Synthesis of mononuclear copper(II) complexes of acyclic Schiff's base ligands: Spectral, structural, electrochemical, antibacterial, DNA binding and cleavage activity

Article abstract of DOI:10.1016/j.saa.2013.11.079

The mononuclear copper(II) complexes (1&2) of ligands L¹ [N,N′-bis(2-hydroxy-5-methylbenzyl)-1,4-bis(3-iminopropyl)piperazine] or L² [N,N′-bis(2-hydroxy-5-bromobenzyl)-1,4-bis(3-iminopropyl) piperazine] have been synthesized and char

Full text of DOI:10.1016/j.saa.2013.11.079

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis of mononuclear copper(II) complexes of acyclic Schiff’s base
ligands: Spectral, structural, electrochemical, antibacterial, DNA binding
and cleavage activity
Arumugam Jayamani a, Vijayan Thamilarasan a, Nallathambi Sengottuvelan a,
,
⇑
Paramasivam Manisankar b, Sung Kwon Kang c, Young-Inn Kim d, Vengatesan Ganesan e
a DDE, Alagappa University, Karaikudi 630 003, India
b Department of Industrial Chemistry, Alagappa University, Karaikudi 630 003, India
c Department of Chemistry, Chungnam National University, Daejeon 305-764, Republic of Korea
d Department of Chemistry Education and Interdisciplinary Program of Advanced Information and Display Materials, Pusan National University, Pusan 609-735, Republic of Korea
e AcmeProGen Biotech (India) Pvt. Ltd., Salem 636 004, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Mononuclear Cu(II) complexes were
synthesized using Schiff’s base acyclic
ligands.
ꢀ
ꢀ
Single crystals X-ray study confirms
the structure of ligands L1 and L2.
Cu(II) ion in complexes was
translocated between two non-
equivalent compartments.
ꢀ
ꢀ
All complexes show efficient DNA
binding and cleavage ability.
Oxidative cleavage mechanism using
singlet oxygen as reactive species.
a r t i c l e i n f o
a b s t r a c t
The mononuclear copper(II) complexes (1&2) of ligands L1 [N,N0-bis(2-hydroxy-5-methylbenzyl)-
1,4-bis(3-iminopropyl)piperazine] or L2 [N,N0-bis(2-hydroxy-5-bromobenzyl)-1,4-bis(3-iminopropyl)
piperazine] have been synthesized and characterised. The single crystal X-ray study had shown that ligands
L1 and L2 crystallize in a monoclinic crystal system with P21/c space group. The mononuclear copper(II)
complexes show one quasireversible cyclic voltammetric response near cathodic region (ꢁ0.77 to
ꢁ0.85 V)inDMF assignable to theCu(II)/Cu(I) couple. Binding interaction ofthe complexes with calf thymus
DNA (CT DNA) investigated by absorption studies and fluorescence spectral studies show good binding
affinity to CT DNA, which imply both the copper(II) complexes can strongly interact with DNA efficiently.
The copper(II) complexes showed efficient oxidative cleavage of plasmid pBR322 DNA in the presence of
3-mercaptopropionic acid as reducing agent through a mechanistic pathway involving formation of singlet
oxygen as the reactive species. The Schiff bases and their Cu(II) complexes have been screened for antibac-
terial activities which indicates that the complexes exhibited higher antimicrobial activity than the free
ligands.
Article history:
Received 29 July 2013
Received in revised form 7 November 2013
Accepted 13 November 2013
Available online 21 November 2013
Keywords:
Copper(II) complexes
Acyclic Schiff’s base
Anti bacterial activity
DNA binding and cleavage studies
Electrochemical studies
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
The developments of compounds cleaving DNA under physio-
logical conditions is of current interest, due to their potential
applications in genomic research and as foot printing and
⇑
Corresponding author. Tel./fax: +91 9488260744.
E-mail address: nsvelan1975@yahoo.com (N. Sengottuvelan).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.11.079

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A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
therapeutic agents [1–3]. Transition metal complexes have been
widely exploited for metallohydrolases capable of mimicking the
function of endonucleases [4] and to develop synthetic binding
and cleavage agents for DNA. Especially, copper(II) complexes with
Schiff’s base ligands have been extensively explored in virtue of
their strong interactions with DNA via surface associations or
intercalation [5] and potential DNA cleavage activities via hydro-
lytic or oxidative mechanisms [6]. Copper(II) complexes are
regarded as the most promising alternatives to cis-platin as
anticancer drugs. The stability and functionality of the Schiff’s base
complexes were enhanced when the ligand molecules has control-
lable molecular motions. The controllable molecular motion can be
induced by variation of a bulk parameter, such as the pH or the
redox potential [7]. Transition metal ions can be translocated be-
tween two non-equivalent coordinating compartments of a ditopic
ligand by varying the pH or redox potential. Enzymes such as
haemocyanin [8] or tyrosinase [9] have a binuclear copper centre
in their active sites. The geometry, the coordination sites, the
bridging ligands between the centre, etc., define the properties of
the binuclear centres Several metal complexes of Schiff bases de-
rived from salicylaldehyde and amines [10,11] were reported and
some of them have been proven to be efficient DNA cleavers
[12,13] and as novel tumour chemotherapeutic and radio imaging
agents [14].
In this work, we have been studying the DNA binding and cleav-
age activity of two new copper(II) complexes of ligands L1 and L2.
The piperazine-imine-phenol Schiff base ligands L1 and L2 have
been chosen considering that the phenolic –OH group may en-
hance the affinity of the complexes towards DNA binding through
formation of hydrogen bonding.
Herein we report synthesis, characterisation, DNA binding and
cleavage properties of copper(II) complexes (1&2). The ligands L1
and L2 have been structurally characterised by X-ray crystallogra-
phy. The redox activity of complexes was evaluated by cyclic
voltammetry. The DNA binding and cleavage ability of all the cop-
per(II) complexes were evaluated using calf thymus and plasmid
pBR322 DNA respectively. The antimicrobial property of ligands
and their complexes were also assessed with two gram negative
and two gram positive bacterium.
auxiliary electrode in nitrogen atmosphere. The concentration of
complexes was 10ꢁ3 M in DMF and tetra(n-butyl)ammonium per-
chlorate (TBAP) (10ꢁ1 M) was used as the supporting electrolyte.
Spectrophotometric titrations were performed on aqueous
solutions (10 mL, made 0.05 M in NaClO4, 25 °C) of the metal
complexes at approximately adjusted pH of 2.0 by adding small
amounts of a standard solution of HClO4. Subsequently, additions
of standard solutions (0.1 M) of NaOH were made until a basic
pH (ꢂ12.0) was attained. Absorption spectra were taken after each
addition of base. In each experiment the overall addition was lim-
ited to about 200 ll, so that volume variation was not significant.
