Anticancer and antifungal activity of copper(II) complexes of quinolin-2(1H)-one-derived Schiff bases

Article abstract of DOI:10.1016/j.ica.2010.08.009

The condensation of substituted aromatic aldehydes with 7-amino-4-methyl-quinolin-2(1H)-one (1) has lead to the isolation of quinolin-2(1H)-one derived Schiff bases (2-14). The copper(II) complexes (2a-14a) of the ligands were also prepared, and together with their corresponding free ligands were fully characterised by elemental analyses, spectral methods (IR, ¹H and ¹³C NMR, AAS, UV-Vis), magnetic and conductance measurements. The bidentate ligands coordinated to the copper(II) ion through the deprotonated phenolic oxygen and the azomethine nitrogen of the ligands in almost all cases. X-ray crystal structures of two of the complexes, 5a and 8a, confirmed the bidentate coordination mode. All of the compounds were investigated for their antimicrobial activities against the fungus, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to have excellent anti-Candida activity but were inactive against Staphylococcus aureus and Escherichia coli. Selected compounds (2-8 and 2a-8a) were also screened for their in vitro anticancer potential using the human hepatic carcinoma cell line, Hep-G₂. Several derivatives were shown to be active comparable to that of cisplatin.

Full text of DOI:10.1016/j.ica.2010.08.009

Inorganica Chimica Acta 363 (2010) 4048–4058
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Anticancer and antifungal activity of copper(II) complexes
of quinolin-2(1H)-one-derived Schiff bases
Bernadette S. Creaven a,b, , Brian Duff a,b, Denise A. Egan a,b, Kevin Kavanagh c, Georgina Rosair d,
⇑
Venkat Reddy Thangella a,b, Maureen Walsh a,b
a Department of Science, Institute of Technology Tallaght, Dublin 24, Ireland
b Centre for Applied Science and Health, Institute of Technology Tallaght, Dublin 24, Ireland
c Department of Biology, National University of Ireland, Maynooth Co., Kildare, Ireland
d Chemistry, School of Engineering and Physical Science, Heriot Watt University, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The condensation of substituted aromatic aldehydes with 7-amino-4-methyl-quinolin-2(1H)-one (1) has
lead to the isolation of quinolin-2(1H)-one derived Schiff bases (2–14). The copper(II) complexes (2a–
14a) of the ligands were also prepared, and together with their corresponding free ligands were fully
characterised by elemental analyses, spectral methods (IR, 1H and 13C NMR, AAS, UV–Vis), magnetic
and conductance measurements. The bidentate ligands coordinated to the copper(II) ion through the
deprotonated phenolic oxygen and the azomethine nitrogen of the ligands in almost all cases. X-ray crys-
tal structures of two of the complexes, 5a and 8a, confirmed the bidentate coordination mode. All of the
compounds were investigated for their antimicrobial activities against the fungus, Candida albicans, and
against Gram-positive and Gram-negative bacteria. The compounds were found to have excellent anti-
Candida activity but were inactive against Staphylococcus aureus and Escherichia coli. Selected compounds
(2–8 and 2a–8a) were also screened for their in vitro anticancer potential using the human hepatic car-
cinoma cell line, Hep-G2. Several derivatives were shown to be active comparable to that of cisplatin.
Ó 2010 Elsevier B.V. All rights reserved.
Received 23 June 2010
Accepted 4 August 2010
Available online 10 August 2010
Keywords:
Quinolin-2(1H)-one
Schiff bases
Copper(II) complexes
Biological activity
X-ray structures
1. Introduction
Quinolinones, an important class of heterocyclic compounds are
part of the quinoline alkaloid family and are also known for their
Antimicrobial drug resistance is of increasing importance as the
phenomenon has considerable impact on human and animal
health. The prevalence of clinical drug resistance has unfortunately
increased significantly in recent decades due to the use and misuse
of antimicrobial drugs and many infectious diseases can no longer
be treated effectively with common anti-infective drugs. Antimi-
crobial resistance is not limited to bacterial species and in the
1990s resistance emerged to one of the most potent antifungal
agents, fluconazole [1]. Antifungal resistance is particularly prob-
lematic as diagnosis is often delayed and there are relatively few
antifungal treatments approved for use by the FDA. Over the last
number of years, our research group has been interested in devel-
oping compounds which have anti-Candida activity as Candida
albicans is associated with fungal infections that typically occur
in severely immunocompromised and/or critically ill patients [2].
diverse biological activity [3]. Quinolinone heterocycles have
emerged as potential therapeutic agents and are the basis of many
medicinal drugs used in the treatment of heart failure, cancer and
inflammatory diseases [4]. They are also used as antibacterial,
antifungal, anti-inflammatory, antitubercular, anticancer, antineo-
plastic, anti-ischemic, anti-allergic, antihypertensive and anti-
ulcerative agents [5–9]. Recently, a novel series of quinolinones
have shown potent inhibitory activity against human immunodefi-
ciency virus type-1 (HIV-1) virus and also exhibited promising
activity against several non-nucleoside reverse transcriptase inhib-
itors (NNRTIs) [10]. One of the 6-functionalised quinolinone deriv-
atives was also reported to possess potent antitumor activity and is
undergoing human phase II/III clinical trails as an orally active
antitumor drug for the treatment of haematological and solid
tumours in the nanomolar range [8].
Schiff bases of azomethine nitrogen donor heterocyclic ligands
are well known due to their wide range of applications in pharma-
ceutical and industrial fields [11]. Transition metal complexes of
Schiff bases have attracted a lot of interest due to their potent
biological activities such as antifungal, antibacterial, anticancer
and herbicidal applications [12–16]. These studies have shown that
⇑
Corresponding author at: Department of Science, Institute of Technology
Tallaght, Dublin 24, Ireland.
E-mail address: bernie.creaven@ittdublin.ie (B.S. Creaven).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.08.009

B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
4049
complexation of metals to Schiff base ligands improves the antimi-
crobial and anticancer activities of the ligands [12]. In addition,
more recently reports of quinolin-2(1H)-one-derived Schiff bases
and their metal complexes have emerged [17–22]. Several Schiff
base ligands derived from pyridine derivatives and their copper(II)
complexes have also been shown to inhibit tumour growth [23].
Our previous work has focussed on the synthesis and therapeu-
tic applications of a series of silver and copper complexes of cou-
marin-derived ligands [24–29]. More recently we have focused
our research efforts on the preparation of a series of coumarin-
and quinolin-2(1H)-one-triazole-derived Schiff bases and their
Cu(II) complexes [30,31]. In this paper, we report a new series of
quinolin-2(1H)-one derived Schiff base ligands and their copper
complexes and the assessment of their antimicrobial activities
against C. albicans, and against Gram-negative and Gram-positive
bacterial species. Our earlier studies had indicated that couma-
rin-derived copper(II) complexes had promising anticancer activ-
ity. Consequently, in the current study we have investigated the
activity of a number of novel copper(II) complexes using the
human-derived hepatic carcinoma cell line, Hep-G2.
and are uncorrected. Values were taken up to 300 °C. All NMR
spectra were run on a JEOL JNM-LA300 FT-NMR (300 MHz 1H
and 75 MHz 13C) in d6-DMSO with 1H NMR spectra recorded in
the region of À5 ppm to 15 ppm from TMS (tetramethylsilane)
with a resolution of 0.18 Hz or 0.0006 ppm. All 13C NMR spectra
were recorded in the region À33 to 233 ppm from TMS with a
resolution of 0.008 ppm. Atomic absorption spectroscopy (AAS)
measurements were recorded on a Perkin–Elmer 460 AAS instru-
ment (emission wavelength 324.8 nm). Solid state magnetic
susceptibility measurements were carried out at room tempera-
ture using a Johnson Matthey Magnetic Susceptibility Balance with
[HgCo(SCN)4] being used as a reference standard. Molar conductiv-
ity was measured on a Systronic conductivity bridge with a
dip-type cell, using 4 Â 10À3 M solution of complexes in DMSO.
