400 mmol L for CT DNA. The
solution in the cuvette was thoroughly mixed before each scan. All the experiments
were carried out at room temperature.
Viscosity experiments were carried on an Ostwald viscometer immersed in a
ꢁ
thermostated water bath maintained at 30.0 ꢄ 0.1 C. DNA samples of approximately
ꢀ
1
.5 mmol L were prepared by sonicating in order minimize the complexities arising
0
from DNA flexibility [15]. Flow time was measured with a digital stopwatch three times
0
for each sample and an average flow time was calculated. Data are presented as (ꢄ/ꢄ )
versus the concentration of the complex, where ꢄ is the viscosity of DNA solution in the
1/3
0
presence of complex and ꢄ is the viscosity of DNA solution in the absence of complex.
Viscosity values were calculated after correcting the flow time of buffer alone (t0),
ꢄ ¼ (tꢀt )/t [16].
0
0
ꢀ
1
The extent of cleavage of SC pUC19 DNA (33.3 mmol L , 0.2 mg) to its nicked
circular (NC) form was determined by agarose gel electrophoresis in 50 mmol L Tris–
1
HCl buffer (pH 7.2) containing 50 mmol L NaCl. The gel electrophoresis experiments
were performed by incubation of 30 mmol L
complex, and 50 mmol L
ꢀ
1
ꢀ
ꢀ1
ꢀ1
of pUC19 DNA, 50 mmol L
3-mercaptopropionic acid (MPA) in Tris–HCl buffer
of
ꢀ
1
ꢁ
(
pH 7.2) at 37 C for 2 h. After incubation, the samples were electrophoresed for 2 h

1
634
N. Raman et al.
at 100 V on 0.8% agarose gel using Tris–acetic acid–EDTA buffer (pH 7.2). The gel was
ꢀ
3
then stained using 1 mg cm EB and photographed under ultraviolet light at 360 nm.
All the experiments were performed at room temperature unless otherwise mentioned.
2
.6. Antimicrobial assays
The ligand and its complexes were tested for their in vitro antimicrobial activity against
Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram-negative
bacteria Escherichia coli and Salmonella typhi by the disk diffusion method using agar
nutrient as the medium and fungi Aspergillus niger, Aspergillus flavus, Candida albicans,
and Rhizoctonia bataicola by disk diffusion method using potato dextrose agar as
ꢀ2
ꢀ1
medium. The stock solution (10 mol L ) was prepared by dissolving the compounds
in DMSO and the solutions were serially diluted in order to find the minimum
inhibitory concentration (MIC) values. In a typical procedure [17], a disk was made
on the agar medium inoculated with microorganisms. The disk was filled with the test
solution using a micropipette and the plate was incubated, 24 h for bacteria and 72 h for
ꢁ
fungi at 35 C. During this period, the test solution diffused and the growth of the
inoculated microorganisms was affected. The inhibition zone was developed, at which
the concentration was noted. Streptomysin and nystatin were used as control drugs.
3
. Results and discussion
The Schiff base and its Cu(II), Co(II), Ni(II), VO(IV), and Zn(II) complexes are air
stable. The ligand is soluble in chloroform, DMF, and DMSO, but the complexes
are soluble only in DMF and DMSO. The ligand and complexes have been
characterized by microanalytical, magnetic susceptibility, molar conductance, FAB-
1
mass, IR, UV-Vis, H-NMR, and electron paramagnetic resonance (EPR) spectral
studies.
3
.1. Elemental analysis and molar conductance
Elemental analyses for the metal complexes agree with the calculated values showing
that the complexes have 1 : 1 metal : ligand ratio. The observed low molar conductances
ꢀ
3
in DMF (10 mol L ) at room temperature are consistent with non-electrolytes.
ꢀ1
The absence of chloride is evident from Volhard’s test and sulfate ion by BaCl test.
2
3
.2. Mass spectra
The FAB-MS of the ligand and its complexes were recorded and compared. The mass
þ
spectrum of the ligand shows (M þ 1) peak at m/z 361 corresponding to [C H N O ] .
