Mononuclear indolyldithiocarbamates of SnCl4 and R2SnCl2: Spectroscopic, thermal characterizations and cytotoxicity assays in vitro

Article abstract of DOI:10.1016/j.jorganchem.2007.12.026

Several mononuclear Sn compounds ranging from mono to tetrakisindoline dithiocarbamates have been synthesized and characterized. Various spectroscopic techniques in combination with microanalytical data lead to the formation of 1:2 and 1:4 (Sn:Naindtc) type complexes depending on the molar ratio of the sodium salt of indolinedithiocarbamate employed. A symmetrical bidentate coordination of the indolinedithiocarbamate has been observed in all the cases as evident by a single sharp band at 1000 cm^-1 in their IR spectra. The compounds were found to adopt an octahedral arrangement around the Sn atom as evident from their ¹¹⁹Sn NMR data. The TGA/DSC profile of the ligand exhibits a two-stage thermogram while the complexes decompose in three steps leading to the formation of tin-sulfide as the eventual end product. The in vitro cytotoxicity of butyl and phenyl analogues has been studied against the standard human tumor cell lines. The compounds have also been screened for their antifungal and antibacterial activity against E. coli, S. aureus, C. albicans and A. flavus. The results indicated the compounds to be active.

Full text of DOI:10.1016/j.jorganchem.2007.12.026

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1049–1057
www.elsevier.com/locate/jorganchem
Mononuclear indolyldithiocarbamates of SnCl4
and R2SnCl2: Spectroscopic, thermal characterizations and
cytotoxicity assays in vitro
Sadaf Khan, Shahab A.A. Nami, K.S. Siddiqi *
Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
Received 17 August 2007; received in revised form 17 December 2007; accepted 20 December 2007
Available online 28 December 2007
Abstract
Several mononuclear Sn compounds ranging from mono to tetrakisindoline dithiocarbamates have been synthesized and character-
ized. Various spectroscopic techniques in combination with microanalytical data lead to the formation of 1:2 and 1:4 (Sn:Naindtc) type
complexes depending on the molar ratio of the sodium salt of indolinedithiocarbamate employed. A symmetrical bidentate coordination
of the indolinedithiocarbamate has been observed in all the cases as evident by a single sharp band at 1000 cmÀ1 in their IR spectra. The
compounds were found to adopt an octahedral arrangement around the Sn atom as evident from their 119Sn NMR data. The TGA/DSC
profile of the ligand exhibits a two-stage thermogram while the complexes decompose in three steps leading to the formation of tin-sulfide
as the eventual end product. The in vitro cytotoxicity of butyl and phenyl analogues has been studied against the standard human tumor
cell lines. The compounds have also been screened for their antifungal and antibacterial activity against E. coli, S. aureus, C. albicans and
A. flavus. The results indicated the compounds to be active.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Indoline; Dithiocarbamates; 119Sn NMR; FAB mass spectrometry; Cytotoxicity; TGA/DSC
1. Introduction
types of compounds possessing aminoalkylation ability
showed that substituted aminoethyl N,N-dialkyldithiocar-
bamates have cytostatic features presumably via a similar
mechanism proposed for antibacterial action [8].
Dithiocarbamates owe special significance due to their
wide application as vulcanization additives, stabilizers for
PVC, fungicides, antibacterial and anticancer agents
[1–3]. The recognition of the importance of Sn–S bond in
biology has led to the study of organotin compounds with
dithiocarbamates [4]. They are given importance due to
their use as chemoprotectants in platinum based chemo-
therapy [5]. In particular, thiocarbonyl and thiol donors
have shown promising properties for use in modulating
cis-platin nephrotoxicity [6]. The antibacterial effect of
dithiocarbamates was reported to arise by the reaction of
HS-groups with physiologically important enzymes
by transferring the alkyl group of the dithioester to the
HS-function of the enzyme [7]. Investigations of various
The dithiocarbamate complexes of organotin have gen-
erated interest because of their dual structure and probable
antitumor properties [9]. They are generally toxic even in
minute quantities. Biological activity of such compounds
is mainly dependant on the organic group bound to tin
atom. [Trialkyltin(IV)]+ and [Triaryltin(IV)]+ are found
to be highly toxic to central nervous system albeit the tox-
icity deceases with increasing size of the organic group [10].
