![Electronic absorption spectra of the Ru(III) complexes: (a) [Ru(DAE)Cl2(H2O)]; (b) [Ru(HME)Cl2(H2O)]; (c) [Ru(MBE)Cl2(H2O)]; (d) [Ru(DEE)Cl2(H2O)].](https://www.researchgate.net/publication/306074582/figure/fig1/AS:1086768619225096@1636117238404/Electronic-absorption-spectra-of-the-RuIII-complexes-a-RuDAECl2H2O-b_Q320.jpg)
![Electronic absorption spectra of the Ru(III) complexes: (a) [Ru(DAE)Cl2(H2O)]; (b) [Ru(HME)Cl2(H2O)]; (c) [Ru(MBE)Cl2(H2O)]; (d) [Ru(DEE)Cl2(H2O)].](https://www.researchgate.net/publication/306074582/figure/fig2/AS:1086768619237381@1636117238436/Electronic-absorption-spectra-of-the-RuIII-complexes-a-RuDAECl2H2O-b_Q320.jpg)
![Electronic absorption spectra of the Ru(III) complexes: (a) [Ru(DAE)Cl2(H2O)]; (b) [Ru(HME)Cl2(H2O)]; (c) [Ru(MBE)Cl2(H2O)]; (d) [Ru(DEE)Cl2(H2O)].](https://www.researchgate.net/publication/306074582/figure/fig3/AS:1086768619237382@1636117238454/Electronic-absorption-spectra-of-the-RuIII-complexes-a-RuDAECl2H2O-b_Q320.jpg)
![Electronic absorption spectra of the Ru(III) complexes: (a) [Ru(DAE)Cl2(H2O)]; (b) [Ru(HME)Cl2(H2O)]; (c) [Ru(MBE)Cl2(H2O)]; (d) [Ru(DEE)Cl2(H2O)].](https://www.researchgate.net/publication/306074582/figure/fig4/AS:1086768619229198@1636117238475/Electronic-absorption-spectra-of-the-RuIII-complexes-a-RuDAECl2H2O-b_Q320.jpg)
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Research Article
Synthesis, Characterization, Anticancer, and Antioxidant Studies
of Ru(III) Complexes of Monobasic Tridentate Schiff Bases
Ikechukwu P. Ejidike and Peter A. Ajibade
Department of Chemistry, Faculty of Science and Agriculture, University of Fort Hare, P.B. X1314, Alice 5700, South Africa
Correspondence should be addressed to Peter A. Ajibade; pajibade@u.ac.za
Received March ; Revised April ; Accepted June
Academic Editor: Claudio Pettinari
Copyright © I. P. Ejidike and P. A. Ajibade. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium,provided the original work is properly cited.
Mononuclear Ru(III) complexes of the type [Ru(LL)Cl2(H2O)] (LL = monobasic tridentate Schi base anion: (Z)-N-(-{(𝐸)-[-(,
-dihydroxyphenyl)ethylidene]amino}ethyl)-N-phenylethanimidamide [DAE], -[(E)-N-{2-[(Z)-(-hydroxy--methoxybenzyl-
idene)amino]ethyl}ethanimidoyl]benzene-,-diol [HME], -[(E)-N-{2-[(Z)-(,-dimethoxybenzylidene)amino]ethyl}ethanim-
idoyl]benzene-,-diol [MBE], and N-(-{(𝐸)-[-(,-dihydroxyphenyl)ethylidene]amino}ethyl)benzenecarboximidoyl chloride
[DEE]) were synthesized and characterized using the microanalytical, conductivity measurements, electronic spectra, and FTIR
spectroscopy. IR spectral studies conrmed that the ligands act as tridentate chelate coordinating the metal ion through the
azomethine nitrogen and phenolic oxygen atom. An octahedral geometry has been proposed for all Ru(III)-Schi base complexes.
In vitro anticancer studies of the synthesized complexes against renal cancer cells (TK-), melanoma cancer cells (UACC-), and
breast cancer cells (MCF-) was investigated using the Sulforhodamine B assay. [Ru(DAE)Cl2(H2O)] showed the highest activity
with IC50 valves of 3.57 ± 1.09,6.44 ± 0.38,and9.06 ± 1.18 𝜇M against MCF-, UACC-, and TK-, respectively, order of activity
being TK- <UACC - <MCF-. e antioxidant activity by DPPH and ABTS inhibition assay was also examined. Scavenging
abilityofthecomplexesonDPPHradicalcanberankedinthefollowingorder:[Ru(DEE)Cl
2(H2O)] >[Ru(HME)Cl2(H2O)] >
[Ru(DAE)Cl2(H2O)] >[Ru(MBE)Cl2(H2O)].
