Doubly end-on azido bridged mixed-valence cobalt trinuclear complex: Spectral study, VTM, inhibitory effect and antimycobacterial activity on human carcinoma and tuberculosis cells

Article abstract of DOI:10.1016/j.saa.2015.04.014

Doubly end-on azido-bridged mixed-valence trinuclear cobalt complex, [Co₃(L)₂(N₃)₆(CH₃OH)₂] (1) is afforded by employing a potential monoanionic tetradentate-N₂O₂ Schi

Full text of DOI:10.1016/j.saa.2015.04.014

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Doubly end-on azido bridged mixed-valence cobalt trinuclear complex:
Spectral study, VTM, inhibitory effect and antimycobacterial activity on
human carcinoma and tuberculosis cells
a,
⇑
b
b
b
c,
⇑
Amitabha Datta , Kuheli Das , Chandana Sen , Nirmal Kumar Karan , Jui-Hsien Huang ,
d
e
b,
⇑
f
f
Chia-Her Lin , Eugenio Garribba , Chittaranjan Sinha , Tulin Askun , Pinar Celikboyun ,
Sandeep B. Mane
Department of Physics, Faculty of Sciences and Arts, University of Balikesir, Cagis Campus, 10145 Balikesir, Turkey
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700032, India
Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan
Department of Chemistry, Chung-Yuan Christian University, Chun-Li 320, Taiwan
Dipartimento di Chimica and Centro Interdisciplinare per lo Sviluppo della Ricerca Biotecnologica e per lo Studio della Biodiversità della Sardegna, Università di Sassari,
Via Vienna 2, I-07100 Sassari, Italy
Department of Biology, Faculty of Sciences and Arts, University of Balikesir, Cagis Campus, 10145 Balikesir, Turkey
g
a
b
c
d
e
f
g
Institute of Chemistry, Academia Sinica, Nangang - 11529, Taipei, Taiwan
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
II
III
3 2 3 6 3 2
Doubly azido-bridged trinuclear cobalt complex, [Co (L) (N ) (CH OH) ] (1) is synthesized where
L = NMe CH CH N@CH(OH)(OMe)C H in moderate yield. The Co atoms adopt a distorted octahedral
2 2 2 6 3
geometry. Complex 1 inhibits the cell growth of human carcinoma cells and exhibits anti-mycobacterial
activity on human tuberculosis cells.
ꢀ
Co /Co -(2-[{[2-(dimethylamino)
ethyl]imino}methyl]-
6
-methoxyphenol).
ꢀ
ꢀ
Doubly azido-bridged Co trinuclear
complex.
It is noteworthy that the CoIII atoms
are diamagnetic in nature where as
1
20
24 h
8 h
4
II
the central Co atom behaves
paramagnetically.
100
*
*
*
*
*
8
6
0
0
ꢀ
ꢀ
The complex decreases the cell
population growth on human
carcinoma cells.
Displays efficacy on the
mycobacterial strains of human
tuberculosis cells.
*
40
2
0
0
0
5
10
25
50
100
Concentration (
μ
M)
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2014
Received in revised form 7 April 2015
Accepted 9 April 2015
Available online 15 April 2015
3 2 3 6 3 2
Doubly end-on azido-bridged mixed-valence trinuclear cobalt complex, [Co (L) (N ) (CH OH) ] (1) is
afforded by employing a potential monoanionic tetradentate-N
2 2
O Schiff base precursor (2-[{[2-
(
dimethylamino)ethyl]imino}methyl]-6-methoxyphenol; HL). Single crystal X-ray structure reveals that
II
III
in 1, the adjacent Co and Co ions are linked by double end-on azido bridges and thus the full molecule
is generated by the site symmetry of a crystallographic twofold rotation axis. Complex 1 is subjected on
⇑
Corresponding authors. Fax: +91 33 2413 7121.
E-mail addresses: amitd_ju@yahoo.co.in (A. Datta), juihuang@cc.ncue.edu.tw
J.-H. Huang), c_r_sinha@yahoo.com (C. Sinha).
(
http://dx.doi.org/10.1016/j.saa.2015.04.014
386-1425/Ó 2015 Elsevier B.V. All rights reserved.
1

4
28
A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
different spectral analysis such as IR, UV–vis, emission and EPR spectroscopy. On variable temperature
magnetic study, we observe that during cooling, the
reaches to the value 1.56 cm K mol at 2 K. Complex 1 inhibits the cell growth on human lung carci-
noma (A549 cells), human colorectal (COLO 205 and HT-29 cells), and human heptacellular (PLC5 cells)
M
v T values decrease smoothly until 15 K and then
Keywords:
Co complex
Crystal structure
EPR
VTM
3
ꢁ1
carcinoma cells. Complex
Mycobacterium tuberculosis H37Rv ATCC 27294 and H37Ra ATCC 25177 strains.
Ó 2015 Elsevier B.V. All rights reserved.
