A trinuclear zinc-Schiff base complex: Biocatalytic activity and cytotoxicity

Article abstract of DOI:10.1002/ejic.201402158

A novel trinuclear zinc(II) complex [Zn₃L₂(μ- O₂CCH₃)₂(CH₃OH)₄] (1) that contains an N,O-donor Schiff base ligand {H₂L = 2-[(2-hydroxyphenylimino)methyl]-6-methoxyphen

Full text of DOI:10.1002/ejic.201402158

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DOI:10.1002/ejic.201402158
A Trinuclear Zinc–Schiff Base Complex: Biocatalytic
Activity and Cytotoxicity
Dhananjay Dey,[a] Gurpreet Kaur,[b] Anandan Ranjani,[c]
Loganathan Gayathri,[c] Prateeti Chakraborty,[d]
Jaydeep Adhikary,[d] Jorge Pasan,[e] Dharumadurai Dhanasekaran,[c]
Angshuman R. Choudhury,[b] Mohammad A. Akbarsha,[f]
Niranjan Kole,[a] and Bhaskar Biswas*[a]
Keywords: Zinc / Schiff bases / Catecholase activity / Medicinal chemistry / Drug delivery / Antitumor agents
A
novel trinuclear zinc(II) complex [Zn3L2(μ-O2CCH3)2-
radical pathway. This is the first example of catecholase oxi-
dation through a trinuclear zinc(II)–Schiff base complex by
means of the formation of a mononuclear intermediate as
[ZnL(dtbc)] (dtbc = 3,5-di-tert-butylcatechol). The fluores-
cence property of 1 indicates that it can serve as a potential
photoactive material. It effectively cleaves the double strand
of pBR 322 plasmid DNA at a given concentration (25 μM).
The complex shows remarkable cytotoxicity against a human
hepatocarcinoma cell line (HepG2).
(CH3OH)4] (1) that contains an N,O-donor Schiff base ligand
{H2L = 2-[(2-hydroxyphenylimino)methyl]-6-methoxyphenol}
has been synthesized and crystallographically characterized.
The X-ray crystal structure of 1 contains three zinc(II) cen-
ters, which have distorted-octahedral coordination geometry,
and the molecule crystallizes in the Pbcn space group. The
zinc(II) complex displays significant catecholase oxidation
activity in methanolic medium through a ligand-centered
polyhedra occur easily. It is no surprise that di- and trinu-
clear ZnII complexes have attracted particular interest as
synthetic structural mimics of the active site of a range of
metalloenzymes,[4,5] such as zinc-dependent aminopeptid-
ases, metallo-β-lactamases, and alkaline phosphatases.
The catalytic role of the zinc ion is ascribed to the orienta-
tion and activation of substrates; the bridging groups keep
the two metal ions at a suitable distance and make a funda-
mental contribution to substrate activation. Substrates, in
principle, can bind to zinc by the substitution of coordi-
nated solvent molecules or by association, thus increasing
the coordination number. This behavior is typical of Lewis
acids, and thus zinc can act like protons in the task. Many
features of zinc, such as its ability in assisting Lewis acti-
vation, nucleophile generation, fast ligand exchange, and
leaving-group stabilization, make ZnII ideal for the catalysis
of hydrolytic reactions, including DNA binding and DNA
cleavage, which are important properties for use as antican-
cer agents.[6–8] However, Schiff bases can accommodate dif-
ferent metal centers that involve various coordination
modes, thereby allowing successful synthesis of homo- and
heterometallic complexes with varied stereochemistry.[9] In-
teraction of polynuclear ZnII complexes with DNA has re-
cently attracted much attention owing to their possible ap-
plications as new cancer therapeutic agents and their photo-
chemical properties, which make them potential probes of
DNA structure and conformation.[10–12] Zinc(II)–Schiff
base complexes have often been found to be photochemi-
Introduction
The development of synthetic analogues for the active
sites of different metalloenzymes that contain polynuclear
metal centers has become an attractive approach to obtain
information on the mechanisms involved in their catalytic
cycles.[1–3] Zinc is an essential metal and one of the most
bio-relevant transition-metal ions next to iron (human be-
ings contain an average of approximately 2–3 g of zinc).
Zinc(II) cations, owing to their d10 electronic configuration,
form complexes with a flexible coordination environment,
and the geometries of these complexes can vary from tetra-
hedral to octahedral, and severe distortions of the ideal
[a] Department of Chemistry, Raghunathpur College,
Purulia 723133, India
E-mail: mr.bbiswas@rediffmail.com
http://www.raghunathpurcollege.ac.in/
[b] Department of Chemical Sciences, Indian Institute of Science
Education and Research, Mohali,
Mohali 140306, India
[c] Department of Microbiology, Bharathidasan University,
Tiruchirappalli 620024, India
[d] Department of Chemistry, The of University Calcutta,
92 A. P. C. Road, Kolkata 700009, India
[e] Laboratorio de Rayos X y Materiales Moleculares, Dpto. de
Física Fundamental II,
Universidad de La Laguna, La Laguna, Spain
[f] Mahatma Gandhi-Doerenkamp Center, Bharathidasan
University,
Tiruchirappalli 620024, India
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402158.