UV–Visible (UV–Vis) spectra of the compounds in DMSO were
recorded on a Shimadzu UV-1601 spectrophotometer.
2.2. Synthesis of 7-amino-4-methylquinolin-2(1H)-one (1)
2. Experimental
7-Amino-4-methylquinolinone (1) was synthesised from 1,3-
phenylenediamine and ethyl acetoacetate according to a literature
procedure [32]. An off-white coloured product 1 was obtained with
moderate yield (47%).
2.1. Materials/instrumentation
All chemicals were purchased from Sigma–Aldrich were reagent
grade and used without further purification. Microanalytical data
were provided by the Microanalytical Laboratory, National Univer-
sity of Ireland, Belfield, and Dublin 4. Infrared spectra were re-
corded in the region of 4000–400 cmÀ1, on a Nicolet Impact 410
Fourier-transform infrared (FTIR) spectrophotometer using OMNIC
software. All spectra were run as KBr discs. Melting point values
were recorded on a Stuart scientific SMP1 melting point apparatus
2.3. Preparation of novel quinolin-2(1H)-one-derived Schiff base
derivatives (2–14)
All of the quinolin-2(1H)-one-derived Schiff base ligands (2–14)
were synthesised by an equimolar condensation reaction between
substituted aromatic aldehydes and 7-amino-4-methylquinolin-
2(1H)-one (1) in hot ethanol. A stirred suspension of 1 (2 mmol,
0.348 g) and the appropriate aromatic aldehyde (2 mmol) in hot
ethanol (40 mL) was refluxed for 4 h. On cooling to room temper-
ature, coloured precipitates (2–14) formed in good yields (>70%),
were filtered off and dried in a vacuum oven for two weeks. The
general structure of the ligands with the numbering system used
in this work is shown in Fig. 1 with detail of the exact structures
given in Table 1. All of the prepared ligands showed poor solubility
in polar and non polar solvents at room temperature and most of
them were only soluble in hot alcohols, acetonitrile, DMF and
DMSO. However, the halogen substituted compounds were soluble
only in hot DMSO and DMF. Analytical data for the ligands is given
in Tables 3–6.
11
R2
CH3
5
8
16
4
R3
R4
R1
15
14
6
3
2
10
9
17
18
7
C
N
12
N
O
1
19
H
13
H
Fig. 1. General structure of
a
quinolin-2(1H)-one derived Schiff base with
numbering system used in this report.
Table 1
Ligand names, their relative substituents and positions of R groups for compounds (2–14).
Compound Name and Number
R groups
R1
R2
R3
R4
(7E)-7-(2,4dihydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (2)
(7E)-7-(2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (3)
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
H
H
H
OH
H
H
H
H
OCH3
H
H
H
H
H
H
H
H
H
H
tBu
Br
Cl
F
(7E)-7-(2,3-dihydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (4)
(7E)-7-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (5)
(7E)-7-(2-hydroxy-3-methoxybenzylideneamino)-4 methylquinolin-2(1H)-one (6)
(7E)-7-(2-hydroxy-4-methoxybenzylideneamino)-4-methylquinolin-2(1H)-one (7)
(7E)-7-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (8)
(7E)-7-(5-bromo-2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (9)
(7E)-7-(5-chloro-2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (10)
(7E)-7-(5-fluoro-2-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (11)
(7E)-7-(2-hydroxy-5-iodobenzylideneamino)-4-methylquinolin-2(1H)-one (12)
(7E)-7-(3-hydroxy-4-methoxybenzylideneamino)-4-methylquinolin-2(1H)-one (13)
(7E)-7-(3-hydroxybenzylideneamino)-4-methylquinolin-2(1H)-one (14)
OH
OC2H5
OCH3
H
tBu
H
H
H
H
OH
OH
H
OCH3
H
I
H
H
H

4050
B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
Table 2
Table 4
Crystal data and structure refinement of complexes 2a and 8a.
Selected IR and UV–Vis data (cmÀ1) for the Schiff base ligands (2–14).
Empirical formula
Formula weight
T (K)
C38H40CuN4O9S (2a)
792.34
100(2)
C52H66CuN4O6 (8a)
906.63
100(2)
Ligand
IR-spectra (
m
max/cmÀ1
)
UV–Vis
–C@O (lactam)
–OH
–C–O
–CH@N
kmax (nm)
2
3
4
5
6
7
8
9
10
11
12
13
14
1651
1659
1650
1650
1659
1673
1654
1655
1659
1692
1652
1660
1653
3464
3457
3388
3458
3457
3456
3448
3439
3446
3434
3432
3442
3455
1230
1269
1277
1250
1251
1235
1247
1276
1280
1285
1280
1277
1250
1575
1601
1604
1599
1600
1603
1608
1603
1605
1608
1600
1600
1613
280, 342, 355
297, 342, 356
276, 342, 355
297, 342, 355
296, 342, 355
278, 341, 356
290, 357
n/m
n/m
296, 342, 354
n/m
279, 356
Wavelength (Å)
Unit cell dimensions
a (Å)
b (Å)
c (Å)
0.71073
0.71073
10.604(9)
11.637(11)
15.027(13)
101.661(15)
96.019(15)
95.741(18)
1792(3)
2
10.07(3)
10.907(2)
22.926(6)
82.078(14)
78.592(13)
69.501(12)
2306.5(10)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
1.468
0.730
1.305
0.528
Absorption coefficient
(mmÀ1
)
267, 283, 355
F (0 0 0)
826
966
n/m = Not measured due to poor solubility.
Crystal size (mm3)
0.38 Â 0.36 Â 0.18
0.55 Â 0.30 Â 0.08
0.91–21.82
À9 6 h 6 10,
À10 6 k 6 10,
0 6 l 6 23
5389
5399
at 21.82° = 76.3%
0.9590 and 0.7599
h Range for data collection (°) 2.24–28.00
Index ranges
suitable for X-ray diffraction measurements were obtained by the
slow diffusion of diethylether into a solution of the complex in a
binary solution of DMSO–MeOH. The analytical data for the com-
plexes is given in Tables 7 and 8.