1 exhibits anti-mycobacterial activity and considerable efficacy on
Inhibitory effect
Anti-mycobacterial activity
Introduction
3 6 3 2 2 2
(N ) (CH OH) ] (1) incorporating with a tetradentate-N O Schiff-
base precursor, (HL, Scheme 2) [25]. Besides spectral and magnetic
study [26], we focus our attention mainly on the inhibitory and
anti-mycobacterial effect of complex 1 among different human
carcinoma and tuberculosis cells. The result from an MTT, [3-(4,5-
Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide], assay
demonstrates that complex 1 decreases the cell population growth
of A549, COLO 205, HT-29 and PLC5 cells. The anti-mycobacterial
activity on M. tuberculosis H37Rv ATCC 27294 and M. tuberculosis
H37Ra ATCC 25177 strains are responded well. Before some articles
are published on mixed [27] or same valence [28,29] cobalt system
alongwith azido-bridging [30,28]. However, we first report the inhi-
bitory and anti-mycobacterial effect on human carcinoma and
tuberculosis cells with a mixed-valence cobalt derivative.
Schiff base ligands have been extensively studied in coordina-
tion chemistry mainly due to their facile syntheses, easily tunable
steric and electronic properties as well good solubility in common
solvents [1]. Transition metal complexes with oxygen and nitrogen
donor Schiff bases are of particular interest [2,3] because of their
ability to possess unusual configurations, be structurally labile.
Any pseudohalide ligand can provide the most interesting electron
exchange pathway due to its structural versatility ranging from a
terminal monodentate to bridging ligand [4]. Among them, azide
ion is the most efficient ligand as regards the superexchange path-
ways between paramagnetic centers [5,6]. The versatility and effi-
ciency of azido ligand lies in its functionality as a bridging bi-, tri-,
and tetradentate ligand [6]. The different types of binding modes of
azide ion are shown in Scheme 1. Depending upon the steric and
electronic demand of the co-ligand, the azido ion has been shown
Experimental
to be able to link metal ions in various bridging modes,
l1,1 (end-
Materials
on, EO) [7–9], 1,3 (end-to-end, EE) [10], etc. to give birth to a vari-
l
ety of cobalt(II) complexes [11] using Schiff bases or other poly-
dentate N-donor organic ligands as auxiliary ligands. In
symmetric bi-bridged end-on azido dimers, the interaction is
strongly ferromagnetic [12–14] while with one or more symmetric
end-to-end azido bridges the interaction is strongly antiferromag-
netic [15,16]. Complexes with asymmetric [17] end-to-end azido
bridges are usually weakly antiferromagnetic [13] whereas com-
plexes with asymmetric end-on azido bridges are rare and show
weak or moderately strong ferromagnetic interaction [18]. The
control of tumor cell escalation by inhibition of the cell cycle and
initiation of apoptosis could assist a therapeutic strategy for treat-
ment of cancer affected cells [19]. Programmed cell death plays a
crucial role in the regulation of cellular homeostasis [20]. Marín-
Hernández and co-workers [21] earlier discussed that some mixed
chelate transition metal-based drugs have potentiality regarding
antitumor activity than cisplatin in in vivo and in vitro studies of
different tumor cells. Tuberculosis quite infectious and chronically
bacterial disease, which is caused by primarily Mycobacterium
tuberculosis and rarely Mycobacterium bovis and Mycobacterium
africanum, effects lung and even can spread to the other organs
All chemicals and solvents used for the synthesis were of
reagent grade, obtained commercially and used as received.
O-vanillin, 2-dimethylaminoethyliamine and sodium azide were
purchased from Aldrich Chemicals. Hydrated cobalt(II) trifluoroac-
etate was prepared by the treatment of basic cobalt(II) carbonate,
CoCO
AR grade, E. Merck), followed by slow evaporation on a steam
bath. It was then filtered through a fine glass frit and stored in a
CaCl desiccators.
3
2
ꢂCo(OH) (AR grade, E. Merck), with 60% trifluoroacetic acid
(
2
Caution! Azido compounds of metal ions are potentially explo-
sive especially in presence of organic ligands. Though no difficul-
ties have been encountered during the preparation and
characterization of our complexes, only a small amount of materi-
als should be prepared and handled with care.
Physical techniques
Elemental analyses were performed on a Heraeus CHN-OS
Rapid Elemental Analyzer. Infrared spectra were recorded on a
Perkin-Elmer 883-Infrared spectrophotometer in the range 4000–
[
22]. Millions of children die every year from this disease [23].
ꢁ
1
4
00 cm as KBr pellets. Electronic spectra were measured on a
Mycobacteria resist many of chemicals, disinfectants antibiotics
and chemo-therapeuticals [24].
Hitachi U 3400 (UV–Vis–NIR) spectrophotometer in methanol.
