Structural characterization and cytotoxicity studies of ruthenium(II)-dmso-chloro complexes of chalcone and flavone derivatives

Article abstract of DOI:10.1016/j.poly.2009.11.012

A synthetic precursor cis-[Ru^IICl₂(dmso)₄] is complexed separately with 3-(4-benzyloxyphenyl)-1-(2-hydroxylphenyl)-prop-2-en-1-one (L¹H) and 2-(4-benzyloxyphenyl)-3hydroxy-chromen-4-one (L²H). The resulting complexes are assigned the composition fac-[RuCl(S-dmso)₃(L¹)] 1 and fac-[RuCl(S-dmso)₃(L²)] 2 using elemental analyses, FAB mass data and spectroscopic (IR, ¹H NMR, UV-Vis, emission) spectral properties. The X-ray diffraction analysis shows that complexes self-associate through non-covalent interactions and provide 1D and 2D supramolecular structures. These complexes are assayed for their cytotoxicity studies on Dalton Lymphoma cell lines.

Full text of DOI:10.1016/j.poly.2009.11.012

Polyhedron 29 (2010) 1055–1061
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structural characterization and cytotoxicity studies of ruthenium(II)–dmso–chloro
complexes of chalcone and flavone derivatives
Rishikesh Prajapati a, Santosh Kumar Dubey a, Ruchi Gaur a, Raj Kumar Koiri b, Brajesh Kumar Maurya b,
Surendra Kumar Trigun b, Lallan Mishra a,
*
a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India
b Biochemistry and Molecular Biology Section, Centre of Advanced Studies in Zoology, Banaras Hindu University, Varanasi 221 005, India
a r t i c l e i n f o
a b s t r a c t
A synthetic precursor cis-[RuIICl2(dmso)4] is complexed separately with 3-(4-benzyloxyphenyl)-1-(2-
hydroxylphenyl)-prop-2-en-1-one (L1H) and 2-(4-benzyloxyphenyl)-3hydroxy-chromen-4-one (L2H).
The resulting complexes are assigned the composition fac-[RuCl(S-dmso)3(L1)] 1 and fac-[RuCl(S-
dmso)3(L2)] 2 using elemental analyses, FAB mass data and spectroscopic (IR, 1H NMR, UV–Vis, emission)
spectral properties. The X-ray diffraction analysis shows that complexes self-associate through non-cova-
lent interactions and provide 1D and 2D supramolecular structures. These complexes are assayed for
their cytotoxicity studies on Dalton Lymphoma cell lines.
Article history:
Received 16 September 2009
Accepted 13 November 2009
Available online 20 November 2009
Keywords:
Chalcone and flavone
Ru(II) complexes
Single crystal X-ray
Cytotoxic assay
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
phenyl)-4-1-benzopyran-4-one]-1 possess potential therapeutic
activities hence are considered leading synthetic targets in the re-
Ruthenium complexes introduced almost two decades ago for
antitumor therapy have great potential as alternative drugs to cis-
platin in view of their low toxicity and good selectivity for solid tu-
mor metastasis [1–4]. Among several synthetic ruthenium-based
anticancer agents, ruthenium–dmso complexes are believed to
have great potential owing to their selectivity for solid tumor
metastases and low toxicity against host [5]. Among the coordina-
tion complexes of ruthenium–chloro–dmso containing heterocyclic
ligands viz. NAMI, Na[trans-RuCl4(S-dmso)(im)] (dmso = dimethyl
sulfoxide; im = imidazole) [6] and NAMI-A, [Him][trans-RuCl4(S-
dmso)(im)] [7] have proved their potential candidature as drug in
the treatment of cancer cells. Moreover, NAMI-A successfully fin-
ished a Phase I clinical trial. It is worth to mention that in contrast
to cisplatin and other platinum based compounds, biological testing
of ruthenium–dmso compounds have indicated that DNA is not the
only responsible target for their antimetastatic activity [8,9].
Additionally, chalcones and flavones are reported to exhibit a
wide spectrum of biological activities, which include potential
applications as new drugs, and agrochemicals [10–12]. Compounds
such as 40-ethoxy-20-hydroxy-4,60-dimethoxy chalcone and 40,6-
dichloroflavone interact directly with viral capsid proteins causing
their uncoating and subsequently liberating viral RNA. Flavone
derivatives especially [5,7-dihydroxy-2-(3-hydroxy-4-methoxy
search area of medicinal chemistry [13].