1. Introduction
Coordination chemistry of transition metal Schi base com-
plexes possessing N, O, and S-donor atoms has received
consideration over the past few decades, due to the imperative
roles these compounds have played in a variety of biochem-
ical procedures like haloperoxidation [], insulin mimicking
[, ], xation of nitrogen [], inhibition of cancer growth,
and prophylaxis against carcinogenesis [, ]. A huge variety
of carbonyl compounds (>C=O) and amines (R-NH2)have
been exploited in the preparation of Schi bases [, ].
e reactivity of aldehyde compounds is generally faster
than those of the ketones in condensation reaction, thereby
resulting in the formation of Schi bases with a centre that
are less steric than the ketone’s, relatively unstable and freely
polymerizable []. is important attribute of Schi base
ligands oers prospects for prompting substrate chirality and
metal centred electronic factor tuning and improving the
solubilityandsteadinessofeitherhomogeneousorheteroge-
neous catalysts [–].
Schi bases have shown an interesting application as an
active corrosion inhibitor that is established on their capabil-
ity to spontaneously form a monolayer upon the surface to be
glazed [], as it is a type of interaction existing between an
inhibitor and a metal surface known as chemisorption [].
It is interesting to note that several commercial inhibitors
contain amines and aldehydes, but seemingly because of the
presence of >C=N bond, this makes Schi bases function
more resourcefully in many ways []. Stabilization of metal
ions in various oxidation states and monitoring their reactiv-
ity for catalytic applications have been linked to Schi bases
[]. e nitrogen-oxygen Schi bases geometry largely relies
on the diamine structural unit, nature of the ancillary ligand,
and the central metal ion []. Schi base-transition metal
complexes have been known to be one of the most modiable
and comprehensively studied systems [] with applications
in clinical and analytical elds [, ]. Antioxidants derived
from metal Schi base ligand combinations have received
current attention for their capability to safeguard living
Hindawi Publishing Corporation
Bioinorganic Chemistry and Applications
Volume 2016, Article ID 9672451, 11 pages
http://dx.doi.org/10.1155/2016/9672451
Bioinorganic Chemistry and Applications
systems and cells from impairment caused by oxidative stress
or free radicals [].
DNA binding, cleavage potentials, scavenging potentials,
and anticancer investigations of Schi base-ruthenium(III)
complexes have been accounted for []. Synthesis, spec-
tral, redox, catalytic, and biological action investigation
of mononuclear Ru(III)-Schi base structures are reported
[]. ,-Bipyridine and tetradentate Schi base ancillary
ligands of mixed-ligand Ru(II) complexes have been reported
for their electrochemical and Na+binding properties [].
Catalytic and growth inhibitory activities of Ru(III) mixed
ligand complexes of -hydroxy--naphthylideneimines have
been reported [].
In this study, we report the synthesis, characteriza-
tion, free radical scavenging, and anticancer studies of
four mononuclear ruthenium(III) complexes of Schi bases
derived from ,-dihydroxyacetophenone and ethylenedi-
amine as the bridging ligand with RCHO moiety alongside
their radicals scavenging action on ,-diphenyl--picrylhy-
drazyl (DPPH) and ,-azino-bis(-ethylbenzothiazoline--
sulfonic acid) (ABTS) and antiproliferative potentials. e
Schi base ligands containing N2O type tridentate parti-
tions were utilized for the synthesis of the mononuclear
ruthenium(III)-Schi base complexes (Scheme ).
2. Experimental
2.1. Chemicals and Instrumentations. All reagents used were
of analytical grade and used as purchased commercially.
Ethylenediamine, N,𝑁-dimethylformamide (DMF) and
ascorbic acid (Vit. C) were received from Merck, ,-
dihydroxyacetophenone and RuCl3⋅H2Owereobtained
from Aldrich. ,-Diphenyl--picrylhydrazyl (DPPH), ,-
azinobis--ethylbenzothiazoline--sulfonic acid (ABTS),
butylated hydroxytoluene (BHT), and rutin hydrate were
received from Sigma Chemical Co. (St. Louis, MO, USA).
Elemental analysis was carried out using Perkin-Elmer
elemental analyzer. IR spectra were recorded on an FT-IR
spectrometer: Perkin-Elmer System (Spectrum ) via
KBr disk method was used for the IR spectra analysis. Freshly
prepared DMF solutions of about −3 M containing Ru(III)
complexes gave the molar conductance at room temperature
with Crison EC-Meter Basic + conductivity cell. Electronic
absorption spectra ranging from to nm were
recorded on a Perkin-Elmer Lambda- spectrophotometer.
Stuart melting point (SMP ) was used for the melting points.
Four N2O type tridentate ligands, (Z)-𝑁-(-{(𝐸)-[-(,-
dihydroxyphenyl)ethylidene]amino}ethyl)-N-phenyletha-
nimidamide [DAE], -[(E)-N-{2-[(Z)-(-hydroxy--me-
thoxybenzylidene)amino]ethyl}ethanimidoyl]benzene-,-
diol [HME], -[(E)-N-{2-[(Z)-(,-dimethoxybenzylide-
ne)amino]ethyl}ethanimidoyl]benzene-,-diol [MBE], and
N-(-{(𝐸)-[-(,-dihydroxyphenyl)ethylidene]amino}eth-
yl)benzenecarboximidoyl chloride [DEE], were synthesized
and reported previously [].
