Coordination of thiosemicarbazones and bis(thiosemicarbazones) to bismuth(III) as a strategy for the design of metal-based antibacterial agents

Article abstract of DOI:10.1002/cbdv.201100447

Complexes [Bi(2Fo4Ph)Cl₂] (1), [Bi(2Ac4Ph)Cl₂] (2), [Bi(2Bz4Ph)Cl₂] (3), [Bi(H₂Gy3DH)Cl₃] (4), [Bi(H₂Gy4Et)(OH)₂Cl] (5), and [Bi(H₂Gy4Ph) Cl₃] (6) were prepared with pyridine-2-carbaldehyde 4-phenylthiosemicarbazone (H2Fo4Ph), 1-(pyridin-2-yl)ethanone 4-phenylthiosemicarbazone (H2Ac4Ph), phenyl(pyridin-2-yl)methanone 4-phenylthiosemicarbazone (H2Bz4Ph), as well as with glyoxaldehyde bis(thiosemicarbazone) (H₂Gy4DH) and its 4-Et (H₂Gy4Et) and 4-Ph (H₂Gy4Ph) derivatives. The complexes exhibited antibacterial activities against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Pseudomonas aeruginosa. Coordination to Bi ^III proved to be an effective strategy to increase the antibacterial activity of the thiosemicarbazones and bis(thiosemicarbazones). Copyright

Full text of DOI:10.1002/cbdv.201100447

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1955
Coordination of Thiosemicarbazones and Bis(thiosemicarbazones) to
Bismuth(III) as a Strategy for the Design of Metal-Based Antibacterial
Agents
by Josane A. Lessa, De´bora C. Reis, Jeferson G. Da Silva, Lucia T. Paradizzi, Nayane F. da Silva,
´
Mariany de Fa´tima A. Carvalho, Sarah A. Siqueira, and Heloisa Beraldo*
Departamento de Quꢀmica, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG,
Brazil
(phone: þ553134095740; fax: 553134095700; e-mail: hberaldo@ufmg.br)
Complexes [Bi(2Fo4Ph)Cl2] (1), [Bi(2Ac4Ph)Cl2] (2), [Bi(2Bz4Ph)Cl2] (3), [Bi(H2Gy3DH)Cl3]
(4), [Bi(H2Gy4Et)(OH)2Cl] (5), and [Bi(H2Gy4Ph)Cl3] (6) were prepared with pyridine-2-carbalde-
hyde 4-phenylthiosemicarbazone (H2Fo4Ph), 1-(pyridin-2-yl)ethanone 4-phenylthiosemicarbazone
(H2Ac4Ph), phenyl(pyridin-2-yl)methanone 4-phenylthiosemicarbazone (H2Bz4Ph), as well as with
glyoxaldehyde bis(thiosemicarbazone) (H2Gy4DH) and its 4-Et (H2Gy4Et) and 4-Ph (H2Gy4Ph)
derivatives. The complexes exhibited antibacterial activities against Staphylococcus aureus, Staph-
ylococcus epidermidis, Enterococcus faecalis, and Pseudomonas aeruginosa. Coordination to BiIII proved
to be an effective strategy to increase the antibacterial activity of the thiosemicarbazones and
bis(thiosemicarbazones).
1. Introduction. – Bacterial infections are major causes of morbidity and mortality
in hospitals around the world. Nosocomial Staphylococcus aureus infections alone
results in 12,000 patient deaths per year [1]. Furthermore, the emergence of resistant
bacteria has contributed to shortening lifecycles of antimicrobial agents [2]. Paradoxi-
cally, as the problems accompanying the emergence of resistance to existing drugs
increase, there has been a decline in the discovery and development of new
antibacterial agents [3].
Bismuth is known to possess good antibacterial activity [4]. Bismuth subsalicylate
(Pepto-Bismolꢁ), colloidal bismuth subcitrate (De-Nolꢁ), and ranitidine bismuth
citrate (Tritecꢁ and Pyloridꢁ) are used worldwide to treat various gastrointestinal
diseases which are related to the infection by Helicobacter pylori [5]. In addition to the
currently used Bi pharmaceuticals, the development of new Bi-based compounds may
provide some promising antimicrobial agents. Bismuth-thiols, for example, have shown
activity against Gram-positive and Gram-negative bacteria. The thiol component
functions as a lipophilic carrier that promotes Bi uptake into bacteria, thus enhancing
the effects of Bi up to 1000-fold [6][7]. These properties indicate that bismuth-thiols
could make excellent antimicrobials [8].
Thiosemicarbazones are thiol/thione compounds which present wide pharmaco-
logical applications as antitumor, antiviral, and antimicrobial agents [9]. Coordination
to Sn, Cu, and Ga improved their antimicrobial activity [10–13]. Thus, the formation of
Bi complexes with thiosemicarbazones could result in more potent compounds, as
previously demonstrated [14][15].
ꢂ 2012 Verlag Helvetica Chimica Acta AG, Zꢃrich