Safety note; Perchlorate salts of metal complexes are potentially
explosive and should be handled with care.
Synthesis of ligands and complexes
Synthesis of ligand L1
A
methanolic (10 mL) solution of 5-methylsalicylaldehyde
(2.2 mM, 0.30 g) was mixed with 1, 4-bis (3-aminopropyl) pipera-
zine (2.2 mM, 0.44 g) dissolved in methanol (10 mL). The mixture
was stirred for 30 min at room temperature to give a clear yellow
solution. Then the content was refluxed for about 3 h. Yellow rod-
shaped crystals were formed at the bottom of the vessel by slow
evaporation of the solvent. The crystals were isolated by filtration,
washed with methanol and dried. Yield: 0.64 g (87%) m.p.: 102 °C.
Anal. Calcd. (%) for C26H36N4O2: C, 71.53; H, 8.31; N, 12.83. Found
(%): C, 71.02; H, 8.76; N, 12.75. FT-IR, (m
, cmꢁ1) (KBr Disc): 3450br,
3012s, 2863s, 2932w, 2979br, 1133s, 1637s (br, broad; s, sharp; m,
medium; w, weak). 1H NMR, (300 MHz, CDCl3): d = 12.78 (Ar-OH,
2H); 8.29 (CH, 2H); 7.32–6.80 (- ArH, 6H); 2.39-3.55(-CH2, 12H);
2.35(-CH3, 6H); 1.82-1.88 (-CH2, 8H). kmax, nm (e
, Mꢁ1 cmꢁ1) in
DMF: 325 (13,200), 270 (14,900).
Synthesis of ligand L2
Ligand L2 was synthesised using the same procedure as L1 using
5-bromosalicylaldehyde (2.2 mM, 0.40 g) instead of 5-methylsali-
cylaldehyde. Yellowish orange, rod-shaped crystals were obtained
at the bottom of the vessel. The crystals were isolated by filtration,
washed with methanol and dried. Yield: 0.70 g (82%) m.p.: 125 °C.
Anal.Calcd. (%) for C24H30 Br2N4O2: C, 50.90; H, 5.34; N, 9.89. Found
(%): C, 50.82; H, 5.76; N, 9.75. FT-IR (m
, cmꢁ1) (KBr Disc): 3423br,
Experimental
3000w, 2857br, 2939s, 1128s, 1628s. 1H NMR (300 MHz, CDCl3):
d = 12.96 (Ar-OH, 2H); 8.19 (CH, 2H); 7.32–6.82(ArH, 6H); 2.39–
Materials and instruments
2.42 (CH2, 12H); 1.86 (CH2, 8H). kmax, nm (e
, Mꢁ1 cmꢁ1) in DMF:
328 (14,200), 272 (15,600).
All the chemicals used were of analytical grade and were used
as received without any further purification. All the solvents were
purified according to standard procedures. CT DNA and pBR322
DNA were purchased from SRL (India), Tris–HCl, Trisbase and NaCl
were purchased from Merck. Double distilled water was used to
prepare all buffer solutions.
The electronic spectra were recorded on a Shimadzu UV-
3101PC spectrophotometer. FT-IR spectra were recorded in the
4000–400 cmꢁ1 region using KBr pellets on a Bruker EQUINOX 55
spectrometer. The 1H NMR spectrum of ligands were recorded in
CDCl3 on a BRUKER 300 MHz spectrometer at room temperature
using TMS as an internal reference. Elemental analysis was carried
out on an Elementarvario MACRO cube elemental analyzer. The
EPR spectra were recorded at room temperature with a Bruker
ESP 300E X-band spectrometer operating at 100 kHz. ESI mass
spectra was obtained from Agilent 6520 Q-T mass spectrometer
Synthesis of copper(II) complexes
[CuL1](ClO4)2(1). To a solution of ligand (L1) (0.20 g, 0.46 mM) in
methanol (10 mL), Cu(ClO4)2.6H2O (0.17 g, 0.46 mM) in 10 mL of
methanol was added drop wise. The mixture was stirred well at
room temperature and the content was refluxed for about 2 h.
The resultant dark green solution was then concentrated to one
third of its volume and washed well with water, ethanol and ether
and dried under vacuum. Yield: 0.27 g (74%). m.p.: 174 °C (dec.).
Anal. Calc. (%) for C26H36Cl2CuN4O10: C, 44.67; H, 5.19; N, 8.01;
Cu, 9.09. Found (%): C, 44.47; H, 5.04; N, 8.08; Cu, 8.95. FT-IR (
m,
cmꢁ1) (KBr Disc): 3450w, 3010s, 2867 m, 2923br, 1630s, 1139s,
625w. kmax, nm (e
, Mꢁ1 cmꢁ1) in DMF: 568 (520), 383 (13,900),
286 (99,200); Conductance (Km/S cm2 molꢁ1) in acetonitrile 165.
g|| = 2.14, g\ = 2.08, and A|| = 324; ESI-MS in CH3CN m/z (%): 380.3
(9) [C26H36N4O2]+, 498.3 (100) [CuL1]+, 696.2(2) [CuL1 + 2ClO4]+.
(CDRI, Lucknow, India).
A Biologic CHI604D electrochemical
analyzer was used for studying the electrochemical behaviour of
complexes using a three-electrode cell in which a glassy carbon
electrode was the working electrode, a saturated Ag/AgCl electrode
was the reference electrode and a platinum wire was used as an
[CuL2](ClO4)2(2). The complex 2 was synthesised using the same
procedure as 1 using ligand L2(0.20 g, 0.35 mM) instead of L1 with
Cu(ClO4)2.6H2O (0.13 g, 0.35 mM) in 10 mL of methanol. Yield:
0.23 g (70%). m.p.: 210 °C (dec.). Anal. Calc. (%) for C24H30Br2Cl2

A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
367
CuN4O10: C, 34.78; H, 3.65; N, 6.76; Cu, 7.67. Found (%): C, 34.56; H,
3.76; N, 6.86; Cu, 7.95. FT-IR (
, cmꢁ1) (KBr Disc): 3425br, 3017 m,
incubation, 5 lL of DNA loading buffer (0.25% bromophenol blue,
m
0.25% xylene cyanol, 30% glycerol in water) were added to each
tube and the sample was loaded onto a 0.8% agarose gel in TBE buf-
fer (89 mM Tris–borate, 1 mM EDTA pH8.4) containing ethidium
2881 m, 2958s, 1625s, 626w. kmax, nm (e
, Mꢁ1 cmꢁ1) in DMF: 571
(1400), 382 (17,300), 287 (99,900); Conductance (Km/S cm2 molꢁ1
in acetonitrile 172. g|| = 2.14, g\ = 1.88 and A|| = 358.