Emission spectra were examined by LS 55 Perkin–Elmer spec-
trofluorometer at room temperature (298 K) in CH CN solution
3
Herein we report the synthesis and X-ray structure of one
symmetric
3 2
l1,1 doubly azido bridged tricobalt complex, [Co (L)
H
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
NMe2
OH
μ−1,1
μ−1,3
μ−1,1,3
μ−1,1,1
μ−1,1,3,3
OMe
Scheme 1. Different modes of azido bridging.
Scheme 2. Synthesis of the ligand, HL.

A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
429
under degassed condition. EPR spectra were recorded from 0 to
0000 Gauss in the temperature range 77–298 K with an X-band
9.15 GHz) Varian E-9 spectrometer. The EPR parameters reported
Table 1
Crystallographic data of 1.
1
(
Empirical formula
Formula weight
Temperature
Wavelength (Å)
Crystal system
Space group
a, Å
C13H21Co1.50N11O3
467.81
150(2)
0.71073
Monoclinic
C2/c
29.9652(13)
8.2241(4)
16.2286(7)
90
110.457(3)
90
in the text were obtained by simulating the spectra with the com-
puter program Bruker WinEPR SimFonia [31]. In all the simula-
tions, second-order effects were taken into account, the ratio
Lorentzian/Gaussian, affecting the line shape, was set to 1 and
the line width used for x, y, z axes was 22, 25 and 30 Gauss, respec-
tively. Magnetization curves versus temperature or applied field
were measured using a Cryogenic SX-600 SQUID magnetometer
on 27.2 mg of a polycrystalline sample. Zero-field cooled (ZFC)
and field cooled (FC) were performed between 2.5 and 300 K. The
sample was placed in a gelatin capsule and data were corrected
for the diamagnetism and sample holder. Ac susceptibility mea-
surements were carried out in a Quantum Design PPMS (Physical
Properties Measurement System) model 6000 with frequencies
ranging between 10 Hz and 10 kHz and constant magnetic field
of 12 Oe.
b, Å
c, Å
a
, deg
b, deg
, deg
c
3
Volume, Å
3747.1(3)
8
Z
Density, Mg/m3
Absorption coefficient, mm
F(000)
1.658
1.386
ꢁ1
1924
ꢁ
3
Crystal size, mm
h range for data collection
Reflections collected
0.32 ꢃ 0.28 ꢃ 0.24
1.4528.84
24,967
Independent reflections
Data/restraints/parameters
4856 [R(int) = 0.0694]
4856/0/262
Synthesis of Schiff base ligand and complex
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0562, wR2 = 0.1444
R1 = 0.0898, wR2 = 0.1616
1.039
1.285 and ꢁ0.888
Preparation of Schiff base ligand, HL
Goodness-of-fit on F2
The tetradentate Schiff base ligand, HL, is prepared [25] by con-
densation of o-vanillin (0.152 g, 1 mmol) with 2-dimethy-
laminoethylamine (0.109 ml, 1 mmol) in methanol (25 ml). After
3
Largest diff. peak and hole, e Å
displacement parameter was calculated from the equivalent isotro-
pic displacement parameter of the bound atom.
2
h reflux, the pale yellow solution is cooled down to room temper-
ature. The solvent is removed under reduced pressure, and the
Schiff-base ligand is obtained as a light-yellow liquid that is used
1
without further purification. H NMR (TMS, CDCL
3
) d: 12.80 (1H,
Cell culture
0
s, H-1), 9.90 (1H, s, H-6,6 ), 6.46–6.86 (3H, d & t, Ar-H), 3.86 (3H,
s, H-6), 3.45 (2H, t, J = 4.5 Hz, H-7), 3.72 (2H, t, J = 3.4 Hz, H-8),
Human lung carcinoma cells (A549 cells) were obtained from
the Bioresource Collection and Research Center (BCRC, Food
Industry Research and Development Institute, Hsinchu, Taiwan).
Human colorectal carcinoma cells (COLO 205 and HT-29 cells)
were provided by Dr. Min-Hsiung Pan (National Kaohsiung
Marine University, Kaohsiung, Taiwan). Human hepatocellular car-
cinoma cells (PLC5 cells) were obtained from the American Type
Culture Collection (ATCC, Bethesda, MD, USA). A549 cells were
grown in a medium consisting of 90% RPMI 1640 with 10% fetal
bovine serum supplemented with 0.1 mM nonessential amino acid,
2
.29 (6H, s, H-9) ppm (see ESI, Fig. S1).
Synthesis of [Co
To a 20 mL methanolic solution of Co(CF
mmol), the Schiff base ligand (1 mmol) is added which results a
3 2 3 6 3 2
(L) (N ) (CH OH) ]
3 2 2
COO) ꢂ6H O (0.393 g,
1
brown solution. After that an aqueous solution (10 ml) of sodium
azide (0.130 g, 2 mmol) is added drop wise and the resulting solu-
tion is kept under boiling for 10 min. On cooling and slow evapora-
tion of the brown solution, the dark brown rectangular shaped
single crystals of the complex (1) are separated out after 3 days.