2
2
20
2
3
Also, the spectrum exhibited fragments at m/z 41, 68, 77, 93, and 145 corresponding
to [CH CN] , [C H O] , [C H ] , [C H O] , and [C H N ] , respectively. The mass
þ
þ
þ
þ
þ
3
4
4
6
5
6
5
9
9
2
spectrum of [CuC H N O ] shows peaks at 422 and 424. The one at 422 may
2
2
20
2
3
þ
represent the molecular ion (M ) peak of the complex and the other peak at 424 is an

ꢀ
-Diketone condensed Schiff base
1635
isotopic fragment (M þ 2). In all the complexes, the strongest peak (base beak) obtained
þ
at m/z 358 represents the stable species [C H N O ] . Further, the spectra exhibited
2
2
18
2
3
þ
þ
fragments at m/z 41, 68, 77, 93, and 145 corresponding to [CH CN] , [C H O] ,
þ þ
C H ] , [C H O] , and [C H N ] , respectively. The m/z of all the fragments of the
6 5 6 5 9 9
3
4
4
þ
[
2
ligand and its complexes confirm that the stoichiometry of the complexes is [ML] except
cobalt complex, in which the mass spectrum shows two prominent peaks at 454
and 418. The peak at 454 may represent the molecular ion peak [M þ 1], confirming
þ
2
þ
the stoichiometry [CoL(H O) ] and the peak at 418 may indicate [CoL] . In all the
2
complexes, the observed peaks are in good agreement with their empirical formula
as indicated from the microanalytical data. Thus, the mass spectral data reinforce the
conclusion drawn from the analytical and conductance values.
3
.3. IR spectra
ꢀ1
The ligand shows a broad band for the –OH group at ca 3100–3000 cm . The
disappearance of this peak in spectra of the complexes indicates the deprotonation of
–
bands at 1634 cm , which shift to lower frequencies in spectra of all the complexes
OH on complexation. The spectrum of the ligand shows the characteristic –C¼N
ꢀ
1
ꢀ
1
1600 cm ), indicating azomethine nitrogen coordination to the metal [18].
(
Accordingly, the ligand is a tetradentate chelate, bonded to the metal via two nitrogens
(
–C¼N) and two phenolic oxygens of the Schiff base. Assignment of the proposed
ꢀ
1
coordination sites is further supported by medium bands at 450 and 480 cm
attributed to ꢅM–N and ꢅM–O, respectively [19]. In addition to the other bands, the
vanadyl complex shows a band at 960 cm attributed to V¼O frequency [20].
,
ꢀ
1
3
.4. Electronic absorption spectra
The absorption spectrum of the ligand recorded in ethanol exhibits bands at 34,482 and
ꢀ
1
0,864 cm , attributed to ꢆ–ꢆ* and n–ꢆ* transitions, respectively. The absorption
3
spectrum of the copper(II) complex in DMF reveals characteristic bands of metal
ꢀ1
to ligand charge transfer (MLCT) transitions at 22,988 and 35,714 cm . A strong
ꢀ1
absorption maximum at 16,391 cm is assigned to d–d transition, characteristic of
9
square-planar d copper complex involving (d , d ! d
2
2
) orbitals [21]. These
2
xz
yz
x ꢀy
2
transitions are usually made up of three spin-allowed transitions namely: B ! A ,
1
g
1g
2
2
2
2
B ! B , and B ! E . Two of these transitions are indicated by weaker
1
g
2g
1g
g
shoulders in the absorption spectrum. The magnetic susceptibility in the solid state
shows that the copper complex is paramagnetic with magnetic moment (1.8 B.M.)
in the range normally found for square-planar copper complexes.
Square-planar complexes of nickel can readily be distinguished from octahedral
ꢀ
1
or tetrahedral derivatives, in that no electronic transition occurs below 10,000 cm [21],
as a consequence of the large crystal field splitting in a square-planar complex. In the
present complex, this band does not appear indicating square-planar geometry.
The electronic absorption spectrum of cobalt complex gives only one d–d band at
ꢀ
1
4
4
ꢀ1
1
5,408 cm corresponding to T ! A and other bands at 29,239 and 45,045 cm
1
g
2g
which are characteristic of octahedral ligand field around Co(II) and can be assigned to
ꢆ ! ꢆ* and n ! ꢆ* charge transfer transitions. The magnetic moment measurement
indicates that the Co(II) complex is paramagnetic and the magnetic moment value is

1
636
N. Raman et al.
nearer to the spin-only value for a high-spin octahedral complex. The magnetic
moment values for high-spin Co(II) octahedral complexes fall in the range of 3.87–
5.20 B.M. [21, 22].
Room temperature magnetic moment of the VO(IV) complex is 1.79 B.M., as
that expected for oxovanadium(IV)-monomeric chelates with one unpaired electron.