)
bromide (0.5 lg/mL). Negative and positive controls were loaded
on each gel electrophoresis and the experiment was carried out
X-ray diffraction analysis
for 1.30 h at 50 V.
Yellow crystals of the ligands L1 and L2 suitable for X-ray dif-
fraction studies were obtained from slow evaporation of chloro-
form solution, after standing for two days. The X-ray diffraction
analysis of the ligands was performed on Bruker SMART APEX-II
Antibacterial screening
Antibacterial activity of the ligands and their complexes were
tested against the bacterial species Staphylococcus aureus, Esche-
richia coli, Bacillus subtlis, Pseudomonas aeruginosa by disc diffusion
method using nutrient agar medium. Nutrient agar (20 mL) were
poured into each sterilized Petri dish (10 ꢃ 100 mm diameter)
and allowed to solidify. After solidification the bacterial culture
were swabbed in nutrient agar plates. For the investigation of the
antibacterial activity, the ligands and their copper complexes were
dissolved in dimethylsulfoxide (DMSO) to a final concentration of
CCD diffractometer using graphite monochromated Mo
Ka
0
radiation (0.71037 ÅA). The structure was solved using the direct
methods and successive Fourier difference synthesis thermal
parameters for all non-hydrogen atoms (SHELXL-97) and all non-
hydrogen atoms were refined anisotrophically by full-matrix
least-square procedures. Hydrogen atoms were added theoretically
and refined with riding model position parameters and fixed
isotropic thermal parameters.
100 lg/mL. Each sample was filled into the Sterilized discs of agar
plates directly. Plates swabbed with the bacteria culture were
incubated at 37 °C for 18 h. At the end of the incubation period,
inhibition zones formed on the medium were evaluated in mm
and studies were performed in duplicate. Solvent control test
was also performed in order to study the effect of DMSO (solvent)
on the growth of microorganism and it did not inhibit growth.
DNA binding and cleavage studies
The binding of CT DNA with copper(II) complexes were studied
using the UV absorption spectral method. Solutions of CT DNA in
50 mM NaCl/5 mM Tris–HCl (pH = 7.4) gave a ratio of A260/A280
as 1.8–1.9, indicating that the DNA was sufficiently free of protein
contamination. The DNA concentration was determined by the UV
absorbance at 260 nm after 1:100 dilutions. The molar absorption
coefficient was taken as 6600 Mꢁ1 cmꢁ1 [15]. Stock solutions were
stored at 4 °C and used within Four days. Absorption titration
experiments were made using different concentration of DNA,
while keeping the complex concentration as constant.
No luminescence was observed for complexes 1&2 at room
temperature in aqueous solution, in any organic solvent examined,
or in the presence of CT-DNA. So the binding of complexes cannot
be directly presented in the emission spectra. Therefore, the
fluorescence spectral method, using ethidium bromide (EB) as a
reference was used to determine the relative DNA binding proper-
ties of complexes 1&2 to CT DNA in 5 mM Tris–HCl/5 mM NaCl buf-
fer, pH 7.2. Fluorescence intensities of EB at 600 nm with an
excitation wavelength of 515 nm were measured at different
complex concentrations. Reduction in the emission intensity was
observed with addition of the complexes. The relative binding ten-
dency of the complexes to CT DNA was determined from a compar-
ison of the slopes of the lines in the fluorescence intensity versus
Results and discussion
Synthesis and characterization
The synthesis of the Cu(II) complexes with the ligands of the
Schiff base type were done using a common procedure, by reaction
of stoichiometric amount of copper perchlorate salts with the
complex concentration plot. The apparent binding constant (Kapp
)
was calculated using the equation KEB/[EB] = Kapp[Complex], where
the complex concentration equalled the value at a 50% reduction of
the fluorescence intensity of EB and KEB = 1.0 ꢃ 107 Mꢁ1
([EB] = 3.3 lM).
The DNA cleavage studies were done by gel electrophoresis
experiment for which pBR322 was used as the plasmid DNA.
DNA cleavage activity was evaluated by monitoring the conversion
of supercoiled plasmid DNA (Sc – form I) to nicked circular DNA
(Nick-form II) and linear DNA (Lin – form III). Each reaction mix-
ture was prepared by adding 6
l
L of water, 2
of 500 mM Tris–HCl/500 mM NaCl buffer
L of 3-mercaptopropionic acid 6 L of the complex
L, the final
buffer concentration was 50 mM and the final metal concentration
varied from 100 to 200 M. For investigation of the mechanistic
lL (200 ng) of super-
coiled DNA,
(pH = 7.4), 4
2 lL
l
l
dissolved in DMF. The final reaction volume was 20
l
l
aspects, the cleavage of pBR322 DNA was also carried out in the
presence of standard hydroxyl radical scavenger such as DMSO
and KI, and singlet oxygen (1O2) quencher such as L-histidine and
NaN3. Samples were typically incubated for 1 h at 37 °C. After
Scheme 1.

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A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
ligands in methanol as given in the Scheme 1. The analytical data
obtained for complexes 1&2 are consistent with the formation of
mononuclear copper complexes. The obtained complexes are insol-
uble in water, methanol, ethanol, and chloroform but soluble in
acetonitrile, Dimethylformamide (DMF) and DMSO.
distance of 2.594 Å for L1 and O8–H8ꢄ ꢄ ꢄN10 for L2 at a bond distance
of 2.575 Å, linking the OH group of the former salicylaldehyde and
the imine N atom of amine stabilises the molecule. In addition, the
L1 is further connected by C8–H8cꢄ ꢄ ꢄH8c at a bond distance of
2.399 Å with another molecule (hydrogen bonds) forming one
dimensional infinite chain which stabilises the crystal packing. In
case of L2 there are four intermolecular interactions noted at
Br7ꢄ ꢄ ꢄN14 (3.21 Å), Br7ꢄ ꢄ ꢄH11B (2.999 Å), C2-H2ꢄ ꢄ ꢄH2 (2.352 Å) and
O8-H8ꢄ ꢄ ꢄH13A (2.622 Å) stabilises the crystal packing. The packing
is further stabilized by Vander Waals interactions.
X-ray crystal studies
The crystals of ligands L1 and L2 were obtained by slow evapo-
ration method using chloroform as solvent were shown in Fig. 1.
