Impact of metallonucleases on DNA interactions: Structural validation and in-vitro antibiogram assay

Article abstract of DOI:10.1016/j.inoche.2014.05.003

Four novel complexes were synthesized using 2-aminobenzophenone Schiff base precursor and characterized by various analytical techniques. FT-IR results demonstrate that the Schiff base ligand, obtained by the condensation of 2-aminobenzophenone with 2-hyd

Full text of DOI:10.1016/j.inoche.2014.05.003

Impact of metallonucleases on DNA interactions: Structural validation and
in-vitro anti biogram assay
Vellaichamy Muniyandi, Narayanaperumal Pravin, Natarajan Raman
PII:
DOI:
Reference:
S1387-7003(14)00211-1
doi: 10.1016/j.inoche.2014.05.003
INOCHE 5579
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Inorganic Chemistry Communications
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Accepted date:
12 March 2014
29 April 2014
6 May 2014
Please cite this article as: Vellaichamy Muniyandi, Narayanaperumal Pravin, Natara-
jan Raman, Impact of metallonucleases on DNA interactions: Structural valida-
tion and in-vitro anti biogram assay, Inorganic Chemistry Communications (2014), doi:
10.1016/j.inoche.2014.05.003
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ACCEPTED MANUSCRIPT
Impact of metallonucleases on DNA interactions: Structural validation and in-vitro anti
biogram assay
Vellaichamy Muniyandi, Narayanaperumal Pravin, Natarajan Raman*
Research Department of Chemistry, VHNSN College, Virudhunagar-626 001, Tamil Nadu, India,
E-mail: ramchem1964@gmail.com Tel: +091-92451-65958
List of Abbreviations Used
DNA = Deoxyribonucleic acid
CT DNA = Calf thymus deoxyribonucleic acid
Tris-HCl = Tris(hydroxymethyl)aminomethane hydrochloride
L = Ligand
M = Metal
DMF = Dimethylformamide
DMSO= Dimethylsulfoxide
SAIF = Sophisticated Analytical Instrument facility
IIT = Indian Institute of Technology
CDRI = Central Drug Research Institute
pBR322 DNA = plasmid Bolivar and Rodriguez 322 deoxyribonucleic acid
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Impact of metallonucleases on DNA interactions: Structural validation and in-vitro anti
biogram assay
Vellaichamy Muniyandi, Narayanaperumal Pravin, Natarajan Raman*
Research Department of Chemistry, VHNSN College, Virudhunagar-626 001, Tamil Nadu, India,
E-mail: ramchem1964@gmail.com Tel: +091-92451-65958
___________________________________________________________________________________________
ABSTRACT
_____________________________________________________________________________
Four novel complexes were synthesized using 2-aminobenzophenone Schiff base
precursor and characterized by various analytical techniques. FT-IR results demonstrate that the
Schiff base ligand, obtained by the condensation of 2-aminobenzophenone with
2-hydroxybenzaldehyde, coordinates to the metal ion via azomethine nitrogen, phenolic oxygen
and carbonyl groups. Furthermore, the intercalative mode of these octahedral complexes with
calf thymus (CT) DNA has been explored using absorption spectra, cyclic votammetric and
viscosity measurements. Gel electrophoresis assay demonstrates the effective cleaving aptitude
of pBR322 DNA by complexes in the presence of an activating agent (H2O2). Moreover, the
in-vitro biological activities of metal complexes have been screened against few pathogenic
bacterial and fungal strains by well diffusion technique. It is found that all the complexes show
potential activities as compared to the free ligand. These findings may lead to develop novel
DNA targeting metallonucleases.
______________________________________________________________________________
Keywords: Intercalative mode; calf thymus DNA; gel electrophoresis; antimicrobial studies
______________________________________________________________________________
*Corresponding author: E-mail: ramchem1964@gmail.com (N.Raman)
Tel.: +091-092451-65958; Fax: +091-4562-281338
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In recent years, research into the reactivity and interactions between transition metal
complexes and biomolecules such as DNA and proteins has resulted in significant advances in
the understanding of biochemical processes and the development of therapeutic drugs [1].