The electronic spectrum of oxovanadium complex exhibits bands at 12,165 and
ꢀ
1
2
2
2
2
1
9,157 cm assigned to B ! E and B ! A , respectively. The geometry of this
2
2
1
five-coordinate mononuclear complex can be described as trigonal bipyramidal
distorted toward a tetragonal pyramid or square pyramid [23].
3
.5. Nuclear magnetic resonance spectra
1
The H-NMR spectra of the ligand and its complexes (zinc and nickel) were recorded
in CDCl and DMSO-d , respectively. The ligand gives the following signals: (phenyl as
3
6
multiplet) at 6.6–7.2 ꢁ, –CH at 2.0 ꢁ, and –CH¼C– at 5.8 ꢁ. The peak at 10.1 ꢁ is
3
attributable to the phenolic –OH group present in 2-aminophenol. The absence of
this peak for the complexes confirms the loss of the ꢀOH proton in complexation. The
azomethine proton signal in the spectra of the complexes shifts downfield compared to
the free ligand, suggesting deshielding of the azomethine group due to coordination.
There is no appreciable change in all of the other signals of the complexes.
3
.6. Electron spin resonance spectra
The X-band ESR spectrum of [CuL] at 300 K shows an intense absorption at
high field. However, this complex in frozen state shows four well-resolved peaks
with low intensities in the low-field region and one intense peak in the high-field
region. The magnetic susceptibility of 1.8 B.M. indicates that the complex is
mononuclear. This is also evident from the absence of a half-field signal, observed
in the spectrum at 1600 G due to the m ¼ ꢄ2 transitions, ruling out Cu–Cu
s
interaction [23].
In square-planar complexes, the unpaired electron is in the d
2
orbital giving B
2
2
x ꢀy
1g
as the ground state with g 4 g 4 2. From the observed values (A ¼ 169 4 A ¼ 52;
k
?
k
?
g ¼ 2.34 4 g ¼ 2.05 4 2) it is clear that the ESR parameters coincide well with related
k
?
square-planar systems [24]. In the axial spectrum, the g-values are related with exchange
interaction coupling constant (G) by the expression, G ¼ g ꢀ2/g ꢀ2. According to
k
?
Hathaway and Tomlinson [25], if the G value is larger than 4, exchange interaction
is negligible. If the value of G is less than 4, the exchange interaction is considerable.
For the present copper complex, the G value of 6.8 suggests that the local tetragonal
axes are aligned parallel or slightly misaligned, consistent with a d
2
2
2
ground state.
The in-plane ꢇ-bonding covalency parameter, ꢈ , is related to A , g , and g
x ꢀy
k
k
?
according to the following equation [26]:
2
ꢈ ¼ ðA =PÞ þ ð g ꢀ 2:0023Þ þ 3=7ð g ꢀ 2:0023Þ þ 0:04:
k
k
?
2
If the value of ꢈ ¼ 0.5, it indicates complete covalent bonding, while the value
2
2
of ꢈ ¼ 1.0 suggests complete ionic bonding. The observed value of ꢈ (0.56)
indicates that the complex has some covalent character. The out-of-plane ꢆ-bonding

ꢀ
-Diketone condensed Schiff base
1637
2
ꢉ ) and in-plane ꢆ-bonding (ꢀ ) parameters are calculated from the following
2
(
expressions:
2
2
2
ꢀ
¼ ð gk ꢀ 2:0023ÞE=ðꢀ8ꢂꢈ Þ
2
ꢉ ¼ ð g? ꢀ 2:0023ÞE=ðꢀ2ꢂꢈ Þ:
In these equations, ꢂ ¼ ꢀ828 cmꢀ for the free metal ion. The observed ꢀ (1.72) and
1
2
2
ꢈ (0.56) values indicate that there is interaction in the out-of-plane ꢆ-bonding, whereas
the in-plane ꢆ-bonding is completely ionic. This is also confirmed by the orbital
reduction factors which are estimated using the following relations:
2
K ¼ ½ð g ꢀ 2:0023ÞDEꢃ=8ꢂ
k
k
o
2
K ¼ ½ð g ꢀ 2:0023ÞDEꢃ=2ꢂ ,
?
