Chiral discrimination asserted by enantiomers of Ni (II), Cu (II) and Zn (II) Schiff base complexes in DNA binding, antioxidant and antibacterial activities

Article abstract of DOI:10.1016/j.saa.2011.06.002

Chiral Schiff base ligands (S)-H₂L and (R)-H₂L and their complexes (S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L) were synthesized, characterized and examined for their DNA binding, antioxidant and antibacterial activities. The

Full text of DOI:10.1016/j.saa.2011.06.002

Spectrochimica Acta Part A 81 (2011) 199–208
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Chiral discrimination asserted by enantiomers of Ni (II), Cu (II) and Zn (II) Schiff
base complexes in DNA binding, antioxidant and antibacterial activities
Noor-ul Hasan Khan , Nirali Pandya , K. Jeya Prathap , Rukhsana Ilays Kureshya,1,
a,∗
a,1
a,1
a,1
b,1
a,1
Sayed Hasan Razi Abdi , Sandhya Mishra , Hari Chandra Bajaj
Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (CSMCRI),
a
Council of Scientific & Industrial Research (CSIR), G. B. Marg, Bhavnagar-364 021, Gujarat, India
b
Discipline of Marine Biotechnology and Ecology, Central Salt and Marine Chemicals Research Institute (CSMCRI),
Council of Scientific & Industrial Research (CSIR), G. B. Marg, Bhavnagar-364 021, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Chiral Schiff base ligands (S)-H L and (R)-H L and their complexes (S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-
L and R-Zn-L) were synthesized, characterized and examined for their DNA binding, antioxidant and
2
2
Received 23 February 2011
Received in revised form 13 April 2011
Accepted 2 June 2011
antibacterial activities. The complexes showed higher binding affinity to calf thymus DNA with binding
5
6
−1
constant ranging from 2.0 × 10 to 4.5 × 10 M . All the complexes also exhibited remarkable superoxide
(
56–99%) and hydroxyl scavenging (45–89%) activities as well as antibacterial activities against gram
Keywords:
Chiral Schiff base complexes
DNA binding
Superoxide dismutase
Antioxidant activity
Antibacterial activity
(
+) and gram (−) bacteria. However, none of the complexes showed antifungal activity. Conclusively, S
enantiomers of the complexes were found to be relatively more efficient for DNA interaction, antioxidant
and antibacterial activities than their R enantiomers. This study reveals the possible utilization of chiral
Schiff base complexes for pharmaceutical applications.
© 2011 Elsevier B.V. All rights reserved.
1
. Introduction
One of the life’s intrinsic biochemical features is the high selec-
the attention of many research groups [5–10]. Studying inter-
action of chiral metal complexes with biomolecules, particularly
with inherently chiral DNA and protein molecules is likely to pro-
vide information on chiral discrimination of diastereomers, which
may provide important leads for developing targeted bioactive
molecules [11–18]. Although, various aspects of chiral discrimina-
tion of metal complexes for their binding with DNA and protein
molecules have been reported in the past, the role of chirality in
free radical scavenging activity and antibacterial activity has not
been well explored [12,18]. The deleterious effect of free radicals,
tivity of chiral molecular species. Consequently, many biological
responses are greatly influenced by the chirality of the incumbent
molecules [1]. It is therefore not surprising to come across incidents
where chirality plays a decisive role in the area of pharmaceuti-
cals, agrochemicals, flavors and fragrances. In most of the cases
only one optical isomer of the drug molecule selectively interacts
with drug-receptor site to show desirable therapeutic activity [2].
Thalidomide—a drug that was prescribed for morning sickness in
pregnant women during 1960s is a classic example of this behavior.
In this particular case it was found that R-enantiomer of thalido-
mide showed drug action, while S-enantiomer caused birth defects
•
−
•
particularly superoxide anions (O2 ) and hydroxyl radical ( OH)
in many serious diseases e.g. cerebral- and -cardiovascular dis-
orders, cancer, rheumatoid arthritis and aging etc. [19–21], has
encouraged the researcher to study the cooperative effects of chiral
metal complexes and to improve their free radical scavenging and
antibacterial activities.
[
3]. Since then, in medicinal research, all the enantiomers of a chi-
ral compound are considered as different “chemicals” and it has
been made mandatory to test each stereoisomer separately for
their drug action. Although pharma-sector is dominated by organic
molecules as drugs, recently there is a great deal of interest in
the biochemical responses of inorganic metal complexes [4]. As a
result, bio-manifestation of chiral metal complexes has attracted
While dealing with biological interactions especially in medic-
inal applications, comparison for the activity of two enantiomers
of a complex is crucial. Recently, we have demonstrated influence
of chirality on DNA interaction of chiral Ru (II) and Mn (III) salen
complexes where one enantiomer of the complex showed better
activity than the other enantiomer [12,18]. In view of the above
and our ongoing interest in the synthesis of chiral Schiff base metal
complexes for various bio-activities, we report here the synthe-
∗ Corresponding author. Tel.: +91 0278 2567760; fax: +91 0278 2566970.
sis of chiral Schiff base ligands (S)-H L and (R)-H L and their Ni,
E-mail address: khan251293@yahoo.in (N.-u.H. Khan).
Tel.: +91 0278 2567760; fax: +91 0278 2566970.
2
2
1
Cu and Zn complexes to evaluate their DNA interaction capacity,
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.06.002

2
00
N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
antioxidant and antibacterial activities. All the complexes exhibited
DNA interaction capacity together with antioxidant and antibacte-
rial activities where was found to be more S enantiomer effective.
Among all the complexes studied the S-Ni-L and S-Cu-L metal com-
plexes showed intercalative DNA binding capacity while R-Ni-L,
R-Cu-L, S-Zn-L and R-Zn-L showed groove or external binding with
DNA.
2
. Experimental
2.1. Materials and methods
Calf thymus DNA (CT-DNA), (S)-(−)-␣-methyl benzyl amine and
(
R)-(+)-␣-methyl benzyl amine, NBT (nitroblue-tetrazolium) were
purchased from Sigma–Aldrich and used as received. EB (ethidium
bromide), riboflavin (vitamin B ), MET (l-methionine), trichloro
2
acetic acid, ammonium acetate were purchased from S D Fine
Chemicals.