Consequently, studies pertaining to the interaction of DNA-complexes are gaining considerable
importance owing to the fact that they provide reliable information through changes which occur
on DNA by various modes of binding viz., non-covalent interaction by intercalation, groove face
binding, external electrostatic binding and covalent interaction with an outer sphere or inner
sphere binding and consecutive strand breakage [2]. The binding of metal ions or metal
complexes causes DNA damage [3,4], with single or double-strand cleavage by different types of
nuclease mechanism, including photoinduced, oxidative or hydrolytic cleavage [5,6]. Due to the
remarkable DNA binding and cleavage properties of the metal complexes, they are suitable
candidates for DNA foot printing agents, photocleavers and antitumor drugs [7-9].
Over the years, Schiff base complexes, particularly Cu(II), Ni(II), Co(II) and Zn(II)
complexes, have got great attention since they act as bio mimetic enzyme models, fluorescent
indicators, oxygen carriers, antimicrobial agents, anticancer properties etc [10-15]. On the other
hand, benzophenone analogues exhibit variable coordinating behavior towards metal ions. In
particular, it has been observed that the introduction of another potential binding site such as an
amino group, modifies both roles of benzophenone as sensitizer [16] and its coordinating ability
[17], suggesting a correlation between these properties. Moreover, benzophenone derivatives are
intermediates in several syntheses of pharmaceuticals [18] and are also very interesting from a
coordinative point of view since they contain both a hetero-atom and a π-donor system. They
may act as either n or π donors depending on the particular metal centre with which they interact
[19, 20]. These facts prompt us to design novel transition metal complexes having DNA binding
and cleavage properties using 2-aminobenzophenone derived Schiff base. Hence, in the present
work, we report the synthesis and characterization of tridentate Schiff base derived from the
mono-condensation of 2-aminobenzophenone with 2-hydroxybenzaldehyde and its transition
metal(II) complexes and evaluation of their role of actions on DNA. Furthermore, the in-vitro
antimicrobial screening has also been carried out. The information obtained from our study
would be helpful in understanding the mechanism of interaction of the complexes with nucleic
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acid and might also be useful in the development of potential probes of DNA structure and
conformation and new therapeutic reagents for some uncommon diseases.
The Schiff base ligand and its Cu(II), Ni(II), Co(II) and Zn(II) complexes were prepared
by a typical procedure [21–27]. The materials and methods for the prepared compounds and their
characterization are depicted as S1 and S2 (Supplementary files). The synthesized compounds
are found to be stable in air at room temperature. The ligand is soluble in common organic
solvents but the complexes are soluble only in DMF and DMSO. The proposed reaction of the
Schiff base and its complexes is illustrated in Scheme 1. The probable composition of complexes
is found to be [ML2] (where M = Cu(II), Ni(II), Co(II) and Zn(II); L = (E)-(2-((2-
hydroxybenzylidene)amino)phenyl)(phenyl)methanone). This stoichiometry is further confirmed
by elemental analysis (Table S1), magnetic susceptibility, NMR, UV–vis, IR, EPR spectra and
molar conductivity measurements.
(Kindly insert Scheme1 here)
The electronic absorption spectroscopy is universally employed to determine the binding
characteristics of metal complexes with DNA [28–30]. The absorption spectrum of Cu(II)
complex in the absence and presence of CT DNA is given in Fig. 1. In the UV region the intense
absorption band with maxima of 326 nm for Cu(II), 326 nm for Ni(II), 329 nm for Co(II) and
334 nm for Zn(II) complexes, is attributed to intra-ligand π–π* transition with the hypochromism
of 15.3 %, 19.3 %, 20.2 % and 31.0 %. These changes are typical of a complex bound to DNA
through intercalation involving insertion of the aromatic chromophore of the azomethine ligand
in between the base pairs of DNA. After intercalating the base pairs of DNA, the π* orbital of the
intercalated ligand could couple with the π orbital of base pairs, thus decreasing the π–π*
transition energy and further resulting in the slight red shift. On the other hand, the coupling of π
orbital is partially filled by electrons, thus decreasing the transition probabilities and
concomitantly resulting in hypochromism.
(Kindly insert Fig. 1 here)
The determined intrinsic binding constants for [CuL2], [NiL2], [CoL2] and [ZnL2] are
1.47 × 105 M−1, 1.33 × 105 M−1, 1.42 × 105 M−1 and 0.71 × 105 M−1 respectively. These values
(Table 1) are comparable to the classical DNA intercalators EB (ethidium bromide, 1.4 × 106
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M−1) [31] and many analogues, such as [Ru(phen)2(phehat)]2+ (2.5 × 106 M−1) and
Ru(bpy)2(ppd)]2+ (1.1 × 106 M−1) [32]. The results suggest that the interaction of the above four
metal complexes with DNA is an intercalative mode.
