Organotin(IV) complexes with pyruvic acid phenylhydrazone (HPAPD): Synthesis, spectral characterization, and invitro antibacterial activity

Article abstract of DOI:10.1080/00958972.2012.687104

The reaction of pyruvic acid phenylhydrazone [HPAPD, (1)] with organotin(IV) chloride(s) leads to the formation of five new organotin(IV) complexes: [MeSnCl₂(PAPD)] (2), [BuSnCl₂(PAPD)] (3), [PhSnCl₂(PAPD)] (4), [Me_2<

Full text of DOI:10.1080/00958972.2012.687104

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Organotin(IV) complexes with pyruvic
acid phenylhydrazone (HPAPD):
synthesis, spectral characterization,
and in vitro antibacterial activity
M.A. Salam a , M.A. Affan a , Fasihuddin B. Ahmad a & MD. Azharul
Arafath b
a Faculty of Resource Science and Technology , Universiti Malaysia
Sarawak , 94300 Kota Samarahan , Sarawak , Malaysia
b Department of Chemistry , Shahjalal University of Science and
Technology , Sylhet 3114 , Bangladesh
Published online: 14 May 2012.
To cite this article: M.A. Salam , M.A. Affan , Fasihuddin B. Ahmad & MD. Azharul Arafath
(2012) Organotin(IV) complexes with pyruvic acid phenylhydrazone (HPAPD): synthesis, spectral
characterization, and in vitro antibacterial activity, Journal of Coordination Chemistry, 65:11,
1999-2007, DOI: 10.1080/00958972.2012.687104
To link to this article: http://dx.doi.org/10.1080/00958972.2012.687104
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Journal of Coordination Chemistry
Vol. 65, No. 11, 10 June 2012, 1999–2007
Organotin(IV) complexes with pyruvic acid phenylhydrazone
(HPAPD): synthesis, spectral characterization,
and in vitro antibacterial activity
M.A. SALAM*y, M.A. AFFANy, FASIHUDDIN B. AHMADy and
MD. AZHARUL ARAFATHz
yFaculty of Resource Science and Technology, Universiti Malaysia
Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
zDepartment of Chemistry, Shahjalal University of Science and
Technology, Sylhet 3114, Bangladesh
(Received 4 December 2011; in final form 12 March 2012)
The reaction of pyruvic acid phenylhydrazone [HPAPD, (1)] with organotin(IV) chloride(s)
leads to the formation of five new organotin(IV) complexes: [MeSnCl2(PAPD)] (2),
[BuSnCl2(PAPD)] (3), [PhSnCl2(PAPD)] (4), [Me2SnCl(PAPD)] (5), and [Ph2SnCl(PAPD)]
(6). The ligand [HPAPD, (1)] and its organotin(IV) complexes (2–6) have been characterized by
CHN analyses, molar conductivity, UV-Vis, FT-IR, 1H, 13C, and 119Sn NMR spectral studies.
Spectroscopic data suggested that HPAPD is coordinated to tin(IV) through the carboxylato-O
and azomethine-N as a mononegative bidentate chelating agent; the coordination number
of tin is five. Compound 1 and its organotin(IV) complexes (2–6) were assayed for in vitro
antibacterial activity against Staphylococcus aureus, Bacillus subtilis, Enterobacter aerogenes,
Escherichia coli, and Salmonella typhi. The screening results show that 2–6 have better
antibacterial activity than 1 and that 6 exhibits significantly better activity than 2–5.
Keywords: Pyruvic acid phenylhydrazone; Organotin(IV) complexes; Spectral analyses;
Antibacterial activity
1. Introduction
The chemistry of hydrazones plays an important role in coordination chemistry.
The chemical properties of hydrazones have been the subject of studies for some time
due to their chelating capability and pharmacological applications [1, 2].
Hydrazones and their metal complexes can also be used as analytical reagents, as a
polymer-coating, ink, pigment, and fluorescent materials [3]. Organotin(IV)-hydrazone
compounds are studied due to their agricultural and industrial applications [4, 5].