The solution of CT-DNA was prepared in phosphate buffer to
give a ratio of UV absorbance at 260 and 280 nm of ca. 1.8–1.9,
indicating that the DNA was sufficiently free from protein [18].
DNA concentration per nucleotide was determined by absorption
−
1
−1
spectroscopy using molar absorption coefficient (6600 M cm )
at 260 nm. All the commercial grade solvents were distilled before
use. NMR spectra were done on a Bruker F113V spectrometer
(
500 MHz, Switzerland) and were referenced internally with TMS.
Elemental analysis of complexes was recorded on CHNS Analyzer,
PerkinElmer model 2400 (USA). FTIR spectra were recorded on a
PerkinElmer Spectrum GX spectrophotometer (USA) in KBr win-
dow. High resolution mass spectra were recorded on a LC–MS
(
USA) (Q-TOF) LC (Waters), MS (Micromass) instruments using ace-
tonitrile as a mobile phase. The spray voltage, tube lens offset,
capillary voltage and capillary temperature were set at 4.50 kV,
◦
3
0.00 V, 23.00 V and 200 C, respectively, and the m/z values were
quoted for the major peak in the isotope distribution. UV–vis and
fluorescence spectra were recorded on a Shimadzu UV 3101 PC
NIR spectrophotometer (Japan) and LS 50B PerkinElmer lumines-
cence spectrophotometer (USA) respectively. Circular dichroism
Scheme 1. Structure of chiral Schiff base metal complexes.
(
CD) spectra were measured on a J-815 CD spectrophotometer
Japan) respectively.
(
in dichloromethane (DCM) and filtered. The filtrate was washed
first with distilled water (3 × 5 mL) and finally with brine (saturated
sodium chloride) solution. The organic layer was dried over anhy-
drous sodium sulphate and filtered. Removal of solvent from the
filtrate to give a green solid (Scheme 1). Similar method was used
to prepare Cu (II) [23] and Zn (II) complexes. The characterization
data for the above synthesized complexes are as follows.
2
.2. Synthesis of chiral Schiff base ligands
(
(
S)-2-((1-phenylethylimino)methyl)phenol [(S)-H L] and
R)-2-(1-phenylethylimino)methyl) phenol [(R)-H L]
2
2
Ligands (S)-H L and (R)-H L were synthesized according
2
2
to the reported procedure [22]. A solution of salicylaldehyde
16.39 mmol) in absolute ethanol (10 mL) was added to
(
a
pre-cooled solution of (S)-(−)-␣-methyl benzyl amine/(R)-(+)-␣-
methyl benzyl amine (16.39 mmol) in absolute ethanol (10 mL)
under vigorous stirring. The resulting solution was subsequently
refluxed with stirring for 6–8 h. The completion of the reaction was
checked by thin layer chromatography (TLC). After the reaction was
completed, the solvent was removed under reduced pressure to get
crude ligand, which was washed with hexane (3 × 20 mL) and re-
crystallized from methanol to get ligands (S)-H L and (R)-H L in
2
.3.1. (S)-H2L
Yellow solid (89%): IR (KBr ꢀ cm−1): 3433, 3033, 2984, 2880,
365, 1625, 1572, 1491, 1454, 1375, 1276, 1203, 1078, 970, 848,
2
7
8
1
61, 644, 535; H NMR (500 MHz, CDCl3, ı ppm): 13.57 (s, 1H, OH),
.406 (s, 1H, H–C N), 7.36–6.86 (m, 9H, aromatic), 4.60–4.56 (q,
J = 6.8 Hz, 1H, CH), 4.54–4.50 (q, J = 6.6 Hz, 1H, CH), 1.65–1.61 (d,
J = 6.6 Hz, 3H, CH ); Analysis. Calcd for C15H15NO: C, 79.97; H, 6.71;
N, 6.22. Found: C, 80.02; H, 6.65; N, 6.18; MS (ESI) m/z = 225 [M] ;
UV–vis ꢁmax: 255 (14,192), 325 (3752) nm.
3
2
2
+
sufficiently high purity.
2.3. Synthesis of chiral Schiff base complexes
2.3.2. (R)-H2L
A solution of nickel acetate (0.665 mmol) in dry methanol
10 mL) was added to the refluxing solution of (S)-H L/(R)-H L
1.33 mmol) in dry methanol (5 mL) and the resulting solution
was refluxed with stirring for 7–8 h under nitrogen atmosphere.
After completion of the reaction (checked on TLC) the solvent was
removed under reduced pressure and the residue was re-dissolved
Yellow solid (90%): IR (KBr ꢀ cm−1): 3432, 3034, 2985, 2880,
(
(
2367, 1624, 1573, 1493, 1451, 1376, 1278, 1080, 971, 845, 760, 645,
537; 1H NMR (500 MHz, CDCl3, ı ppm): 13.56 (s, 1H, OH), 8.41 (s,
1H, H–C N), 7.32–6.83 (m, 9H, aromatic), 4.60–4.56 (q, J = 6.8 Hz,
1H, CH), 4.53–4.50 (q, J = 6.6 Hz, 1H, CH), 1.64–1.61 (d, J = 6.6 Hz,
2
2
3H, CH ); Analysis. Calcd for C15H15NO: C, 79.97; H, 6.71; N, 6.22.
3

N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
201
+
Found: C, 79.95; H, 6.68; N, 6.18; MS (ESI) m/z = 225 [M] ; UV–vis
2.4. DNA binding experiments
ꢁmax: 255 (13,330), 325 (3406) nm.
The stock solution of chiral Schiff base complexes in DMSO
10 mmol) were used for spectroscopic titration of DNA solution
(
2
.3.3. (S)-Ni-L
−
1
in phosphate buffer (10 mM, pH 7.0), by keeping the concentra-
tion of DMSO as 0.5% throughout the experiments. Accordingly,
incremental quantity of DNA solution 0–55 ␮M was added to the
fixed concentration of chiral Schiff base metal complex solution
S-Ni-L/R-Ni-L/S-Cu-L/R-Cu-L/S-Zn-L/R-Zn-L (50 ␮M) and the spec-
tra were recorded at 250–500 nm. The intrinsic binding constant
was determined by monitoring the changes of absorbance at LMCT
position.