(Kindly insert Table 1 here)
Optical photophysical probes provide necessary but not ample evidence to support a
binding model. Hydrodynamic measurements that are sensitive to length change (i.e. viscosity
and sedimentation) are regarded as the least ambiguous and the most critical tests of a binding
model in solution in the absence of crystallographic structural data [33]. A classical intercalation
model results in the lengthening of the DNA helix as the base pairs are separated to
accommodate the binding molecule leading to an increase in the DNA viscosity. However, a
partial and/or non-classical intercalation of ligand may bend (or kink) DNA helix, resulting in
the decrease of its effective length and concomitantly its viscosity [34]. The effects of all the
compounds and together with ethidium bromide [EB] on the viscosity of CT DNA are shown in
Fig. 2. On increasing the amount of metal complexes, the relative viscosity of DNA moderately
increased steadily, which is similar to the behavior of ethidium bromide. The results suggest that
all the metal complexes bind DNA with intercalative mode. The viscosity measurements clearly
show that all the compounds can intercalate between adjacent DNA base pairs, causing an
extension in the DNA helix and thus increasing the viscosity of DNA with an increasing
concentration of the complexes. On the basis of all the spectroscopic studies together with the
viscosity measurements, we find that the metal complexes can bind to CT DNA via an
intercalative mode.
(Kindly insert Fig. 2 here)
The application of electrochemical methods to the study of organic and
metallointeraction to DNA provides a useful complement to the previously used methods of
investigation, such as UV–visible spectroscopy and viscosity studies [35]. Small molecules,
which are not amenable to such methods either because of weak absorption bands or because of
overlap of electronic transition with those of the DNA molecules, can potentially be studied via
voltammetric techniques. Cyclic voltammogram of Cu(II) complex in the absence and presence
of CT DNA is shown in Fig. 3. As seen in this figure, in the absence of CT DNA the cyclic
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voltammogram featured three anodic peaks Epa (0.421, -0.267 and -0.581 V) and three cathodic
peaks Epc (0.051, -0.216 and -1.049 V) at 0.1 V s-1. The first reduction and oxidation potential
observed at Epc = 0.051 V and Epa = 0.421 V is assigned to the redox couple Cu(III)/Cu(II). The
second reduction and oxidation potential observed at Epc = -0.216 V and Epa = -0.267 V can be
attributed to the redox couple Cu(II)/Cu(I). The third reduction and oxidation potential observed
at Epc = -1.049 V and Epa = -0.581 V can be attributed to the redox couple Cu(I)/Cu(0). The
ratios of ipa /ipc peak currents are 0.24, 0.63 and 0.77 respectively, indicating a quasi-reversible
redox process.
(Kindly insert Fig.3 here)
For the cyclic voltammogram of Ni(II) complex in the absence of DNA, the first redox
couple cathodic peak appeared at −1.032 V for Ni(II) → Ni(I), (Epa = -0.441 V, Epc = -1.032 V,
∆Ep = -0.591 V, and E1/2 = -0.736 V). The ratios of ipa /ipc peak currents are 1.96 respectively,
indicating a quasi-reversible redox process. The cyclic voltammogram of Co(II) complex
featured two anodic peaks Epa (-0.209 and -0.848 V) and two cathodic peaks Epc (-0.320 and
-1.007 V) at 0.1 V s-1. The first reduction and oxidation potential observed at Epc = -0.320 V and
Epa = -0.209 V is assigned to the redox couple Co(II)/Co(I). The second reduction and oxidation
potential observed at Epc = -1.007 V and Epa = -0.848 V can be attributed to the redox couple
Co(I)/Co(0). The ratios of ipa /ipc peak currents are 0.13 and 0.86 respectively, indicating a
quasi-reversible redox process. In Zn(II) complex, in the absence of DNA the cathodic peak was
appeared at −0.992 V for Zn(II) → Zn(0), (Epa = -0.467 V, Epc = −0.992 V, ∆Ep = -0.525 V,
and E1/2 = -0.729 V). The ratio of ipa /ipc peak current is approximately equal to unity (1.73),
indicating a quasi-reversible redox process (Table 2). The incremental addition of CT DNA to
the complexes revealed that the redox couples caused a more positive shift in E1/2 and decrease of
ΔEp. The ipa/ipc values also decreased in the presence of DNA. Bard has reported [36] that if E1/2
is shifted to more positive value, the interaction mode is intercalative binding. The above results
of metal-DNA interaction by the cyclic voltammogram studies confirm that Cu(II), Ni(II), Co(II)
and Zn(II) complexes bind to DNA via intercalation binding mode.