2.2. Preparation of the Tridentate Schi Bases (DAE,
HME, MBE, and DEE). Ethylenediamine (. mol)
dissolved in mL of alcohol was slowly added to ,-
dihydroxyacetophenone (. mol) dissolved in same alco-
hol ( mL) and allowed to stir for minutes at room tem-
perature and then followed by drop-wise addition of
appropriate aldehyde (RCHO, mmol) dissolved in mL
alcohol for minutes time interval at room temperature and
further stirred for minutes. e mixture was le standing
with continuous stirring for approximately hours at room
temperature, aer which the desired tridentate compounds
were ltered and washed with ethanol to give crystalline
solid. e crude product was recrystallized from warm
ethanol. e products were dried in the vacuum at ∘C
overnighttogiveanalyticallypureproductsingoodyields
(.% to .%).
2.3. Synthesis of Ru(III)-Tridentate Schi Base Complexes.
Ru(III) complexes were prepared by adding (. mmol)
ethanol solution of ruthenium(III) chloride to a warm
ethanolic solution (. mmol) of [DAE]/[HME]/[MBE]/
[DEE], respectively. e colour of the solutions changed
immediately, magnetically stirred and kept under reux for
hours. e precipitated solids were ltered by suction from
the reaction medium, washed with ethanol and then with
diethyl ether, and dried over anhydrous calcium chloride. e
yields were about .–.%. e synthesis of the complexes
is explained in Scheme .
2.3.1. Synthesis of [OHC6H3OH:C(CH3):N(C2H4)N:C(CH3):
NHC6H5RuCl2(H2O)]
[Ru(DAE)Cl2(H2O)]⋅H2O. Dark-green solid; Yield: . mg
(.%); F. Wt: . g; Anal. Calcd. for C18H24N3O4RuCl2
(%): C ., H ., N .; Found (%): C ., H ., N
.; IR (KBr) ]max/cm−1: (O-H), (C=N), ,
(C-O), (Ru-N), (Ru-O); UV-Vis (DMF): 𝜆max/nm
(cm−1): ( ), ( ), ( ), ( ),
( ), (); Decomp. Temp, ∘C, -∘C; Λ𝜇:
. 𝜇Scm−1.
2.3.2. Synthesis of [OHC6H3OH:C(CH3):N(C2H4)N:CH:
C6H3OHOCH3RuCl2(H2O)]
[Ru(HME)Cl2(H2O)]⋅H2O. Darkish-green Solid; Yield:
. mg (.%); F. Wt: . g; Anal. Calcd. for
C18H23N2O6RuCl2(%): C ., H ., N .; Found (%):
C.,H.,N.;IR(KBr)]max /cm−1: (O-H),
(C=N), , (C-O), (Ru-N), (Ru-O); UV-Vis
(DMF): 𝜆max/nm (cm−1): ( ), ( ),
( ), ( ), ( ), ( ); Decomp.
Temp, ∘C, -∘C; Λ𝜇:.𝜇Scm−1.
2.3.3. Synthesis of [OHC6H3OH:C(CH3):N(C2H4)N:
CH:C6H5(OCH3)2RuCl2(H2O)]
[Ru(MBE)Cl2(H2O)]⋅H2O. Darkish-green Solid; Yield:
.mg(.%);F.Wt:.g;Anal.Calcd.for
C19H25N2O6RuCl2(%):C.,H.,N.;Found
Bioinorganic Chemistry and Applications
Cl
Cl
NN
O
HO
HO
H
Ru
OH
Cl
Cl
NN
O
HO
H
Ru
Cl
Cl
NN
O
HO
Cl
Ru
MBE/ethanol/reux
DAE/ethanol/reux
Cl
Cl
NN
O
NH
Ru
HME/ethanol/reuxDEE/ethanol/reux
H3C
H3C
CH3
OCH3
OCH3
OCH3
OH2
OH2
OH2
OH2
H3C
H3C
C18H21N3O2
C18H20N2O4
C17 H17CIN2O2
C19 H22N2O4
RuCl3·3H2O
S : Structure of mononuclear ruthenium(III)-Schi base complexes.
(%): C ., H ., N .; IR (KBr) ]max/cm−1:(O-
H), (C=N), , (C-O), (Ru-N), (Ru-O);
UV-Vis (DMF): 𝜆max/nm (cm−1): ( ), ( ),
( ), ( ), (), ( ); Decomp.
Temp, ∘C, -∘C; Λ𝜇:.𝜇Scm−1.
2.3.4. Synthesis of [OHC6H3OH:C(CH3):N(C2H4)N:C(Cl):
C6H5RuCl2(H2O)]
[Ru(DEE)Cl2(H2O)]⋅H2O. Dark-green Solid; Yield: . mg
(.%); F. Wt: . g; Anal. Calcd. for C17H20N2O4RuCl3
(%): C ., H ., N .; Found (%): C ., H ., N
.; IR (KBr) ]max/cm−1: (O-H), (C=N), ,
(C-O), (Ru-N), (Ru-O); UV-Vis (DMF): 𝜆max/nm
(cm−1): ( ), ( ), ( ), ( ),
( ); Decomp. Temp, ∘C, -∘C; Λ𝜇:.𝜇Scm−1.