The details of the crystal data and refinement for L1 and L2 were
given in Table 1, selected bond lengths and angles are listed in
Table 2. Both the crystals, crystallizes in the monoclinic crystal sys-
tem with space group P21/c with molecular formulae C26H36N4O2
(L1) and C24H30Br2N4O2 (L2). As depicted in Fig. 1(a) and (b), the
L1 and L2 contain one crystallographically unique piperazine ring
and two 5-methyl salicylaldehyde and 5-bromosalicylaldehyde
respectively. The piperazine ring of the ligands can be regarded
as three moieties: plane A composed of N(14A)–C(15A)–C(16), ring
B composed of C(15)–C(16)–C(15A)–C(16A), and plane C composed
of N(14)–C(15)–C(16A) for both the ligands. The atoms of ring B are
perfectly coplanar for the mean deviation from the plan is
0.0000 Å, and N(14) atom and N(14A) atom lies above or below
the plan by ꢁ1.458 and 1.458 Å for L1 and by ꢁ1.456 and 1.456 Å
for L2 with respect to one another. Furthermore the dihedral angle
between the plane A and B is 57.6° for L1 and 57.8° for L2, equal to
that of B and C for both ligands respectively, and that of A and C is
0° for both ligands. Therefore, plane A and C parallel to each other,
indicating that the piperazine ring in both the ligands adopts the
stable chair conformation, not the boat conformation [16].
Spectral characterization
The FT-IR spectrum of ligands showed the band at 1281 cmꢁ1
associated with phenolic
broad peak at 3423–3450 cmꢁ1 is assigned to the phenolic
group. The ligands and complexes show a sharp band in the region
of 1620–1650 cmꢁ1 due to thepresence of
(C@N) in the ligand and
m(C-O) stretching frequency and the
m
(OH)
m
in complexes [18]. The effective Schiff base condensation is con-
firmed by the formation of this new peak and the disappearance
of the
m
(C@O) peak at 1680 cmꢁ1 in the reactant molecule (5-
methyl salicylaldehyde). Both the copper(II) complexes showed a
strong band around 1000–1100 cmꢁ1 and a sharp band in the
region around 625 cmꢁ1 due to the antisymmetric stretch and anti-
symmetric bend of the perchlorate ions, respectively. No splitting
of the perchlorate peak indicates that the perchlorate ions are
not coordinated to the Cu(II) ions and are present as counter ions
in crystal lattice [19,20]. Conductivity measurement of mononu-
clear copper(II) complexes in acetonitrile are in the range of
165–172 Km/S cm2 molꢁ1 indicates that the complex is 1:2 electro-
lyte type [21].
The bond length of azomethine C9@N10 Å in L1 and L2 were
consistent with normal C@N bond lengths [17]. The bond angle
of C(13)N(14)C(15) was found to be 110° but the bond angle of
C(9)N(10)C(11) bond angle at 119.6° which clearly indicates the
formation of C@N bond confirming the formation of Schiff’s base
in both ligands. In the crystal structure of L1 the 5-methylsalicylal-
dehyde group is in the same plane of piperazine unit with torsion
angle of 179.89° in the place of azomethine group, but in case of L2
5-bromosalicylaldehyde is not parallel to piperazine moiety, it has
the torrision angle of 178.18° in the place of azomethine group. The
difference between both the structures may be attributed due to
the presence of electron withdrawing bromine atom in L2.
The absorption spectral data for Schiff’s base ligands and their
complexes were obtained in DMF solution. In the UV region, band
at 325 nm (13,200 cmꢁ1) for L1 and 328 nm (14,200 cmꢁ1) for L2
are due to the n ? pꢅ transition of azo-methine (C@N) function
of Schiff’s base and the band at 270 nm (14,900 Mꢁ1 cmꢁ1) for L1
and at 272 nm (15,600 Mꢁ1 cmꢁ1) for L2 are due to
p ?
pꢅ of the
aromatic moiety in ligands. In case of complexes, the peaks in
the region of 286 and 289 nm are obtained due to
p
?
pꢅ transition
of coordinated ligands. In the UV region of complexes show broad,
slightly intense bands between 382 and 383 nm could be assigned
to ligand to metal charge transfer transition [22]. In the visible re-
gion of both complexes the broad absorption band at about 568–
571 nm, which is assigned to a d–d transition, which is consistent
with the square-planar geometry of the Cu(II) complexes. For
The packing of the L1 and L2 in the unit cell showing the inter-
molecular and intramolecular interactions were depicted in Fig. 2.
An intramolecular hydrogen bonding O7–H7ꢄ ꢄ ꢄN10 at
a bond
Fig. 1. OPTEP view of the molecular structure and atom labeling scheme of L1 (a) and L2 (b).

A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
369
Table 1
Crystallographic data & structure refinement parameters for ligands L1 and L2.
L1
L2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
a (Å)
C26 H36 N4 O2
436.59
296(2)
0.71073
Monoclinic, P21/c
23.952(7)
5.8556(14)
8.969(3)
C24 H30 Br2 N4 O2
566.34
296(2)
0.71073
Monoclinic, P21/c
10.0467(2)
6.54420(10)
19.1166(3)
90
B (Å)
c (Å)
a
(°)
90
b (°)
98.727(16)
90
1243.3(6)
2, 1.166
0.075
472
102.1260(10)
90
1228.94(4)
2, 1.530
3.326
576
c
(°)
Volume (Å3)
Z, calculated density (mg mꢁ3
)
)
Absorption coefficient (mmꢁ1
F(000)
Crystal size (mm)
0.32 ꢃ 0.30 ꢃ 0.11
0.17 ꢃ 0.15 ꢃ 0.14
Theta range for data collection (°)
Limiting indices, h, k, l
Reflections collected/unique
R int
0.86–25.49
2.07–28.30
ꢁ26 6 h 6 27, ꢁ7 6 k 6 4, ꢁ10 6 l 6 8
9411/2240
0.1133
ꢁ13 6 h 6 13, ꢁ8 6 k 6 8, ꢁ25 6 l 6 25
27402/3051
0.0814
Data/restraints/parameters
2240/0/150
1.064
3051/0/149
0.812
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0626, wR2 = 0.1813
R1 = 0.1050, wR2 = 0.2451
0.213 and ꢁ0.283
R1 = 0.0300, wR2 = 0.0574
R1 = 0.0694, wR2 = 0.0639
0.214 and ꢁ0.363
Largest difference peak and hole/e Åꢁ3
Table 2
Selected bond lengths (Å) and bond angles (°) for L1 and L2.