DNA quenching experiments in the presence of EB was car-
ried out in phosphate buffer (10 mM, pH 7.0) by keeping the fixed
concentration of EB solution (4 ␮M), DNA (100 ␮M) but varying
the concentration of chiral Schiff base metal complexes (S-Ni-
L and R-Ni-L (0–25 ␮M) and S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L
Green solid (80%): IR (KBr ꢀ cm ): 3393, 2977, 2934, 1573,
413, 1280, 1198, 1153, 1028, 937, 889, 809, 758, 679, 617; 1
1
H
NMR (500 MHz, CDCl3, ı ppm): 8.416 (s, 1H, H–C N), 7.37–6.83
(
(
(
m, 18H, aromatic), 4.61–4.57 (q, J = 6.6 Hz, 1H, CH), 4.54–4.51
q, J = 6.6 Hz, 1H, CH), 1.65–1.62 (d, J = 6.6 Hz, 3H, CH ); C NMR
500 MHz, CDCl ) ı 164.11, 161.81, 144.52, 132.96, 132.05, 129.36,
13
3
3
1
27.94, 127.09, 119.28, 117.68, 69.19, 25.59; Analysis. Calcd for
C30H28N O Ni: C, 71.03; H, 5.56; N, 5.52. Found: C, 71.01; H, 5.52;
2
2
+
N, 5.48; MS (ESI) m/z = 507 [M] ; UV–vis ꢁmax: 276 (19,440), 324
3638), 393 (9046) nm.
(
2.3.4. (R)-Ni-L
Green solid (78%): IR (KBr ꢀ cm−1): 3391, 2975, 2933, 1575,
413, 1338, 1197, 1153, 1081, 1028, 936, 890, 857, 758, 678,
(0–220 ␮M)) respectively. The emission spectra were recorded
1
6
7
4
at 500–700 nm where the excitation wavelength was kept at
1
16, 526; H NMR (500 MHz, CDCl3, ı ppm): 8.42 (s, 1H, H–C N),
4
78 nm.
Circular dichroism (CD) spectra were recorded on a Jasco J-
15 spectrometer at a scanning speed of 50 nm/min at room
.38–6.84 (m, 18H, Aromatic), 4.61–4.58 (q, J = 6.6 Hz, 1H, CH),
.55–4.51 (q, J = 6.6 Hz, 1H, CH), 1.66–1.62 (d, J = 6.6 Hz, 3H, CH );
C NMR (500 MHz, CDCl ) ı 164.13, 161.82, 144.54, 132.99, 132.08,
29.37, 127.98, 127.11, 119.30, 117.69, 69.20, 25.61; Analysis Calcd
3
8
13
3
temperature using fixed concentration of the chiral Schiff base com-
plexes (50 ␮M) in DMSO in the absence and presence of increasing
amount of DNA (0–60 ␮M). Each CD spectrum has been subtracted
with that of free DNA and thus the spectrum purely reflect the
changes in the enantiomer of the complex upon binding with
DNA.
1
for C30H28N O Ni: C, 71.03; H, 5.56; N, 5.52. Found: C, 70.91; H,
5
3
2
2
+
.52; N, 5.48; MS (ESI) m/z = 507 [M] ; UV–vis ꢁmax: 276 (18,126),
24 (3692), 393 (7952) nm.
2
.3.5. (S)-Cu-L
Viscosity measurements were conducted on Ostwald’s vis-
Dark Green solid (79%): IR (KBr ꢀ cm−1): 3437, 2969, 2927, 1618,
534, 1449, 1398, 1326, 1197, 1097, 1025, 888, 751, 697, 592; Anal-
◦
cometer at 30 ± 0.01 C using fixed concentration of DNA solution
1
(50 ␮M) with increasing concentration of chiral Schiff base metal
complexes S-Ni-L/R-Ni-L/S-Cu-L/R-Cu-L/S-Zn-L/R-Zn-L (0–60 ␮M)
in phosphate buffer (10 mM, pH 7.0) for flow time measure-
ments. Each sample was measured in triplicate and the average
flow time was calculated with a digital stopwatch. Data were
ysis. Calcd for C30H28N O Cu: C, 70.36; H, 5.51: N, 5.51. Found: C,
7
2
2
+
0.34; H, 5.49; N, 5.47; MS (ESI) m/z = 512 [M] ; UV–vis ꢁmax: 277
(
36,830), 315 (21,710), 386 (20,240) nm.
1/3
presented as (ꢃ/ꢃ0)
versus the ratio of the concentration of
2.3.6. (R)-Cu-L
Dark Green solid (75%): IR (KBr ꢀ cm−1): 3433, 2968, 2930, 1615,
532, 1451, 1326, 1326, 1197, 1077, 1026, 928, 890, 750, 697, 595;
the compound and DNA, where ꢃ is the viscosity of DNA in the
presence of the complex, and ꢃ0 is the viscosity of DNA alone
1
[
24].
To determine the stability of DNA, thermal denaturation exper-
iments were carried out on a TCC 260 temperature controller
programmer on UV-3101 PC spectrophotometer by mixing the
solutions of metal complex S-Ni-L/R-Ni-L/S-Cu-L/R-Cu-L/S-Zn-L/R-
Zn-L (20 ␮M) and solution of DNA (0.4 mM) in phosphate buffer
Analysis. Calcd for C30H28N O Cu: C, 70.36; H, 5.51; N, 5.51. Found:
2
2
+
C, 70.31; H, 5.49; N, 5.49; MS (ESI) m/z = 512 [M] ; UV–vis ꢁmax: 279
30,128), 315 (21,560), 386 (20,460) nm.
(
2.3.7. (S)-Zn-L
Dark Yellow solid (76%): IR (KBr ꢀ cm−1): 3633, 3433, 3033,
880, 2358, 1622, 1578, 1493, 1453, 1378, 1277, 1079, 970, 912,
(
10 mM, pH 7.0). The resulting mixture was incubated for 2 min at
2
7
◦
different temperatures (35–95 C) and the absorption intensity was
recorded at 260 nm. The Tm value was determined from the graph
at the midpoint of temperature curve.
