Chalcone-derived thiosemicarbazones and their zinc(II) and gallium(III) complexes: Spectral studies and antimicrobial activity

Article abstract of DOI:10.1080/00958972.2012.757762

Chalcone-derived 3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCTPh) (1), 3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4ClPh) (2), 3-(4-bromophenyl)-1-pyridin-2-ylprop-2-en-1- one thiosemicarbazone (HPyCT4BrPh) (

Full text of DOI:10.1080/00958972.2012.757762

This article was downloaded by: [Georgetown University]
On: 19 July 2013, At: 05:12
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Chalcone-derived thiosemicarbazones
and their zinc(II) and gallium(III)
complexes: spectral studies and
antimicrobial activity
JEFERSON G. DA SILVA a , CAMILA C.H. PERDIGÃO a , NIVALDO L.
SPEZIALI b & HELOISA BERALDO a
a Departamento de Química, Universidade Federal de Minas
Gerais, Belo Horizonte, Brazil
b Departamento de Física, Universidade Federal de Minas Gerais,
Belo Horizonte, Brazil
Accepted author version posted online: 11 Dec 2012.Published
online: 29 Jan 2013.
To cite this article: JEFERSON G. DA SILVA , CAMILA C.H. PERDIGO , NIVALDO L. SPEZIALI & HELOISA
BERALDO (2013) Chalcone-derived thiosemicarbazones and their zinc(II) and gallium(III) complexes:
spectral studies and antimicrobial activity, Journal of Coordination Chemistry, 66:3, 385-401, DOI:
10.1080/00958972.2012.757762
To link to this article: http://dx.doi.org/10.1080/00958972.2012.757762
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry
Vol. 66, No. 3, 10 February 2013, 385–401
Chalcone-derived thiosemicarbazones and their zinc(II) and
gallium(III) complexes: spectral studies and antimicrobial
activity
JEFERSON G. DA SILVA†, CAMILA C.H. PERDIGÃO†, NIVALDO L. SPEZIALI‡ and
HELOISA BERALDO†*
†Departamento de Química, Universidade Federal de Minas Gerais, Belo Horizonte,
Brazil; ‡Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte,
Brazil
(Received 16 July 2012; in final from 16 October 2012)
Chalcone-derived 3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCTPh) (1),
3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4ClPh) (2), 3-(4-
bromophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4BrPh) (3), and 3-(4-nitro-
phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4NO2Ph) (4) were obtained as
well as their gallium(III) and zinc(II) complexes [Ga(PyCTPh)2]NO3 (Ga1), [Ga(PyCT4ClPh)2]
NO3 (Ga2), [Ga(PyCT4BrPh)2]NO3 (Ga3), [Ga(PyCT4NO2Ph)2]NO3 (Ga4), [Zn(PyCTPh)2]
(Zn1), [Zn(PyCT4ClPh)2] (Zn2), [Zn(PyCT4BrPh)2] (Zn3), and [Zn(PyCT4NO2Ph)2] (Zn4). The
chalcones, thiosemicarbazones, and zinc(II) complexes were not active against Pseudomonas
aeruginosa. The thiosemicarbazones proved to be more active than the parent chalcones against
Staphylococcus aureus and Candida albicans. Coordination to zinc(II) resulted in activity improve-
ment of most thiosemicarbazones against S. aureus. Coordination to gallium(III) significantly
improved the antimicrobial activity of all thiosemicarbazones against the studied micro-organisms,
suggesting this to be an effective strategy for antimicrobial activity enhancement.
Keywords: Chalcones; Thiosemicarbazone; Zinc(II) complexes; Gallium(III) complexes;
Antimicrobial
1. Introduction
Chalcones (figure 1) are flavonoid compounds bearing the 1,3-diarylprop-2-en-1-one
framework. They are the first isolable compounds from flavonoid biosynthesis in plants,
with widespread distribution in fruits, vegetables, spices, tea, and soy [1]. These
compounds exhibit a diverse range of pharmacological activities, presenting cytotoxic,
antitumor, antiinflammatory, antiplasmodial, immunosuppressive, antimicrobial, and
antioxidant properties [1,2].
Thiosemicarbazones also have wide pharmacological versatility and present cytotoxic,
antitumor, antimalarial, antimicrobial, and antiviral properties [3]. In many cases, metal
coordination leads to an improvement of thiosemicarbazones pharmacological activities and
synergistic effects involving both metal and the thiosemicarbazone have been reported [3–7].
*Corresponding author. Email: hberaldo@ufmg.br
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.757762

386
J.G. Da Silva et al.
Figure 1. Structural framework of chalcones.
The mechanism of action of metal ions may involve binding to proteins, interaction with
microbial membrane with changes in structure and permeability, and interaction with
nucleic acids preventing microbial replication [8].
Zinc is the second most prevalent trace element, after iron, and is involved in structure
and function of over 300 enzymes. Use of zinc as a nutritional supplement has become
common in many countries [9]. Zinc salts, primarily zinc citrate, are widely used as anti-
microbials. Zinc exhibits activity against oral Streptococci, particularly Streptococcus
mutans [8]. Zinc supplementation shows beneficial effects against infectious diseases,
especially diarrhea, and it has been shown that zinc supplementation can improve mucosal
innate immunity through induction of antimicrobial peptide secretion from intestinal
epithelial cells [10].
Gallium has efficacy in the treatment of disorders such as accelerated bone resorption,
autoimmune diseases and allograft rejection, certain cancers, and infectious diseases [11].
The antimicrobial properties of gallium compounds have been demonstrated by other
authors [11] and by our group [6,12,13].
The mechanism of antimicrobial action of gallium(III) is related to iron metabolism.
Gallium(III) mimics iron(III) due to their similar charge-to-radius ratio. Hence, gallium(III)
Figure 2. Structural representation for the chalcone precursors (A) and chalcone-derived thiosemicarbazones (B).

Chalcone-derived thiosemicarbazones
387
binds to ferric sites on transferrin and is acquired from transferrin by certain bacteria.
However, unlike iron(III), it is not reducible to a divalent form under physiological condi-
tions, which precludes its participation in crucial bacterial iron-dependent DNA-synthetic
pathways [14]. Iron metabolism is a key vulnerability of infecting bacteria because
organisms require iron for growth. A “Trojan horse” strategy that used gallium to disrupt
bacterial iron metabolism has been reported in an experiment which showed that gallium
inhibits Pseudomonas aeruginosa growth and biofilm formation and kills planktonic and
biofilm bacteria in vitro [15].
Coordination of thiosemicarbazones to gallium(III) leads to improvement of antimicro-
bial properties [6,12,13] as well as their cytotoxic activity [16]. Combining a chalcone
with a thiosemicarbazone framework could lead to compounds with interesting pharmaco-
logical profile. Thus, in the present work, a family of four chalcone-derived thiosemicarba-
zones were obtained (see figure 2) as well as their zinc(II) and gallium(III) complexes.
The antimicrobial activities of the chalcone precursors (see figure 2) and the corresponding
thiosemicarbazones and their zinc(II) and gallium(III) complexes were investigated.
2. Experimental
2.1. Materials and measurements
All chemicals were purchased from Aldrich and used without purification.
Elemental analyses were performed on a Perkin Elmer CHN 2400 analyzer. A YSI
model 31 conductivity bridge was employed for molar conductivity measurements. High
resolution mass spectra (HRMS) were recorded with a Shimadzu IT-TOF mass spectrome-
ter. DMSO solutions of the compounds were diluted in methanol and applied in the
electrospray ionization source for direct injection. Mass spectra were obtained in the full
scan mode within the m/z 100–1000 range. Electronic spectra were obtained with an
UV-2401PC – (P/N 206-82201) – Shimadzu. Infrared spectra were recorded on a Perkin
Elmer FT-IR Spectrum GX spectrometer using KBr pellets. NMR spectra were obtained at
room temperature with a Bruker DRX-400 Avance (200 MHz) spectrometer using
deuterated dimethyl sulfoxide (DMSO-d6) as the solvent and tetramethylsilane as internal
1
reference. H resonances were assigned on the basis of chemical shifts and multiplicities.
The carbon type (C, CH) was determined by using distortionless enhancement by polariza-
tion transfer (DEPT 135) experiments. Single-crystal X-ray diffraction measurements were
carried out on a GEMINI-Ultra diffractometer (LabCri-UFMG) using graphite-Enhance
Source Mo Kα radiation (λ = 0.71073 Å) at 120 K. Data collection, cell refinement
results, and data reduction were performed using CRYSALISPRO software [17]. The
semi-empirical from equivalents absorption correction method was applied [17]. Structures
were solved by direct methods using SHELXS-97 [18]. Full-matrix least-squares
refinement procedure on F2 with anisotropic thermal parameters was carried out using
SHELXL-97 [18]. Positional and anisotropic atomic displacement parameters were refined
for all nonhydrogen atoms. Hydrogen atoms were placed geometrically and the positional
parameters were refined using a riding model.
2.2. Syntheses
All compounds were obtained as described in scheme 1.