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cally active and behave like photoluminiscent materials.[13] tions are occupied by two methanol molecules (O5/O5i and
Recently, DNA binding studies and the antimicrobial ac- O6/O6i) at each terminal ZnII center. However, the coordi-
tivity of a similar trinuclear zinc–Schiff base complex have nation geometry of the central zinc ion (Zn2) might also be
been investigated by Biswas et al.[14] In this present work, best described as distorted octahedra formed by six oxygen
we have crystallographically characterized a novel trinu- atoms from the same Schiff base ligands and bridging acet-
clear ZnII–Schiff base complex with potential ligand-cen- ate ions that coordinate the terminal zinc ions. Thus two
tered catalytic activity relevant to catechol oxidase, and the phenoxo-oxygen (O2/O2i) from two Schiff base ligands and
molecule exhibits remarkable cytotoxicity against a human two acetate ions act as bridges between the two terminal
hepatocarcinoma cell line (HepG2) in terms of attacking zinc ions (Zn1 and Zn1i) and the central zinc ion (Zn2).
the DNA in cancer cells. We have also investigated the The four equatorial positions are occupied by two phenoxo
DNA cleavage activity and luminescence property of the oxygen atoms (O2/O2i), one methoxo (O7), and one acetato
Zn–Schiff base complex that contains three metal ions in oxygen (O3), and the axial positions are coordinated by one
close proximity.
methoxo oxygen (O7i) and one acetato oxygen (O3i). The
three zinc ions are in a nearly linear arrangement (ЄZn1–
Zn2–Zn1i = 150.3°). The distances between the central zinc
ion (Zn2) and the two terminal zinc ions (Zn1/Zn1i) are
3.3482(2) Å. The crystal packing shows an extended hydro-
gen-bonding scheme (Figure S1 in the Supporting Infor-
mation). In fact, methoxo oxygen atoms act as hosts to
form hydrogen bonds towards C–H bonds, thus leading to
a three-dimensional (3D) supramolecular arrangement
(Figure S1 in the Supporting Information). The structural
parameters are listed in Table 2. Selected bond lengths and
angles are presented in Table S1 of the Supporting Infor-
mation, and the relevant hydrogen-bonding parameters are
summarized in Table S2 of the Supporting Information.
Results and Discussion
Synthesis and Formulation
The Schiff base ligand H2L was synthesized by a 1:1 con-
densation of O-aminophenol and O-vanillin in dehydrated
alcohol in a literature report.[14] Trinuclear zinc(II) complex
1 was prepared using the reaction between zinc(II) acetate
dihydrate and the ligand in
a methanolic medium
(Scheme 1). The coordination geometry of 1 was deter-
mined mainly by single-crystal X-ray diffraction study
along with different spectroscopic and analytical tech-
niques. The yellowish-orange crystals suitable for X-ray
data collection were obtained by slow evaporation of result-
ant reaction mixture. The different formulations were con-
1
firmed by elemental analysis, IR, UV/Vis, H NMR spec-
troscopy, mass spectral analysis, thermogravimetric analy-
sis, and crystallographic structure analysis of the com-
pound.
Description of Crystal Structure
The X-ray structural determination of compound 1 re-
veals a trinuclear neutral zinc(II) complex with Pbcn space
group in which the central ZnII ion is lying on a center of
inversion. An ORTEP view of the μ-acetato-μ-phenoxotri-
zinc(II) complex of 1 with an atom-labeling scheme is
shown in Figure 1. The trinuclear complex is built up of
two mononuclear ZnL moieties linked through bridging
acetate and μ2-phenolato groups to the central Zn atom.
The coordination geometry around the terminal Zn centers
(Zn1 and Zn1i) might be regarded as distorted-octahedral
geometry in which the equatorial plane of a terminal Zn1/
Figure 1. An ORTEP diagram of [Zn3L2(μ-O2CCH3)2(CH3OH)4]
(1) with atom-numbering scheme and 30% probability ellipsoids.
Absorption and Fluorescence Spectra of the Ligand and
Zinc Complex and Their Solution Properties
The Schiff base ligand (H2L) and trinuclear zinc(II) com-
Zn1i atom is formed by phenoxo-bridged oxygen (O2/O2i), plex is soluble in common organic solvents such as meth-
phenoxo oxygen (O1/O1i), imine nitrogen (N1/N1i), and the anol, acetonitrile, and dichloromethane. The complex is
bridging acetate oxygen atom (O4/O4i), and the axial posi- stable in the solid state as well as in the solution phase. The
Scheme 1. Preparative procedure of the ligand and zinc complex (1).
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UV/Vis spectra for the ligand and the trinuclear zinc(II) bands at approximately 423 nm. Upon addition of 3,5-dtbc
complex show high-intensity transitions in the range of 200 a new band was generated at approximately 408 nm, and
to 470 nm. The Schiff base ligand H2L shows the character- with time the spectral run that was carried out immediately
istic absorption bands at 233, 275, 347, and 461 nm. The exhibited an incremental increase in the absorbance nearly
bands at 233 and 275 nm are assigned to a π–π* transition above that band. Since it is well established in the literature
of the C=N chromophore, whereas the band at 347 nm is that 3,5-dtbq shows band maxima in the range from 386 to
due to the n–π* transition, and 461 nm is for intraligand 410 nm in pure methanol,[16c,17] the experiment unequivo-
charge transfer[15] (Figure S2 in the Supporting Infor- cally proves oxidation of 3,5-dtbc to 3,5-dtbq catalyzed by
mation). On complexation, these bands were shifted to a the trinuclear ZnII complex. The formation of the respective
lower wavelength (hypsochromic shift) region (307 and quinone derivative, 3,5-dtbq, was purified by column
423 nm), thus suggesting the coordination of the imine chromatography using a hexane/ethyl acetate eluant mix-
nitrogen and phenolate oxygen with the ZnII ion (Figure S2 ture. The product was isolated by slow evaporation of the
in the Supporting Information). Upon excitation at 307 nm eluant and was identified by H1 NMR spectroscopy (Fig-
in methanolic solution, the zinc complex exhibits a broad ure S4 in the Supporting Information). H1 NMR (CDCl3,
emission centered at 472 nm. Fluorescence properties of the 300 MHz): δH = 1.22 (s, 9 H), 1.26 (s, 9 H), 6.21 (d, J =
complex (Figure S2 in the Supporting Information) indicate 2.13 Hz, 1 H), 6.92 (d, J = 2.10 Hz, 1 H) ppm.
that it can serve as a potential photoactive material. To
probe the solution stability of the complex, we have per-
formed UV/Vis spectral measurements for methanolic solu-
tion of the complex at room temperature at various time
intervals. The ligand-field (LF) band in the visible region
(423 nm) of the complex remained unaffected over a period
of at least 5 days, which revealed that the complex is stable
in solution at room temperature. The ESI mass spectral
study of 1 further corroborates the solution stability.