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CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
In the present work, BiIII complexes with pyridine-2-carbaldehyde 4-phenylthiose-
micarbazone (H2Fo4Ph), 1-(pyridin-2-yl)ethanone 4-phenylthiosemicarbazone (H2Ac-
4Ph), phenyl(pyridin-2-yl)methanone 4-phenylthiosemicarbazone (H2Bz4Ph), as well
as with glyoxaldehyde (¼ethanediol) bis(thiosemicarbazone) (H2Gy4DH), and its 4-
ethyl (H2Gy4Et) and 4-phenyl (H2Gy4Ph) derivatives (Fig. 1) were prepared, and
assayed against Staphylococcus aureus, S. epidermidis, Enterococcus faecalis, and
Pseudomonas aeruginosa bacterial strains.
Fig. 1. Generic representation for a) pyridin-2-yl-derived 4-phenylthiosemicarbazones and b) glyoxalde-
hyde bis(thiosemicarbazones)
2. Results and Discussion. – 2.1. Formation of the BiIII Complexes. Microanalyses
and molar conductivity data are compatible with the formation of [Bi(2Fo4Ph)Cl2] (1),
[Bi(2Ac4Ph)Cl2] (2), [Bi(2Bz4Ph)Cl2] (3), in which an anionic thiosemicarbazone is
attached to BiIII together with two chlorides, and with the formation of [Bi(H2-
Gy4DH)Cl3] (4), [Bi(H2Gy4Et)(OH)2Cl] (5), and [Bi(H2Gy4Ph)Cl3] (6). In 4 and 6, a
neutral bis(thiosemicarbazone) is coordinated to BiIII together with three Clꢀ ions,
whereas in 5 a neutral bis(thiosemicarbazone) is attached to the metal center together
with one Clꢀ and two HOꢀ ligands.
2.2. Spectroscopic Characterization. The vibrations attributed to ˜n(C¼N) at 1596–
1575 cmꢀ1 in the IR spectra of H2Fo4Ph, H2Ac4Ph, and H2Bz4Ph are shifted to 1601–
1597 cmꢀ1 in the spectra of complexes 1–3, in agreement with coordination of the
imine N-atom [16–18]. The ˜n(CS) absorption observed at 788–774 cmꢀ1 in the spectra
of the free thiosemicarbazones is shifted to 759–747 cmꢀ1 in the spectra of complexes
1–3, indicating coordination of the S-atom. The 30–50-cmꢀ1 shift is compatible with
complexation of a thiolate S-atom [16–20]. The in-plane deformation mode of the
pyridine ring at 600–584 cmꢀ1 in the spectra of the thiosemicarbazones is shifted to
632–587 cmꢀ1 in the spectra of 1–3, suggesting coordination of the hetero-aromatic N-
atom [16–20].
In the spectra of 1–3, the absorptions at 512–431 and 422–404 cmꢀ1 were
attributed to the ˜n(BiꢀNimine) and ˜n(BiꢀS) vibrations, respectively, and those at 321–
200 cmꢀ1 were assigned to ˜n(BiꢀNpy) vibrations [21–23]. Therefore, in these
complexes the thiosemicarbazones are attached to the metal through the NpyꢀNꢀS
chelating system. Besides, one absorption attributed to ˜n(BiꢀCl) at 333–331 cmꢀ1 was
observed in the spectra of 1–3 [21].

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1957
The vibrations attributed to ˜n(C¼N) at 1596–1570 cmꢀ1 in the IR spectra of
bis(thiosemicarbazones) H2Gy4DH, H2Gy4Et, and H2Gy4Ph are shifed to 1616–
1595 cmꢀ1 in the spectra of complexes 4–6, in agreement with coordination of the
imine N-atom [16–19]. The ˜n(CS) absorption observed at 836–771 cmꢀ1 in the spectra
of the free bis(thiosemicarbazones) is shifted to 834–761 cmꢀ1 in the spectra of 4–6,
indicating coordination of the S-atom. This shift is compatible with complexation of a
thione S-atom [16–20].
In the spectra of complexes 4–6, the absorptions at 331–285 and 273–248 cmꢀ1
were attributed to the ˜n(BiꢀNimine) and ˜n(BiꢀS) [24] vibrations, respectively. Therefore,
in these complexes the bis(thiosemicarbazones) are attached to BiIII through the N2ꢀS2
chelating system. One absorption attributed to ˜n(BiꢀCl) at 237–188 cmꢀ1 was
observed in the spectra of 4–6 [21]. One additional absorption at 440 cmꢀ1 in the
spectrum of 5 was assigned to ˜n(BiꢀO) [25].
The NMR spectra of thiosemicarbazones H2Fo4Ph and H2Ac4Ph, and their
complexes 1 and 2, respectively, were recorded in (D4)MeOH, whereas the spectra for
H2Bz4Ph and its complex 3 were recorded in (D6)DMSO. These are the only solvents
that dissolve both ligands and complexes. The 1H resonances were assigned on the basis
of chemical shifts and multiplicities. We could not obtain 13C-NMR spectra of 1 and 2
due to their low solubility in (D4)MeOH. For 3, the C-atom type (C, CH) was
determined by using distortionless enhancement by polarization transfer (DEPT-135)
experiments. The assignments of the protonated C-atoms were accomplished by 2D
hetero-nuclear multiple quantum coherence experiments (HMQC).
Only one signal was observed for each H-atom in the 1H-NMR spectra of H2Fo4Ph
and H2Ac4Ph, indicating the presence of only the (E)-isomer in solution [16]. The
1H-NMR spectrum of H2Bz4Ph shows duplicated signals indicating the presence of the
(Z)- and (E)-isomers (78 and 22%, resp.) in solution. In the first, HꢀN(2) is H-bonded
to the heteroaromatic N-atom, while in the second HꢀN(2) is H-bonded to the solvent
[16][17][21]. The signals of HꢀN(2) at 13.19 and 10.59 ppm were attributed to the (Z)-
and (E)-isomers, respectively [16][17][21].
In complexes 1–3, the signals of all H-atoms undergo significant shifts in relation to
their positions in the free bases. In the spectra of 1 and 2, only one signal was observed
for each H-atom, suggesting the presence of only one isomer in solution. The crystal
structure of [Bi(2Ac4Ph)(DMSO)Cl2] (2a) reveals that the thiosemicarbazone adopts
the (E)-configuration (see Sect. 2.3). In 1H-NMR the spectrum of 3, two signals were
observed for each H-atom, suggesting the presence of (Z)- and (E)-isomers (64 and
36%, resp.). The absence of the HꢀN(2) signal in the spectrum of 3 indicates
deprotonation with coordination of an anionic thiosemicarbazone. In the 13C-NMR
spectrum of complex 3, two signals were observed for each C-atom, as well (see Fig. 2).
Since significant shifts in the signals of C¼N, C¼S, and the pyridine C-atoms were
verified, we can rule out the possibility of decomplexation in the solvent, and assume
that (Z)- and (E)-isomers coexist in solution. In this case, the thiosemicarbazone is
probably coordinated in a tridentate form through the NpyꢀNimineꢀS chelating system in
the (E)-isomer, and in a bidentate form through the NimineꢀS system in the (Z)-isomer
[16][17][21].
1
The H- and 13C-NMR spectra of bis(thiosemicarbazones) H2Gy4DH, H2Gy4Et
and H2Gy4Ph were recorded in (D6)DMSO. The 1H resonances were assigned on the