The crystals are filtered off and washed with water. A dark brown
crystal of 1 is selected for X-ray data collection. Yield: 64%. Anal.
2 mM L-glutamine, 1 mM sodium pyruvate and 100 U/mL peni-
cillin–streptomycin. COLO 205 cells and HT-29 cells were grown
in 90% RPMI 1640 medium supplemented with 10% fetal bovine
Calc. for C13
H
21Co1.50
N
11
O
3
: C, 33.38; H, 4.53; N, 32.93. Found: C,
serum, 100 units/mL penicillin, and 100
PLC5 cells were grown in 90% Dulbecco’s modified Eagle’s medium,
supplemented with 10% fetal bovine serum, 2 mM -glutamine,
1.5 g/L sodium bicarbonate, 0.1 mM non-essential amino acids,
.0 mM sodium pyruvate, 100 units/mL penicillin and 100 g/mL
streptomycin. Human cancer cells were grown at 37 °C in a humid-
lg/mL streptomycin.
3
3.59; H, 4.62; N, 32.72%.
L
X-ray crystallography
1
l
Details concerning crystal data, data collection characteristics
and structure refinementare summarized in Table 1. The single crys-
tal X-ray diffractionmeasurement was carried outon a BrukerAPEX-
II CCD diffractometer, fine focus sealed tube equipped with graphite
2
ified incubator with a 5% CO atmosphere.
Cell viability by MTT assay
monochromatic Mo-Ka radiation (k = 0.71073 Å). The x: 2h scan
technique was applied within a h range of 1.45–28.84°. No signifi-
cant crystal decay was observed. Data were corrected for absorption
The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetra-
zolium bromide] (Sigma Chemical Co., St. Louis, MO, USA) assay
was performed according to the method of Mosmann [35].
Human colorectal carcinoma cells were plated into 96-well micro-
empirically by means of
w scans. A total of 24967 reflections were
collected, from which 4856 independent [R(int) = 0.0694] reflec-
tions were measured. The intensity data were corrected for
Lorentz and polarization effects and an empirical absorption correc-
tion was also employed using the SAINT program [32]. The struc-
tures were solved with the direct method of SHELXS-97 [33] and
4
titer plates at a density of 1 ꢃ 10 cells/well. After 24 h, culture
medium was replaced by 200 lL (0–100 lM) of compound, and
the cells were incubated for 24 and 48 h. The final concentration
of solvent was less than 0.1% in cell culture medium. Culture med-
ium was removed and replaced by 90 lL fresh culture medium.
2
refined on F by full-matrix least-square techniques using the
SHELXTL-97 [34] program. The non-hydrogen atoms of the com-
plexes were refined with anisotropic temperature parameters. The
hydrogen atom positionswere calculated and they were constrained
to idealized geometries and treated as riding where the H atom
Ten microliters of sterile filtered MTT solution (5 mg/mL) in phos-
phate buffered saline (PBS, pH = 7.4) was added to each well,
thereby reaching a final concentration of 0.5 mg MTT/mL. After
5 h, the remaining unconsumed dye was removed, and the

4
30
A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
insoluble formazan crystals were dissolved in 200
l
L/well DMSO
Results and discussion
and measured spectrophotometrically in a VersaMax tunable
micro plate reader (Molecular Devices, Sunnyvale, CA, USA) at
Crystal structure
5
70 nm. The relative cell viability (%) related to control wells con-
taining cell culture medium without samples was calculated by
570 nm [sample] A570 nm [control] ꢃ 100.
Complex 1 features a doubly end-on azido bridged mixed-va-
lence cobalt trinuclear unit as depicted in Fig. 1. The necessary
bond lengths and angles are summarized in Table 2. The solid crys-
A
Inoculum preparation
tallizes in the monoclinic unit cell of C2/c space group with the tri-
1
cobalt complex situates in a special position of 0, y, /
4
such that
For the cultivation of mycobacteria, the MGIT (Mycobacteria
Growth Indicator Tube), a fluorescent compound is embedded in
silicone on the bottom, then 4 mL of modified Middle brook 7H9
Broth base are added to the mixture. After that 0.5 mL of OADC
enrichment, (an oleic acid, albumin, dextrose and catalase) and
PANTA (Polymyxin B, Amphotericin B, Nalidixic acid,
Trimethoprim and Azlocillin) antibiotic mixture to prevent the
growth of any non-mycobacteria (0.1 mL) are added to this
medium. Oleic acid plays an important role in metabolism of
mycobacteria; Albumin acts as a protective agent; Dextrose is an
energy source; Catalase destroys toxic peroxides. Tubes are incu-
bated at 37 °C. For positive control, MGIT tubes are prepared by
inoculating bacteria. An un-inoculated MGIT tubes are used as a
negative control. Blood Agar is used for checking the growth of
other bacteria. Tubes reading daily starts on the second day of
incubation using a Micro MGIT fluorescence reader which has a
long wave UV light [36]. To prepare inoculums from a positive
BACTEC MGIT tube, the positive tubes (day 1 or day 2 positive)
are used directly as inoculums. The positive tubes between day 3
and day 5 are diluted as 1:4 ratio by sterile saline. Inoculums, pre-
pared from a MGIT 7 mL positive tube (from day 1 to day 5), ranges
only half of the tricobalt complex exists in an asymmetric unit.