(Kindly insert Table 2 here)
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Differential pulse voltammogram of the Cu(II) complex in the absence and presence of
varying concentration of DNA is shown in Fig. 4. Increase in concentration of DNA causes a
negative potential shift along with significant decrease of current intensity. The shift in potential
is related to the ratio of binding constant:
E0 - E0 = 0.0591 log (K+/K2+)
b
f
where E0 - E0 are formal potentials of the Cu(II), Ni(II), Co(II) and Zn(II) complex couples in
b
f
the bound and free form respectively. In the present study, all the complexes exhibited one
electron transfer during the redox process. The ratio of the binding constants (K[red]/K[oxd]) for
DNA binding of synthesized complexes was calculated and found to approximately equal to
unity. The above electrochemical experimental results indicate the preferential stabilization of
Cu(II), Ni(II), Co(II) and Zn(II) forms over other forms on binding to DNA. In this study, the
synthesized complexes reveal that both anodic and cathodic peak potential shifts are either
positive or negative. In this regard, the present Cu(II) complex shows a positive potential shift
along with significant decreasing of current intensity during the addition of increasing amount of
DNA. It indicates that copper ion stabilizes the duplex (GC pairs) by intercalating way.
(Kindly insert Fig. 4 here)
Gel electrophoresis is an extensively used technique for the study of compounds with
nucleic acids. In this method, isolation of the molecules is on the basis of their relative rate of
movement through a gel under the influence of an electric field. DNA is negatively charged and
when it is placed in an electric field, it migrates towards the anode. The extent of migration of
DNA is decided by the strength of electric field, buffer and density of agarose gel and size of the
DNA. Natural-derived plasmid DNA mainly has a closed-circle supercoiled form (Form I)
as well as nicked form (Form II) and linear form (Form III) as small fractions. Intercalation of
small molecules to plasmid DNA can loosen or cleave the supercoiled form DNA which
decreases its mobility rate and can be separately visualized by agarose gel electrophoresis
method whereas simple electrostatic interaction of small molecules to DNA does not
significantly influence the supercoiled form of plasmid DNA, thus the mobility of supercoiled
DNA is not changed.
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To appraise the DNA cleavage ability of our synthesized metal(II) complexes,
supercoiled (SC) pBR322 DNA was incubated with the complexes in 5 mM Tris–HCl/50 mM
NaCl buffer at pH 7.2 for 2 h. The cleavage experiments were carried out in the presence of
activating agent, H2O2 under aerobic conditions and are shown in Fig. 5. The intensity of
supercoiled SC (Form I) diminished gradually and completely converted to nicked form (NC)
(Form II). The intensity of the NC (Form II) band increased whereas the production of linear
form L (Form III) of DNA also increased in the presence of H2O2 [37,38]. Control experiments
have suggested that untreated DNA did not show any cleavage (lane 1). Moreover,
uncoordinated ligand and free metal salt also did not show any apparent cleavage (lanes 3 and 8).
These experimental facts demonstrate that a combination of all the metal(II) complexes and
activating agent (H2O2) are required to show effective cleavage of plasmid DNA. It is obvious
that Cu(II) (Fig. 4; lane 7) has more ability to cleave the supercoiled plasmid DNA when
compared to that of other complexes. It is believed that the cleavage ability of complexes is due
to the reaction of metal ions with H2O2 which produces diffusible hydroxyl radicals or molecular
oxygen at ease which in turn damage DNA through Fenton-type chemistry [39].
(Kindly insert Fig. 5 here)
The antimicrobial screenings of the free ligand and the complexes were tested for their
effect on certain bacteria and fungi. The minimal inhibitory concentrations of tested compounds
against certain bacteria and fungi are shown in Tables 3 and 4. The remarkable activity of the
Schiff base ligand may be occurred from the hydroxyl group which may play an important role
in the antibacterial activity as well as the presence of –CH=N group which imports in elucidating
the mechanism of transformation reaction in biological systems. The obtained results indicate
that the complexes have higher activity than the ligand against the same microorganisms under
identical experimental conditions. This suggests that the chelation could facilitate the ability of a
complex to cross a cell membrane and can be explained by Tweedy’s chelation theory [40].