1958
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
Fig. 2. 13C-NMR Spectra of a) H2Bz4Ph and b) [Bi(2Bz4Ph)Cl2] (3) in the 115–180-ppm range
((D6)DMSO)
basis of chemical shifts and multiplicities. The C-atom type (C, CH) was determined by
using distortionless enhancement by polarization transfer (DEPT-135) experiments.
1
In the H-NMR spectra of 4–6, the signals of all H-atoms from the bis(thiosemi-
carbazones) were observed, indicating that they are coordinated to BiIII as neutral
ligands. These signals are not duplicated, indicating that the two ꢄarmsꢅ of the
bis(thiosemicarbazones) are coordinated to the metal center in a similar way. However,
1
the signals of the ligands do not undergo significant shifts in the H- and 13C-NMR
spectra of 4–6 in relation to their position in the free bis(thiosemicarbazones).
To investigate if coordination did not affect the chemical shifts of the bis(thiose-
1
micarbazone), or if decomplexation occurred, we recorded the H-NMR spectra of
complex 6 in (D7)DMF and (D6)acetone (data not shown). The signals of the
bis(thiosemicarbazone) of 6 displayed minor changes regardless of the solvent used.
Thus, probably in 6, as well as in the other complexes, coordination to BiIII did not affect
the chemical shifts of the bis(thiosemicarbazones). Coordination of neutral ligands to
BiIII probably did not lead to large variations in electron density, which would account
for the similarities between the spectra of the free bis(thiosemicarbazones) and those of
their BiIII complexes.
2.3. X-Ray Crystallography. Upon slow evaporation of 2 in acetone/DMSO 9 :1
crystals of [dichlorido(O-dimethylsulfoxide)[1-(pyridin-2-yl)ethanone 4-phenylthiose-
micarbazonato]bismuth(III)] ([Bi(2Ac4Ph)(DMSO)Cl2]; 2a) were formed. The
molecular structure of 2a with the atom numbering scheme is depicted in Fig. 3.

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1959
Fig. 3. Asymmetric unit of [Bi(2Ac4Ph)(DMSO)Cl2] (2a) showing the labelling scheme of the non-H-
atoms and their displacement ellipsoids at the 50% probability level. For comparison purposes in the
crystal structure, the adopted atom numbering is in agreement with that used in the previous publications
of our group.
Selected intramolecular bond lengths and angles for H2Ac4Ph [26] and
[Bi(2Ac4Ph)(DMSO)Cl2] (2a) are compiled in Table 1.
[Bi(2Ac4Ph)(DMSO)Cl2] (2a) crystallizes as a neutral complex. In 2a, an anionic
thiosemicarbazone binds to the BiIII center through the NpyꢀNimineꢀS chelating system.
A dimethyl sulfoxide (DMSO) is also coordinated to the metal through the O-atom,
and two Clꢀ ions complete the coordination sphere of BiIII.
A Clꢀ ligand from an adjacent molecule interacts weakly with the BiIII center
forming dimeric units (see Fig. 4). Due to the Lewis acidic character of BiIII, additional
intra- or intermolecular contacts are usually established in the presence of donor atoms,
thus increasing coordination number [28]. Hence, in 2a we consider that BiIII is
heptacoordinated. Furthermore, according to the ꢄsemi bonding conceptꢅ, the bonds at
the Bi-atom might be generally described in terms of primary bonds (normal covalent
bonds), and secondary bonds or interactions, with interatomic distances significantly
longer than a covalent bond but shorter than the sum of the Van der Waals radii for the
two elements concerned [28]. The behavior reported here was similar to that observed
for other BiIII complexes [29].
When comparing the BiꢀCl bonds (Table 1), we observe that the Bi1ꢀCl1 bond
length (2.7674(18) ꢆ) is longer than the Bi1ꢀCl2 length (2.671(2) ꢆ), which suggests
the presence of an interaction of Cl1 with another metal center. In fact, the Bi2· · ·Cl1
interaction occurs, resulting in a Cl1 bridge between two adjacent Bi centers. The
bridge is asymmetric, since the Bi2· · ·Cl1 bond length is 3.128(2) ꢆ. However, this
distance is well within the limits of what may be considered a weakly bonding

