Potential bioactive Vanillin-Schiff base di- and tri-organotin(IV) complexes of 4-((3,5-dimethylphenylimino)methyl)-2-methoxyphenol: Synthesis, characterization and biological screenings

Article abstract of DOI:10.1007/s13738-013-0301-x

Eight different di- and triorganotin(IV) complexes of vanillin-Schiff base of the type R₂SnClL and R₃SnL [R = Me (1,6), n-Bu (2,7), Ph (3,8), tert-Bu (4), Cy (5) and L = 4-((3,5-dimethylphenylimino)methyl)-2- methoxyphenol] were synthesized. The products were characterized by elemental analysis, FT-IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The ligand 4-((3,5-dimethylphenylimino)methyl)-2-methoxyphenol is also characterized by single crystal X-ray analysis. In the ¹H NMR spectra of 1 and 6, the ² J(^119/117Sn-¹H) in the Sn-CH₃ moiety has 57 and 54 Hz values, respectively, that confirm the formation of four-coordinated Sn species. Moreover, the ¹³C NMR value for ipso carbon of SnPh is 139 ppm which also confirms the formation of four-coordinated Sn species. The title ligand and its complexes were also screened for their biological activities such as interaction with DNA, enzymatic, antimicrobial, cytotoxic and antioxidant activities. The antimicrobial and cytotoxic activities of triorganotin(IV) derivatives are relatively higher than their corresponding diorganotin(IV) analogues due to their greater lipophilicity and permeability through cell membrane. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-013-0301-x

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0301-x
ORIGINAL PAPER
Potential bioactive Vanillin–Schiff base di- and tri-organotin(IV)
complexes of 4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenol: synthesis, characterization and biological
screenings
•
Muhammad Sirajuddin Saqib Ali
•
•
•
Farooq Ali Shah Muhammad Ahmad
Muhammad Nawaz Tahir
Received: 29 April 2013 / Accepted: 20 June 2013
Ó Iranian Chemical Society 2013
Abstract Eight different di- and triorganotin(IV) com-
plexes of vanillin-Schiff base of the type R2SnClL and
R3SnL [R = Me (1,6), n-Bu (2,7), Ph (3,8), tert-Bu (4),
Cy (5) and L = 4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenol] were synthesized. The products were
Keywords Schiff base ꢀ Organotin(IV) compound ꢀ
Crystal structure ꢀ DNA-binding ꢀ Enzymatic activity
Introduction
1
characterized by elemental analysis, FT-IR, H, 13C and
119Sn NMR spectroscopy. The ligand 4-((3,5-dimethyl-
phenylimino)methyl)-2-methoxyphenol is also character-
ized by single crystal X-ray analysis. In the 1H NMR
spectra of 1 and 6, the 2J(119/117Sn-1H) in the Sn-CH3
moiety has 57 and 54 Hz values, respectively, that confirm
the formation of four-coordinated Sn species. Moreover,
the 13C NMR value for ipso carbon of SnPh is 139 ppm
which also confirms the formation of four-coordinated Sn
species. The title ligand and its complexes were also
screened for their biological activities such as interaction
with DNA, enzymatic, antimicrobial, cytotoxic and anti-
oxidant activities. The antimicrobial and cytotoxic activi-
ties of triorganotin(IV) derivatives are relatively higher
than their corresponding diorganotin(IV) analogues due to
their greater lipophilicity and permeability through cell
membrane.
Schiff bases are studied widely due to their interesting
characteristics, including photochromic and thermochro-
mic properties, proton transfer tautomeric equilibria,
biological and pharmacological activities, as well as
suitability for analytical applications. Due to synthetic
flexibility and simple preparation procedure these com-
pounds have gained a great deal of attention as suitable
ligands for coordination and determination of various
metal ions [1]. Schiff base ligands are considered as
‘‘privileged ligands’’ due to their ease of preparation and
their use as fluorogenic agent, pesticides, herbicidal
agents, blocking agents, as well as catalysis [2]. Some of
Schiff base complexes are used as model molecules for
biological oxygen carrier systems [3]. Tetradentate Schiff
base ligands are well known to form stable complexes,
where the coordination takes place through the N2O2
donor set [4–6].
Over the recent decades, studies on coordination of
Schiff bases to organotin(IV) compounds have got enor-
mous attention with respect to their potential applications
in medicinal chemistry and biotechnology and their struc-
tural variety [7–9]. Schiff base ligands are potential anti-
cancer, anti-bacterial and anti-viral agents and these
activities tend to increase in metal Schiff base complexes
[10]. Schiff bases react with organotin(IV) halides to form
variety of structures [11–13].
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-013-0301-x) contains supplementary
material, which is available to authorized users.
M. Sirajuddin ꢀ S. Ali (&) ꢀ F. A. Shah ꢀ M. Ahmad
Department of Chemistry, Quaid-i-Azam University,
Islamabad 45320, Pakistan
e-mail: drsa54@yahoo.com
M. Sirajuddin
e-mail: m.siraj09@yahoo.com
The study of organotin(IV) complexes has gained
growing interest in the past few decades due to their ability
to interact with DNA, signifying their potential application
M. N. Tahir
Department of Physics, University of Sargodha,
Sargodha, Pakistan
123

J IRAN CHEM SOC
in cancer chemotherapy [14–17]. Several organotin(IV)
Schiff base complexes have been explored for their struc-
tural diversity and biocidal activities [18–20]. Cagnoli et al.
[21], found some organotin(IV) complexes to be even more
active in vitro than the clinically used cis-platin. Usually,
triorganotin(IV) compounds exhibit a higher biological
activity than their di- and monoorganotin(IV) analogues,
which has been related to their ability to bind to proteins
[22, 23]. Organotin(IV) compounds have been receiving
increasing attention in recent years due to their antitumor
activity and it has been observed that several diorganotin
adducts show potentials antineoplastic and antituberculosis
activities. Also, dialkyltin(IV) compounds have selective
effects on lymphocytes, which can be used in cancer che-
motherapy or to control other pathological effects [24].
Against human tumor cell lines, triphenyltin derivatives are
highly active, being characterized by very low LD50 values
[25].
Experimental
Materials and methods
Reagents, Me3SnCl, n-Bu3SnCl, tert-Bu3SnCl, Ph3SnCl,
Cy3SnCl, vanillin, 3,5-dimethylaniline were obtained from
Aldrich (USA) and were used without further purification.
All the solvents purchased from E. Merck (Germany) were
dried before use according to the literature procedure [33].
The melting points were determined in a capillary tube
using a Gallenkamp (UK) electrothermal melting point
apparatus. IR spectra in the range of 4,000–100 cm-1 were
obtained on a Thermo Nicolet-6700 FT-IR Spectropho-
tometer. Microanalysis was done using a Leco CHNS 932
1
apparatus. H and 13C NMR were recorded on a Bruker-
300 MHz FT-NMR Spectrometer, using CDCl3 as an
internal Ref. [1H (CDCl3) = 7.25 and 13C (CDCl3) = 77].
Chemical shifts are given in ppm and coupling constants
(J) values are given in Hz. The multiplicities of signals in
1H NMR are given with chemical shifts; (s = singlet,
d = doublet, t = triplet, m = multiplet). 119Sn-NMR
spectra were recorded at 298 K of samples dissolved in
DMSO-d6 with a 400 MHz JEOL ECS instrument. The
measurements were recorded at a working frequency of
149.4 MHz and the chemical shifts were referenced to
Me4Sn as external standard. The absorption spectra were
measured on a Shimadzu 1800 UV–Visible Spectropho-
tometer. Viscosity was measured by Ubbelohde viscometer
at room temperature. The electrical conductance was
measured on a WTW Series Inolab Cond 720. The GC-MS
spectrum was taken on a gas chromatograph, model GC-
6890 N coupled with mass Spectrometer, model MS-5973
MSD (mass selective detector). Separation was performed
The binding of small molecules with the DNA is of great
importance because of advantages of these molecules as
potential drugs. The concept of intercalation into DNA was
first formulated by Lerman [26] in 1961; it has become
widely recognized that many compounds of pharmaco-
logical interest, including anticancer drugs and antibiotics
correlate their biological and therapeutic activities with the
ability of intercalative interaction with DNA [27]. This
non-covalent binding has an important function in life
phenomena at the molecular level, deciding the interaction
specificity of drug with DNA.
The study of drug–DNA interaction is important for
understanding the molecular mechanisms of the drug
action and designing specific DNA-targeted drugs [28].
Such interactions are studied using a variety of techniques
like cyclic voltammetry, UV–visible, fluorescence, Raman
and NMR spectroscopy [29]. The interaction of some metal
chelates of Co(III), Ru(II) and Os(II) with DNA were
studied by cyclic voltammetry [30], but their lower affinity
to DNA encouraged the researchers to concentrate their
effort on other potential metal complexes. Interest about
DNA–organotin(IV) systems arises from the large indus-
trial uses of organotins, their consequent spread out in the
environment and the related biological actions [31, 32].
In the present study we have synthesized a Schiff base
ligand and its complexes with tri- and diorganotin(IV)
compounds. The synthesized ligand and its complexes
were characterized by various techniques including FT-IR,
NMR, elemental analysis and single crystal analysis. Bio-
logical aspects including interaction with DNA, enzyme
inhibition, antibacterial, antifungal, cytotoxic and antioxi-
dant activities of the synthesized ligand and its complexes
were studied.
on
a capillary column DB-5MS (30 m 9 0.32 mm,
0.25 lm of film thickness). The mass Spectrometer cou-
pled with GC was set to scan in the range of m/z 50–550
with electron impact (EI) mode of ionization. The X-ray
diffraction data were collected on a Bruker SMART APEX
CCD diffractometer, equipped with a 4 K CCD detector set
60.0 mm from the crystal. The crystals were cooled to
100 1 K using the Bruker KRYOFLEX low-temperature
device and Intensity measurements were performed using
graphite monochromated Mo-Ka radiation from a sealed
ceramic diffraction tube (SIEMENS). Generator settings
were 50 kV/40 mA. The structure was solved by Patterson
methods and extension of the model was accomplished by
direct methods using the program DIRDIF or SIR2004.
Final refinement on F2 carried out by full-matrix least
squares techniques using SHELXL-97, a modified version
of the program PLUTO (preparation of illustrations) and
PLATON package.
123