À13 6 h 6 13,
À15 6 k 6 15,
À18 6 l 6 19
28 058
8562
at 25.00° = 99.9%
0.8798 and 0.7688
Reflections collected
Independent reflections
Completeness to h
Maximum and minimum
transmission
2.5. X-ray crystallography
Refinement method
Full-matrix least-
squares on F2
8562/5/500
Full-matrix least-
squares on F2
5399/313/589
1.055
R1 = 0.1162,
wR2 = 0.2853
R1 = 0.1910,
X-ray crystallographic studies were carried out at Heriot Watt
University, Edinburgh, United Kingdom. A single crystal is coated
in Paratone-N heavy oil then mounted on a Hampton Research
Cryoloop and placed in a cold stream of nitrogen gas (100 K) on a
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
0.930
Final R indices [I > 2
r(I)]
R1 = 0.0550,
wR2 = 0.1284
R1 = 0.1062,
wR2 = 0.1572
0.505 and À0.801
Bruker Nonius X8 Apex2 CCD diffractometer running the APEX
2
R indices (all data)
[33] software suite. Data collection consisted of, on average, 3000
frames from a combination of phi and omega scans. After unit cell
determination, the data were integrated using SAINT then scaled
wR2 = 0.3243
0.843 and À0.637
Largest difference in peak
and hole (e ÅÀ3
)
with SADABS (TWINABS for 8a) before Space group determination with
XPREP, structure solution with XS and structure refinement with XL.
Pictures are prepared using the graphics program XP. The quality of
the datasets is checked using the IUCr checkcif facility. The crystal
of 8a was not single and very weakly diffracting and the anisotropy
of many atoms was restrained with the SHELXL [34] command ISOR.
Crystal data and structure refinement of copper(II) complexes 2a
and 8a are given in Table 3.
2.4. Synthesis of copper(II) complexes of quinolin-2(1H)-one-derived
Schiff base ligands (2a-14a)
All of the copper(II) complexes (2a–14a) were synthesised by
the following general procedure. Copper(II) acetate (0.125 mmol,
0.0227 g) (2a–4a, 6a–8a and 10a–14a) or copper(II) perchlorate
hexahydrate (2 mmol, 0.0463 g) (5a and 9a) was dissolved in
methanol (30 mL) and added drop-wise with stirring to a hot
methanolic solution of the appropriate ligand (0.25 mmol) to a fi-
nal volume of 60 mL. The resulting mixture was refluxed with stir-
ring for 5 h until a precipitate formed. Workup afforded coloured
complexes (2a–14a) in good yields (>70%). All of the complexes
were re-crystallised from an appropriate solvent system but suit-
able crystals were isolated only for complexes 2a and 8a. Crystals
2.6. Biological testing
2.6.1. Anti-Candida susceptibility testing
The metal-free ligands (2–14) and their Cu(II) complexes
(2a–14a) were tested for their antifungal activity against a clinical
isolate of the fungal strain C. albicans (ATCC 10231) and a commer-
cially available antifungal drug, Amphotericin B. The screening was
Table 3
Analytical data for the series of quinolin-2(1H)-one derived Schiff base ligands (2–14).
Ligand
Mw (g/mol)
Yield (%)
Empirical formula
Found (Calc) (%)
C
M.P. (°C)
H
N
2
3
4
5
6
7
8
9
10
11
12
13
14
294.30
278.31
294.30
322.36
308.33
308.33
390.52
357.20
312.75
296.30
404.2
72
79
74
75
73
70
60
76
78
65
68
62
61
C
C
C
C
C
C
C
C
C
C
C
C
C
17H14N2O3
17H14N2O2
17H14N2O3
19H18N2O3
18H16N2O3
18H16N2O3
25H30N2O2
17H13BrN2O2
17H13ClN2O2
17H13FN2O2
17H13IN2O2
18H16N2O3
17H14N2O2
69.07 (69.38)
73.12 (73.37)
69.28 (69.38)
70.62 (70.79)
69.90 70.12
69.60 (70.12)
76.66 (76.89)
57.21 (57.16)
65.42 (65.29)
68.64 (68.91)
50.82 (50.51)
70.01 (70.12)
72.57 (73.37)
4.78 (4.79)
5.03 (5.07)
4.42 (4.79)
5.60 (5.63)
5.06 (5.23)
5.18 (5.23)
7.63 (7.74)
3.56 (3.67)
4.06 (4.19)
4.25 (4.42)
3.35 (3.24)
5.02 (5.23)
5.05 (5.07)
9.36 (9.52)
9.96 (10.07)
9.29 (9.52)
8.68 (8.69)
9.09 (9.09)
9.07(9.09)
7.22 (7.17)
7.54 (7.84)
8.92 (8.96)
9.15 (9.45)
6.88 (6.93)
9.22 (9.09)
10.09 (10.07)
280–282
278–280
298–300
268–270
288–290
286–288
298–300
>300
>300
>300
> 300
>300
308.33
278.31
290–292

B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
4051
Table 5
Characteristic 1H NMR chemical shift values (ppm), peak multiplicity and coupling constant J (Hz) for the synthesised ligands recorded in d6-DMSO.
Ligand (1H, s, H3) (1H, s)
(1H, s) R1 (1H, s)
R2
R3
R4
H19 (1H)
(vinyl)
(CH@N) (NH)
2
3
4
5
6.35
6.38
6.38
6.38
8.83
8.98
8.98
8.98
11.60
11.64
11.64
11.65
13.28 (OH) 6.31, 1H, d, J = 2.20
12.76 (OH) 6.93, 1H, m
12.80 (OH) n/a (br, OH)
12.89 (OH) 1.36, 3H, t, CH3, J = 7.0 4.05, 7.14, 1H, dd, J = 1.31, 8.07 6.88, 1H,pt, J = 7.89, 7.89
2H, q, OCH2, J = 7.0
10.37, 1H, s, OH
7.03, 1H, m
6.44, 1H, dd, J = 2.20, 8.44 7.50, d, J = 8.62
7.42, 1H, m 7.70, dd, J = 1.83, 8.07
6.96, 1H, dd, J = 1.50, 7.89 6.79, 1H, pt, J = 7.70, 7.89 7.14, dd, J = 1.50, 7.0
7.26, dd, J = 1.50, 7.34
6
7
8
9
10
11
12
13
14
6.36
6.36
6.36
6.36
6.38
6.30
6.37
6.35
6.35
8.98
8.90
9.03
8.95
8.95
8.94
8.93
8.46
8.55
11.63
11.62
11.66
11.63
11.65
11.64
11.65
11.59
11.62
12.82 (OH) 3.61, 3H, s, OCH3,
13.41 (OH) 6.51, 1H, d, J = 2.37
13.79 (OH) 1.31, 9H, s, t-Bu
12.61 (OH) 6.95,1H, d, J = 8.80
12.63 (OH) 6.99,1H, d, J = 8.80
12.31 (OH) 6.96, 1H, dda
7.13, 1H, dd, J = 1.50, 8.80 6.89, 1H, pt, J = 7.89, 8.07 7.24, dd, J = 2.02, 8.34
4.06, 3H, s, OCH3
6.57, 1H, dd, J = 2.38, 8.80 7.23, d, J = 8.62
7.19, 1H, d, J = 1.70
1.43, 9H, s, t-Bu
7.44, 1H, d, J = 1.86
7.91, d, J = 2.57
7.78, d, J = 2.75
7.53, ddc
8.07, d, J = 2.41
7.10, d, J = 8.62
7.37, d, m
7.54, 1H, dd, J = 2.57, 8.80 –Br–
7.42, 1H, dd, J = 2.57, 8.89 –Cl–
7.25, 1H, dddb
–F–
7.69, 1H, dd, J = 2.38, 8.71 –I–
12.80 (OH) 6.83, 1H, d, J = 8.62
7.05 (1H)
7.07 (1H)
9.40, 1H, s, OH
9.75, 1H, s, OH
3.46, 3H, s, OCH3
6.92, 1H, m
7.08, 1H, d, J = 8.62
7.31, 1H, m
a
b
c
JH–H
oJH–H
JH–H
+
+
+
2JH–F = 4.58, 9.17.
mJH–H 1JH–F = 3.30, 8.99, 8.44.