Several metal complexes from our laboratory have already been
reported as cytotoxic [14] in vitro as well as in vivo inducing apop-
tosis in Dalton’s Lymphoma (DL) cells [15]. Thus in persuasion of
our studies on cytotoxic ruthenium complexes, attempts are made
to complex a representative chalcone (L1H) and flavone (L2H) with
well known precursor cis-[Ru(dmso)4Cl2] in anticipation to substi-
tute its either two dmso or a dmso and a Cl substituent. The result-
ing complexes fac-[RuCl(S-dmso)3(L1)]
1
and fac-[RuCl(S-
dmso)3(L2)] 2, are structurally characterized. The preliminary level
in vitro anticancer screening of these complexes using MTT assay
on DL cell lines is also described. The DL cell lines have been chosen
as tumor model in view of their successful applications for other
anticancer drugs like cisplatin [16–18].
2. Experimental
2.1. Materials and methods
Starting materials were purchased from Sigma–Aldrich and
used without further purification. Compounds were analyzed for
C, H, N measurements from Central Drug Research Institute, Luc-
know, India whereas Infrared, UV–Vis and luminescence spectra
were recorded on VARIAN 3100 FTIR, Shimadzu UV-1601 and
Perkin–Elmer LS-45 spectrophotometer, respectively. However,
1H NMR spectra were recorded on JEOL AL 300 MHz spectrometer
* Corresponding author. Tel.: +91 542 6702449; fax: +91 542 2368174.
E-mail address: lmishrabhu@yahoo.co.in (L. Mishra).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.11.012

1056
R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
using TMS as internal reference. The starting material cis-
[RuIICl2(dmso)4] was prepared from RuCl3ꢀ3H2O using reported
procedure [19].
culture medium, were added in 48 and 72 h experimental sets
for all the compounds separately. The final concentration of dmso
was 0.01% in each well. A separate well containing 0.01% dmso
only was run also as dmso control.
Cell growth was determined by the 3-(4,5-dimethylthiazol-2-
yl)-2,5-diphenyltetrazolium bromide (MTT) assay, which is based
on ability of the viable cells to reduce a soluble yellow tetrazolium
salt to a blue formazan crystals [24,25]. Briefly, after 48 and 72 h of
the treatment, the MTT dye (10 ll/100 ll of medium), prepared in
phosphate buffered saline (PBS) was added to all the wells. The
plates were then incubated for 4 h at 37 °C, medium was discarded
and 100 ll of dmso was added to each well. Optical density was
measured at 570 nm. Percent of viable cells are determined by tak-
ing the cell counts in the untreated sets as 100%. By the help of
semi logarithmic dose-response plots, constructed using GRAPHPAD
PRISM5 software [26], the IC50 values were determined as concentra-
tion of the compound that inhibited DL cell growth by 50%.
2.2. X-ray crystallographic studies
Suitable X-ray quality crystals of the complexes 1 and 2 were
grown from dichloromethane/petroleum ether (40–60 °C) solvent
mixture at room temperature, and X-ray crystallographic data are
recorded by mounting
a
single-crystal of complex
1
(0.33 ꢁ 0.26 ꢁ 0.21) mm3 and complex
2
(0.33 ꢁ 0.29 ꢁ 0.27)
mm3 on glass fibers. Oxford diffraction XCALIBUR-S CCD area detec-
tor diffractometer equipped with an LN-2 low-temperature attach-
ment was used for the cell determination and intensity data
collection. Appropriate empirical absorption corrections were ap-
plied using multi-scan programs. Monochromated Mo Ka radiation
(k = 0.71073 Å) was used for the measurements. The crystal struc-
tures were solved by direct methods and refined by full matrix least
squares SHELXL-97 [20]. Drawings were carried out using MERCURY
[21], DIAMOND [22] and special computations were carried out with
PLATON [23] Pertinent crystallographic data are presented in Table
1 whereas important bond lengths and bond angles for complexes
1 and 2 are listed in Table 2.
2.4. Preparation of 3-(4-benzyloxyphenyl)-1-(2-hydroxylphenyl)-
prop-2-en-1-one (L1H) and 2-(4-benzyloxyphenyl)-3hydroxy-
chromen-4-one (L2H)
The synthetic details for the preparation of chalcone (L1H) and
flavones derivative (L2H) is described by us elsewhere [27].