J IRAN CHEM SOC
Synthesis
triethylammoniun chloride salt occurred and the filtrate
was rotary evaporated to get the desire product.
Synthesis of ligand: 4-((3,5-dimethylphenylimino)methyl)-
2-methoxyphenol (HL)
Trimethyltin(IV) 4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate; (1)
Stoichiometric amounts of vanillin and 3,5-dimethylaniline
(5 mmol of each) were added to freshly dried toluene. The
reaction mixture was stirred and refluxed for 3–4 h and the
water formed during the reaction was removed using Dean
and Stark apparatus. Volume of the reaction mixture was
reduced to one-third of its original solvent volume and left
to crystallize at room temperature. The red crystals of HL
suitable for single crystal analysis were isolated from the
mother liquor and dried. The chemical reaction is shown in
Scheme 1.
Yield: 78 %, molecular formula: C19H25NO2Sn, mol. wt.:
418.12, physical state: liquid, IR (cm-1): m 1,625 (C=N),
1,427 and 1,581 (Ar. C=C), 1,280 (Phen. C-O str. vib.), 546
1
(Sn-C), 464 (Sn-O), H NMR (CDCl3, ppm): 2.41 (s, 6H,
H1, H10), 6.95 (s, 1H, H3), 6.92 (s, 2H, H4, H40), 8.4 (s,
1H, H6), 7.25 (s, 1H, H8), 7.67 (d, 1H, H9,
3J[1H-1H] = 9 Hz)), 7.00 (d, 1H, H10, 3J[1H-1H] = 9 Hz),
2
3.92 (s, 3H, H13), 0.64 (s, Sn-CH3, J[119/117Sn-1H = 57,
13
56 Hz]), C NMR (CDCl3, ppm): 21.9 (2C, C1, C10),
138.8 (2C, C2, C20), 129.1 (1C, C3), 118.8 (2C, C4, C40),
149.2 (1C, C5), 160.1 (1C, C6), 127.4 (1C, C7), 108.6 (1C,
C8), 125.4 (1C, C9), 113.3 (1C, C10), 148.0 (1C, C11),
153.3 (1C, C12) 55.7 (1C, C13), 20.9 (Sn-CH3, 1J[119/
117Sn-1H = 389, 372 Hz])), 119Sn NMR (DMSO, ppm):
-200.5, molar conductance (Km, S.cm2.mol-1): 15 at
25 °C.
Yield: 85 %, m.p.: 99 °C, Anal. Calc. for C16H17NO2:
mol. wt.: 255.31, C, 75.27; H, 6.71; N, 5.49, Found: C,
75.30; H, 6.70; N, 5.50 %, IR (cm-1): m 1,625 (C=N),
1,426 and 1,581 (Ar C=C), 3,320 (OH), 1,252 (Phen. C–O
1
str. vib.), H NMR (CDCl3, ppm): 2.38 (s, 6H, H1, H10),
6.90 (s, 1H, H3), 6.87 (s, 2H, H4, H40), 8.37 (s, 1H, H6),
7.24 (s, 1H, H8), 7.64 (d, 1H, H9, 3J[1H-1H] = 9 Hz), 6.99
(d, 1H, H10, 3J[1H-1H] = 9 Hz), 6.61 (s, 1H, OH), 3.94 (s,
13
3H, H13), C NMR (CDCl3, ppm): 21.4 (2C, C1, C10),
Tri-n-butyltin(IV) 4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate; (2)
138.8 (2C, C2, C20), 129.1 (1C, C3), 118.7 (2C, C4, C40),
149.1 (1C, C5), 160 (1C, C6), 127.4 (1C, C7), 108.5 (1C,
C8), 125.3 (1C, C9), 114.3 (1C, C10), 147 (1C, C11), 152.1
(1C, C12), 56.0 (1C, C13), molar conductance (Km,
S.cm2.mol-1): 13 at 25 °C.
Yield: 75 %, molecular formula: C28H43NO2Sn, mol. wt.:
544.36, physical state: liquid, IR (cm-1): m 1,625 (C=N),
1,427 and 1,582 (Ar. C=C), 1,282 (Phen. C-O str. vib.), 558
1
(Sn-C), 464 (Sn-O), H NMR (CDCl3, ppm): 2.39 (s, 6H,
H1, H10), 6.99 (s, 1H, H3), 6.89 (s, 2H, H4, H40), 8.37 (s,
General procedure for the synthesis of organotin(IV) Schiff
base complexes (1–8)
1H, H6), 7.25 (s, 1H, H8), 7.67 (d, 1H, H9,
3
3J[1H-1H] = 9 Hz), 6.99 (d, 1H, H10, J[1H-1H] = 9 Hz),
3
3.91 (s, 3H, H13), 1.30 (t, 2H, Ha, J[1H-1H] = 16.5 Hz),
1.28 g (5 mmol) of HL was dissolved in 60 mL freshly
dried toluene and to it 0.69 mL (5 mmol) of Et3N was
added. The reaction mixture was stirred and refluxed for
about 30 min and then calculated amount (5 mmol) of
R3SnCl and R2SnCl2 (R = Me (1), n-Bu (2), Ph (3), tert-
Bu (4), Cy (5)) was added (Scheme 2). The reaction mix-
ture was again stirred and refluxed for about 6–7 h. The
mixture was then allowed to stand overnight so that tri-
ethylammoniun chloride salt may settle down. The contents
of the flask were then filtered till no further formation of
1.65 (m, 2H, Hb), 1.31 (m, 2H, Hc, 0.95 (t, 3H, Hd,
3J[1H-1H] = 14.7 Hz), 13C NMR (CDCl3, ppm): 21.4 (2C,
C1, C10), 138.7 (2C, C2, C20), 129.1 (1C, C3), 118.8 (2C,
C4, C40), 149.4 (1C, C5), 160.1 (1C, C6), 127.3 (1C, C7),
108.6 (1C, C8), 125.4 (1C, C9), 113.2 (1C, C10), 147.4
(1C, C11), 153.2 (1C, C12), 55.8 (1C, C13), 19.7 (Ca,
1J[119/117 Sn-13Ca] = 395, 383 Hz), 27 (Cb, 2J[119Sn-
13Cb] = 22 Hz), 28 (Cc, 3J[119Sn-13Cc] = 63 Hz), 14
(Cd) (SnCH2CH2CH2CH3), 119Sn NMR (DMSO, ppm):
H3C
H31'C
2'
10
4'
4
9
6
CH
Toluene, Reflux, 3-4 h
7
5
11
NH2
O
C
H
OH
3
N
OH
-H2O
2
12
8
13
OCH3
H3C
H31C
OCH3
Scheme 1 Chemical reaction and structural representation of ligand (HL)
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J IRAN CHEM SOC
Scheme 2 Chemical reaction and structural representation of organotin(IV) Schiff base complexes along with numbering
-198.4: molar conductance (Km, S.cm2.mol-1): 19 at
25 °C.
2.59 %, IR (cm-1): m 1,625 (C=N), 1,426 and 1,581 (Ar.
C=C), 1,280 (Phen. C-O str. vib.), 557 (Sn-C), 464 (Sn-O),
1H NMR (CDCl3, ppm): 2.37 (s, 6H, H1, H10), 6.89 (s, 1H,
H3), 6.86 (s, 2H, H4, H40), 8.36 (s, 1H, H6), 7.24 (s, 1H,
H8) 7.42 (d, 1H, H9, 3J[1H-1H] = 9 Hz), 6.99 (d, 1H, H10,
3J[1H-1H] = 9 Hz), 3.96 (s, 3H, H13), 1.28 (s, 27H, {Sn–
C(CH3)3}, 3J[119/117Sn-1H] = 117, 112.2 Hz): 13C NMR
(CDCl3, ppm): 21.4 (2C, C1, C10), 138.8 (2C, C2, C20),
129.1 (1C, C3), 118.7 (2C, C4, C40), 149.1 (1C, C5), 159.9
(1C, C6), 127.4 (1C, C7), 108.5 (1C, C8), 125.3 (1C, C9),
113.2 (1C, C10), 147.3 (1C, C11), 153.2 (1C, C12), 56.0
(1C, C13), 44.5 (Ca, 1J[119/117Sn-13C] = 468, 447 Hz), 30
(Cb, 2J[119Sn-13C] = 138 Hz): 119Sn NMR (DMSO, ppm):
-190.3: molar conductance (Km, S.cm2.mol-1): 15 at
25 °C.
Triphenyltin(IV) 4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate; (3)
Yield: 78 %, molecular formula: C34H31NO2Sn, mol. wt.:
604.33, physical state: liquid, IR (cm-1): m 1,625 (C=N),
1,428 and 1,582 (Ar. C=C), 1,280 (Phen. C-O str. vib.), 555
1
(Sn-C), 451 (Sn-O), H NMR (CDCl3, ppm): 2.41 (s, 6H,
H1, H10), 6.93 (s, 1H, H3), 6.91 (s, 2H, H4, H40), 8.40 (s,
1H, H6), 7.25 (s, 1H, H8) 7.64 (d, 1H, H9,
3J[1H-1H] = 9 Hz), 7.06 (d, 1H, H10), 3J[1H-1H] = 9 Hz),
3.92 (s, 3H, H13), 7.72–7.77 (m, 1H, Hb), 7.48–7.55 (m,
1H, Hc), 7.27–7.33 (m, 1H, Hd), 13C NMR (CDCl3, ppm):
21.4 (2C, C1, C10), 138.8 (2C, C2, C20), 129.1 (1C, C3),
118.8 (2C, C4, C40), 149.1 (1C, C5), 160 (1C, C6), 127.3
(1C, C7), 108.6 (1C, C8), 125.4 (1C, C9), 113.2 (1C, C10),
147.4 (1C, C11), 153.1 (1C, C12), 55.6 (1C, C13), 139
(Cipso), 136.2 (Cortho), 129.1 (Cmeta), 129.9 (Cpara) (SnPh),)
2J[119/117Sn-13Cortho] = 49 Hz, 3J[119Sn-13Cmeta] = 63 Hz,
119Sn NMR (DMSO, ppm): -205: molar conductance (Km,
S.cm2.mol-1): 18 at 25 °C.
Tricyclohexyltin(IV) 4-((3,5-dimethylphenylimino)methyl)-
2-methoxyphenolate; (5)
Yield: 73 %, molecular formula: C34H49NO2Sn, mol. wt.:
622.47, m.p: 93–95 °C, Anal. Calc. for C34H49NO2Sn: C,
65.60; H, 7.93; N, 2.25; found: C, 65.50; H, 7.89; N,
2.28 %, IR (cm-1): m 1,624 (C=N), 1,427 and 1,582 (Ar.
C=C), 1,279 (Phen. C-O str. vib.), 560 (Sn-C), 491 (Sn-O),
1H NMR (CDCl3, ppm): 2.37 (s, 6H, H1, H10), 6.89 (s, 1H,
H3), 6.85 (s, 2H, H4, H40), 8.36 (s, 1H, H6), 7.24 (s, 1H,
H8) 7.62 (d, 1H, H9, 3J[1H-1H] = 9 Hz), 6.98 (d, 1H, H10,
3J[1H-1H] = 9 Hz), 3.98 (s, 3H, H13), 1.30 (m, 1H, Ha),
Tri-tert-butyltin(IV) 4-((3,5-dimethylphenylimino)methyl)-
2-methoxyphenolate; (4)
Yield: 75 %, molecular formula: C28H43NO2Sn, mol. wt.:
544.36, m.p: 89–91 °C, Anal. Calc. for C28H43NO2Sn: C,
61.78; H, 7.96; N, 2.57; found: C, 61.75; H, 7.95; N,
1.63 (m, 2H, Hb), 1.84 (m, 2H, Hc), 1.84 (m, 2H, Hd), 13
NMR (CDCl3, ppm): 21.3 (2C, C1, C10), 138.8 (2C, C2,
C
123

