DNA binding properties of two ruthenium(III) complexes containing schiff bases derived from salicylaldehyde: Spectroscopic and electrochemical evidence of CT DNA intercalation

Article abstract of DOI:10.5562/cca2216

The interaction of CT DNA by two anionic Ru(III) complexes with N-substituted salicylidenimine ligands was investigated by spectroscopic titration and cyclic voltammetry. The result gives a surprising evidence for intercalation of DNA by the negatively ch

Full text of DOI:10.5562/cca2216

CROATICA CHEMICA ACTA
CCACAA, ISSN 0011-1643, e-ISSN 1334-417X
Croat. Chem. Acta 86 (2) (2013) 215–222.
http://dx.doi.org/10.5562/cca2216
Original Scientific Article
DNA Binding Properties of Two Ruthenium(III) Complexes
Containing Schiff Bases Derived from Salicylaldehyde:
Spectroscopic and Electrochemical Evidence of CT DNA Intercalation
Nevzeta Ljubijankić, Adnan Zahirović, Emir Turkušić,
and Emira Kahrović*
Department of Chemistry, Faculty of Science, University of Sarajevo,
Zmaja od Bosne 35, 71000 Sarajevo, Bosnia and Herzegovina
RECEIVED NOVEMBER 28, 2012; REVISED MAY 15, 2013; ACCEPTED MAY 22, 2013
Abstract. The interaction of CT DNA by two anionic Ru(III) complexes with N-substituted salicylide-
nimine ligands was investigated by spectroscopic titration and cyclic voltammetry. The result gives a
surprising evidence for intercalation of DNA by the negatively charged complex species containing non
typical intercalating ligands with Kb of order 104 M−1. Na[RuCl2(N-R-5-X-salim)2], where R represents
butyl or phenyl and X = H, Cl, were characterized on the basis of elemental analysis, MALDI-TOF mass
spectrometry, infrared, UV / visible spectroscopic measurements and cyclic voltammetry. (doi:
10.5562/cca2216)
Keywords: Schiff base, ruthenium, DNA intercalation, spectroscopy, cyclic voltammetry
INTRODUCTION
salicylaldehyde containing attached quaternary ammo-
nium group to increase hydrophilic character.16−18
Furthermore, some ruthenium complexes with
salicyladi-mines showed significant biological activity
against some bacteria, in contrast to the less active free
ligands.19 In addition, two dichloro-bis[N-phenyl-5-
Ruthenium compounds have been the subject of great
interest and impressive development in last decades for
many reasons, especially due to their catalytic1−4 and
anticancer activities.5−11 Ruthenium generally demon-
strates affinity toward N-donor molecules such as
proteins and DNA. The mechanism of the action of
antitumor-active ruthenium compounds is not entirely
known. Closely, it is thought that the complexes
containing chlorides, or other easily leaving groups,
can hydrolyze in vivo, allowing the covalent binding
of the nucleobases from DNA to ruthenium.12 Many
Ru(II) and Ru(III) compounds with numerous different
ligands are reasonably synthesized and investigated for
the purpose of possible application in medicine and
catalysis. There are no many complexes containing
Schiff bases derived from salicyladehyde described
in literature, although such ligands generally show
considerable stereochemical flexibility and capability to
tune the reduction potential of metal center, acting as
N- or N,O ligands.13,14 Some of them are described as
very good catalysts in organic synthesis because the
presence of salicylaldimine in the molecule increases
the stability and catalytic activity.15 Such ligands are
derived from 2,4,6-tris substituted phenylamines and
substituted-salicylideniminato-N,O]ruthenate(III)
are
described as electrochemical mediators for the low
potential amperometric determination of ascorbic
acid.20,21
We aimed to investigate interaction of Ru(III)
complexes containing simple Schiff bases derived from
salicylaldehyde with DNA and we report spectroscopic
and electrochemical evidence of CT DNA intercalation
by two dichloro-bis[N-substituted-5-X-salicylideni-
minato-N,O]ruthenate(III)
compounds,
hereinafter
Na[RuCl2(N-R-5-X-salim)2] where R represents butyl or
phenyl, while X = H, Cl
.
EXPERIMENTAL
Chemicals were purchased from commercial
sources and used without further purification. Calf
thymus DNA (CT DNA) was purchased from Sigma
Aldrich.
