Complexation of 2-acetylpyridine- and 2-benzoylpyridine-derived hydrazones to copper(II) as an effective strategy for antimicrobial activity improvement

Article abstract of DOI:10.1016/j.poly.2012.03.017

Complexes [Cu(2AcPh)Cl]·2H₂O (1), [Cu(2AcpClPh)Cl] ·2H₂O (2), [Cu(2AcpNO₂Ph)Cl] (3), [Cu(2BzPh)Cl] (4). [Cu(2BzpClPh)Cl] (5) and [Cu(2BzpNO₂Ph)Cl] (6) were obtained with 2-acetylpyridine-phenylhydrazone (H2AcPh)

Full text of DOI:10.1016/j.poly.2012.03.017

Polyhedron 38 (2012) 285–290
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Complexation of 2-acetylpyridine- and 2-benzoylpyridine-derived hydrazones
to copper(II) as an effective strategy for antimicrobial activity improvement
Angel A. Recio Despaigne a, Fernanda B. Da Costa a, Oscar E. Piro b, Eduardo E. Castellano c, Sonia R.W.
Louro d, Heloisa Beraldo a,
⇑
a Departamento de Química, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil
b Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and Instituto IFLP (CONICET, CCT-La Plata), C.C. 67, 1900 La Plata, Argentina
c Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970 São Carlos, SP, Brazil
d Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, 22453-900 Rio de Janeiro, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Complexes [Cu(2AcPh)Cl]Á2H2O (1), [Cu(2AcpClPh)Cl]Á2H2O (2), [Cu(2AcpNO2Ph)Cl] (3), [Cu(2BzPh)Cl] (4).
[Cu(2BzpClPh)Cl] (5) and [Cu(2BzpNO2Ph)Cl] (6) were obtained with 2-acetylpyridine-phenylhydrazone
(H2AcPh), 2-acetylpyridine-para-chloro-phenylhydrazone (H2AcpClPh), 2-acetylpyridine-para-nitro-phen-
ylhydrazone (H2AcpNO2Ph), 2-benzoylpyridine-phenylhydrazone (H2BzPh), 2-benzoylpyridine-para-
chloro-phenylhydrazone (H2BzpClPh) and 2-benzoylpyridine-para-nitro-phenylhydrazone (H2BzpNO2Ph).
The hydrazones showed poor antibacterial effect against Staphylococcus aureus, Enterococcus faecalis and
Pseudomonasaeruginosa butdemonstrated significantantifungal activity againstCandidaalbicans. Uponcoor-
dination to copper(II) the antibacterial and antifungal activities appreciably increased. H2AcpClPh,
H2BzpClPh and their copper(II) complexes (2) and (5), respectively, were as active as fluconazole against
C. albicans.
Received 31 January 2012
Accepted 9 March 2012
Available online 17 March 2012
Keywords:
Hydrazones
Copper(II) complexes
Antimicrobial activity
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
In addition, we also demonstrated that zinc(II) complexes with
salicylaldehyde-derived hydrazones [27] proved to present a wider
Hydrazones have attracted considerable attention due to their
interesting chemical and structural properties. Their optical, ther-
mal and photoelectrical properties have been reported in the litera-
ture [1]. They are employed in the polymer industry as plasticising
agents, antioxidants and polymerisation initiators [2]. Hydrazone
derivatives are reported to possess antimicrobial [3–5], anti-
tubercular [6–8], anticonvulsant [9,10], anti-inflammatory [11,12],
antiviral [13,14], and anti-proliferative [15,16] activities. In
addition, some aroylhydrazones have shown cytotoxic activity and
their binding to cellular Fe results in oxidative damage to vital
bio-molecules [17]. Metal complexes of hydrazones also exhibit
a wide range of pharmacological applications as antimicrobial
[18–20], cytotoxic [21,22], and as DNA-binding agents [21,23].