2.4. In Vitro Antiproliferative Activity. e potentials of the
Ru(III)-tridentate Schi base complexes to interfere with the
growth of TK- renal cell line, UACC- melanoma cell line,
and MCF- breast cell lines were determined by SRB assay
as previously described []. – passages of MCF-, TK-,
and UACC- cell lines with plating densities of – cells
per well were precultured into -well microtitre plates for
h at ∘Cwith%air,%CO
2,and%relativehumidity
in RPMI medium, supplemented with % fetal bovine serum
(FBS), 𝜇gmL
−1 (gentamicin), and mM L-glutamine [].
e compounds were dissolved in DMSO and treated with
the cells aer h and diluted in RPMI medium giving rise
to concentrations comprising ., ., , , and 𝜇M.
Wells containing culture medium were used as control
while the wells containing complete culture medium with no
cellswereusedastheblanks.Parthenolidewasusedasthe
standard drug in this study. e plates were then incubated
for h aer the addition of the compounds. Viable cells were
xed to the bottom of each well with cold % trichloroacetic
acid, washed, dried, and dyed by SRB. e unbounded dye
was separated, while the protein-bound dye was extracted
with mM Tris base and multiwell spectrophotometer at
the wavelength nm was used for its optical density
determination. IC50 values were determined by plotting the
percentage viability against concentration of compounds on
a logarithmic graph to obtain % of cell growth inhibition
relative to the control.
2.5. Antioxidant Assay
2.5.1. Scavenging Activity of 1,1-Diphenyl-2-picrylhydrazyl
(DPPH) Radical. e antioxidant activity of the prepared
Ru(III) complexes was studied using spectrophotometer by
,-diphenyl--picrylhydrazyl (DPPH) method. is com-
pound is known as a stable readily accessible free radical,
with solubility in methanol giving a purple solution, and
Bioinorganic Chemistry and Applications
when reacted with antioxidant species changes to an equiv-
alent light yellow colour. e radical scavenging potentials
of the complexes with DPPH radical were evaluated as
described []. mL solution of the compounds in DMF with
concentrations ranging from to 𝜇g/mL was mixed
thoroughly with equivalent amount of .mM DPPH in
methanol; the mixtures were then allowed to react in the dark
forhalfanhour.Measurementofthemixtureabsorbance
was achieved spectrophotometrically at nm. Vitamin C
and rutin were used as the standard drugs. All test analysis
was carried out in triplicate. e ability of the ruthenium
compounds to scavenge DPPH radical was calculated via the
following equation:
DPPH radical scavenging activity (%)
=Absorbance of control −Absorbance of sample
Absorbance of control
× 100.
()
2.5.2. ABTS: 2,2-Azino-bis(3-ethylbenzothiazoline-6-sulfonic
acid) Radical Scavenging Assay. ABTS scavenging ability
of the Ru(III)-tridentate Schi base complexes adopted a
described method []. mM ABTS solution and . mM
potassium persulfate solution in equal amounts ( : ) were
used for working solution preparation and allowed to react
inthedarkforhatroomtemperature.Anabsorbance
of 0.706 ± 0.001 units at nm required for the analysis
was obtained by diluting mL ABTS+solution. Test samples
( mL) were mixed with mL of the ABTS+solution, and
absorbance was read spectrophotometrically at nm. e
test samples’ ABTS scavenging capacity alongside standard
drugs was evaluated. Triplicate analysis was carried out. e
percentage inhibition of ABTS radical scavenging activity was
obtained following a previous report [].
3. Results and Discussion
3.1. Synthesis and Characterization. e obtained com-
pounds were of coloured powders, stable in atmosphere
with a general formula: [Ru(LL)Cl2(H2O)] (LL = monobasic
tridentateSchibaseanion:DAE,HME,MBE,andDEE).
ey were prepared by treating [RuCl3⋅H2O] with the
corresponding Schi base in an equal mole ratio in alcohol
as depicted in the Scheme . All the complexes are dark-
green and sparingly soluble in general organic solvents but
soluble in polar aprotic solvent such as DMF and DMSO;
the melting point analysis showed that the Ru(III) complexes
were decomposing before melting. e physicoanalytical
data collected for the compounds are in agreement with
the structural formulae proposed, thus conrming the sug-
gested mononuclear composition for the Ru(III) complexes
(Scheme ).
3.2. Molar Conductivity Measurements. e molar conduc-
tance of the synthesized Ru(III) complexes was measured
in DMF at −3 Msolution.evalueswerefoundtobein
the range of .–. 𝜇Scm−1 suggesting the nonelectrolytic
nature of the complexes in solution [, ].