388
J.G. Da Silva et al.
Scheme 1. General syntheses of chalcone-derived thiosemicarbazones (1–4) and their complexes (Ga1–Ga4 and
Zn1–Zn4). (i) NaOH 10%; (ii) thiosemicarbazide; (iii) gallium nitrate; (iv) zinc chloride; and sodium acetate.
2.2.1. Synthesis of the chalcone precursors: 3-phenyl-1-pyridin-2-ylprop-2-en-1-one
(PyCPh), 3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one (PyC4ClPh), 3-(4-bromo
phenyl)-1-pyridin-2-ylprop-2-en-1-one (PyC4BrPh), and 3-(4-nitrophenyl-1-pyridin-2-
ylprop-2-en-1-one (PyC4NO2Ph). The chalcones were obtained as previously reported
[19]. A solution of NaOH 10% (7.5–12.5 mL) was added dropwise to a mixture of 2-ace-
tylpyridine (10 mmol) and the desired aldehyde (10 mmol) in methanol (15 mL). The
reaction mixture was kept under stirring for 1 h at room temperature. The resulting solids
were filtered off, washed with water, and dried in vacuo.
2.2.2. Synthesis of the chalcone-derived thiosemicarbazones. To a mixture of the
desired chalcone (4 mmol) and thiosemicarbazide (4 mmol) in methanol (20 mL), five drops
of HCl were added to catalyze the reaction. The reaction mixture was kept under stirring
for 2 h at room temperature. The resulting solids were filtered off, washed with water and
diethyl ether, and dried in vacuo.
2.2.2.1. 3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCTPh) (1). Pale
canary yellow solid. Anal. Calcd for C15H14N4S (%): C, 63.80; H, 5.00; N, 19.84. Found:
C, 63.61; H, 4.89; N, 20.10. FW: 282.37 g molÀ1. HRMS: m/z [M À H]À calcd for
C15H13N4S: 281.0861. Found: 281.0866. UV–vis [DMF, cmÀ1 (log ɛ)]: 28,011 (4.37).
Selected IR bands (KBr, cmÀ1): (NHNH2) 3416, 3254, (C=N) 1567, (C=S) 750, ρ(py) 538.
1H NMR [200 MHz, DMSO-d6, ppm]: 11.25 (s, 1H, N3–H), 8.64 (d, 1H, H6,

Chalcone-derived thiosemicarbazones
389
3JH6-H5 = 4.4 Hz), 8.46 (s, 1H, N4–H), 8.02–7.92 (m, 2H, H3 and N4–H), 7.85 (t, 1H, H4,
3JH4-H3 = 3JH4-H5 = 7.6 Hz), 7.80–7.60 (m, 3H, H10, H12 and H16), 7.51–7.27 (m, 4H, H5,
3
H13, H14 and H15), 7.17 (d, 1H, H9, JH9-H10 = 16.1 Hz). 13C NMR [50 MHz, DMSO-d6,
ppm]: 179.0 (C8=S), 155.3 (C2), 148.2 (C6), 145.9 (C7=N), 140.0 (C10), 136.8 (C4),
136.2 (C11), 129.1 (C14), 128.6 (C13 and C15), 127.8 (C12 and C16), 123.8 (C5), 123.6
(C3), 117.1 (C9). Yield: 69%.
2.2.2.2.
3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one
thiosemicarbazone
(HPy
CT4ClPh) (2). Pale canary yellow solid. Anal. Calcd for C15H13ClN4S (%): C, 56.87; H,
4.14; N, 17.68. Found: C, 56.89; H, 3.99; N, 17.74. FW: 316.81 g molÀ1. HRMS: m/z
[M À H]À calcd for C15H12ClN4S: 315.0471. Found: 315.0482. UV–vis [DMF, cmÀ1 (log
ɛ)]: 27,548 (4.45). Selected IR bands (KBr, cmÀ1): (NHNH2) 3422, 3268, (C=N) 1562,
1
(C=S) 778, ρ(py) 548. H NMR [200 MHz, DMSO-d6, ppm]: 11.26 (s, 1H, N3–H), 8.62
3
(d, 1H, H6, JH6-H5 = 4.8 Hz), 8.45 (s, 1H, N4–H), 8.06–7.94 (m, 2H, H3, N4–H), 7.86 (t,
3
1H, H4, JH4-H3 = 3JH4-H5 = 7.4 Hz), 7.82–7.70 (m, 3H, H10, H12 and H16), 7.54–7.38 (m,
3
3H, H5, H13 and H15), 7.17 (d, 1H, H9, JH9-H10 = 16.2 Hz). 13C NMR [50 MHz, DMSO-
d6, ppm]: 179.1 (C8=S), 155.2 (C2), 148.2 (C6), 145.5 (C7=N), 138.5 (C10), 136.8 (C4),
135.2 (C11), 133.5 (C14), 129.4 (C13 and C15), 128.6 (C12 and C16), 123.8 (C5), 123.6
(C3), 117.8 (C9). Yield: 61%.
2.2.2.3. 3-(4-bromophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4
BrPh) (3). Yellow solid. Anal. Calcd for C15H13BrN4S (%): C, 49.87; H, 3.63; N, 15.51.
Found: C, 49.75; H, 3.89; N, 15.21. FW: 361.26 g molÀ1. HRMS: m/z [M À H]À calcd for
C15H12BrN4S: 358.9966. Found: 358.9976. UV–vis [DMF, cmÀ1 (log ɛ)]: 27,548 (4.45).
Selected IR bands (KBr, cmÀ1): (NHNH2) 3350, 3312, 3236, (NHpyridinium) 2690 (broad),
1
(C=N) 1560, (C=S) 780, ρ(py) 554. H NMR [200 MHz, DMSO-d6, ppm]: E configura-
tion = 11.44 (s, 1H, N3H), 8.87–8.72 (m, 1H, H6), 8.63 (s, 1H, N4–H), 8.42 (s, 1H, N4–H),
8.34–8.03 (m, 1H, H5), 7.85–7.51 (m, 7H, H5, H3, H12, H16, H13, H15, and H10), 7.13
3
(d, 1H, H9, JH9-H10 = 16.2 Hz); Z configuration = 13.07 (s, 1H, SH), 8.87–8.72 (m, 1H,
H3), 8.68 (s, 1H, N4–H), 8.34–8.03 (m, 3H, H5, H10, and N4–H), 7.85–7.51 (m, 5H, H4,
3
H12, H16, H13, and H15), 7.37 (m, 1H, H6), 7.13 (d, 1H, H9, JH9-H10 = 16.2 Hz).
13C NMR [50 MHz, DMSO-d6, ppm] main signals: E configuration = 179.2 (C8=S), 155.4
(C2), 148.7 (C6), 141.2 (C7=N), 135.7 (C11), 121.4 (C14); Z configuration = 178.2 (C8=S),
151.1 (C2), 145.7 (C6), 135.1 (C11), 122.6 (C14). Yield: 75%.
2.2.2.4. 3-(4-nitrophenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4-
NO2Ph) (4). Citrine solid. Anal. Calcd for C15H13N5O2S (%): C, 55.03; H, 4.00; N, 21.39.
Found: C, 54.83; H, 3.96; N, 21.02. FW: 327.36 g molÀ1. HRMS: m/z [M À H]À calcd for
C15H12N5O2S: 326.0712. Found: 326.0718. UV–vis [DMF, cmÀ1 (log ɛ)]: 32,154 (4.27),
25,316 (4.40). Selected IR bands (KBr, cmÀ1): (NHNH2) 3418, 3270, (C=N) 1570, (C=S)
1
822, ρ(py) 596. H NMR [200 MHz, DMSO-d6, ppm]: 11.40 (s, 1H, N3–H), 8.62 (d, 1H,
3
H6, JH6-H5 = 4.1 Hz), 8.52 (s, 1H, N4–H), 8.25 (d, 2H, H13 and H15,
3JH13-H12 = 3JH15-H16 = 8.7 Hz), 8.11–7.81 (m, 6H, N4–H, H3, H12, H16, H10, and H4),
3
3
3
7.45 (dd, 1H, H5, JH5-H4 = 7.2 Hz, JH5-H3 = 4.9 Hz), 7.32 (d, 1H, H9, JH9-H10 = 16.1 Hz).
13C NMR [50 MHz, DMSO-d6, ppm]: 179.2 (C8=S), 155.0 (C2), 148.3 (C6), 147.1
(C7=N), 144.7 (C14), 143.0 (C11), 137.4 (C10), 136.9 (C4), 128.7 (C12 and C16), 123.8
(C3, C5, C13 and C15), 121.1 (C9). Yield: 68%. Upon slow evaporation in 9:1 acetone/
DMSO solution, crystals of HPyCT4NO2Ph were formed.