In some cases, coordination to metal ions results in improvement
of the pharmacological activity of organic compounds. In fact, as we
previously reported, the antimicrobial activity of thiosemicarbazones
significantly enhances upon coordination to copper(II) [24,25]. In a
previous work we also demonstrated that upon complexation to
n-butyltin and phenyltin the antibacterial and antifungal properties
of 2-acetylpyridine-derived hydrazones substantially increase [26].
pharmacological profile as anti-inflammatory agents than their
hydrazone ligands [28].
Here we report studies on the coordination of 2-acetylpyridine-
phenylhydrazone (H2AcPh), 2-acetylpyridine-para-chloro-phen-
ylhydrazone (H2AcpClPh), 2-acetylpyridine-para-nitro-phenylhydraz-
one (H2AcpNO2Ph), 2-benzoylpyridine-phenylhydrazone (H2BzPh),
2-benzoylpyridine-para-chloro-phenylhydrazone (H2BzpClPh) and
2-benzoylpyridine-para-nitro-phenylhydrazone (H2BzpNO2Ph) (see
Fig. 1) to copper(II) as a strategy aimed to increase the hydrazones’ anti-
microbial activity. All compounds were tested against fungi Candida
albicans, Gram-positive bacteria Staphylococcus aureus and Enterococ-
cus faecalis, and Gram-negative bacteria Pseudomonas aeruginosa.
2. Materials and methods
2.1. Apparatus
All common chemicals were purchased from Aldrich and used
without further purification. Partial elemental analyses were per-
formed on a Perkin Elmer CHN 2400 analyzer. Thermo-gravimetric
curves were obtained with a TGA50H thermo-balance (Shimadzu)
in the 25–750 °C temperature range, under dynamic nitrogen
atmosphere and at a heating rate of 10 °CminÀ1. An YSI model 31
⇑
Corresponding author. Tel.: +55 31 3409 5771; fax: +55 31 3409 5700.
E-mail address: hberaldo@ufmg.br (H. Beraldo).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.03.017

286
A.A. Recio Despaigne et al. / Polyhedron 38 (2012) 285–290
m
(Cu–Nazom) 415 m;
m
(Cu–O) 332 s. Molar conductivity (1 Â 10À3
molLÀ1, dimethylformamide, DMF): 37.50
X .
À1 cm2 molÀ1
2.3.2. [Cu(2AcpClPh)Cl]Á2H2O (2) [chloro(2-acetylpyridine-para-
chloro-phenylhydrazonato) copper(II)] dihydrate
Green solid. Yield: 90%. Anal. Calc. (C14H15Cl2CuN3O3): C, 41.24;
H, 3.71; N, 10.31. Found: C, 41.50; H, 3.66; N, 10.26%. Thermo-
gravimetry (30–750 °C range): Calc. for weight loss of two water
molecules: 8.82%. Found: 8.94%. Selected IR bands (cmÀ1):
m
(CN)
1602 m;
644 m;
m(C@C) + m(CN); 1562 m; 1534 m; m(NC) 1485 s; q
(py)
m
(Cu–Nazom) 416 m; m(Cu–O) 333 s. Molar conductivity
Fig. 1. Structural representation for 2-acetylpyridine- and 2-benzoylpyridine-
derived hydrazones.
(1 Â 10À3 molLÀ1, dimethylformamide, DMF): 36.66
X .
À1cm2molÀ1
conductivity bridge was employed for molar conductivity measure-
ments. Infrared spectra were recorded on a Perkin Elmer FT-IR Spec-
trum GX spectrometer using KBr plates (4000–400 cmÀ1) and Nujol
mulls between CsI plates (400–200 cmÀ1). The molecular structure
2.3.3. [Cu(2AcpNO2Ph)Cl] (3) [chloro(2-acetylpyridine-para-nitro-
phenylhydrazonato) copper(II)]
Green solid. Yield: 87%. Anal. Calc. (C14H11ClCuN4O3): C, 43.99;
H, 2.90; N, 14.66. Found: C, 43.55; H, 2.84; N, 14.3%. Selected IR
bands (cmÀ1):
m(CN) 1600 m;
m
(C@C) +
m(CN); 1568 m; 1527 m;
of
a copper complex derived from complex (3), [Cu(2Acp-
NO2Ph)Cl(DMSO)] (3a) (see Section 2.3), was investigated using sin-
gle-crystal X-ray diffraction methods. The measurements were
performed on an Enraf–Nonius Kappa-CCD diffractometer with
m
(NC) 1495 m;
q
(py) 649 m;
m
(Cu–Nazom) 417 m; m(Cu–O) 326 s.