[Zn3L2(μ-O2CCH3)2(CH3OH)4] (1) exhibits the ESI-MS
(MeOH) molecular ion peak at m/z 921.9673 [1 + H+] in
methanol medium (base peak, calcd. 922.0635 (Figure S3
in the Supporting Information).
Catechol Oxidase Activity
3,5-Di-tert-butylcatechol (3,5-dtbc) is the most widely
used substrate for the study of potential catecholase activity
of biomimicking coordination compounds, primarily for
the following reasons: (i) its low reduction potential makes
it easy to oxidize, (ii) the bulky tert-butyl substituent pre-
vents further over-oxidation reactions such as ring-opening
and (iii) the oxidation product, 3,5-di-tert-butylquinone
(3,5-dtbq), is highly stable and has a characteristic absorp-
tion band maxima at 401 nm in pure methanol.[16b,16c]
As a model of the catechol oxidase enzyme, we have
taken one trinuclear complex of ZnII and examined its effi-
ciency towards oxidation of 3,5-dtbc to 3,5-dtbq
(Scheme 2). The catalytic activity of complex 1 was pursued
by treating 1ϫ10–4 moldm–3 complex solutions with
1ϫ10–2 moldm–3 of 3,5-dtbc. The reaction was monitored
for 1.5 h after addition of 3,5-dtbc to the solution of the
complex in methanol (Figure 2). Initially, complex 1 shows
Figure 2. UV/Vis spectral change of complex at a regular interval
of 5 min with 3,5-dtbc.
The kinetics of the 3,5-dtbc oxidation were determined
by monitoring the increase in the product 3,5-dtbq. The
experimental conditions were the same as reported by Das
et al. earlier.[16] The complex illustrated saturation kinetics
in which an action based on the Michaelis–Menten model
seemed to be appropriate. The value of the Michaelis bind-
ing constant (Km), maximum velocity (Vmax), and rate con-
stant for dissociation of substrate (i.e., turnover number,
kcat) were calculated for the trinuclear zinc complex from
the graphs of 1/V versus 1/[S] (Figures S5 and S6 in the
Supporting Information), known as the Lineweaver–Burk
graph, using Equation (1):
1/V = {Km/Vmax}{1/[S]} + 1/Vmax
(1)
To reveal the high catalytic activity of 1, we drew a com-
parison between our zinc–Schiff base complex and some
other phenoxo-bridged and/or acetato-bridged dinuclear
copper and zinc–Schiff base complexes.[17] The data ob-
tained from the Lineweaver–Burk plot model were used for
a comparison of catalytic activity towards the oxidation of
Scheme 2. Catalytic oxidation of 3,5-dtbc to 3,5-dtbq in air-satu-
rated methanol solvent.
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Table 1. Kinetic parameters for the oxidation of 3,5-dtbc catalyzed by 1 in methanol.
Complex
Vmax [ms–1]
Km [m]
Kcat [h–1]
Ref.
1[a]
3ϫ10–3
1.06ϫ10–3
3.47ϫ10–3
1.04ϫ10–3
4.34ϫ10–3
1.93ϫ10–3
1.05ϫ10–4
1.33ϫ103
this work
[17a]
[Cu2(L1)(μ-OAc)](ClO4)2
[Cu2(Sbal)2(H2O)x]
[Cu2(L2)2(NCO)2]
[Zn2L3Cl3]
6.17ϫ10–4
6.5ϫ10–3
9.84ϫ10–3
8.25ϫ10–4
9.78ϫ10–4
0.9ϫ102
1.28ϫ103
0.98ϫ102
2.97ϫ103
3.52ϫ103
[17b]
[17c]
[16]
[Zn2(L4)2(CH3COO)2]
[16]
[a] Standard error for Vmax [ms–1] = 2.86ϫ10–4; standard error for Km [m] = 1.21ϫ10–4.
3,5-dtbc as shown in Table 1. The kinetic parameters of 1
We also recorded ESI-MS spectra of a 1:100 mixture of
are also presented in Table 1.
complex 1 and 3,5-dtbc in methanol solvent to gain insight
It is unlikely that in zinc complexes with Schiff base-type into this oxidation reaction in solution state. The spectrum
ligands the metal center(s) are involved in the redox process (Figure S7 in the Supporting Information) exhibits a base
with regard to the two-electron oxidation of 3,5-dtbc, as peak at m/z 243 (100%) that corresponds to the quinine
proposed for the copper system. To elucidate the reason sodium aggregate [3,5-dtbq – Na]+. The peak at m/z 550.17
behind catecholase activity exhibited by our synthesized corroborates the formation of [ZnL(dtbc)] species as an in-
ZnII complex, an EPR study was performed. The EPR termediate (Scheme 3).[16a] The peak at m/z 306.11 indicates
study at 77 K, carried out immediately after mixing the ZnII the formation of a mononuclear species as [ZnL], and no
complex with 3,5-dtbc under an inert atmosphere, disclosed peaks appeared above m/z 572.18, which reflects that the
the possible cause of the redox process. Figure 3 shows a trinuclear zinc–Schiff base complex breaks down into mo-
broad, nearly isotropic EPR signal at g ≈ 2.06. Control ex- nonuclear units during the coordination of dtbc to 1 in
periments under identical experimental conditions show methanol.
that the ZnII complex, as well as a mixture of zinc acetate
salt and 3,5-dtbc, are EPR-silent. Thus, the EPR signal,
which is a definite indication of the formation of some li-
gand-centered radical species, is generated only when the
ZnII complex is mixed with 3,5-dtbc, and radical formation
is most likely responsible for that oxidation as reported by
Das et al.[16a] This reaction was also followed in the pres-
ence of a radical scavenger, 2,2,6,6-tetramethylpiperidinoxyl
(TEMPO). Notably, no oxidation of catechol was observed
Scheme 3. Formation of mononuclear intermediate species during
the course of catechol oxidation.
in the presence of two equivalents of TEMPO with respect
to the catalyst used. This result further corroborates that
the catechol oxidation catalyzed by the ZnII complex origi-
nates through radical generation. Moreover, in the catalytic
reaction, when performed under an inert atmosphere, no
3,5-dtbq formation was observed. However, upon exposure
of the reaction mixture to a dioxygen atmosphere, immedi-
ately 3,5-dtbq formation was noticed. This observation in-
deed indicates that dioxygen is one of the active participants
in the catalytic cycle; it converts the semibenzoquinone rad-
ical, formed in the first step of catalysis, to the quinone with
subsequent regeneration of the catalyst.