390
J.G. Da Silva et al.
2.2.3. Synthesis of gallium(III) and zinc(II) complexes with chalcone-derived
thiosemicarbazones. Gallium nitrate or zinc chloride (0.5 mmol) was added to a solution
of the desired thiosemicarbazone (1 mmol) in methanol (15 mL). The reaction mixture was
kept under reflux and stirring for 15 min. Then, a solution containing sodium acetate
(1.0 mmol) and the thiosemicarbazone (0.05 mmol) in 5 mL of methanol was added to the
reaction mixture which was kept under reflux for 5 h. The obtained solids were filtered off,
washed with isopropanol, and dried in vacuo.
2.2.3.1. Bis[3-phenyl-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] gallium(III)
nitrate [Ga(PyCTPh)2]NO3 (Ga1). Yellow solid. Anal. Calcd for C30H26GaN9O3S2 (%): C,
51.89; H, 3.77; N, 18.15. Found: C, 51.95; H, 3.80; N, 18.29. FW: 694.44 g molÀ1. HRMS
m/z [M À NO3]+ calcd for C30H26GaN8S2: 631.0978. Found: 631.0971. UV–vis [DMF,
cmÀ1 (log ɛ)]: 32,680 (4.74), 22,779 (4.61), 21,978 (4.62). Selected IR bands (KBr, cmÀ1):
1
(NHNH2) 3448, 3248, (C=N) 1514, (C=S) 724, ρ(py) 588, (NO3) 1385, 1324. H NMR
3
[200 MHz, DMSO-d6, ppm]: 9.10 (d, 1H, H10, JH10-H9 = 16.2 Hz), 8.69 (d, 1H, H3,
3
3JH3-H4 = 8.3 Hz), 8.50 (s, 2H, N4–H2), 8.26 (t, 1H, H4, JH4-H3 = 3JH4-H5 = 7.8 Hz),
8.04–7.87 (m, 3H, H6, H12, and H16), 7.76 (d, 1H, H9, 3JH9-H10 = 16.2 Hz), 7.63 (t, 1H, H5,
3
3JH5-H4 = 5.2 Hz, JH5-H3 = 7.5 Hz), 7.57–7.39 (m, 3H, H13, H14, and H15). 13C NMR
[50 MHz, DMSO-d6, ppm]: 178.3 (C8=S), 145.9 (C2), 145.1 (C6), 144.6 (C10), 142.8 (C4),
139.0 (C7=N), 137.0 (C11), 130.4 (C14), 129.3 (C13 and C15), 128.6 (C12 and C16), 127.1
(C5), 124.0 (C3), 115.7 (C9). Molar conductivity (1 mmol LÀ1, DMF): 69.5 Ω-1 cm2 molÀ1
.
Yield: 70%.
2.2.3.2. Bis[3-(4-chlorophenyl)-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] gallium
(III) nitrate [Ga(PyCT4ClPh)2]NO3 (Ga2). Yellow solid. Anal. Calcd for C30H24Cl2Ga-
N9O3S2 (%): C, 47.20; H, 3.17; N, 16.51. Found: C, 47.07; H, 3.19; N, 16.65. FW:
763.33 g molÀ1. HRMS: m/z [M À NO3]+ calcd for C30H24Cl2GaN8S2: 699.0198. Found:
699.0208. UV–vis [DMF, cmÀ1 (log ɛ)]: 32,051 (4.84), 22,728 (4.71), 21,930 (4.73).
Selected IR bands (KBr, cmÀ1): (NHNH2) 3454, 3278, (C=N) 1520, (C=S) 728, ρ(py) 649,
(NO3) 1384, 1285. 1H NMR [200 MHz, DMSO-d6, ppm]: 9.16 (d, 1H, H10,
3
3JH10-H9 = 15.9 Hz), 8.69 (d, 1H, H3, JH3-H4 = 8.1 Hz), 8.54 (s, 2H, N4–H2), 8.24 (t, 1H,
3
3
H4, JH4-H3 = 3JH4-H5 = 7.7 Hz), 8.00 (d, 2H, H12 and H16, JH13-H12 = 3JH15-H16 = 8.3 Hz),
3
3
7.92 (d, 1H, H6, JH6-H5 = 4.6 Hz), 7.74 (d, 1H, H9, JH9-H10 = 15.9 Hz), 7.68–7.51 (m, 3H,
H5, H13, and H15). 13C NMR [50 MHz, DMSO-d6, ppm]: 178.6 (C8=S), 146.0 (C2),
144.6 (C6), 143.8 (C10), 142.8 (C4), 138.5 (C7=N), 136.0 (C11), 134.8 (C14), 130.3
(C13 and C15), 129.3 (C12 and C16), 127.0 (C5), 123.9 (C3), 116.2 (C9). Molar
conductivity (1 mmol LÀ1, DMF): 75.8 Ω-1 cm2 molÀ1. Yield: 65%.
2.2.3.3. Bis[3-(4-bromophenyl)-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] gallium
(III) nitrate [Ga(PyCT4BrPh)2]NO3 (Ga3). Yellow solid. Anal. Calcd for C30H24Br2Ga-
N9O3S2 (%): C, 42.28; H, 2.84; N, 14.79. Found: C, 42.38; H, 2.95; N, 14.75. FW:
870.24 g molÀ1. HRMS: m/z [M À NO3]+ calcd for C30H24Br2GaN8S2: 786.9188. Found:
786.9213. UV–vis [DMF, cmÀ1 (log ɛ)]: 31,949 (4.81), 22,831 (4.65), 21,930 (4.68).
Selected IR bands (KBr, cmÀ1): (NHNH2) 3456, 3277, (C=N) 1519, (C=S) 728, ρ(py) 651,
(NO3) 1385, 1299. 1H NMR [200 MHz, DMSO-d6, ppm]: 9.18 (d, 1H, H10,
3
3JH10-H9 = 15.9 Hz), 8.71 (d, 1H, H3, JH3-H4 = 8.3 Hz), 8.54 (s, 2H, N4–H2), 8.25 (t, 1H,
3
H4, JH4-H3 = 3JH4-H5 = 7.8 Hz), 8.02–7.86 (m, 3H, H6, H12, and H16), 7.84–7.67 (m, 3H,
3
H9, H13, and H15), 7.61 (d, 1H, H5, JH5-H4 = 3JH5-H6 = 7.0 Hz). 13C NMR [50 MHz,