Molar conductivity (1 Â 10À3 molLÀ1, dimethylformamide, DMF):
5.28
X .
À1 cm2 molÀ1
graphite-monochromated Mo K
a
(k = 0.71073 Å) radiation. Diffrac-
scans with -offsets) with
Upon re-crystallization of complex (3) in 1:9 DMSO:acetone
[Cu(2AcpNO2Ph)Cl(DMSO)] (3a) was formed.
tion data were obtained ( and
u
x
j
COLLECT [29]. Integration and scaling of the reflections were per-
formed with HKL DENZO-SCALEPACK suite of programs [30]. The unit cell
parameters were obtained by least-squares refinement based on
the angular settings for all collected reflections using HKL SCALEPACK
[30]. The data were corrected numerically for absorption with PLATON
[31]. The structure was solved by direct methods with SHELXS-97 [32]
and the molecular model refined by full-matrix least-squares proce-
dure on F2 with SHELXL-97 [33].
Electron paramagnetic resonance (EPR) spectra were obtained
on a Bruker ESP300E equipment with a frequency modulation of
100 kHz and a magnetic field modulation of 0.4–1mT. Room
temperature spectra of the samples in the solid state and as DMSO
solutions (1 mmolLÀ1) were obtained in glass capillaries of 1.2 mm
internal diameter. Frozen DMSO solution spectra were acquired at
liquid N2 temperature (77 K) in 3 mm internal diameter TeflonÒ
tubes.
2.3.4. [Cu(2BzPh)Cl] (4) [chloro(2-
benzoylpyridinephenylhydrazonato) copper(II)]
Green solid. Yield: 86%. Anal. Calc. (C19H14ClCuN3O): C, 57.15; H,
3.53; N, 10.52. Found: C, 57.22; H, 3.41; N, 10.4%. Selected IR bands
(cmÀ1):
(NC) 1494 s;
m
(CN) 1596 m;
m(C@C) + m(CN) 1596 m; 1552 m; 1487 m;
m
q
(py) 645 m; m(Cu–Nazom) 421 m; m(Cu–O) 304 s.
Molar conductivity (1 Â 10À3 molLÀ1, dimethylformamide, DMF):
21.56
X .
À1 cm2 molÀ1
2.3.5. [Cu(2BzpClPh)Cl] (5) [chloro(2-benzoylpyridine-para-chloro-
phenylhydrazonato) copper(II)]
Green solid. Yield: 86%. Anal. Calc. (C19H13Cl2CuN3O): C, 52.61;
H, 3.02; N, 9.69. Found: C, 52.75; H, 2.99; N, 9.85%. Selected IR bands
(cmÀ1):
m(CN) 1594 m;
m(C@C) +
m
(CN) 1594 m; 1576 m; 1556 m;
(Cu–O) 314 s. Mo-
dimethylformamide, DMF):
m
(NC) 1495 s;
q
(py) 645 m;
m
(Cu–Nazom) 424 m; m
lar conductivity (1 Â 10À3 molLÀ1
,
37.40
X .