DNA Cleavage Studies
The irradiation of pBR322 plasmid DNA in the presence
of the zinc complex was studied so as to determine the effi-
ciency with which it sensitizes DNA cleavage. This can be
achieved by monitoring the transition from the naturally
occurring, covalently closed circular form (Form I) to the
open circular relaxed form (Form II). This occurs when one
of the strands of the plasmid is nicked, and can be deter-
mined by gel electrophoresis of the plasmid. Extended irra-
diation results in a buildup of nicks on both strands of the
plasmid, which eventually results in its opening to the linear
form (Form III). When circular plasmid DNA is subjected
to gel electrophoresis, relatively fast migration will be ob-
served for the supercoiled form (Form I). Form II will mi-
grate slowly and Form III will migrate between Form II
and Form I.[18,19],
The ability of the zinc(II)–Schiff base complex to cleave
DNA was assayed with the aid of gel electrophoresis on
pBR 322 DNA as the substrate in a medium of 5 mm tris-
(hydroxymethyl)aminomethane (Tris)-HCl/50 mm NaCl
Figure 3. EPR plot of Zn complex and Zn complex + dtbc.
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buffer (pH 7.1) in the absence of external additives. The tant for a drug to act as an anticancer agent,[20,21] the cyto-
DNA was mixed with different concentrations (25, 50, 75, toxicity of the complex dissolved in DMSO was investigated
and 100 μg) of zinc(II)–Schiff base complex and was incu- against a human hepatocarcinoma cell line (HepG2) by car-
bated at 37 °C for 1 h (Figure 4). Lane 1 in Figure 4 shows rying out an MTT assay. The IC50 values were obtained by
the pBR 322 DNA control. Lane 2 in Figure 4 shows the plotting the cell viability against the concentration of the
DNA treated with 25 μg of the zinc(II)–Schiff base com- complex (Figure 5). The results revealed that the IC50 at
plex. There was a complete cleavage of the DNA with the 48 h [(60Ϯ0.2) μm] is lower than that at 24 h [(70Ϯ0.1) μm],
addition of 25 μg of the complex. Further addition of dif- which clearly indicates that the complex exhibits cytotoxi-
ferent concentrations (50, 75, and 100 μg) of the complex city against HepG2 in a dose- and duration-dependent
in lane 3, lane 4, and lane 5 of Figure 4 did not show bands manner. Thus, the cytotoxicity exhibited by the complex is
for the DNA. This finding clearly suggests that the concen- consistent with its strong binding with DNA, and its effi-
tration of the complex needed to cleave the pBR 322 DNA ciency in cleaving DNA in the absence of an external agent
was 25 μg.
is responsible for its potency in inducing cell death through
different modes.
Figure 4. DNA cleavage activities of 1. Lane 1: Control pBR 322
DNA. Lane 2: pBR 322 DNA + 25 μg of 1. Lane 3: pBR 322 DNA
+ 50 μg of 1. Lane 4: pBR 322 DNA + 75 μg of 1. Lane 5: pBR
322 DNA + 100 μg of 1.
To confirm the cleavage activity of the zinc(II)–Schiff
base complex with the DNA, a UV spectroscopic analysis
was performed for the control pBR 322 DNA and DNA
with different concentrations of the complex (Table S3 in
the Supporting Information). The concentration of the
DNA showed a gradual decrease with increasing concentra-
tions of the complex (Figure S8 in the Supporting Infor-
mation). The concentration of DNA sample could be deter-
mined by the use of UV spectrophotometry. DNA absorbs
UV light very efficiently, which makes it possible to detect
and quantify at concentrations as low as 2.5 ngμL–1. The
nitrogenous bases in nucleotides have an absorption maxi-
mum at about 260 nm. The DNA concentration was calcu-
lated using the formula: DNA concentration (μgmL–1) =
(OD 260)ϫ(dilution factor)ϫ(50 μg DNA per mL)/
(1 OD260 unit).
Figure 5. MTT assay of 1 for 24 and 48 h.
Acridine Orange/Ethidium Bromide (AO/EB) Staining
Apoptotic cell death is known as being characterized by
different cellular changes such as cell shrinkage, nuclear
condensation, DNA fragmentation, membrane blebbing,
and the formation of apoptotic bodies. These apoptotic
characteristics as produced in the HepG2 human hepato-
carcinoma cell by the [Zn3L2(μ-O2CCH3)2(CH3OH)4] (1)
complex were analyzed by adopting AO/EB staining. In this
staining method, the fluorescence pattern depends on the
viability and membrane integrity of the cells. In general,
dead cells are permeable to ethidium bromide and fluoresce
orange-red, whereas live cells are permeable to acridine
orange only and thus fluoresce green. The cytological
changes that were observed in the treated cells are classified
into four types on the basis of the fluorescence emission
and morphological features of chromatin condensation in
the AO/EB stained nuclei: (i) Viable cells, which have highly
organized nuclei, fluoresce green; (ii) early apoptotic cells,
which show nuclear condensation, emit orange-green fluo-
rescence; (iii) in late apoptotic cells with highly condensed
or fragmented chromatin the nuclei fluoresce orange to red;
and (iv) necrotic cells fluoresce orange to red with no indi-
cation of chromatin fragmentation. All these morphological
changes were observed after treatment of the cancer cells
with the complex. Figure 6 indicates the apoptotic and nec-
rotic morphologies induced by the complex at IC50 concen-
tration for 24 h. Since the zinc complex is a completely neu-
tral molecule, it has the natural ability to cross the cell
The control had 6 μgmL–1 of DNA. There was a gradual
decrease in the concentration of the DNA when added with
increasing concentrations of the zinc(II)–Schiff base com-
plex. This clearly shows that the complex played a major
role in the cleavage of the pBR 322 DNA.