1JH–F = 12.27.
+
Table 6
Characteristic 13C NMR chemical shift values (ppm), for the ligands recorded in d6-DMSO.
C-2
C3
C-13
C-15
C-5
C-6
C-8
C-18
C-19
(C@O)
(vinyl)
(CH@N)
(C–OH)
2
3
4
5
6
7
8
9
10
11
12
13
14
161.40
160.22
161.90
161.81
161.79
162.00
161.17
161.8
161.79
161.86
161.80
162.0
120.0
163.5
163.0
126.20
126.10
126.16
126.14
126.17
125.85
127.31
125.20
125.10
126.17
125.30
125.85
125.55
114.50
119.30
118.99
117.23
115.86
114.24
119.94
110.28
110.0
110.38
110.40
114.24
113.24
108.50
114.63
114.59
114.57
114.60
107.60
114.09
107.78
108.0
108.01
107.90
109.60
110.60
106.90
124.40
120.40
120.44
120.44
106.89
140.11
119.0
134.90
132.62
122.73
123.96
123.69
134.0
108.05
108.10
108.13
108.13
119.92
107.48
96.89
96.89
96.75
96.50
120.92
121.92
164.08
164.63
164.38
164.23
163.5
161.79
149.80
149.46
149.50
163.14
148.89
159.50
159.50
153.05
159.80
n/a
165.20
162.0
125.38
130.74
131.0
162.10
162.38
162.40
161.30
161.50
118.0
156.61a
na
116.69b
139.50
134.0
108.89
119.10
161.50
n/a
134.0
n/a = Not assigned
a
1
d, JC–F = 67.2 Hz.
b
2
d, JC–F = 93.6 Hz.
carried out according to the broth microdilution susceptibility
protocol method (NCCLS) [35]. Isolates were grown for 24 h on
SDA plates at 37 °C. Cells were suspended in sterile PBS (phosphate
buffered saline) to a concentration equal to a 1.0 McFarland stan-
dard (1 Â 106) and further diluted (1:100) with minimal media
(MM). All compounds were prepared as 1% (v/v) solutions in DMSO
absorbance of the cultures was measured at 600 nm using a haem-
ocytometer and cultures were diluted to an optical density of 0.1.
The cell suspension (50
plate containing test compounds diluted in nutrient broth medium
in serial dilutions from 200 to 0.39 M. Test compounds were ini-
lL) was added to the wells of a 96 well
l
tially prepared in 100% DMSO and then diluted with nutrient
broth, as above, so that the final concentration of DMSO in the cell
suspension was never more than 5% (v/v). Plates were incubated at
30 °C for 24 h. The optical density was measured spectrophotomet-
rically (Dynex Technology) at 540 nm. Each compound was
screened in triplicate and three independent experiments were
performed. The MIC50 was defined as the concentration of test
compound which inhibited 50% visible growth of the strain in 24 h.
and each compound was tested in the range of 1–50 l .
g mLÀ1
Plates were incubated in an Anthos plate reader for 24 h at 37 °C
with continuous shaking. Each compound was screened in tripli-
cate and three independent experiments were performed. The
stock solution of the compounds which were prepared initially at
lower concentration (0.001 g mLÀ1
) yielded a clear solution.
However, some of the compounds did not dissolve well in DMSO
and those compounds were tested as suspensions.
2.6.3. Assessment of anti-proliferate activity using MTT assay
2.6.2. Antibacterial screening method
Selected compounds (2–8 and 2a–8a) were screened for their
in vitro anticancer potential using the human-derived hepatic car-
cinoma cell line, Hep-G2. Cisplatin, the simple copper(II) salts, the
metal-free ligands (2–8) together with the copper(II) complexes
(2a–8a) were each dissolved in DMSO, diluted in culture media
and used to treat model cells at various drug concentrations for
periods of 96 h, prior to MTT assay. The maximum percentage of
DMSO present in any well was 0.25% (v/v). Cells were seeded in
sterile 96 well flat-bottomed plates (Sarstedt) at a density of
2.5 Â 104 cells/mL and grown in 5% CO2 at 37 °C. At the end of
the required incubation period, a miniaturised viability assay using
Only those complexes (2a–8a) and their respective ligands
(2–8) which showed good solubility in DMSO were tested for
their antibacterial activity against a Gram-negative bacterium
Escherichia coli and a Gram-positive bacterium Staphylococcus
aureus (clinically isolated from wound infections) for their antibac-
terial activity. The screening was carried out according to a litera-
ture reported method [24]. All media, buffers, and solutions used
during the course of this study were sterilised by autoclaving at
120 °C for 15 min. Bacterial strains were grown for 24 h in nutrient
broth medium at 30 °C and 200 rpm in an orbital incubator. The

4052
B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
Table 7
Analytical data for the series of copper(II) complexes (2a–14a).
Complex
Mw (g/mol)
leff
Yield
(%)
Empirical formula
Found (Calc) (%)
C
(B.M.)
H
N
Cu
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
12a
13a
14a
650.14
618.14
650.14
905.15
678.19
678.19
842.57
775.93
687.03
654.12
869.93
755.92
933.72
1.69
1.61
1.7
1.77
1.73
1.66
1.7
1.66
1.68
1.6
1.63
1.69
1.62
81
72
88
73
84
79
78
71
73
76
75
76
73
C
C
C
C
C
C
C
C
C
C
C
34H26CuN4O6
34H26CuN4O4
34H26CuN4O6
38H34 Cl2CuN4O14
36H30CuN4O6
36H30CuN4O6
50H58CuN4O4
34H24 Br2CuN4O4
34H24Cl2CuN4O4
34H24CuF2N4O4
34H24CuI2N4O4
62.07 (62.81)
65.21(66.06)
62.20 (62.81)
51.05 (50.42)
64.67 (63.76)
63.34 (63.76)
70.45 (71.27)
51.92 (52.63)
59.28 (59.44)
62.76 (62.43)
47.10 (46.94)
54.12 (54.02)
43.89 (43.73)
4.09 (4.03)
4.22 (4.24)
3.99 (4.03)
4.13 (3.79)
4.67 (4.46)
4.29 (4.46)
6.67 (6.94)
3.03 (3.12)
3.59 (3.52)
3.80 (3.70)
2.93 (2.78)
3.06 (2.93)
2.47 (2.37)
8.26 (8.62)
8.62 (9.06)
8.41(8.62)
6.20 (6.19)
8.27 (8.26)
8.03 (8.26)
6.39 (6.65)
6.89 (7.22)
7.86 (8.15)
8.45 (8.57)
6.16 (6.44)
7.59 (7.41)
5.97 (6.00)
9.50 (9.77)
9.95 (10.28)
9.92 (9.77)
6.74 (7.00)
9.05 (9.37)
9.10 (9.37)
7.10 (7.54)
7.95 (8.19)
8.94 (9.25)
9.94 (9.71)
7.55 (7.30)
8.14 (8.41)
6.64 (6.81)
C34H22Cl4CuN4O4
34H22 Br4CuN4O4
C
Table 8
spectroscopies and CHN analysis and all relevant data is given in
Tables 3–6.