Organotin compounds are also known to exert therapeutic
effects on various tumor cells. Dialkyltin(IV) appear to be
most effective probably due to the presence of R2Sn(IV)2+
.
Some of the organotin complexes possess antitumor activ-
ity although their mechanism of action is still unknown
[11]. It has been shown that organotin compounds are
active against two leukemia cell lines [12].
*
Corresponding author. Tel.: +91 9837284930.
E-mail address: khwajas_siddiqi@yahoo.co.in (K.S. Siddiqi).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.026

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S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
Indoline and its derivatives are used in photoactive
ice bath followed by the addition of 10 mL NaOH
(20.0 mmol, 0.8 g) dissolved in aqueous methanol. A shiny
yellow product was obtained on standing the reaction mix-
ture overnight. The product was, thoroughly washed with
water, methanol and dried in vacuo over calcium chloride.
devices and as catalyst for asymmetric syntheses [13,14].
The protecting group on the nitrogen has a strong influence
upon the regiochemistry of indoline reactions [15,16]. Over
one thousand indole containing alkaloids are known, some
of which are used in pharmacology [17].
During the recent years interest has been developed in
evaluating the antimicrobial activity of many indoline deriv-
atives and their dithiocarbamates. A cumulative study of the
synthesis, characterization, antimicrobial and cytotoxic
assays has seldom been done. Transition metal complexes
of monothiocarbamates and dithiocarbamates of indoline
have been synthesized and characterized [18], in no case,
however, their organotin(IV) and SnCl4 derivatives have
been synthesized and antimicrobial properties screened.
In the present project synthesis and characterization of
(CH3)2SnCl2, (C4H9)2SnCl2, (C6H5)2SnCl2 and SnCl4 com-
plexes with indoline dithiocarbamate has been reported.
They have been characterized by FT-IR, NMR, FAB-
MS, TGA/DSC and elemental analysis. Also an attempt
has been made to identify the symmetrical and unsymmet-
rical nature of bonding of the dithiocarbamate. Since the
indoline and dialkyltin(IV) complexes are extensively used
in clinical trials on humans, it was found worth studying
their antitumor activity against the standard human tumor
cell lines. These compounds have also been screened for
their antifungal and antibacterial activity against E. coli,
S. aureus, C. albicans and A. flavus.
2.3. Synthesis of dimethyltin indolinebisdithiocarbamate,
[(CH3)2Sn(indtc)2]
To a stirred solution of the indoline dithiocarbamate
(5 mmol, 1.1 g) in 20 mL of methanol was added
(2.5 mmol, 0.55 g) dimethyltin dichloride in 10 mL of the
same solvent to obtain an immediate precipitation. The
reaction mixture was then stirred for 3 h at room tempera-
ture. The product was separated by filtration, washed with
methanol and anhydrous diethyl ether and dried in vacuo.
2.4. Synthesis of dibutyltin indolinebisdithiocarbamate,
[(C4H9)2Sn(indtc)2]
To a well stirred solution of the ligand (5 mmol, 1.1 g) in
20 mL of methanol was added (2.5 mmol, 0.76 g) dibutyltin
dichloride in 10 mL of the same solvent to obtain an imme-
diate precipitation. The reaction mixture was then stirred
for 3 h at room temperature. The product was filtered,
washed with methanol and anhydrous diethyl ether and
dried in vacuo.
2.5. Synthesis of diphenyltin indolinebisdithiocarbamate,
[(C6H5)2Sn(indtc)2]
2. Experimental
2.1. Materials and methods
To the solution of the ligand (5 mmol, 1.1 g) in 20 mL of
methanol was added (2.5 mmol, 0.86 g) diphenyltin dichlo-
ride in 10 mL of the same solvent to obtain an immediate
precipitation. The product was separated by filtration,
washed with methanol and anhydrous diethyl ether and
dried in vacuo.