Anticancer Activity of the Zinc(II) Complex
The binding affinity of this type of trinuclear zinc–Schiff
base complex to CT DNA[14] (Kb ≈ 104 m–1) prompted us
to carry out a DNA cleavage and cytotoxicity study against
the hepatocarcinoma cell line.
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
Bromide (MTT) Assay
Since the present zinc(II)–Schiff base complex has the membrane with ease and cause apoptosis of the affected
ability to strongly bind and cleave DNA in the absence of cells. Figure 7 shows the efficacy of the complex to induce
a reductant, and since DNA cleavage is considered impor- 53% apoptosis, and there is no indication of necrotic cell
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death by the complex for 24 h relative to untreated controls.
The IC50 values and morphological changes corroborate the
potential anticancer activity of the molecule. However, fur-
ther studies are needed in this direction to confirm the
mode of cell death induced by the complex.
Figure 8. Representative morphological changes observed for
[Zn3L2(μ-O2CCH3)2(CH3OH)4] (1) by means of Hoechst 33258
staining against HepG2 human hepatocarcinoma cell at 24 h of
incubation.
Figure 6. Left: Representative morphological changes produced in
HepG2 cells by [Zn3L2(μ-O2CCH3)2(CH3OH)4] (1) as revealed in
AO/EB staining after 24 h of incubation.
Figure 9. The effect of [Zn3L2(μ-O2CCH3)2(CH3OH)4] (1) on
HepG2 cells as revealed in Hoechst staining. The relative percen-
tage of morphological changes was determined and classified into
two categories: normal and abnormal nuclei relative to the control
cells after 24 h of incubation.
Conclusion
Herein, we report the synthesis and single-crystal isola-
tion of a new acetato-bridged trinuclear zinc(II) complex of
the type [Zn3L2(μ-O2CCH3)2(CH3OH)4], in which L is a
tridentate N,N,O-donor Schiff base ligand. The trinuclear
zinc complex is highly active in catalyzing the aerobic oxi-
dation of 3,5-dtbc to 3,5-dtbq. The reaction follows Mi-
chaelis–Menten enzymatic reaction kinetics with a high
turnover number in methanol. The EPR experiment clearly
exhibits generation of the ligand radical complex in the
presence of 3,5-dtbc, thus showing ligand-centered catechol
Figure 7. The effect of [Zn3L2(μ-O2CCH3)2(CH3OH)4] (1) on
HepG2 cells as revealed in acridine orange and ethidium bromide
staining. The relative percentage of morphological changes was de-
termined and classified into three categories: viable, apoptosis, and
necrosis relative to the control cells after 24 h of incubation.
Hoechst Staining
Morphological changes in the nucleus and chromatin oxidation by 1. It effects more efficient cleavage of double-
were revealed by means of the Hoechst 33528 staining stranded DNA without the requirement of an external
method. The cells treated with IC50 concentration of the agent. The trinuclear zinc complex exhibits the remarkable
complex showed some changes in their morphology of nu- anticancer activity against human hepatocarcinoma cell line
clei relative to the control untreated nuclei. In the untreated (HepG2) in terms of attacking the DNA in cancer cells. On
control cells the nuclei were round with intact chromatin, the basis of the above in vitro studies, research is in progress
whereas after treatment with the complex for 24 h changes in our laboratories to unveil the molecular mechanisms by
such as chromatin marginalization, condensation, and frag- which the complex elicits its biological activity. Moreover,
mentation were observed. Figure 8 indicates the apoptotic detailed experimentation on this complex related to DNA
nuclear morphology induced at IC50 concentration by the cleavage and cytotoxicity will help to determine clinically
complex for 24 h. It is interesting that 55% of treated cells relevant information for developing possible new anticancer
exhibited abnormal nuclei (Figure 9).
drugs.
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Table 2. Crystal data and structure refinement parameters for 1.
Experimental Section
Empirical formula
Formula weight
C36H44N2O14Zn3
924.84
Synthesis of the Ligand and Zinc(II) Complex
Chemicals, Solvents and Starting Materials: High purity O-vanillin
(Fluka, Germany), O-aminophenol (E. Merck, India), zinc acetate
dihydrate (E. Merck, India), 3,5-di-tert-butylcatechol (Aldrich,
UK), and all reagents were purchased from their respective compa-
nies and used as received.
T [K]
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
295(2)
0.71073
orthorhombic
Pbcn
20.1214(16)
9.2144(8)
c [Å]
α [°]
β [°]
20.9937(17)
90
102.665(4)
90
3892.4(6)
4
1.571
1.903
General Syntheses: The Schiff base ligand was synthesized using a
procedure reported in the literature.[14] O-Aminophenol (0.1092 g,
1 mmol) was heated under reflux conditions with O-vanillin
(0.1523 g, 1 mmol) in dehydrated alcohol (20 mL). After 10 h the
reaction solution was kept in an open atmosphere and a red crystal-
line compound was separated out from solution, which was dried
and stored under vacuum over CaCl2 for subsequent use, yield
γ [°]
V [Å3]
Z
ρ [gcm–3]
Absorption coefficient [mm–1]
F(000)
1
0.213 g (87.2%). H NMR (400 MHz, [D6]DMSO): δ = 12.58 (s, 1
H), 8.70 (s, 1 H), 7.26–6.90 (7 H, Ar–H), 5.94 (s, 1 H), 3.93 (s, 3
1904
Crystal size [mm3]
θ Range for data collection [°]
Index ranges (h, k, l)
Reflections collected
Independent reflections
R(int)
0.2ϫ0.2ϫ0.2
3.1 to 27.50
–26,26; –11,11; –27, 27
40204
4431
0.097
H) ppm. IR (KBr pellet): ν = 3365 (s) (νOH), 1618 (s), 1595 (s)
˜
(νC=N), 1509 (s), 1462 (s), 1333 (s), 1245 (s) (νOAr) cm–1. UV/Vis:
λmax = 233, 275, 347, 461 nm. C14H13NO3 (H2L, 243.26): calcd. C
69.12, H 5.39, N 5.76; found C 69.03, H 5.30, N 5.68.