Selected IR, UV–Vis and Molar conductivity data (cmÀ1) for the Cu(II) complexes
(2a–14a).
The IR spectra of the ligands have been summarised in Table 4.
The absence of the aldehydic carbonyl stretching bands and the
appearance of the characteristic azomethine mC@N bands at ca.
1600 cmÀ1 confirmed the formation of the Schiff bases. The broad-
ness of the mOH band at ca. 3450 cmÀ1 may be attributed to the
Complex
IR-spectra (
m
max/cmÀ1
)
UV–Vis
Molar conductivity
–C@O
–CH@N
–C–O
kmax (nm)
KM [S molÀ1 cm2]
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
12a
13a
14a
1648
1666
1664
1654
1665
1644
1676
1665
1667
1667
1665
1652
1651
1585
1607
1594
1604
1603
1610
1612
1601
1603
1600
1598
1600
1598
1223
1247
1266
1223
1245
1226
1233
1264
1264
1268
1261
1259
1260
307, 390
341, 355, 390
342, 401
299, 408
296, 340, 401
303, 385
301, 425
n/m
n/m
n/m
n/m
n/m
1.27
0.51
1.28
14.45
1.6
intramolecular hydrogen bond between CH@N(imine
and
nitrogen)
OH(phenolic) [37,38]. In all of the compounds, the stretching vibra-
tion of the lactam carbonyl was observed as a sharp band in the re-
gion of 1690–1650 cmÀ1. Medium intensity bands in the range of
1285–1230 cmÀ1 were also observed and were attributed to the
phenolic mC–O vibration [39]. The presence of additional bands be-
tween 1577 and 1400 cmÀ1 are attributed mC@C bands of the aro-
matic rings.
1.71
0.4
n/m
n/m
n/m
n/m
n/m
n/m
The main 1H NMR signals for each of the ligands are shown in
Table 5. Formation of the ligands (2–14) was confirmed by the
absence of the NH2 proton signal at d 5.71 ppm assigned to the
starting material, 7-amino-4methyl-quinolin-2(1H)-one and the
presence of an azomethine proton signal at 8.46–9.03 ppm. In
addition, the disappearance of the aldehydic proton signal from
the corresponding starting aldehydes, the appearance of aromatic
proton signals in the region 6.51–7.90 ppm and an OH proton sig-
nal between 9.40–13.79 ppm further confirmed the formation of
the ligands. The signal corresponding to the hydroxyl group at po-
sition 15 (C15) was shifted downfield because of intramolecular
hydrogen bonding between it and the nitrogen of azomethine
(O–HÁ Á ÁN=@CH) [40]. In ligands 2, 13 and 14, where there was
no possibility of hydrogen bonding with the azomethine nitrogen,
the corresponding signal was shifted upfield. Ligand 2 showed two
different OH proton signals at 13.28 (H-bonding) and 10.37 ppm
(no H-bonding) for positions 15 and 17, respectively. In the NMR
spectrum of 7, the OH proton signal was observed downfield at
13.41 ppm, whereas for 13 the OH signal appeared upfield at
9.40 ppm. The upfield shift was attributed to the lack of intramo-
lecular hydrogen bonding with the azomethine nitrogen in the lat-
ter compound. The positions of the proton signals compared
favourably to literature values of similar Schiff base compounds
derived from quinolin-8-amine, (pyridin-2-yl)methanamine and
3,5-di-t-butyl-4 hydroxyaniline reported by Creber et al. [41].
The main 13C NMR signals for the ligands are shown in Table 6.
The 13C NMR spectra of the Schiff base were characterised by the
presence of characteristic signals at ca. 164–140 ppm of the azo-
methine carbon (C@N, C-13), lactam carbonyl carbon (C@O, C-2),
C–OH (C-15), and C-4 (C–CH3) carbons and the upfield signals cor-
responding to vinyl (C-3) and the aromatic carbons (C-5, C-6, C-8,
C-18, and C-19). The spectra were further characterised by the ab-
sence of the aldehydic proton signal at ca. 190 ppm from the corre-
n/m
n/m = Not measured due to poor solubility.
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium
bro-
mide (MTT) was carried out according to the method described
by Mosmann [36]. In metabolically active cells, MTT is reduced
by the mitochondrial enzyme succinate dehydrogenase to form
insoluble purple formazan crystals that are subsequently solubi-
lised, and the optical density (OD) measured spectrophotometri-
cally. Drug-treated cells were assayed by the addition of 20 lL of
5 mg/mL MTT in 0.1 M phosphate buffer saline (PBS), pH 7.4.
Following incubation for 4 h at 37 °C, the overlying medium was
aspirated with a syringe and 100 lL of DMSO was added to dis-
solve the formazan crystals. Plates were agitated at high speed to
ensure complete dissolution of crystals and OD was measured at
550 nm using an Anthos HT-II microtitre plate reader. Viability
was expressed as a percentage of solvent-treated control cells. This
assay had five replicates and each experiment was carried out on at
least three separate occasions. The IC50 was calculated and defined
as the drug concentration (
viability.
lM) causing a 50% reduction in cellular
3. Results and discussion
3.1. Synthesis and characterisation of novel quinolin-2(1H)-one
derived Schiff base ligands (2–14)
A series of quinolin-2(1H)-one-derived Schiff bases (2–14) were
synthesised by an equimolar condensation reaction between
substituted aromatic aldehydes and 7-amino-4-methylquinolin-
2(1H)-one in hot ethanol (Scheme 1). The ligands were character-
ised by melting point and IR, 1H NMR, 13C NMR, and UV–Vis

B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
4053
R2
CH3
CH3
R2
R3
R4
R1
R3
R4
R1
Reflux 4h
Ethanol
+
H2O
+
H
C
H
N
N
H
O
H2N
N
H
O
C
O
R4
R3
R2
H
R1
CH3
N
O
CH
R2
R3
OH
N
O
Cu(II) salt
Cu
MeOH
reflux 5 h
C
H
N
N
H
O
O
N
R2
R3
H
N
O
CH
H
R4
Scheme 1. General reaction scheme for the synthesis of Schiff base ligands and their copper(II) complexes.
sponding aromatic aldehydes (starting material) and the presence
of a methyl carbon signal (C-11) at ca.18 ppm. In all of the spectra
the azomethine (C@N) carbon was located at about 163 ppm and
the lactam carbonyl was observed at ca.161 ppm. 13C NMR signals
at C-5, C-19 and C-15 were affected by the deshielding character of
the imine group whereas the 13C NMR signal of the vinyl carbon at
C-3 position also appeared downfield because of its proximity to
the lactam carbonyl.
sis and molar conductivity results. In contrast to the other com-
plexes isolated, 5a exhibited a sharp band at 3424 cmÀ1 which
was attributed to the phenolic hydroxyl group. Therefore, it was
concluded that in complex 5a, the mode of coordination of metal
ion to the ligand was via the nitrogen of azomethine and the oxy-
gen atom of the phenolic groups, a coordination mode noted in
similar Schiff base complexes of Ni(II), isolated by Majumder
et al. [47].