* Author to whom correspondence should be addressed. (E-mail: emira_kahrovic@yahoo.com)

216
N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
Synthesis
Physical Measurements
Preparation of Ligands
Elemental analyses were performed on a Perkin Elmer
N-substituted-5-X-salicylidenimines, hereinafter N-R-5-
XsalimH (R = C4H9, C6H5, X = H, Cl) were prepared by
simple condensation of butyl amine with salicylalde-
hyde and aniline with 5-chlorosalicylalde-hyde in molar
ratio 1 : 1 at room temperature. Solid N-phenyl-5-chlo-
rosalicylidenimine was recrystallized from ethanol at
70 °C with 70−80 % yield.
2400 Series CHNS/O Analyzer. Mass spectra were
obtained on a matrix-assisted laser desorption / ioniza-
tion–time–of-flight MALDI-TOF/TOF mass spectrome-
ter (4800 Plus MALDI TOF/TOF analyzer, Applied
Biosystems Inc., Foster City, CA, USA) equipped with
Nd:YAG laser operating at 355 nm with firing rate
200 Hz in the negative ion reflector mode. 1600 shots
per spectrum was taken with mass range 10−1500 Da,
focus mass 500 Da and delay time 100 ns. Small
amount of sample (on pipette tip) was resuspended in
10 µl of DHB MALDI matrix (5 mg/mL; dissolved in
50/50 acetonitrile/water, v/v) and 1 µl was spotted on
MALDI plate. The spectrum was internally calibrated
providing measured mass accuracy within 5 ppm
of theoretical mass riboflavin and 3-aminosalicylic
acid were used as internal calibrants in negative ion
mode.
The infrared spectra were recorded as KBr pellets
on a Perkin Elmer spectrum BX FTIR System in the
region 4000−400 cm−1. UV/visible spectra, hydrolyses
and CT DNA binding were measured on a Perkin Elmer
lambda 35 spectrophotometer. Hydrolysis experiments
were performed by adding the concentrated solution of
complexes in DMSO to water buffered solutions (phos-
phate buffer, pH 7.5). The stock solution of CT DNA
was prepared in Tris-HCl buffer at pH 7.4 and stored at
4 °C maximally 1−4 days. The concentration of DNA
was calculated on the basis of extinction coefficient
6600 M−1 cm−1 at 260 nm.23 The purification of DNA by
phenol extraction methods improved the ratio of UV
absorbance at 260 and 280 nm A260/A280 ca. 1.8, indicat-
ing that DNA was satisfactory free from proteins. The
absorption of DNA itself was removed by adding the
same amount of DNA in reference solutions as in ruthe-
nium complex-DNA solutions. Concentrated stock solu-
tions of complexes were prepared by initial dissolving
compounds in small amount of DMSO and diluting to
the required concentrations.
Preparation of Complexes Na[RuCl2(N-R-5-X-salim)2]
Sodium dichloro-bis[N-phenyl-5-chlorosalicylidenimi-
nato-N,O]ruthenate(III), Na[RuCl2(N-Ph-5-Cl-salim)2].
Dichloro-bis[N-phenyl-5-chlorosalicylideniminato-
N,O]ruthenate (III), hereinafter Na[RuCl2(N-Ph-5-Cl-
salim)2], was prepared according to the published pro-
cedure22 and precipitated as sodium salt. 0.46 g
(2 mmol) N-Ph-5-Cl-salimH in 30 mL ethanol absolute
was added to the solution of 0.26 g (1 mmol)
RuCl3 · 3H2O in absolute alcohol (10 mL). The mixture
was refluxed for 3 hours at 65−70 °C and the volume
was reduced in rotary evaporator to the half of the initial
volume. The precipitation was performed by adding the
water solution of 0.058 g NaCl (1 mmol) / 1 mL. The
dark green solid was washed with diethyl ether and
dried over P2O5. Yield: 55 %.
Anal. Calc. for NaRuC26H18Cl4O2N2; (%):
C, 49.30; H, 2.86; N, 4.42. Found (%): C, 48.36;
H, 2.91; N, 4.21. MALDI-TOF MS m/z: 633.91
([C26H18 Cl4O2N2Ru]−, 100 %). IR(KBr) νmax / cm−1:
1583 vs (C=N), 1352 m (C−O phen), 424 w (Ru−O),
669 w (Ru-N). UV / Vis [CH2Cl2], λmax/nm: 340 and
495 (ε / M−1 cm−1): 6600 and 4144.