A solution (10 cm3) of H2L (0.486 g, 2 mmol) in methanol was
added dropwise to a solution of Zn(OAc)2·2H2O (0.657 g, 3 mmol)
in the same solvent (15 cm3). The yellow solution was filtered and
the supernatant liquid was kept in air for slow evaporation, yield
0.453 g (69% based on metal salt). 1H NMR (400 MHz, [D6]-
DMSO): δ = 8.90 (s, 1 H), 7.58 (s, 1 H), 6.99–6.40 (5 H, Ar–H),
Data/restraints/parameters
4431/0/240
1.037
R1 = 0.0584, wR2 = 0.1508
0.156/–0.710
GoF on F2
Final R indices [IϾ2σ(I)]
Largest diff. peak/hole [eÅ–3]
length (wavelength scans) of these solutions were recorded at regu-
lar time intervals of 5 min in the wavelength range 300–500 nm. To
determine the dependence of rate on the substrate concentration
and various kinetic parameters, a 10–4 m solution of the complex
was treated with at least 10 equiv. of substrate so as to maintain
the pseudo-first-order condition. The reaction was followed spec-
trophotometrically by monitoring the increase in the absorbance at
408 nm (Quinone band maxima) as a function of time (time scan).
4.13–4.09 (3 H, μ-OAc), 3.78 (3 H, –OCH ) ppm. IR (KBr): ν =
˜
3
3421 (νOH), 1608, 1587 (νC=N), 1475, 1442, 1389 (νOAc) cm–1. UV/
Vis: λmax = 249, 303, 367, 422 nm. C36H44N2O14Zn3 (1, 924.89):
calcd. C 46.75, H 4.79, N 3.03; found C 46.82, H 4.70, N 3.09.
Physical Measurements: Elemental analyses (carbon, hydrogen, and
nitrogen) were performed with a PerkinElmer 2400 CHNS/O ele-
mental analyzer. Infrared spectra were recorded with a Perkin–El-
mer RX1 FTIR spectrometer (4000–300 cm–1) with a crystalline
sample in a KBr pellet. Ground-state absorption was measured
with a JASCO V-530 UV/Vis spectrophotometer. Fluorescence
spectra were recorded with a Hitachi F-4500 fluorescence spectro-
photometer. The EPR spectrum was recorded with a Bruker EMX
DNA Cleavage Studies: Cleavage of DNA by [Zn3L2(μ-O2CCH3)2-
(CH3OH)2] (1) was monitored by agarose gel electrophoresis tech-
niques. The complex (25, 50, 75, and 100 μg) solutions were incu-
bated with bacterial DNA for an hour at 37 °C. After incubation,
bromophenol blue dye (2 μL) was mixed with the complex and
loaded carefully into the electrophoresis chamber wells along with
the control DNA. Tris-acetateethylenediaminetetraacetic acid
(TAE) buffer was used as a running buffer and finally loaded onto
agarose gel; a constant electrical current (50 V) was passed through
it for 30 min. Then the bands were observed in the gel that con-
tained EB under the gel documentation system and photographed
to determine the extent of DNA cleavage. The results were then
compared with the control.
1
X-band spectrometer. The H NMR spectra were recorded with a
Bruker AC300 spectrometer. Thermal analysis was carried out with
a Perkin–Elmer Diamond TG/DTA system. The electrospray ion-
ization (ESI) mass spectrum was recorded with a Waters micro Q-
TOF mass spectrometer.
X-ray Diffraction Study: Single-crystal X-ray diffraction data were
collected with a Rigaku XtaLABmini diffractometer equipped with
a Mercury CCD detector. The data were collected with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 295(2) K
using ω scans (Table 2). The data were reduced using the Crystal
Clear suite, and the space group determination was carried out
using Olex2. The structure was resolved by direct methods and re-
fined by full-matrix least-squares procedures using the SHELXL-
97 software package with the OLEX2 suite.[22,23] CCDC-975401
contains the supplementary crystallographic data for compound 1.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
To confirm the cleavage activity of the complex, UV spectroscopic
analysis was performed. The DNA (1 μL) was diluted with TE
buffer (50 μL), and the absorbance was taken at 260 nm for the
control DNA, along with the test samples that contained different
concentrations of the complex and the DNA. The concentration of
the DNA was calculated using the formula: DNA concentration
(μgmL–1) = (OD 260)ϫ(dilution factor)ϫ(50 μg DNA per mL)/
(1 OD260 unit).
Anticancer Activity of Complex 1
Catalytic Oxidation of 3,5-dtbc: To examine the catecholase activity
of the complex, a 10–4 m solution of 1 in methanol solvent was
treated with 3,5-di-tert-butylcatechol (3,5-dtbc; 100 equiv.) under
aerobic conditions at room temperature. Absorbance versus wave-
Cell Culture: The HepG2 human hepatocarcinoma cell line was
obtained from the National Center for Cell Science (NCCS), Pune,
India. The cells were cultured in Dulbecco’s modified eagle medium
(DMEM) (Sigma–Aldrich, St. Louis, MO, USA) supplemented
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with 10% fetal bovine serum (Gibco) and penicillin (100 UmL–1) Dr. T. K. Paine, IACS, Kolkata for his valuable cooperation with
and streptomycin (100 μgmL–1) as antibiotics (Gibco) in 96-well
culture plates at 37 °C under a humidified atmosphere of 5% CO2
in a CO2 incubator (Forma, Thermo Scientific, USA). All experi-
ments were performed using cells from passage 15 or less.
mass spectral studies. The single-crystal X-ray facility of the De-
partment of Chemical Sciences, IISER Mohali is acknowledged for
the data collection. G. K. thanks the Council of Scientific and In-
dustrial Research (CSIR), New Delhi for a fellowship.