3.2. Synthesis and characterisation of copper(II) complexes (2a–14a)
3.2.2. Magnetic susceptibility of copper(II) complexes (2a–14a)
The effective magnetic moment values (
l
eff) of copper(II) com-
Ligands (2–14) were reacted in a 2:1 mole ratio with either
copper(II) acetate or copper(II) perchlorate hexahydrate in an
appropriate solvent to afford copper(II) complexes (2a–14a) of
the corresponding ligands (Scheme 1). All of the complexes were
characterised by IR, UV–Vis, magnetic moments, molar conductiv-
ity, X-ray crystallography where possible, and CHN analyses and
the data shown in Tables 7 and 8.
plexes were calculated using the formula
l
eff = 2.84 (vcorr  T)1/2
B.M. The magnetic moment values of the complexes are given in
Table 7. The effective magnetic moments obtained for the com-
plexes are in the range of 1.60–1.77 B.M. which is consistent with
the presence of one unpaired electron [48]. Generally mononuclear
copper(II) complexes (those lacking of Cu–Cu interactions) exhibit
magnetic moments in the range 1.75–2.20 B.M. corresponding to
one unpaired electron (3d94s0), regardless of the stereochemistry
[21,49]. The observed magnetic moments values are within the ex-
pected range for mononuclear copper(II) complexes.
3.2.1. IR spectra of copper(II) complexes (2a–14a)
Comparison of the infrared spectral data of complexes (Table 8)
and their corresponding ligands (Table 5) confirmed that complex-
ation had occurred as significant shifts in the bands of the azome-
3.2.3. Electronic spectra of copper(II) complexes (2a–8a)
thine group
m
CH@N, lactam
m
C@O, phenolic
m
OH and
m
C–O groups were
The electronic spectral data in DMSO are given for ligands 2–8
and their respective Cu(II) complexes in Tables 5 and 8, respec-
tively. The spectra were not recorded for the complexes 9a–14a
which had poor solubility in DMSO. The electronic spectral data
of 2–8 exhibited two bands in the UV region around 276–305,
340–357 and their complexes (2a–8a) had an additional band at
observed. The expected mode of interaction between the Schiff
base ligand and the copper(II) ion was via coordination of the cop-
per ion to the azomethine nitrogen group and the phenolic oxygen
[42]. The strong band at 1604–1575 cmÀ1 assigned to
m(C@N) in the
free ligand was shifted to either lower or higher wavenumber in
most of the complexes, indicating the participation of the azome-
thine nitrogen in the coordination [43]. The medium intensity band
at 1285–1230 cmÀ1 assigned to m(C–O) in the free ligand was also
shifted to lower frequency (1268–1223 cmÀ1) in the complexes.
The change in the intensity of this band confirmed the involvement
of the phenolic oxygen in the coordination. Moreover, the appear-
ance of additional weak bands in the region 485–425 and ꢀ585–
ca. 385–425 nm. The bands at 276–300 nm were assigned to
*
p
?
p
intra ligand transitions that were localised on the conju-
gated system of the aromatic moieties [50–52]. The other absorp-
tion bands observed in the region of 340–357 nm were assigned to
*
*
the
p ? p and n ? p electronic transitions of the azomethine and
the lactam carbonyl groups [53,54]. The electronic spectra of the
complexes showed an additional broad band tailing into the visible
region around 385–425 nm which was not seen in the free ligands.
This band was assigned to the ligand-to-metal charge-transfer tran-
sition. The expected characteristic d–d transitions in the visible re-
gion for the complexes were not detected even when concentrated
solutions were used. It was assumed that the bands were lost or
530 cmÀ1 which were attributed to
m(M–O) and m(M–N),
respectively further confirmed complexation [44].
In the spectra of complex 5a, bands at 1099 and 622 cmÀ1 were
assigned to non-coordinated perchlorates counter anions [45–47]
and the presence of these ions was confirmed by elemental analy-

4054
B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
hidden under the dominant and overlapping charge-transfer band
at 385–425 nm as has been found for other Schiff base systems
[55–57].
3.2.4. Molar conductivity of copper(II) complexes (2a–8a)
The molar conductivities of copper(II) complexes (2a–8a) in
DMSO solvent (4.0 Â l0À3 M) are given in Table 8. Conductance
measurements were not carried out for all of the complexes due
to their poor solubility. The conductance values measured (in the
range 0.40–14.45 S cm2 molÀ1) were too low to account for any
dissociation, hence the complexes were considered nonelectro-
lytes. 5a had a higher molar conductivity than the other complexes
due to the presence of two perchlorates anions in the complex.
3.2.5. Crystal structure of copper(II) complexes 2a and 8a
Crystal data and structure refinement of compounds 2a and 8a
are given in Table 2 and selected bond lengths and angles are pre-
sented in Table 9. The X-ray crystal structure and the crystal pack-
ing diagrams for 2a are shown in Figs. 2 and 3, respectively. From
Fig. 2 it was clearly observed that the Schiff base ligand 2 acted as a
monoanionic bidentate N, O-donor chelate and formed a neutral,
mononuclear, four coordinated complex [58]. Two MeOH mole-
cules and one DMSO molecule are also present within the asym-
metric unit. The ligand coordinated to the copper(II) ion via the
phenolic oxygen (at C15) and the nitrogen of the imine bond as ex-
pected [59,60]. The copper atom was surrounded by a N2O2 donor
set formed by the phenolic oxygens: Cu1–O20 = 1.915(3) and Cu1–
O1 = 1.916(3) Å and the nitrogen of azomethines from two ligand
molecules: Cu1–N28 = 1.964(3), Cu1–N9 = 1.975(3) Å. In all of the
four copper-ligand bond distances, the bond distances between
Cu–N are significantly longer than those of Cu–O bonds. Elongated
Cu–N bonds have also been observed for other Schiff base com-
plexes [61]. The largest distortion from regular square planar
geometry is shown in the trans O–Cu–N angles [145.69(11)° and
140.36(11)°]. In similar structures the geometry around the metal
centre was also considered as distorted square planar coordination
with significant tetrahedral distortion [62–68]. Due to the coordi-
nation of the metal ion to the phenolic oxygen, reduced bond dis-
tances were observed for coordinated C–O [O1–C2 = 1.329(4) Å]
compared to non-coordinated C–O [O4–C4 = 1.359(4) Å] bond
lengths.
Fig. 2. Crystal structure of complex 2a. Displacement ellipsoids drawn at the 50%
probability level.
