One - Pot synthesis, characterization, DNA binding and enzymatic studies of 4-methyl trans -cinnamate zinc(II)-mixed ligand complexes

Article abstract of DOI:10.1080/00958972.2015.1073269

Four new zinc(II) complexes formulated as [Zn(L)₂] (1), [Zn(L)₂(phen)] (2), [Zn(L)₂(bipy)H₂O] (3), and [Zn(en)₂(H₂O)₂](L)₂(H₂O)₂ (4), where HL =

Full text of DOI:10.1080/00958972.2015.1073269

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
One-pot synthesis, characterization, DNA
binding and enzymatic studies of 4-methyl trans-
cinnamate zinc(II)-mixed ligand complexes
Syeda Tahira Hafeez, Muhammad Nawaz Tahir, Saqib Ali, Muhammad Iqbal,
Hussain Gulab & Khurram Shahzad Munawar
To cite this article: Syeda Tahira Hafeez, Muhammad Nawaz Tahir, Saqib Ali, Muhammad Iqbal,
Hussain Gulab & Khurram Shahzad Munawar (2015) One-pot synthesis, characterization, DNA
binding and enzymatic studies of 4-methyl trans-cinnamate zinc(II)-mixed ligand complexes,
Journal of Coordination Chemistry, 68:20, 3636-3650, DOI: 10.1080/00958972.2015.1073269
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1073269
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Date: 28 September 2015, At: 02:57

Journal of Coordination Chemistry, 2015
Vol. 68, No. 20, 3636–3650, http://dx.doi.org/10.1080/00958972.2015.1073269
One-pot synthesis, characterization, DNA binding and
enzymatic studies of 4-methyl trans-cinnamate zinc(II)-mixed
ligand complexes
SYEDA TAHIRA HAFEEZ†, MUHAMMAD NAWAZ TAHIR‡, SAQIB ALI*†,
MUHAMMAD IQBAL§, HUSSAIN GULAB§ and
KHURRAM SHAHZAD MUNAWAR†
†
Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
Department of Physics, University of Sargodha, Sargodha, Pakistan
Department of Chemistry, Bacha Khan University, Charsadda, Pakistan
‡
§
(Received 12 January 2015; accepted 7 July 2015)
2 2 2 2
Four new zinc(II) complexes formulated as [Zn(L) ] (1), [Zn(L) (phen)] (2), [Zn(L) (bipy)H O] (3),
and [Zn(en) (H O) ](L) (H O) (4), where HL = 4-methyl trans-cinnamic acid, bipy = 2,2′-bipyri-
2
2
2
2
2
2
dine, phen = 1,10-phenanthroline, and en = ethylenediamine, have been synthesized and character-
ized by FT-IR and NMR spectroscopy. Single-crystal XRD revealed distorted square-pyramidal
structure for 3 and octahedral for 4. The complexes were screened for DNA interaction via vis-
commetry and UV–visible spectroscopy. The apparent binding constants were calculated to be
4
5
4
4
1
.18 × 10 , 1.26 × 10 , 4.64 × 10
,
and 1.89 × 10 for 1–4, respectively. The binding propensity to
> K > K > K . Furthermore, these complexes demon-
salmon sperm DNA was in the order: K
2
3
4
1
strated efficient inhibition of alkaline phosphatase, which was attributed to the binding of zinc(II) to
the enzyme’s active site.
Keywords: Zinc(II)-mixed ligand complexes; DNA binding; Alkaline phosphatase inhibition
1. Introduction
Carboxylate ligands have diverse coordination modes and give rise to a variety of complexes.
The need for characterization of the metal enzyme centers and also exploration for new mag-
netic or catalytic materials causes an incessant interest in carboxylate chemistry [1]. Simple
aromatic carboxylic acids (e.g. cinnamic acid) have biological applications and their binding
with metals can have synergistic or antagonistic effect on biological activity [2]. Cinnamic
*
Corresponding author. Email: drsa54@hotmail.com
2015 Taylor & Francis
©