Stannic chloride, Organotins (Merck, Across), Carbon
disulfide (Merck) and Indoline (Koch Light) were used as
received. Methanol was distilled and dried before use. Ele-
mental analysis was carried out with a Flash EA-1112 Ana-
lyzer, CE Instrument. IR spectra (4000–200 cmÀ1) were
scanned with CsI on Nexus FT-IR Thermo Nicolet. The
conductivity measurements were carried out with a CM-
82T Elico conductivity bridge in DMSO. TGA/DSC was
performed with a Universal V3.8 B TA SDT Q600 Build
51 Thermal Analyzer under nitrogen atmosphere using alu-
mina powder as reference material. The heating rate was
maintained at 10 °C/min. The FAB mass spectra were
recorded on a JEOL SX 102/Da-6000 Mass Spectrome-
ter/Data System using Argon/Xenon (6 kV, 10 mA) as
the FAB gas. The accelerating voltage was 10 kV and the
spectra were recorded at room temperature. m-Nitro-
benzoyl alcohol (NBA) was used as the matrix.
2.6. Synthesis of dichlorotin indolinebisdithiocarbamate,
[(Cl)2Sn(indtc)2]
To a solution of the ligand (5 mmol, 1.1 g) in 20 mL of
methanol was added (2.5 mmol, 4.49 mL) tin tetrachloride
in 10 mL of the same solvent. This mixture was then stirred
for 3 h at room temperature, which afforded the product. It
was filtered, washed with methanol and anhydrous diethyl
ether and dried in vacuo.
2.7. Synthesis of tin tetrakis indolinedithiocarbamate,
[Sn(indtc)4]
2.2. Synthesis of ligand (Naindtc)
To a well stirred solution of the ligand (5 mmol, 1.1 g) in
20 mL of methanol was added (1.25 mmol, 2.24 mL) tin
tetrachloride in 10 mL of the same solvent to obtain an
immediate precipitation. The product was separated by fil-
tration, washed with methanol and anhydrous diethyl ether
and dried in vacuo.
The ligand was prepared by a modified procedure given
in the literature [17]. To a 40 mL methanolic solution of ind-
oline (20.0 mmol, 2.19 mL) was added neat carbon disulfide
(20.0 mmol, 1.2 mL) dropwise with continuous stirring in an

S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
1051
3. Results and discussion
ure of the dithiocarbamato moiety [21]. We have observed
a single sharp band at 1043 cmÀ1 in the ligand, which was
found to be shifted, by ꢀ25 cmÀ1 in the compounds (2–5)
indicating bidentate coordination of the ligand to tin
atom. However, a doublet is observed at 998 cmÀ1 in case
of 6 implying the presence of both monodentate as well as
bidentate dithiocarbamato moiety. This fact is further
supported by 119Sn NMR data. Furthermore, the C–N
stretching frequency is also diagnostic in deciding the nat-
ure of dithiocarbamato group as evidenced by a large
number of reports [1]. In our case the m(C–N) at
1465 cmÀ1 in the ligand was found to be shifted to higher
wavenumber (1477–1483 cmÀ1) in complexes which is
intermediate between m(C–N) and m(C@N) confirming a
partial double bond character [22]. On the above findings
the following resonance forms can be postulated for the
ligand, Naindtc:
The ligand was obtained as sodium salt by the reaction
of indoline with carbon disulfide and sodium hydroxide in
methanol as shown below:
NaOH
CS2
+
N
H
N
C
Na S
S
Na(indtc)
The organotin dithiocarbamates were obtained by the
reaction of R2SnCl2 with Naindtc in 1:2, and SnCl4 in
1:2 and 1:4 molar ratios, respectively. The general chemical
reaction is given as:
N
C
N
C
N
C
N
C
S
S
S
S
S
S
S
S
IV
II
II
II
An interesting feature of these complexes is the concom-
itant strengthening of the C–N with C–S bond in the com-
plexes which can be due to the coordination of the S–S
chelate with Sn atom leading to a dispersal of electronic
charge over the NCS2 region [23]. The Sn–sulfur coordina-
tion is further supported by the presence of new medium to
weak intensity bands in the 408–386 cmÀ1 region, which
are found to be absent in its precursor [24].