Ligand L1
Ligand L2
0
Bond angles (°)
0
Bond angles (°)
Bond distances (ÅA)
Bond distances (AÅ)
C(1)–C(9)
C(2)–O(7)
O(7)–H(7)
N(10)–C(11)
N(14)–C(15)
C(2)–C(3)
1.460(4)
1.345(3)
0.940(4)
1.461(4)
1.458(3)
1.383(4)
1.502(4)
1.261(3)
1.452(3)
1.458(3)
C(6)–C(1)–C(2)
C(6)–C(1)–C(9)
C(2)–C(1)–C(9)
O(7)–C(2)–C(3)
O(7)–C(2)–C(1)
C(6)–C(5)–C(8)
C(2)–O(7)–H(7)
N(10)–C(9)–C(1)
C(9)–N(10)–C(11)
N(10)–C(11)–C(12)
N(14)–C(13)–C(12)
C(16)–N(14)–C(15)
N(14)–C(15)–C(16)#1
N(14)–C(16)–C(15)#1
118.5(3)
120.9 (2)
120.6(2)
120.0(2)
121.3(3)
121.8(3)
109.0(3)
122.4(2)
119.6(2)
112.3(2)
114.2(2)
108.0(2)
111.7(2)
111.0(2)
C(1)–Br(7)
C(4)–O(8)
O(8)–H(8)
N(10)–C(11)
N(14)–C(15)
C(2)–C(3)
1.902(2)
1.350(3)
0.82(2)
1.462(3)
1.456(2)
1.375(3)
1.458(3)
1.267(3)
1.465(2)
1.458(2)
C(6)–C(1)–C(2)
120.0(2)
C(6)–C(1)–Br(7)
C(2)–C(1)–Br(7)
O(8)–C(4)–C(3)
O(8)–C(4)–C(5)
C(6)–C(5)–C(9)
119.47(18)
120.48(18)
118.4(2)
121.8(2)
120.51(19)
105.2(19)
121.7(2)
118.93(19)
111.50(18)
114.19(17)
108.37(16)
111.50(17)
110.53(17)
C(5)–C(8)
C(5)–C(9)
C(4)–O(8)–H(8)
C(9)–N(10)
C(13)–N(14)
N(14)–C(15)
C(9)–N(10)
C(13)–N(14)
N(14)–C(16)
N(10)–C(9)–C(5)
C(9)–N(10)–C(11)
N(10)–C(11)–C(12)
N(14)–C(13)–C(12)
C(15)–N(14)–C(16)
N(14)–C(15)–C(16)#1
N(14)–C(16)–C(15)#1
square planar complexes with dx2ꢁy2 ground state, three spin al-
lowed transitions are possible viz., 2B1g ? 2A1g (dx2ꢁy2 ? dz2),
2B1g ? 2B2g (dx2ꢁy2 ? dxy) and 2B1g ? 2Eg (dx2ꢁy2 ? dxz, dyz) but it
is often difficult to resolve into three bands since the four lower
orbitals are so close together in energy that individual transfer
from these to the upper d level cannot be distinguished. The third
peak in the wavelength range 568–571 nm corresponds to d–d
transition of this type as expected for square planar copper(II)
complexes [23–25]. Therefore, it appears that there is a distorted
square-planar geometry of the Cu centers in the copper(II)
complexes.
Electron Spray Ionization (ESI) mass data of 1 shows the molec-
ular ion peak at m/z 696.2(2) which is assignable to [CuL1 + 2ClO4]+
and the loss of perchlorate ions forms a base peak at m/z
498.3(100) due to the formation of (CuL1]+. Few other intense
peaks are also obtained for 1 at m/z 380.3, 249.8, and 211.2. The
pH-controlled complexation–decomplexation
The solution of 0.05 M in sodium perchlorate of the mononu-
clear copper(II) complexes was acidified to pH 2 and was titrated
with standard NaOH. The titration curve disclosed a single depro-
tonation event, with a pKa = 7.85 0.05, to be ascribed to the
acid–base equilibrium. Titration with base induces decolorisation
of the blue to green solution and a considerable change of the
absorption spectrum, as shown in Fig. 3. In particular, the strong
band at 389 nm (
develops at 338 nm (
[CuL1] complex. In case of [CuL2] complex, the strong band at
387 nm (
– 7487 Mꢁ1 cmꢁ1) decreases, while a new band develops
at 336 nm (
– 5348 Mꢁ1 cmꢁ1, limit value at pH 12). Quite inter-
e
– 8870 Mꢁ1 cmꢁ1) decreases, while a new band
– 6750 Mꢁ1 cmꢁ1, limit value at pH 12) for
e
e
e
estingly, on increasing pH the molar absorbance of the new band
superimposes well with the concentration profile of the [CuII(L)]+
species, as shown in Fig. 3(a) and (b). The shift of the wavelength
in the visible region from 560-570 nm to 590-600 nm on varying
the pH (acidic to basic) of the mononuclear copper(II) complexes
indicates that the colour and spectral changes are associated to
mass spectra of mononuclear copper(II) complexes
1 was
displayed in Fig. S1. The ESI mass spectral data of the Schiff base
copper(II) complexes are in good agreement with the proposed
structure of mononuclear copper(II) complexes.

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A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
Table 3
Electrochemical data of mononuclear copper (II) complexes.
E1pc
E1pa
E11=2
Complexes
D
E1
[CuL1](ClO4)2
[CuL2](ClO4)2
ꢁ0.85
ꢁ0.77
ꢁ0.51
ꢁ0.49
ꢁ0.68
ꢁ0.63
340
280
Fig. 4. Cyclic voltammogram of the mononuclear copper(II) complexes. (1)
[CuL1](ClO4)2, (2) [CuL2](ClO4)2 (Reduction process).
Fig. 2. Crystal packing diagram of L1 (a) and L2 (b).
The mononuclear complex 1 shows one quasi-reversible reduc-
tion wave (E1pc = ꢁ0.85 V and Ep1a = ꢁ0.51 V) in the cathodic poten-
tial at E1/2 = ꢁ0.68 V versus Ag/AgCl and the complex 2 shows a
quasi-reversible reduction wave (E1pc = ꢁ0.77 V and Ep1a = ꢁ0.49 V)
in the cathodic potential at E1/2 = ꢁ0.63 V versus Ag/AgCl. The
potentials at the reduction wave of the [CuL2](ClO4)2 was lower
than that of [CuL1](ClO4)2 is due to the electron-withdrawing bro-
mide ion that is present at the para position to the phenolic group
which decreases the electron density at the metal centre leading to
easy reduction, and shifts the reduction potential to less negative
potential [26,27].
the deprotonation process and thus the molecular motion [7] i.e.
the change of the position of copper atom from N4 compartment
to N2O2 compartment, is achieved on varying the pH of the
complex solution.