60, 697, 536, 447; H NMR (500 MHz, CDCl3 ı ppm): 8.42 (s, 1H,
1
,
H–C N), 7.38–6.83 (m, 18H, Aromatic), 4.61–4.58 (q, J = 6.6 Hz, 1H,
CH), 4.54–4.51 (q, J = 6.6 Hz, 1H, CH), 1.66–1.62 (d, J = 6.6 Hz, 3H,
CH ); C NMR (500 MHz, CDCl ) ı 164.19, 144.58, 133.03, 129.42,
1
3
3
3
2
.5. Antioxidant activity
1
28.01, 127.14, 119.36. 117.72, 69.24, 25.69; Analysis. Calcd for
C30H28N O Zn: C, 70.11; H, 5.49; N, 5.45. Found: C, 70.08; H, 5.44;
2
2
2
.5.1. Scavenger measurements of superoxide radical and
+
N, 5.39; MS (ESI) m/z = 514 [M] ; UV–vis ꢁmax: 276 (22,568), 322
5066), 392 (11,506) nm.
hydroxyl radical
(
The superoxide radicals were generated in the test system using
NBT/VitB /MET and determined spectrometrically by nitroblue
2
2
.3.8. (R)-Zn-L
tetrazolium photo reduction method [18,21,25]. The suppression
of superoxide radicals was calculated by measuring the absorbance
at 560 nm. The chiral metal complexes S-Ni-L/R-Ni-L/S-Cu-L/R-Cu-
L/S-Zn-L/R-Zn-L (5–25 ␮M) were added to a solution containing
Dark Yellow (78%): IR (KBr ꢂ cm−1): 3631, 3429, 3033, 2879,
360, 1621, 1492, 1451, 1378, 1276, 1079, 971, 913, 760, 694,
2
5
7
4
1
35, 444; H NMR (500 MHz, CDCl3, ı ppm): 8.42 (s, 1H, H–C N),
.38–6.84 (m, 18H, Aromatic), 4.62–4.58 (q, J = 6.6 Hz, 1H, CH),
.55–4.52 (q, J = 6.6 Hz, 1H, CH), 1.66–1.63 (d, J = 6.6 Hz, 3H, CH );
C NMR (500 MHz, CDCl ) ı 164.21, 144.59, 133.05, 129.44,
28.04, 127.16, 119.39. 117.73, 69.27, 25.70; Analysis. Calcd for
[
NBT (65 ␮M), L-MET (13 mM), VitB (1.5 ␮M), EDTA (0.1 mM)] and
2
3
the resulting solution was made up to 2 mL with phosphate buffer
(10 mM, pH 7.0) in dark. The above mixture was illuminated with a
white fluorescence lamp (15 W) for 15 min and the absorbance (Ai)
was measured at 560 nm. The above mixture containing no metal
complex was used as a control and its absorbance was taken as
A0. All the experiments were conducted in triplicate and data were
13
3
1
C30H28N O Zn: C, 70.11; H, 5.49; N, 5.45. Found: C, 70.02; H, 5.42;
2
2
+
N, 5.41; MS (ESI) m/z = 514 [M] ; UV–vis ꢁmax: 276 (22,736), 322
5104), 392 (10,370) nm.
(

2
02
N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
expressed as mean and standard deviation. The suppression ratio
was calculated by using following equation.
S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L were recorded in
aqueous DMSO (0.5%). The chiral Schiff base ligands showed charac-
teristic charge transfer (CT) bands at 255 nm and 326 nm, however,
in the complex formation the peaks were shifted to 275–277 nm
and 315–325 nm respectively. After coordination with metal ions
generate new broad ligand to metal charge transfer (LMCT) peak at
the position of 380–400 nm.
ꢀ
ꢁ
A − A
•
−
0
i
O2 scavenging activity (%) =
× 100
(1)
A
0
The hydroxyl radical scavenging study was carried out by
reported procedure [26] with minor modification. The formalde-
hyde formed during the oxidation of dimethyl sulphoxide by the
3
+
Fe –ascorbic acid was used to measure the concentration of gener-
3.2. Solubility and stability
ated hydroxyl radical [27]. A solution of 0.1 mM EDTA/167 mM Fe3
+
(
(
as a 1:2 mixture with EDTA)/33 mM DMSO in phosphate buffer
150 mM, pH 7.4) was mixed with the varying concentration of
The complexes were highly soluble in MeOH, EtOH, DMF, DMSO,
CH2Cl2 and DCM. The aqueous DMSO solution of these complexes
did not show any change in their UV–vis spectrum profile over a
period of 48 h at ambient temperature demonstrating the stabil-
ity of these complexes under ambient condition (data is given in
Supporting Information as Figs. S1–S3).
the chiral Schiff base metal complexes and the reaction was ini-
tiated by the addition of 2 mM ascorbic acid. The resulting mixture
◦
was incubated for 30 min at 37 C. After completion of the reaction,
25 ␮L trichloroacetic acid (17.5%, w/v) was added to quench the
1
reaction. The formaldehyde thus formed was assayed spectropho-
tometrically by the method of Nash [28]. All the experiments were
performed in triplicate with appropriate controls and the follow-
ing expression was used to calculate hydroxyl radical scavenging
activity.
3.3. DNA binding and antioxidant activity
3.3.1. Electronic absorption spectroscopy
The change in absorbance and shift in wavelength after the
addition of increasing concentration of DNA solution in a fixed
concentration of chiral metal complexes gave valuable informa-
tion on the mode of interaction [29]. Strong intercalative binding
of small molecule to DNA is known to cause much larger shifts
and hypochromism of the spectral bands [29–31]. The absorption
spectra of chiral Schiff base metal complexes S-Ni-L, R-Ni-L, S-Cu-
L, R-Cu-L, S-Zn-L and R-Zn-L with increasing concentration of DNA
showed hypochromism at LMCT position (Figs. 1–3). Interestingly,
hypochromism at LMCT position of complex S-Ni-L was associ-
ated with a major blue shift, while complex S-Cu-L displayed major
red shift suggesting their intercalative mode of binding (Table 1).
However, complexes R-Ni-L, R-Cu-L, S-Zn-L and R-Zn-L showed
minor hypochromism and minor shift at LMCT band, indicating
mainly groove binding or non-intercalative nature of these com-
plexes. Interestingly, in the presence of DNA, complexes S-Ni-L and
R-Ni-L showed hyperchromism at 324 nm while S-Zn-L and R-Zn-
L showed hyperchromism at 322 nm. The complexes S-Cu-L and
R-Cu-L showed hypochromism at the position of 315 nm. Among
all the complexes used in the present study the S-Ni-L complex
showed strongest interaction with DNA.