Studies have been reported on the synthesis, antitumor activities, and structural
elucidations of various organotin(IV) derivatives of hydrazones [6, 7]. In addition to
antitumor activities, organotin(IV) complexes with Schiff bases have interesting
structural possibilities. Reaction of Schiff bases and the alkyltin in different solutions
*Corresponding author. Emails: salambpx@yahoo.com; masalam20@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.687104

2000
M.A. Salam et al.
has resulted in different products, as recently reported for some diorganotin(IV)
complexes of pyruvic acid isonicotinyl hydrazone and pyruvic acid salicylhydrazone [8].
In previous work, we reported the X-ray crystal structure of pyruvic acid
phenylhydrazone (HPAPD) [9]. From the literature survey, studies on organotin(IV)
complexes derived from pyruvic acid hydrazone ligands containing ON-donors are still
lacking. We have synthesized a series of organotin(IV) complexes with the Schiff base,
HPAPD. These complexes have been characterized by elemental analysis, molar
1
conductivity, UV-Vis, FT-IR, H, 13C, and 119Sn NMR spectral studies. The anti-
bacterial activities of the studied compounds have been investigated against
Staphylococcus aureus, Bacillus subtilis, Enterobacter aerogenes, Escherichia coli, and
Salmonella typhi.
2. Experimental
2.1. Materials and methods
All reagents were purchased from Fluka, Aldrich, and JT Baker. Solvents were purified
according to standard procedures [10]. UV-Vis spectra were recorded in CHCl3 solution
with a Perkin Elmer Lambda 25 UV-Vis spectrophotometer. Infrared (IR) spectra were
recorded as KBr discs using a Perkin Elmer Spectrum GX Fourier-Transform
1
spectrometer from 4000 to 370 cmꢀ1 at room temperature. H, 13C, and 119Sn NMR
spectra were recorded on a JEOL 500 MHz-NMR spectrophotometer with chemical
shifts given in ppm relative to SiMe4 and SnMe4 in CDCl3 solvent. CHN analyses were
obtained with a Flash EA 1112 series CHN elemental analyzer. Molar conductivity
measurements were carried out with a Jenway 4510 conductivity meter using DMF.
2.2. Synthesis of HPAPD (1)
Pyruvic acid (0.440 g, 5 mmol) was dissolved in 10 mL absolute ethanol with constant
stirring. An ethanolic solution of phenylhydrazine (0.540 g, 5 mmol) was then added to
the solution dropwise. The resulting reaction mixture was refluxed for 4 h (scheme 1).
On cooling the solution to room temperature, a light-orange powder separated, which
-H2O
Pyruvic acid
Phenylhydrazine
Scheme 1. Synthesis of pyruvic acid phenylhydrazone [HPAPD] (1).

Pyruvic acid organotin(IV) complexes
2001
was filtered and washed with ethanol. Light-orange microcrystals were recrystallized
from ethanol and dried in vacuo over silica gel. Yield: 0.724 g, 73%: m.p.: 187–189ꢁC:
UV-Vis (CHCl3) ꢀmax (nm): 298, 338: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3333 (br, OH), 3285
1
(s, NH), 1709 (m, C¼O), 1595 (m, C¼N), 991 (m, N–N). H NMR (CDCl3, ppm)
ꢂ: 11.56 (s, 1H, COOH), 9.43 (s, 1H, N–H), 7.28–7.25 (m, 5H, phenyl ring), 2.13 (s, 3H,
N¼C–CH3). 13C NMR (CDCl3, ppm) ꢂ: 165.71 (COOH), 143.10 (C¼N), 132.24–122.17
(phenyl ring), 9.04 (CH3). Anal. Calcd for C9H10N2O2 (%): C, 60.66; H, 5.65; N, 15.72.
Found (%): C, 60.61; H, 5.59; N, 15.68.