Chalcone-derived thiosemicarbazones
391
DMSO-d6, ppm]: 178.6 (C8=S), 145.9 (C2), 144.6 (C6), 143.9 (C10), 142.8 (C4),
138.4 (C7=N), 136.4 (C11), 132.2 (C13 and C15), 130.5 (C12 and C16), 127.0
(C5), 123.6 (C14), 123.8 (C3), 116.2 (C9). Molar conductivity (1 mmol LÀ1, DMF):
67.9 Ω-1 cm2 molÀ1. Yield: 72%.
2.2.3.4. Bis[3-(4-nitrophenyl)-1-pyridin-2-ylpro-2-en-1-one thiosemicarbazonato] gallium
(III) nitrate [Ga(PyCT4NO2Ph)2]NO3 (Ga4). Orange solid. Anal. Calcd for C30H24Ga-
N11O7S2 (%): C, 45.93; H, 3.08; N, 19.64. Found: C, 45.85; H, 3.03; N, 19.62. FW:
784.44 g molÀ1. HRMS: m/z [M À NO3]+ calcd for C30H24GaN10O4S2: 721.0679. Found:
721.0667. UV–vis [DMF, cmÀ1 (log ɛ)]: 29,851 (4.79), 21,787 (4.68), 21,231 (4.70).
Selected IR bands (KBr, cmÀ1): (NHNH2) 3446, 3296, (C=N) 1514, (C=S) 728, ρ(py) 658,
(NO3) 1385, 1295. 1H NMR [200 MHz, DMSO-d6, ppm]: 9.28 (d, 1H, H10,
3
3JH10-H9 = 15.9 Hz), 8.88 (s, 2H, N4–H2), 8.73 (d, 1H, H3, JH3-H4 = 8.1 Hz), 8.47–8.16
(m, 5H, H13, H15, H4, H12, and H16), 8.03–7.83 (m, 2H, H6, and H9), 7.63 (dd, 1H,
3
3
H5, JH5-H4 = 7.1 Hz, JH5-H6 = 5.3 Hz). 13C NMR [50 MHz, DMSO-d6, ppm]: 178.8
(C8=S), 147.2 (C2), 145.4 (C14), 144.3 (C6), 143.4 (C11), 142.5 (C4), 141.8 (C10), 137.3
(C7=N), 129.0 (C12 and C16), 126.6 (C5), 124.0 (C13 and C15), 123.4 (C3), 119.1 (C9).
Molar conductivity (1 mmol LÀ1, DMF): 66.3 Ω-1 cm2 molÀ1. Yield: 84%.
2.2.3.5. Bis[3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazonato] zinc(II) [Zn
(PyCTPh)2] (Zn1). Yellow solid. Anal. Calcd for C30H26N8S2Zn (%): C, 57.37; H, 4.17;
N, 17.84. Found: C, 57.30; H, 4.13; N, 17.79. FW: 628.10 g molÀ1. UV–vis [DMF, cmÀ1
(log ɛ)]: 22,676 (4.60). Selected IR bands (KBr, cmÀ1): (NHNH2) 3442, 3304, (C=N)
1
1510, (C=S) 726, ρ(py) 582. H NMR [200 MHz, DMSO-d6, δ (ppm)]: 8.23 (d, 1H, H10,
3
3JH10-H9 = 16.7 Hz), 8.04 (d, 1H, H3, JH3-H4 = 8.6 Hz), 7.94–7.81 (m, 2H, H4, and H6),
3
7.77 (d, 2H, H12 and H16, JH12-H13 = 3JH16-H15 = 7.3 Hz), 7.66 (d, 1H, H9,
3JH9-H10 = 16.7 Hz), 7.51–7.23 (m, 6H, H14, N4–H2, H13, H15, and H5). 13C NMR
[50 MHz, DMSO-d6, ppm]: 183.3 (C8=S), 149.7 (C2), 146.4 (C6), 139.5 (C7=N),
138.9 (C4), 137.8 (C10), 137.3 (C11), 128.7 (C13 and C15), 128.5 (C14), 127.2 (C12
and C16), 123.5 (C5), 121.7 (C3), 118.5 (C9). Molar conductivity (1 mmol LÀ1, DMF):
0.5 Ω-1 cm2 molÀ1. Yield: 92%.
2.2.3.6. Bis[3-(4-chlorophenyl)-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] zinc(II)
[Zn(PyCT4ClPh)2] (Zn2). Yellow solid. Anal. Calcd for C30H24Cl2N8S2Zn (%): C, 51.70;
H, 3.47; N, 16.08. Found: C, 51.76; H, 3.50; N, 16.12. FW: 696.99 g molÀ1. UV–vis
[DMF, cmÀ1 (log ɛ)]: 22,371 (4.64). Selected IR bands (KBr, cmÀ1): (NHNH2) 3448,
1
3288, (C=N) 1512, (C=S) 730, ρ(py) 636. H NMR [200 MHz, DMSO-d6, ppm]: 8.42 (d,
3
3
1H, H10, JH10-H9 = 16.4 Hz), 8.08 (d, 1H, H3, JH3-H4 = 8.1 Hz), 7.92–7.75 (m, 4H, H4,
3
H6, H12, and H16), 7.73 (d, 1H, H9, JH9-H10 = 16.6 Hz), 7.55–7.37 (m, 4H, N4–H2, H13,
and H15), 7.28 (t, 1H, H5, JH5-H6 = 3JH5-H4 = 7.0 Hz). 13C NMR [50 MHz, DMSO-d6,
3
ppm]: 183.6 (C8=S), 149.8 (C2), 146.3 (C6), 138.9 (C4), 138.6 (C7=N), 136.8 (C10),
136.4 (C11), 132.8 (C14), 128.8 (C13 and C15), 128.6 (C12 and C16), 123.4 (C5), 121.4
(C3), 118.8 (C9). Molar conductivity (1 mmol LÀ1, DMF): 0.2 Ω-1 cm2 molÀ1. Yield: 96%.
2.2.3.7. Bis[3-(4-bromophenyl)-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] zinc(II)
[Zn(PyCT4BrPh)2] (Zn3). Yellow solid. Anal. Calcd for C30H24Br2N8S2Zn (%): C, 45.85;
H, 3.08; N, 14.26. Found: C, 45.79; H, 3.11; N, 14.34. FW: 785.90 g molÀ1. UV–vis
[DMF, cmÀ1 (log ɛ)]: 22,321 (4.61). Selected IR bands (KBr, cmÀ1): (NHNH2) 3436,
1
3290, (C=N) 1516, (C=S) 728, ρ(py) 635. H NMR [200 MHz, DMSO-d6, ppm]: 8.41 (d,