À1 cm2 molÀ1
2.2. Syntheses of 2-acetylpyridine-phenylhydrazone (H2AcPh),2-acetyl
pyridine-para-chloro-phenylhydrazone (H2AcpClPh), 2-acetylpyridin-
e-para-nitro-phenylhydrazone (H2AcpNO2Ph), 2-benzoylpyridine-phe
nylhydrazone (H2BzPh), 2-benzoylpyridine-para-chloro-phenylhydra
zone (H2BzpClPh) and 2-benzoylpyridine-para-nitro-phenylhydrazone
(H2BzpNO2Ph)
2.3.6. [Cu(2BzpNO2Ph)Cl] (6) [chloro(2-benzoylpyridine-para-nitro-
phenylhydrazonato) copper(II)]
Green solid. Yield: 74%. Anal. Calc. (C19H13ClCuN4O3): C, 51.36; H,
2.95; N, 12.61. Found: C, 51.21; H, 2.94; N, 12.15%. Selected IR bands
(cmÀ1):
m(CN) 1595 m;
m(C@C) +
m
(CN) 1596 m; 1556 m; 1526 m;
(Cu–O) 307 s. Mo-
dimethylformamide, DMF):
m
(NC) 1497 s;
q
(py) 647 m;
m(Cu–Nazom) 424 m; m
The syntheses of all hydrazones were performed as reported
previously [26,34].
lar conductivity (1 Â 10À3 molLÀ1
,
20.68
X .
À1 cm2 molÀ1
2.3. Syntheses of the copper(II) complexes with H2AcPh, H2AcpClPh,
H2AcpNO2Ph, H2BzPh, H2BzpClPh and H2BzpNO2Ph
2.4. In vitro antimicrobial activity
Antimicrobial activity was evaluated by minimum inhibitory
concentration (MIC) using the macro-dilution test [35]. S. aureus
ATCC6538 and P. aeruginosa ATCC9027 were stored in Mueller Hin-
ton Broth and E. faecalis ATCC19433 in Brain Heart Infusion. They
were sub-cultured for testing in the same medium and grown at
37 °C. Then the bacterial cells were suspended, according to Clini-
cal and Laboratory Standards Institute (CLSI) guidelines [36], to
produce a suspension of about 105 CFU (colony forming units)
mLÀ1. C. albicans ATCC10231 stored in Sabouraud Broth was sub-
cultured for testing in the same medium and grown at 37 °C. Then
the yeast cells were suspended according to the McFarland proto-
col [36] in saline solution to produce a suspension of about
The copper(II) complexes were obtained by refluxing an ethanol
solution of the desired ligand with copper chloride in 1:1 ligand-
to-metal molar ratio. The solids were washed with ethanol
followed by diethylether and then dried in vacuo.
2.3.1. [Cu(2AcPh)Cl]Á2H2O (1) [chloro(2-acetylpyridinephenyl
hydrazonato) copper(II)] dihydrate
Green solid. Yield: 90%. Anal. Calc. (C14H16ClCuN3O3): C, 45.04; H,
4.32; N, 11.26. Found: C, 44.99; H, 4.29; N, 11.24%. Thermogravime-
try (30–750 °C range): Calc. for weight loss of two water molecules:
9.64%. Found: 9.83%. Selected IR bands (cmÀ1):
m
(CN) 1600 m;
m(C@C) +
m(CN) 1586 m; 1566 m;
m(NC) 1493 s;
q(py) 647 m;
103 cells mLÀ1
.

A.A. Recio Despaigne et al. / Polyhedron 38 (2012) 285–290
287
For both the antibacterial and antifungal activity evaluations se-
rial dilutions of the compounds, previously dissolved in DMSO,
were prepared in test tubes. A 24-h old inoculum (100 L) was
l
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 after incubation at 37 °C. Tests using tetracy-
cline (in the case of S. aureus), ciprofloxacin (in the case of E. faecal-
is) or fluconazole (in the case of C. albicans) as reference and DMSO
as negative control were carried out in parallel. The final DMSO
concentration never exceeded 1%. In all cases no inhibition was
observed with 5% v/v DMSO. All tests were performed in triplicates
with full agreement among the results.