2.3. Synthesis of [MeSnCl2(PAPD)] (2)
HPAPD (0.356 g, 2.0 mmol) was dissolved in absolute methanol (10 mL) under nitrogen
in a Schlenk round bottom flask. Then, 10 mL methanolic solution of methyltin(IV)
trichloride (0.48 g, 2.0 mmol) was added dropwise. The resulting reaction mixture was
refluxed for 4 h (scheme 2) and cooled to room temperature. The microcrystals were
filtered off, washed with a small amount of cold methanol, and dried in vacuo over silica
gel. Yield: 0.62 g, 74%: m.p.: 224–226ꢁC. Molar conductance (DMF) ꢀꢀ1 cm2 molꢀ1
:
7.5: UV-Vis (CHCl3) ꢀmax (nm): 312, 368, 411: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3331 (s,
NH), 1603 [m, ꢁasy(COOꢀ)], 1370 [m, ꢁsym(COOꢀ)], 1584 (m, C¼N), 1024 (m, N–N),
602 (w, Sn–C), 550 (w, Sn–O), 436 (w, Sn–N). 1H NMR (CDCl3, ppm, 2J[119Sn, 1H]) ꢂ:
9.76 (s, 1 H, N–H), 7.29–7.18 (m, 5H, phenyl ring), 2.70 (s, 3H, N¼C–CH3), 1.20 (s, 3H,
Sn–CH3), [75.3 Hz]. 13C NMR (CDCl3, ppm) ꢂ: 173.25 (COOꢀ), 150.08 (C¼N), 132.03–
114.11 (phenyl ring), 19.69 (CH3), 9.21 (Sn–CH3). 119Sn NMR (CDCl3, ppm) ꢂ:
ꢀ170.06. Anal. Calcd for C10H12N2O2Cl2Sn (%): C, 31.45; H, 3.16; N, 7.33. Found
(%): C, 31.40; H, 3.12; N, 7.10.
The other complexes (3–6) were synthesized using a similar procedure to
organotin(IV) complex (2) using appropriate organotin(IV) chloride(s) (scheme 2).
Orgnotin(IV) chloride(s)
Refluxed, 4 h
N2 atmosphere
Abs.MeOH
Pyruvic acid phenylhydrazone
R'
R = Me,
R' = Cl,
X = Cl (2)
(3)
R = Bu, R' = Cl,
R = Ph, R' = Cl,
R = Cl, R' = Me,
X = Cl
(4)
X = Cl
(5)
X = Me
R = Cl, R' = Ph, X = Ph (6)
Scheme 2. The reaction scheme for the synthesis of organotin(IV) complexes (2–6).

2002
M.A. Salam et al.
2.4. Synthesis of [BuSnCl2(PAPD)] (3)
Yield: 0.71 g, 77%: m.p.: 218–220ꢁC. Molar conductance (DMF) ꢀꢀ1 cm2 molꢀ1: 5.8:
UV-Vis (CHCl3) ꢀmax (nm): 300, 354, 402: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3286 (s, NH),
1611 [m, ꢁasy(COOꢀ)], 1375 [m, ꢁsym(COOꢀ)], 1581 (m, C¼N), 1072 (m, N–N), 600
(w, Sn–C), 557 (w, Sn–O), 463 (w, Sn–N). 1H NMR (CDCl3, ppm) ꢂ: 9.65 (s, 1H, N–H),
7.29–7.24 (m, 5H, phenyl ring), 2.55 (s, 3 H, N¼C–CH3), 2.01–2.00 (t, 2H, Sn–CH2–
CH2–CH2–CH3), 1.67–1.61 (m, 2H Sn–CH2–CH2–CH2–CH3), 1.50–1.28 (m, 2H, Sn–
CH2–CH2–CH2–CH3), 0.99–0.91 (t, 3H, Sn–CH2–CH2–CH2–CH3). 13C NMR (CDCl3,
ppm) ꢂ: 172.42 (COOꢀ), 151.23 (C¼N), 132.78–114.87 (phenyl ring), 27.08 (Sn–CH2–
CH2–CH2–CH3), 24.69 (Sn–CH2–CH2–CH2–CH3), 22.65 (Sn–CH2–CH2–CH2–CH3),
20.75 (Sn–CH2–CH2–CH2–CH3), 15.95 (CH3). 119Sn NMR (CDCl3, ppm) ꢂ: ꢀ174.5.