392
J.G. Da Silva et al.
3
3
1H, H10, JH10-H9 = 16.3 Hz), 8.07 (d, 1H, H3, JH3-H4 = 8.0 Hz), 7.94–7.55 (m, 7H, H4,
3
H6, H12, H16, H3, H13, and H15), 7.46 (s, 2H, N4–H2), 7.27 (t, 1H, H5, JH5-
H4 = 3JH5-H6 = 6.4 Hz). 13C NMR [50 MHz, DMSO-d6, ppm]: 183.7 (C8=S), 149.8 (C2),
146.3 (C6), 138.9 (C4), 138.6 (C7=N), 136.9 (C10), 136.8 (C11), 131.5 (C13 and C15),
129.1 (C12 and C16), 123.4 (C5), 121.4 (C3 and C14), 118.8 (C9). Molar conductivity
(1 mmol LÀ1, DMF): 2.7 Ω-1 cm2 molÀ1. Yield: 73%.
2.2.3.8. Bis[3-(4-nitrophenyl)-1-pyridin-2-ylprop-2en-1-one thiosemicarbazonato] zinc(II)
[Zn(PyCT4NO2Ph)2] (Zn4). Orange-red solid. Anal. Calcd for C30H24N10O4S2Zn (%): C,
50.18; H, 3.37; N, 19.51. Found: C, 50.05; H, 3.34; N, 19.46. FW: 718.06 g molÀ1. UV–
vis [DMF, cmÀ1 (log ɛ)]: 31,348 (4.67), 26,385 (4.46), 20,877 (4.61). Selected IR bands
(KBr, cmÀ1): (NHNH2) 3446, 3296, (C=N) 1512, (C=S) 727, ρ(py) 630. 1H NMR
3
[200 MHz, DMSO-d6, ppm]: 8.73 (d, 1H, H10, JH10-H9 = 16.2 Hz), 8.28 (d, 1H, H3,
3JH3-H4 = 8.7 Hz), 8.20–7.99 (m, 3H, H3, H13, and H15), 7.97–7.61 (m, 6H, H6, H12,
3
3
H16, H9, and N4–H2), 7.29 (dd, 1H, H5, JH5-H4 = 7.2 Hz, JH5-H6 = 5.3 Hz). 13C NMR
[50 MHz, DMSO-d6, ppm]: 184.5 (C8=S), 149.8 (C2), 146.6 (C14), 146.3 (C6), 144.7
(C11), 139.1 (C4), 137.4 (C7=N), 135.9 (C10), 128.0 (C12 and C16), 123.8 (C13
and C15), 123.4 (C5), 121.7 (C3), 121.2 (C9). Molar conductivity (1 mmol LÀ1, DMF):
0.5 Ω-1 cm2 molÀ1. Yield: 95%.
2.3. Crystal structure determination
The crystal structure of 4 was determined using single-crystal X-ray diffractometry. Molec-
ular plot and crystal packing figures were prepared using ORTEP [20] and MERCURY
[21], respectively. Tables were generated using WINGX suite [22]. A summary of the
crystal data, data collection details, and refinement results are listed in table 1.
2.4. In vitro antimicrobial activity
Antibacterial activity was evaluated by minimum inhibitory concentration (MIC) using the
macrodilution test [23,24]. Staphylococcus aureus ATCC 6538 or P. aeruginosa ATCC
27853 stored in Mueller Hinton broth were subcultured for testing in the same medium
and grown at 37 °C. Then, the bacterial cells were suspended, according to the McFarland
protocol [24] in saline solution, to produce a suspension of 105 colony-forming units/mL
(CFU mLÀ1). 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 μg mLÀ1. A 24-h-old inoculum (100 μL) was added to each tube. The MIC, defined as
the lowest concentration of the test compound which inhibits the visible growth after 20 h,
was determined visually after incubation for 20 h at 37 °C. Tests using tetracycline as refer-
ence and DMSO as negative control were carried out in parallel. All tests were performed
in triplicate with full agreement between the results.
Antifungal activity was evaluated by MIC using the macrodilution test [23,25]. Candida
albicans ATCC 10231 stored in Sabouraud broth was subcultured for testing in the same
medium and grown at 37 °C. Then, yeast cells were suspended according to the McFarland
protocol [25] in saline solution to produce a suspension of 105 CFU mLÀ1. 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 μg mLÀ1. A 24-h-old inoculum

Chalcone-derived thiosemicarbazones
Table 1. Crystal data and structure refinement results for 4.
393
Compound
HPyCT4NO2Ph (4)
C15H13N5O2S
327.36
Empirical formula
Molecular weight (g molÀ1
)
Crystal system, space group
Monoclinic, Pc
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
7.8859(1)
16.7965(2)
11.2801(2)
90
93.427(1)
90
V (Å3)
1491.44(4)
Z
4
Dcalc (g cmÀ3
)
1.458
F(0 0 0)
680
Crystal size (mm)
0.54 Â 0.24 Â 0.10
Absorption coefficient (mmÀ1
h range for data collection (°)
)
0.235
2.86 to 26.37
Index ranges
À9 6 h 6 9
À20 6 k 6 20
À14 6 l 6 14
Reflections collected
48,255
Reflections unique/R(int)
3054/0.0394
99.9
0.9769 and 0.8837
R1 = 0.0241, wR2 = 0.0670
R1 = 0.0254, wR2 = 0.0675
1.066
Completeness to theta = 26.37° (%)
Max. and min. transmission
Final R indices [I > 2σ(I)]
R indices (all data)
Goodness-of-fit on F2
Absolute structure parameter
0.10(5)
0.222/À0.171
Largest diff. peak and hole (e ÅÀ3
)
(100 μL) was added to each tube. The MIC was determined visually after incubation for
20 h at 37 °C. Tests using fluconazole as reference and DMSO as negative control were
carried out in parallel. No inhibition was observed with 5% v/v DMSO. All tests were
performed in triplicate with full agreement between the results.
3. Results and discussion
3.1. Formation of chalcone-derived thiosemicarbazones and their metal complexes
Formation of the thiosemicarbazones (1–4) was confirmed by microanalyses, infrared,
NMR, and HRMS data. Microanalyses and molar conductivities were compatible with the
formation of the gallium(III) complexes [Ga(PyCTPh)2]NO3 (Ga1), [Ga(PyCT4ClPh)2]
NO3 (Ga2), [Ga(PyCT4BrPh)2]NO3 (Ga3), and [Ga(PyCT4NO2Ph)2]NO3 (Ga4) and the
zinc(II) complexes [Zn(PyCTPh)2] (Zn1), [Zn(PyCT4ClPh)2] (Zn2), [Zn(PyCT4BrPh)2]
(Zn3), and [Zn(PyCT4NO2Ph)2] (Zn4). In all complexes, the thiosemicarbazone is
attached to the metal center as an anion.
3.1.1. HRMS data. HRMS data were used to further characterize the thiosemicarbazones
and their complexes. The thiosemicarbazones exhibited a peak at m/z 281.0866 (1),