Cinnamate zinc(II) complexes
3637
acids and their derivatives are ubiquitous in plant species and possess pharmacological
properties such as antioxidant, antidiabetic, and hepatoprotective [3]. They can scavenge free
radicals and provide protection against certain kinds of mutagens and carcinogens [4].
It is of our interest to study the interaction of 4-methyl trans-cinnamic acid with zinc(II)
and also to evaluate the effect of N, N-donor ligands on these complexes. Zinc is an essen-
tial and beneficial element for human growth. It regulates the activity of more than 300
metalloenzymes. Zinc also possesses antiviral, antibacterial, and wound-healing properties
[
2]. The relatively less explored zinc complexes can mimic active sites of the enzymes con-
taining zinc and can serve as model complexes to study biological systems and have
applications in supramolecular chemistry [5]. Zinc(II) ions are potent inhibitors of alkaline
phosphatase (ALP), a hydrolase enzyme responsible for recycling of phosphates within the
body. The inhibitory effect is due to the replacement of magnesium ions by zinc(II) on the
enzyme’s active site [6].
Design and synthesis of DNA-targeting complexes has significance and application in
biotechnology, molecular biology, and medicine [7–9]. The interaction with DNA can be
through covalent or non-covalent binding such as intercalation, groove, or electrostatic
binding [7, 8, 10–12]. The nature of the metal center, ligands, co-ligands, or cofactors, pH,
temperature, ionic strength, and reaction time are factors in the complex–DNA interactions.
The understanding of such factors would help in designing new drugs [13, 14].
Mixed-ligand metal complexes of 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), or
their modified variants can bind to DNA via a multitude of mechanisms and can cleave
DNA duplex by virtue of their inherent chemical and photochemical reactivities [15]. Vari-
ous analytical techniques can be used to study DNA interactions such as luminescence,
fluorescence, viscosity measurements, UV–visible spectroscopy, and voltammetry [7, 10].
In the present study, we report synthesis and characterization of four new zinc(II)-mixed
ligand complexes with oxygen- and nitrogen-donor ligands. Complexes 1–4 have been
characterized by FT-IR and NMR spectroscopy. X-ray single-crystal structures for 2 and 4
are also reported. The interaction between salmon sperm DNA (SSDNA) and the complexes
was investigated by UV–visible absorption spectroscopy and viscometry. The values of
DNA-binding constant (K ) and Gibb’s free energy change have been calculated. The
b
complexes were also screened for their ALP inhibition activity.
2
2
. Experimental
.1. Materials
Zn(CH COO) ·2H O, 4-methyl trans-cinnamic acid, 1,10-phenanthroline, 2,2′-bipyridine,
3
2
2
ethylenediamine, Na CO , NaHCO and SSDNA were obtained from Fluka, Switzerland
2
3
3,
and used without purification. Methanol and DMSO were purchased from Merck, Germany
and used without purification. Singly distilled water was used in the reactions. p-Nitro-
phenyl phosphate hexahydrate (p-NPP) was purchased from Sigma Aldrich, USA. ALP was
extracted from human serum.
2
.2. Physical measurements
The melting points were recorded on a Gallenkamp (UK) electrothermal melting point
−
1
apparatus. IR spectra were recorded from 4000 to 400 cm using a Thermo Nicolet-6700