Anal. Calcd for C13H18N2O2Cl2Sn (%): C, 36.83; H, 4.28; N, 6.60. Found (%):
C, 36.75; H, 4.25; N, 6.57.
2.5. Synthesis of [PhSnCl2(PAPD)] (4)
Yield: 0.75 g, 78%: m.p.: 212–214ꢁC. Molar conductance (DMF) ꢀꢀ1 cm2 molꢀ1: 8.6:
UV-Vis (CHCl3) ꢀmax (nm): 299, 352, 406: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3284 (s, NH),
1605 [m, ꢁasy(COOꢀ)], 1367 [m, ꢁsym(COOꢀ)], 1580 (m, C¼N), 1022 (m, N–N), 614
(w, Sn–C), 579 (w, Sn–O), 448 (w, Sn–N). 1H NMR (CDCl3, ppm) ꢂ: 9.62 (s, 1H, N–H),
7.29–7.21 (m, 10H, phenyl ring), 2.52 (s, 3H, N¼C–CH3). 13C NMR (CDCl3, ppm) ꢂ:
175.21 (COOꢀ), 154.56 (C¼N), 132.70–115.60 (phenyl ring), 16.45 (CH3). 119Sn NMR
(CDCl3, ppm) ꢂ: ꢀ178.3. Anal. Calcd for C15H14N2O2Cl2Sn (%): C, 40.58; H, 3.17;
N, 6.31. Found (%): C, 40.52; H, 3.15; N, 6.25.
2.6. Synthesis of [Me2SnCl(PAPD)] (5)
Yield: 0.62 g, 74%: m.p.: 208–210ꢁC. Molar conductance (DMF) ꢀꢀ1 cm2 molꢀ1: 6.5:
UV-Vis (CHCl3) ꢀmax (nm): 301, 347, 412: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3288 (s, NH),
1604 [m, ꢁasy(COOꢀ)], 1376 [m, ꢁsym(COOꢀ)], 1579 (m, C¼N), 1076 (m, N–N), 620
(w, Sn–C), 536 (w, Sn–O), 462 (w, Sn–N). 1H NMR (CDCl3, ppm, 2J[119Sn, 1H]) ꢂ: 9.66
(s, 1H, N–H), 7.35–7.16 (m, 5H, phenyl ring), 2.65 (s, 3H, N¼C–CH3), 1.06 (s, 6H,
Sn–CH3), [79.5 Hz]. 13C NMR (CDCl3, ppm) ꢂ: 171.88 (COOꢀ), 150.50 (C¼N), 132.75–
118.22 (phenyl ring) 14.76 (CH3), 9.15 (Sn–CH3). 119Sn NMR (CDCl3, ppm) ꢂ: ꢀ179.2.
Anal. Calcd for C11H15N2O2ClSn (%): C, 36.55; H, 4.18; N, 7.75. Found (%): C, 36.51;
H, 4.13; N, 7.70.
2.7. Synthesis of [Ph2SnCl(PAPD)] (6)
Yield: 0.92 g, 74%: m.p.: 218–220ꢁC. Molar conductance (DMF) ꢀꢀ1 cm2 molꢀ1: 10.2:
UV-Vis (CHCl3) ꢀmax (nm): 314, 342, 408: FT-IR (KBr disc, cmꢀ1) ꢁmax: 3286 (s, NH),
1602 [m, ꢁasy(COOꢀ)], 1371 [m, ꢁsym(COOꢀ)], 1584 (m, C¼N), 1023 (m, N–N), 602 (w,
1
Sn–C), 557 (w, Sn–O), 449 (w, Sn–N). H NMR (CDCl3, ppm) ꢂ: 9.70 (s, 1H, N–H),
7.26–7.21 (m, 10H, phenyl ring), 2.55 (s, 3H, N¼C–CH3). 13C NMR (CDCl3, ppm) ꢂ:
174.11 (COOꢀ), 148.03 (C¼N), 132.29–114.01 (phenyl ring), 16.93 (CH3). 119Sn NMR

Pyruvic acid organotin(IV) complexes
2003
(CDCl3, ppm) ꢂ: ꢀ175.1. Anal. Calcd for C27H24N2O2ClSn (%): C, 57.63; H, 4.30;
N, 4.80. Found (%): C, 57.59; H, 4.26; N, 4.77.