Chelation considerably reduces the polarity of the metal ion because of partial sharing of its
positive charge with donor groups and possible electron delocalization over the whole chelate
ring. This fact could enhance the lipophilic character of the central metal atom which
subsequently favors its permeation through the lipid layer of the cell membrane. The variation in
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the effectiveness of different compounds against different organisms depend either on the
impermeability of the cells of the microbes or on differences in ribosome of microbial cells.
(Kindly insert Tables 3 and 4 here)
In summary, few novel complexes (metallonucleases) having (E)-(2-((2-
hydroxybenzylidene)amino)phenyl)(phenyl)methanone have been synthesized and characterized.
The electronic absorption and EPR data reveal that all the complexes are adopting an octahedral
geometry around the central metal ion. The DNA interaction of all the complexes has been
evaluated by various photo physical methods which exhibit that all the complexes can bind to
DNA via intercalation in the order of Zn(II) < Ni(II) < Co(II) < Cu(II). Further, the experimental
results reveal that the Cu(II) complex can bind to DNA more strongly than the other three
complexes. The DNA cleaving activity of all the metal complexes with pBR322 DNA under
aerobic conditions is more pronounced in presence of the oxidant (H2O2). We hope the results
will be of value in further understanding the DNA damage induced by Cu(II) complex, as well as
laying the foundations for the discovery of new antitumor drugs.
Acknowledgments
The authors express their sincere thanks to the College Managing Board, Principal and
Head of the Department of Chemistry, VHNSN College, Virudhunagar, India for providing
necessary research facilities. SAIF, IIT Bombay and CDRI, Lucknow, are gratefully
acknowledged for providing instrumental facilities.
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[22] [L], Yield: 74 % Anal. Calc. for C20H15NO2: C, 79.6; H, 4.8; N, 4.6 % ; Found C, 79.7;
H, 5.0; N, 4.6 %. IR data (KBr, cm-1); 3431 ν(OH), 1651 ν(C=O), 1641 ν(CH=N).
1H NMR (): 6.8-7.3 (aromatic) (m); 5.7 (-OH phenolic) (s); δ 9.2 (1H, s, -CH=N).
UV–vis, (DMSO, cm-1); 32,176, 33,487
[23] All the transition metal complexes were prepared by adding the ethanolic solution of
respective Schiff base ligand (0.02 mol) with metal chlorides (0.01 mol) dissolved in
ethanol while stirring for ca. 6 h. The complexes formed and were filtered and washed
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[24] [CuL2], Yield: 64 %, Anal. Calc. for C40H28N2O4Cu: C, 72.3; H, 4.2; N, 4.2; Cu, 9.6 %;
Found C, 72.0; H, 3.9; N, 3.8; Cu, 9.2 %. IR data (KBr, cm-1); 1633 ν(C=O), 1612
ν(CH=N), 486 ν(M-N), 551 ν(M-O). UV–vis, (DMSO, cm-1); 35,568, 37,647, 14,852. μeff
(BM): 1.84
[25] [NiL2], Yield: 63 %, Anal. Calc. for C40H28N2O4Ni: C, 72.8; H, 4.1; N, 4.1; Ni, 8.8 %;
Found C, 72.8; H, 4.3; N, 4.3; Ni, 8.9 %. IR data (KBr, cm-1); 1629 ν(C=O), 1619
ν(CH=N), 480 ν(M-N), 551 ν(M-O). UV–vis, (DMSO, cm-1); 14,761, 15,456, 23,469. μeff
(BM): 3.21
[26] [CoL2], Yield: 67 %, Anal. Calc. for C40H28N2O4Co: C, 72.5; H, 4.1; N, 4.0; Co, 8.6 %;
Found C, 72.8; H, 4.3; N, 4.1; Co, 8.9 %. IR data (KBr, cm-1); 1624 ν(C=O), 1626
ν(CH=N), 487 ν(M-N), 561 ν(M-O). UV–vis, (DMSO, cm-1); 15,129, 16,564, 20,135. μeff
(BM): 4.88
[27] [ZnL2], Yield: 69 %, Anal. Calc. for C40H28N2O4Zn: C, 72.0; H, 3.8; N, 4.0; Zn, 9.6 %;
Found C, 72.1; H, 4.2; N, 4.2; Zn, 9.8 %. IR data (KBr, cm-1); 1632 ν(C=O),
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1
1615 ν(CH=N), 480 ν(M-N), 559 ν(M-O). H NMR (): 6.6-7.4 (aromatic) (m); δ 8.1
(1H, (s) -CH=N). UV–vis, (DMSO, cm-1); 32,242, 33,327. μeff (BM): diamagnetic
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Figure Captions
Scheme 1. Synthesis of Schiff base ligand and its metal complexes.