Cytotoxicity Assay (MTT Assay): The complex in the concentra-
tion range 50–500 μmmL–1 dissolved in DMSO was added to the
wells 24 h after seeding 5ϫ103 cells per well in fresh culture me-
dium (200 μL). A solution of DMSO was used as the solvent con-
trol. A miniaturized viability assay using MTT was carried out ac-
cording to the method described by Mosmann.[24] After 24 and
48 h, MTT solution (20 μL) [5 mgmL–1 in phosphate-buffered sa-
line (PBS)] was added to each well. The plates were then wrapped
with aluminum foil and incubated for 4 h at 37 °C. The purple
formazan product was dissolved by the addition of DMSO
(100 μL) to each well. The absorbance was monitored at 570 nm
(measurement) and 630 nm (reference) with a 96-well plate reader
(Bio-Rad, Hercules, CA, USA). Data were collected for three repli-
cates each and used to calculate the mean. The percentage inhibi-
tion was calculated, from this data, using the formula shown below.
[1] J. Reedijk, E. Bouwman, Bioinorganic Catalysis, 2nd ed. (Eds.:
J. Reedijk, E. Bouwman), Dekker, New York, 1993.
[2] S. J. Lippard, J. M. Berg, Principles of Bioinorganic Chemistry,
University Science Books, Mill Valley, CA, 1994.
[3] a) K. D. Karlin, Science 1993, 261, 701–708; b) D. E. Wilcox,
Chem. Rev. 1996, 96, 2435–2458; c) T. M. T. Hall, J. A. Porter,
P. A. Beachy, D. J. Leahy, Nature 1995, 378, 212–216.
[4] a) T. W. Reid, I. B. Wilson, in: The Enzymes, 3rd ed., vol. 4
(Ed.: P. D. Boyer), Academic Press, New York, 1971, p. 373; b)
G. Parkin, Chem. Rev. 2004, 104, 699–767; c) H. Vahrenkamp,
Dalton Trans. 2007, 4751–4759.
[5] a) H. Sakiyama, R. Mochizuki, A. Sugawara, M. Sakamoto,
Y. Nishida, M. Yamasaki, J. Chem. Soc., Dalton Trans. 1999,
997–1000; b) N. V. Kaminskaia, B. Spingler, S. J. Lippard, J.
Am. Chem. Soc. 2000, 122, 6411–6422; c) N. Mitiæ, S. J. Smith,
A. Neves, L. W. Guddat, L. R. Gahan, G. Schenk, Chem. Rev.
2006, 106, 3338–3363; d) A. Tamilselvi, M. Nethaji, G. Mu-
gesh, Chem. Eur. J. 2006, 12, 7797–7806.
[6] a) J. Chen, X. Wang, Y. Zhu, J. Lin, X. Yang, Y. Li, Y. Lu, Z.
Guo, Inorg. Chem. 2005, 44, 3424–3430; b) H. Sakiyama, K.
Ono, T. Suzuki, K. Tone, T. Ueno, Y. Nishida, Inorg. Chem.
Commun. 2005, 8, 372–374.
[7] a) C. Metcalfe, J. A. Thomas, Chem. Soc. Rev. 2003, 32, 215–
224; b) R. Jikido, H. Shiraishi, K. Matsufuji, M. Ohba, H.
Furutachi, M. Suzuki, H. Okawa, Bull. Chem. Soc. Jpn. 2005,
78, 1795–1803.
Acridine Orange (AO) and Ethidium Bromide (EB) Staining: Acri-
dine orange and ethidium bromide staining was performed as de-
scribed by Spector et al.[25] The cell suspension of each sample that
contained 5ϫ105 cells was treated with AO and EB solution
(25 μL, 3.8 μm of AO and 2.5 μm of EB in PBS) and examined with
a fluorescent microscope (Carl Zeiss, Germany) using a UV filter
(450–490 nm). Three hundred cells per sample were counted in
triplicate for each dose point. The cells were scored as viable, apop-
totic, or necrotic as judged by the staining, nuclear morphology,
and membrane integrity,[25] and the percentages of apoptotic and
necrotic cells were then calculated. Morphological changes were
also observed and photographed.
[8] a) H. Zhang, C.-S. Liu, X.-H. Bu, M. J. Yang, Inorg. Biochem.
2005, 99, 1119–1124; b) S. R. Seidel, P. J. Stang, Acc. Chem.
Res. 2002, 35, 972–983.
[9] a) C. R. Choudhury, S. K. Dey, N. Mondal, S. Mitra, S. O. G.
Mahalli, K. M. A. Malik, J. Chem. Crystallogr. 2001, 31, 57–
62; b) C. Biswas, M. G. B. Drew, E. Ruiz, M. Estrader, C. Diaz,
A. Ghosh, Dalton Trans. 2010, 39, 7474–7484; c) S. Thakurta,
J. Chakraborty, G. Rosair, J. Tercero, M. S. El Fallah, E. Gar-
ribba, S. Mitra, Inorg. Chem. 2008, 47, 6227–6235; d) J.-P. Co-
stes, J. Garcia-Tojal, J.-P. Tuchagues, L. Vendier, Eur. J. Inorg.
Chem. 2009, 3801–3806; e) F.-S. Guo, J.-L. Liu, J.-D. Leng,
Z.-S. Meng, Z.-J. Lin, M.-L. Tong, S. Gao, L. Ungur, L. F.
Chibotaru, Chem. Eur. J. 2011, 17, 2458–2466; f) A. Majumder,
G. M. Rosair, A. Mallick, N. Chattopadhyay, S. Mitra, Polyhe-
dron 2006, 25, 1753–1762.
Hoechst 33528 Staining: The human hepatocarcinoma (HePG2)
cells were cultured in six-well plates and treated with IC50 concen-
tration of complexes. After 24 h of incubation, the treated and un-
treated cells were harvested and stained with Hoechst 33258
(1 mgmL–1, aqueous) for 5 min at room temperature. A drop of
cell suspension was placed on a glass slide, and a cover slip was
laid over to reduce light diffraction. At random 300 cells in dupli-
cate were observed at 400ϫ under a fluorescent microscope (Carl
Zeiss, Jena, Germany) fitted with a 377–355 nm filter, and the per-
centage of cells that reflected pathological changes was calculated.