3. Results and discussion
Microanalyses suggest the formation of [Cu(L)Cl]ÁnH2O (n = 0 or
2) complexes, in which the hydrazones coordinate as anionic
ligands. The molar conductivity data reveal that the complexes
are non-electrolytes, in accordance with the proposed formula-
tions. Crystallization water molecules in complexes (1) and (2)
were confirmed by thermo-gravimetric analyses.
3.1. Structural characterization of [Cu(2AcpNO2Ph)Cl(DMSO)] (3a)
Fig. 2. Drawing of [Cu(2AcpNO2Ph)Cl(DMSO)] (3a) showing the labeling of the non-
H atoms and their displacement ellipsoids at the 50% probability level. Copper–
ligand bonds are indicated by full lines.
Crystal data and refinement results are summarized in Table 1.
An ORTEP [37] drawing of 3a is shown in Fig. 2 and bond distances
and angles around the metal are in Table 2.
The copper(II) ion is in a fivefold distorted pyramidal environ-
ment, coordinated at the pyramid base to an anionic hydrazone
molecule acting as a tridentate ligand through the pyridine and
imine nitrogens [d(Cu–N1) = 2.049(2) Å, d(Cu–N2) = 1.936(2) Å]
and the carbonyl oxygen [d(Cu–O1) = 1.994(1) Å], and to a chloride
ion [d(Cu–Cl) = 2.2364(6) Å]. The pyramid apex is occupied by the
oxygen atom of a DMSO molecule [d(Cu–O) = 2.267(2) Å]. On the
Table 2
Selected bond distances (Å) and angles (°) in the molecular structures of
[Cu(2FopNO2Ph)Cl(DMSO)] and [Cu(2AcpNO2Ph)Cl(DMSO)] (3a).
Compound
[Cu(2FopNO2Ph)Cl(DMSO)] [39]
[Cu(2AcpNO2Ph)Cl(DMSO)]
Bond lengths
N1–C2
C2–C7
N2–C7
N2–N3
N3–C8
O1–C8
Cu–N1
Cu–N2
1.363(3)
1.459(4)
1.284(3)
1.363(3)
1.331(3)
1.285(3)
2.043(2)
1.942(2)
1.988(2)
2.2354(7)
2.242(2)
1.356(3)
1.474(3)
1290(3)
1.365(2)
1.327(3)
1.284(2)
2.049(2)
1.936(2)
1.994(1)
2.2364(6)
2.267(2)
Table 1
Crystal data and structure refinement results for [Cu(2AcpNO2Ph)Cl(DMSO)] (3a).
Compound
[Cu(2AcpNO2Ph)Cl(DMSO)] (3a)
C16H17ClCuN4O4S
460.39
296(2)
0.71073
monoclinic
P21/c
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Cu–O1
Cu–Cl
Cu–O
Bond angles
N1–C2–C7
C2–C7–N2
C7–N2–N3
N2–N3–C8
N3–C8–O1
C6–N1–M
C2–N1–M
C7–N2–M
N3–N2–M
C8–O1–M
N1–Cu–N2
N2–Cu–O1
N1–Cu–O1
N2–Cu–Cl
O1–Cu–Cl
N1–Cu–Cl
N1–Cu–O
N2–Cu–O
O1–Cu–O
O–Cu–Cl
114.2(2)
114.8(2)
122.9(2)
107.3(2)
125.1(2)
129.2(2)
112.3(2)
118.6(2)
118.5(2)
110.6(2)
79.86(9)
78.52(8)
158.06(8)
162.64(7)
100.63(5)
98.88(6)
93.78(8)
95.06(8)
91.80(7)
102.29(5)
115.00(17)
112.55(18)
122.01(17)
107.91(16)
125.45(18)
127.86(16)
112.19(13)
120.32(14)
117.66(12)
109.70(13)
79.24(7)
Unit cell dimensions
a (Å)
b (Å)
12.8481(4)
7.8598(2)
19.0296(5)
107.587(2)
1831.85(9)
4, 1.669