J IRAN CHEM SOC
C20), 129.2 (1C, C3), 118.7 (2C, C4, C40), 149.0 (1C, C5),
160 (1C, C6), 127.3 (1C, C7), 108.4 (1C, C8), 125.2 (1C,
C9), 114.2 (1C, C10), 147.1 (1C, C11), 153.5 (1C, C12),
56.1 (1C, C13), 33.8 (Ca, 1J[119/117Sn-13Ca] = 316,
302 Hz), 29 (Cb, 2J[119/117Sn-13Cb] = 65, 62 Hz), 31 (Cc,
3J[119/117Sn-13Cc] = 15 Hz), 27 (Cd, 4J[119Sn-13Cd] =
8 Hz), 119Sn NMR (DMSO, ppm): -226.1: molar con-
ductance (Km, S.cm2.mol-1): 16 at 25 °C.
Diphenyltin(IV) [4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate]chloride; (8)
Yield: 70 %, molecular formula: C28H26ClNO2Sn, mol.
wt.: 562.67, m.p: 110–112 °C: Anal. Calc. for
C28H26ClNO2Sn: C, 59.77; H, 4.66; N, 2.49; found: C,
59.20; H, 4.60; N, 2.55 %.: IR (cm-1): m 1,625 (C=N),
1,427 and 1,580 (Ar. C=C), 1,280 (Phen. C-O str. vib.), 558
1
(Sn-C), 451 (Sn-O), 303 (Sn-Cl), H NMR (CDCl3, ppm):
2.50 (s, 6H, H1, H10), 6.93 (s, 1H, H3), 7.02 (s, 2H, H4,
H40), 8.47 (s, 1H, H6), 7.25 (s, 1H, H8) 7.55 (d, 1H, H9,
3J[1H-1H] = 9 Hz), 7.10 (d, 1H, H10), 3.94 (s, 3H, H13),
Dimethyltin(IV) [4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate]chloride; (6)
7.60 (m, 1H, Hb), 7.48 (m, 1H, Hc), 7.40 (m, 1H, Hd), 13
C
Yield: 70 %, molecular formula: C18H22ClNO2Sn, mol.
wt.: 438.54, m.p: 150–152 °C, Anal. Calc. for
C18H22ClNO2Sn: C, 49.30; H, 5.06; N, 3.19; found: C,
49.33; H, 5.02; N, 3.20 %, IR (cm-1): m 1,625 (C=N),
1,427 and 1,586 (Ar. C=C), 1,279 (Phen. C-O Str. vib.),
NMR (CDCl3, ppm): 21.4 (2C, C1, C10), 138.9 (2C, C2,
C20), 129.1 (1C, C3), 118.9 (2C, C4, C40), 149.7 (1C, C5),
160.4 (1C, C6), 127.6 (1C, C7), 108.8 (1C, C8), 125.5 (1C,
C9), 113.4 (1C, C10), 147.7 (1C, C11), 153.2 (1C, C12),
55.9 (1C, C13), 139 (Cipso), 136.2 (Cortho), 129.2 (Cmeta),
1
555 (Sn-C), 490 (Sn-O), 302 (C-Cl), H NMR (CDCl3,
129.9 (Cpara) (SnPh), 2J[119Sn-13Cortho = 64 Hz], 3J[119Sn-
ppm): 2.37 (s, 6H, H1, H10), 6.89 (s, 1H, H3), 6.85
(s, 2H, H4, H40), 8.35 (s, 1H, H6), 7.24 (s, 1H, H8), 7.63
(d, 1H, H9, 3J[1H-1H] = 9 Hz), 6.98 (d, 1H, H10,
3J[1H-1H] = 9 Hz), 3.92 (s, 3H, H13), 1.08 (s, Sn–CH3),
2J[119Sn-1H] = 54 Hz), 13C NMR (CDCl3, ppm): 21.4 (2C,
C1, C10), 138.8 (2C, C2, C20), 129.1 (1C, C3), 118.7 (2C, C4,
C40), 148.9 (1C, C5), 159.7 (1C, C6), 127.3 (1C, C7), 108.4
(1C, C8), 125.2 (1C, C9), 113.1 (1C, C10), 147.1 (1C, C11),
13
C
meta
= 49 Hz],) 4J[119/117Sn-13Cpara = 13 Hz], 119Sn
NMR (DMSO, ppm): -200: molar conductance (Km,
S.cm2.mol-1): 17 at 25 °C.
Studies of DNA interaction by UV–visible
spectroscopy
1
153.7 (1C, C12) 55 (1C, C13), 20.3 (Ca, J[119Sn-13C] =
CT-DNA (20 mg) was dissolved in double-deionized water
(pH = 7.0) and stored at 4 °C. The nucleotide to protein
(N/P) ratio of *1.9 was obtained from the ratio of absor-
bance at 260 and 280 nm (A260/A280 = 1.9), indicating that
the DNA is sufficiently free from protein [34]. The DNA
concentration was determined via absorption spectroscopy
using the molar absorption coefficient of 6,600 M-1cm-1
(260 nm) for CT-DNA [35]. The compounds were dis-
solved in 80 % ethanol at a concentration of 0.392 mM.
The UV absorption spectra were obtained by keeping the
concentration of the compound fixed while varying the
DNA concentration. Equivalent solutions of DNA were
added to the complex and reference solutions to eliminate
the absorbance of DNA itself. Compound-DNA solutions
were allowed to incubate for 30 min at room temperature
before measurements were made. Absorption spectra were
recorded using cuvettes of 1 cm path length at room
temperature.
386 Hz), 119Sn NMR (DMSO, ppm): -190 Hz, molar con-
ductance (Km, S.cm2.mol-1): 14 at 25 °C.
Di-n-butyltin(IV) [4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenolate]chloride; (7)
Yield: 81 %, molecular formula: C24H34ClNO2Sn, mol.
wt.: 522.7, m.p: 89–90 °C, Anal. Calc. for C24H34
ClNO2Sn: C, 55.15; H, 6.56; N, 2.68; found: C, 55.20; H,
6.60; N, 2.65 %, IR (cm-1): m 1,623 (C=N), 1,427 and
1,583 (Ar. C=C), 1,275 (Phen. C-O str. vib.), 555 (Sn-C),
1
464 (Sn-O), 303 (C-Cl), H NMR (CDCl3, ppm): 2.37 (s,
6H, H1, H10), 6.9 (s, 1H, H3), 6.88 (s, 2H, H4, H40), 8.36
(s, 1H, H6), 7.24 (s, 1H, H8), 7.66 (d, 1H, H9,
3
3J[1H-1H] = 9 Hz), 6.99 (d, 1H, H10, J[1H-1H] = 9 Hz),
3
3.94 (s, 3H, H13), 1.01 (t, 2H, Ha, J[1H-1H] = 15.5 Hz),
1.81 (m, 2H, Hb), 1.40 (m, 2H, Hc), 0.95 (t, 3H, Hd,,
3J[1H-1H] = 13.5 Hz) : 13C NMR (CDCl3, ppm): 21.3 (2C,
C1, C10), 138.8 (2C, C2, C20), 129.1 (1C, C3), 118.9 (2C,
C4, C40), 148.4 (1C, C5), 159.9 (1C, C6), 127.4 (1C, C7),
108.6 (1C, C8), 125.3 (1C, C9), 113.3 (1C, C10), 147.3
(1C, C11), 152 (1C, C12), 56 (1C, C13), 21 (Ca, 1J[119/117
Sn-13Ca] = 398, 385 Hz), 27 (Cb, 2J[119 Sn-13Cb] =
49 Hz), 27 (Cc, 3J[119Sn-13Cc] = 62 Hz), 14 (Cd)
(SnCH2CH2CH2CH3), 119Sn NMR (DMSO, ppm): -192.2:
molar conductance (Km, S.cm2.mol-1): 15 at 25 °C.
Enzymatic activity
Assay of alkaline phosphatase activity
The inhibition of alkaline phosphatase was assayed by
monitoring the rate of hydrolysis of p-nitrophenyl phos-
phate at 25 °C in 0.1 M Na2CO3-NaHCO3 (sodium car-
bonate–bicarbonate) buffer (pH 10.1) [36, 37]. The enzyme
123