3.3. Infrared Spectra. Valuable evidence concerning the envi-
ronment of the functional group attached to the ruthenium
atom has been obtained from the FTIR spectra. e IR
spectra of the ligands, when compared with those of the
newly synthesized complexes, conrm the coordination of
N2O type tridentate ligands to the ruthenium ion. e
classication was achieved by comparing the spectra of the
ligands with those originating from the coordination between
ruthenium(III) metal ion and the active sites. e Schi
bases showed the broad bands in the – cm−1 range
attributable to the ](OH) cm−1 vibration. Ligand infrared
spectra showed that a band at – cm−1 is attributed to
](C=N) stretching of the azomethine group based on earlier
reports []. is ](C=N) shi to – cm−1 in all the
complexes by about – cm−1 signies the participation of
azomethine nitrogen in the coordination sphere with the
ruthenium(III) ion for all the complexes [, ]. A medium
band that corresponds to phenolic oxygen atom ](C-O) is
observed at and cm−1 for the free ligands.
e higher shiing of ](C-O) stretching vibrations as
observed in the ruthenium(III) complexes spectra suggests
that the phenolic OH group of Schi base, DAE, HME,
MBE, and DEE, is involved in coordination with ruthenium
ion aer deprotonation [, ]. Seemingly, the DAE, HME,
MBE, and DEE ligands act as a tridentate chelating com-
pound, coordinating to the metal ion via the two nitrogen
atoms of the azomethine group as well as O atom of phenolic
group [, ]. is is further supported by the displacement
of ](O-H)intherange–cm
−1 in all the complexes.
e presence of coordinated water gave a broad band that
appeared in the regions – and – cm−1;thiscan
be due to ](O-H) stretching and ](O-H) rocking vibrations,
respectively, which further conrms the presence of nonli-
gand assignable to the rocking mode of water [, ]. New
weak nonligand bands that are not found in the DAE, HME,
MBE, and DEE ligands appeared in the ranges – cm−1
and – cm−1 in the complexes spectra attributed to
](Ru-N) and ](Ru-O)vibrations,respectively[,].Aband
ranging from – cm−1 appeared in the spectra of the
Ru(III)-Schi base complexes indicating the presence of two
chloride ions in trans position around ruthenium centre [–
].
3.4. Electronic Absorption Spectra Studies. e UV-Vis spec-
tra of the Ru(III)-Schi base complexes in DMF solutions
were recorded at room temperature ranging from to
nm. e nature of DAE, HME, MBE, and DEE ligands
eld around the ruthenium ion was obtained from the
electronic spectra. e free ligands showed absorption bands
within the range of – nm attributable to 𝜋∗←𝜋and
𝜋∗←𝑛transitions relating the benzene ring (Figure ). e
shiing of these bands in the complexes spectra followed the
participation of the imine group nitrogen and phenolic group
oxygen in bonding [, ]. Ground state of ruthenium(III) is
2T2g, where initial excited doublet levels in order of increasing
Bioinorganic Chemistry and Applications
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
260 320 380 440 500 560 620 680
Absorbance (a.u.)
Wavelength (nm)
(a)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
260 320 380 440 500 560 620 680
Absorbance (a.u.)
Wavelength (nm)
(b)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
260 320 380 440 500 560 620 680
Absorbance (a.u.)
Wavelength (nm)
(c)
0
0.1
0.2
0.3
0.4
260 320 380 440 500 560 620 680
Absorbance (a.u.)
Wavelength (nm)
(d)
F : Electronic absorption spectra of the Ru(III) complexes: (a) [Ru(DAE)Cl2(H2O)]; (b) [Ru(HME)Cl2(H2O)]; (c)
[Ru(MBE)Cl2(H2O)]; (d) [Ru(DEE)Cl2(H2O)].
energy are 2A2gand 2T1g,arisingfromt
4
2ge1
gconguration
[].
Ru3+ ion, with a d5electronic conguration, possesses
high oxidizing properties and large crystal eld parameter.
Also,chargetransferbandsofthetypeL
𝜋y→T2gwere
noticeable within low energy region, obscuring weaker bands
that is due to d-d transitions [, ]. e extinction coef-
cient bands around – nm regions are found to be
low when compared to the charge transfer bands. ese
bands have been assigned to 2T2g→2A2gtransition and
areinagreementwiththeassignmentmadeforsimilar
octahedral ruthenium(III) complexes [, ]. Absorption
bands within the – nm regions were assigned to the
charge transfer transitions [, ]. Overall, the absorption
spectra of the Ru(III)-Schi base complexes are typical of
octahedral environment about the ruthenium(III) ions [].
3.5. Antiproliferative Activity. Investigation into the struc-
ture-activity relationship of the isolated Ru(III)-N2OSchi
base complexes with respect to dierent functional groups
on the ligands used for ruthenium ion complex formation
has been conducted via antiproliferative studies. ree of the
Ru(III)-Schi base compounds alongside parthenolide were
subjected to cell lines tests at dierent sample concentrations
ranging from . to 𝜇M towards renal cancer cell (TK-
), melanoma cancer cell (UACC-), and breast cancer
cell (MCF-). e cancer cell lines were incubated for h,
followed by the addition of the compounds of various
concentrations via Sulforhodamine B (SRB) assay [].
e ruthenium(III) compounds and standard drug
(parthenolide) IC50 values are presented in Table and
revealed that the test samples showed signicant inhibition
against the tested cell lines. Figures – represent the cell
viability percentages of ruthenium(III)-Schi base complexes
and parthenolide drug against TK-, UACC-, and MCF-
cell lines, at dierent concentrations of ruthenium(III)
compounds or parthenolide. A high level of antiprolifera-
tive potentials against the studied cell lines was exhibited
by parthenolide in accordance with earlier reports [].
e obtained results revealed that treatment of cell lines with
Bioinorganic Chemistry and Applications
T : In vitro antiproliferative studies of Ru(III)-Schi base complexes against TK-, UACC-, and MCF- cell lines.