Sodium
dichloro-bis[N-butylsalicylideniminatoN,O]-
ruthenate(III), Na[RuCl2(N-Bu-5-H-salim)2]. To the
solution of RuCl3 · 3H2O (0.10 g, 0.38 mmol) in 5 mL
absolute ethanol, 0.76 mmol freshly prepared
butylsalicylidenimine was added. Reaction mixture
was kept at 80 °C within 90 minutes in rotary
evaporator whereby the resulting solution has changed
the color from brown to dark green. Precipitation
was performed with 1 mL water solution of NaCl
(0.02 g, 0.38 mmol). The resulting solution was kept
overnight in ice-salt bath afterward the dark solid was
filtered off and washed with ice-cold diethyleter.
Yield: 43 %.
Cyclic voltammograms of Na[RuCl2(N-R-5-X-
salim)2] were recorded on an electrochemical work-
station Autolab potentiostat/galvanostat (PGSTAT 12)
in DMF (N,N-dimethylformamide) solution with sodium
perchlorate as supporting electrolyte using glassy car-
bon working electrode and Ag/AgCl reference electrode
in the range of potential of −1.5 to +0.1 V, with scan
rate rate 0.8 V s−1. Working electrode was polished prior
to measurements with 1 μm diamond paste. Electro-
chemical titrations of ruthenium compounds with CT
DNA were recorded by cyclic voltammetry in Tris–HCl
buffered water solution (pH 7.4), at ambient tempera-
ture in 5 mL-volume conical compartment self-made
Anal.
Calc.
for
NaC22H28Cl2O2N2Ru;
Na+[RuCl2C22H28O2N2]−; (%): C, 48.30; H, 5.16;
N, 5.12. Found (%): C, 48.06; H, 5.28; N, 4.81.
MALDI-TOF MS m/z: 524.0604 ([RuCl2C22H28O2N2]−,
100 %). IR(KBr) νmax / cm−1: 1606 vs (C=N), 1305 m
(C−O phen), 404 w (Ru−O), 669 w (Ru−N). UV / Vis
[CH2Cl2], λmax / nm: 415, (ε / M−1 cm−1): 1408.
Croat. Chem. Acta 86 (2013) 215.

N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
217
cell. The volume of the cell is adapted to the experi-
ments meaning to the required volumes of Na[RuCl2(N-
R-5-X-salim)2] solutions (2 mL) and added μL-amounts
(0−60) of CT DNA.
Na[RuCl2(N-Bu-salim)2] are assigned to the stretching
frequency of –CH=N−, compared to the frequencies at
1615 and 1633 cm−1 in free ligands, respectively. The
shift of the frequencies after coordination toward lower
wavenumbers for 32 and 27 cm−1 is a proof of strongly
bound azomethine nitrogen on ruthenium. Taking into
account the shifts as the rough measure of weakening
of C=N from azomethine the absorptions at 669 cm−1
were assigned to Ru−N in both compounds. On
contrary, phenolic C−O bond shows shift from 1271
and 1280 cm−1 in corresponding free ligands to 1305
and 1352 cm−1 in Na[RuCl2(N-Ph-5-Cl-salim)2] and
RESULTS AND DISCUSSION
Synthesis and Spectroscopic Studies
Synthesis
Na[RuCl2(N-R-5-X-salim)2] compounds were synthe-
sized from RuCl3 and freshly prepared ligands, butylsa-
licylidenime (R = C4H9, X = H) and N-phenyl-5-chlo-
rosalicylidiemine (R= C6H5, H = Cl), in absolute ethanol
solutions in molar ratio 1 : 2. The water suspended in
liquid Schiff base was not removed before the use
because the synthesis of final product was not affected
by the presence of water; moreover it is known that, in
some cases, the traces of water in butylsalicylidenimine
assists replacement of leaving group by Schiff base in
starting compound.24 The precipitations of anionic
complexes were performed by water solution of sodium
chloride. The dark green solids are quite stable in air,
insoluble in water, soluble in acetonitrile, DMF,
acetone, ethyl alcohol, DMSO, CH2Cl2. The molar ratio
of ruthenium and Schiff bases had to provide coordina-
tion of two anionic O, N ligands, keeping in octahedral
environment of ruthenium, two chlorides as easily leav-
ing groups. The characterization of compounds is based
on elemental CHN analytical data, mass spectrum
MALDI-TOF (Matrix Assisted Laser Desorption / Ioni-
zation; Time of flight mass analyzer), infrared and UV /
visible spectroscopic measurements. Mass spectra
showed molecular ions (M−) at m/z (100 %) = 524.06
which corresponds to [C22H28Cl2O2N2Ru]− and m/z
(100 %) found for [C26H18Cl4O2N2Ru] 633.91.