1960
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
Table 1. Selected Bond Lengths [ꢆ] and Angles [8] for 1-(Pyridin-2-yl)ethanone 4-Phenylthiosemicarba-
zone (H2Ac4Ph) [26] and [Bi(2Ac4Ph)(DMSO)Cl2] (2a)
Bonds
H2Ac4Ph
2a
Bonds
H2Ac4Ph
2a
S1ꢀC8
C2ꢀC7
N2ꢀC7
N2ꢀN3
N3ꢀC8
N4ꢀC8
N4ꢀC9
1.677(2)
1.486(2)
1.284(3)
1.376(2)
1.358(3)
1.346(3)
1.421(3)
1.738(7)
1.486(9)
1.278(9)
1.372(7)
1.306(9)
1.359(8)
1.411(8)
N1ꢀBi1
N2ꢀBi1
S1ꢀBi1
Cl1ꢀBi1
Cl2ꢀBi1
O01-Bi1
–
–
–
–
–
–
2.570(6)
2.455(5)
2.6205(16)
2.7674(18)
2.671(2)
2.544(4)
Angles
H2Ac4Ph
2a
Angles
H2Ac4Ph
2a
N1ꢀC2ꢀC7
C2ꢀC7ꢀN2
C7ꢀN2ꢀN3
N2ꢀN3ꢀC8
N3ꢀC8ꢀS1
N4ꢀC8ꢀN3
N4ꢀC8ꢀS1
C8ꢀN4ꢀC9
N1ꢀBi1ꢀN2
N1ꢀBi1ꢀS1
N1ꢀBi1ꢀCl1
N1ꢀBi1ꢀCl2
N1ꢀBi1ꢀO01
116.2(2)
114.9(2)
118.8(2)
118.9(2)
119.7(1)
114.8(2)
125.5(2)
127.6(2)
ꢀ
115.9(6)
119.5(6)
115.4(5)
116.6(5)
127.9(5)
118.9(6)
113.2(5)
130.7(6)
65.02(18)
137.04(14)
80.37(14)
83.67(14)
150.23(17)
N2ꢀBi1ꢀS1
–
–
–
–
–
–
–
–
–
–
–
–
72.15(13)
84.28(13)
87.86(14)
140.77(17)
92.49(6)
98.35(7)
71.49(11)
163.99(7)
111.46(13)
83.28(13)
83.0(2)
N2ꢀBi1ꢀCl1
N2ꢀBi1ꢀCl2
N2ꢀBi1ꢀO01
S1ꢀBi1ꢀCl1
S1ꢀBi1ꢀCl2
S1ꢀBi1ꢀO01
Cl1ꢀBi1ꢀCl2
Cl1ꢀBi1ꢀO01
Cl2ꢀBi1ꢀO01
O01ꢀBi1ꢀCl1ia)
N1ꢀBiꢀCl1ia)
ꢀ
ꢀ
ꢀ
73.2(1)
ꢀ
a) Cl1i atoms generated by 1ꢀx, 1ꢀy, 1ꢀz symmetry transformations. Data calculated by the Mercury
proGram [27].
interaction between BiIII and Cl, significantly longer than a covalent bond (2.49 ꢆ) but
shorter than the sum of their Van der Waals radii (4.2 ꢆ) [28]. Cl1 and Cl2 occupy the
axial positions of the BiIII coordination sphere, with the Cl1ꢀBi1ꢀCl2 angle being
163.99(7)8 (Table 1). The N1, N2, S1, Cl1, and O01 atoms occupy the equatorial
position. The mean deviation from the plane formed by the N1ꢀN2ꢀS1ꢀBi1ꢀCl1ꢀO01
atoms is 0.2511 ꢆ, with major deviations involving the O01 (ꢀ0.4816 ꢆ) and Cl1
(0.3802 ꢆ) atoms.
The coordinated thiosemicarbazone is found in the (E,Z) conformation with
respect to the C7¼N2, and N3¼C8 bonds, different from the (E,E)-conformation
observed for H2Ac4Ph [26]. This conformation change upon coordination occurs
frequently [16][21][30] and was accompanied by a variation in the N2ꢀN3ꢀC8ꢀS1
torsion angle, from 172.7(1)8 in H2Ac4Ph to ꢀ1.8(5)8 in 2a. As can be seen in Table 1,
the most significant changes upon coordination involved the shortening of the N3ꢀC8
bond length and increasing of the C8ꢀS1 bond length, due to deprotonation at N3ꢀH.
The bond angles are more affected by changes in conformation and by the geometric
restrictions due the formation of five-membered chelate rings (see Table 1).
In the supramolecular arrangement of this complex, the presence of intermolecular
N4ꢀH4A· · ·Cl2i H-bonds (symmetry code: i¼xꢀ1, y, z; Table 2) results in a one-
dimensional infinite chain along the (100) direction, as depicted in Fig. 5.

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1961
Fig. 4. Perspective view of [Bi(2Ac4Ph)(DMSO)Cl2] (2a) showing, in dashed lines, the interactions
forming dimers
Fig. 5. Molecular packing of [Bi(2Ac4Ph)(DMSO)Cl2] (2a) showing the one-dimensional infinite chain
along the (100) direction. The H-bonds are indicated by dashed lines.
Table 2. H-Bond Distances [ꢆ] and Angle [8] for [Bi(2Ac4Ph)(DMSO)Cl2] (2a)
DꢀH· · ·A
N4ꢀH4A· · ·Cl2ia)
d(DꢀH)
0.86
d(H· · ·A)
d(D· · ·A)
/(DꢀH· · ·A)
165.6
2.75
3.592(6)
a) Symmetry transformations used to generate equivalent atoms: i¼xꢀ1, y, z.

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CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
2.4. Antibacterial Activity. Table 3 contains the minimum inhibitory concentrations
(MICs) against the growth of Staphylococcus aureus, S. epidermidis, Enterococcus
faecalis, and Pseudomonas aeruginosa for the thiosemicarbazones, bis(thiosemicarba-
zones), and their BiIII complexes, together with values obtained for the drugs used as
positive controls. BiCl3 was not tested due to its low solubility.
Table 3. Minimum Inhibitory Concentrations (MICs) against Staphylococcus aureus, S. epidermidis,
Enterococcus faecalis, and Pseudomonas aeruginosa for H2Fo4Ph, H2Ac4Ph, H2Bz4Ph, H2Gy4DH,
H2Gy4Et, and H2Gy4Ph, and Their BiIII Complexes 1–6, Respectively, Tetracycline Hydrochloride, and
Ciprofloxacin
Compound
MIC [mmol lꢀ1
]
S. aureus
S. epidermidis
E. faecalis
P. aeruginosa
H2Fo4Ph
1
190.0
6.1
>386.2
>401.8
397.0
99.9
98.8
23.8
H2Ac4Ph
2
370.0
5.7
179.4
91.9
384.7
22.8
45.0
96.0
H2Bz4Ph
3
75.9
5.5
>302.9
>308.9
76.0
93.2
82.6
40.1
H2Gy4DH
4
>509.1
>100.1
>504.21
>196.30
>509.10
190.52
>244.8
>94.3
H2Gy4Et
5
>205.5
>384.40
>181.88
>384.05
193.01
>201.6
>92.8
11.1
H2Gy4Ph
6
>144.5
>274.92
>101.22
286.14
17.86
>144.5
>72.9
2.4
Tetracycline hydrochloride
Ciprofloxacin
0.3
ꢀ
–
0.6
–
1.2
29
–
In general, the bis(thiosemicarbazones) exhibited lower antibacterial activities than
the mono-thiosemicarbazones. Upon coordination to BiIII, the antibacterial activities of
both thiosemicarbazones and bis(thiosemicarbazones) increased against the Gram-
positive bacteria. The increase in activity upon coordination was more pronounced
against S. aureus. In fact complexes 1–3 proved to be 15 to 64 times more potent against
S. aureus than the free ligands. However, in the case of Gram-negative bacteria (P.
aeruginosa), coordination resulted in improved activity only in complex 1.
Complexes 4–6 were more active than the free bis(thiosemicarbazones) against the
Gram-positive strains. Although the free bis(thiosemicarbazones) showed lower
activities than the mono-thiosemicarbazones, complex 6 was the most effective
compound against S. aureus (MIC 2.4 mmol lꢀ1).
4. Conclusions. – Coordination to BiIII proved to be an efficient strategy to increase
the antibacterial activity of the studied thiosemicarbazones and bis(thiosemicarba-
zones), and to increase the solubility and bioavailability of Bi. The ligands could act as
metal carriers or activity could be attributed to the complex per se. In the case of the
antibacterial activity of complexes 1–3, a synergistic effect involving the thiosemi-
carbazone and the metal also could take place.