2.8. Antibacterial test
The synthesized ligand (1) and 2–6 were screened in vitro for their antibacterial activities
against S. aureus (ATCC 6538), B. subtilis (ATCC 6633), E. aerogenes (ATCC 13048),
E. coli (ATCC 15224), and S. typhi (ATCC 10749) bacterial strains using the agar-well
diffusion method [11]. Wells (size of well 6 mm in diameter) were dug in the media with
the help of a sterile metallic borer with centers at least 24 mm. Eight-hour-old bacterial
inoculums containing 104–106 colony forming units (CFU) mLꢀ1 were spread on the
surface of the nutrient agar using a sterile cotton swab. Recommended concentration of
the test sample (2 mg mLꢀ1 in DMSO) was introduced in the respective wells. Other
wells supplemented with DMSO and reference antibacterial drug (doxycycline) served
as negative and positive controls, respectively. All tests were performed in triplicate
with full agreement between the results. The plates were incubated immediately at 37ꢁC
for 20 h. Activity was determined by measuring the diameter of zones showing complete
inhibition (mm). Growth inhibition was calculated with reference to the positive
control.
3. Results and discussion
3.1. Synthesis
HPAPD was synthesized by the condensation of pyruvic acid and phenylhydrazine
in absolute ethanol in 1 : 1 mole ratio (scheme 1). Complexes 2–6 were obtained
by direct reaction of organotin(IV) chloride(s) and HPAPD in absolute methanol
under N2 (scheme 2). The physical properties and analytical data of 1–6 are given
in Section 2. Compounds 2–6 were stable under N2 and soluble in CHCl3, CH2Cl2,
DMF, DMSO, and MeCN, but insoluble in methanol, ethanol, hexane, pentane, THF,
and ether. The structures of these compounds and coordination behavior of tin(IV)
have been examined by different analytical techniques such as elemental analysis,
molar conductivity, multinuclear NMR (1H, 13C, and 119Sn) spectroscopy. The
molar conductances of 2–6 are 5.8–10.2 ꢀꢀ1 cm2 molꢀ1, respectively, indicating non-
electrolytes [12].
3.2. UV-Vis spectra
The UV-Vis spectra of 1–6 were carried out in a DMF solution (1 ꢂ 10ꢀ4 mol Lꢀ1) at
room temperature. The electronic spectrum of HPAPD showed absorptions at 298 and
338 nm assigned to ꢃ!ꢃ* transition of aromatic ring and n!ꢃ* transition of imine
(4C¼N), respectively [13]. After complexation, UV-Vis spectra of 2–6 exhibited three
absorptions at 299–314, 342–368, and 402–412 nm, respectively. The ꢃ!ꢃ* transition
of aromatic ring and n!ꢃ* transition of imine function are observed at higher
wavelength in the complexes due to slight shift as a result of coordination. The new

2004
M.A. Salam et al.
band at 402–414 nm is assigned to the ligand!metal charge transfer [14]. The shift of
the ꢀmax band from the ligand to the tin(IV) complex is a clear indication that
coordination occurred between tin(IV) and 1.