J IRAN CHEM SOC
Scheme 3 Hydrolysis of p-
nitrophenyl phosphate catalyzed
by alkaline phosphatase
O
O
P
Alkaline
phosphatase
O2N
OH
HO
P
O
+
+ H O
O
O2N
O
2
O
O
p-nitrophenyl phosphate
p-nitrophennol
(yellow colored)
(colorless)
catalyzes the hydrolysis of phosphate monoesters resulting
in the formation of inorganic phosphate and an alcohol.
The identity of the alcohol varies depending on the specific
phosphatase. The assay of alkaline phosphatase activity
takes advantage of the fact that the enzyme is non-specific
and utilizes the non-biological substrate p-nitrophenyl
phosphate (colorless) to give yellow-colored p-nitrophenol
upon hydrolysis which helps to monitor the reaction as
shown in Scheme 3 [37].
were prepared in methanol and 400 lL of DPPHꢀ solution
was added to sample solutions at different concentrations
(500, 1,000, 1,500, 2,000 and 2,500 lL) and appropriately
diluted with methanol to total volume of 3.0 mL. 400 lL
of DPPHꢀ stock solution was also diluted to 3.0 mL using
methanol solvent to make the control. The mixture was
then incubated for 40 min at room temperature and in
darkness. During incubation, a reduction occurred of a part
of the free radical form DPPHꢀ, dependent on the concen-
tration of the antioxidant added. Then, absorption was
measured at a characteristic DPPHꢀ wavelength equal to
517 nm and absorption of the solvent was corrected
throughout using the same solvent in the reference cell.
The scavenging effect was calculated using the following
equation [39, 40]:
Stock solutions of 50 lM inhibitors (compounds) in one
mL DMSO were prepared at room temperature. The buffer
and substrate were mixed in 1:4 ratio to make the reagent
solution. Then from the reagent solution 2,000 lL (2 mL)
was taken in the cell to which 40 lL enzyme and varying
concentrations of the inhibitor were added. The activity of
the alkaline phosphatase in the presence and absence of
inhibitor was measured spectrophotometerically. The
release of yellow-colored p-nitrophenol chromophore was
monitored at 405 nm wavelength. Enzyme activity has
been expressed as the lM of p-nitrophenol released per
min for 5 min for each concentration of the inhibitor and
then their average value taken. The inhibition of enzyme by
inhibitor was calculated by the following formula [38]:
Ao ꢁ As
Scavenging activity ð%Þ ¼
ꢂ 100
ð2Þ
Ao
where As is the absorbance of the DPPHꢀ in the presence of
the tested compound and Ao is the absorbance of the DPPHꢀ
in the absence of the tested compound (control). The data
for antioxidation are presented as mean SD of three
determinations.
Units/mL enzyme =
À
Á
Antibacterial assay
DA405n m
min Test
DA405 nm
min Blank
ꢁ
total VmLðreagent þ enzyme þ inhibitorÞ ꢂ D:F
18:5 ꢂ VmL of enzyme taken
The synthesized ligand and its organotin(IV) complexes
were tested against six bacterial strains: two Gram-Positive
[Micrococcus luteus (ATCC10240) and Staphylococcus
aureus (ATCC6538)] and four Gram-negative [Esche-
richia coli (ATCC15224), Enterobacter aerogenes
(ATCC13048), Bordetella bronchiseptica (ATCC4617)
and Klebsiella pneumonia (MTCC618)]. The agar well-
diffusion method was used for the determination of anti-
bacterial activity [41]. Broth culture (0.75 mL) containing
ca. 106 colony-forming units (CFU) per mL of the test
strain was added to 75 mL of nutrient agar medium at
45 °C, mixed well, and then poured into a 14-cm sterile
petri plate. The media was allowed to solidify, and 8 mm
wells were dug with a sterile metallic borer. Then a DMSO
solution of test sample (100 lL) at 1 mg/mL was added to
the respective wells. DMSO served as negative control, and
the standard antibacterial drugs Roxyithromycin (1 mg/mL)
and Cefixime (1 mg/mL) were used as positive control.
Triplicate plates of each bacterial strain were prepared
which were incubated aerobically at 37 °C for 24 h. The
ð1Þ
D.F = Dilution factor.
18.5 = Millimolar extinction coefficient of p-nitrophe-
nol at 405 nm.
By the addition of inhibitor the activity of the enzyme
decreased and at higher concentration it was almost com-
pletely inhibited in some cases.
DPPH free radical scavenging activity
A methanol solution of the free radical DPPHꢀ of absorp-
tion approximately 0.9 was mixed with a proper amount
of methanol solution of an antioxidant (compound).
Free radical scavenging activity of the synthesized ligand
HL and some of the representative organotin(IV) com-
plexes (1, 3, 5 and 7) was determined by measuring the
change in the absorbance of DPPHꢀ (1,1-diphenyl-2-
picrylhydrazylradical) at 517 nm spectrophotometerically.
Stock solutions of 500 lM of all tested samples and DPPHꢀ
123

J IRAN CHEM SOC
Fig. 1 GC-MS spectrum of HL. a GC spectrum and b MS spectrum
activity was determined by measuring the diameter of zone
showing complete inhibition (mm).
containing Sabouraud dextrose agar (SDA) medium (4 mL)
were autoclaved at 121 °C for 15 min. Tubes were allowed to
cool at 50 °C and non-solidified SDA was loaded with
66.6 lL of compound from the stock solution (12 mg/mL in
DMSO) to make 200 lg/mL final concentration. Tubes were
then allowed to solidify in slanting position at room temper-
ature. Each tube was inoculated with 4 mm diameter piece of
inoculum from 7-day-old fungal culture. The media supple-
mented with DMSO and Turbinafine (200 lg/mL) were used
Antifungal assay
Antifungal activity against five fungal strains (Fusarium
moniliformis, Aspergillus niger, Fusarium solani, Mucor
species and Aspergillus fumigatus) was determined using
Agar tube dilution method [41]. Screw capped test tubes
123

J IRAN CHEM SOC
CH3
CH3
Scheme 4 Fragmentation
pattern of HL
.+
O
.+
-H.
N
CH
OH
N
CH
OCH3
m/z = 255
m/z = 254
CH3
OCH3
CH3
-CH3
.+
+.
+.
N
N
CH
O
CH
OH
CH3
CH3
m/z = 239
CH3
OCH3
OH
m/z = 105
-CH2
m/z = 136
-CH2
.+
O
+.
N
CH
-C2H2
m/z = 225
+.
OCH3
CH2
-CH2
m/z = 91
-CH2
+.
C4H3
m/z = 51
+.
m/z = 77
as negative and positive control, respectively. The tubes were
incubated at 28 °C for 7 days and growth was determined by
measuring linear growth (mm) and growth in the media was
determined by measuring linear growth (mm) and growth
inhibition was calculated with reference to growth in vehicle
control as shown in the following equation:
Results and discussion
Mass spectrometry
The possible suggested molecular ion fragments obtained
from the mass spectrum of HL measured in positive mode
are given in Scheme 4 while its GC-MS spectrum is given
in Fig. 1. In Fig. 1 (a) represents the GC spectrum while
(b) represents the MS spectrum. In the GC spectrum, a
sharp singlet has appeared confirming the purity of the
compound. The compound showed a molecular ion peak
(parent peak) of maximum intensity with m/z = 255. The
initial fragmentation is due to the loss of a hydrogen ion
giving an ion peak at m/z = 254 which is of second
maximum intensity. The fragment with m/z = 254 gives a
mass fragment of m/z = 239 by losing CH3 which then
further lose CH2 group to give a mass fragment of m/
z = 225.
% Growth inhibition
ꢀ
ꢁ
Linear growth in test sampleðmmÞ
Linear growth in controlðmmÞ
¼ 100 ꢁ
ꢂ 100
ð3Þ
Cytotoxicity
Cytotoxicity was studied by the brineshrimp lethality assay
method [41, 42]. Brineshrimp (Artemia salina) eggs were
hatched in artificial sea water (3.8 g sea salt/L) at room tem-
perature (22–29 °C). After 2 days these shrimps were trans-
ferred to vials containing 5 mL of artificial sea water (10
shrimps per vial) with 10, 100 and 1,000 lg/mL final con-
centrations of each compound taken from their stock solutions
of 12 mg/mL in DMSO. After 24 h the number of surviving
shrimps was counted. Data were analyzedwith a biostat 2009
computerprogram (Probit analysis)todetermine LD50 values.
The molecular ion peak undergoes two major frag-
mentation pathways with m/z = 105 and 136. The former
undergoes cleavage to give a mass peak at m/z = 91 by the
elimination of methylene group (CH2) and then undergo
further fragmentation to give a peak at m/z = 77 which can
be attributed to the phenyl radical ion. The mass fragment
123