?
o
ꢀ
1
where ꢂ is the spin orbit coupling constant for the copper(II) ion (ꢀ828 cm ). K and
o
k
K are the parallel and perpendicular components of the orbital reduction factor (K),
?
respectively. Significant information about the nature of bonding in the copper(II)
complex can be derived from the relative magnitudes of K and K . In the case of pure
k
r
ꢇ-bonding K ꢅ K ¼ 0.77, whereas K 5 K implies considerable in-plane ꢆ-bonding
k
r
k
r
while for out-of-plane ꢆ-bonding K 4 K . For the present complex, the observed order
k
r
is K (0.96) 4 Kr (0.54) implying a greater contribution from out-of-plane ꢆ-bonding
k
than from in-plane ꢆ-bonding.
EPR spectra of the vanadyl complex recorded in DMSO solution at 300 and 77 K
show typical 8-line and 16-line patterns, respectively. The room temperature (300 K)
spectrum shows that a single vanadium is present in the molecule, i.e., it is a monomer.
In the frozen solid state, the spectrum shows two types of resonance: one due to the
parallel features and the other due to the perpendicular features which show an axially
symmetric anisotropy with a well-resolved 16-line hyperfine splitting characteristic of an
interaction between the electron and the vanadium nuclear spin. The observed
anisotropic parameter values (gk ¼ 1:94, g? ¼ 1:97, Ak ¼ 170, and A? ¼ 78) indicate
that the unpaired electron is present in the d orbital with square-pyramidal geometry
xy
around the oxovanadium(IV) chelate [27].
2
The molecular orbital coefficients ꢈ and ꢀ were also calculated for the complex
2
by the following equations [28]:
2
2
ꢈ ¼ ð2:0023 ꢀ gk ÞE=8ꢂꢀ
2
ꢀ
¼ 7=6ðꢀAk=p þ A?=p þ gk ꢀ 5=14gk ꢀ 9=14geÞ
2
2
ꢉ ¼ ð2:0023 ꢀ g?ÞE=2ꢂꢈ ,
ꢀ
4
ꢀ1
ꢀ1
where p ¼ 128 ꢂ 10 cm , ꢂ ¼ 135 cm , and E is the electronic transition energy of
2
2
2
2
B ! E. The lower value of ꢈ ¼ 0.77 compared to ꢀ ¼ 0.89 indicates that the in-plane
2
ꢆ-bonding is more covalent than the in-plane ꢇ-bonding.
3
.7. Thermogravimetric analysis
Thermal analysis plays an important role in the study of physicochemical behaviors and
ꢁ
stability. All the complexes were unaffected up to ꢆ250 C except the cobalt complex,
ꢁ
which lost two water molecules at 150–220 C. The presence of coordinated water

1
638
N. Raman et al.
Figure 1. The structure of complexes (M ¼ Ni(II), Cu(II), and Zn(II)).
confirms the results of analytical and IR spectra. The anhydrous complexes remained
ꢁ
stable up to ꢆ350 C and thereafter showed rapid degradation due to decomposition
of the organic constituents of the complex molecules. The decomposition continued
ꢁ
up to ꢆ750 C and a stable product (as oxide) was formed as indicated by consistency
in weight in the plateau of the thermogram.
Based on the above spectral data, the structures of the complexes are given
in figure 1.
3
3
.8. DNA binding studies
.8.1. Electronic spectra. The absorption spectra of the copper complex in the absence
and presence of CT DNA are shown in figure 2. With increasing CT DNA
concentration, the hypochromism in the band at 405.5 nm reaches as high as 2.5%
with a blue shift of 10 nm at a [DNA] : [complex] ratio of 10. These spectral
characteristics suggest that copper complex interacts with DNA through a mode that
involves a stacking interaction between the aromatic chromophore and the base pairs of
DNA. After intercalating the base pairs of DNA, the ꢆ* orbital of the intercalated
ligand can couple with the ꢆ orbital of the base pairs, thus decreasing the ꢆ–ꢆ*
transition energy and resulting in the bathochromism. The coupling ꢆ orbital is
partially filled by electrons, thus decreasing the transition probabilities and concom-
itantly resulting in hypochromism. To quantitatively compare the affinity of the
synthesized complexes toward DNA, the intrinsic binding constants Kb of the
synthesized complexes to CT DNA were determined by monitoring the changes of
absorbance at 405.5 nm (for copper complex), 398.6 nm (for zinc complex), 395.0 nm
(for cobalt complex), and 397.3 nm (for nickel complex) with the increasing concen-
tration of DNA. The intrinsic binding constant K is obtained from the ratio of slope to
b
the intercept of plots [DNA]/(" ꢀ" ) versus [DNA]. The K values are shown in table 1.
a
f
b

ꢀ
-Diketone condensed Schiff base
1639
Figure 2. Electronic absorption spectrum of [CuL] in the absence (dotted line) and presence (solid line) of
increasing amounts of DNA.