Fig. 1. Absorption spectrum of [CuL2] in buffer pH = 7.2 at 25 0C in presence of
increasing amount
of DNA. The arrow indicates upon increasing the amount of DNA.
Fig. 2. Effect of increasing amounts of [EB] (●), [CuL2] (Ж), [CoL2] (▲), [NiL2] (■), [ZnL2] (●) and L () on the
viscosity of DNA. R = [complex]/[DNA] or [EB]/[DNA].
Fig. 3. Cyclic voltammogram of [CuL2] in buffer pH = 7.2 at 25 0C in presence of
increasing amount
of DNA. The arrow indicates upon increasing the amount of DNA.
0
Fig. 4. Differential pulse voltammogram of [CuL2] in buffer pH = 7.2 at 25 C in presence of
increasing amount of DNA. The arrow indicates upon increasing the amount of DNA.
Fig. 5. Gel electrophoresis pattern showing cleavage of pBR322 supercoiled DNA (10 μM) by Cu(II), Ni(II),
Co(II) and Zn(II) complexes (60μM) in the presence of H2O2 (100 μM). Lane 1: DNA alone; lane 2: DNA +
H2O2; lane 3: L + DNA + H2O2; lane 4: [ZnL2] + DNA +H2O2; lane 5: [NiL2] + DNA + H2O2; lane 6: [CoL2] +
DNA + H2O2; lane 7: [CuL2] + DNA + H2O2; lane 8: CuCl2 (500 μM) + DNA + H2O2.
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Scheme 1. Synthesis of Schiff base ligand and its metal complexes.
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0
Fig. 1. Absorption spectrum of [CuL2] in buffer pH = 7.2 at 25 C in presence of increasing amount of
DNA. The arrow indicates upon increasing the amount of DNA.
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Fig. 2. Effect of increasing amounts of [EB] (●), [CuL2] (Ж), [CoL2] (▲), [NiL2] (■), [ZnL2] (●) and L () and
[on the viscosity of DNA. R = [complex]/[DNA] or [EB]/[DNA].
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Fig. 3. Cyclic voltammogram of [CuL2] in buffer pH = 7.2 at 25 0C in presence of
increasing amount
of DNA. The arrow indicates upon increasing the amount of DNA.
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Fig. 4. Differential pulse voltammogram of [ZnL2] in buffer pH = 7.2 at 25 0C in presence of
increasing amount of DNA. The arrow indicates upon increasing the amount of DNA.
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Fig. 5. Gel electrophoresis pattern showing cleavage of pBR322 supercoiled DNA (10 μM) by Cu(II), Ni(II),
Co(II) and Zn(II) complexes (60μM) in the presence of H2O2 (100 μM). Lane 1: DNA alone; lane 2: DNA +
H2O2; lane 3: L + DNA + H2O2; lane 4: [ZnL2] + DNA +H2O2; lane 5: [NiL2] + DNA + H2O2; lane 6: [CoL2] +
DNA + H2O2; lane 7: [CuL2] + DNA + H2O2; lane 8: CuCl2 (500 μM) + DNA + H2O2.
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Impact of metallonucleases on DNA interactions: Structural validation and in-vitro anti
biogram assay
Vellaichamy Muniyandi, Narayanaperumal Pravin, Natarajan Raman*
Research Department of Chemistry, VHNSN College, Virudhunagar-626 001, Tamil Nadu, India,
E-mail: ramchem1964@gmail.com Tel: +091-92451-65958
Pictogram
Graphical abstract
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Table captions
Table 1 Electronic absorption spectral parameters for the interaction of DNA with Cu(II), Ni(II),
Co(II) and Zn(II) complexes.
Table 2 Electrochemical parameters for the interaction of DNA with Cu(II), Ni(II), Co(II) and
Zn(II) complexes.