394
J.G. Da Silva et al.
315.0482 (2), 358.9976 (3), and 326.0718 (4) in the negative ionization mode which
was attributed to the ion fragment [M À H]À, indicating the presence of an anionic
thiosemicarbazone. The appearance of this ion is associated with the high stability of the
anionic form resulting from increased conjugation.
In spectra of the gallium(III) complexes, a peak at m/z 631.0971 (Ga1), 699.0208
(Ga2), 786.9213 (Ga3), and 721.0667 (Ga4) was observed in the positive ionization
mode, due to formation of [Ga(L)2]+. The presence of this peak is in accordance with
molar conductivity data that indicated that the complexes are 1 : 1 electrolytes in solution.
For the zinc(II) complexes, no peaks attributable to ionization were observed, in accor-
dance with molar conductivity data which indicated that the complexes are nonelectrolytes.
3.1.2. Electronic spectra. The electronic spectra of the chalcone precursors showed an
absorption at ca. 30,769–31,546 cmÀ1, attributable to the n→π⁄ transition of the enone
function. Upon formation of the thiosemicarbazones, absorptions at 25,316–28,011 cmÀ1
,
attributable to n→π⁄ transitions of the azomethine and thioamide functions overlapped in
the same envelope, were observed [26]. In the case of 4, the transitions appeared at lower
energies and a π→π⁄ transition was also noticed at 32,154 cmÀ1, which could not be
observed in spectra of 1–3. This difference is probably due to the presence of the electron-
withdrawing NO2 group in 4.
In spectra of the gallium(III) complexes, the π→π⁄ transitions of the aromatic rings are
at ca. 29,851–32,680 cmÀ1. Two n→π⁄ transitions attributed to C=N and C=S
were observed at ca. 21,787–22,831 cmÀ1 and ca. 21,231–21,978 cmÀ1, respectively. In the
zinc(II) complexes, the C=N and C=S n→π⁄ transitions were observed at ca.
20,877–22,371 cmÀ1
.
Upon coordination to both metals, the n→π⁄ transitions of the azomethine and
thioamide functions shifted to lower energies due to the formation of a highly delocalized
system upon deprotonation of the ligand [27,28].
3.1.3. Infrared spectra. Upon formation of the thiosemicarbazones, the ν(C=O)
vibration at 1670–1677 cmÀ1 in infrared spectra of the chalcones disappeared along with
the appearance of a new absorption at 1560–1570 cmÀ1, attributed to ν(C=N) [29]. New
absorptions were observed at 3150–3450 cmÀ1, which were attributed to ν(N–H) of the
thioamide [5,29], and a strong absorption at 750–822 cmÀ1 that was assigned to ν(C=S)
[29]. In the spectrum of 3, a new absorption was observed at 2500–2800 cmÀ1 which was
attributed to ν(S–H), indicating the presence of thione-thiol tautomerism [30], or to ν(N–
H) of a pyridinium ion [31].
The ν(C=N) absorption underwent a shift in spectra of the complexes, suggesting coor-
dination of the imine nitrogen [5,6,32]. The ν(C=S) vibration at 750–822 cmÀ1 in the
uncomplexed thiosemicarbazones shifted to 724–730 cmÀ1 in spectra of the complexes,
indicating coordination of sulfur [5,6,16]. The in-plane deformation mode of the pyridiner-
ing at 538–596 cmÀ1 in spectra of the free bases shifted to 588–658 cmÀ1 in the com-
plexes, suggesting coordination of the heteroaromatic nitrogen [16,29].
For the gallium(III) complexes, new absorptions attributed to the symmetric and asym-
metric stretching of NO from nitrate were observed at ca. 1385 cmÀ1 and 1285–
1324 cmÀ1, respectively [6,16,33].

Chalcone-derived thiosemicarbazones
395
3.1.4. NMR spectra. Immediately after dissolution, only one signal was observed for
each hydrogen atom in spectra of 1, 2, and 4, but duplicate signals were found for carbon
atoms due to the time required for recording 13C NMR spectra. The signal of N3–H was
1
observed at 11.21, 11.26, and 11.40 ppm for 1, 2, and 4, respectively. H NMR spectra
registered one hour after dissolution showed duplicated signals, in accordance with the
presence of two species in solution. The signals of all hydrogen and carbon atoms are
1
duplicated in H and 13C NMR spectra of 3, even immediately after dissolution, indicating
the presence of two isomers in DMSO-d6.
An NOEDIFF experiment was recorded for 1 immediately after dissolution by irradiating
at 11.21 ppm (figure 3), which is the position of N3–H. One NOE signal at 7.76 ppm
(J = 16 Hz), attributed to H10, indicates that the compound adopts the E configuration in rela-
tion to the C7-N2 bond. Hence, the predominant form of 1 is E. Similarly, the E configuration
is dominant for 2 and 4. 1H NMR spectra of 1, 2, and 4 registered one hour after dissolution
showed a signal at 12.89, 13.07, and 13.33 ppm, respectively, which is characteristic of the
Z isomer, in which N3–H is hydrogen bonded to the pyridine nitrogen. The presence of the
E and Z isomers is frequently observed for 2-benzoylpyridine-derived thiosemicarbazones
[31,34,35].
Hereafter, attributions are given only for the main isomer (E) of 1, 2, and 4. The high
value of the H9/H10 coupling constant (J = 16 Hz) indicates that these two hydrogen atoms
are trans to each other in relation to the C9–C10 bond and that the configuration is E in
relation to this bond. Thus, immediately after dissolution, the compounds adopt the EE
configuration in relation to C7–N2 and C9–C10. After one hour, one observes the presence
of the EE and ZE configurations in equilibrium in the solution. Crystal structure
determination of 4 revealed that the compound adopts the ZE configuration.
Figure 3. 1H NMR spectra of HPyCTPh (1) (DMSO-d6, 200 MHz). (a) Spectrum obtained immediately after
dissolution. (b) NOEDIFF spectrum (irradiation at 11.21 ppm). (c) Spectrum obtained 1 h after dissolution.

396
J.G. Da Silva et al.
Figure 4. Generic structure of chalcone-derived thiosemicarbazones showing the E (A) and Z (B) configurational
isomers, and the Z zwitterionic form (C).
NMR data do not allow the attribution of the conformation in relation to the C8–N3
bond. The two resonances observed for N4H2 in the 1H NMR spectra of 1, 2, and 4
indicated hindered rotation around the –C=S–NH2 bond due to its partial double bond
character [36].
Signals at 13.07 and 11.44 ppm in the spectrum of 3 may be attributed to N3–H of
the Z and E isomers, respectively. The absence of the signal at 4.0 ppm attributable to
S–H proton in the spectrum of 3 provided strong evidence for the presence of the thione
form in solution [37]. Since the Z isomer is present, transference of the hydrogen from
N3–H to the pyridine nitrogen could have occurred. Therefore, the broad absorption at
2500–2800 cmÀ1 in the infrared spectrum of 3 is most likely attributable to ν(N–H) of
the pyridinium ion, with formation of a zwitterion containing a sulfur in the thiolate
form in a highly delocalized system involving the heteroaromatic ring and the
thiosemicarbazone chain (figure 4).
Only one signal was observed for each hydrogen atom and each carbon atom in the
1
NMR spectra of the complexes. In the H NMR spectra of all complexes, the signal of
N3–H was no longer observed, indicating deprotonation upon complexation and the pres-
ence of an anionic thiosemicarbazones. Only one signal was observed for N4H2 in accord
with the higher rigidity of the C8–N3 bond in the complexes, which acquired double bond
character upon deprotonation at N3.
In 13C NMR spectra of the complexes, the signals of C7 and C8 shifted in relation to
their positions in the free thiosemicarbazone, suggesting coordination through the sulfur
1
and the imine nitrogen. The H and 13C signals of the pyridine hydrogen and carbon atoms
underwent significant shifts in the spectra of the complexes, suggesting coordination
through the aromatic nitrogen. Hence, in all complexes, two thiosemicarbazone ligands are
attached to the metal through the Npy–N–S chelating system and adopt the EZE conforma-
tion in relation to the C7–N2, N3–C8, and C9–C10 bonds.
3.2. Crystal structure of HPyCT4NO2Ph (4)
The ORTEP diagram of 4 is shown in figure 5. Selected intramolecular bond lengths and
angles and hydrogen bonding parameters in the structure are given in tables 2 and 3,
respectively. Figure 6 shows a perspective view of the crystal packing.
4 crystallized in the monoclinic system, space group Pc, with two independent
molecules (A and B) in the asymmetric unit (figure 5). In A, sulfur was numbered S1 and
in molecule B, S11. In these molecules, the C=N–N–C(=S)N skeleton is almost planar
(rms deviation from the least-squares plane of 0.0735 and 0.0177 Å for A and B,