Na[RuCl2(N-Bu-salim)2] as
a result of increased
electronic density on C−O(Ru) after deprotonization of
C−O(H). The absorptions in the region 2850−2900 cm−1
were assigned to CH vibrations while moderate
absorption at 1518 cm−1 belongs to skeletal C=C vibra-
tions. The weak absorptions, appeared around 425 cm−1
after coordination of Schiff bases, were attributed
to Ru–O.
UV/Visible Spectroscopy
Electronic spectra of free Schiff bases and correspond-
ing complexes were recorded in CH2Cl2 solutions.
Na[RuCl2(N-Bu-5-H-salim)2] exhibits one broad ab-
sorption band centered about 415 nm arising from
intraligand transition of whole molecule of Schiff base.
Compared to free ligand , when Ru−N bond is formed,
the lone pair on nitrogen atom becomes stabilized and
absorption assigned to n → π* showed hypsohromic
shift (blue shift) for 7 nm. In Na[RuCl2(N-Ph-5-Cl-
salim)2] this absorption appears around 495 nm.
Weakly defined broad absorption centered around
350 nm, assigned to the transition of –HC=N- group, is
superimposed by Cl → Ru(III) LMCT transition in
Na[RuCl2(N-Bu-5-H-salim)2] while in phenyl derivative
a well defined band appears around 338 nm. Weak
broad absorption for both compounds, centered on
Infrared Spectroscopy
Infrared spectra of titled compounds and free ligands
clearly demonstrate the mode of binding via azomethine
nitrogen and deprotonated phenolic oxygen to
ruthenium strongly supporting the octahedral structure
of the compounds. Strong absorptions at 1583
and 1606 cm−1 in Na[RuCl2(N-Ph-5-Cl-salim)2] and
600 nm in the region of d-d spin allowed transition of
low spin t2g Ru(III), can be assigned to (2T2g
→
5
2A2g).25,26
Figure 2. Hydrolysis of Na[RuCl2(N-Bu-salim)2] in phosphate
buffer (pH 7.50; 0.1 M NaCl); c = 5.5 × 10−4 M; t = 120 min.
Figure 1. Scheme of preparation of Na[RuCl2(N-R-5-X-
salim)2]; R = C4H9 (Bu); C6H5 (Ph); X = H, Cl.
Croat. Chem. Acta 86 (2013) 215.

218
N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
Figure 3. Hydrolysis of Na[RuCl2(N-Ph-5-Cl-salim)2] in
phosphate buffer (pH 7.50; 0.1 M NaCl); c = 1.22 × 10−4 M;
t = 90 min.
Figure 4. Cyclic voltammograms of Na[RuCl2(N-Bu-salim)2]
and Na[RuCl2(N-Ph-5-Cl-salim)2]; DMF solution, supporting
electrolyte NaClO4; working electrode-glassy carbon vs
Ag/AgCl reference electrode; scan rate 0.8 V s−1; E = 0.5 (Epa
+ Epc); ∆Ep = Epa − Epc.
Behavior in Solutions
Understanding of behavior of compounds in solution,
e.g. hydrolysis and electron transfer processes are
thought to be very important for potential biological
activity and possible antitumor purpose of complex
compounds. The hydrolyses of Na[RuCl2(N-R-5-X-
salim)2] compounds under physiological condition in
phosphate buffer (pH 7.5; 0.1 M NaCl) designates
reasonable stabilization of ruthenium(III) after chelation
and blue shift of the LMCT bands over the time.
defined Epa anodic peaks at −0.277 and −0.309 V
respectively, while Epc cathodic peaks change slightly
from −0.901 to −0.905 V. The half-wave potentials,
assigned to Ru(III)/Ru(II) couple, (E1/2) = −0.607 V for
Na[RuCl2(N-Bu-salim)2] and (E1/2) = −0.588 V for
Na[RuCl2(N-Ph-5-Cl-salim)2], in addition to peak-to-
peak separation values and apparent reduction waves as
result of stabilization of Ru(III) after coordination
trough phenolic oxygen from salycilidenimine,27,28
suggest the quasi-reversible one-electron transfer
processes (Figure 4, Table 1).