i
)Methanol
ii)3hStirring
N
C
N
C
R2SnCl2
+
2NaCl
NaS
S
S
S
S
R
Sn
R
S
C
N
3.2. NMR spectroscopy
1
The H NMR spectrum of the free ligand show signals
for methylene proton bound to nitrogen at 3.80 ppm and
are found to be unaffected by coordination (Table 3).
The signals at 2.14 ppm belong to cyclic chain proton
(Ar–CH2–C), which are also insensitive to Sn coordination
[25]. A multiplet was observed at 6.9 ppm corresponding to
the presence of aromatic protons. The 1H NMR spectra of
compound 2 exhibits a sharp singlet at 1.52 ppm corre-
sponding to the protons of methyl groups attached to the
Sn atom [26]. However, in the case of compound 3, three
sets of signals are observed. As the butyl group is attached
to electropositive Sn atom via carbon nuclei, a shielding
effect is experienced through the carbon chain [27]. The
methyl protons of the butyl group are observed as a triplet
at 0.91 ppm while broad signals are observed at 1.65 and
1.38 ppm for the methylene protons. The aromatic protons
The compounds are stable to moisture and heat, are
non-conducting in DMSO [19] and give satisfactory ele-
mental analysis (Table 1). They are soluble in chloroform
and dichloromethane.
3.1. Infrared spectroscopy
The most significant IR bands are listed in Table 2. The
m(C–S) in the region 1000 70 cmÀ1 is quite cardinal in
deciding the nature of the dithiocarbamato group [20]. A
singlet in the above region suggests bidentate symmetrical
bonding while the splitting of this band into a doublet
may be attributed to the unsymmetrical monodentate nat-

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S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
Table 1
Physicochemical properties of the ligand and its mononuclear compounds
Compounds (molecular
formula)
Colour
Yield
(%)
Molar conductance
(ohmÀ1 molÀ1 cm2)
Anal. (%) Found (calc.)
C
H
N
S
Sn
Na(indtc) (1)
Yellow
55
62
67
70
68
55
12.3
22.4
31.2
18.8
35.2
22.7
49.6 (49.8) 3.8 (3.7) 6.5 (6.4) 29.8 (29.5)
Sn(indtc)2(CH3)2 (2)
Sn(indtc)2(C4H9)2 (3)
Sn(indtc)2(C6H5)2 (4)
Sn(indtc)2Cl2 (5)
Sn(indtc)4 (6)
Light-yellow
Light-yellow
Light-yellow
Yellow
44.3 (44.5) 4.2 (4.5) 5.1 (5.2) 23.9 (23.7) 22.2 (22.0)
50.2 (50.3) 5.4 (5.5) 4.3 (4.5) 20.8 (20.6) 19.4 (19.1)
54.4 (54.5) 3.8 (4.0) 4.1 (4.2) 19.5 (19.3) 17.8 (17.9)
37.6 (37.7) 2.2 (2.1) 4.8 (4.9) 22.5 (22.3) 20.9 (20.7)
48.1 (48.3) 3.4 (3.6) 6.4 (6.2) 28.8 (28.6) 31.3 (13.2)
Yellow
(CH3)2 = dimethyl, (C4H9)2 = dibutyl, (C6H5)2 = diphenyl.