2.3. In vitro cytotoxicity assay experiment
2.5. Synthesis of fac-[RuCl(S-dmso)3(L1)] 1
The cell toxicity in vitro The DL (Dalton’s Lymphoma: a trans-
plantable T cell lymphoma) cells were collected from the mouse
ascite as described earlier [15]. The viable DL cells, determined
by trypan blue exclusion test, were seeded onto 96 well plates in
A methanolic solution (30 cm3) of cis-[RuIICl2(dmso)4] (484 mg,
1 mmol) was added dropwise to a solution of L1H (330 mg,
1 mmol) in methanol (25 mL) containing equimolar NEt3, while
stirring was continued for 12 h at room temperature. The red crys-
talline solid thus obtained was filtered and washed with methanol
followed by diethyl ether and then dried in vacuo. Yield: 0.419 g
(60%). M.p.: >200 °C. Anal. Calc. for C28H35O6S3ClRu: C, 48.0; H,
5.0; S, 13.7. Found: C, 48.4; H, 5.1; S, 13.6%. FAB-MS: m/z: 700
100 ll of the RPMI-1640 culture medium supplemented with
10% fetal bovine serum and allowed to grow in a CO2 incubator
with 5% CO2 at 37 °C. Stock solutions of test compounds were pre-
pared in DMSO. After 24 h incubation, different concentrations
(10ꢂ7–10ꢂ3 M) of the compounds, made by serial dilutions in the
Table 1
Summary of crystallographic data for complexes 1 and 2.
Parameters
1
2
CCDC deposition number
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
656402
C28H35ClO6RuS3
700.26
150(2)
triclinic
650283
C28H33ClO7RuS3
714.24
150(2)
monoclinic
P21/n
15.549(14)
12.132(2)
17.028(6)
90.00
ꢀ
P1
8.323(16)
12.323(15)
15.269(3)
b (Å)
c (Å)
a
(°)
81.06(13)
b (°)
89.87(16)
73.09(14)
1478.80(4)
2, 1.573
0.873
107.30(2)
90.00
2259.77(14)
4, 1.547
0.846
1464
c
(°)
Volume (Å3)
Z, calculated density (mg mꢂ3
)
)
Absorption coefficient (mmꢂ1
F(0 0 0)
720
Reflections collected/unique
Data/restraints/parameters
Rint
13880/5182
5182/0/358
0.0390
19101/5394
5394/0/367
0.0588
Index ranges
ꢂ9 ꢃ h ꢃ 9
ꢂ14 ꢃ k ꢃ 14
ꢂ18 ꢃ l ꢃ 18
3.45–25.00
99.7
0.8380 and 0.7616
Full-matrix, least squares on F2
0.0371, 0.1038
0.0449, 0.1111
1.061
ꢂ18 ꢃ h ꢃ 18
ꢂ14 ꢃ k ꢃ 14
ꢂ19 ꢃ l ꢃ 20
3.02–25.00
99.8
h Range for data collection (°)
Completeness to h = 25.00 (%)
Maximum and minimum transmission
Refinement method
Final R indices [I > 2
R indices (all data) R1, wR2
0.8038 and 0.7677
r(I)] R1, wR2
0.0340, 0.0639
0.0752, 0.0722
0.848
0.455 and ꢂ0.316
Goodness-of-fit (GOF)
Largest differences in peak and hole (e Åꢂ3
)
0.832 and ꢂ0.932

R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
1057
Table 2
Selected bond lengths (Å) and bond angles (°) for complexes 1 and 2.