3
638
S.T. Hafeez et al.
1
13
(
ATR) FT-IR spectrophotometer. H and C NMR spectra were recorded on a Bruker
Avance Digital 300 MHz FT NMR spectrometer (Switzerland), at room temperature, using
1
13
DMSO as an internal reference [δ H (DMSO) = 2.5 and δ C (DMSO) = 40 ppm]. Chemi-
cal shifts are given in ppm and coupling constant (J) values are in Hz. X-ray single crystal
analyses data were collected on a Bruker Kappa APEX-II CCD diffractometer using gra-
phite-monochromated Mo-Kα radiation (λ = 0.71073 Å). The crystal structures were solved
2
by direct methods followed by final refinement on F with full-matrix least-squares using
SHELXL-97 [16, 17]. DNA-binding studies by UV–visible spectroscopy and enzyme
inhibition studies were performed on a UV-1601 Shimadzu spectrophotometer at room
temperature (25 ± 1 °C).
2
.3. Procedure for the synthesis of 1–4
2
.3.1. [Zn(L) ] (1). Sodium bicarbonate (0.252 g, 3 mmol) was dissolved in distilled water
2
(about 25 mL). An equimolar quantity of 4-methyl trans-cinnamic acid was added dropwise
to the continuously stirring solution of sodium bicarbonate. The temperature of reaction
mixture was adjusted to 50 °C. After complete neutralization of acid with base, aqueous
solution of zinc acetate dihydrate (0.329 g, 1.5 mmol) was added dropwise. The reaction
mixture was stirred for another 2–3 h under the same conditions. The final product was
filtered, washed with distilled water, and air dried (figure 1).
−1
Color and state: white powder; Yield: 0.64 g (79%); m.p.: 365–366 °C; FT-IR (cm) :
507 ν(OCO)asym, 1380 ν(OCO)sym, Δν = 127, 1638 ν(C=C), 3022 ν(Ar–H), 2914 ν(CH3),
20 ν(Zn–O).
1
4
2
.3.2. [Zn(L) phen] (2). The sodium salt of 4-methyl trans-cinnamic acid (NaL) was
2
prepared by the same method as that for 1. After addition of zinc acetate dihydrate
Figure 1. Scheme for synthesis of 1–4.

Cinnamate zinc(II) complexes
3639
(
0.329 g, 1.5 mmol) followed by 2–3 h stirring, 1,10-phenanthroline (0.297 g, 1.5 mM) was
added. Stirring was continued for another 4–5 h under the same conditions. The final
product was filtered, washed with distilled water, and air dried (figure 1).
−
1
Color and state: white powder; Yield: 0.78 g (70%); m.p.: 341–342 °C; FT-IR (cm) :
507 ν(OCO)asym, 1354 ν(OCO)sym, Δν = 153, 1641 ν(C=C), 3066 ν(Ar–H), 2922 ν(CH3),
21 ν(Zn–N), 418 ν(Zn–O).
1
5
2
.3.3. [Zn(L) (bipy)H O] (3). Complex 3 was prepared by same procedure as 2, except
2
2
2
,2′-bipyridine (0.234 g, 1.5 mM) was used as co-ligand instead of 1,10-phenanthroline in
the final step (figure 1). The final product was crystallized in methanol.
−
1
Color and state: white crystalline; Yield: 0.75 g (72%); m.p.: 319–320 °C; FT-IR (cm) :
575 ν(OCO)asym, 1372 ν(OCO)sym, Δν = 203, 1636 ν(C=C), 3031 ν(Ar–H), 2925 ν(CH3),
24 ν(Zn–N), 421 ν(Zn–O).
1
5
2
2
.3.4. [Zn(en) (H O) ](L) (H O) (4). Complex 4 was also prepared by same method as
and 3, with ethylenediamine added as co-ligand in the final step (figure 1). For 4, the pro-
2
2
2
2
2
2
duct was soluble in water which was rotary evaporated. The solid residue was washed with
methanol and recrystallized in distilled water.
−
1
Color and state: white crystalline; Yield: 0.74 g (75%); m.p.: 149–150 °C; FT-IR (cm) :
561 ν(OCO)asym, 1385 ν(OCO)sym, Δν = 176, 1640 ν(C=C), 3031 ν(Ar–H), 2920 ν(CH3),
37 ν(Zn–N), 431 ν(Zn–O).
1
5
2
.4. DNA interaction studies by viscosity measurements
Ubbelohde viscometer was used to perform viscometric measurements. Experiments were
performed at 25 ± 1 °C and flow time was measured using a digital stop watch. The average
of triplicate measurements was taken for each measurement. Between the successive
measurements, the viscometer was rinsed with acetone and air dried. Data are presented as
o 1/3
plots of relative viscosity (η/η ) , versus compound-DNA ratio [(Compound)/(DNA)],
o
where η and η are DNA viscosities, in the presence and absence of the complex, respec-
tively [18, 19].
2.5. DNA interaction studies by UV–visible spectroscopy
Solution of commercial SSDNA was prepared in distilled water and kept at 4 °C. From the
absorbance at 260 and 280 nm (A260/A280), nucleotide to protein (N/P) ratio was greater
than 1.8, which indicated that the DNA was free from protein. The SSDNA concentration
was calculated via absorption spectroscopy using the molar absorption coefficient (ε) value
−
1
−1
–5
of 6600 M cm (260 nm) for DNA [20–23] and was found to be 4.75 × 10 M. This
stock solution was used to prepare working solutions by dilution. Both the sample and the
SSDNA solution were prepared in 50% aqueous DMSO.
During the UV absorbance titrations, the concentration of the compound (0.25 mM) was
kept constant, while that of DNA was varied. To the sample and the reference solutions, an
equivalent concentration of DNA was added to correct for the absorbance of DNA. Before
the absorbance measurements, compound-DNA solutions were allowed to equilibrate for