Electrochemical studies
The electrochemical behaviour of the complexes have been
studied using cyclic voltammetry in the potential range of 0 to
ꢁ1.80 V in dimethylformamide containing 10ꢁ1
M
tetra(n-
So the one redox couple of a single electron transfer for mono-
nuclear complexes was assigned as,
butyl)ammonium perchlorate. The voltammetric data are summa-
rized in Table 3. Cyclic voltammograms for all the complexes (scan
rate 50 mV sꢁ1) were displayed in Fig. 4. Controlled potential
electrolysis performed at a potential 100 mV morenegative than
the reduction wave indicates the consumption of one electron
per molecule for both the first and second reduction wave.
CuII ꢀ CuI
Thus, the cavity of the complex easily holds the reduced cation and
stabilizes the formation of Cu(I) in the compartment.
Fig. 3. Absorption spectra of 1 (a) and 2 (b) in water (10ꢁ5 M) measured during a titration with NaOH (pH range: 2–12).

A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
371
intrinsic binding constant of 1&2 with those of some other mono
and binuclear Schiff base copper(II) complexes (Table 4), we
conclude that these complexescan strongly bind to DNA and their
binding constant is remarkable. Furthermore, the Kb values of 1&2
complexes are also higher than those of some other mononuclear
Schiff’s base copper(II) complexes as listed in Table 4 [32–37] and
other well-established intercalation agents (ꢇ104) [38–40]. This
indicates that diverse bridging ligands have a profound effect on
DNA-binding ability, as revealed by the different binding constants.
ESR spectra
The ESR spectra of the mononuclear copper(II) complexes (1&2)
show four lines with nuclear hyperfine spin 3/2 due to hyperfine
splitting. For the mononuclear copper(II) complex 1, the observed
g\, g|| and A|| values are 2.05, 2.14 and 324 respectively and for
mononuclear copper(II) complex 2, g\, g|| and A|| values are 1.88,
2.14 and 358 respectively. The observed ESR spectral values are
similar to a piperazine based mononuclear Cu(II) complex [28].
The fact that g|| > g\, confirms a square planar geometry with a
1
Fluorescence spectral studies
(dx2ꢁy2
)
as ground state in complexes 1&2. For a Cu(II) complex,
g|| is a parameter sensitive enough to indicate covalence. The fact
that g|| less than 2.3 is an indication of significant covalent charac-
ter to the M–L bond [29].
The fluorescence spectroscopy technique is an effective method
to study metal complex interaction with DNA. The emission spec-
tra of EB bound to DNA in the absence and presence of complexes
1&2 are shown in Fig. 6. The addition of the complex to DNA
pretreated with EB causes an appreciable reduction in the fluores-
cence intensity, indicating that complexes 1&2 compete with EB to
bind with DNA. The reduction of the emission intensity gives a
measure of the DNA binding propensity of the complexes and
stacking interaction between adjacent DNA base pairs [41].
According to the classical Stern–Volmer equation I0/I = 1 + K [Q];
I0 and I are the fluorescence intensities in the absence and presence
of the quencher, respectively; K is a linear Stern–Volmer quenching
constant; [Q] is the concentration of the quencher. The fluores-
cence quenching curve of DNA-bound EB by complexes 1&2 illus-
trates that the quenching of EB bound to DNA by complexes 1&2
is in good agreement with the linear Stern–Volmer equation. In
the linear fit plot of I0/I versus [complex]/[DNA], K is given by the
ratio of the slope to the intercept. The K values for complexes
1&2 are 1.25 (R = 0.992) and 1.65 (R = 0.991), respectively (I0 is
the emission intensity of EB-DNA in the absence of complex; I is
the emission intensity of EB-DNA in the presence of complex).
The apparent DNA binding constants (Kapp) of 3.67 ꢃ 105 Mꢁ1 and
4.13 ꢃ 105 Mꢁ1 were derived {KEB/([Complex]/[EB])} for complexes
1&2 respectively. The Kapp values imply that all the complexes can
strongly interact with DNA and are protected by DNA efficiently,
since the hydrophobic environment inside the DNA helix reduces
the accessibility of solvent water molecules to the complex and
the complex’s mobility is restricted at the binding site [42]. The
presence of 5-methyl (or bromo)salicylaldehyde groups and also
the hydrophobic property of the rigid ligand facilitate the DNA
binding [43,44].
DNA binding studies
Absorption spectral studies
Absorption titration experiments were performed with fixed
concentrations of the copper(II) complexes (40 lM) while gradu-
ally increasing the concentration of DNA (10 mM) at 25 °C. While
measuring the absorption spectra, an equal amount of DNA was
added to both the compound solution and the reference solution
to eliminate the absorbance of DNA itself. We have determine
the intrinsic binding constant to CT DNA by monitoring the absorp-
tion intensity of the charge transfer spectral bands near 260 and
275 nm for the complexes of [CuL1] and [CuL2], respectively.
Upon addition of increasing amount of CT DNA, a significant
‘‘hyperchromic’’ effect in the intraligand bands at 246–280 nm
was observed accompanied by a moderate red shift of 2–3 nm,
indicative of stabilization of the DNA helix. These spectral charac-
teristic suggest that the complexes and ligand bind either to the
external contact (electrostatic binding) or to the major and minor
grooves of DNA. Moreover, this ‘‘hyperchromic effect’’ can be ex-
plained on the basis of two phenomena. Firstly, the large surface
area of the ligand as well as presence of planar aromatic chromo-
phore facilitates a strong binding interaction of the complexes with
CT DNA there by, providing ample opportunity for the complex to
bind with the CT DNA via, partial insertion of the aromatic moiety
in between the stacking base pair. The binding interaction between
the cationic complex and CT DNA leads to diffusion-limited ion-
pair formation at higher concentration of the complex such that
the complex is fitted along the contour of DNA double helix in an
induced-fit fashion. Thus, the complexes preferably bind to the
DNA helix via, groove binding interactions. This groove binding re-
sults in structural reorganization of CT DNA which entails partial
unwinding or damage of the double helix at the exterior phosphate
backbone leading to the formation of a cavity to accommodate the
complex [30]. The spectrophotometric titration of the complex 1&2
are shown in Fig. 5. To compare quantitatively the binding strength
of all the copper(II) complexes, the intrinsic binding constants Kb of
all the complexes with CT DNA were determined according to the
following equation [31].