Compound 1
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–S(1)
Ru(1)–S(3)
Ru(1)–S(2)
Ru(1)–Cl(1)
O(1)–C(1)
O(2)–C(7)
C(8)–C(9)
S(1)–O(3)
2.026(2)
2.061(2)
2.246(10)
2.255(10)
2.266(9)
2.404(9)
1.296(4)
1.261(4)
1.329(5)
1.477(3)
O(1)–Ru(1)–O(2)
O(2)–Ru(1)–S(1)
O(2)–Ru(1)–S(3)
O(1)–Ru(1)–S(2)
S(1)–Ru(1)–S(2)
O(1)–Ru(1)–Cl(1)
S(1)–Ru(1)–Cl(1)
S(2)–Ru(1)–Cl(1)
C(13)–O(6)–C(16)
C(1)–C(6)–C(7)
88.93(9)
89.73(7)
173.67(7)
88.30(7)
92.31(3)
86.17(7)
93.11(3)
172.81(3)
119.3(3)
122.8(3)
O(1)–Ru(1)–S(1)
O(1)–Ru(1)–S(3)
S(1)–Ru(1)–S(3)
O(2)–Ru(1)–S(2)
S(3)–Ru(1)–S(2)
O(2)–Ru(1)–Cl(1)
S(3)–Ru(1)–Cl(1)
O(6)–C(16)–C(17)
O(6)–C(16)–C(17)
C(9)–C(8)–C(7)
178.51(7)
85.70(7)
95.59(4)
88.14(7)
95.05(3)
87.16(7)
89.13(3)
111.60(3)
111.6(3)
122.6(3)
Compound 2
Ru(1)–O(4)
Ru(1)–O(5)
Ru(1)–S(1)
Ru(1)–S(3)
Ru(1)–S(2)
Ru(1)–Cl(1)
O(4)–C(7)
2.086(2)
2.098(2)
2.246(10)
2.245(11)
2.275(13)
2.418(13)
1.271(4)
1.354(4)
1.384(5)
1.443(4)
O(4)–Ru(1)–O(5)
O(5)–Ru(1)–S(1)
O(5)–Ru(1)–S(3)
O(4)–Ru(1)–S(2)
S(1)–Ru(1)–S(2)
O(4)–Ru(1)–Cl(1)
S(1)–Ru(1)–Cl(1)
S(2)–Ru(1)–Cl(1)
C(7)–O(4)–Ru(1)
C(13)–O(6)–C(14)
80.69(9)
170.63(7)
92.14(7)
89.08(7)
92.38(4)
84.93(7)
93.35(4)
171.70(4)
111.5(2)
122.9(3)
O(4)–Ru(1)–S(1)
O(4)–Ru(1)–S(3)
S(1)–Ru(1)–S(3)
O(5)–Ru(1)–S(2)
S(3)–Ru(1)–S(2)
O(5)–Ru(1)–Cl(1)
S(3)–Ru(1)–Cl(1)
O(7)–C(22)–C(23)
C(15)–O(5)–Ru(1)
C(19)–O(7)–C(22)
89.94(7)
171.82(7)
97.22(4)
87.30(7)
94.55(4)
86.07(7)
90.68(4)
110.1(4)
109.3(2)
116.0(3)
O(5)–C(15)
C(14)–C(15)
O(7)–C(22)
[M]+, 664 [MꢂCl]+, 587 [MꢂCl-dmso]+, 508 [MꢂCl-2dmso]+. IR (KBr
NEt3 at pH ꢄ9.0. The colour of reaction mixture changes from light
brown to dark reddish brown. The reaction mixture was then stir-
red on a steam bath for 0.5 h. The reddish solution was then re-
duced to one fourth of its initial volume and left at room
temperature for 24 h. The crystalline solid thus obtained was fil-
tered and then washed with methanol followed by diethyl ether
and finally dried in vacuo. Yield: 0.464 g (65%). M.p.: >200 °C. Anal.
Calc. for C28H33O7S3ClRu: C, 47.1; H, 4.6; S, 13.4. Found: C, 47.1; H,
4.5; S, 13.3%. FAB-MS: m/z: 715 [M+1], 679 [MꢂCl]+, 602 [MꢂCl-
pellet, cmꢂ1): 3016(m)
t(C–H), 1606(s) t(C@O), 1096(s) t(S@O),
426(m)
t
(Ru–S). 1H NMR (CDCl3, d ppm): 5.12 (s, 2H; OCH2),
3.09–3.55 (m, 18H; dmso), 7.76 (s, 2H; HC@CH), 6.52–7.74 (m,
13H; phenyl). UV–Vis (dmso, 10ꢂ4 M): kmax (nm) (emax Mꢂ1 cmꢂ1
)
234 (39800), 364 (37800), 498sh (8400). Emission at kex 498 nm
(dmso, 10ꢂ4 M): non-emissive.