Cyclic Voltammetry Measurements
Ru(III)/Ru(II) reduction potentials change with ligand
environment and is thought to be very important for
possible antitumor properties of a compound. The elec-
tronic effect of nitrogen from azomethine group and
phenolate oxygen on reduction potential is different.
More electronegative and smaller oxygen atom, hard in
character stabilizes Ru(III), while nitrogen, as softer,
prefers lower oxidation state. Kinetically, Ru(II) com-
pounds are more labile than Ru(III) which are believed
to can be activated by reduction in vivo. Few
compounds like gluthation in cells and ascorbic acid in
blood are thought to contribute to the reduction in vivo.
Cyclic voltammograms of Na[RuCl2(N-Bu-salim)2] and
Na[RuCl2(N-Ph-5-Cl-salim)2] in DMF solution with
sodium perchlorate as supporting electrolyte show
CT DNA Binding
Spectroscopic Study
Interaction of metal complex compounds with DNA is
taken as important initial signal about possible evalua-
tion of biological properties of a compound. Activity of
ruthenium compounds toward DNA, as a key target for
anticancer drugs, may originate from either their cova-
lent interaction with DNA nucleobases or non-covalent
binding such as electrostatic interaction of positively
charged species with phosphate backbone and intercala-
tion as well. Electronic absorption is very useful method
to determine the binding properties of metal complexes
Table 1. Characteristic potentials of Na[RuCl2(N-Ph-5-Cl-salim)2] and Na[RuCl2(N-Bu-salim)2] from cyclic voltammetry meas-
urements in DMF solution with NaClO4 supporting electrolyte
Complex
Epc / V
−0.905
−0.901
Epa / V
−0.309
−0.277
E1/2 / V
−0.607
−0.589
ΔE / V
0.596
0.624
Na[RuCl2(N-Ph-5-Cl-salim)2]
Na[RuCl2(N-Bu-salim)2]
Croat. Chem. Acta 86 (2013) 215.

N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
219
Figure 5. Graphical calculation of Kb (4.32 × 104 M−1) on the basis of spectrophotometric titration of Na[RuCl2(N-Ph-5-Cl-
salim)2] by CT DNA. Insets: upper left- experimental data for Kb calculation; bottom right-absorption spectra of 8.03 × 10−5
Na[RuCl2(N-Ph-5-Cl-salim)2] with increasing concentration of CT DNA (stock solution c = 7.98 × 10−3 M).
M
with DNA. Spectroscopic study of interaction of
Na[RuCl2(N-Ph-5-Cl-salim)2] and Na[RuCl2(N-Bu-
salim)2] with CT DNA has performed by titration of
fixed concentration of complex compounds with
increasing concentrations of calf thymus DNA (CT
DNA) in the [DNA] / [complex] ratio range 0−2.88 and
0−3.51, respectively. The constants of binding, Kb were
calculated on the basis of equation (1):29
Weak bathochromic shifts, hypochromism and
constant binding values of order 104 M−1 indicate that
both compounds, containing Schiff bases derived from
salicylaldehyde, act as moderate DNA-intercalators.30
Electrochemical Study
Electrochemical method is useful complement method
for UV / visible spectroscopic investigation of metal
complex intercalative mode binding to DNA. Here we
describe electrochemical measurements of redox
couples RuIIIcomplex / RuII
in the presence of incre-
complex
asing amounts of CT DNA (Figures 7 and 8, Tables 2
and 3).
(1)
Shifts of E1/2 for both compounds toward more
positive values, with increasing concentration of added
DNA, suggest different ability of Ru(II) and Ru(III)
compounds to bind DNA as a result of intercalation
mode of binding. Changes in peak-to-peak separation,
after addition of DNA, indicate an increase in reversibil-
ity of one-electron redox processes.
εa, εf and εb represent apparent extinction coefficients for
particular measurements (Aobs / [DNA]), free complex
and completely bound form, respectively. By plotting
[DNA] / (εa − εf) vs [DNA], Kb is obtained as the ratio of
the slope and intercept. Experimental data of spectro-
scopic measurements for interaction metal compounds-
DNA are given in Figures 5 and 6.
Croat. Chem. Acta 86 (2013) 215.