3
640
S.T. Hafeez et al.
10 min. Absorbance spectra were recorded using a UV-1601 Shimadzu spectrophotometer
at 25 ± 1 °C.
2.6. Assay of ALP activity
The inhibition of ALP was assayed by monitoring the rate of hydrolysis of p-nitrophenyl
phosphate (pNPP) at 25 °C. The assays were prepared using the same method as reported
earlier by our research group [24–27] with slight modifications. The working substrate
solution was prepared by mixing four parts of reagent A (diethanolamine pH 9.8,
−
3
−3
2
mol dm and magnesium chloride 0.5 mmol dm ) and one part of reagent B (p-nitro-
−
3
phenyl phosphate 50 mmol dm ). The substrate solution was incubated for 5 m at 25 °C.
Two milliliters of the substrate was taken in a cuvette and 40 µL of human serum having
an activity of 165 IU L was added. After incubation for 1 min, the absorbance was mea-
sured to check the activity of the enzyme. ALP hydrolyzed the p-NPP and yellow-colored
p-nitrophenol was produced as shown in figure 2.
−
1
Varying concentrations of solutions of 1–4 (20, 40, 60, and 80 μL) from a 12.5 mM stock
solution were added periodically into the cuvette and the mixtures were further incubated
for 3 min. The release of the yellow-colored p-NPP chromophore was monitored at
λ = 405 nm. For accurate results, absorbance measurements were recorded per minute up to
5
min, and the average value of this period was used, from which the % inhibition was
calculated.
3
3
. Results and discussion
.1. FT-IR data
The frequencies of interest are those associated with the carboxylate group, Zn–O and
Zn–N. The asymmetric and symmetric vibrations for the COO group appeared at 1507 and
−
1
1
380, 1507 and 1354, 1575 and 1372, 1561, and 1385 cm for 1–4, respectively. The
difference between the two vibration modes, i.e. Δν is used as a spectroscopic criterion to
predict binding mode of the carboxylate moiety with the metal center [28]. The peak posi-
tion of asymmetric and symmetric vibrations for COO is sensitive to electronic charge den-
sity of C–O bond; higher the difference in their electronic charge density, higher will be the
value of asymmetric vibration and lower will be that of symmetric vibration [4].
−
1
The broadbands observed for 3 and 4 from 2550 to 3600 cm correspond to the O–H of
water. The C–H stretching vibrations for the aromatic moiety were observed at 3022, 3066,
−
1
−1
3031, and 3031 cm
for 1–4, respectively. The band at 2914–2925 cm
for 1–4
Figure 2. Hydrolysis of p-nitrophenyl phosphate by ALP.