1.483
940
c (Å)
b (°)
Volume (Å3)
Z, DCalc (mg/m3)
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm3)
Crystal shape/color
0.046 Â 0.126 Â 0.271
prism/green
79.15(6)
Theta range for data collection (°)
Index ranges
2.82–25.74
156.81(6)
168.92(5)
100.21(4)
99.38(5)
88.56(6)
93.12(6)
À15 6 h 6 15, À9 6 k 6 9, À23 6 l 6 23
18528/3478 (0.05)
2981
Reflections collected/unique (Rint
Observed reflections [I > 2 (I)]
Completeness to h = 26.00° (%)
Refinement method
Weights, w
)
r
99.0
Full-matrix least-squares on F2
[r
2(Fo2) + (0.0469P)2 + 0.56P]À1
P = [Max(Fo2,0)+2Fc2]/3,
P = [Max(Fo2,0)+2Fc2]/3
3478/0/247
100.91(6)
97.84(4)
Data/restraints/parameters
Goodness-of-fit on F2
1.037
Final R indicesa [I > 2
R indices (all data)
r(I)]
R1 = 0.0292, wR2 = 0.0754
R1 = 0.0364, wR2 = 0.0800
pyramid base, trans O1–Cu–N1 and N2–Cu–Cl bond angles are
156.81(6) and 168.92(5)°, respectively, and cis L–Cu–L angles are
in the 79.15(6)–100.21(4)° range. The tau parameter,
Largest difference in peak and hole 0.232 and À0.677
(eÅÀ3
)
s
= (b À
a)/
a
60 (b is the N2–Cu–Cl angle and is the O1–Cu–N1 angle), which
a
R1
=
R
||Fo| À |Fc||/
R
|Fo|, wR2 = [
R
w(|Fo|2 À |Fc|2)2/
R .
w(|Fo|2)2]1/2

288
A.A. Recio Despaigne et al. / Polyhedron 38 (2012) 285–290
defines the degree of trigonality, was determined as 0.2018, in
accordance with distorted square pyramidal structure [38].
The hydrazone anion is nearly planar [rms deviation of atoms
from the least-squares plane of 0.060 Å] with the chlorine and
metal ion laying close onto this plane [at 0.020(2) and 0.233(1) Å,
respectively].
As expected, the molecular structure is very similar to the closely
related [chloro(dimethylsulfoxide)(2-formylpyridine-para-nitro-
phenylhydrazonato) copper(II)] [Cu(2FopNO2Ph)Cl(DMSO)], which
only differs in that a H-atom rather than a methyl group is attached
to the carbon C7 [39]. In fact, the best least-square superposition
of the common skeletal structure of [Cu(2AcpNO2Ph)Cl] and
[Cu(2FopNO2Ph)Cl] [39] fragments, performed with the Kabsh’s
procedure [40], leads to a rms deviation between homologous
non-H atoms of 0.142 Å. Small deviations are also observed when
comparing the more weakly bonded DMSO apical ligand. In fact,
the Cu–O bond distance is 0.025(2) Å larger in the present complex
as compared with that containing the formyl derivative [39] and
L–Cu–O bond angles differ in up to 9.11(8)°.
C8–O1 and C8–N3 distances of 1.284(2) and 1.327(3) Å are con-
sistent with the formal partial double bond character expected
upon deprotonation at N3 to form the anionic ligand.