Table 1. Absorption spectral properties of synthesized complexes with CT DNA.
ꢂ
max
4
Hypochromism
(%)
K
(L mol )
b
ꢂ 10
–
1
Complexes
Free
Bound
Dꢂ (nm)
[
[
[
[
[
CuL]
ZnL]
CoL(H
NiL]
VOL]
405.5
398.6
395.0
397.3
389.0
395.5
392.5
391.6
392.0
388.7
10.0
6.1
3.4
5.3
0.3
12.5
4.1
2.8
3.9
2.5
1.4
1.6
1.9
–
2
O)
2
]
ꢀ1.5
Comparing the intrinsic binding constant of the synthesized complexes with those of the
DNA-intercalators, it is deduced that all the synthesized complexes except vanadyl
complex bind strongly to DNA by intercalation. From table 1, only very weak
hypochromism (ꢀ1.5%) and no significant spectral shifts are found after vanadyl
complex is mixed with DNA, indicating that the vanadyl complex forms weaker adduct
to CT DNA than the other complexes due to the square-pyramidal geometry of the
vanadyl complex.
3
.8.2. Electrochemical studies. Cyclic and DPV measurement techniques are extremely
useful in probing the nature and mode of DNA binding of metal complexes. Typical
cyclic voltammogram of copper complex in the absence and in the presence of varying
amount of [DNA] is shown in figure 3.
In the absence of CT DNA, only one redox couple cathodic peak appears at ꢀ0.286 V
for Cu(II) ! Cu(I) (E ¼ 0.040 V, E ¼ ꢀ0.286 V, DE ¼ 0.326 V, and E ¼ 0.123 V).
pa
pc
p
1/2
This redox couple ratio I /I is approximately unity indicating that the reaction on the
pc pa

1
640
N. Raman et al.
Figure 3. Cyclic voltammogram of [CuL] in the absence (dotted line) and presence (solid line) of DNA.
Table 2. Electrochemical parameters for the interaction of DNA with Co(II), Ni(II), and Cu(II) complexes.
E
1/2 (V)
Bound
DE
Free
p
(V)
Bound
Complexes
Redox couple
Free
K[red]/K[oxd]
Ipc/Ipa
[
[
[
CoL(H
NiL]
CuL]
2
O)
2
]
Co(III)/Co(II)
Ni(II)/Ni(I)
Cu(II)/Cu(I)
ꢀ0.482
ꢀ0.342
ꢀ0.123
ꢀ0.468
ꢀ0.332
ꢀ0.097
0.099
0.315
0.326
0.028
0.275
0.263
1.23
0.79
0.65
0.82
0.91
0.89
GC electrode surface is quasi-reversible. The incremental addition of CT DNA to the
complex causes a negative shift in E1/2 and a decrease in DE (table 2). The I /I values
p
pc pa
also decrease in the presence of DNA due to the decrease in the apparent diffusion
coefficient of the copper(II) complex upon complexation with DNA. These results show
that copper(II) complex stabilizes the duplex (GC pairs) by intercalation.
In the absence of CT DNA, the redox couple cathodic peak appears at 0.282 V for
Co(III) ! Co(II) (E ¼ 0.681 V, E ¼ 0.282 V, DE ¼ 0.099 V, and E ¼ 0.482 V) and
pa
pc
p
1/2
a second redox couple cathodic peak appears at ꢀ0.082 V for Co(II) ! Co(I)
(
less than unity indicating a quasi-reversible redox process. The incremental addition of
E
pa
¼ 0.299 V, E ¼ ꢀ0.082 V, DE ¼ 0.381 V, and E ¼ 0.481 V). The ratio I /I is
pc
p
1/2
pc pa
CT DNA to the complex causes a negative shift in E1/2 of 14 mV and a decrease in DEp
of 71 mV for the first redox couple. The I /Ipa values also decrease in the presence
pc
of DNA. The decrease of the anodic and cathodic peak currents of the complex in the
presence of DNA is due to decrease in the apparent diffusion coefficient of the
cobalt(III) complex upon complexation with the DNA. The second redox couple
of cobalt(II) complex shows no significant change of potential or intensity of current.