Chalcone-derived thiosemicarbazones
397
Figure 5. ORTEP diagram for HPyCT4NO2Ph (4) with thermal ellipsoids at the 50% probability level and
labeling scheme of the nonhydrogen atoms. Hydrogen atoms are drawn as circles of arbitrary radii.
respectively). The angles between the plane of the thiosemicarbazone moiety and the plane
of the pyridine ring are quite similar in the two molecules, i.e. 14.87(8)° and 13.36(9)° in
A and B, respectively. However, the angle between the plane of the chalcone-derived chain
Table 2. Selected bond lengths (Å) and angles (°) for 4.
Bond lengths
S1–C8
1.681(2)
1.363(3)
1.361(2)
1.309(3)
1.347(3)
1.483(3)
1.473(3)
1.335(3)
1.462(3)
1.397(3)
1.408(3)
S11–C108
N13–C108
N13–N12
1.675(2)
1.360(3)
1.354(2)
1.300(3)
1.348(3)
1.498(3)
1.471(3)
1.328(3)
1.466(3)
1.390(3)
1.407(3)
N3–C8
N3–N2
N2–C7
N1–C2
C7–C2
N12–C107
N11–C102
C107–C102
C107–C109
C110–C109
C111–C110
C111–C112
C111–C116
C7–C9
C10–C9
C11–C10
C11–C12
C11–C16
Angles
N1–C2–C7
C9–C7–C2
N2–C7–C9
C7–N2–N3
N2–N3–C8
N3–C8–S1
N4–C8–N3
C10–C9–C7
C9–C10–C11
C12–C11–C10
C13–C12–C11
C16–C11–C10
C12–C11–C16
117.9(2)
118.0(2)
114.8(2)
119.4(2)
118.6(2)
118.8(2)
116.8(2)
125.5(2)
124.9(2)
119.0(2)
121.5(2)
122.8(2)
118.3(2)
N11–C102–C107
C109–C107–C102
N12–C107–C109
C107–N12–N13
N12–N13–C108
N13–C108–S11
N14–C108–N13
C110–C109–C107
C109–C110–C111
C112–C111–C110
C113–C112–C111
C116–C111–C110
C112–C111–C116
117.4(2)
118.1(2)
115.4(2)
119.4(2)
120.2(2)
119.1(2)
117.3(2)
124.6(2)
126.0(2)
118.2(2)
121.3(2)
123.0(2)
118.9(2)

398
J.G. Da Silva et al.
Table 3. Hydrogen bonds for 4 [Å and °].
D–H–A
D–H
H–A
D–A
D–H–A
N3–H3–N1
0.88
0.88
0.88
0.88
0.88
1.95
2.74
1.90
2.44
2.36
2.632(3)
3.556(2)
2.598(3)
3.160(2)
3.225(3)
132.9
155.5
135.1
139.1
165.7
N4–H4B–S11a
N13–H13–N11
N14–H14A–O2b
N14–H14B–O12c
Notes: Symmetry transformations used to generate equivalent atoms: a = xÀ1, y, z; b = x + 1, yÀ1, z; c = x + 1, y,
z + 1.
Figure 6. View of the crystal packing of HPyCT4NO2Ph (4).
attached to C7 and the plane of the pyridine ring is different for the two molecules, i.e.
32.87(6)° and 9.00(9)°, for A and B, respectively.
The molecule of 4 adopts the ZEE conformation in relation to the C7–N2, N3–C8, and
C9–C10 bonds. The presence of the ZE conformation in relation to C7–N2 and N3–C8 is
quite common in 2-benzoylpyridine-derived thiosemicarbazones [29,34,38]. In fact, bond
lengths within the pyridine ring and the thiosemicarbazone chain in 4 (table 2) are very
similar to those of 2-benzoylpyridine thiosemicarbazone (H2BPyTSC) [38]. Intramolecular
N3–H3∙∙∙N1 and N13–H13∙∙∙N11 hydrogen bonds were observed in molecules A and B,
respectively, which result in the Z configuration in relation to the C7–N2 bond.
In the molecular packing of 4, intermolecular hydrogen bonds involving N4–H or
N14–H and S11, O2, and O12 lead to formation of an infinite 2D network parallel to the
(1 0 À1) plane (see table 3 and figure 6).

Chalcone-derived thiosemicarbazones
3.3. In vitro antimicrobial activity
399
Table 4 reports the MIC of the studied compounds against S. aureus, P. aeruginosa, and
C. albicans, together with MIC values for the reference drugs tetracycline hydrochloride
and fluconazole.
The chalcones, thiosemicarbazones (1–4), and zinc(II) complexes (Zn1–Zn4) are not
active against P. aeruginosa in the assayed conditions. The activity of the chalcones
followed the order PyCPh < PyC4ClPh < PyC4BrPh ꢀ PyC4NO2Ph against S. aureus and
the order PyCPh < PyC4ClPh ꢀ PyC4BrPh < PyC4NO2Ph against C. albicans, indicating
that the presence of the halogen or the nitro substituent in the para position of the chal-
cone phenyl ring leads to activity improvement. The chalcone-derived thiosemicarbazones,
except 4, were in general more active than the parent compounds against S. aureus and
C. albicans. The activities of the thiosemicarbazones followed the order 1 < 2 < 3 against
S. aureus and the order 3 < 1 < 2 against C. albicans. Interestingly, the nitro derivative (4)
proved to be inactive against both micro-organisms in the assayed conditions. The low
solubility of 4 may, at least in part, account for its lack of activity.
Coordination to zinc(II) resulted in activity improvement of the thiosemicarbazones
against S. aureus, but was not a good strategy for activity enhancement against C. albicans.
Although gallium nitrate proved to be inactive against the assayed micro-organisms,
coordination of gallium(III) to the thiosemicarbazones significantly enhanced antimicrobial
activity. Coordination to gallium(III) resulted in activity improvement of all thiosemicarba-
zones against the three studied micro-organism strains, indicating this to be an effective
strategy for antimicrobial activity enhancement. As previously suggested, the mechanism of
antibacterial [6] and antifungal [13] activity of gallium(III) complexes probably involves
perturbation of iron metabolism.
Table 4. MIC against S. aureus ATCC 6538, P. aeruginosa ATCC 27853, and C. albicans ATCC 10231 for the
chalcones, thiosemicarbazones, their metal complexes, the metal salts, tetracycline, and fluconazole.
MIC (μ mol LÀ1
)
Compounds
S. aureus
P. aeruginosa
C. albicans
PyCPh
HPyCTPh (1)
[Ga(PyCTPh)2]NO3 (Ga1)
[Zn(PyCTPh)2] (Zn1)
PyC4ClPh
30.3
21.3
4.46
5.07
8.13
9.96
1.81
4.74
6.19
2.21
0.96
2.21
6.19
>74.1
15.6
36.4
565
>145
>84.1
17.83
>88.8
>119
>88.4
16.08
>83.8
>87.63
>68.51
28.85
>60.5
>100
>79.4
29.7
31.1
11.3
16.8
22.6
18.9
8.76
13.5
19.2
18.94
19.55
14.36
>67.8
12.8
>157
15.21
>68.6
1742
>929
467
HPyCT4ClPh (2)
[Ga(PyCT4ClPh)2]NO3 (Ga2)
[Zn(PyCT4ClPh)2] (Zn2)
PyC4BrPh
HPyCT4BrPh (3)
[Ga(PyCT4BrPh)2]NO3 (Ga3)
[Zn(PyCT4BrPh)2] (Zn3)
PyC4NO2Ph
HPyCT4NO2Ph (4)
[Ga(PyCT4NO2Ph)2]NO3 (Ga4)
[Zn(PyCT4NO2Ph)2] (Zn4)
Thiosemicarbazide
Gallium nitrate
>74.5
4916
997
>2346
7.31
1802
>1067
0.37
–
Zinc chloride
Tetracycline hydrochloride
Fluconazole
–
12.9
–