Table 2
Diagnostic IR bands of the ligand and its compounds
Compound
m(Sn–S)
m(Sn–C)
m(CÁ Á ÁÁS)
m(CÁ Á ÁÁN)
Ring vibrations
Naindtc (1)
–
–
1043 s
1066 s
1068 s
1066 s
1070 s
1074 s
1465 s
1477 s
1479 s
1477 s
1483 s
1481 s
1606 m
1602 m
1604 m
1607 m
1601 m
1600 m
Sn(indtc)2(CH3)2 (2)
Sn(indtc)2(C4H9)2 (3)
Sn(indtc)2(C6H5)2 (4)
Sn(indtc)2Cl2 (5)
Sn(indtc)4 (6)
404 w
408 w
401 w
392 w
386 w
582 m
597 m
604 w
578 w
586 w
Table 3
NMR chemical shifts of the compounds (in ppm)
Compound
NMR
CH3
a-CH2
b-CH2
v-CH2
d-CH3
C6H5
N(CH2)
(CH2)ring
NCSS (CH2)aro
Naindtc (1)
1H
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3.80
53.43
–
2.14
25.63
–
–
6.91
126.8
–
13C
193.3
–
119Sn
Sn(indtc)2(CH3)2 (2)
Sn(indtc)2(C4H9)2 (3)
Sn(indtc)2(C6H5)2 (4)
Sn(indtc)2Cl2 (5)
1H
1.57
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3.76
53.42
–
2.16
25.42
–
–
6.92
128.9
–
13C
196.2
À274.5
119Sn
1H
–
–
–
1.21
28.42
–
1.38
29.92
–
1.65
26.12
–
0.91
13.45
–
–
–
–
3.81
53.28
–
2.18
25.63
–
–
6.89
129.6
–
13C
198.5
À296.3
119Sn
1H
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
6.58
123.5
–
3.75
52.61
–
2.16
25.62
–
–
6.91
128.7
–
13C
199.5
À301.2
119Sn
1H
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3.77
53.42
–
2.17
25.72
–
–
6.90
127.9
–
13C
197.6
À358.6
119Sn
Sn(indtc)4 (6)
1H
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3.79
52.58
–
2.16
25.82
–
–
6.91
128.9
–
13C
198.6
À428.5
119Sn
of the phenyl group directly attached to the Sn atom in 4
were observed at 6.58 ppm. The equivalence of the methyl,
butyl and phenyl protons in compounds 2–4 indicates trans
arrangement of the alkyl and aryl groups on Sn atom [28].
Highest downfield shift is observed for the methylene pro-
tons (1.21 ppm) directly attached to the Sn atom.
shifted downfield to about 5–6 ppm indicative of the metal
coordination [1]. The downfield shift is consistent with the
dispersal of electronic cloud over the entire MS2CN region.
In order to provide further structural evidence, which
establishes the structure of the compound in solution, we
recorded 119Sn NMR spectra.
The 13C NMR spectrum of the compounds exhibits two
signals for N(CH2) carbons at 54.6 and 50.2 ppm while the
ring methylene carbons were found to resonate at 25.8 and
24.0 ppm respectively. The CS2 resonances for compound 1
were observed at 193.3 ppm while in complexes (2–6) it was
It is well known that the high coordination number at
the Sn center relates to high shielding effect. 119Sn NMR
chemical shift may be used to give tentative indications
of the environment around tin atoms. It has been reported
that the magnitude of the chemical shift in organotin(IV)

S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
1053
complexes is related to the coordination number of the
metal center. Holecek et al. [29] have suggested values from
+200 to À60 for four-coordinated, À90 to À190 for five-
coordinated and À210 to À400 ppm for six-coordinated
tin atoms in solution, respectively. The 119Sn NMR spectra
of compounds (2–6) exhibit chemical shift in the region
À274.5 and À428.5 ppm, suggesting the presence of six-
coordinated [30] Sn. An interesting feature is observed on
examining the 119Sn NMR chemical shifts. It was found
that 119Sn NMR signals shift to more positive frequencies
on increasing the number of sulfur ions in the metal coor-
dination sphere. This shift may be attributed to the loss of
chloride ions, which facilitate the p back donation from p-
electrons of the chloride to the empty 5d orbital of Sn cen-
ter [31].
possible fragments of the compounds are given in Schemes
2 and 3.