This indicates that the second redox species does not stabilize the duplex DNA.

ꢀ
-Diketone condensed Schiff base
1641
In the absence of CT DNA, the redox couple cathodic peak appears at ꢀ0.500 V for
Ni(II) ! Ni(I) (E ¼ ꢀ0.185 V, E ¼ ꢀ0.500 V, DE ¼ 0.315 V, and E ¼ 0.342 V)
pa
pc
p
1/2
and a second redox couple cathodic peak appears at ꢀ0.926 V for Ni(I) ! Ni(0)
(
E
¼ ꢀ0.643 V, E ¼ ꢀ0.926 V, DE ¼ 0.283 V, and E ¼ 0.785 V). The ratio I /I is
pa
pc
p
1/2
pc pa
less than unity. Incremental addition of DNA on Ni(II) complex shows a decrease in the
current intensity and positive shift of the potential on the redox couple Ni(II) ! Ni(I)
and no significant change in the current intensity and potential on the redox couple
of Ni(I) ! Ni(0). The resulting changes in the current and potential demonstrate the
interaction between Ni(II) and DNA.
In the absence of CT DNA, the redox couple anodic peak appears at þ1.253 V with
the addition of DNA to Zn(II) complex showing a decrease in the current intensity and
negative shift of the oxidation peak potential. The changes in the current and potential
demonstrate the interaction between Zn(II) and DNA. The electrochemical parameters
of the Co(II), Ni(II), and Cu(II) complexes are shown in table 2.
DPVs of the Cu(II), Co(II), and Ni(II) complexes show a positive potential shift
along with a significant decrease of current intensity. The shift in potential is related to
the ratio of binding constants
ꢀ
ꢁ
K½redꢃ
K½oxdꢃ
o0
ꢀ Efo0 ¼ 0:0591 log
E
,
b
o0
o0
where Eb and Ef are formal potentials of the Co(III)/Co(II) or Ni(II)/Ni(I) or
Cu(II)/Cu(I) or Zn(II)/Zn(0) complex couple in the bound and free form, respectively.
The ratio of the binding constants (K[red]/K[oxd]) for DNA binding of synthesized
complexes were calculated and found to be less than unity. The above electrochemical
experimental results indicate the preferential stabilization of Co(II), Ni(II), Cu(II), and
Zn(II) forms over the other forms on binding to DNA.
DPV of the Zn(II) complex shows a negative potential shift along with significant
decreasing of current intensity during the addition of increasing amounts of DNA
consistent with zinc ion stabilizing the duplex (GC pairs) by intercalation. Hence, for
the complex of the electroactive species (Zn(II)) with DNA, the electrochemical
reduction reaction can be divided into two steps:
2
þ
2þ
Zn ꢀ DNA Ð Zn þ DNA
2þ
ꢀ
0
Zn þ 2e Ð Zn
The dissociation constant (K ) of the Zn(II)–DNA complex was obtained using the
following equation:
d
ꢂ
ꢃ
Kd
2
p
2
p
2
p
2
p
I ¼
I o ꢀ I þ I o ꢀ ½DNAꢃ,
½
DNAꢃ
2
p
2
p
where K is the dissociation constant of Zn(II)ꢀDNA, and I o and I the reduction
d
current of Zn(II) in the absence and presence of DNA, respectively. Using the above
equation, the dissociation constant was determined. The low dissociation constant
ꢀ
10
ꢀ1
(
2.6 ꢂ 10 mol L ) for Zn(II) was indispensable for the catalytic function and the
structural stability of zinc enzymes which participate in replication, degradation,
and translation of genetic material of all species. Zn(II) ions were probably interacting
not only with the active site of the enzyme during these processes, as already well known
in the literature [25], but also with DNA.