DNA cleavage studies
The DNA cleavage activity of complexes 1&2 have been studied
by supercoiled pBR322 DNA as a substrate in a medium of 50 mM
Tris–HCl/50 mM NaCl buffer (pH = 7.4) in the presence of mercap-
topropionic acid as a reducing agent. When the original super-
coiled form (Form I) of plasmid DNA is nicked, an open circular
relaxed form (Form II) will exist in the system and the linear form
(Form III) can be found upon further cleavage. During electropho-
resis, the compact Form I migrates relatively faster while the
nicked Form II migrates slowly, and the linearized form (Form III)
migrates between Forms I and II.
½DNAꢆ=ðea
ꢁ
ef Þ ¼ ½DNAꢆ=ðeb
ꢁ
ef Þ þ 1=Kbðeb
ꢁ
ef
Þ
where [DNA] is the concentration of DNA in base pairs, the apparent
Fig. 7 exhibits the results of the gel electrophoresis separations
of plasmid pBR322 DNA by the complexes 1&2 in the presence of
mercaptopropionic acid(MPA) which shows that the DNA cleavage
of complexes 1&2 (lanes 3 and 4) have no conversion of super-
absorption coefficients ea ef and eb correspond to Aobsd/[Cu2], the
,
extinction coefficient for the free complexes and the extinction
coefficient for the complexes in the fully bound form, respectively.
In plots of DNA]/(eb
–e
f) versus [DNA], K is given by the ratio of the
coiled form to nicked form at 200 lM concentrations of complexes
slope to the intercept. The Kb values obtained from the absorption
spectral technique for the complexes [CuL1] and [CuL2] were calcu-
lated as 4.89 ꢃ 105 and 7.89 ꢃ 105 Mꢁ1, respectively. The binding
constant of the copper(II) complexes of L1 is comparatively lower
than that of the copper(II) complexes of L2, may be due to the
presence of electron withdrawing group (Br) in L2. Comparing the
without the addition of reducing agent. But Form I (Super coiled
DNA) was mostly converted to Form II (Nicked Circular DNA) at
100 lM concentration of the complexes 1&2 (lanes 5 and 6 respec-
tively) in the presence of MPA. A minimum amount of DNA was
completely cleaved to Form III (linear) as the concentration of
complexes increased to 200 lM (lanes 7 and 8). The presence of

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A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
Fig. 5. Absorption spectra of (a) [CuL1] (ClO4)2 and (b) [CuL2] (ClO4)2(10ꢁ5 M) in 5 mM Tris–HCl/20 mM NaCl buffer at pH 7.2 in the absence and presence of increasing
amounts of DNA.
Table 4
Intrinsic binding constants (Kb) and cleavage properties.
ꢁ1
Compound
DNA binding constant Kb (mol Lꢁ1
)
)
DNA cleavage studies
Reference
[Cu(L1)](ClO4)2
[Cu(L2)](ClO4)2
[Cu2(L1)](ClO4)2
[Cu2(L2)](ClO4)2
[Cu(L3)(phen)Cl]
[Cu(L3)(bpy)Cl]
[Cu2L4(OAc)(CH3OH)] CH3OH
[Cu (L5)]
4.89 ꢃ 105
7.89 ꢃ 105
8.02 ꢃ 105
1.09 ꢃ 104
5.72 ꢃ 104
1.55 ꢃ 104
1.16 ꢃ 105
2.71 ꢃ 104
6.94 ꢃ 104
8.56 ꢃ 104
7.15 ꢃ 104
1.01 ꢃ 105
2.76 ꢃ 105
6.07 ꢃ 105
Oxidative cleavage
Oxidative cleavage
Oxidative cleavage
Oxidative cleavage
Notable cleavage
Notable cleavage
Effective DNA-cleavage activity via hydrolytic-cleavage mechanism
Moderate cleavage
-
Oxidative cleavage
Oxidative cleavage
Oxidative cleavage
Hydrolytic-cleavage
Hydrolytic-cleavage
This work
This work
This work
This work
[32]
[33]
[34]
[39]
[35]
[22]
[22]
[36]
[37]
[CuL6Cl2]
[Cu(L7)](ClO4)2
[Cu(L8)](ClO4)2
[Cu(buobb)2](pic)2
[Cu2L9]
[Cu2L10
]
[37]
L1 = N,N0-bis(2-hydroxy-5-methylbenzyl)-1,4-bis(3-iminopropyl)piperazine.
L2 = N,N0-bis(2-hydroxy-5-bromobenzyl)-1,4-bis(3-iminopropyl)piperazine.
L3 = Schiff’s base formed from o-aminophenol and 2-methylacetoacetanilide.
L4 = 1,3-bis (5-methylsalicylideneimino)propan-2-ol.
L5 = Schiff’s base formed from isatinmonohydrazone and 2,3,5-trichlorobenzaldehyde.
L6 = Schiff’s base formed from 5-nitro-o-vanillin and diaminoethane.
L7 = 2-hydroxybenzyl(2-(pyridin-2-yl)ethylamine.
L8 = 2-hydroxybenzyl(2-(pyridin-2-yl)methylamine).
Buobb = 1,3-bis(1-butylbenzimidazol-2-yl)-2-oxopropane.
pic = 2,4,6-trinitrophenol.
L9 = 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane.
L10 = 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane.
Fig. 6. Emission spectra of EB bound to DNA in the presence of complexes1 (a) and 2 (b) ([EB] = 3.3
plots of emission intensity I0/I versus [DNA]/[complex].
lM, [DNA] = 40 lM, [complex] = 0–25 lM, kex = 510 nm). Inset shows the

A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
373
Table 5
Antibacterial activities of Ligands and its complexes.
Compound
Zone inhibition diameter (mm)
Gram negative bacterium
Gram positive bacterium
E. coli
Psuedomonas
B. subtlis
S. aureus
L1
7
8
12
18
2
5
9
7
10
20
22
6
9
21
25
L2
[CuL1](ClO4)2
[CuL2](ClO4)2
10
Fig. 7. Cleavage of SC pBR322 DNA (0.2 lg, 33.3 lM) by Cu(II) complexes 1&2 in the
presence of the reducing agent MPA (0.71 mM) in 50 mM Tris–HCl/50 mM NaCl
buffer (pH 7.2). Lane 1, DNA control; lane 2, DNA + MPA; lanes 3&4
DNA + 1&2(200
tively; lanes 7&8, DNA + MPA + 1&2 (200
l
M) respectively; lanes 5&6, DNA + MPA + 1&2(100
M) respectively.