Cinnamate zinc(II) complexes
3641
corresponds to C–H bond of the methyl. The vibration bands at 1638, 1641, 1636, and
−
1
1
640 cm correspond to –C=C– present in conjugation with the aromatic moiety. For 2–4,
−
1
bands corresponding to Zn–N vibration appeared at 521, 524, and 537 cm , respectively.
The absorption band corresponding to Zn–O bond stretching was observed in the range of
20, 418, 421, and 431 cm for 1–4, respectively.
−
1
4
3
.2. NMR data
1
13
H NMR and C NMR chemical shifts of HL and its complexes are given in table 1 (atom
numbering is given in figure 3), where comparative NMR analysis shows complex forma-
1
tion. In NaL, O–H signal (at 12.38 ppm) of HL disappeared. In H NMR of all four com-
plexes, signals owing to olefinic protons are from 6.41 to 7.42 ppm, and one signal of
methyl proton is obtained at 2.30–2.35 ppm. Two signals for 1 and 4, while six signals for
2 and 3 appeared in the aromatic region. These additional four signals (for 2 at 9.18 (d),
8.10 and 8.13 ppm (dd), 8.88 and 8.90 (dd), 8.25 ppm (s) and for 3 at 8.81 (d), 7.72 (m),
8.21 (m) and 8.61 ppm (d)) correspond to 1,10-phenanthroline and 2,2′-bipyridine, respec-
tively. In 4, two singlets corresponding to the ethylenediamine (at 1.93 ppm (s) for NH2
and at 2.78 ppm (s) for CH ) also appeared along with the signals belonging to carboxylate.
2
For 3 and 4, singlets at 3.39 and 3.35 ppm gave evidence of coordinated water.
1
3
The C NMR data of HL was also compared with its Zn(II) complexes. In the ligand
1
spectrum, signal at 168.16 ppm was assigned to carboxylate carbon C . The peak position
1
is sensitive to change in its environment and is indicative of complexation. Signal for C
appeared at 168.16 ppm for HL and at 172.69, 173.30, and 171.33 ppm for 1, 3, and 4,
1
respectively. When the carboxylate moiety binds bidentate to the metal center, C gets
1
deshielded. In our complexes, C undergoes deshielding of 3–5 ppm. This may be due to
monodentate binding of 4-methyl trans-cinnamate to zinc. The observation was further
strengthened by crystal structures of 3 and 4. Signals for bipy appeared at 149.59, 120.74,
1
2
40.23, 126.54, and 149.13 ppm for 3. In 4, signal for CH of ethylenediamine appeared at
4.72 ppm.
2
1
13
Table 1.
H and C NMR data (ppm) of zinc(II) complexes with 4-methyl trans-cinnamic acid (HL).
1
13
H/
C
4-methyl trans-cinnamic acid (HL)
NaL
1
2
3
4
O–H
H
12.38 (s)
7.21 (d)
–
–
–
–
–
2
7.21 (d)
[16.20]
6.31 (d)
[15.90]
7.11 (d)
[7.80]
7.37 (d)
[15.90]
6.48 (d)
[15.90]
7.20 (d)
[7.50]
7.42 (d)
[15.90]
6.41 (d)
[15.90]
7.22 (d)
[7.50]
7.47 (d)
[7.50]
7.35 (d)
[15.90]
6.44 (d)
[15.90]
7.17 (d)
[7.50]
7.39 (d)
[16.20]
6.47 (d)
[15.90]
7.19 (d)
[8.10]
[
15.90]
6.47 (d)
16.20]
7.56 (d)
7.50]
7.60 (d)
7.50]
3
H
[
5
6
8
,5∑
H
H
H
[
, 6∑
7.339 (d)
[8.10]
7.49 (d)
[7.50]
7.46 (d)
[7.50]
7.42 (d)
[8.10]
[
2.31 (s)
168.16
144.40
140.61
118.54
128.66
129.97
131.95
21.47
2.197 (s)
175.88
140.77
140.23
122.94
127.64
129.49
132.20
20.36
2.31 (s)
172.69
140.94
139.32
123.13
128.04
129.86
132.98
21.40
2.32 (s)
2.30 (s)
173.30
141.01
139.31
123.03
128.01
129.84
132.96
21.39
2.35 (s)
171.33
139.89
138.18
122.95
127.49
129.73
133.98
21.33
1
2
3
4
5
6
7
8
C
C
C
C
C
C
C
C
–
–
–
–
–
–
–
–
,5∑
, 6∑
1
1
Note: Values in square brackets show the [ H, H] coupling in Hz.