ꢀ
ꢁ
A − A
•OH scavenging activity (%) =
0
i
× 100
(2)
A
0
2.6. Antibacterial activity
The agar cup method was employed to determine the antimicro-
bial activities of Schiff base metal complexes against the three gram
(
+), three gram (−) and two fungal organisms. Broth micro dilu-
tion method was used to determine the MICs (minimum inhibitory
concentrations) for the complexes dissolved in DMSO against test
organisms. All the tests were performed in duplicate and modal
values were selected. Each microorganism was inoculated on to
the surface of Nutrient agar (N-agar). The wells (6 mm in diameter)
were cut from the agar and 0.1 mL solution of complex was deliv-
◦
ered in to them. After incubation for 24 h (48 h for fungi) at 37 C,
all the plates were examined for the zone of growth inhibition, and
diameters of these zones were measured in millimeter.
3
. Results and discussion
The absorbance at LMCT position of the complexes was used to
calculate the intrinsic binding constant using following functional
equation [32].
3
.1. Synthesis and general properties
The chiral Schiff base metal complexes S-Ni-L, R-Ni-L, S-Cu-L, R-
[
DNA]
[DNA]
1
Cu-L, S-Zn-L and R-Zn-L were prepared in high yields (∼70%) by the
=
+
(3)
(
εa − εf)
(ε − ε )
K (ε − ε )
b
f
b
b
f
reaction of the chiral Schiff base ligands (S)-H L/(R)-H L with Ni (II),
2
2
Cu (II) and Zn (II) acetates respectively (Scheme 1). The complexes
were characterized by various spectroscopic and analytical tech-
niques (data is given in experimental section). All the complexes
where [DNA] is the concentration of DNA in base pairs, εa, εf and
εb correspond to Aobs/[M], the extinction coefficient of the free chi-
ral Schiff base metal complex, and the extinction coefficient of the
chiral Schiff base metal complex in the fully bound form, respec-
tively. The Kb was obtained from the ratio of slope to intercept by
using the plot of [DNA]/(εa − εf) versus [DNA]. The binding constant
(Kb) of the chiral Schiff base metal complexes with DNA are given
in Table 1. The Kb values of the complexes S-Ni-L and S-Cu-L were
found to be in the range of classical intercalator ethidium bromide
(EB, Kb = 1.4 × 10 M ) [32] suggesting their intercalative binding
while the lower Kb values showed by rest of the complexes (R-Ni-
L, R-Cu-L, S-Zn-L, R-Zn-L) evident their groove or external binding
nature. Among all the complexes studied, the S-enantiomers had
better binding efficiency than their R counter parts.
+
displayed the molecular ion peak corresponding to [M] in their
ESI–MS spectra. IR spectra of the ligands showed two characteris-
−1
tic peak near 1626 and 3300 cm assigned to ꢀ (H–C N) and ꢀ
OH) respectively. After coordination with metal ions, the charac-
(
teristic ꢀ (H–C N) peak shifted to lower wave number while the
intensity of phenolic OH peak diminished significantly, confirming
1
6
−1
its involvement in complex formation. The H NMR spectrum of the
chiral Schiff base ligand, showed singlet at ı 13.57 for its OH pro-
ton and azomethine proton was appeared as a singlet at ı 8.41 ppm.
The CH proton was appeared as quartet at ı 4.60 (q, J = 6.8 Hz) and
4
1
.54 (J = 6.6 Hz) and CH3 protons were appeared as doublet at ı
.65 (J = 6.6 Hz). After coordination with metal ions, the character-
istic ꢀ (H–C N) peak in IR was shifted to lower wave number and
phenolic OH peak decreased significantly confirming the coordina-
tion through azomethine nitrogen and phenolic oxygen atoms. The
UV–vis spectra of chiral Schiff base ligands and chiral complexes
3.3.2. Determination of thermodynamic parameters
The thermodynamic parameters were further used to under-
stand the nature of binding forces between the chiral Schiff base
◦
metal complexes with DNA. Standard entropy changes (ꢄS ) and

N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
203
Fig. 1. Absorption spectra of chiral Ni (II) Schiff base complexes (50 ␮M) (A) S-Ni-L (B) R-Ni-L in phosphate buffer (10 mM, pH 7.0) in the presence of increasing concentration
of DNA (0–55 ␮M). Inset plot is [DNA]/(εa – εf) vs. DNA.
Fig. 2. Absorption spectra of chiral Cu (II) Schiff base complexes (50 ␮M) (A) S-Cu-L (B) R-Cu-L in phosphate buffer (10 mM, pH 7.0) in the presence of increasing concentration
of DNA (0–55 ␮M). Inset plot is [DNA]/(εa – εf) vs. DNA.
Fig. 3. Absorption spectra of chiral Zn (II) Schiff base complexes (50 ␮M) (A) S-Zn-L (B) R-Zn-L in phosphate buffer (10 mM, pH 7.0) in the presence of increasing concentration
of DNA (0–55 ␮M). Inset plot is [DNA]/(εa – εf) vs. DNA.

2
04
N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
Table 1
Binding constant of S and R enantiomers of chiral Schiff base metal complexes.
Kb × M−
1
Entry
Complexes
ꢁmax
ꢁmax (DNA + complexes)
ꢄꢁ (nm)
6
5
1
2
3
4
5
6
S-Ni-L
R-Ni-L
S-Cu-L
R-Cu-L
S-Zn-L
R-Zn-L
276, 324, 393
276, 324, 393
277, 315, 386
277, 315, 386
276, 322, 392
276, 322, 392
277, 326, 385
276, 324, 390
278, 316, 392
277, 315, 389
276, 324, 389
276, 322, 389
1, 2, 8
0, 0, 3
1, 1, 6
0, 0, 3
0, 2, 4
0, 0, 3
4.5 (± 0.9) × 10
5.1 (± 0.9) × 10
6
1.06(± 0.4) × 10
5
2.3 (± 0.5) × 10
5
6.5 (± 0.8) × 10
5
2.0(± 0.5) × 10
(S)-Ni-L
(R)-Ni-L
(S)-Cu-L
(R)-Cu-L
(S)-Zn-L
(R)-Zn-L
Ni-L and (R)-Ni-L are given in supporting information in Section 1.