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1963
Experimental Part
General. All common chemicals were purchased from Aldrich and used without further purification.
The thiosemicarbazones were prepared according to standard procedures [16][31]. IR Spectra: Perkin
Elmer FT-IR Spectrum GX spectrometer; KBr pellets (4000–400 cmꢀ1) and nujol mulls between CsI
plates (400–200 cmꢀ1). NMR Spectra: Bruker DPX-200 Avance (200 MHz) spectrometer; (D6)DMSO,
(D4)MeOH, or (D7)DMF as solvents and TMS as internal reference. Partial elemental analyses: Perkin
Elmer CHN 2400 analyzer. An YSI model 31 conductivity bridge was employed for molar-conductivity
measurements.
Syntheses of pyridine-2-carbaldehyde 4-phenylthiosemicarbazone ((2E)-N-phenyl-2-(pyridin-2-
ylmethylidene)hydrazinecarbothioamide; H2Fo4Ph), 1-(pyridin-2-yl)ethanone 4-phenylthiosemicarba-
zone (¼(2E)-N-phenyl-2-[1-(pyridin-2-yl)ethylidene]hydrazinecarbothioamide; H2Ac4Ph), phenyl-
(pyridin-2-yl)methanone 4-phenylthiosemicarbazone (¼(2E)-N-phenyl-2-[phenyl(pyridin-2-yl)methy-
lidene]hydrazinecarbothioamide; H2Bz4Ph), glyoxaldehyde bis(thiosemicarbazone) (¼(2E,2’E)-2,2’-
(1E,2E)-ethane-1,2-diylidenedihydrazinecarbothioamide; H2Gy4DH), glyoxaldehyde bis(4-ethylthiose-
micarbazone) (¼(2E,2’E)-2,2’-(1E,2E)-ethane-1,2-diylidenebis(N-ethylhydrazinecarbothioamide);
H2Gy4Et), and glyoxaldehyde bis(4-phenylthiosemicarbazone) (¼(2E,2’E)-2,2’-(1E,2E)-ethane-1,2-
diylidenebis(N-phenylhydrazinecarbothioamide); H2Gy4Ph). All thiosemicarbazones [32] and bis(thio-
semicarbazones) [33] were prepared as previously described.
Bismuth(III) Complexes with H2Fo4Ph, H2Ac4Ph, and H2Bz4Ph. The BiIII complexes were
obtained by mixing an EtOH soln. (20 ml) of the desired thiosemicarbazone (1 mmol) with BiCl3 in a 1:1
ligand-to-metal molar ratio at r.t. with stirring for 3.5 h. The resulting solids were filtered off, washed with
EtOH, followed by Et2O, and dried in vacuo.
Dichlorido(pyridine-2-carbaldehyde 4-phenylthiosemicarbazonato)bismuth(III) ([Bi(2Fo4Ph)Cl2];
1). Yellow solid. Yield 78%. M.p. 238.6–240.58. IR (KBr): 1601s (C¼N), 747m (C¼S), 632w (py). IR
(CsI/nujol): 512m (BiꢀNimine), 421m (BiꢀS), 200w (BiꢀNpy), 333m (BiꢀCl). 1H-NMR (200 MHz,
(D4)MeOH; main signals): 8.70 (d, HꢀC(6), py); 8.21 (d, HꢀC(3), py); 8.15–7.90 (m, HꢀC(4) of py,
CH¼N); 7.67 (t, HꢀC(5), py). LM ¼15.75 Wꢀ1 cm2 molꢀ1 in DMF. Anal. calc. for C13H11BiCl2N4S
(535.20): C 29.17, H 2.07, N 10.47; found: C 29.79, H 1.46, N 9.75. FW: 536.21 g molꢀ1
.
Dichlorido[1-(pyridin-2-yl)ethanone 4-phenylthiosemicarbazonato]bismuth(III) ([Bi(2Ac4Ph)Cl2];
2). Yellow solid. Yield 92%. M.p. 2538 (dec.). IR (KBr): 1594s (C¼N), 759m (CS), 601w (py). IR (CsI/
nujol): 510m (BiꢀNimine), 422m (BiꢀS), 202w (BiꢀNpy), 332m (BiꢀCl). 1H-NMR (200 MHz,
(D4)MeOH; main signals): 8.99 (d, J¼5.2, HꢀC(6), py); 8.35–8.20 (m, HꢀC(3), HꢀC(4), py); 7.79 (t,
HꢀC(5), py); 2.81 (s, Me). LM ¼16.63 Wꢀ1 cm2 molꢀ1 in DMF. Anal. calc. for C14H13BiCl2N4S (549.23): C
30.62, H 2.39, N 10.20; found: C 30.13, H 2.64, N 10.50. FW: 549.23 g molꢀ1
.
Dichlorido[phenyl(pyridin-2-yl)methanone
4-phenylthiosemicarbazonato]bismuth(III)]
([Bi(2Bz4Ph)Cl2]; 3). Yellow solid. Yield 83%. M.p. 3008 (dec.). IR (KBr): 1542s (C¼N), 755m (CS),
587w (py). IR (CsI/nujol): 431w (BiꢀNimine), 404m (BiꢀS), 231 (BiꢀNpy), 331w (BiꢀCl). 1H-NMR
(200 MHz, (D6)DMSO): 9.79 (s, HꢀN(4), (Z)); 9.53 (s, HꢀN(4), (E)); 9.29 (d, J¼4.6, HꢀC(6) (py),
(Z)); 9.22 (d, J¼4.6, HꢀC(6) (py), (E)); 8.06 (t, J¼7.6, HꢀC(4) (py), (E,Z)); 7.68 (d, J¼8.0, HꢀC(3)
(py), (Z)); 7.24 (t, J¼7.0, HꢀC(5) (py), (E,Z)); 6.90 (d, J¼8.0, HꢀC(3) (py), (E)). 13C-NMR
(200 MHz, (D6)DMSO; main signals): 168.8 (C(3), (Z)); 166.9 (C(3), (E)); 159.7 (C(2) (py), (Z));
158.4 (C(2) (py), (E)); 150.6 (C¼N, (E)); 149.9 (C¼N, (Z)); 149.6 (C(6) (py), (Z)); 149.3 (C(6) (py),
(E)); 141.0 (C(1) (Ph), (Z)); 140.9 (C(1) (Ph), (E)); 139.8 (C(4) (py), (Z)); 139.3 (C(4) (py), (E));
136.0 (C(1) of PhꢀC¼N, (Z)); 135.3 (C(1) of PhꢀC¼N, (E)); 127.9 (C(3) (py), (Z)); 126.5 (C(5) (py),
(E)); 125.5 (C(5) (py), (Z)); 125.3 (C(3) (py), (E)). LM ¼11.07 Wꢀ1cm2 molꢀ1 in DMF. Anal. calc. for
C19H15BiCl2N4S (611.30): C 37.33, H 2.47, N 9.17; found: C 37.56, H 2.20, N 8.27. FW: 611.30 g·molꢀ1
.
Syntheses of Bismuth(III) Complexes with Glyoxaldehyde Bis(thiosemicarbazone) (H2Gy4DH),
Glyoxaldehyde Bis(4-ethylthiosemicarbazone) (H2Gy4Et), and Glyoxaldehyde Bis(4-phenylthiosemicar-
bazone) (H2Gy4Ph). The BiIII complexes were obtained by mixing a MeOH soln. (10 ml) of the desired
bis(thiosemicarbazone) (1 mmol) with BiCl3 in a 1:1 ligand-to-metal molar ratio at reflux for 4 h with
stirring. The resulting solids were filtered off, washed with MeOH, followed by acetone, and dried in
vacuo.