3
642
S.T. Hafeez et al.
1
13
Figure 3. Numbering scheme of HL for H and C NMR interpretation.
3.3. Single crystal X-ray analysis
Crystallographic data and summary of the refinement parameters for the complexes are
given in table 2.
3
.3.1. Crystal structure of 3. Crystal structure for 3 along with the atom connectivities is
shown in figure 4. The crystal was refined in the monoclinic crystal system with space group
Table 2. Crystal data and refinement parameters for 3 and 4.
Complex
3
4
Chemical formula
Formula weight
T (K)
C
30
H
28
N
2
O
5
Zn
24 42 4 8
C H N O Zn
561.910
296(2)
579.99
296(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
P n
5.6114(7)
8.1426(10)
28.490(3)
90
0.71073
Monoclinic
P 2 /n
7.6168(5)
6.0296(3)
30.9371(19)
90
1
α (°)
β (°)
γ (°)
V (Å )
Z
95.023(9)
90
1296.8(3)
2
0.991
584
96.142(3)
90
1412.67(15)
2
3
−
1
Absorption coefficient (mm
F(0 0 0)
)
0.921
616
Crystal size (mm)
θ range for data calculation
Reflection collected
Independent reflection
0.35 × 0.20 × 0.18
1.43–26.00
4856
0.35 × 0.28 × 0.25
2.65–26.00
2773
3417
1.018
2307
1.031
2
Goodness-of-fit on F
Final R indices [I > 2σ(I)]
R
1
= 0.0623
1
R = 0.0387
wR
2
= 0.1137
= 0.0942
wR
R = 0.0495
1
2
= 0.0896
R indices (all data)
R
1
wR
2
= 0.1262
2
wR = 0.0950
Data/restraints/parameters
4856/4/350
2773/6/133

Cinnamate zinc(II) complexes
3643
Figure 4. ORTEP drawing with the numbering scheme of 3 (thermal ellipsoids are drawn at 50% probability
level).
Pn. The molecular structure of 3 revealed that in the complex, zinc is five coordinated,
bonded to two oxygens of two carboxylate ligands, two nitrogens of bipy, and a water mole-
cule. Both carboxylates show monodentate coordination, while bipy is bidentate. The crystal
data are given in table 2, while selected bond lengths and angles are given in table 3.
The geometry around zinc can be characterized by τ (∑) value, i.e. structural distortion
index, ∑ = (β − α)/60, where 1β corresponds to the largest and α to the second largest basal
angle around zinc. For 3, it was calculated to be 0.21. For the perfect square-pyramidal
geometry, ∑ is zero (α = β = 180°), and for the perfect trigonal-bipyramidal geometry, it is
unity (α = 120°) [29, 30]. The calculated ∑ value of 0.21 for the complex suggests a
distorted square-pyramidal arrangement around zinc(II).
The two carboxylate groups chelate to zinc in an asymmetric manner, which is reflected
by a shorter Zn–O1 [1.992(5) Å] bond and a longer Zn–O3 [2.055(5) Å] bond. The
asymmetric coordination is further confirmed by an unequal O–C bond distance. The shorter
Zn–O1 bond is accompanied by a longer O1–C1 bond distance [1.294(8) Å] and the longer
Zn–O3 is accompanied by a shorter O3–C11 bond distance [1.268(9) Å]. The steric
hindrance induced by the bulky carboxylate ligands, electron pair repulsion and the
presence of bipyridine may be responsible for this discrepancy.
The Zn–OH2O bond length is 2.054(6) Å. The nitrogens of bipy also have asymmetric
bond distances; Zn–N1 [2.122(7) Å] and Zn–N2 [2.180(7) Å].
The water molecule in the structure is responsible for intramolecular as well as inter-
molecular H-bonding; bipyridine rings also undergo intermolecular H-bonding as evident
from the packing diagram shown in figure 5. The molecules form 1-D polymeric chains
with base vector [1 0 0].
3
.3.2. Crystal structure of 4. The crystal structure of 4 is depicted in figure 6. Selected
bond lengths and angles for 4 are given in table 3, while crystallographic parameters are
given in table 2. In this complex, zinc(II) is coordinated with two ethylenediamine groups
and two water molecules. All six bonds around zinc are coordinate covalent type. The
geometry around zinc is octahedral and the space group is P 2 /n with monoclinic crystal
1
system. The bond distances around zinc are almost symmetric for ethylenediamine and
same is the case for both water molecules.