lM) respec-
presence of singlet oxygen quencher sodium azide (lanes 3 and
4) and do not exhibit DNA damage activity in the presence of
singlet oxygen quencher L-histidine (lanes 6 and 7). These observa-
tions suggest that complexes 1&2 mediated cleavage reactions pro-
ceed via an oxidative pathway mechanism and imply that singlet
oxygen plays a vital role in the cleavage chemistry. In the presence
of MPA, the Cu(II) complexes 1&2 remarkably degrade pBR322
DNA by an oxidative (O2-dependent pathway) cleavage mecha-
nism using singlet oxygen as the reactive species [51]. The complex
2 shows better chemical nuclease activity than complex 1. The
structure of the ligand plays an important role in the cleavage
[52] which shows a better DNA cleavage ability after combining
to the metal ions, so a synergistic effect might exist in the system.
l
mercaptopropionic acid has a significant effect on DNA cleavage
due to formation of reduced copper ions which is more remarkable
for 1 where the linear form is observed in large extent. As evident
from the literature, complexes of polyamine ligands and the num-
ber of chelating metal atoms play an important role due to their
good nuclease activity [45]. The cleavage ability of the complexes
might be due to the binding affinity of the complex to the DNA,
can almost promote the probability of double strand scission once
the DNA has undergone a single strand break [15]. Therefore, we
conclude that both the complexes show nuclease activity in the
presence of reducing agent due to the enhanced stabilization of
the Cu(I) species, as evidenced by the highest Cu(II)/Cu(I) redox po-
tential and it is clear that the cleavage of pBR322 DNA is highly
dependent on the number of copper ions as well as the presence
of an aromatic moiety in the complexes [46–48].
The cleavage mechanism of pBR322 DNA induced by complexes
1&2 was investigated (Fig. 8(a) and (b)) and clarified in the
presence of singlet oxygen quenchers [49] sodium azide and
L-histidine, and hydroxyl radical scavengers [50] DMSO and KI. It
is remarkable from Fig. 8(a) that DMSO (lanes 3 and 4) and KI
(lanes 6 and 7) are completely ineffective, and these results rule
out the possibility of DNA cleavage by hydroxyl radicals. Fig. 8(b)
shows that the complexes 1&2 exhibits reduced DNA damage in
Antibacterial activity
The inhibition efficiencies of the Schiff’s base ligands and their
copper(II) complexes were tested against two gram positive (S.
aureus, Bacillus subtilis) and two gram negative bacterium (E. coli
and P. aeruginosa). The DMSO used as solvent was kept as control
in all plates does not show any zone of inhibition which implies
that the solvent not interferes in the antimicrobial activity for
the tested microorganisms. The experimental result shown in
Table 5 indicates that, both the complexes are having higher inhi-
bition efficiency than their free ligands which can be explained on
the basis of chelate formation. When the antimicrobial activity of
metal complexes are investigated, the following factors [53–55]
should be considered: (i) the chelate effect of ligands; (ii) the nat-
ure of the N-donar ligands; (iii) the total charge of the complex;
(iv) existence and the nature of the ion neutralizing the ionic com-
plex and (v) the nuclearity of the metal centre in the complex. The
chelation reduces the polarity of ligand due to the overlap of the
ligand orbital and partial sharing of the positive charge of the cop-
per ion with donor groups. Further, it increases the delocalization
of p-electrons over the whole chelate ring and enhances the lipo-
philic nature of the complexes. This increased lipophilicity en-
hances the transportation of the complexes into lipid membrane
and restricts further multiplicity of the microorganisms. The varia-
tion in the effectiveness of different compounds against different
organisms depends either on the impermeability of the cells of
the microbes or on differences in ribosome of microbial cells. On
comparing the gram negative and positive bacterium, the com-
plexes exhibit higher efficiency for gram positive bacterium than
that of gram negative bacterium. Thus the synergistic effect of cop-
per ion and counter ions induces the copper(II) complexes to have
comparatively greater inhibition than that of their respective free
ligands.
Fig. 8. Cleavage of SC pBR322 DNA (0.2
1&2(100 M) in the presence of the reducing agent MPA (0.71 mM) in 50 mM
Tris–HCl/50 mM NaCl buffer (pH 7.2). (a) Lane 1, DNA control; lane 2, DNA + M-
PA + DMSO; lanes 3&4, DNA + MPA + DMSO + 1&2(100 M) respectively; lanes 5,
DNA + MPA + KI; lanes 6&7, DNA + MPA + KI + 1&2(100 M) respectively. (b) Lane 1,
DNA control; lane 2, DNA + MPA + NaN3; lanes 3&4, DNA + MPA + NaN3 + 1&2(100 -
M) respectively; lane 5, DNA + MPA + L-histidine; lanes 6&7, DNA + MPA + L-
histidine + 1&2(100 M) respectively.
lg, 33.3 lM) by Cu(II) complexes
Conclusions
l
l
l
In this study, we have synthesized and characterised two mono-
nuclear Cu(II) complexes using Schiff’s base ligands and studied
their antibacterial activity, DNA binding and cleavage activity.
The single crystals X-ray study confirms the structure of ligands
l
l

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A. Jayamani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 365–374
L1 and L2. The spectral and structural data evidences for proposed
coordination behaviour and geometries of the synthesized Schiff’s
base copper(II) complexes. The electrochemical study reveals that
one electron reduction transfer occurs for both mononuclear com-
plexes. The copper ion in the mononuclear copper complexes has
been translocated between two non-equivalent coordinating com-
partments of a ditopic ligand by varying the pH of the complex
solution. The copper(II) complexes show efficient DNA binding
ability and the binding constant values of both complexes are in
the order of 2 > 1 which show good DNA binding propensity. The
DNA cleavage studies for synthesised complexes 1&2 in the pres-
ence of mercatopropionic acid showed the DNA to be cleaved
through an oxidative (O2-dependent pathway) cleavage mecha-
nism using singlet oxygen as the reactive species, because
L-histidine and azide ions were obviously inhibiting the cleavage
activity. All the copper(II) complexes show good antimicrobial
activity due to synergetic effect of copper atom and the complexes
give greater zone of inhibition for gram positive bacterium than
that of gram negative bacterium.
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Acknowledgements
The authors gratefully acknowledge the financial support of this
work by the Department of Science and Technology, New Delhi
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Appendix Supplementary. material
Crystallographic data in CIF format for compound L1 and L2 have
been deposited at the Cambridge Crystallographic Data Centre,
CCDC Nos. 848543 and 886285 respectively. Copies of CIFs are
available free of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44 1223 336 033; email: depos-
it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk). The CIF format
of L1 and L2 were given in the supplementary material. The mass
spectrum of complex 1 was given in the supplementary material.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.11.079.
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