The full molecule is generated by the site symmetry of a crystallo-
graphic twofold rotation axis. There are geometrically same two
II
III
cobalt centers (Co and Co ), consisting with a N
4
O
2
donor set
II
III
for Co1 (Co ) and N
5
O donor set for Co3 (Co ). In the trimeric unit,
the cobalt atoms are held together by doubly end-on azide bridges.
The coordination environment in the central Co1 atom can be
described as a distorted (4 + 2) (NNNN + OO) octahedron. It is coor-
dinated by two cis methanol molecules and four bridging azide
ligands. The four atoms constructing the basal plane of the octahe-
dron are the two nitrogen (N6 and N6#1) atoms from two bridging
azides and the two oxygen (O2 and O1) atoms from two coordi-
nated methanol molecules. The axial cite is occupied two bridging
N atoms, subjecting the longer axial distance [2.215(4) Å] than
equatorial bond lengths [2.098(3) and 2.099(3) Å]. The Co1 atom
lies not in the basal plane but slightly out of it at a distance of
0
.08 Å. The deviation from the octahedral geometry is indicated
by the bond angles involving trans positions [169.05(13)° and
70.87(18)°], differs from 180°. In this structure, the Co1ꢂ ꢂ ꢂCo3 dis-
1
tance is 3.2326(6) Å, and the Co1–N9–Co3 and Co1–N6–Co3 angles
are 99.79(15) and 105.29(14)° taking Co1N9, Co1N6, Co3–N9 and
Co3–N6 distances 2.215(4), 2.099(3), 2.008(3) and 1.966(3) Å,
respectively. The Co3 atom at the flank is also in distorted octahe-
dral coordination geometry. It is coordinated with one terminal
and two cis bridging azide ligands and the tridentate ONN ligand
via the amine and imine nitrogen atoms, as well phenolato oxygen
atom. The extent of distortion at this cobalt atom is less than that
at the central cobalt atom as evidenced by the three larger quasi-
linear bond angles, which are 173.86(14), 174.99(15), and
176.78(13)°. The bonding distances and angles between the triden-
tate ONN ligand to this cobalt atom are entirely normal with
respect to end-on azido bridged cobalt compound in the literature
[27]. The Co–N distance from the terminal azide is short
[1.938(4) Å] compared with those from the bridging azide
[1.966(3) and 2.008(3) Å]. These Co-N terminal and bridging bond
distances are well comparable with previous literature [28,42],
[1.942(5) and 1.954(6) Å]. One of bridging azide ligands is notice-
ably bent with a short N–N–N bond angle of 170.0(7)°, compared
with those of 174.6(5) and 179.1(5)° at the other two azide ligands.
5
5
between 0.8 ꢃ 10 and 3.2 ꢃ 10 CFU/mL. Each assay is performed
according to the MGIT manual fluorometric susceptibility test pro-
cedure recommended by the manufacturer [36,37].
Anti-mycobacterial susceptibility assay
The activity of complex 1 against M. tuberculosis strains was
tested using the Microplate Presto Blue Assay (MPBA) by the
method described Collins & Franzblau [38] and modified by
Jimenez-Arellanes et al. [39]. 128
l
L of compound and 72
l
l
L of
L of
7
7
H9 broth were transferred in the first column; then 100
H9 broth was transferred from the column 2 to column 8.
Column 9 and 10 were positive and negative control respectively.
00 L of mixture of broth and compound were transferred from
column 1 to column 2 then mixed by pipettes three times and go
on the same to provide serial 1:2 dilutions. 100 L of excess med-
ium was discarded from the wells in column 8. Afterwards, 20
1
l
l
lL
of M. tuberculosis inoculum was added to the wells column 1 to 8
and positive control columns. Negative control columns were not
inoculated with bacteria. Positive control columns include 7H9
broth and bacteria; and negative control columns were include
7
6
H9 broth and compound. Final test concentrations ranges were
4–1 g/mL in the mixture. Microplates were inoculated with
L) per wells except for the negative
control and incubated at 37 °C for 6 days. Presto blue (15 L, Life
Technologies) was then added to the bacterial growth control wells
without compound) and the microplates were incubated at 37 °C
l
the bacterial suspension (20
l
l
(
for an additional 24 h. If the dye turned from blue to pink (indicat-
ing positive bacterial growth); then Presto blue solution was added
to the other wells to determine the MIC values. All tests were per-
formed in triplicate. The minimal inhibitory concentration (MIC)
was defined as the lowest concentration of sample that prevents
a color change to pink. The minimal bactericidal concentration
(
MBC) was corresponded to the minimum compound concentra-
tion which is not cause a color change in the cultures when
re-incubated in fresh medium [40,41]. Streptomycin (STR), etham-
butol (EMB), and isoniazid (INH) were used as standard drugs.