J IRAN CHEM SOC
of m/z = 91 undergoes elimination of C2H2 group to give a
peak at m/z = 65 with another rout which then gives an ion
peak at m/z = 51 by the elimination of CH2 group. GS-MS
spectrum analysis can not be done for organotin(IV)
complexes because of their non-volatile nature.
tri-tert-butyltin(IV) complex the butyl protons appear as
singlet having 2J[119/117Sn-1H] coupling of 117, 112 Hz. In
tricyclohexynltin(IV) complex the cyclohexyl protons
appear as multiplet in the range of 1.30–1.99 ppm [46].
The signal attributable to the imine proton (HC=N) in the
spectra of free ligand and all complexes is unaltered and
also not flanked by satellites, which indicates non-coordi-
nating behavior of N atom to Sn [47].
IR spectra
The IR spectrum of the free ligand was compared with the
spectra of tri- and diorganotin(IV) complexes to understand
the binding mode of the Schiff base to tin(IV). Weak broad
band at 3,320 cm-1 in free ligand assigned to (mO–H) was
absent in the spectra of all complexes showing the depro-
tonation of Schiff base which indicates the coordination of
Schiff base through phenolic oxygen atom [43]. Further,
the IR spectrum of the Schiff base displays a peak at
1,252 cm-1, characteristic of the phenolic (mC-O) vibra-
tion, undergoes a positive shift in the spectra of the com-
plexes indicating coordination of the Schiff bases through
the phenolic oxygen atom. A strong peak attributable to
(mC=N) which occurs at 1,625 cm-1 in free ligand as well
as in the spectra of all complexes indicating that imine
nitrogen atom is not participating in complexation with tin
atom. The interesting feature in the spectra of complexes is
the appearance of new peaks observed in the region of
546–560 cm-1 (mSn-C) and 451–491 cm-1 (mSn-O),
respectively, confirming the complex formation [44]. This
also further supports the coordination of the Schiff bases
through the phenolic oxygen atom.
In the 13C NMR spectra of the ligand and complexes the
peak for imine carbon (C-6) that occurs at 160 ppm
remains constant after complexation indicating the non-
coordinating behavior of N atom. The 13C NMR spectra of
complexes show a slight downfield shift of the phenolic
carbon resonances compared with the free ligand. The shift
is a consequence of phenolic electron density transfer from
the ligand to the acceptor [48]. The downfield shifting of
the phenolic carbon in almost all of the complexes indi-
cates the participation of the phenolic group in coordina-
tion with tin(IV), i.e., formation of Sn-O bond [49]. The
13C chemical shift of the ipso-carbon of the SnPh3 moiety
is 139 ppm in CDCl3 solution which indicates the four-
coordinated tin specie [50].
The 119Sn NMR spectra of complexes show only a
sharp singlet indicating the formation of a single species.
However, these values are strongly dependent on the nature
and orientation of the organic groups bonded to tin. The
shifts observed in complexes can be explained quantita-
tively in terms of an increase in electron density on the tin
atom as the coordination number increases. The 119Sn
chemical shift values measured in coordinating solvent for
the synthesized compounds show penta-coordination
around tin, probably with trigonal bipyrimidal geometry. In
non-coordinating solvents, the compounds exist as isolated
molecules or ionic-pairs with their tin atoms in pseudo-
tetrahedral environments. In coordinating solvents, the tin
atoms in the compounds are five-coordinate owing to the
participation of the solvent in bonding [51].
NMR spectra
The conclusion drawn from 1H NMR spectral studies
provides further support to the mode of bonding discussed
above. A singlet at 6.61 ppm due to the phenolic proton of
1
the Schiff base disappeared in the H NMR spectra of the
organotin(IV) complexes indicating, thereby, the substitu-
tion of the phenolic proton by the organotin(IV) moiety.
Other protons in the phenyl rings are found in their normal
chemical shift range. The signals at 3.49 0.03 ppm in
the Schiff bases assigned to the –OCH3 protons remain
unchanged on complexation and thus clearly indicates the
non-involvement of this group in complex formation.
There is a small upfield shift in the signals of the aromatic
protons of the ligand upon complexation with the organo-
tin(IV) moiety. The complexes R3SnL (1–5) and R2SnClL
(6–8) show additional signals due to the presence of R
groups bonded to Sn(IV). The methyltin (Sn-CH3) sharp
singlet for complex 1 and 6 at 0.64 ppm and 1.08 ppm has
2J[119Sn-1H] coupling of 57 and 54 Hz, respectively. In tri-
and dibutyltin(IV) complexes the butyl protons appear as
multiplets and triplets. The aromatic protons in Ph-Sn
appear as multiplet in the range of 6.91–7.77 ppm [45]. In
Equations 4–7 [52–54] can be used to correlate the
coordination pattern of tin(IV) in di- and trimethyltin(IV)
derivatives with the 1,2J coupling constants: in tetra-coor-
1
dinated tin compounds (h B 112°) Js are predicted to be
smaller than about 400 Hz, whereas Js should be below
2
1
60 Hz; for penta-coordinated tin (h = 115–130°), Js fall
in the 450–670 Hz range and the Js fall in the 65–80 Hz
2
1
range; finally, for hexa-coordinated tin (h = 135°) Js and
2Js are generally larger than 670 and 83 Hz, respectively
[55]. For methyltin compounds, Eq. 4 (or 5) can be used to
give relationship between the magnitude of |2J(119Sn,1H)|
and the Me-Sn-Me angle h. A similar behavior in principle
2
is found for J(119Sn,13C) but the magnitude of this cou-
pling is less predictable. Equation 8 can be used to relate
n
the bond angle C-Sn-C (h) for Bu2Sn [56, 57]. In the
present study the h values for tri- and dimethyltin(IV) are
123

J IRAN CHEM SOC
110.5o and 109o, respectively, which confirm the tetrahe-
dral geometry around the tin in solution. h value of 106.9
for 2J(119Sn,13C) for tetra-coordinated phenyltin(IV)
derivatives has been reported earlier [58], while in present
case the value is 107.3 (Table 1).
X-ray crystal study
The ortep diagram of 4-((3,5-dimethylphenylimi-
no)methyl)-2-methoxyphenol is shown in Fig. 2 while
crystal data, selected bond distances and angles are given
in Tables 2 and 3, respectively. Unit cell and H-bonds are
shown in Fig. 3. The space group of the crystal is P21. The
bond lengths within the phenyl ring range from 1.373(2) to
ꢂ
ꢂ
À
Á
1J 119 Sn;13
C
¼ 11:4h ꢁ 875
ð4Þ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
À
Á
À
Á
Á
h ¼ 0:0161 2J 119Sn;1 H
þ 133:4
ꢁ 1:32 2J 119Sn;1 H
2
ꢂ
˚
1.404(3)A, typical of aromatic character [59]. The structure
of the ligand consists of 1D-polymeric chain by H-bonding.
The –OH and –OCH3 are cis to each other. The hydroxyl H
atom is involved in an intramolecular interaction with the
oxygen of the –OCH3 group. Details of hydrogen bonds are
given in Table 4.
ðIn non-coordinating solventsÞ
ð5Þ
ꢂ
ꢂ
ꢂ
Á
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
À
À
h ¼ 0:0105 2J 119Sn;1 H
þ 122:4
ꢁ 0:799 2J 119Sn;1 H
2
ðIn coordinating solventsÞ
UV–visible absorption study of complex-DNA
interaction
ð6Þ
ð7Þ
ꢂ
ꢂ
ꢂ
ꢂ
À
Á
1J 119 Sn;13
C
C
¼ ð10:7 ꢃ 0:5Þ h ꢁ ð778 ꢃ 64Þ
ꢂ
ꢂ
ꢂ
ꢂ
À
Á
1J 119 Sn;13
¼ ð9:99 ꢃ 0:73Þ h ꢁ ð746 ꢃ 100Þ
The interaction of ligand and its and tri- and diorgano-
tin(IV) complexes with DNA were examined by UV–vis-
ible spectroscopy, to get some more information about their
mode of interaction and binding strength. The effect of
varying concentration (0.058–0.23 lM) of DNA on the
electronic absorption spectra of 0.392 mM of HL and its
organotin(IV) complexes were studied and two of repre-
sentative spectra (compounds 2 and 3) are shown in Figs. 4
and 5. The strong absorption by these compounds in the
near UV region (336–352.5 nm) is attributed to the long-
living triplet excited state of the aromatic system. The
absorption spectra of HL upon increasing the concentration
of DNA showed gradual decreases in the peak intensities
with a small red shift. This phenomenon is usually asso-
ciated with molecular intercalation into the base stack of
ð8Þ
Table 1 (C-Sn-C) angles (°) based on NMR parameters of selected
organotin(IV) derivatives
Compound 1J(119Sn-13C) (Hz) 2J(119Sn-1H) (Hz) Angle(°)
h(1J)
h(2J)
1
2
6
7
388.78
395
57
–
109.1 110.5
114
108.7 109
114.5
–
385.5
398
54
–
–
Fig. 2 ORTEP drawing of HL
with atomic numbering scheme
123