Compounds Molecular formula Anticancer activity IC50 (𝜇M) h
TK- UACC- MCF-
[Ru(DAE)Cl2(H2O)]C18H24N3O4RuCl29.06 ± 1.18 6.44 ± 0.38 3.57 ± 1.09
[Ru(HME)Cl2(H2O)]C18H23N2O6RuCl241.09 ± 4.44 6.31 ± 1.47 4.88 ± 1.28
[Ru(DEE)Cl2(H2O)]C17H20N2O4RuCl313.10 ± 2.81 5.14 ± 1.09 3.43 ± 1.48
Parthenolide∗C15H20O30.50 ± 1.43 0.89 ± 2.18 0.44 ± 2.02
∗Standard cytotox in drug: cell lines were tre ated with d ierent concentrations of the compounds to achieve %i nhibition of the culture growt h when cultured
for h. Value represents mean ±SD of three independent experimentations.
0
20
40
60
80
100
0.01
0.1
1
10
100
% cell viability
[Parthenolide]
Concentration (𝜇M)
[Ru(DAE)Cl2(H2O)]
[Ru(HME)Cl2(H2O)]
[Ru(DEE)Cl2(H2O)]
F : In vitro antiproliferative activity of Ru(III) complexes and
parthenolide against human breast cancer cell line (MCF-).
dierent concentrations of Ru(III)-Schi base complexes e-
ciently aected cell viability towards MCF- cells, as displayed
in Figures – and Table . e Ru(III) compounds exhibited
low to strong in vitro antiproliferative activities against
the selected cell lines as compared to the standard drug
(parthenolide). [Ru(DAE)Cl2(H2O)], [Ru(HME)Cl2(H2O)],
and [Ru(DEE)Cl2(H2O)] induced more ecient cell death
with IC50 values of 3.57±1.09,4.88±1.28,and3.43±1.48 𝜇M,
respectively, towards human breast cancer cell (MCF-) cells
than other investigated cell lines, compared with IC50 values
of 0.44 ± 2.02𝜇M MCF-, for the standard cytotoxin drug
parthenolide.
e order of activity of the complexes against
human melanoma cancer cell (UACC-) is as
follows: [Ru(DEE)Cl2(H2O)] >[Ru(HME)Cl2(H2O)] >
[Ru(DAE)Cl2(H2O)]. With respect to previous report by
Shier [], compounds exhibiting IC50 activity ranging from
to 𝜇M are referred to as weak anticancer drugs, while
those with IC50 action between and 𝜇M are moderate,
and the compounds possessing activity less than (<).𝜇M
0
20
40
60
80
100
0.01
0.1
1
10
100
% cell viability
[Parthenolide]
Concentration (𝜇M)
[Ru(DAE)Cl2(H2O)]
[Ru(HME)Cl2(H2O)]
[Ru(DEE)Cl2(H2O)]
F : In vitro antiproliferative activity of Ru(III) complexes and
parthenolide against human melanoma cancer cell (UACC-).
are considered as strong agents. us, the Ru(III) complexes
exhibited a weak to strong activity against the investigated
cancer cell lines with the following order of activity: MCF-
>UACC- >TK-. However, [Ru(DAE)Cl2(H2O)]
showed the highest antiproliferative activity with IC50
valves of 3.57 ± 1.09,6.44 ± 0.38,and9.06 ± 1.18 𝜇Mfor
MCF-, UACC-, and TK-, respectively. e biochemical
activitycouldbeduetothemethoxy,alkyl,chloridegroup
substituents and bridge spacer: ethylenediamine, which
couldhaveplayedavitalroleinantiproliferativepotentials
of the Ru(III)-N2O Schi base complexes. In vitro anticancer
activity of the synthesized Ru(III) complexes in this study
was compared with Ru complexes reported by other authors
and found that [Ru(DAE)Cl2(H2O)], [Ru(HME)Cl2(H2O)],
and [Ru(DEE)Cl2(H2O)] complexes exhibited higher
antitumor activities. [RuCl(CO)(PPh3)L] reported by Raja et
al. [] against human cervical carcinoma cell line, (HeLa)
aer exposure for h, gave an IC50 valueintherangeof
. 𝜇Mand[RuCl
2(AsPh3)L] with an IC50 value of . 𝜇M
[]. Raju et al. [] reported ruthenium(III) Schi base
complexes of the type [RuX2(PPh3)2(L)] (where X = Cl or
Bioinorganic Chemistry and Applications
0
20
40
60
80
100
0.01
0.1
1
10
100
% cell viability
[Parthenolide]
[Ru(DAE)Cl2(H2O)]
[Ru(HME)Cl2(H2O)]
[Ru(DEE)Cl2(H2O)]
Concentration (𝜇M)
F : In vitro antiproliferative activity of Ru(III) complexes and
parthenolide against human renal cancer cell (TK-).