3.4. Thermal studies (TGA/DSC)
Thermogravimetric analysis of the ligand and its com-
pounds has been carried out to study the pyrolysis pattern
in the temperature range 25–580 °C. The thermogram of
the ligand exhibits weight loss in two steps over the temper-
ature range 145–180 and 205–320 °C. These are in agree-
ment with the expulsion of CS2 and indoline moieties,
respectively [34]. The compounds start decomposing above
215 °C and the thermogram exhibits three distinct decom-
position steps at 215, 354 and 447 °C. Since the TG curves
of the compounds do not display noticeable weight loss up
to ca. 215 °C it confirms the absence of water of hydration
or water of coordination [35]. This behaviour also reveals
greater thermal stability for compounds than its precursor.
It is also supported by elemental analysis (Table 1) and
infrared spectra (Table 2). A typical TGA plot of com-
pound 2 is exhibited in Fig. 1. The first decomposition step
of the compounds exhibits 58% weight loss corresponding
to the decomposition of alkyl or aryl groups [36]. The sec-
ond thermolytic stage accounts for the degradation of ind-
oline nucleus which is a common feature of heterocyclic
compounds while the third step at 450 °C, is accompanied
by 20% weight loss corresponding to the expulsion of
remaining part of the organic moiety. Finally the TG curve
shows a plateau above 540 °C corresponding to the forma-
tion of tin-sulfide as the final product [37].
3.3. Mass spectrometry
The FAB mass spectral data and fragmentation pattern
of compounds 1, 2 and 4 are shown under Schemes 1–3
along with m/z and percent intensity. The mass spectrum
of the ligand, Naindtc exhibits a low intensity molecular
ion peak at m/z 217 while the base peak is observed at
m/z 78 due to [C6H6]+ fragment (Scheme 1). The disap-
pearance of any peak above 217 implies the formation of
anhydrous ligand, which is also evident from the TGA/
DSC plot [32]. However, in case of compounds 2 and 4,
the reported mass spectral data is in accordance with the
principal isotope 120Sn. The molecular ion peak is observed
only in case of methyl analogue, 2 at m/z 539. The base
peak (100 %) are observed at 78 due to [C6H6]+ and at
118 due to [C8H8N]+ fragment for compounds 2 and 4,
respectively [33]. The absence of any higher peaks implies
the formation of mononuclear compounds. The other
3.5. Antimicrobial assay
The antibacterial and antifungal activity of a solution of
freshly synthesized compounds in dichloromethane was
tested against some gram positive and gram negative bacte-
ria such as, E. coli, S. aureus, C. albicans and A. flavus. The
activity was then compared with some reference antibiotics
that were purchased from the market. The results revealed
that the dithiocarbamato compounds had activity compa-
rable with the reference drug (Table 4).
SNa
S
S
S
N
C
N
C
Na
All the compounds and the parent ligand were screened
for their activity against the test organisms. The hole plate
diffusion method was adopted for the activity measure-
ments [38]. The bacterial strains were grown in nutrient
agar slants and the fungal strains were grown in Sabouraud
dextrose agar slants. The viable bacterial cells were
swabbed onto Nutrient agar plates and the fungal spores
onto Sabouraud dextrose agar plates. The compounds were
dissolved in dichloromethane to a final concentration of
0.1%. A 0.5 cm diameter well was cut in a medium inocu-
lated with the respective cultures, and the test solutions
of the compounds in different concentrations (5 and 1 lg)
for bacterial cultures and (15 and 50 lg) for fungal cultures
were allowed to stay in the wells. The petri plates were
incubated for 36 h for bacterial cultures and 72 h for fungal
cultures. All the compounds were screened against
217 (32)
194 (21)
Compound 1
CS2
N
C2H4N
78 (62)
118 (43)
Scheme 1. Fragmentation pattern of ligand Naindtc (1).