2.6. Synthesis of fac-[RuCl(S-dmso)3(L2)] 2
dmso]+, 524 [MꢂCl-2dmso]+. IR (KBr pellet, cmꢂ1): 3034(m)
t(C–
H), 1605(s)
t
t(C@O), 1107(s) t(C–O–C), 1080(s) t(S@O), 428(m)
This complex was also prepared using procedure similar to that
used for complex 1 by the addition of a methanolic solution of cis-
[RuIICl2(dmso)4] (484 mg, 1 mmol) (25 mL) to a solution of L2H
(344 mg, 1 mmol) in methanol containing equimolar amount of
(Ru–S). 1H NMR (dmso-d6, d ppm): 5.16 (s, 2H; OCH2), 7.07–
8.65 (m, 13H; phenyl), 3.16–3.69 (m, 18H; dmso). UV–Vis (dmso,
10ꢂ4 M): kmax (nm) (emax Mꢂ1 cmꢂ1) 228 (31600), 342 (17430),
OH
O
H
+
OCH2Ph
CH3
4-Benzyloxy benzaldehyde
Ethanol
O
2'-Hydroxy acetophenone
NaOH 50%
O
OH
O
fac-[RuCl(S-dmso)3(L1)] 1
NEt3/cis-[RuCl2(dmso)4]
L1H
Ethanol
+
MeOH
fac-[RuCl(S-dmso)3(L2)] 2
NaOH 10%/
H2O2 30%
O
O
L2H
OH
O
Scheme 1. Synthesis of ligands (L1H and L2H) and their complexes (1 and 2).

1058
R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
469sh (16200). Emission at kex 469 nm (dmso, 10ꢂ4 M): kmax (nm)
(intensity in a.u.) 531 (24.1).
respectively. Another peak observed at 1110 cmꢂ1 is assigned to
(C–O–C) vibration [28].
The
(C@O) vibration observed at 1606 and 1605 cmꢂ1 in the IR
t
t
spectra of complexes 1 and 2, respectively show that C@O group of
the corresponding ligand had coordinated to Ru(II) ion. However,
3. Result and discussion
no peak due to t(O–H) is observed in corresponding IR spectra of
complexes. Thus, it may be considered that OH group is deproto-
3.1. Structural characterization
nated during coordination with the metal ion. Additional peaks ob-
Synthetic routes for the preparation of ligands and their Ru(II)
complexes are depicted in Scheme 1. The complexes are found
air stable and soluble in organic solvents such as acetonitrile,
dimethylformamide (dmf), dimethyl sulfoxide (dmso) and dichlo-
romethane (dcm). Electrical conductivity of the complexes mea-
sured in dmso (10ꢂ3 M) solution shows that complexes are non-
electrolyte in nature. The IR spectrum of L1H displays characteristic
served at 1100–1050 and 425–430 cmꢂ1 are assigned to
t
(S@O)
and
t(Ru–S) vibrations [29], respectively. The structures of com-
plexes are further supported by their 1H NMR spectral data. The
1H NMR spectrum of complex 1 shows peaks at d (ppm) 5.12 (s,
2H; OCH2), 3.09–3.55 (m, 18H; dmso), 7.76 (s, 2H; HC@CH),
6.52–7.74 (m, 13H; phenyl). No peak corresponding to phenolic
OH group is observed in the spectra of both the complexes 1 and
2. Hence it again supports that deprotonated OH group had coordi-
nated with Ru(II) ion. Additional peaks observed in 1H NMR
peaks at 3450 and 1637 cmꢂ1 assigned to
tions, respectively. However, L2H shows sharp and strong peaks at
3441 and 1607 cmꢂ1 assigned as
(OH) and (C@O) vibrations,
t(OH) and t(C@O) vibra-
t
t
Fig. 1. ORTEP view of complexes 1 (a) and 2 (b), with atom numbering scheme and thermal ellipsoids drawn at the 50% probability level. H-atoms have been removed for
clarity.
Table 3
Selected parameters for weak interactions in complexes 1 and 2.