Fig. 1. Perspective view of complex 1. Ellipsoids are drawn from 40% probability
level. Hydrogen atoms have been omitted for clarity.

A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
431
Table 2
Selected bond lengths (Å) and angles (°) of 1.
Co(1)–O(3)
Co(3)–N(1)
Co(3)–N(6)
Co(1)–N(9)–Co(3)
N(1)–Co(3)–N(6)
O(2)–Co(3)–N(2)
N(5)–N(4)–N(3)
2.098(3)
1.889(4)
1.966(3)
99.79(15)
173.86(14)
176.78(13)
174.6(5)
Co(1)–N(6)
Co(3)–O(2)
Co(3)–N(9)
Co(1)–N(6)–Co(3)
N(3)–Co(3)–N(9)
N(8)–N(7)–N(6)
N(11)–N(10)–N(9)
2.099(3)
1.895(3)
2.008(3)
105.29(14)
174.99(15)
170.0(7)
179.1(5)
Co(1)–N(9)
Co(3)–N(3)
Co(3)–N(2)
2.215(4)
1.938(4)
2.020(3)
500
337 nm
400
HL
λexc= 282 nm
300
200
100
410 nm
435 nm
λexc= 345 nm
complex
450
0
3
00
350
400
500
550
Wavelength (nm)
Fig. 4. Temperature dependence of the dc
M
v T for complex 1 measured in a
Fig. 2. Emission spectra of HL (in MeOH) and Co-complex (in DMF).
constant magnetic field of 1 T. The solid line represents the theoretical fitting
results (see text).
Fig. 3. EPR spectra of complex 1 recorded at 80 K on a: (a) polycrystalline powder
and (b) DMF solution. Diphenylpicrylhydrazyl (dpph) is the standard field marker
(g = 2.0036).
Fig. 5. Molar magnetization in N
of magnetic field. The solid line represents the theoretical fitting results (see text).
B
l units of complex 1 measured at 2 K as a function
III
II
The Co –Co distance, 3.2326(6) Å is slightly longer than a similar
trinuclear system, 3.105(1) Å [28], whereas lower than those
(
II
II
3.7121(16) and 3.828(9) Å) found in case of Co –Co system
29]. An intramolecular hydrogen bond exists between the proton
on a coordinated methanol molecule and the phenolato oxygen
ꢁ1
well resolved strong band at 2042 cm and a bifurcated peak at
[
ꢁ1
2
068 cm are obtained, which indicates to mN@N stretching fre-
quency of the azide group represented as bridging and terminal
ligands respectively [43]. The ligand coordination to the cobalt
center is substantiated by two bands appearing at 426 and
atom of the tridentate ligand with the Hꢂ ꢂ ꢂO contact distance of
2
.611(4) Å and O–Hꢂ ꢂ ꢂO contact angle of 111°.
ꢁ1
3
27 cm attributable to mCo–N and mCo–O, respectively. The UV–vis-
Infrared and electronic spectra
ible spectra have been generated for HL in methanol and complex 1
in DMF solution. In ligand, the maximum absorption bands are
ꢁ1
ꢁ1
ꢁ1
In free ligand (HL), FTIR bands at 3436 and 1660 cm corre-
spond to (O–H) and (C@N) stretching frequencies respectively.
The (C@N) band is shifted to 1632 cm for 1 which indicates
the coordination of azomethine-N with metal ion. In the spectra,
observed
at
225
(
e
= 4365 M cm
)
and
p
282 nm
transition.
ꢁ
1
ꢁ1
⁄
⁄
m
m
(e
= 2452 M cm ) which may be
p
?
p
and n ?
ꢁ1
m
On complexation, the absorption band is shifted to 266
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
(e = 927 M cm ) and 345 nm (e = 394 M cm ) in 1 alongwith

4
32
A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
ꢁ
ꢁ1
a broad dd transition band at 517 nm (
T
e
= 59 M 1 cm ) due to
R
benzene (U = 0.42) [45]. The quantum yield of the complex is very
negligible, may be due to the paramagnetic quenching.
4
4
1g(F) ? T1g(P), supporting the presence of octahedral cobalt
complex [44]. The band at 652 nm (e = 15 M cm ) is probably
due to the T1g ? A2g transition (see ESI, Fig. S2).