J IRAN CHEM SOC
Table 2 Crystal data and structure refinement parameters for HL
Formula
C16 H17 NO2
Formula weight
Crystal system
Space group
255.31
Monoclinic
P21
˚
a (A)
8.4750(3)
11.1556(4)
15.1128(6)
90
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90
90
3
˚
V (A )
1,428.82(9)
4
Z
d (g cm-3
l(Mo Ka) (mm-1
)
1.187
Fig. 3 Unit cell representation of HL viewed along b-axis. H-bond-
ing is shown by dotted lines
)
0.078
F(000)
544
˚
Table 4 Hydrogen-bond geometry (A, °) for ligand HL
Crystal habit/size (mm)
Prisms/
0.40 9 0.30 9 0.25
D–HꢀꢀꢀꢀA
D–H
HꢀꢀꢀꢀA
DꢀꢀꢀꢀA
D–HꢀꢀꢀꢀA
T (K)
296 (2)
˚
O2–H2ꢀꢀꢀꢀO1
O2–H2ꢀꢀꢀꢀN1
O4–H4ꢀꢀꢀꢀO3
O4–H4ꢀꢀꢀꢀN2
C11–H11ꢀꢀꢀꢀO2
C27–H27ꢀꢀꢀꢀO4
0.8200
0.8200
0.8200
0.8200
0.9300
0.9300
2.2500
2.0700
2.2300
2.0700
2.4900
2.4900
2.679(2)
2.837(2)
2.675(2)
2.841(2)
3.347(2)
3.350(2)
113.00
156.00
114.00
156.00
154.00
154.00
Radiation (A) (Mo Ka)
0.71073
h min–max (°)
Total reflections
3.02–25.25
4,151
Tot., Uniq. Data, R(int)
Observed data [I [ 0.0 sigma(I)]
5,778, 4,151, 0.0159
3,566
Nref, Npar
4,151, 351
w = 1/[r2(Fo)2 ? (0.0468 P)2 ? 0.0830
Symmetry codes: (i) 1 - x, -1/2 ? y, 1 - z; (ii) -x, -1/2 ? y,
1 - z; (iii) 1 ? x, y, z
P] where P = [(Fo)2 ? 2(Fc)2]/3
R, wR2, S
0.0336, 0.0802, 1.035
-0.090, 0.102
1.035
Min. and Max. Resd. Dens. [e/Ang3]
the DNA [60]. The strength of this electronic interaction is
expected to decrease as the cube of the distance between
the chromophore and the DNA bases. By decreasing the
distance between intercalated HL and DNA bases, hypo-
chromism takes place obviously. Thus, this is consistent
with the combination of HL p electrons and p electrons of
DNA bases. Consequently, the energy level of the p–p*
electron transition decreases, which causes a red shift. This
contributes to the hypochromic effect discussed above [61].
In case of complexes hyperchromism was observed with
significant shift in spectral profile which is indication of
electrostatic mode of interaction between the negatively
charged oxygen of the phosphate group of DNA and the
positively charged tin atom, a hard Lewis acid which
additionally binds electrostatically to the phosphate back-
bone of the DNA helix [62]. Hyperchromic effect and
hypochromic effect are the spectra features of DNA con-
cerning its double-helix structure.
Goodness-of-fit
˚
Table 3 Selected bond lengths (A) and bond angles (°) for HL
Bond lengths
O1–C12
O1–C16
1.366(2)
1.399(3)
1.355(2)
1.422(3)
1.278(3)
1.376(3)
C12–C13
C13–C14
C1–C6
1.404(3)
1.373(2)
1.385(3)
1.387(3)
1.394(2)
1.511(4)
O2–C13
N1–C1
C1–C2
N1–C9
C10–C11
C3–C7
C11–C12
Bond angles
O2–C13–C12
O2–C13–C14
O1–C12–C13
O1–C12–C11
N1–C9–C10
N1–C1–C6
N1–C1–C2
121.95(16)
118.99(17)
114.02(17)
125.66(17)
124.39(16)
117.15(17)
123.75(17)
C11–C12–C13
C12–C13–C14
C9–C10–C11
C2–C1–C6
120.32(16)
119.06(17)
122.35(17)
119.00(19)
118.75(17)
118.87(16)
120.58(17)
C11–C10–C15
C9–C10–C15
C10–C11–C12
Based upon the variation in absorbance, the association
constants of these complexes with DNA were determined
according to Benesi-Hildebrand Eq. 9 [63]:
123

J IRAN CHEM SOC
Fig. 4 Absorption spectra of
0.392 mM n-Bu3SnL in the
absence (a) and presence of
0.058 lM (b), 0.115 lM (c),
0.173 lM (d), 0.230 lM DNA
(e). The arrow direction
indicates increasing
concentrations of DNA
Fig. 5 Absorption spectra of
0.392 mM Ph3SnL in the
absence (a) and presence of
0.058 lM (b), 0.115 lM (c),
0.173 lM (d), 0.230 lM DNA
(e). The arrow direction
indicates increasing
concentrations of DNA
examining the changes in the absorbance for the complexes
with increasing concentration of DNA. Kb was obtained
from the ratio of slope to the intercept from the plot of
1/[DNA] versus Ao/A–Ao. The intrinsic binding constant
values (Kb) for the HL, 2 and 3 were found to be
1.1 9 104, 4.35 9 103, 3.9 9 103 M-1, respectively. The
interaction of these drugs with DNA is a spontaneous
process as indicated by their negative values of DG
(-23.08, -20.76, -20.49 kJ mol-1 for HL, 2 and 3,
respectively).
A0
eG
eG
1
¼
þ
ð9Þ
A ꢁ A0 eHꢁG ꢁ eG eHꢁG ꢁ eG K½DNAꢄ
where K is the association constant, A0 and A are the
absorbances of the drug and its complex with DNA,
respectively, and eG and eHꢁG are the absorption coeffi-
cients of the drug and the drug-DNA complex, respec-
tively. In order to compare quantitatively the binding
strength of the HL and its complexes with DNA, the
intrinsic binding constants (K or Kb) were obtained by
123

J IRAN CHEM SOC
due to its hard Lewis acidic property, thus, neutralizing the
negative charge of the DNA resulting in significant con-
traction and conformational changes in the DNA helix that
leads to the breakage of the secondary structure of the
DNA [66]. The same result has also observed in case of
UV–visible spectroscopy as discussed in Sect. 3.4.
Enzymatic study
The effect of various concentrations of HL and its
organotin(IV) complexes on the activity of the enzyme,
Alkaline Phosphatase EC 3.1.3.1 was studied for the
hydrolysis of pNPP. Alkaline Phosphatases catalyze the
transfer of phosphate groups to water (hydrolysis) or
alcohol (transphosphorylation) using a wide variety of
phosphomonoesters and are characterized by a high pH
optima and a broad substrate specificity [67]. From the
study we have observed that the presence of HL and its
organotin(IV) complexes resulted in the deactivation of the
enzyme. The activity of enzyme was markedly decreased
by increasing the concentration of HL and its organo-
tin(IV) complexes and it was almost completely lost at high
concentrations. The remarkable activity of the ligand may
be due to OH group, which can play an important role in
the enzymatic activity [68]. Among the studied azomethine
and its organotin(IV) complexes highest activity was
exhibited by Ph3Sn(IV) derivative. The lower activity of
organotin(IV) complexes (except for triphenyltin(IV)) can
most probably due to the formation of the stable bond upon
complexation between the tin and oxygen atoms. The dif-
ferent behavior of triphenyltin(IV) complex can be due to
weaker interactions of ligand with tin because of bulky
phenyl groups, thereby regulating the formation of
R3Sn ? (IV) moiety that plays a key role in the inhibition
of alkaline phosphatase enzyme. The inhibition profile is
shown in Fig. 7.
Fig. 6 Effects of increasing amount of HL, compounds 2 and 3 on
relative viscosity of CT-DNA at 25 0.1 °C. [DNA] = 2.97 9
10-4
M
Viscosity measurement
Binding of small molecules to DNA can change not only
the helical twist, but also the contour of length and stiffness
(both bending and torsional) and can induce systematic
bend into the DNA double helix. A hydrodynamic method
such as viscometric measurements in which the solution
viscosity of DNA is responsive to the changes in the
effective length of DNA molecules is one of the most
decisive tests for understanding the binding mode of DNA
in solution, i.e., intercalation or other binding modes.
Generally, an increase in the relative viscosity is attributed
to a length increase of the DNA double helix due to
intercalation. On the other hand, a decrease in the relative
viscosity due to the reduction of the effective length of
DNA molecules results from the bending of the DNA
double helix caused by electrostatic interaction between the
anion site of phosphate of DNA and the cation site of
molecule [64, 65]. The values of relative viscosity (g/go)1/3
were calculated from (t/to)1/3 ratio for all samples, where t,
to, g and go represent the time and viscosity of DNA
solution with and without compound, respectively. (g/go)1/3
was plotted versus [compound]/[DNA] ratio (Fig. 6). As
evidenced from Fig. 6 the relative viscosity of HL
increases with increasing the [HL]/[DNA] ratio, indicating
the intercalative mode of interaction of HL with DNA. On
the other hand, the relative viscosity of compounds 2 and 3
decreases with increasing the [compound]/[DNA] ratio,
indicating the electrostatic mode of interaction of com-
pounds 2 and 3 with DNA. The electrostatic mode of
interaction of Sn(IV) complexes is due to the fact that
Sn(IV) is a hard acid and prefers to combine with a hard
oxygen base. Cationic Sn(IV) exerts electrostatic interac-
tion toward the polyanionic phosphate backbone of DNA
Antioxidant activity
The DPPH radical is a stable free radical (due to extensive
delocalization of the unpaired electron) having kmax at
517 nm. When this compound abstracts a hydrogen radical
from external source absorption vanishes due to the
absence of free electron delocalization [69]. The antioxi-
dant activity of the synthesized ligand HL and its
organotin(IV) complexes has attracted increasing interests
and been noticeably examined. The proposed mechanism
for the antioxidant activity of HL and its organotin(IV)
complexes is given in Scheme 5. It is evident from Table 5
that the scavenging activity increases with increasing
sample concentration in the range tested. As shown in
Table 5, the free ligand HL has scavenging activity
between 9.8 and 74 % within the investigated concentration
123