1964
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
Trichlorido[glyoxaldehyde bis(thiosemicarbazonato)]bismuth(III) ([Bi(H2Gy4DH)Cl3]; 4). Yellow
solid. Yield 79%. M.p. 224.68 (dec.). IR (KBr): 3369m, 3258m, 3174m (NꢀH), 1595s (C¼N), 834m
1
(C¼S). IR (CsI/nujol): 271w (BiꢀS), 331w (BiꢀN), 204w (BiꢀCl). H-NMR (200 MHz, (D6)DMSO):
7.70 (s, 2 CH¼N); 11.68 (s, 2 HꢀN(2)); 8.31 (s, HꢀN(4)); 7.88 (s, HꢀN(4)). 13C-NMR (200 MHz,
(D6)DMSO): 178.0 (C(3)); 140.5 (C¼N). LM ¼8.04 Wꢀ1 cm2 molꢀ1 in DMF. Anal. calc. for
C4H8BiCl3N6S2 (519.62): C 9.25, H 1.55, N 16.17; found: C 10.05, H 1.51, N 16.31%. FW: 519.62 g molꢀ1
.
[Chlorido(dihydroxido)[glyoxaldehyde bis(4-ethylthiosemicarbazonato)]bismuth(III) ([Bi(H2-
Gy4Et)(OH)2Cl]; 5). Yellow solid. Yield 83%. M.p. 218.7–219.68. IR (KBr): 3370m, 3154m (NꢀH),
1616s (C¼N), 750m (C¼S). IR (CsI/nujol): 248w (BiꢀS), 296w (BiꢀN), 237w (BiꢀCl), 440w (BiꢀO).
1H-NMR (200 MHz, (D6)DMSO): 11.70 (s, 2 HꢀN(2)); 8.52 (t, J¼5.7, 2 HꢀN(4)); 7.72 (s, 2 CH¼N); 3.53
(qd, J¼13.5, 6.6, 2 CH2); 1.10 (t, J¼7.1, 2 Me ) . 13C-NMR (200 MHz, (D6)DMSO): 176.4 (C¼S)); 140.0
(C¼N); 38.3 (CH2); 14.3 (Me). LM ¼5.93 Wꢀ1 cm2 molꢀ1 in DMF. Anal. calc. for C8H18BiClN6O2S2
(538.83): C 17.83, H 3.37, N 15.60; found: C 18.08, H 3.20, N 15.58%. FW: 538.83 g molꢀ1
.
Trichlorido[glyoxaldehyde bis(4-phenylthiosemicarbazonato)]bismuth(III) ([Bi(H2Gy3Ph)Cl3]; 6).
Yellow solid. Yield 90%. M.p. 255.0–256.28. IR (KBr): 3297m, 3158m (NꢀH), 1602s (C¼N), 761m
1
(C¼S). IR (CsI/nujol): 285w (BiꢀN), 273w (BiꢀS), 188w (BiꢀCl). H-NMR (200 MHz, (D6)DMSO):
7.89 (s, 2 CH¼N); 10.19 (s, 2 HꢀN(4)); 12.15 (s, 2 HꢀN(2)). 13C-NMR (200 MHz, (D6)DMSO): 175.9
(C¼S)); 140.6 (C¼N). LM ¼20.86 Wꢀ1 cm2 molꢀ1 in DMF. Anal. calc. for C16H16BiCl3N6S2 (671.81): C
28.61, H 2.40, N 12.51; found: C 28.39, H 2.28, N 12.29%. FW: 671.81 g molꢀ1
.
3.3. X-Ray Crystallography. The crystal structure of 2a was determined by single-crystal X-ray
diffractometry1). Measurements were carried out on an Oxford-Diffraction GEMINI-Ultra diffractom-
eter using graphite-enhance source MoKa radiation (l 0.71073 ꢆ) at 293(2) K and 1 atm. The data
collection, cell refinement, and data reduction were performed using the CRYSALISPRO software [34].
Semi-empirical from equivalents absorption correction method was applied [34].
The structure was solved by direct methods using SHELXS-97 [35]. Full-matrix least-squares
refinement procedure on F2 with anisotropic thermal parameters was carried on using SHELXL-97 [35].
Positional and anisotropic atomic displacement parameters were refined for all non-H-atoms. The H-
atoms were placed geometrically and the positional parameters were refined using a riding model.
Table 4 contains the crystal data and refinement results for the determined structure of 2a. Molecular
graphics and packing figures were plotted using XP in SHELXTL-PC [36] and Mercury [27], resp.
3.4. Antibacterial Activity. Studies of antibacterial activity were performed in accordance with the
National Committee for Clinical Laboratory Standards (NCCLS) to determine broth microdilution
minimum inhibitory concentration (MIC) values [37][38]. Staphylococcus aureus (ATCC 6538),
Staphylococcus epidermidis (ATCC 12228), Enterococcus faecalis (ATCC 19433), and Pseudomonas
aerugionosa (ATCC 9027) stored on MuellerꢀHinton agar (MHA) were inoculated into MuellerꢀHinton
Broth (MHB) and incubated aerobically at 358 for 24 h. Then, the bacterial cells were suspended,
according to the McFarland protocol in saline soln. [38], to produce a suspension of ca. 105 CFU mlꢀ1
(colony-forming units per ml). The cultures were further diluted tenfold to attain inoculum size of 1.2ꢁ
104 CFU mlꢀ1. Serial dilutions of the compounds, previously dissolved in DMSO, were prepared in test
tubes to final concentrations of 512, 256, 128, 64, 32, 16, 8, 4, 2, and 1 mg mlꢀ1, then the inoculum (100 ml)
was added to each tube. The MIC, defined as the lowest concentration of the test compound, which
inhibits the visible growth, was determined visually after incubation for 20 h at 378. Tests using
tetracycline hydrochloride and ciprofloxacin as reference and DMSO as negative control were carried
out in parallel. All tests were performed in triplicates with full agreement between the results.
This work was supported by CNPq and INCT-INOFAR, and Proc. CNPq 573.364/2008-6). The
authors express sincere thanks to LabCri (UFMG) and, particularly, to Prof. Nilvado L. Speziali for
access to X-ray facilities.
1
)
CCDC No. 859622 contains the supplementary crystallographic data for [Bi(2Ac4Ph)Cl2DMSO]
(2a). These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/
data_request/cif.