[10] X. Sheng, X. Guo, X.-M. Lu, G.-Y. Lu, Y. Shao, F. Liu, Q.
Xu, Bioconjugate Chem. 2008, 19, 490–498.
[11] A. Silvestri, G. Barone, G. Ruisi, M. T. Lo Giudice, S. Tummi-
nello, J. Inorg. Biochem. 2004, 98, 589–594.
[12] M. Navarro, E. J. Cisneros-Fajardo, A. Sierralta, M. Fernan-
dez-Mestre, P. Silva, D. Arrieche, E. Marchan, J. Biol. Inorg.
Chem. 2003, 8, 401–408.
[13] a) S. Basak, S. Sen, S. Banerjee, S. Mitra, G. Rosair, M. T. G.
Rodriguez, Polyhedron 2007, 26, 5104–5112; b) A. Gupta, J.
Adhikary, T. K. Mondal, D. Das, Ind. J. Chem. A 2011, 50,
1463–1468.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental information such as the UV/Vis and fluores-
1
cence spectrum of 1, ESI mass spectra, H NMR spectrum of 3,5-
dtbq, rate versus [substrate] plot, Lineweaver–Burk plot, DNA
cleavage assay, and bond length and angle parameters is given.
[14] B. Biswas, N. Kole, M. Patra, S. Dutta, M. Ganguly, J. Chem.
Sci. 2013, 125, 1445–1453.
Acknowledgments
[15] J. G. Sole, L. E. Bausa, D. Jaque, An Introduction to Optical
Spectroscopy of Inorganic Solids, John Wiley & Sons, 2005.
[16] a) A. Guha, T. Chattopadhyay, N. D. Paul, M. Mukherjee, S.
Goswami, T. K. Mondal, E. Zangrando, D. Das, Inorg. Chem.
2012, 51, 8750–8759; b) K. S. Banu, T. Chattopadhyay, A.
Banerjee, M. Mukherjee, S. Bhattacharya, G. K. Patra, E. Zan-
grando, D. Das, Dalton Trans. 2009, 8755–8764; c) I. A. Koval,
P. Gamez, C. Belle, K. Selmeczib, J. Reedijk, Chem. Soc. Rev.
2006, 35, 814–840.
The work is supported financially by the Department of Science
and Technology (DST), New Delhi, India under the FAST
TRACK SCHEME for YOUNG SCIENTIST (No. SB/FT/CS-
088/2013 dtd. 21/05/2014). Generous help from Prof. D. Das of the
Department of Chemistry, The University of Calcutta, Kolkata and
Dr. T. Chattopadhyay of Panchokot Mahavidyalaya, Purulia, India
is also gratefully acknowledged. The authors also sincerely thank
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[17] a) R. E. H. M. B. Osório, R. A. Peralta, A. J. Bortoluzzi, V. R.
de Almeida, B. Szpoganicz, F. L. Fischer, H. Terenzi, A. S.
Mangrich, K. M. Mantovani, D. E. C. Ferreira, W. R. Rocha,
W. Haase, Z. Tomkowicz, A. dos Anjos, A. Neves, Inorg. Chem.
2012, 51, 1569–1589; b) C.-T. Yang, M. Vetrichelvan, X. Yang,
B. Moubaraki, K. S. Murray, J. J. Vittal, Dalton Trans. 2004,
113–121; c) A. Biswas, L. K. Das, A. Ghosh, Polyhedron 2013,
61, 253–261.
[21] S. Ramakrishnan, E. Suresh, A. Riyasdeen, V. S. Periasamy,
M. A. Akbarsha, M. Palaniandavar, Dalton Trans. 2011, 40,
3245–3256.
[22] a) G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–
122; b) O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K.
Howard, H. Puschmann, J. Appl. Crystallogr. 2009, 42, 339–
341.
[23] L. J. Farrugia, J. Appl. Crystallogr. 2012, 45, 849–854.
[18] V. G. Vaidyanathan, B. U. Nair, J. Inorg. Biochem. 2003, 94, [24] T. Mosmann, J. Immunol. Methods 1983, 65, 55–63.
121–126.
[25] D. L. Spector, R. D. Goldman, L. A. Leinwand, Cell: A Labo-
ratory Manual, Culture and Biochemical Analysis of Cells, vol.
1, Cold Spring Harbor Laboratory Press, Cold Spring Harbor,
New York, 1998, p. 34.1–34.9.
[19] a) X. W. Liu, J. Li, H. Li, K. C. Zheng, H. Chao, L. N. Ji, J.
Inorg. Biochem. 2006, 100, 385–395; b) H. Chao, W. J. Mei,
Q. W. Huang, L. N. Ji, J. Inorg. Biochem. 2002, 92, 165–170.
[20] L. A. Basile, A. L. Raphael, J. K. Barton, J. Am. Chem. Soc.
1987, 109, 7550–7551.
Received: March 10, 2014
Published Online: ᭿
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Schiff Base Ligands
D. Dey, G. Kaur, A. Ranjani, L. Gayathri,
P. Chakraborty, J. Adhikary, J. Pasan,
D. Dhanasekaran, A. R. Choudhury,
M. A. Akbarsha, N. Kole,
A
crystallographically
characterized
trinuclear zinc(II) complex [Zn3L2-
(μ-O2CCH3)2(CH3OH)4] (1) that contains
an N,O-donor Schiff base ligand
{H2L = 2-[(2-hydroxyphenylimino)methyl]-
6-methoxyphenol} exhibits potential lig-
and-centered catalytic activity relevant to
catechol oxidase. The molecule shows re-
markable cytotoxicity against a human
hepatocarcinoma cell line (HepG2).
B. Biswas* ....................................... 1–10
A Trinuclear Zinc–Schiff Base Complex:
Biocatalytic Activity and Cytotoxicity
Keywords: Zinc / Schiff bases / Catecholase
activity / Medicinal chemistry / Drug deliv-
ery / Antitumor agents
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