Br; L = monobasic bidentate ligand) complex to have IC50
valueintherangeof.𝜇M.
3.6. Antioxidant Capacity. Dierent antioxidant techniques
andmodicationshavebeenputforwardtoevaluateantiox-
idants reactivity and functionality in foods and biological
systems as a means of checkmating variety of patholog-
ical activities such as cellular injury and aging process;
thesedamagingoccurrencesarecausedbyfreeradicals.
Hence,twofreeradicalswereusedforin vitro antioxi-
dants activities of the test samples in this study, namely,
,-diphenyl--picrylhydrazyl (DPPH) and ,-azino-bis(-
ethylbenzothiazoline--sulfonic acid) (ABTS).
3.6.1. DPPH Radical Scavenging Assay. e activity of antiox-
idants on DPPH radical is believed to be centred on their
ability to donate hydrogen []. DPPH has been a stable
free radical, with the ability to accept hydrogen radical or an
electron and then become a stable molecule [].
e mode of rummaging the DPPH radical has
extensively been used to appraise antioxidant activities of
test samples in a moderately short period of time compared
to other procedures []. e reduction in the DPPH radical
capability is calculated by the decrease in its absorbance
at nm prompted by antioxidants []. e reduction of
DPPH radical intensity in this study is due to the interaction
of Ru(III) complexes with radical and as such scavenging
the radicals by hydrogen donation (Scheme ). e DPPH
activities by the Ru(III)-N2O Schi base complexes exhibit
strong electron donating power when compared to the
standards: ascorbic acid and rutin as displayed in Figure .
e calculated IC50 and its corresponding 𝑅2(correlation
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500 600
% scavenging activity
DPPH radical scavenging activity
Vit. C
Rutin
Complexes concentrations (𝜇g/mL)
[Ru(DEE)Cl2(H2O)]
[Ru(MBE)Cl2(H2O)]
[Ru(HME)Cl2(H2O)]
[Ru(DAE)Cl2(H2O)]
F : DPPH scavenging potential of Ru(III)-Schi base com-
plexes.
coecient) values of Ru(III) compounds are listed in Table .
Compounds [Ru(DAE)Cl2(H2O)], [Ru(HME)Cl2(H2O)],
[Ru(MBE)Cl2(H2O)], and [Ru(DEE)Cl2(H2O)] with an IC50
value of 1.60±0.68,1.54±0.44,1.63±1.05,and1.51±0.50𝜇M,
respectively, exhibited higher activity against DPPH than
the commercially available Vit. C and rutin (standard);
however, [Ru(DEE)Cl2(H2O)] showed the highest activity of
all investigated ruthenium(III) samples with an IC50 value of
1.51 ± 0.50 𝜇M.
Scavenging ability of the test samples on the
DPPH radical can be ranked in the following order:
[Ru(DEE)Cl2(H2O)] >[Ru(HME)Cl2(H2O)] >
[Ru(DAE)Cl2(H2O)] >[Ru(MBE)Cl2(H2O)] >[Vit. C]
>[rutin]. e scavenging eect of the DAE, HME, MBE, and
DEE ligands is lower as compared to their corresponding
Ru(III) complexes, owing to the coordination of the organic
molecules to the Ru3+ ion. It is further supported by the
observed discolouration from purple DPPH radical solution
to yellow solution showing scavenging of the DPPH radicals
by hydrogen donation (Scheme ). Hence, these complexes
could be eective therapeutic agent’s preparation for the
treatment of chronic conditions such as cardiovascular,
neurodegenerative, and arteriosclerosis diseases [].
3.6.2. 2,2-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)
Radical Scavenging Activity. To further conrm the synthe-
sized Ru(III)-N2O Schi base complexes antiradical poten-
tial, we examined the ABTS assay in this study. A well-known
protonated radical like ,-azinobis--ethylbenzothiazoline-
-sulfonic acid (ABTS) possesses characteristic absorbance
maxima at nm and decreases with the scavenging of the
proton radicals []. e assay measures radical scavenging by
electron donation. e outcome of Ru(III)-N2OSchibase
complexes alongside the standard drugs on ABTS radical is
presented in Table . At nm, the absorbance of active
ABTS∗solution noticeably declined upon the addition of
dierent concentrations of ruthenium(III) samples; the same
trend was also observed for the standard drugs: butylated
Bioinorganic Chemistry and Applications
NNN
H
+
Cl
Cl
NN
O
HO
H
Ru
Cl
Cl
NN
O
H
Ru
+
DPPH radical Reduced DPPH
Antioxidant
OH2OH2
O2N
O2N
O2N
O2N
NO2
H3CH3C
OCH3OCH3
OCH3
OCH3
NO2
517 nm
O
∙
N
∙
S : Conversion of DPPH∗(purple) to its corresponding hydrazine form (yellow) by the addition of Ru(III) compounds to DPPH∗
due to proton transfer.