1
642
N. Raman et al.
3.8.3. Viscosity measurements. Interactions between complexes and DNA were
investigated by viscosity measurements. Optical photophysical probes provided
necessary, but not sufficient clues to support a binding model. Hydrodynamic
measurements sensitive to length change (i.e., viscosity and sedimentation) are regarded
as the least ambiguous and the most critical tests of binding mode in solution in the
absence of crystallographic structural data [29]. A classical intercalation model usually
results in lengthening the DNA helix, as base pairs were separated to accommodate the
binding ligand leading to the increase of DNA viscosity. The viscosity of CT DNA
increases with the increase in the ratio of Co(II), Cu(II), and Zn(II) complexes to CT
DNA. The absence of viscosity in vanadyl complex indicates that it may bind to DNA
only by electrostatic force.
3
.9. DNA cleavage studies
Gel electrophoresis using pUC19 DNA was performed with the ligand and its
complexes in the presence and absence of MPA as reductant. At micromolar
concentrations, for 2 h incubation period, the ligand exhibits no significant activity
in the presence of MPA. The nuclease activity is greatly enhanced by the incorporation
of metal ion in the ligand. The complexes cleave DNA more efficiently in the presence
of reductant, which may be attributed to the formation of hydroxyl free radical.
The production of a hydroxyl free radical due to the reaction between the metal
complexes and oxidant may be explained as shown below:
.
The HO participates in the oxidation of deoxyribose moiety, followed by hydrolytic
cleavage of the sugar phosphate backbone [30]. The more pronounced nuclease activity
of these adducts in the presence of reductant is due to the increased production of
hydroxyl radicals. Vanadyl complex does not cleave DNA in the presence of MPA,
suggesting that it binds with DNA through electrostatic mode which is further
supported by the weak hypochromism in electronic absorption spectrum and no change
in the viscosity effect with DNA.
3
.10. Antimicrobial activity
The ligand and its complexes were tested for their in vitro antimicrobial activity against
Gram-positive bacteria S. aureus and B. subtilis and Gram-negative bacteria E. coli
and S. typhi by the disk diffusion method, using agar nutrient as the medium and
against fungi A. niger, A. flavus, C. albicans, and R. bataicola by disk diffusion method
using potato dextrose agar as medium. The MIC values of the compounds against
the growth of microorganisms are summarized in tables 3 and 4.
The metal complexes exhibit higher antimicrobial activity than the free ligand
31, 32].
[

ꢀ
-Diketone condensed Schiff base
Table 3. Antibacterial activity of compounds.
MIC (mg mL
B. subtilis
1643
ꢀ
1
)
Compound
S. aureus
E. coli
S. typhi
L
49
23
31
21
28
24
18
44
19
23
15
19
17
12
51
17
20
13
18
16
10
61
24
21
18
20
19
14
[
[
[
[
[
CuL]
NiL]
ZnL]
VOL]
CoL(H
2
2
O) ]
Streptomycin
Table 4. Antifungal activity of compounds.
MIC (mg mL
ꢀ1
)
Compound
A. niger
A. flavus
C. albicans
R. bataicola
L
52
12
16
13
14
19
10
63
10
18
12
13
15
8
69
13
19
15
14
17
12
59
14
21
16
17
24
11
[
[
[
[
[
CuL]
NiL]
ZnL]
VOL]
CoL(H
2
2
O) ]
Nystatin
4. Conclusions
The ligand and its complexes have been characterized by microanalytical data, IR,
1
UV-Vis, H-NMR, ESR, and mass spectra. The complexes have composition [ML] for
Cu(II), Ni(II), VO(IV), and Zn(II), but [CoL(H O) ] for Co(II). Intercalative binding
2
2
of the Co(II), Cu(II), and Zn(II) complexes with DNA has been supported by electronic
absorption spectra, cyclic voltammetry, differential pulse voltammetry, and viscometric
studies. The electrostatic binding mode of vanadyl complex with DNA is observed
from weak hypochromism and no significant spectral shift in electronic absorption
spectrum. It is further confirmed by the absence of effect on the viscosity of DNA. The
synthesized complexes except vanadyl complex exhibit nuclease activity in the presence
of hydroxyl radicals. The results from in vitro antifungal and antibacterial tests showed
that all the complexes are more active than the ligand.
Acknowledgments
The authors gratefully acknowledge the financial support of this work by the
Department of Science and Technology, New Delhi, India. They express their
heartfelt thanks to the VHNSN College Managing Board for providing the research
facilities.

1
644
N. Raman et al.
References
[
[
1] S. Chan, W.T. Wong. Coord. Chem. Rev., 138, 219 (1995).