3.2. Infrared spectra
The
1585 cm
1604 cmÀ1 in the spectra of the complexes, indicating coordination
of the azomethine nitrogen N2 [39,41]. The (C@O) absorption at
m
À(1C@C) +
m(C@N) composed mode observed at 1580–
in the spectra of the hydrazones shifts to 1487–
m
1660–1680 cmÀ1 in the spectra of the uncomplexed hydrazones
disappears in those of the complexes, in agreement with coordina-
tion of an enolate oxygen. The pyridine in-plane deformation mode
at 610–620 cmÀ1 in the spectra of the free hydrazones shifts to
644–649 cmÀ1 in those of the complexes, suggesting coordination
of the heteroaromatic nitrogen [39,41]. New absorptions at 415–
424 cmÀ1 and 286–305 cmÀ1 were attributed to
m
m
(Cu-N) and
(Cu–Npy) [42], respectively, and bands in the 305–333 cmÀ1
range were assigned to m(Cu–O). Therefore, the infrared data for
Fig. 3. EPR spectra of the Cu(II) complexes (1–6) in the solid state at room temperature.
Fig. 4. EPR spectra of DMSO solutions of the Cu(II) complexes (1–6) (ꢀ1 mM) at 77 K. Insets: (a) room temperature spectrum of 2 in DMSO, (b) second derivative spectrum of
4 at the perpendicular region.

A.A. Recio Despaigne et al. / Polyhedron 38 (2012) 285–290
289
Table 3
Minimum inhibitory concentrations (MIC) of the hydrazones and their copper(II) complexes.
Compound
MIC (l )
mol LÀ1
S. aureus
E. faecalis
P. aeuroginosa
C. albicans
H2AcPh
428
49
197
10
>819
131
>738
122
>696
>523
>657
62
>601
237
>577
112
>2322
–
422
>535
383
>505
337
>554
>670
>510
>613
232
>577
>441
>1255
15
179
229
86
[Cu(2AcPh)Cl]Á2H2O (1)
H2AcpClPh
[Cu(2AcpClPh)Cl]Á2H2O (2)
H2AcpNO2Ph
[Cu(2AcpNO2Ph)Cl] (3)
H2BzPh
[Cu(2BzPh)Cl] (4)
H2BzpClPh
[Cu(2BzpClPh)Cl] (5)
H2BzpNO2Ph
52
353
>673
177
20
>619
114.1
>600.5
140.6
>656
0.36
–
111
220
105
107
69
47
>750
306
>1671
–
[Cu(2BzpNO2Ph)Cl] (6)
CuCl2Á2H2O
Tetracycline hydrochloride
Fluconazole
–
–
79
Ciprofloxacin
–
0.25
–
–
the complexes indicate coordination of the hydrazones through the
Npy–N–O chelating system and also the presence of a chloride ion
at the fourth coordination site.
3.4. Antimicrobial activity
The minimum inhibitory concentrations (MICs) of the hydra-
zones and their copper(II) complexes against S. aureus, E. Faecalis,
P. aureginosa and C. albicans and are reported in Table 3.
3.3. EPR spectra
The hydrazones showed poor activity against Gram-positive and
Gram-negative bacteria with values of MIC higher than those of the
control drugs. The compounds were inactive against E. faecalis. Nev-
ertheless, they showed significant activity against C. albicans. In fact,
The EPR spectra of 1–6 in the solid state at room temperature
are presented in Fig. 3. They are all very similar, and are character-
istic of mononuclear Cu(II) complexes with axial symmetry. The
values of g|| and g\, 2.24 and 2.08, respectively, are in the range
for this kind of complexes [43]. The values are consistent with a
dx2Ày2 ground state. The spectra lack the 4-line hyperfine splitting
due to the interaction with Cu(II) nuclear magnetic moment (I = 3/
2), as it is frequently the case for concentrated solid samples where
exchange interactions are present [44,45]. Given that these are
magnetically non-diluted systems, the lines are markedly broad-
ened due to magnetic dipole–dipole interactions.