3.3. IR spectra
HPAPD displayed absorptions at 3333 cmꢀ1 and 3285 cmꢀ1 attributed to the OH and
NH, respectively. Other absorptions at 1709, 1595, and 991 cmꢀ1 are due to ꢁ(C¼O),
ꢁ(C¼N), and ꢁ(N–N), respectively. The ꢁ(C¼O), ꢁ(C¼N), and ꢁ(Sn–O) provide
valuable information about the formation of tin(IV) complex and coordination mode of
the ligand. Compound 1 showed a broad OH absorption at 3333 cmꢀ1, which is absent
in the spectra of 2–6, suggesting 1 is coordinated to tin(IV) through carboxylate oxygen
after deprotonation. The ꢁ(C¼O) of COOH at 1709 cmꢀ1 for 1 was absent in IR spectra
of 2–6. Two new absorptions were observed at 1611–1602 cmꢀ1 and 1376–1367 cmꢀ1
,
attributed to ꢁasy(COOꢀ) and ꢁsym(COOꢀ), respectively, in spectra of 2–6. The
magnitude of D[ꢁasy(COOꢀ)ꢀꢁsym(COOꢀ)] is 238–228 cmꢀ1, indicating the presence
of monodentate carboxylate [15]. A medium band at 1595 cmꢀ1 of 1 for ꢁ(C¼N) shifts
to lower wavenumber at 1584–1579 cmꢀ1 in spectra of 2–6, suggesting the coordination
of the azomethine nitrogen to tin [16]. The ꢁ(N–N) of 1 at 991 cmꢀ1 shifts to higher
frequencies at 1076–1022 cmꢀ1 in 2–6. This observation also suggests the coordination
of azomethine nitrogen to Sn(IV). Absorptions at 620–600 cmꢀ1 in spectra of 2–6 are
assigned to ꢁ(Sn–C). New absorptions at 579–536 cmꢀ1 in 2–6 are assigned to ꢁ(Sn–O),
comparable with the literature [17]. Another new band at 462–436 cmꢀ1 is characteristic
of Sn–N absorption in 2–6. IR spectra indicate the coordination of 1 to tin(IV) via
carboxylate-O and azomethine-N.
3.4. 1H, 13C, and 119Sn NMR spectra
1H NMR spectra of 1 and organotin(IV) complexes (2–6) were recorded in CDCl3.
Compound 1 showed resonances at 11.56, 9.43, 7.28–7.25, and 2.13 ppm due to OH,
NH, aromatic-H, and N¼C–CH3, respectively. After complexation, the OH signal was
absent in 2–6, suggesting deprotonation and coordination. The NH signal shifts
downfield at 9.76–9.62 ppm in 2–6, deshielded by the adjacent nitrogen of (N¼C–CH3).
The resonance of the phenyl protons in 2–6 appears as a multiplet at 7.29–7.16 ppm.
The azomethine proton (N¼C–CH3) signal appears at 2.13 ppm in 1, which is shifted
downfield (2.70–2.52 ppm) in 2–6. This downfield shift indicates that the azomethine
nitrogen is coordinated to tin (IV). The methyl attached to organotin(IV) in 2 and 5
are sharp singlets at 1.20 and 1.06 ppm, respectively, with well-defined satellites.
The 2J[119Sn, 1H] values of 2, 75.3 Hz and 5, 79.5 Hz support the five-coordinate
environment around tin in the solution [18, 19]. The butyl groups attached to tin(IV)
in 3 gave four resonances, 2.01–2.00 ppm (triplet, Sn–CH2–CH2–CH2–CH3), 1.67–
1.61 ppm (multiplet, Sn–CH2–CH2–CH2–CH3), 1.50–1.28 ppm (multiplet, Sn–CH2–
CH2–CH2–CH3), and 0.99–0.91 ppm (triplet, Sn–CH2–CH2–CH2–CH3). 1H NMR
information supports the IR data of 2–6.
In 13C NMR spectra, the position of the phenyl carbon signals undergo minor
variation in 2–6 compared to those observed in 1. In 1, the chemical shifts at 165.71,
143.10, 132.24–122.17, and 9.04 ppm are due to ꢂ(COOH), ꢂ(C¼N), ꢂ(phenyl ring), and

Pyruvic acid organotin(IV) complexes
2005
ꢂ(CH3), respectively. In 2–6, the position of the carboxylate carbon shifts to lower field
at 175.21–171.88 ppm in comparison with 1, indicating the participation of the
carboxylate (COOꢀ) in coordination to tin(IV) [20]. The chemical shifts of carbon
in C¼N and CH3 in 2–6 shift downfield at 154.56–148.03 and 19.69–14.76 ppm,
respectively, supporting H3C–C¼N coordination to tin(IV). The carbon signals in
phenyl rings in 2–6 are at 132.78–114.01 ppm, while the four resonances at 27.08, 24.69,
22.65, and 20.75 ppm are assigned to Sn–CH2CH2CH2CH3 of 3. Methyl group(s)
attached to tin(IV) in 2 and 5 are at 9.21 and 9.15 ppm, respectively.