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1965
Table 4. Crystal Data and Refinement Results for [Bi(2Ac4Ph)(DMSO)Cl2] (2a)
Empirical formula
C16H19BiCl2N4OS2
627.35
Formula weight
Crystal system
Space group
Triclinic
ꢀ
P1
Unit cell dimensions
a [ꢆ]
b [ꢆ]
c [ꢆ]
a [8]
b [8]
g [8]
7.9293(2)
10.3773(3)
14.6909(4)
109.604(2)
90.301(2)
108.125(2)
1074.11(5)
2/1.940
Volume [ꢆ3]
Z/Density calc. [Mg/m3]
Absorption coefficient [mmꢀ1
F(000)
]
8.663
600
Crystal size [mm]
q Range for data coll. [8]
Index range
Reflec. collect./unique (Rint
Completeness [%]
0.59ꢁ0.13ꢁ0.02
2.88 to 26.37
ꢀ9ꢂhꢂ9; ꢀ12ꢂkꢂ12; ꢀ18ꢂlꢂ18
23945/4367 (0.0678)
99.9 (to 26.378)
)
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.8478 and 0.0799
4367/0/235
1.071
Final R indices [I>2s(I)]
R indices (all data)
R1¼0.0374, wR2¼0.0967
R1¼0.0446, wR2¼0.0995
3.365/ꢀ1.322
Larg. peak/hole, [e ꢆꢀ3
]
REFERENCES
[1] L. B. Rice, Biochem. Pharmacol. 2006, 71, 991.
[2] H. Kresse, M. J. Belsey, H. Rovini, Nat. Rev. Drug Discovery 2007, 6, 19.
[3] K. J. Simmons, I. Chopra, C. W. G. Fishwick, Nat. Rev., Microbiol. 2010, 8, 501.
[4] A. R. Shaikh, R. Giridhar, M. R. Yadav, Int. J. Pharm. 2007, 332, 24.
[5] N. Yang, H. Sun, Coord. Chem. Rev. 2007, 251, 2354.
[6] W. G. Veloira, P. Domenico, J. J. LiPuma, J. M. Davis, E. Gurzenda, J. A. Kazzaz, J. Antimicrob.
Chemother. 2003, 52, 915.
[7] P. Domenico, R. J. Salo, S. G. Novick, P. E. Schoch, K. Van Horn, B. A. Cunha, Antimicrob. Agents
Chemother. 1997, 41, 1697.
[8] J. P. Folsom, B. Baker, P. S. Stewart, J. Appl. Microbiol. 2011, 111, 989.
[9] H. Beraldo, D. Gambino, Mini. Rev. Med. Chem. 2004, 4, 31, and refs. cit. therein.
[10] G. L. Parrilha, J. G. da Silva, L. F. Gouveia, A. K. Gasparoto, R. P. Dias, W. R. Rocha, D. A. Santos,
N. L. Speziali, H. Beraldo, Eur. J. Med. Chem. 2011, 46, 1473.
˜
[11] I. C. Mendes, F. B. Costa, G. M. de Lima, J. D. Ardisson, I. Garcia-Santos, A. Castineiras, H.
Beraldo, Polyhedron 2009, 28, 1179.
[12] I. C. Mendes, J. P. Moreira, A. S. Mangrich, S. P. Balena, B. L. Rodrigues, H. Beraldo, Polyhedron
2007, 26, 3263.
[13] T. O. Bastos, B. M. Soares, P. Silva Cisalpino, I. Castro Mendes, R. G. dos Santos, H. Beraldo,
Microbiol. Res. 2010, 165, 573.
[14] K. Nomiya, K. Sekino, M. Ishikawa, A. Honda, M. Yokoyama, N. C. Kasuga, H. Yokoyama, S.
Nakano, K. Onodera, J. Inorg. Biochem. 2004, 98, 601.
[15] R. Diemer, U. Dittes, B. Nuber, V. Seifried, W. Opferkuch, B. K. Keppler, Metal-Based Drugs 1995,
2, 271.