Similar calculations were followed for other complexes as well.
16
15
14
13
12
y = -0.0469x + 31.038
2
R
= 0.9737
◦
◦
ꢄH
RT
ꢄS
R
y = -0.0272x + 22.986
2
ln K = −
+
(5)
b
R
= 0.9973
y = -0.0164x + 18.879
2
◦
R
= 0.9944
The data in Table 2, S1 and S2 showed negative value of ꢄG and
◦
◦
y = -0.0181x + 19.213
2
positive value of ꢄS and ꢄH for S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-
Zn-L, and R-Zn-L complexes indicated that the reaction process is
spontaneous and the binding is mainly entropy driven. Therefore,
it is inferred that the hydrophobic interaction plays a major role in
the binding of Schiff base complexes with DNA [34].
R
= 0.9879
y = -0.0243x + 20.508
2
R
= 0.9749
323
328
1
333
/T x 10-5
y = -0.0109x + 15.856
2
R
= 0.9973
Fig. 4. The Van’t Hoff plot for the interaction of chiral Schiff base metal complexes
with DNA.
3.3.3. Fluorescence quenching studies
The EB displacement assay usually used to determine
Stern–Volmer constant of the complexes to bind with DNA partic-
ularly when the complexes failed to show any luminescence upon
excitation of CT and LMCT band. In the present study, the solu-
tions of chiral Schiff base complexes S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L,
S-Zn-L and R-Zn-L in different solvents did not show any lumines-
cence irrespective of the presence and absence of DNA. Therefore,
EB which is known to emit intense fluorescence in the presence
of DNA due to the strong intercalation of EB between the base
pairs of DNA was used as a spectral probe [30]. The intense fluo-
rescence obtained by the interaction of EB and DNA got diminished
by the addition of chiral Schiff base complexes (Fig. 5) suggest-
ing their competitive binding [35]. Also the addition of increasing
concentration of the chiral Schiff base metal complexes to EB solu-
tion in the absence of DNA result in no change in the emission
intensity of EB, thus evident for no interaction between the metal
complex and EB. The complexes S-Ni-L and R-Ni-L were found
to have stronger binding capacity at 0–25 ␮M concentration than
other complexes which required relatively higher concentrations
(0–220 ␮M, Figs. S4 and S5) to get comparable decrease in emission
intensity.
◦
standard enthalpy changes (ꢄH ) between complex and DNA are
interpreted in three ways: (i) ꢄH and ꢄS > 0 (endothermic) indi-
cates that the interaction is originated from hydrophobic forces,
ii) ꢄH and ꢄS < 0 (exothermic) is interpreted in term of van
der Waals interactions and hydrogen bond being major source of
DNA interaction, and (iii) if ꢄH < 0 and ꢄS > 0, the electrostatic
forces are dominant factor for the interaction between complex
with DNA [33]. The temperature dependent binding constant was
measured and following relation was used to calculate Gibbs free
energy.
(
◦
ꢄG = −RT ln Kb
(4)
In the above equation R, T and K are the gas constant, temper-
b
ature and binding constant respectively. The binding enthalpy of
chiral Schiff base metal complexes was calculated by using slope of
the Van’t Hoff equation and binding entropy was calculated from
the intercept of linear Van’t Hoff equation as given below. The graph
is given in Fig. 4. The detail calculations for DNA binding with (S)-
6
5
4
3
2
1
000000
000000
000000
000000
000000
000000
0
6
5
4
3
2
1
000000
000000
000000
000000
000000
000000
0
(B)
(
A)
5
00
600
700
800
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 5. The emission spectra of DNA bound EB in the presence of (A) S-Ni-L (B) R-Ni-L in phosphate buffer (10 mM, pH 7.0) in the presence of increasing concentration of
complexes (0–25 ␮M). DNA = 100 ␮M.

N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
205
Table 2
a
Thermodynamic parameters and binding constant of chiral Schiff base complexes S-Ni-L and R-Ni-L to DNA in phosphate buffer (10 mM, pH 7.0).
◦
−1
◦
−1
◦
−1
T (K)
Kb
ꢄG (kJ mol
)
ꢄH (kJ mol
)
ꢄS (J mol K
)
6
298
303
308
4.5 × 10
5
5
−1
−1
(
5.18 × 10 ) M
−37.95 (−32.60)
−39.36 (−33.42)
−40.539 (−34.19)
38.99 (15.04)
257.99 (159.74)
6
6.1 × 10
(
5.78 × 10 ) M
6
7.5 × 10
5
−1
(
6.3 × 10 ) M
a
Results in parenthesis are for R-Ni-L enantiomer.
Based on Figs. 5, S4 and S5 the Stern–Volmer constant were
calculated by using following functional equation [3].
the complexes S-Cu-L and R-Cu-L showed hypochromism and a
blue shift of 7 nm and 5 nm respectively at 328 nm. On the other
hand, addition of DNA to the complexes S-Zn-L and R-Zn-L caused
hyperchromism and a red shift of 3 nm at 310 nm in both the cases.
The above CD spectral changes clearly demonstrate the different
matching of enantiomers of the complexes with DNA.
I0
=
1 + K · r
(6)
I
In the above equation I and I are the emission intensities in the
0
absence and presence of chiral Schiff base metal complexes and r
is the ratio of the total concentration of chiral metal complexes to
DNA and K is given by the ratio of slope to the intercept (data is
given in Table 3).
The Stern–Volmer constant value for S-Ni-L was higher than
rest of the complexes. Moreover, S-enantiomers showed stronger
binding with DNA than their R-counterparts in all the complexes,
suggesting that the DNA which is essentially chiral in nature indeed
show stereochemical preference for binding with external chiral
molecules. These results are in consonance with the electronic
absorption titration studies given earlier in the section.
3
.3.5. Viscosity study
Viscosity measurement studies on interaction of chiral Schiff
base complexes with DNA were carried out to further strengthen
the findings on chiral discrimination as obtained in earlier sections.
In the absence of crystallographic structural data, hydrodynamic
measurement is considered as least ambiguous and the most crit-
ical test to find binding mode of DNA with metal complexes. The
sensitivity of this method is largely depend on the changes in the
length of DNA that occur as result of its different binding modes
with guest molecules [18,29].