119Sn NMR chemical shifts of 2–6 were recorded in CDCl3. 119Sn NMR spectroscopy
gives information to determine the coordination number around tin. The 119Sn NMR
of 2–6 shows only one resonance in the range ꢀ170.6 to ꢀ179.2 ppm, indicating
five-coordinate organotin(IV) [21–25].
3.5. Antibacterial activity
Compound 1 and its organotin(IV) complexes (2–6) were tested for antibacterial
activity against S. aureus, B. subtilis, E. aerogenes, E. coli, and S. typhi. The agar well-
diffusion method was used in these assays and each experiment was performed in
triplicate. The zone of inhibition represents the mean value of three readings, as given
in table 1, along with the values for [n-BuSnCl3]. Doxycyclin antibiotic was used as a
standard drug in these assays. Compound 1 was inactive against all bacteria. n-BuSnCl3
shows almost the same antibacterial activity against all bacterial species with inhibition
zones of 12.9–12.5 mm. Antibacterial data indicate that 2–6 have remarkable and
significant activities toward all bacterial strains but lower activity than the reference
drug. Compounds 5 and 6 have significant activities against all the five tested strains.
Compounds 3 and 4 also have significant activities against all test strains except
E. aerogenes. Some microorganisms have the ability to degrade or reduce the toxicity of
particular tin complexes [26, 27]. Lipopolysaccharides form an outer lipid membrane
and contribute to the complex antigenic specificity of Gram(ꢀ) cells [28]. The effect of
various compounds may then vary among microorganisms due to difference in the
structures of the cell. The antibacterial activities shown by these compounds indicate
Table 1. Results of antibacterial activity of the free HPAPD (1) and its
organotin (IV) derivativesa (2–6) (inhibition zone in mm).
Zone of inhibition (mm)
Compound
S. aureus
B. subtilis
E. aerogenes
E. coli
S. typhi
HPAPD (1)
n-BuSnCl3
2
3
4
–
–
–
–
–
12.9
21.1
22.4
24.9
25.2
32.3
38.8
12.8
11.4
24.1
23.8
24.7
26.5
31.5
12.6
21.7
–
12.5
13.2
23.7
21.1
22.3
23.8
35.2
12.6
14.8
23.3
23.5
21.8
22.7
29.7
–
5
22.1
24.8
30.4
6
Doxycyclin
aIn vitro, agar well-diffusion method, concentration: 2 mg mLꢀ1 in DMSO, reference drugs,
Doxycycline: 2 mg mLꢀ1 in DMSO: Dash (–) indicated inactivity.

2006
M.A. Salam et al.
that coupling of HPAPD with R/R2Sn(IV) results in complexes with important
biological properties. Organotin(IV) compounds (2–6) exhibit more inhibitory effects
than the parent ligand or starting organotin(IV) chloride (n-BuSnCl3). Among the
organotin(IV) complexes (2–6), 6 is more active, attributed to the presence of bulky
phenyl groups which facilitate binding to biological molecules through ꢃ–ꢃ interac-
tions. This antibacterial result is similar to those previously reported for other tin
compounds [29–33].
4. Conclusions
We have obtained a series of new organotin(IV) complexes by direct reactions of
HPAPD with corresponding organotin(IV) chloride(s) in absolute methanol. The
synthesized ligand (1) and 2–6 have been characterized by electronic, IR, and NMR
spectral studies, showing that the monodeprotonated ligand is coordinated to tin(IV)
through carboxylate-O and azomethine-N. The tin is from the spectroscopic charac-
terization of five coordinate in 2–6. Bioactivity studies showed that 2–6 are more potent
antibacterial agents than 1, with diphenyltin(IV) complex (6) more active than 2–5.
Acknowledgments
This work was financially supported by the Ministry of Science Technology and
Innovation (MOSTI) under a research grant (No. 06-01-09-SF0046). The authors
would like to thank Universiti Malaysia Sarawak (UNIMAS) for the facilities to carry
out the research work.
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