400
J.G. Da Silva et al.
4. Conclusion
Chalcone-derived thiosemicarbazones were obtained, which present antibacterial and
antifungal activities. In some cases, the thiosemicarbazones proved to be more potent as
antimicrobial agents than the chalcone counterparts. Coordination of the thiosemicarbazones
to zinc(II) resulted in activity improvement against S. aureus, but not against C. albicans.
Coordination of the thiosemicarbazones to gallium(III) resulted in activity improvement
against all studied micro-organisms. The thiosemicarbazones proved to be active against
gram-positive S. aureus bacteria while their gallium(III) complexes were active against both
gram-positive S. aureus and gram-negative P. aeruginosa strains. Hence, complexation to
gallium(III) led to a broadening of the antibacterial spectrum of the studied thiosemicarba-
zones. Since gallium nitrate is inactive against all micro-organisms, coordination to the
thiosemicarbazones resulted in significant improvement of gallium’s antimicrobial profile.
The literature contains many reports on the antimicrobial properties of both chalcones
[1] and thiosemicarbazones [3] and their metal complexes [39–43]. The preparation of
chalcone-derived thiosemicarbazones and their zinc(II) and gallium(III) complexes revealed
to be an effective strategy of obtaining potent antimicrobial agents which could constitute
interesting drug candidate prototypes.
Supplementary data
CCDC 890760 contains the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallographic Data Center via
http://www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
This work was supported by CNPq and INCT-INOFAR (Proc. CNPq 988573.364/2008-6)
from Brazil.
References
[1] Z. Nowakowska. Eur. J. Med. Chem., 42, 125 (2007).
[2] M.L. Go, X. Wu, X.L. Liu. Curr. Med. Chem., 12, 483 (2005).
[3] H. Beraldo, D. Gambino. Mini Rev. Med. Chem., 4, 31 (2004).
[4] A.E. Liberta, D.X. West. Biometals, 5, 121 (1992).
[5] I.C. Mendes, J.P. Moreira, A.S. Mangrich, S.P. Balena, B.L. Rodrigues, H. Beraldo. Polyhedron, 26, 3263
(2007).
[6] J.G. Da Silva, L.S. Azzolini, S.M.S.V. Wardell, J.L. Wardell, H. Beraldo. Polyhedron, 28, 2301 (2009).
[7] W.B. Júnior, M.S. Alexandre-Moreira, M.A. Alves, A. Perez-Reboleleo, G.L. Parrilha, E.E. Castellano,
O.E. Piro, E.J. Barreiro, H. Beraldo. Molecules, 16, 6902 (2011).
[8] J. Sheng, P.T.M. Nguyen, R.E. Marquis. Arch. Oral Biol., 50, 747 (2005).
[9] Y. Oyama, H. Matsui, M. Morimoto, Y. Sakanashi, Y. Nishimura, Y. Okano. Toxicol. Lett., 171, 138 (2007).
[10] P. Talukder, T. Satho, K. Irie, T. Sharmin, D. Hamady, Y. Nakashima, F. Miake. Int. Immunopharmacol., 11,
141 (2011).
[11] L.R. Bernstein. Pharmacol. Rev., 50, 665 (1998).
[12] J.A. Lessa, G.L. Parrilha, H. Beraldo. Inorg. Chim. Acta., 393, 53 (2012).
[13] T.O. Bastos, B.M. Soares, P.S. Cisalpino, I.C. Mendes, R.G. dos Santos, H. Beraldo. Microbiol. Res., 573,
165 (2010).
[14] R.J. Martens, N.A. Miller, N.D. Cohen, J.R. Harrington, L.R. Bernstein. J. Equine Vet. Sci., 27, 341 (2007).
[15] Y. Kaneko, M. Thoendel, O. Olakanmi, B.E. Britigan, P.K. Singh. J. Clin. Invest., 117, 877 (2007).
[16] I.C. Mendes, M.A. Soares, R.G. Santos, C. Pinheiro, H. Beraldo. Eur. J. Med. Chem., 44, 1870 (2009).

Chalcone-derived thiosemicarbazones
401
[17] Oxford Diffraction. CrysAlis PRO CCD and CrysAlis PRO RED: Version 1.171.33.55 (release 05 01 2010
CrysAlis171.NET), Oxford Diffraction Ltd., Yarnton, Oxfordshire, England (2010).
[18] G.M. Sheldrick. Acta Cryst., A64, 112 (2008).
[19] V.V. Zakharychev, A.V. Kuzenkov. Chem. Heterocycl. Comp., 43, 989 (2007).
[20] L.J. Farrugia. J. Appl. Cryst., 30, 565 (1997).
[21] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge,
R. Taylor, P.A. Wood. J. Appl. Cryst., 41, 466 (2008).
[22] L.J. Farrugia. J. Appl. Cryst., 32, 837 (1999).
[23] J. Pernak, J. Rogoza, I. Mirska. Eur. J. Med. Chem., 36, 313 (2001).
[24] National Committee for Clinical Laboratory Standards. Methods for Dilution Antimicrobial Susceptibility
Tests for Bacteria that Grow Aerobically; Approved Standard, 6th Edn, NCCLS document M7-A6 (ISBN
1-56238-486-4). NCCLS, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898, USA
(2003).
[25] National Committee for Clinical Laboratory Standards. Reference Method for Broth Dilution Antifungal
Susceptibility Testing of Yeasts; Approved Standard, 2nd Edn, NCCLS document M27-A2 [ISBN 1-56238-
469-4]. NCCLS, Pennsylvania, USA (2002).
[26] M. Joseph, A. Sreekanth, V. Suni, M.R.P. Kurup. Spectrochim. Acta A, 64, 637 (2006).
[27] K.S.O. Ferraz, N.F. Silva, J.G. Da Silva, N.L. Speziali, I.C. Mendes, H. Beraldo. J. Mol. Struct., 1008, 102
(2012).
[28] E.B. Seena, M.R.P. Kurup. Spectrochim. Acta, Part A, 69, 726 (2008).
[29] I.C. Mendes, J.P. Moreira, N.L. Speziali, A.S. Mangrich, J.A. Takahashia, H. Beraldo. J. Braz. Chem. Soc.,
17, 1571 (2006).
[30] P. Sengupta, R. Dinda, S. Ghosh. Transition Met. Chem., 27, 665 (2002).
[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,
H. Beraldo. J. Inorg. Biochem., 105, 1729 (2011).
[32] A.P. Rebolledo, M. Vieites, D. Gambino, O.E. Piro, E.E. Castellano, C.L. Zani, E.M. Souza-Fagundes,
L.R. Teixeira, H. Beraldo. J. Inorg. Biochem., 99, 698 (2005).
[33] K. Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th Edn, p. 254,
John Wiley and Sons, New York, NY (1986).
[34] A.P. Rebolledo, G.M. de Lima, L.N. Gambi, N.L. Speziali, D.F. Maia, C.B. Pinheiro, J.D. Ardisson,
H. Beraldo. Appl. Organomet. Chem., 17, 945 (2003).
[35] J.G. Da Silva, S.M.S.V. Wardell, J.L. Wardell, H. Beraldo. J. Coord. Chem., 62, 1400 (2009).
[36] O.E. Offiong. Spectrochim. Acta, Part A, 50, 2167 (1994).
[37] O.M.I. Adlly. Spectrochim. Acta, Part A, 79, 1295 (2011).
[38] J.S. Casas, E.E. Castellano, J. Ellena, M.S.G. Tasende, A. Sánchez, M.J. Vidarte. Inorg. Chem., 42, 2584
(2003).
[39] U. El-Ayann. J. Coord. Chem., 65, 629 (2012).
[40] N.V. Savawant, J.B. Biswal, S.S. Garje. J. Coord. Chem., 64, 1758 (2011).
[41] M. Muthukumar, P. Viswanathamurthi. J. Coord. Chem., 63, 1263 (2010).
[42] S. Sumathi, P. Tharmaraj, C.D. Sheela, R. Ebenezer. J. Coord. Chem., 64, 1707 (2011).
[43] S. Sumathi, P. Tharmaraj, C.D. Shella, R. Ebenezer, P.S. Bhava. J. Coord. Chem., 64, 1673 (2011).