A classical intercalator such as EB shows a significant increase
in the relative viscosity of the DNA solution on intercalation due to
the increase in the overall length of DNA and therefore results in an
increase in DNA viscosity. In contrast, the groove binding and par-
tial interacting molecules cause minor or no effect on the relative
3
.3.4. Circular dichorism spectroscopy
The CD spectra have been utilized as a powerful tool for
exploring the chiral aspect of compounds and to provide valuable
information on the mode of binding between the DNA helix and
chiral complexes [17,18,36]. The CD spectra of complexes S-Ni-L,
R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L in DMSO are shown in
Fig. 6, Figs. S6 and S7.
The CD spectra of free S-Ni-L, S-Cu-L, S-Zn-L and their respec-
tive enantiomers R-Ni-L, R-Cu-L, R-Zn-L showed LMCT bands with
opposite configuration at ∼373 nm. The interaction of complexes
with DNA in LMCT region showed decrease in spectral strength
by 64%, 59% and 50% for S-Ni-L, S-Cu-L and S-Zn-L while 25%, 30%
and 21% for R-Ni-L, R-Cu-L and R-Zn-L respectively. The addition
of DNA to the complexes S-Ni-L and R-Ni-L resulted with emer-
gence of a new peak at 305 nm, which showed a red shift of 8 nm
and 4 nm respectively on increasing DNA concentration. However,
1/3
viscosity on DNA [30]. The plots of relative viscosity (ꢃ/ꢃ0) versus
[
complex]/DNA] ratio (Fig. 7) illustrated a significant increase in
the relative viscosity of DNA in the presence of complexes S-Ni-
L and S-Cu-L suggesting their intercalative mode of binding. On
the other hand, marginal changes in relative viscosity of DNA with
the complexes S-Zn-L, R-Ni-L, R-Cu-L, and R-Zn-L indicates their
groove or external binding nature. In a nutshell, binding affinity
of the chiral Schiff base complexes with DNA, follows the order of
S-Ni-L > S-Cu-L > S-Zn-L > R-Ni-L > R-Cu-L > R-Zn-L.
3.3.6. Thermal denaturation study
The thermal behaviors of DNA in the presence of metal com-
plexes can provide better insight for conformational changes, DNA
duplex stability and interaction strength between complexes and
DNA. The duplex DNA at its melting temperature unwinds to give
single strand DNA and shows an increase in absorbance at 260 nm.
8
6
4
(
S)-Ni-L
(
S)-Ni-L (R)-Ni-L (S)-Cu-L (R)-Cu-L (S)-Zn-L (R)-ZN-L
2
0
2
2
1
.6
.2
.8
-
2
4
6
8
(
R)-Ni-L
-
-
-
1.4
1
300
350
400
450
0
0.2
0.4
0.6
0.8
1
1.2
Wavelength (nm)
Complex/DNA
Fig. 6. CD spectra of chiral Schiff base S-Ni-L and R-Ni-L complexes in the presence
of increasing concentration of DNA. Complex concentration = 50 ␮M.
Fig. 7. The relative viscosity of DNA (50 ␮M) in the presence of S and R enantiomers
of chiral Schiff base metal complexes (0–60 ␮M).

2
06
N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
Table 3
Stern–Volmer constant of S and R enantiomers of chiral Schiff base complexes to DNA.
Complexes
ꢁmax (DNA + EB)
ꢁmax (DNA + EB + complexes)
ꢄꢁ (nm)
K
S-Ni-L
R-Ni-L
S-Cu-L
R-Cu-L
S-Zn-L
R-Zn-L
603
603
603
603
612
612
613
607
626
617
625
621
10
4
23
14
13
9
2.49 ± 0.12
1.69 ± 0.13
1.18 ± 0.10
0.33 ± 0.012
0.56 ± 0.010
0.37 ± 0.013
A classical intercalator such as EB stabilizes the duplex DNA caus-
ing the DNA to melt at higher temperature [37,38]. The melting
curves of DNA in the presence and absence of the chiral Schiff base
complexes are shown in Fig. 8.
5 uM
10 uM
15 uM
20 uM
25 uM
1
00
80
60
◦
◦
The Tm of DNA was found to be 70 C, which increased to 80 C
◦
and 75 C in the presence of S-Ni-L and S-Cu-L respectively, sug-
gesting their intercalative mode of binding. However, complexes
S-Zn-L and R-Ni-L had little effect on the Tm value of DNA due to
poor interaction among them. Ironically, interaction of R-Cu-L and
4
2
0
0
◦
R-Zn-L with DNA showed a decrease in Tm value (65 C) for reasons
unknown as of now (Fig. 8).
0
(S)-Ni-L
(R)-Ni-L (S)-Cu-L (R)-Cu-L (S)-Zn-L (R)-Zn-L
Complexes
3.3.7. Antioxidant activity
Schiff base metal complexes per se are known to show various
biological activities including biocidal and antioxidant activities
39], however chiral aspect of these complexes vis-à-vis bioactiv-
Fig. 9. Scavenging effect of the chiral Schiff base complexes on superoxide radical
by MET/VitB2/NBT system.
[
ity has not been well explored. In view of this and significant DNA
binding affinity shown by the Schiff base complexes used in the
present study, it was considered sensible to study other potential
aspects of these compounds such as antioxidant and antibacterial
activity [40].
The chiral Schiff base metal complexes at the same concentra-
tion (5–25 ␮M) were also screened for the OH radical scavenging
•
activity (Fig. 10). It is evident from the results that S-Cu-L and S-Zn-
L are better scavenging agents (82% and 89%) than R-Cu-L, R-Zn-L,
S-Ni-L and R-Ni-L, which showed 51, 54, 73 and 45% scavenging
activities respectively at a concentration of 25 ␮M. Here again, S-
enantiomers of the complexes were found to be more effective than
R-enantiomers. It indicates that transition-metal ions like Ni (II), Cu
•
−
Reactive oxygen species (ROS) e.g. superoxide (O2 ) and
•
hydroxyl ( OH) radical are responsible for the disintegration of
cell membrane and damage to protein and DNA structures. Several
non-chiral metal complexes have been reported earlier to show
anti-ROS activity [21,25,40–43]. Since the chiral metal complexes
studied in the present work showed strong chirality dependent
DNA binding, we hypothesized similar manifestation of these com-
(
II) and Zn (II) may have chirality driven differential and selective
•−
•
nature for scavenging O2 and OH radical. This trend can be corre-
lated with the fact that S enantiomers of the complexes have shown
stronger DNA binding ability than their R enantiomers.