D–Hꢀ ꢀ ꢀA (Å)
D–H (Å)
Hꢀ ꢀ ꢀA (Å)
Dꢀ ꢀ ꢀA (Å)
DHA (°)
Symmetry code
Compound 1
C(9)–H(9)ꢀ ꢀ ꢀO(2)
0.93
0.93
0.93
0.93
0.93
0.96
0.96
0.96
0.96
0.96
0.96
2.38
2.46
2.54
2.49
2.52
2.76
2.53
2.25
2.43
2.80
2.41
2.724(4)
3.386(4)
3.404(4)
3.266(4)
3.440(5)
3.625(4)
3.142(5)
3.057(5)
3.172(4)
3.376(5)
2.922(5)
102
171
155
141
170
151
121
141
134
120
113
–
C(12)–H(12)ꢀ ꢀ ꢀO(4)
C(14)–H(14)ꢀ ꢀ ꢀO(3)
C(18)–H(18)ꢀ ꢀ ꢀO(3)
C(20)–H(20)ꢀ ꢀ ꢀO(4)
C(23)–H(23B)ꢀ ꢀ ꢀCl(1)
C(25)–H(25A)ꢀ ꢀ ꢀO(3)
C(25)–H(25B)ꢀ ꢀ ꢀO(5)
C(26)–H(26A)ꢀ ꢀ ꢀO(5)
C(28)–H(28B)ꢀ ꢀ ꢀCl(1)
C(28)–H(28C)ꢀ ꢀ ꢀO(1)
ꢂx, 1 ꢂ y, ꢂz
1 ꢂ x, ꢂy, ꢂz
1 ꢂ x, ꢂy, ꢂz
x, y, ꢂ1 + z
ꢂx, ꢂy, ꢂz
–
–
ꢂx, ꢂy, 1 ꢂ z
–
–
Compound 2
C(1)–H(1A)ꢀ ꢀ ꢀO(1)
C(1)–H(1B)ꢀ ꢀ ꢀO(4)
C(3)–H(3B)ꢀ ꢀ ꢀO(3)
C(3)–H(3C)ꢀ ꢀ ꢀO(1)
C(4)–H(4A)ꢀ ꢀ ꢀO(5)
C(6)–H(6B)ꢀ ꢀ ꢀCl(1)
C(11)–H(11)ꢀ ꢀ ꢀO(1)
C(12)–H(12)ꢀ ꢀ ꢀO(3)
C(17)–H(17)ꢀ ꢀ ꢀO(5)
C(20)–H(20)ꢀ ꢀ ꢀO(2)
C(21)–H(21)ꢀ ꢀ ꢀO(6)
C(24)–H(24)ꢀ ꢀ ꢀO(7)
0.96
0.96
0.96
0.96
0.96
0.96
0.93
0.93
0.93
0.93
0.93
0.93
2.55
2.36
2.31
2.47
2.49
2.72
2.33
2.57
2.28
2.53
2.26
2.38
3.487(5)
2.873(5)
3.093(5)
3.153(5)
2.999(4)
3.382(5)
3.217(5)
3.439(5)
2.924(4)
3.427(5)
2.630(5)
2.736(6)
165
113
138
128
113
127
158
156
126
161
103
102
ꢂx, 1 ꢂ y, 1 ꢂ z
–
–
–
–
–
x, ꢂ1 + y, z
x, ꢂ1 + y, z
–
1 ꢂ x, ꢂy, 1 ꢂ z
–
–

R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
1059
spectrum of complex 2 are assigned at d 5.16 (s, 2H) OCH2, 7.07–
8.65 (m, 13H) phenyl and at d 3.16–3.69 ppm (m, 18H) are methyl
protons of dmso.
In the UV–Vis spectra, the peaks are observed at kmax 234, 364,
498 nm and 228, 342, 469 nm (Fig. S1, Supplementary Informa-
tion). These peaks are assigned to intra-ligand and MLCT transi-
tions, respectively. The MLCT transition of complex 1 occurs at
lower energy as compared to its position in complex 2. This could
be considered owing to highly conjugated skeleton of the ligand
present in the complex 1.
bio-molecules. The bond distances varies as (Ru–Cl) > (Ru–
S) > (Ru–O). The C1–O1–Ru1–O2–C7 atoms lie in same plane. How-
ever, C1–C6 and C17–C22 rings are bent towards C10–C15 ring
with a dihedral angle of 10.5(5)° and 76.4(2)°, respectively. Benzyl
ring is almost perpendicular to C10–C15 ring. The two oxygen
atoms of ligand are bonded to Ru(II) centre at distances Ru(1)–
O(1) 2.026(2) Å and Ru(1)–O(2) 2.061(2) Å which are found in con-
sistence with the reported values [31,32]. Additionally, Ru–S dis-
tance varies from 2.246(10) to 2.266(9) Å whereas, Ru–Cl bond
length is found to be 2.404(9) Å which are again consistent with
the values reported for cis-[RuCl2(dmso)4] complex [33].
