A.Z. El-Sonbati et al. / Journal of Molecular Liquids 209 (2015) 635–647
637
bond angles and calculated quantum chemical parameters for the ligands
(HLn) were investigated. The ligands considering that the phenolic\\OH
group may enhance their affinity towards DNA binding through forma-
tion of hydrogen bonding. The Ru(III) complexes were tested as a
catalysts for the dehydrogenation of benzylamine to benzonitrile with
N-methylmorpholine-N-oxide as co-oxidant at room temperature.
concentrated to half of its original volume by evaporation and allowed
cooling at room temperature. During this, a microcrystalline solid was
separated, which was isolated by filtration, washed with hot ethanol,
ether and dried in a vacuum desiccator over anhydrous CaCl2.
ꢀ
ꢁ
½RuCl3ðbipyÞꢀ þ 2HLn→ RuðLnÞ2ðbipyÞ Cl:
2. Materials and methods
2.4. DNA binding experiments
2.1. Materials and apparatus
The binding properties of the ligands to CT-DNA have been studied
using electronic absorption spectroscopy. The stock solution of CT-
DNA was prepared in 5 mM Tris–HCl/50 mM NaCl buffer (pH = 7.2),
which a ratio of UV absorbances at 260 and 280 nm (A260/A280) of ca.
1.8–1.9, indicating that the DNA was sufficiently free of protein
[24], and the concentration was determined by UV absorbance at
260 nm (ε = 6600 M–1 cm–1) [25]. Electronic absorption spectra
(200–700 nm) were carried out using 1 cm quartz cuvettes at 25 °C
All reagents were purchased from Aldrich, Fluka and Merck and were
used without any further purification. CT-DNA was purchased from SRL
(India). Double distilled water was used to prepare all buffer solutions.
Microanalytical data (C, H and N) were collected on Automatic
Analyzer CHNS Vario ELIII, Germany. Spectroscopic data were
obtained using the following instruments: FTIR spectra (KBr discs,
4000–400 cm−1) by Jasco FTIR-4100 spectrophotometer; the 1H NMR
spectra by Bruker WP 300 MHz using DMSO-d6 as a solvent containing
TMS as the internal standard. UV–Visible spectra by Perkin-Elmer
AA800 spectrophotometer Model AAS. The molecular structures of the in-
vestigated compounds were optimized by HF method with 3-21G basis
set. The molecules were built with the Perkin Elmer ChemBio Draw and
optimized using Perkin Elmer ChemBio3D software [21,22]. Thermal
analysis of the ligands and their Ru(III) complexes was carried out using
a Shimadzu thermogravimetric analyzer under a nitrogen atmosphere
with heating rate of 10 °C/min over a temperature range from room
temperature up to 800 °C. Magnetic susceptibility measurements were
determined at room temperature on a Johnson Matthey magnetic suscep-
tibility balance using Hg[Co(SCN)4] as calibrant. Conductivity measure-
by fixing the concentration of ligand (1.00 × 10−3 mol L−1
)
,
while gradually increasing the concentration of CT-DNA (0.00 to
1.30 × 10−4 mol L−1). An equal amount of CT-DNA was added to both
the compound solutions and the reference buffer solution to eliminate
the absorbance of CT-DNA itself. The intrinsic binding constant Kb of
the compound with CT-DNA was determined using the following
Eq. (1) [26]:
½DNAꢀ=ðєa–єf Þ ¼ ½DNAꢀ=ðєb–єf Þ þ 1=Kbðєa–єf Þ
ð1Þ
where [DNA] is the concentration of CT-DNA in base pairs, єa is the
extinction coefficient observed for the Aobs/[compound] at the given
DNA concentration, єf is the extinction coefficient of the free compound
in solution and єb is the extinction coefficient of the compound when
fully bond to DNA. In plots of [DNA]/(єa–єf) versus [DNA], Kb is given
by the ratio of the slope to the intercept.
ments of the complexes at 25
1 °C were determined in DMF
(10−3 M) using conductivity/TDS meter model Lutron YK-22CT.
2.2. Synthesis of azo dye ligands (HLn)
The azo dye ligands (Fig. 1), 4-(4-hydroxy-5-(aryldiazenyl)-2-
thioxothiazol-3(2H)-yl)benzenesulfonamide (HLn) were prepared [1]
by coupling of 3-sulfamoylphenylrhodanine with aniline and its
p-derivatives. A stoichiometric amount of aniline or its p-derivatives
(0.01 mol) in 25 mL of hydrochloric acid (0.01 mol) was added
dropwise to a solution of sodium nitrite (0.01 mol) in 20 mL of water
at −5 °C. The formed diazonium chloride was consecutively coupled
with an alkaline solution of 3-sulfamoylphenylrhodanine (0.01 mol).
The colored precipitate, which was formed immediately, was filtered
through a sintered glass crucible, washed several times with water
and ethanol and dried in a vacuum desiccator over anhydrous CaCl2.
The products were purified by recrystallization from ethanol.
2.5. Catalytic oxidation of benzylamine by trans-[Ru(Ln)2(bipy)]Cl /NMO
To a solution of the catalyst trans-[Ru(Ln)2(bipy)]Cl (0.01 mmol) in
5 cm3 dimethyl formamide, benzylamine (2 mmol) was added with
stirring. N-methylmorpholine-N-oxide (NMO) (10 mmol) was then
dissolved in DMF and the reaction mixture was further stirred for 3 h
at room temperature. The mixture was reduced in vacuo and the residues
were collected in diethylether, filtered through a bed of silica gel and
dried over anhydrous MgSO4. The produced benzonitrile was isolated
and weighed [27].
The resulting formed ligands are:
HL
76
74
72
70
68
66
4
HL1
thioxothiazol-3(2H)-yl)benzenesulfonamide.
HL2 4-(4-hydroxy-5-((4-methylphenyl)diazenyl)-2-
=
4-(4-hydroxy-5-((4-methoxyphenyl)diazenyl)-2-
=
thioxothiazol-3(2H)-yl)benzenesulfonamide.
HL3 = 4-(4-hydroxy-5-(phenyldiazenyl)-2-thioxothiazol-3(2H)-
yl)benzenesulfonamide.
HL4 = 4-(4-hydroxy-5-((4-nitrophenyl)diazenyl)-2-thioxothiazol-
3(2H)-yl)benzenesulfonamide.
HL
3
HL
HL
2
1
2.3. Synthesis of Ru(III) complexes (1–4)
Ruthenium(III) complexes (Fig. 2) were synthesized according to
the general procedure [23]: a stoichiometric amount of the desired
ligand (0.02 mol) in ethanol (20 cm3) was added dropwise to a hot
ethanol solution (20 cm3) of [RuCl3(bipy)] (0.01 mol) with stirring
and the reaction mixture was refluxed for 3 h. The solution was
R
σ
Fig. 3. The relation between Hammett's substitution coefficient (σR) vs. yield (%) of ligands
(HLn).