1966
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
[16] D. C. Reis, M. C. X. Pinto, E. M. Souza-Fagundes, S. M. S. V. Wardell, J. L. Wardell, H. Beraldo,
Eur. J. Med. Chem. 2010, 45, 3904.
[17] A. P. Rebolledo, M. Vieites, D. Gambino, O. E. Piro, E. E. Castellano, C. L. Zani, E. M. Souza-
Fagundes, L. R. Teixeira, A. A. Batista, H. Beraldo, J. Inorg. Biochem. 2005, 99, 698.
[18] A. E. Graminha, C. Rodrigues, A. A. Batista, L. R. Teixeira, E. S. Fagundes, H. Beraldo,
Spectrochim. Acta, Part A 2008, 69, 1073.
[19] A. P. Rebolledo, G. M. de Lima, L. N. Gambi, N. L. Speziali, D. F. Maia, C. B. Pinheiro, J. D.
´
Ardisson, M. E. Cortes, H. Beraldo, Appl. Organomet. Chem. 2003, 17, 945.
[20] J. A. Lessa, D. C. Reis, I. C. Mendes, N. L. Speziali, L. F. Rocha, V. R. A. Pereira, C. M. L. Melo, H.
Beraldo, Polyhedron 2011, 30, 372.
[21] K. Nakamoto, ꢄInfrared Spectra of Inorganic and Coordination Compoundsꢅ, Wiley-Interscience,
New York, 1970.
[22] G. Q. Zhong, S. R. Luan, P. Wang, Y. C. Guo, Y. R. Chen, Y. Q. Jia, J. Therm. Anal. Calorim. 2006,
86, 775.
[23] J. G. Shao, Y. X. Yang, B. W. Li, L. P. Zhang, Y. R. Chen, X. L. Liu, J. Therm. Anal. Calorim. 2009,
96, 277.
[24] H. P. S. Chauhan, N. M. Shaik, U. P. Singh, Appl. Organomet. Chem. 2006, 20, 142.
[25] X. Li, A. A. Gewirth, J. Am. Chem. Soc. 2003, 125, 7086; R. P. Oertel, R. A. Plane, Inorg. Chem.
1968, 7, 1192.
˜
[26] E. Bermejo, A. Castineiras, R. Domꢀguez, R. Carballo, C. Maichle-Moessmer, J. Straehle, D. X.
West, Z. Anorg. Allg. Chem. 1999, 625, 961.
[27] C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-
Monge, R. Taylor, J. van de Streek, P. A. Wood, J. Appl. Crystallogr. 2008, 41, 466.
[28] C. Silvestru, H. J. Breunig, H. Althaus, Chem. Rev. 1999, 99, 3277.
[29] J. R. Eveland, K. H. Whitmire, Inorg. Chim. Acta 1996, 249, 41.
[30] K. O. S. Ferraz, G. M. M. Cardoso, C. M. Bertollo, E. M. Souza-Fagundes, N. Speziali, C. L. Zani,
I. C. Mendes, M. A. Gomes, H. Beraldo, Polyhedron 2011, 30, 315.
[31] J. A. Lessa, J. C. Guerra, L. F. de Miranda, C. F. D. Romeiro, J. G. Da Silva, I. C. Mendes, N. L.
Speziali, E. M. Souza-Fagundes, H. Beraldo, J. Inorg. Biochem. 2011, 105, 1729.
´
[32] A. Perez-Rebolledo, G. M. de Lima, N. L. Speziali, O. E. Piro, E. E. Castellano, J. D. Ardisson, H.
Beraldo, J. Organomet. Chem. 2006, 691, 3919.
[33] H. Beraldo, L. P. Boyd, D. X. West, Transition Met. Chem. 1998, 23, 67.
[34] CRYSALISPRO, Oxford Diffraction Ltd., Version 1.171.34.34 (release 05-01-2010 CrysAlis171.-
NET).
[35] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
[36] SHELXTL, Reference Manual (Version 6.14), Bruker Analytical X-Ray Systems, Inc., Madison,
WI, USA, 1998.
[37] NCCLS, ꢄMethod for Dilution Antimicrobial Susceptibility Test for Bacteria That Grow Aerobi-
callyꢅ – Approved Standard-sixth Edition, M7-A6, National Committee for Clinical Laboratory
Standards, Villanova, PA, 2005.
[38] Clinical and Laboratory Standards Institute, ꢄPerformance Standards for Antimicrobial Suscept-
ibility Testing; Fifteenth Informational Supplementꢅ, CLSI document M100-S15 (ISBN 1-56238-
556-9). Clinical and Laboratory Standards Institute, 940 West Valley Road, Suite 1400, Wayne,
Pennsylvania 19087-1898, USA, 2005.
Received December 31, 2011