ꢁ1
ꢁ1
4
4
EPR spectra
EPR spectra on the polycrystalline sample of 1 were recorded
Emission spectra
from 80 to 300 K. These can be interpreted postulating that the
external ions are Co(III) with a diamagnetic and EPR-silent t 62 g
,
Emission spectroscopy studies of the ligand and Co-complex,
are carried out in methanol and DMF, respectively and the spectra
is shown in Fig. 2. When the ligand solution is excited at 282 nm
the emission band is observed at 337 nm whereas a weak emission
band appears at 410 and 435 nm for the complex on excitation at
whereas the central ion is a paramagnetic Co(II) which can be
investigated by EPR spectroscopy. The spectrum at 300 K is not
resolved, but the resolution increases at lower temperatures and
that measured at 80 K is shown in Fig. 3a. This behavior is compat-
ible and explainable with the short spin–lattice relaxation time for
high-spin Co(II) complexes. At liquid nitrogen temperature, no
hyperfine structure arising from an electron-nucleus interaction
3
45 nm. Longer wavelength of excitation (MLCT/d–d bands) does
not show any emission. The fluorescence quantum yield of the
ligand ( : 0.06) and complex ( complex,: 0.003) are determined
5
9
U
L
U
for the Co isotope (100% abundance, I = 7/2) is observed, but res-
onances at g ꢄ 4.50, 2.31 and 2.04 are detected. The value of g
using carbazole as reference with known quantum yield value in
A 120
B 120
2
4
4 h
8 h
24 h
48 h
1
00
100
*
*
*
*
*
*
*
*
*
*
*
*
8
6
4
2
0
0
0
0
0
*
80
60
40
20
0
*
0
5
10
25
50
100
0
5
10
25
50
100
Concentration (
μ
M)
Concentration (
μ
M)
C
D
1
20
00
80
1
1
20
00
2
4
4 h
8 h
24 h
48 h
1
*
*
*
*
*
*
*
*
*
*
*
*
*
80
60
40
20
0
*
*
6
0
40
20
0
0
5
10
25
50
100
0
5
10
25
50
100
Concentration (
μ
M)
Concentration ( M)
μ
E 120
00
2
4
4 h
8 h
1
*
*
*
*
*
*
80
60
40
20
0
*
0
5
10
25
50
100
Concentration (
μ
M)
Fig. 6. Effect of 1 on the cell viability of A549 cells (A), COLO 205 cells (B), COLO HT-29 cells (C), PLC5 cells (D) and NIH3T3 cells (E). Cells were treated with 100
compounds for 24 and 48 h. The reported values are the means ± SD (n = 3). p < 0.05 is significantly different from that of the control.
l
M
⁄

A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
433
Table 3
Anti-mycobacterial activity (MIC and MBC,
lg/mL) of complex 1.
Complex
The minimal inhibitory concentration (MIC)
The minimal bactericidal concentration (MBC)
Clinical isolate 1 (7/16) Clinical isolate 2 (16/6)
Mycobacterium
Mycobacterium
tuberculosis RA
tuberculosis RV
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
32
1
8
32
8
32
8
32
8
ETH
1.87
1.87
3.74
7.48
3.74
3.74
1.87
>7.48
larger than 4.0 is typical of high-spin Co(II) complexes [46], and has
been measured for other hexacoordinated Co(II) complexes with
tetragonal symmetry [47–50]. The spectrum can be associated
with the Kramer doublet ±1/2 arising from the S = 3/2 ground state
[
1 2
51], which must present two signals approximately at g = g .
Similar behavior was observed for others Co(III)/Co(II)/Co(III) com-
plexes with the Co(II) ion exhibiting a high-spin configuration
[
52,53]. The EPR spectrum in a frozen DMF glass is characterized
by comparable pattern (Fig. 3b), indicating that the arrangement
of the solid state is retained in the solution, in agreement with
the previous observations for other similar trinuclear cobalt spe-
cies [53].
Magnetic moments
The magnetic susceptibility
M
v of complex 1 was measured on
polycrystalline samples between 2 K and 300 K. The thermal
dependence of the
ature, the value of
value for S = 3/2 with g = 2 (1.875 cm K mol ), as expected for
M
v T product is shown in Fig. 4. At room temper-
3
ꢁ1
v
M
T is 3 cm K mol , larger than the spin-only
Fig. 7. Antimycobacterial activity of compound 1 and a standard drug against
Mycobacterium spp.
3
ꢁ1
Co(II) systems with significant orbital contributions of the dis-
from an MTT assay demonstrate that 1 decreases the cell popula-
tion growth of A549 cells, COLO 205 cells, HT-29 cells, and PLC5
cells. Moreover, the 50% inhibitory concentration (IC50), as deter-
mined by MTT assay after 48 h of incubation, show the highest
torted octahedral Co(II) [54]. Upon cooling, the
M
v T values
decrease smoothly until approximately 15 K and then more
3
ꢁ1
abruptly to the value 1.56 cm K mol at 2 K. These magnetic data
III
II
are consistent with a mixed valence state Co (S = 0)–Co (S = 3/2)–
Co (S = 0) of complex 1. In order to interpret the magnetic proper-
III
activity for complex 1 with an IC50 value of 46.00 ± 1.09 lM. It is
further tested by an in vivo model to justify whether it is effective
for the prevention of human cancer. Fig. 6 also shows the effect of
complex 1 on cell population growth in human fibroblasts cells
(NIH3T3). The investigation regarding the apoptotic properties of
1 on human fibroblasts cells (NIH3T3) suggests that a mitochon-
dria-mediated pathway is induced by this complex.
ties of 1, the following general Hamiltonian was used with S = 3/2
and two parameters for the g-value (g||, g ).