1054
S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
CH
3
S
S
S
S
C2H6
Sn
N
Sn
N
C
C
C
N
C
N
S
S
S
S
CH3
506(43)
536(38)
Compound2
C9H8NS2
S
S
H3C Sn
148(31)
CH3
Sn
C
N
312(24)
2C
SnS
N
118(59)
78 (73)
Scheme 2. Fragmentation pattern of compound, Sn(indtc)2(CH3)2 (2).
flucanazole as reference for fungal cultures and gentamycin
for bacterial cultures in their standard concentration of
200 lg/well. The activity of the compounds was evaluated
by measuring the diameter of the inhibition zone around
the respective wells. The results are presented in the Table
4. The compounds display stable inhibition zones and are
more active than the ligand. They possess potential inhibi-
tory activity in amounts as low as 1 lg/well for bacterial
cultures and 15 lg/well for fungal cultures. The activity
of the compounds is measured in terms of inhibition of
the replication of DNA by interacting with the enzyme
prosthetic group. It has been observed that the activity of
dibutyltin dithiocarbamate is lower than that of tin(IV)
complex, while that of methyl and phenyl analogues is
quite comparable. Higher activity of Cl2Sn(indtc)2 is prob-
ably due to the chloride, which is more labile than the alkyl
groups. Since it is relatively less hydrophobic compound it
may easily penetrate the cell membrane as compared to the
others [39]. The possible inhibitory action of the complexes
can be due to their inhibition of the replication of DNA by
interacting with the enzyme prosthetic group. These com-
pounds are found to be quite active due to their membrane
penetrating activity. However, the reduced activities in
some cases can be attributed to their inability to form
hydrogen bonds with the cell constituents [40].
3.6. Cytotoxicity screenings
The in vitro cytotoxicity test of the compounds 2–6 was
performed using microculture sulforhodamine B (SRB) test
for estimation of cell viability [41]. The human cancer cell
lines used in the present study are WIDR (colon cancer),

S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
1055
C6H5
S
S
S
S
C6H5
Sn
N
Sn
N
C
C
C
N
C
N
S
S
S
S
C6H5
C6H5
660(n.o.)
583(
44)
Compound4
C15H13NS2
C20H18N
S
Sn
C
N
S
S
SnS2
S
N
C
312(31)
SnS
2C
376(27)
N
118(59)
C2H4N
78(53)
Scheme 3. Fragmentation pattern of compound, Sn(indtc)2(C6H5)2 (4).
cer) (ER)-/ progesterone receptor (PgR)- and H226 (non
small cell lung cancer). The test and reference compounds
were dissolved to a concentration of 250000 ng/mL in full
medium, by 20-fold dilution of a stock solution, which con-
tained 1 mg compound/200 lL. The compounds were dis-
solved in dichloromethane.
The experiment was started on day 0. On day 0, 10000
cells per well were seeded into 96-wells flat-bottomed
microtiter plates (falcon 3072, DB). The plates were incu-
bated for 48 h at 37 °C, 8% CO2 to allow the cells to adhere
to the bottom. On day 2, a threefold dilution sequence of
ten steps was made in full medium, starting with the
250000 ng/mL stock solution. Every dilution was used in
quadruplicate by adding 150 lL to a column of four wells.
This procedure resulted in a highest concentration of
625000 ng/mL present in column 12. Column 2 was used
as a blank. After incubation of four days, the plates were
washed with PBS twice. Subsequently 200 lL of Fluorosce-
Fig. 1. TGA curve showing the degradation of compound 2.