J IRAN CHEM SOC
Fig. 7 Inhibition of ALP by HL
and its organotin(IV) complexes
Table 5 Antioxidant scavenging activity data of HL and its organotin(IV) complexes on DPPHꢀ free radical at different concentrations
Compounds
DPPH scavenging activity (%) SD
625 lM
312.5 lM
62.5 lM
31.3 lM
6.3 lM
0.6 lM
0.1 lM
HL
74 0.2
65 0.4
61 0.7
66 0.3
56.6 0.7
60 0.2
80.5 0.2
36 0.3
15.1 0.2
27.8 0.9
8.9 0.6
12 0.7
9.8 0.8
9.6 0.2
7.8 0.2
3.8 0.2
9.7 0.3
20.7 0.8
1
81.3 0.4
90 0.5
58.6 0.9
87.3 0.8
78.9 0.2
81.7 0.5
92.3 0.5
55.3
1
12.2 0.4
7.9 0.9
4.2 0.2
13.3 0.7
30.4 0.4
3
39.5 0.2
56.6 0.2
73.9 0.7
65.2 0.5
5
80.8 0.2
83.7 0.8
92.3 0.9
27.9 0.2
46.96 0.6
50.3 0.5
7
Ascorbic acid
70.3
1
SD standard deviation
range due to the OH group which can react with DPPH radical
by the typical H-abstraction reaction (HAT) to form a stable
macromolecular radical [70]. The antioxidant activity is
increased by the presence of a Sn(IV) metal center, as previ-
ously reported for other metals [71]. The maximum activity is
shown by phenyltin derivative (compound 3) which has the
scavenging activity between 7.8 and 90 %. In free ligand, the
abstraction of phenolic hydrogen is easy but in case of com-
plexes the more chances for the hydrogen abstraction is from
the CH=N group rather than the OCH3 group. This is because
of the fact that pKa value of azomethine proton (CH=N) is
lower than that of the methoxy proton as it is attached with
doublyboundednitrogenatom. Alsoazomethinegroupproton
is sp2 hybridized in nature while that of the methoxy group is
sp3 hybridized. Ifthe hydrogenabstraction comesfromCH=N
group, the negatively charged comes on the sp2 carbon and is
in conjugation with the benzene ring so the stability of the
resulting anion is higher while in case the hydrogen
abstraction comes from methoxy group, the negatively
chargedcomesonthesp2 carbonandisnotinconjugationwith
the benzene ring so the stability of the resulting anion is less.
Antibacterial activity
The synthesized ligand and complexes were screened for
antibacterial activity by agar well diffusion [48]. The data
are given in Table 6. The data reveal that the ligand shows
no activity while its organotin(IV) derivatives show mod-
erate antibacterial activity. However, the antibacterial
activity is less than that of the standard drug.
Antifungal activity
The synthesized ligand di- and triorganotin(IV) derivatives
of 4-((3,5-dimethylphenylimino)-methyl)-2-methoxyphe-
nol] were tested for their antifungal activity by tube
123

J IRAN CHEM SOC
Scheme 5 Proposed
mechanism for the antioxidant
activity of HL and its
organotin(IV) complexes
Table 6 Antibacterial activity data of HL and its organotin(IV) compounds
Zone of inhibition (mm)
Ref. drugs
Name of bacterium
HL
(1)
(2)
(3)
(4)
(5)
(6)
Roxythromycin
Cefixime
Staphylococcus aureus
Klebsiella pneumoniae
Micrococcus luteus
–
–
–
–
–
–
12
–
20
14
20
15
19
19
20
18
15
14
17
23
22.5
15
24
19.5
–
14
10.5
11
13.5
–
17
16
13
12
–
36
26
35
20
26
35
22
21
30
16
22
26
14
14
16
17
Bordetella bronchiseptica
Escherichia coli
Bordetella bronchiseptica
–
–
15
diffusion [70]. The data are given in Table 7. Most of the
compounds showed moderate fungicidal activity as com-
pared with the reference standard drugs. Compound (3) is
found to be best for the inhibition of fungal growth except
in the case of Candida albicans, while compound (2) has
the least activity.
linkage and hetero aromatic moiety in the synthesized
complexes exhibit extensive biological activities due to
increased liposolubility of the molecules in crossing cell
membrane of the microorganism. The presence of electron
donor group (–OCH3) in the complexes also plays a role in
enhancing the inhibition activity [72, 73].
Though the exact biochemical mechanism is not com-
pletely understood, the mode of action of antimicrobials
may involve various targets in the microorganisms. Metal
complexes also disturb the respiration process of the cell
and thus block the synthesis of proteins, which restricts
further growth of the organisms. This enhancement in
inhibiting the growth of bacteria and fungi can also be
explained on the basis of their structure. The azomethine
Cytotoxicity
The cytotoxicity was studied by the brine shrimp lethality
method and the results are summarized in Table 8. The
LD50 data show that all the tested compounds, even the
ligand, are toxic with LD50 values in the range
0.42–44.55 lg/mL in comparison with reference drug
123

J IRAN CHEM SOC
Table 7 Antifungala, b data of HL and its organotin(IV) compounds
characterized by single crystal analysis. The ligand was
treated with different di- and triorganotin(IV) chlorides to
form the corresponding complexes. The ligand coordinates
through oxygen to the Sn atom lead to the formation of four
coordinated tin specie. However, the 119Sn-NMR in coor-
dinating solvent (DMSO) gives pseudotetrahedral envi-
ronments around the tin atom that is due to the coordinating
nature of the solvent. The results of UV–visible spectros-
copy and viscometry revealed intercalative mode of inter-
action of HL and electrostatic mode of interaction of
complexes with DNA. The negative values of Gibb’s free
energy change show the spontaneity of these interactions.
The antimicrobial and cytotoxic activities of triorgano-
tin(IV) derivatives are relatively higher than their corre-
sponding diorganotin(IV) analogues which is due to their
greater ability to bind to protein. Moreover, the synthesized
compounds show moderate antioxidant activities.
Compound
Percent Inhibition
Flavus F.
solani
A.
niger
Mucor
sp.
A.
fumigates
HL
1
35
65
90
94
67
45
–
62
80
30
80
40
78
2
20
72
43
57
3
24
65
54
78
4
25
69
35
55
5
32
56
100
65
45
67
Positive
control
100
100
100
100
a
Concentration: 200 lg/mL of media
b
Percent inhibition of fungal growth = 100 - gt/gc 9 100, where
gt = linear growth in test (mm) and gc = linear growth in vehicle
control (mm)
Table 8 Cytotoxicity data of HL and its organotin(IV) compounds
Acknowledgments M. Sirajuddin (Pin# P7-017) gratefully
acknowledges the HEC Islamabad, Pakistan, for financial support.
Compound
No. of shrimps killed out of 30 per dilutiona LD
b,c
50
1,000 lg/mL
100 lg/mL
10 lg/mL
HL
29
30
30
30
30
30
0
24
27
30
27
30
24
0
3
25
25
23
19
22
0
44.55
0.42
5.05
1.46
8.24
1.89
References
1
2
1. N. Galic, Z. Cimerman, V. Tomisic, Spectrochim. Acta Part A.
71, 1274 (2008)
2. W. Rehman, A. Badshah, S. Khan, L.T.A. Tuyet, Europ.
J. Medical Chem. 44, 3981 (2009)
3. R.E. Hester, E.M. Nour, J. Raman Spectrosc. 11, 49 (1981)
4. E.M. Nour, A.A. Taha, I.S. Alnaimi, Inorg. Chim. Acta. 141, 139
(1988)
5. E.M. Nour, A.M. Al-Kority, S.A. Sadeek, S.M. Teleb, Synth.
React. Inorg. Met. Org. Chem. 23, 39 (1993)
6. W. Wang, F.L. Zeng, X. Wang, M.Y. Tan, Polyhedron. 15, 1699
(1996)
7. L. Pellerito, L. Nagy, Coor. Chem. Rev. 224, 111 (2002)
8. S. Mishra, M. Goyal, A. Singh, Main Group Met. Chem. 25, 437
(2002)
3
4
5
Vehicle control
a
Against brine-shrimps (in vitro)
b
Data is based on mean value of 3 replicates each of 10, 100 and
1,000 lg/mL
c
Compared with standard drug MS -222 (Tricaine methanesulfo-
nate) with LD50 value of 4.30 lg/mL
MS-222 (Tricaine Methanesulfonate) with LD50 value
4.3 lg/mL. Complexes 1, 3 and 5 were the most toxic as
compared with tested compounds and reference drugs. The
biological activities of the organotin(IV) complexes are
comparable to those previously reported [74].
9. A. Saxena, J.P. Tandon, A.J. Crowe, Polyhedron. 4, 1085 (1985)
10. A.D. Tiwari, A.K. Mishra, S.B. Mishra, B.B. Mamba, B. Maji, S.
Bhattacharya, Spectrochim. Acta Part A. 79, 1050 (2011)
11. J.S. Casas, A. Castineiras, F. Condori, M.D. Couce, U. Russo, A.
Sanchez, R. Seoane, Polyhedron. 22, 53 (2003)
12. R.G. Zarracino, J.R. Quinones, H. Hopfl, J. Organomet. Chem.
664, 188 (2002)
13. C. Pettiniari, F. Marchetti, R. Pettiniari, D. Martini, A. Drozdov,
S. Troyanov, Synthesis and characterisation of tin(IV) and
organotin(IV) derivatives 2-{[(2-hydroxyphenyl) imino]methyl}phe-
nol. Inorg. Chim. Acta. 325, 103 (2001)
14. S. Tabassum, C. Pettinari, J. Organomet. Chem. 691, 1761 (2006)
15. M. Gielen, M. Biesemans, R. Willem, Appl. Organomet. Chem.
19, 440 (2005)
16. P. Yang, M. Guo, Coord. Chem. Rev. 185, 189 (1999)
17. A.J. Crowe, Antitumor activity of tin compounds, in Metal
compounds in cancer therapy, ed. by S. P. Fricker (Chapman &
Hall, London, 1994)
18. T.B. Baul, C. Masharing, G. Ruisi, R. Jirasko, M. Holcapek, D. de Vos,
D. Wolstenholme, A. Linden, J. Organomet. Chem. 692, 4849 (2007)
19. H.D. Yin, S.W. Chen, L.W. Li, D.Q. Wang, Inorg. Chim. Acta.
360, 2215 (2007)
Conductometric study
The conductance of these complexes has been recorded
in 80 % ethanol at room temperature in the range
5–19 lS cm-1 at 25 °C, suggesting their non-electrolytic
nature [75].
Conclusion
The
ligand
4-((3,5-dimethylphenylimino)methyl)-2-
methoxyphenol was successfully synthesized and
123