\
ꢀ
ꢁ
1
3
^
^
2
^
2
^
2
H ¼ D S ꢁ SðS þ 1Þ þ EðS ꢁ S Þ þ gbH ꢂ S
ð1Þ
z
x
y
Taking into account rhombic distortions of the crystal field in
the Hamiltonian, the low temperature magnetic behavior of the
system is better resolved in comparison with only axial distortions.
Anti-mycobacterial activity
ꢁ1
The solid line in Fig. 4 shows the best fit found with D = 61.4 cm
,
In the anti-mycobacterial assay, complex 1 was tested against
M. tuberculosis H37Rv ATCC 27294, M. tuberculosis H37Ra ATCC
E/D = 0.33, g|| = 2.7 and g = 1.95, comparable with other octahe-
\
dral Co(II) systems [55,56]. The molar magnetization was mea-
sured as a function of the applied magnetic field at 2 K (Fig. 5).
As well established, the combined effects of distorted octahedral
crystal field and spin–orbit coupling produces six Krame r´ s dou-
blets, where only the ground-state Krame r´ s doublet is thermally
populated at low temperature [54]. Therefore the Co(II) ion can
be described by an effective spin 1/2. The solid line in Fig. 5 repre-
sents the theoretical magnetization curve for a system in a ground
2
2
5177 strains alongwith two clinical strains (strain 1 and strain
). The results are depicted in Table 3 and Fig. 7. M. tuberculosis
H37Rv and M. tuberculosis H37Ra were a drug susceptibility pro-
files consisting well-known indicator organisms that they used to
for the drug sensitivity tests [37]. The results showed that com-
pound 1 exhibited anti-mycobacterial activity against all the tested
M. tuberculosis strains, with MICs at 8
the range of 32 g/mL. This complex showed a bactericidal
activity and killed the bacteria. Trias et al. [57] showed that
Mycobacteriumcheionae developed a pore-forming protein as a
mycobacterial porin. On the study of permeability of
lg/mL and MBC were in
l
0
state with effective spin S = 1/2 and effective g value of 4.43.
Effects on cell-population growth in human carcinoma cells
Mycobacteriumsmegmatis, Trias
& Benz [58] reported that
Fig. 6 shows the effects of complex 1 on cell population growth
in human cancer cells [including human lung (A549 cells), human
colorectal (COLO 205 and HT-29 cells), and human hepatocellular
mycobacterial porin formed an important hydrophilic structure
which small molecules pass through the pores and diffuse into
the cytoplasm. In this study, we reported that complex 1 showed
a considerable efficacy on the mycobacterial strains and compared
the effect with a known drug ETH (Ethambutol). The mycobacteria
cell wall includes a large amount of complex lipids, lipopolysaccha-
rides and mycolic acids. This constitution makes the cell wall a
(
PLC5 cells) carcinoma cells]. To assess the inhibitory effect of
the complex on the growth of human cancer cells, the cells are cul-
tured for 24 and 48 h with or without test compound (0–100 M),
and population growth is determined by MTT assay. The results
l

4
34
A. Datta et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 427–434
hydrophobic strong barrier against antimicrobial agents [59,60].
Recently, the studies on the effect of pyridine based inhibitors
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[
Conclusion
[
[
[
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A monoanionic tetradentate-N
2
O
2
Schiff base precursor (HL), is
mixed-valence trinuclear cobalt complex
] (1). In solid state, it shows that there are
used to afford
Co (L) (N (CH
a
OH)
[
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[
3
2
3
)
6
3
2
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II
III
geometrically same two cobalt centers (Co and Co ) and the full
molecule is generated by the site symmetry of a crystallographic
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ꢁ1
value of
the spin-only value for S = 3/2 with g = 2 (1.875 cm K mol ) and
the related data is well consistent with mixed valence
M
v T is 3 cm K mol at room temperature, larger than
3
ꢁ1
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Co (S = 0)–Co (S = 3/2)–Co (S = 0) system. Complex 1 restrains
the cell growth of different human carcinoma cells (A549, COLO
2
05, HT-29 and PLC5) and shows efficaciousness on mycobacterial
strains (H37Rv and H37Ra), involved in tuberculosis. Future work
will explore the mechanistic pathway and modification that
corresponds to several applications among mixed-valence metal
complexes of newly designed organic precursors.
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Amitabha Datta would like to thank the Scientific
Technological Research Council of Turkey (TÜBITAK) for the grant
2221 – Fellowship for Visiting Scientist). Kuheli Das and
Chittaranjan Sinha would like to thank DST (Department of
Science and Technology, New Delhi, India) for the grant (SR/S1/
IC-31/2008). Jui-Hsien Huang thanks the National Changhua
University of Education for providing the X-ray diffractometer
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