The two quinolinone moieties were arranged in cis rather than
trans positions [69]. Hence, there are potential p–p stacking inter-
actions where the centroid–centroid distance is 3.485(4) Å (though
the slippage is 0.884 Å) between the ring C31–C36 and its symme-
try equivalent generated by the symmetry operation Àx, Ày, 1 À z
[70]. This arrangement is complemented by centrosymmetric
NHÁ Á ÁO hydrogen bonded ring with a graph set notation of
R4,4(8) [71] which holds two adjacent complexes in a dimeric
arrangement. This hydrogen bonding motif is undertaken by only
one of the two quinolinone groups. The NH in the other quinoli-
none group makes a single NHÁ Á ÁO hydrogen bond with the DMSO
solvent whilst the lactam carbonyl (O14) makes an OÁ Á ÁHO hydro-
gen bond with the uncoordinated [72] phenolic oxygen (O4). Inter-
molecular hydrogen bonds with solvent molecules extend the
hydrogen bonding network into three dimensions, assisting in sta-
bilising the crystal structure [73]. These hydrogen bonds are shown
in Table 10.
The individual metal complexes are stabilised by the formation
of two adjacent six-membered chelate rings [74]. Both rings are al-
most planar with Cu1 lying 0.095 Å off the plane defined by N9, C2,
C7, C8, O1 but lying 0.278 Å from the plane defined by O20, C21,
C26, C27, N28. The benzyl and quinolinone sections are not co pla-
nar, with the angle between the planes defined by the atoms form-
ing the aromatic rings (benzene ring C2 to C7) and (quinoline C10
to C19) being 52.9(2)°. In the other, second Schiff base ligand, the
equivalent angle is 30.3(2)° which is significantly less twisted. This
second ligand also has the larger deviation of Cu1 from the plane
defined by the chelating ring. The bond lengths and bond angles
are almost identical in both chelate rings.
Table 9
Selected bond lengths (Å) lengths and angles (°) for complexes 2a and 8a.
(2a) Bond lengths (Å)
(2a) Bond angles (°)
Cu(1)–O(20)
Cu(1)–O(1)
Cu(1)–N(28)
Cu(1)–N(9)
O(1)–C(2)
1.915(3)
1.916(3)
1.964(3)
1.975(3)
1.329(4)
1.359(4)
1.310(4)
1.310(4)
1.441(4)
1.310(4)
O(20)–Cu(1)–O(1)
O(20)–Cu(1)–N(28)
O(1)–Cu(1)–N(9)
N(28)–Cu(1)–N(9)
O(1)–Cu(1)–N(28)
O(20)–Cu(1)–N(9)
C(2)–O(1)–Cu(1)
C(8)–N(9)–Cu(1)
C(10)–N(9)–Cu(1)
C(11)–C(10)–N(9)
C(21)–O(20)–Cu(1)
95.10(11)
95.20(12)
94.61(11)
98.01(12)
145.69(11)
140.36(11)
127.8(2)
123.0(2)
119.0(2)
121.9(3)
125.9(2)
C(4)–O(4)
O(20)–C(21)
C(27)–N(28)
N(28)–C(29)
O(20)–C(21)
The crystal structure 8a (Figs. 4 and 5) also showed that the
mode of coordination of ligand 8 to copper(II) ion was via the phe-
nolic oxygen (at C15) and the nitrogen of the imine bond as ob-
served for the complex 2a. Selected bond lengths and bond
angles are presented in Table 11. The two quinolinone moieties
were again arranged in cis rather than trans positions and there
were two MeOH solvent molecules also present within the asym-
metric unit. The copper atom was surrounded by a N2O2 donor
set formed by the phenolic oxygens Cu1–O1 = 1.845(9) and Cu1–
O29 = 1.866(3) Å and the nitrogen of azomethines from two mole-
cules of ligand Cu1–N9 = 1.920(3) and Cu1–N37 = 1.934(3) Å. In all
(8a) Bond lengths (Å)
(8a) Bond angles (°)
Cu(1)–O(1)
Cu(1)–O(29)
Cu(1)–N(9)
Cu(1)–N(37)
O(1)–C(2)
1.845(9)
O(1)–Cu(1)–O(29)
O(1)–Cu(1)–N(9)
O(29)–Cu(1)–N(9)
O(1)–Cu(1)–N(37)
O(29)–Cu(1)–N(37)
N(9)–Cu(1)–N(37)
O(1)–Cu(1)
C(8)–N(9)–Cu(1)
C(30)–O(29)–Cu(1)
C(36)–N(37)–Cu(1)
101.5(4)
93.1(4)
139.5(5)
133.2(5)
92.9(5)
104.3(5)
128.2(8)
125.8(9)
128.7(9)
126.6(10)
1.866(10)
1.920(11)
1.934(12)
1.322(16)
1.284(16)
1.392(17)
C(8)–N(9)
N(9)–C(10)

B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
4055
Fig. 3. Crystal packing structure for complex 2a.
of the four copper–ligand bond distances, the bond distances be-
tween Cu and N are significantly larger than those of Cu–O bonds.
However, these bond distances are slightly smaller than the bond
distances observed for complex 2a but can be regarded as normal
compared with the distances found in similar Schiff base com-
pounds [69]. 8a exhibited similar trans [139.5(5)°, 133.2(5)°] and
bite [93.1(4)°, 92.9(5)°] angles around the metal centre. The geom-
etry around the metal centre was also considered as distorted
square planar with significant tetrahedral distortion arrangement
as observed for complex 2a. The same centrosymmetric N–HÁ Á ÁO
dimeric hydrogen bonding arrangement is present in 8a as in 2a,
but in 8a, both quinolinone groups have the R4,4(8) network. How-
ever the phenol ring substituents are all hydrocarbons so the net-
work exists as a stack propagated along the a axis as opposed to
the three-dimensional network found in 2a. The quinolinone rings
appear to stack in a way to allow p–p interactions but the closest
centroid–centroid distance is 3.719(9) Å. The hydrogen bonds are
listed in Table 11. The solvent molecules (MeOH), present in the
crystal structure do not extend the hydrogen bonding network be-
yond the stack being linked to one uncoordinated lactam carbonyl
(O17 or O45) each.
4. Biological studies
Fig. 4. Crystal structure of complex 8a. Displacement ellipsoids drawn at the 40%
probability level.
4.1. Antimicrobial activity of Schiff base ligands and their copper(II)
complexes
ligand 2 also has 2 hydroxy groups on the aromatic ring but they
are m- rather than o-dihydroxy. Of the halogen substituted com-
pounds, the activity of the fluoro-derivative was considerable bet-
ter than that of the iodo-, bromo- or chloro- analogues. A similar,
trend was also reported by Kalkhambkar et al. in their antimicro-
bial activity of a series of halogenated (F, Cl and Br) quinolin-
2(1H)-one and coumarin derivatives where the fluoro-derivatives
showed excellent activity compared to the corresponding chloro
and bromo derivatives. Despite these findings, it is difficult to
identify a structure activity relationship (SAR) with respect to
electronic and steric properties of a compound. It was found that
substitution of a methoxy group (15) in place of ethoxy group
(14) had little effect on activity indicating that the bulky nature
of the substituent has no effect on the activity of a compound at
this position. It may prove difficult to identify a real SAR when
the target of the ligands remained unidentified to date.