J IRAN CHEM SOC
20. H.D. Yin, M. Hong, G. Li, D.Q. Wang, J. Organomet. Chem. 690,
3714 (2005)
21. M. Cagnoli, A. Alama, F. Barbieri, F. Novelli, C. Bruzzo, F.
Sparatore, Anticancer Drugs 9, 603 (1998)
49. V. Barba, E. Vega, R. Luna, H. Hopfl, I.H. Beltran, S.L. Zamu-
dio-Rivera, J. Organomet. Chem. 692, 731 (2007)
50. A. Lycka, M. Nadvornik, K. Handlir, J. Holecek, Collect. Czech.
Chem. Commun. 49, 2903 (1984)
22. A.G. Davies, P.J. Smith, Adv. Inorg. Chem. Radiochem. 23, 1
(1980)
23. B.M. Elliot, W.N. Aldridge, J.M. Bridges, J. Biochem. 177, 461
(1979)
24. S.E.H. Etaiw, A.S. Sultan, A.S.B. El-din, Europ. J. Med. Chem.
46, 5370 (2011)
25. S.E.H. Etaiw, A.S. Sultan, A.S.B. El-din, M.M. El-bendary, Or-
ganomet. Chem. 696, 1668 (2011)
26. L.S. Lerman, J. Mol. Biol. 3, 18 (1961)
27. M.J. Waring, The molecular basis of antibiotic action (John
Wiley and Sons, New York, 1972)
28. R.K. Gilpin, Anal. Chem. 69, 145R (1997)
29. Y.G. Jun, X.J. Juan, C.H. Yuan, L.Z. Zhou, Chin. J. Chem. 22,
1325 (2004)
51. J. Holecek, A. Lycka, D. Micak, L. Nagy, G. Vanko, J. Brus,
S.S.S. Raj, H.K. Fun, S. Weng, Collect. Czech. Chem. Commun.
64, 1028 (1999)
52. T.P. Lockhart, W.F. Manders, J.J. Zuckerman, J. Am. Chem. Soc.
107, 4546 (1985)
53. T.P. Lockhart, W.F. Manders, Inorg. Chem. 25, 892 (1986)
54. T.P. Lockhart, W.F. Manders, J. Am. Chem. Soc. 109, 7015 (1987)
55. G. Casella, F. Ferrante, G. Saielli, Inorg. Chem. 47, 4796 (2008)
56. J. Holecek, M. Nadvornik, K. Handlir, A. Lycka, J. Organomet.
Chem. 315, 299 (1986)
57. S.J. Blunden, P.A. Cussack, D.G. Gillies, Magn. Reson. Chem.
24, 921 (1986)
58. J. Holecek, A. Lycka, K. Handlir, M. Nadvornik, Collect. Czech
Chem. Commun. 53, 571 (1988)
30. M. Rodriguez, A.J. Bard, Anal. Chem. 62, 2658 (1990)
31. R. Barbieri, L. Pellerito, G. Ruisi, A. Silvestri, A. Barbieri
Paulsen, G. Barone, S. Posante, M. Rossi, in Chemical processes
in the marine environment, eds. by A. Gianguzza, E. Pelizzetti, S.
Sammartano (Springer, Berlin, 2000)
32. P.J. Smith (ed.), Chemistry of Tin (Blackie Acad. and Prof.,
London, 1998)
33. W.L.F. Armarego, C.L.L. Chai, Purification of laboratory
chemicals, 5th edn. (Butterworth-Heinemann, London, 2003)
34. C.V. Sastri, D. Eswaramoorthy, L. Giribabu, B.G. Maiya, J.
Inorg. Biochem. 94, 138 (2003)
35. S. Dey, S. Sarkar, H. Paul, E. Zangrando, P. Chattopadhyay,
Polyhedron. 29, 1583 (2010)
36. J. Ahlers, Biochem. J. 149, 535 (1975)
37. K. Jiao, W. Sun, H.Y. Wang, Chin. Chem. Lett. 13, 69 (2002)
38. K. Walter, C. Schu¨tt, in Methods of enzymatic analysis, 2nd edn,
ed. by H.U. Bergmeyer (Academic Press, New York, 1974)
39. M.M. Hossain, M.F. Aziz, R. Ahmed, M. Hossain, A. Mahmuda,
T. Ahmed, M.H. Mazumder, Int. J. Pharm. Sci. 2, 60 (2010)
40. Z.A. Taha, A.M. Ajlouni, W. Al Momani, A.A. Al-Ghzawi,
Spectrochim. Acta Part A. 81, 570 (2011)
59. F.H. Allen, O. Kennard, D.G. Waston, L. Brammer, A.G. Orpen,
R. Taylor, J. Chem. Soc. Perkin Trans. 2, S1 (1987)
60. A.A. Ensafi, R. Hajian, S. Ebrahimi, J. Braz. Chem. Soc. 20, 266
(2009)
61. R. Hajian, N. Shams, M. Mohagheghian, J. Braz. Chem. Soc. 20,
1399 (2009)
62. F.A. Shah, M. Sirajuddin, S. Ali, S.M. Abbas, M.N. Tahir, C.
Rizzoli, Inorg. Chim. Acta. 400, 159 (2013)
63. M. Sirajuddin, S. Ali, A. Badshah, J. Photochem. Photobiol. B
124, 1 (2013)
64. M. Sirajuddin, S. Ali, N.A. Shah, M.R. Khan, M.N. Tahir,
Spectrochim. Acta Part A. 94, 134 (2012)
65. M. Tariq, N. Muhammad, M. Sirajuddin, S. Ali, N.A. Shah, M.R.
Khan, M.N. Tahir, J. Organomet. Chem. 723, 79 (2013)
66. M.R. Malik, V. Vasylyeva, K. Merz, N. Metzler-Nolte, M. Sa-
leem, S. Ali, A.A. Isab, K.S. Munawar, S. Ahmad, Inorg. Chim.
Acta. 376, 207 (2011)
67. F.J. Huoa, C.X. Yin, Y.B. Wu, P. Yang, Russ. J. Inorg. Chem. 55,
1087 (2010)
68. C.A. Kontogiorgis, D. Hadjipavlou-Litina, J. Enzyme Inhib, Med.
Chem. 18, 63 (2003)
41. A. Rehman, M.I. Choudhary, W.J. Thomsen, Bioassay techniques
for drug development (Harwood Academic Publishers, Amster-
dam, 2001)
42. B.N. Mayer, N.R. Ferrigni, J.E. Putnam, L.B. Jacobson, D.E.
Nichols, J.L. Mclaughlin, Planta Med. 45, 31 (1982)
43. T. Sedaghat, S. Menati, Inorg. Chem. Commun. 7, 760 (2004)
44. A. Graisa, Y. Farina, E. Yousif, E.E. Saad, Intern. J. Chem. 1, 34
(2009)
69. M.C. Foti, C. Daquino, C. Geraci, J. Org. Chem. 69, 2309 (2004)
70. A. Corona-Bustamante, J.M. Viveros-Paredes, A. Flores-Parra,
A.L. Peraza-Campos, F.J. Martinez-Martinez, M.T. Sumaya-
Martinez, A. Ramos-Organillo, Molecules 15, 5445 (2010)
71. S. Ahmad, S. Ali, S. Shahzadi, F. Ahmed, K.M. Khan, Turk.
J. Chem. 15, 5445 (2010)
72. M.A. Neelakantan, M. Esakkiammal, S.S. Mariappan, J. Dhar-
maraja, T. Jeyakumar, Indian J. Pharm. Sci. 72, 216 (2010)
73. M.A. Neelakantan, F. Rusalraj, J. Dharmaraja, S. Johnsonraja, T.
Jeyakumar, P.M. Sankaranarayana, Spectrochim. Acta A. 71,
1599 (2008)
74. M. Sirajuddin, S. Ali, A. Haider, N.A. Shah, A. Shah, M.R. Khan,
Polyhedron. 40, 19 (2012)
75. M. Sirajuddin, S. Ali, Synthesis and characterization of potential
bioactive organotins (LAP Lambert Academic Publishing, Ger-
many, 2013)
45. S. Shahid, S. Ali, M. Hussain, M. Mazhar, S. Mahmood, S.
Rehman, Turk. J. Chem. 26, 589 (2002)
46. M. Hanif, M. Hussain, S. Ali, M.H. Bhatti, M.S. Ahmed, B.
Mirza, H.S. Evans, Turk. J. Chem. 31, 349 (2007)
47. J.S. Casas, A. Castineiras, F. Condori, M.D. Couce, U. Russo, A.
Sanchez, R. Seoane, J. Sordo, J.M. Varela, Polyhedron. 22, 53
(2003)
48. C. Ma, Y. Han, R. Zhang, Inorg. Chim. Acta. 360, 2439 (2007)
123