IGROV (ovarian cancer), M19 MEL (melanoma), A498
(renal cancer), MCF-7 (breast cancer) estrogen receptor
(ER)/progesterone receptor (PgR)+, EVSA-T (breast can-

1056
S. Khan et al. / Journal of Organometallic Chemistry 693 (2008) 1049–1057
Table 4
Inhibition zone in mm
Compounds
E. coli
S. aureus
A. flavus
C. albicans
5 lg
1 lg
5 lg
1 lg
5 lg
1 lg
5 lg
1 lg
Naindtc (1)
14.2
15.6
11.2
21.9
25.0
22.5
26.0
11.2
13.6
10.2
20.2
22.6
20.3
26.0
15.7
21.5
17.5
21.9
28.7
19.3
30.0
13.2
20.3
15.8
20.5
25.5
18.4
30.0
15.4
11.0
9.5
16.4
19.8
13.2
20.0
13.7
10.0
9.0
15.9
18.6
12.0
22.0
10.4
16.9
10.2
15.3
20.3
17.3
22.0
10.2
14.8
10.0
14.8
20.6
16.5
22.0
Sn(indtc)2(CH3)2 (2)
Sn(indtc)2(C4H9)2 (3)
Sn(indtc)2(C6H5)2 (4)
Sn(indtc)2Cl2 (5)
Sn(indtc)4 (6)
Gentamycin/Flucanazole
Table 5
Inhibition doses ID50 values (ng/mL) of test compounds in vitro using SRD as cell viability test
Test compound
Cell line 1 A498
Cell line 2
EVSA-T
Cell line 3
H226
Cell line 4
IGROV
Cell line 5
M19 MEL
Cell line 6
MCF-7
Cell line 7
WIDR
Sn(indtc)2(C4H9)2 (3)
Sn(indtc)2(C6H5)2 (4)
DOX
CPT
5FU
2185
2205
94
2256
143
30
355
375
12
422
475
3
3105
3185
201
3275
340
165
170
64
170
297
7
485
489
20
560
442
27
670
650
12
705
750
20
950
924
10
990
225
<3.2
<3.2
MTX
TAX
2225
<3.2
<3.3
<3.2
<3.2
<3.2
<3.2
DOX: doxorubicin; CPT: cis-platin; 5-FU: 5-fluorouracil; MTX: methotrexate; TAX: taxol.
in Diacetate stock solution diluted to 2 lg/mL with PBS
was added to each of the control, experimental and blank
wells. The plates were then incubated for 30 min. at
37 °C. Fluorescence generated from each well was mea-
sured at an excitation wavelength of 485 nm and an emis-
sion wavelength of 540 nm using an automated
microplate reader (Labsystems Multiskan MS). Data was
used for the construction of concentration–response curves
and the determination of ID50 values by use of Deltasoft 3
software.
plexes being the most effective [42,43]. It has been
suggested that these behaviors are exhibited due to the
interaction of organotin compounds with DNA at the level
of phosphate group, which may be followed by the interca-
lation of the ligand into DNA [44,45]. Different active
organotin compounds may still show slight variations in
‘in vitro’ cytotoxicity due to different kinetic and mechanis-
tic behavior [46].
4. Conclusion
The results of the in vitro cytoxicity test of compounds
dibutyltin indoline bis(dithiocarbamate), [(C4H9)2Sn(ind-
tc)2] and diphenyltin indoline bis(dithiocarbamate),
[(C6H5)2Sn(indtc)2] are given in Table 5, as the inhibition
doses ID50 observed against a panel of seven human tumor
cell lines i.e. WIDR (colon cancer), IGROV (ovarian can-
cer), M19 MEL (melanoma), A498 (renal cancer), MCF-
7 (breast cancer) estrogen receptor (ER)/progesterone
receptor (PgR)+, EVSA-T (breast cancer) (ER)-/progester-
one receptor (PgR)- and H226 (non small cell lung cancer).
The cytotoxicity results were compared with those
obtained for some clinically used reference compounds like
doxorubicin DOX, cisplatin CPT, 5-fluorouracil 5-FU,
methotrexate MTX and taxol TAX.
The compounds reported here have been obtained as
amorphous powders soluble in chloroform and dichloro-
methane. Spectroscopic techniques suggest and support
the probable mode of coordination in all the compounds
where coordination is predominantly bidentate with an
exception in the case of Sn(indtc)4. The ‘in vitro’ antimicro-
bial assays of the synthesized complexes against the bacte-
rial and fungal strains establish their inhibitory effect.
Cytotoxicity assays of the compounds confirm the potency
of these compounds, which can be used for clinical trials
after further research.
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et al. who reports that organotin(IV) complexes exert ther-
apeutic effects on various tumor cells; dialkyltin(IV) com-
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