220
N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
Figure 6. Graphical calculation of Kb (1.81 × 104 M−1) on the basis of spectrophotometric titration of Na[RuCl2(N-Bu-salim)2] by
CT DNA. Insets: upper left- absorption spectra of 9.80 × 10−5 M Na[RuCl2(N-Bu-salim)2] with increasing concentration of CT
DNA (stock solution c = 9.75 × 10−3); bottom right-experimental data for Kb calculation.
10−5
M
Figure 8. Cyclic voltammograms of 4.9
× M
10−5
Figure 7. Cyclic voltammograms of
5
×
Na[RuCl2(N-Bu-salim)2] in 1) absence; 2) presence of 9.8 ×
10−5 M DNA ([DNA] / [complex] = 2); 3) presence of 5.88 ×
10−4 M DNA ([DNA] / [complex] = 12); pH 7.4, Tris-HCl
buffer. Working electrode-glassy carbon vs Ag/AgCl reference
electrode; scan rate 0.8 V s−1; E1/2 = 0.5 (Epa + Epc);
∆Ep = Epa − Epc.
Na[RuCl2(N-Ph-5-Cl-salim)2] in 1) absence DNA; 2) presence
of 9.8 × 10−5 M DNA ([DNA] / [complex] = 2); 3) presence of
5.88 × 10−4 M DNA. ([DNA] / [complex] = 12); pH 7.4, Tris-
HCl buffer. Working electrode-glassy carbon vs Ag/AgCl
reference electrode; scan rate 0.8 V s−1; E1/2 = 0.5 (Epa + Epc);
∆Ep = Epa − Epc.
Croat. Chem. Acta 86 (2013) 215.

N. Ljubijankić et al., DNA Binding Properties of Two Ruthenium(III) Complexes
221
Table 2. Characteristic potentials of Na[RuCl2(N-Ph-5-Cl-salim)2] in absence CT DNA (1) and presence (2, 3) of CT DNA
recorded by cyclic voltammetry in Tris–HCl buffered water solution, pH 7.4
Scan No.
[DNA]/[complex]
E
pc / V
Epa / V
−0.351
−0.301
−0.251
E1/2 / V
−0.476
−0.438
−0.401
ΔE / V
0.249
0.274
0.150
1
2
3
0
2
−0.600
−0.575
−0.550
12
Table 3. Characteristic potentials of Na[RuCl2(N-Bu-salim)2] in absence CT DNA (1) and presence (2, 3) of CT DNA recorded
by cyclic voltammetry in Tris–HCl buffered water solution, pH 7.4
Scan No.
[DNA]/[complex]
E
pc / V
Epa / V
−0.105
−0.155
−0.141
E1/2 / V
−0.178
−0.170
−0.156
ΔE / V
0.146
0.030
0.030
1
2
3
0
2
−0.251
−0.185
−0.171
12
CONCLUSION
We showed here that ruthenium(III) complexes
containing unlike, non-fused kinds of aromatic ligands,
Some ruthenium complexes with planar and fused aro-
matic π-electronic acceptor system or similar aromatic
heterocyclic rings are described as DNA intercalators
which are able to keep base pair separated distorting
double helix structure of DNA.31,32 Less extended planar
ligands may cause partial intercalation due to omitting
of the ancillary ligands and phosphate backbone e.g. in
the cases of some 1,10-phenanthroline compounds.33,34
Although two easily leaving chlorides in the structures
of Na[RuCl2(N-R-5-X-salim)2] do not exclude a priori
covalent binding or even electrostatic interaction of
neutral and positively charged complex species
produced by loss of chlorides, our spectroscopic and
electrochemical investigations suggest an intercalative
mode of binding with constant of order 104 M−1. Possi-
bly, this is the first report on anionic Ru(III) compounds
with Schiff bases derived from salicyladehyde and
simple amines which act as DNA intercalators.
such
as N-phenyl-5-chlorosalicylidenimine
and
N-butylsalicylidenimine cause intercalation of CT DNA.
In the case of Na[RuCl2(N-Ph-5-Cl-salim)2], with
π-system aromatic ring-azomethine-aromatic ring (two
aromates bridged by azometine), Kb = 4.32 × 104 M−1
value indicates good intercalating properties. The varia-
tion in structure of Schiff base ligands by altering one
aromatic ring with butyl (aromatic – azomethine − bu-
tyl) in Na[RuCl2(N-Bu-salim)2] do not affect Kb value
significantly (Kb = 1.81 × 104 M−1). This implies that
aromatic − azomethine part of Schiff base acts as an
intercalating chromophore for DNA bases.
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