The anti-Candida activity of the ligands (2–14), their copper (II)
complexes (2a–14a) and the metal salts used in the synthesis of
the complexes is given in Table 12 expressed as MIC50 values (a
minimal concentration required to inhibit a 50% of cells growth).
No inhibition of growth was found for the free copper(II) salts.
Most of the quinolinone ligands and their copper(II) complexes dis-
played considerable activity against C. albicans, comparable to that
of a commercially available antifungal drug, Amphotericin B. If one
considers the activity of the ligands first, the most active ligands
are those with either two hydroxyl groups or one hydroxyl group
and an alkoxy group on the phenyl ring (4, 5, 6, and 7). However,
Table 10
Hydrogen bond parameters for 2a.
In general it can be seen that coordination to copper(II) resulted
in improved activity and all of the complexes, with the exception of
the fluoro-derivative, which exhibited greater activity (IC50 = ꢀ4–
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
1.83
1.98(4)
1.96
1.96(4)
1.88
d(DÁ Á ÁA)
\(DHA)
O(4)–H(4)Á Á ÁO(1S)#1
N(13)–H(13)Á Á ÁO(14)#2
O(23)–H(23)Á Á ÁO(33)#3
N(32)–H(32)Á Á ÁO(3S)#4
O(1S)–H(1S)Á Á ÁO(14)
O(2S)–H(2S)Á Á ÁO(1)#5
0.84
0.81(4)
0.84
0.93(4)
0.84
0.84
2.659(4)
2.793(5)
2.678(4)
2.867(4)
2.698(4)
2.809(4)
168.9
172(4)
142.5
163(4)
165.9
175.1
51
l
M) than their corresponding free ligands (IC50 = ꢀ10–80
lM).
The decreased activity of the complex 11a compared to that of li-
gand 11 could be attributed to its poor solubility but this should
also apply to complexes 9a–14a, as all of these complexes were
considerably less soluble than their respective free ligands. We
propose that complexation to the copper(II) ion may block the tar-
1.97
Note: Symmetry transformations used to generate equivalent atoms: (i) x, y À 1,
z À 1; (ii) Àx + 1, Ày, Àz + 1; (iii) x, y, z À 1; (iv) x + 1, y, z; (v) x, y + 1, z + 1.

4056
B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
Fig. 5. Crystal packing structure for complex 8a.
Table 11
Hydrogen bond parameters for 8a.
pound 1 and the metal salts used in the synthesis of the complexes
were also determined. Surprisingly, none of the ligands or their
copper(II) complexes showed bacterial growth inhibition at maxi-
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
2.81
1.87
1.87
2.54
1.84(3)
d(DÁ Á ÁA)
3.46(2)
2.745(16)
2.743(18)
2.720(17)
2.722(16)
\(DHA)
mum concentrations of 200 lM (data not shown). Inactivity
N(44)–H(44)Á Á ÁN(44)#1
N(44)–H(44)Á Á ÁO(45)#1
N(16)–H(16)Á Á ÁO(17)#2
O(58)–H(58)Á Á ÁO(17)#3
O(60)–H(60)Á Á ÁO(45)#3
0.88
0.88
0.88
0.84
132.0
176.3
171.8
93.4
against both Gram-negative and Gram-positive species recorded
for the ligands and complexes together with their significant
anti-Candida activity suggested that they are highly selectivity
against fungal pathogens. The selectivity might be result from
the well established structural differences between fungal and bac-
terial cells [75], although the exact reasons remain as yet unclear.
0.889(19)
169(14)
Note: Symmetry transformations used to generate equivalent atoms: Àx, Ày + 1, Àz,
x, y, z + 1.
4.2. Anticancer activity of Schiff base ligands and their copper(II)
complexes
get site of the ligand. The trend in activity of the complexes mirrors
those seen with the ligands, with complexes 4a–7a showing good
activity. In fact all of the complexes have good activity except the
fluoro- and iodo-derivatives, but as many of the complexes had to
be tested as suspensions, it is difficult to assign clearly defined
SAR’s.
Selected compounds (2–8 and 2a–8a) were also screened for
their in vitro anticancer potential using the human hepatic carci-
noma cell line, Hep-G2. The anticancer activity of Schiff base li-
gands (2–8) and their Cu(II) complexes (2a–8a) were expressed
as IC50 S.E.M values as shown in Table 13. With the exception
of compounds 2 and 8, all of the tested metal-free ligands showed
The in vitro antibacterial activity of the most soluble Schiff base
ligands (2–8), their metal(II) complexes (2a–8a), the starting com-
moderate cytotoxicity (IC50 = ꢀ175–1000
were capable of killing cancer cells at low concentration
(IC50 = 39.67 5.24 and 44.33 4.70 M). The solubility of all of
lM). However, 2 and 8
l
Table 12
these ligands in complete culture media was very good and it is
Anti Candida activity of ligands and their copper(II) complexes expressed as MIC50
.
very difficult to see a correlation between compounds 2 and 8 in
Ligand
MIC50
(l
M)
Complex
MIC50 (lM)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
36.9
90.4
95.6
10.5
17.1
17.2
17.6
26.7
29.1
98.4
18.2
80.1
>100
>100
>100
0.61
–
–
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
12a
–
8.2
11.8
4.5
4.3
4.3
7.4
19.8
8.9
8.6
57.5
51.5
–
Table 13
Anticancer activity of ligands and their copper(II) complexes expressed IC50
values as measured using Hep-G2 cell line following 96 h exposure.
(lM)
Ligand
IC50
(
l
M)
Complex
IC50
–
(lM)
1
>1000
–
2
3
4
5
6
7
8
39.67 5.24
411.66 7.26
>1000
398.33 33.21
175.67 12.20
521.67 41.26
44.33 4.70
15.00 2.65
2a
3a
4a
5a
6a
7a
8a
–
47.00 9.54
74.83 8.91
129 16.26
17.90 3.75
105.33 25.41
53.17 1.59
39.67 10.18
–
–
–
–
–
–
–
Cu(II) salts
Amphotericin B
Cisplatin

B.S. Creaven et al. / Inorganica Chimica Acta 363 (2010) 4048–4058
4057
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aromatic ring (8), it is realistic to expect that it is quite lipophilic,
whilst the m-dihydroxy substituted ligand (2) should be quite
hydrophilic.
It is interesting to note that, most of the complexes (except 2a)
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investigated here had a potent antifungal effect being capable of
inhibiting growth of C. albicans by 50% even at a concentration of
ꢀ4
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This research was supported by the Technological Sector Re-
search Programme, Strand 1, under the European Social Fund and
the Programme for Research in Third Level Institutes. The research
was carried out by the Centre for Pharmaceutical Research and
Development (CPRD) and the Centre for Applied Science for Health
located at Institutes of Technology, Tallaght, Dublin, and the Na-
tional University of Ireland, Maynooth, Co., Kildare, Ireland. VRT
would also like ITT Dublin for PhD continuation funding.
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