2] E.-J. Gao, Q. Wu, C.-S. Wang, M.-C. Zu, L. Wang, H.-Y. Liu, Y. Huang, Y.-G. Sun. J. Coord. Chem.,
62, 3425 (2009).
[
3] F. Liang, P. Wong, X. Zhou, T. Li, Z.Y. Li, H.K. Lin, D.Z. Gao, C.Y. Zheng, C.T. Wu. Bioorg. Med.
Chem. Lett., 14, 1901 (2004).
[
4] C.N. Sudhamani, H.S. Bhojya Naik, T.R. Ravikumar, M.C. Prabhakara. Spectrochim. Acta, 72A,
643 (2009).
[
[
[
[
5] J. Sun, S.-Y. Deng, J. He, L. Jiang, Z.-W. Mao, L.-N. Ji. J. Coord. Chem., 62, 3284 (2009).
6] L.N. Ji, X.H. Zon, J.G. Liu. J. Coord. Chem. Rev., 216, 513 (2001).
7] N. Raman, A. Sakthivel, R. Jeyamurugan. J. Coord. Chem., 69, 3425 (2009).
8] Q.L. Zhang, J.H. Liu, J.Z. Liu, P.X. Zhang, X.Z. Ren, Y. Liu, Y. Huang, L.N. Ji. J. Inorg. Biochem., 98,
1405 (2004).
[
9] S. Murali, C.V. Sastri, B.G. Maiya. Proc. Indian Acad. Sci. (Chem. Sci.), 114, 403 (2002).
[
10] D.D. Perrin, W.L.F. Armarego, D.R. Perrin. Purification of Laboratory Chemicals, 2nd Edn, Pergamon
Press, Oxford (1980).
[
[
[
[
[
[
[
11] J. Marmur. J. Mol. Biol., 3, 208 (1961).
12] M.E. Reichmann, S.A. Rice, C.A. Thomas, P. Doty. J. Am. Chem. Soc., 76, 3047 (1954).
13] M. Yamamata, Y. Watanabe, T. Mitsudo, Y. Nakagami. Bull. Chem. Soc., Jpn., 51, 835 (1978).
14] D.S. Sigman, A. Spassky, S. Rimsky, H. Buc. Biopolymers, 24, 183 (1985).
15] J.B. Charies, N. Dattagupta, D.M. Crothers. Biochemistry, 21, 3933 (1982).
16] S. Satyanarayana, J.C. Daborusak, J.B. Charies. Biochemistry, 32, 2573 (1983).
17] M.J. Pelzer, E.C.S. Chan, N.R. Krieg. Antibiotics and Other Chemotherapeutic Agents in
Mirobiology, 5th Edn, Blackwell Science, New York (1998).
[
[
18] A. Ei-Dissouky. Spectrochim. Acta, 43A, 1182 (1987).
19] K. Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd Edn,
Wiley Interscience, New York (1977).
[20] N. Raman, S.J. Raja, A. Sakthivel. J. Coord. Chem., 62, 691 (2009).
[21] A.B.P. Lever. Inorganic Electronic Spectroscopy, 2nd Edn, Elsevier, New York (1968).
[22] N. Nishat, S. Asma, S. Dhyani. J. Coord. Chem., 62, 3003 (2009).
[23] N. Raman, R. Jeyamurugan. J. Coord. Chem., 62, 2375 (2009).
[24] R.K. Ray, G.M. Kauffman. Inorg. Chim. Acta, 173, 207 (1990).
[25] B.J. Hathaway, A.A.G. Tomlinson. Coord. Chem. Rev., 5, 1 (1970).
[26] K. Jayasubramanian, S.A. Samath, S. Thambidurai, R. Murugesan, S.K. Ramalingam. Transition Met.
Chem., 20, 76 (1995).
[
[
[
[
[
[
27] S.S. Dodwad, R.S. Dharmnaskar, P.S. Prabhu. Polyhedron, 8, 1748 (1989).
28] L.J. Boucher, T.F. Yen. Inorg. Chem., 8, 689 (1968).
29] B.C. Baguley, M. Lebret. Biochemistry, 23, 937 (1984).
30] P. Merfley, E.R. Robinson. Mutat. Res., 86, 155 (1981).
31] Y. Anjaneyalu, R.P. Rao. Synth. React. Inorg. Met.-Org. Chem., 16, 257 (1986).
32] L. Mishra, V.H. Singh. Indian J. Chem., 32A, 446 (1993).