The crystal packing behaviour of the complex 1 consists of 2D
layered structure along the crystallographic [0 1 0] direction
(Fig. 2). The adjacent two Ru(II) centers are separated by a distance
of 8.32(2) Å in the chain. However, the shortest interlayer distance
(calculated between the two ruthenium atom centers between the
adjacent chains) is found as 12.32(2) Å.
PLATON analysis of the structre confirms the presence of eleven
non-conventional hydrogen bonds, out of which; in two cases,
Cl(1) acts as acceptor and is involved in weak intearcation with
H(23B) and H(28B), at Hꢀ ꢀ ꢀA distance of 2.76(2) Å H(23B)–Cl(1)
(intermolecular) and 2.80(2) Å H(28B)–Cl(1) (intramolecular) as
depicted in Fig. 3.
Molecular structure of the complex 2 is depicted in Fig. 1. The
monoclinic crystal contains four discrete complex molecules and
are arranged in a chain and showing no solvent accessible voids
in the packing of this complex. However, Kitaigorodskii packing in-
dex [30] is found 67.2% with the presence of 4 grid points. The
weaker force study using PLATON programme indicates that 12
non-conventional H-bonds are formed in its packing structure.
These non-conventional bonds involve C–H as H-donor and O as
H-acceptor in most of the cases whereas in one case Cl acts as H-
acceptor.
Thus, on the basis of spectral (IR, 1H NMR) data along with ele-
mental analysis and FAB mass data, the composition of the com-
plexes are assigned as fac-[RuCl(S-dmso)3(L1)] 1 and fac-[RuCl(S-
dmso)3(L2)] 2. However, their molecular structures are further
investigated using their X-ray diffraction data.
The molecular structures along with crystallographic number-
ing schemes of the complexes (1 and 2) are illustrated in Fig. 1. A
computational program PLATON [23] is used to study the involve-
ment of weaker interactions and bond distances data are shown
in Table 3.
Complex 1 crystallizes in a triclinic crystal system with space
ꢀ
group P1. The unit cell contains two discrete molecules; arranged
in a head to tail fashion, extending along the axis. No solvent acces-
sible voids could be seen from its packing behaviour. The Kitaigo-
rodskii packing index [30] is found to be 69.8% with the presence of
6 grid points. The non-classical hydrogen bond (11) distances are
listed in Table 3.
The coordination core (O2S3Cl) consisting of a deprotonated
bidentate ligand (L1; O, O), three dmso (S, S, S) and one chlorine
atom provides a distorted octahedral geometry around Ru(II) ion.
Three S-dmso molecules display facial geometry. Thus, hetero-
coordination core specially of weaker ligands surrounding Ru(II)
ion makes this complex quite interesting in view of the possibility
of making selective substitutions by another ligand especially of
In this complex too, each Ru(II) ion is surrounded by hetero-
coordination core consisting of one chlorine atom, three dmso mol-
ecules (S, S, S) and one deprotonated bidentate (O, O) flavone li-
gand in a distorted octahedral arrangement. Coordinated three S-
dmso molecules are found to be in facial geometry. The distances
Ru(1)–O(4) 2.086(2) to Ru(1)–O(5) 2.098(2) Å, Ru–S 2.246(10)–
2.275(13) Å and Ru–Cl at 2.418(13) Å are found in the range of re-
ported values. The C7–O4–Ru1–O5–C15 are co-planar with the
three phenyl rings while benzyl ring deviate from planarity with
a dihedral angle of 18.4(3)°.
The crystal packing diagram of complex 2 as depicted in Fig. S2
(Supplementary Information) shows that a 1D chain like structure
Fig. 2. Perspective view of 1 along the [0 1 0] direction, showing the 2D layered
structure (H-atoms are omitted for clarity).
Fig. 3. Intermolecular C–Hꢀ ꢀ ꢀCl interaction in 1 (ligand framework are omitted for
clarity).

1060
R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
with Ru(II) centers separated at 19.72(2) Å is formed. The inter
chain Ruꢀ ꢀ ꢀRu distance is found to be 8.54(9) Å.