The EPR spectra of DMSO solutions of the complexes were re-
corded at 77 K (Fig. 4). The spectrum of 1 (Fig. 4a) is a superposi-
tion of an axially symmetric component that shows three of the
4-line hyperfine splitting, with parameters g|| = 2.25, g\ = 2.08,
A|| = 17.0 mT, and a very broad component; those of 2 and 3 display
only the broad component, where the parallel region is barely no-
ticed. The spectra of 4, 5 and 6 (Fig. 3b), however, do not present
the broad component, and show the hyperfine splitting features
at the parallel region. These results show that the complexes with
2-acetylpyridine derivatives aggregate in DMSO, while those with
2-benzoylpyridine derivatives do not, probably because of the
bulkier substituents. Complex (4) presents a single component
spectrum with g|| = 2.265, g\ = 2.064, and A|| = 16.3 mT. Complexes
(5) and (6) display, besides the spectrum of complex (4), a second
minor component with g|| = 2.194 and A|| = 15.6 mT, indicating two
Cu(II) microenvironments.
Although Cu(II) interacts with at least two nonequivalent N
atoms in complexes 1–6 (N1 and N2 in Fig. 2), the spectra of 1–3
do not exhibit resolved nitrogen super-hyperfine structure
(Fig. 4a). Nitrogen super-hyperfine structure is noticed in the
perpendicular region on the spectra of (4–6) (Fig. 4b). The inset
presents the 2nd derivative spectrum of 4 at this region, which
reveals the super-hyperfine splitting constant AN = 1.65 mT, but
the number of super-hyperfine lines is unclear mainly because of
the unresolved hyperfine splitting at the perpendicular region.
DMSO solutions of the complexes at room temperature show
identical broad EPR spectra (inset of Fig. 4a), indicating absence
of motional narrowing.
the determined MIC values of H2AcpClPh (86
H2BzpClPh (69
molLÀ1), were comparable to that of the control
drug fluconazole (MIC = 79
molLÀ1). Hence the presence of a
l ) and
molLÀ1
l
l
para-chloro substituent in the phenyl ring seems to contribute to
an increase of antifungal activity in these compounds.
In general, the antimicrobial activities of the compounds
improved after coordination to copper(II). The best results were ob-
tained for complexes (1) (MIC = 49
and (4) (MIC = 20
molLÀ1) against S. aureus, and (4) (MIC = 62
molLÀ1) against E. faecalis, respectively. Unfortunately, these MIC
values are higher than those of the control drugs tetracycline
(MIC = 0.36
molLÀ1 against S. aureus) and ciprofloxacin (MIC =
0.25
molLÀ1 against E. faecalis), respectively.
Complexes (2) (MIC = 52
molLÀ1) and (5) (MIC = 47
were more active than their respective hydrazones (MIC = 86 and
69
molLÀ1, respectively) against C. albicans. The MIC values of
the hydrazones are similar to that of the control drug fluconazole
(MIC = 79
molLÀ1), while those of (2) and (5) are lower than that
l l )
molLÀ1), (2) (MIC = 10 molLÀ1
l
l
l
l
l
l )
molLÀ1
l
l
of fluconazole, hence suggesting that the complexes could be inter-
esting as new antifungal drug candidates.
4. Conclusions
The studied 2-acetylpyridine- and 2-benzoylpyridine-derived
hydrazones showed poor antimicrobial effect against Gram-positive
S. aureus and E. faecalis and Gram-negative P. aeruginosa bacteria, but
exhibited significant antifungal activity against C. albicans. In gen-
eral, upon coordination to copper(II) the antibacterial effect against
S. aureus and E. faecalis appreciably increased, although the MIC val-
ues for the complexes were higher than those determined for the
control drugs tetracycline and ciprofloxacin. Coordination to cop-
per(II) resulted in complexes with increased antifungal activity
against C. albicans than fluconazole used as control.
As already mentioned, we demonstrated that upon coordination
to copper(II) the antimicrobial activity of 2-acetylpyridine- and 2-
benzoylpyridine-derived thiosemicarbazones increases [24,25].
The enhancement of the antimicrobial activities of hydrazone

290
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financial support. O.E.P. is a Research Fellow of CONICET, Argen-
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Appendix A. Supplementary data
CCDC 863627 contains supplementary crystallographic data for
[Cu(2AcpNO2Ph)Cl(DMSO)] (3a). These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
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