•
−
•
plexes on the scavenging of O2 and OH radical activity.
As shown in Fig. 9, increasing concentration (5–25 ␮M) of all
the complexes showed increasing inhibitory activities against ROS.
Among the studied complexes S-Cu-L and S-Zn-L showed highest
superoxide scavenging ability of 98% and 99% respectively, in con-
trast to 64% and 70% inhibition obtained for their R counterparts at
a concentration of 25 ␮M. Nickel complexes S-Ni-L and R-Ni-L also
showed considerably high scavenging activity 78% and 56% respec-
tively. As hypothesized, all the S-enantiomers of the complexes
3
.4. Antibacterial activity
The current issue on drug-resistance pathogens often referred as
“super bugs” has led greater demand for the discovery of new chem-
ical scaffolds with antimicrobial activity. Several metal complexes
have already shown their worth as antibacterial agents [21,44,45]
however, the role of chirality in this aspect is less explored [12].
Therefore, we evaluated the antibacterial activity of the chiral Schiff
base complexes using agar cup method with three gram (+), three
gram (−) and two fungal pathogens as representative microbes
•
−
scavenging activity than their respective R-
showed higher O2
enantiomers.
5
uM
10 uM
15 uM
20 uM
25 uM
DNA (S)-Ni-L (R)-Ni-L (S)-Cu-L (R)-Cu-L (S)-Zn-L (R)-Zn-L
1
00
0.88
8
0
0
0
0
0
.8
0
0
0
0
.72
.64
.56
.48
6
4
2
0.4
25
35
45
55
65
75
85
95
105
0
0
(
S)-Ni-L
(R )-Ni-L
(S)-Cu-L
(R)-Cu-L
(S)-Zn-L
(R)-Zn-L
Temp C
Complexes
Fig. 8. Thermal denaturation graph of DNA (0.4 mM) in the presence of S and R
enantiomers of chiral Schiff base metal complexes (20 ␮M).
Fig. 10. Scavenging effect of chiral Schiff base metal complexes on hydroxyl radical.

N.-u.H. Khan et al. / Spectrochimica Acta Part A 81 (2011) 199–208
207
Table 4
Data for antimicrobial activity using chiral Schiff base complexes.
Compound
B. subtilis
B. cereus
S. aureus
E. coli
S. typhi
P. aeruginosa
C. albicans
WDa
MICb
WD
MIC
WD
MIC
WD
MIC
WD
MIC
WD
MIC
WD
MIC
Controld
NAc
20
NA
NA
24
21
20
18
23
19
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
21
NA
NA
23
21
21
19
22
18
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
20
NA
NA
31
29
16
18
29
25
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
19
NA
NA
20
17
18
16
19
16
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
19
NA
NA
21
16
18.
16
18
15
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
20
NA
NA
19
16
17
15
18
16
–
12.5
–
–
12.5
25
12.5
25
12.5
25
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
–
–
–
–
–
–
–
–
–
–
Standarde
(
(
(
(
(
(
(
(
S)-H2L
R)-H2L
S)-Ni–L
R)-Ni–L
S)-Cu–L
R)-Cu–L
S)-Zn–L
R)-Zn–L
a
b
c
Diameter of zone of inhibition (mm) including well diameter (6 mm) 200 ␮g of both compound and antibiotics were used.
Minimum inhibitory concentration values given as ␮g/ml for both compound and antibiotics.
Not active.
Control DMSO.
d
e
Standard streptomycin.
(
Table 4). It is evident from Table 4 that all the complexes exhib-
[3] S.K. Teo, W.A. Colburn, W.G. Tracewell, K.A. Kook, D.I. Stirling, M.S. Jaworsky,
M.A. Scheffler, S.D. Thomas, O.L. Laskin, Clin. Pharmacokinet. 43 (2004)
ited considerable higher activity against gram (+) and gram (−)
bacteria which was as good as the activity found for standard
antibiotic—streptomycin. Significantly, the S enantiomers of the
metal complexes showed higher antibacterial activity than their
R counterparts. Ironically, none of these complexes showed any
activity against fungi. The order of antibacterial activity was found
to be S-Ni-L > S-Zn-L > R-Ni-L > S-Cu-2 > R-Zn-L > R-Cu-L which also
demonstrate the enantiomeric effect.
311–327.
[
4] B. Lippert, Cisplatin: Chemistry and Biochemistry of a Leading Anticancer Drug,
Verlag Helvetica Chimica Acta, Postfach, CH-8042 Zürich, Switzerland, 1999,
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[
5] M. Chauhan, F. Arjmand, Chem. Biodivers. 3 (2006) 660–676.
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[
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4
. Conclusion
[
10] C.-W. Jiang, J. Inorg. Biochem. 98 (2004) 497–501.
Chiral Schiff base complexes of Ni, Cu and Zn were synthe-
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A 66 (2007) 163–170.
sized in their enantiomerically pure form and were evaluated for
their DNA binding ability, antioxidant and antibacterial activity.
Various spectrometric methods concluded that the complex S-
Ni-L has higher DNA binding ability than other chiral Schiff base
metal complexes used in the present study. Interestingly, the S-
Ni-L and S-Cu-L complexes bind with DNA through intercalation
while R-Ni-L, R-Cu-L, S-Zn-L and R-Zn-L interact with DNA through
groove or external binding. Discernible differences were observed
in the interaction of the different enantiomers with DNA. The
S enantiomers of the complexes showed stronger DNA binding
ability than the R enantiomers. Additionally, chiral Schiff base com-
[
12] N.H. Khan, N. Pandya, R.I. Kureshy, S.H.R. Abdi, S. Agrawal, H.C. Bajaj, J. Pandya,
A. Gupte, Spectrochim. Acta Part A 74 (2009) 113–119.
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2005) 17327–17332.
(
[
14] P.U. Maheswari, V. Rajendiran, M. Palaniandavar, R. Parthasarathi, V. Subrama-
nian, J. Inorg. Biochem. 100 (2006) 3–17.
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Chem. 45 (2006) 37–50.
[
[
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