(as anticipated by their structural difference) in culture when incu-
bation was restricted to 48 h. The complex 1 is found to be the
Thus, both complexes crystallize in different crystal system pro-
viding different mode of packing with different metal–ligand bond
distances. However, it is quite interesting to observe that both
assemble structures are getting stabilized by non-covalent hydro-
gen bonds.
most cytotoxic with IC50 value of 0.319
of compounds 2 and L1H with the IC50 values of 0.816
1.337
M, respectively. Nonetheless, L2H was found to be the least
cytotoxic with the IC50 of >5 M. After 72 h treatment the pattern
of IC50 values of all the compounds show a similar trend, however,
within a very narrow range of 0.032 M for 1 to 0.054
M for L2H.
lM followed by the activity
lM and
l
l
l
l
Similar type of dose and incubation time dependent cytotoxic pat-
tern is also observed when data is presented as percentage of via-
ble DL cells in all experimental sets (Fig. 4).
Some novel dinuclear ruthenium–arene compounds have also
been tested on human ovarian carcinoma (A2780) and colon ade-
nocarcinoma (SW480), however, showing 4–5 times higher IC50
3.2. In vitro cytotoxicity assay
The cell toxicity was measured using MTT assay technique as
this is reported as a reliable method to determine bioactivity of
the compounds [34]. Dalton lymphoma (DL) has been successfully
used earlier to estimate the anticancer potential of a novel Ru(II)
complex both in vitro and in vivo [15]. Therefore, to have a preli-
minary level screening of these newly synthesized compounds,
MTT assay is performed for the evaluation of their anticancer po-
tential on DL cells in vitro. DMSO has been reported to be non-toxic
to the DL cells in vitro [35]. We also performed MTT assay in the
well containing 0.01% dmso and it showed 100% cell viability thus
suggested no toxicity of dmso on DL cells. However, as shown in
Table 4, all the compounds show different responses on DL cells
values than the cytotoxicity of cisplatin (IC50 = 0.33
lM) and oxa-
liplatin (IC50 = 0.40 M) [36]. In vitro cytotoxicity of some ruthe-
l
nium(III) dimethyl sulfoxide pyridinehydroxamic acid complexes
have also been evaluated on KB oral carcinoma cells which after
48 and 72 h of treatment showed IC50 of 246–301
211 M, respectively [37]. The IC50 of another well known antican-
cer compound 5-fluorouracil, tested on the DL cells, has been re-
ported to be 37.4 [38]. Recently, we have reported
lM and 284–
l
l
M
a
concentration dependent cytotoxicity of a Ru(II) complex against
the DL cells [15], however, in comparison, IC50 values of L1H, 1,
L2H and 2 are in the range of micro- to nano-molar concentrations
(Table 4) which is not only much lower than these reported com-
pounds but are also several times lower than the cisplatin and oxa-
liplatin and thus suggesting potent cytotoxicity of the compounds
reported here. Furthermore, the compounds 1 and 2 show lower
IC50 values than those of the corresponding ligands when tested
alone. This suggests that interaction of both the ligands with
Ru(II)-metal centre enhances their anticancer activity in vitro.
Some Ru(II) complexes have also been reported to show their
IC50 in micromolar range [39]. However, in comparison, Ru(II) com-
plexes in the present study show significantly lower IC50 values
Table 4
IC50 values (
incubation.
l
M) of L1H, 1, L2H and 2 on Dalton lymphoma cells after 48 h and 72 h of
Compound
48 h
72 h
Dmso controla
none
1.337
0.319
>5
none
0.034
0.032
0.054
0.042
L1H
1
L2H
2
0.816
a
DL cells incubated with 0.01% dmso, as solvent control, did not produce any
cytotoxicity.
120
100
80
60
40
20
0
0 M
(a)
(b)
10-7
10-6
10-5
10-4
10-3
M
M
M
M
M
L1H
1
L2H
2
120
100
80
60
40
20
0
0 M
10-7
10-6
10-5
10-4
10-3
M
M
M
M
M
L1H
1
L2H
2
Fig. 4. Effect of L1H, 1, L2H and 2 on DL cell viability. DL cells were treated with L1H, 1, L2H and 2 for 48 h (a) and 72 h (b) at the indicated concentrations, and viability was
measured by MTT assay.

R. Prajapati et al. / Polyhedron 29 (2010) 1055–1061
1061
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