T : Radical scavenging abilities (IC50 ±SD, 𝜇M) of Ru(III)-Schi base complexes and standard drugs.
Compounds DPPH radical scavenging activity ABTS radical scavenging activity
IC50 (𝜇M) 𝑅2IC50 (𝜇M) 𝑅2
Ru(DAE)Cl2(H2O) 1.60 ± 0.68 . 3.30 ± 0.89 .
Ru(HME)Cl2(H2O) 1.54 ± 0.44 . 4.27 ± 1.17 .
Ru(MBE)Cl2(H2O) 1.63 ± 1.05 . 3.30 ± 1.48 .
Ru(DEE)Cl2(H2O) 1.51 ± 0.50 . 3.24 ± 0.93 .
Rutin∗2.52 ± 1.60 . 2.83 ± 1.84 .
Vit. C ∗1.92 ± 1.07 . ——
BHT∗——1.64 ± 1.54 .
𝑛=3,𝑋±SEM; IC50: growth inhibitory concentration; when the inhibition of the tested compounds was %, the tested compound concentration was IC50.
𝑅2: correlation coecient. ∗Standards.
hydroxytoluene (BHT) and rutin hydrate with the percentage
inhibition displayed in Figure .
e ecacy of the tested samples in quenching ATBS∗
radicals in the system was observed at 𝜇g/mL, the lowest
concentration, and Ru(III) complexes exhibited higher ABTS
% inhibition than the standards. [Ru(DEE)Cl2(H2O)] com-
plex exhibited the highest ABTS scavenging activity amongst
the studied ruthenium(III) complexes with an IC50 value
of 3.24 ± 0.93𝜇Mand.𝑅2(correlation coecient) as
listed in Table while complexes of [Ru(DAE)Cl2(H2O)],
[Ru(HME)Cl2(H2O)], and [Ru(MBE)Cl2(H2O)] had an IC50
value of 3.30 ± 0.89,4.27 ± 1.17,and3.30 ± 1.48𝜇M,
respectively.
e ABTS scavenging activity pattern of the complexes
is ranked in the following order: [Ru(HME)Cl2(H2O)]
<[Ru(MBE)Cl2(H2O)] = [Ru(DAE)Cl2(H2O)] <
[Ru(DEE)Cl2(H2O)]. With this result, the antiradical
studies showed that the synthesised Ru(III)-N2OSchibase
complexes may be useful in developing therapeutic agent
for averting cell oxidative damage and as radicals chain
terminator. is is because various free radicals generated in
the system oen lead to cancer, cellular injury, aging process,
and cardiovascular diseases [].
4. Conclusion
In this study, we present the synthesis of Ru(III) Schi base
complexes formulated as [Ru(LL)Cl2(H2O)] (LL = DAE,
HME, MBE, and DEE). e complexes were character-
ized using the microanalytical, conductance, electronic, and
vibrational spectral analysis. FTIR spectral data showed that
the ligand acts as tridentate chelating ligand, coordinating
through azomethine nitrogen and phenol oxygen atom.
e microanalyses were in conformity with the proposed
structures. Conductance measurements showed the com-
plexes to be nonelectrolytes in DMF. Octahedral structures
were assigned to these complexes based on the elemental
and spectral information. In vitro antiproliferative studies
of the Ru(III) complexes gave a weak to strong inhibition
against the studied cancer cell lines, with the following
activity order: MCF- >UACC- >TK-. Signicantly,
Bioinorganic Chemistry and Applications
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500
ABTS % inhibitor
ABTS radical scavenging activity
Rutin
BHT
Complexes concentrations (𝜇g/mL)
[Ru(DEE)Cl2(H2O)]
[Ru(MBE)Cl2(H2O)]
[Ru(HME)Cl2(H2O)]
[Ru(DAE)Cl2(H2O)]
F : ABTS rummaging activity of Ru(III)-Schi base com-
plexes.
further investigation on the compounds free radical scav-
enging properties revealed that Ru(III)-Schi base complexes
possessed considerable antioxidant activities. e outcome
from DPPH and ABTS inhibition studies revealed that the
compounds are procient in donating electron or hydrogen
atom and subsequently terminate the chain reactions in
a dose-dependent pattern. Scavenging ability of the test
samples on the DPPH radicals can be ranked in the fol-
lowing order: [Ru(DEE)Cl2(H2O)] >[Ru(HME)Cl2(H2O)] >
[Ru(DAE)Cl2(H2O)] >[Ru(MBE)Cl2(H2O)]. us, Ru(III)-
N2O Schi base complexes showed stronger inhibition of
DPPH at various concentrations.
Competing Interests
No conict of interests regarding the publication of this paper
is declared by the authors.
Acknowledgments
e authors acknowledge Govan Mbeki Research and Devel-
opment Centre (GMRDC), University of Fort Hare, for
nancial support and IPE acknowledges National Research
Foundation and Sasol Inzalo Foundation for the award of
Ph.D. scholarship.
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