Table 3 Minimum inhibitory concentration of the synthesized compounds against the growth of
bacteria (μM).
Table 4 Minimum inhibitory concentration of the synthesized compounds against the growth of
fungi (μM).
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Table 1 Electronic absorption spectral parameters for the interaction of DNA with Cu(II), Ni(II),
Co(II) and Zn(II) complexes.
Λ max
*K ×105 M-1
Compound
∆λ /nm
%H#
b
Free
Bound
[CuL2]
[NiL2]
[CoL2]
[ZnL2]
326
326
329
334
330
327
327
331
4
1
2
3
15.3
19.3
20.2
31.0
1.47 ± 0.9
1.33 ± 0.3
1.42 ± 0.5
0.71 ± 0.2
%H# = [(Afree-Abound)/Afree] x 100%.
*Kb = Intrinsic DNA binding constant determined from the UV–Vis absorption spectral titration.
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Table 2 Electrochemical parameters for the interaction of DNA with Cu(II), Ni(II), Co(II) and
Zn(II) complexes.
Data from cyclic voltammetric measurements: aE1/2 is calculated as the average of anodic (EPa) and cathodic (Epc)
Redox couple
aE1/2 (V)
b∆Ep (V)
Compound
Ipa/Ipc
Free
Bound
Free
Bound
Cu(III) → Cu(II)
Cu(II) → Cu(I)
Cu(I) → Cu(0)
Ni(II) → Ni(I)
0.236
-0.241
-0.815
0.277
-0.208
-0.774
-0.37
0.051
-0.468
-0.338
0.107
-0.416
0.77
0.63
0.24
[CuL2]
[NiL2]
[CoL2]
[ZnL2]
-0.736
-0.706
-0.591
-0.464
1.96
Co(II) → Co(I)
Co(I) → Co(0)
-0.264
-0.927
-0.234
-0.906
-0.111
-0.159
-0.103
-0.109
0.13
0.86
Zn(II) → Zn(0)
-0.729
-0.711
-0.525
-0.395
1.73
b
peak potentials; E1/2a = Epa + Epc / 2 ; Ep = Epa─Epc
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Table 3 Minimum inhibitory concentration of the synthesized compounds against the growth
of bacteria (μM).
Minimum inhibitory concentration (MIC) ( × 104 μM)
Compound
S.
P.
E.
S.
K.
aureus
aeruginosa
coli
epidermidis
pneumoniae
16.9
4.9
15.8
5.6
16.4
4.2
16.2
4.7
14.5
5.9
[L]
[CuL2]
6.1
5.7
7.5
7.4
9.0
8.9
7.7
5.1
8.2
6.2
[NiL2]
[CoL2]
11.6
13.8
1.9
10.5
1.8
12.9
1.3
11.4
2.3
[ZnL2]
aStreptomycin
1.7
a Streptomycin is used as the standard
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Table 4 Minimum inhibitory concentration of the synthesized compounds against the growth
of fungi (μM).
Minimum inhibitory concentration (MIC) ( × 104 μM)
Compound
A.
F.
C.
R.
C.
niger
solani
lunata
bataticola
albicans
13.9
7.5
19.3
7.3
16.5
6.7
11.9
6.9
14.9
5.9
[L]
[CuL2]
10.2
7.9
10.4
9.2
10.5
7.9
9.7
8.3
10.3
6.8
[NiL2]
[CoL2]
11.3
10.3
1.6
11.1
1.2
12.5
1.0
11.1
1.5
[ZnL2]
aNystatin
1.1
a Nystatin is used as the standard
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Impact of metallonucleases on DNA interactions: Structural validation and in-vitro anti
biogram assay
Vellaichamy Muniyandi, Narayanaperumal Pravin, Natarajan Raman*
Research Department of Chemistry, VHNSN College, Virudhunagar-626 001, Tamil Nadu, India,
E-mail: ramchem1964@gmail.com Tel: +091-92451-65958
Synopsis:
The synthesized 2-aminobenzophenone based complexes exert their promising in vitro DNA
binding and cleavage potency as well as they can act as anti-microbial agents. The data reveal
that our complexes are dynamic DNA targets.
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Research Highlights
 The newly synthesized complexes will act as potential therapeutic agents.
 These metal complexes display better DNA binding and chemical nuclease activity.
 2-aminobenzophenone based metal complexes are found to be good antimicrobial agents.
 Developing novel DNA targeting metal complexes.
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