3
644
S.T. Hafeez et al.
Table 3. Selected bond lengths (Å) and angles (°) of
3
and 4.
Complex
3
4
Bond lengths (Å)
Zn–O1
Zn–O3
Zn–O5
Zn–N1
Zn–N2
N1–C1
N2–C2
O1–C1
O2–C1
O2–C3
O3–C3
O3–C11
1.992(5)
2.055(5)
2.054(6)
2.122(7)
2.180(7)
—
2.2574(17)
—
—
2.136(2)
2.1379(19)
1.472(3)
1.468(2)
—
—
1.294(8)
1.206(10)
—
—
1.268(9)
1.218(11)
—
1.2352(17)
1.2630(15)
—
O4–C11
—
Bond angles (°)
O1–Zn–O1
O1–Zn–O3
O1–Zn–O5
O3–Zn–O5
O1–Zn–N1
O1–Zn–N2
O3–Zn–N1
O3–Zn–N2
O5–Zn–N1
O5–Zn–N2
N1–Zn–N2
N1–Zn–N1
N2–Zn–N2
C1–N1–Zn
C2–N2–Zn
Zn–O1–C1
Zn–O3–C11
N1–C1–C2
N2–C2–C1
O2–C3–O3
—
96.1(2)
120.3(2)
86.1(2)
105.2(2)
97.8(2)
154.3(2)
86.7(2)
95.2(3)
141.7(3)
76.4(3)
—
—
—
—
109.9(5)
127.8(5)
—
—
—
180.00
—
—
—
89.67(7)
92.58(7)
—
—
—
—
98.32(7)
180.00
180.00
108.54(15)
107.31(12)
—
—
109.8(2)
108.95(13)
123.62(11)
In 4, zinc carries +2 charge, which is balanced by carboxylate ligands present outside the
coordination sphere. There are also two water molecules present outside the coordination
sphere. Figure 7 shows packing diagram of 4. The molecules form a 2-D polymeric network
with base vector [1 0 0], [0 1 0], and in the plane (0 0 1).
3
.4. DNA-binding studies by UV–visible spectroscopy
The interaction of the synthesized complexes with DNA was studied by electronic absorp-
tion spectroscopy. The effect of increasing concentration of SSDNA on the complex was
studied by comparing absorbance of the free complex (0.25 mM) and the complex–DNA
adduct. The absorbance titration experiments were performed by keeping the concentration
of complex constant and varying DNA concentration (2.26–13.57 μM). Successive addition
of DNA produces change in electronic absorption spectrum of the complex, indicating
interaction of the complex with DNA.

Cinnamate zinc(II) complexes
3645
Figure 5. Packing diagram of 3 (hydrogens not involved in H-bonding are omitted for clarity).
Figure 6. ORTEP drawing with the numbering scheme of 4 (thermal ellipsoids are drawn at 50% probability
level).
Benesi–Hildebrand equation [equation (1)] [7, 8] was employed to evaluate binding
parameters:

3
646
S.T. Hafeez et al.
Figure 7. Packing diagram of 4 (hydrogens not involved in H-bonding are omitted for clarity).
Ao
eG
eG
1
¼
þ
ꢁ
(1)
A ꢀ Ao
eHꢀG ꢀ eG eHꢀG ꢀ eG K½DNAꢂ
where K is binding constant, A and A are absorbances of the complex–DNA adduct and pure
o
complex, εH−G, and ε are molar absorption coefficients of the complex–DNA adduct and
G
complex, respectively. Association/binding constants were calculated from the intercept-
to-slope ratio of the plot of 1/[DNA] along the abscissa and A /A − A along the ordinate
o
o
[
31]. The change in Gibb’s free energy was calculated using the following equation [7, 8]:
DG ¼ ꢀRT ln ðKÞ
(2)
Figure 8 depicts the absorption spectrum of 1 along with plots of A /(A − A ) versus 1/
o
o
[DNA] for 1–4, respectively. The best fit line, superimposed on the data according to
equation (1) yields DNA-binding constants (K) and Gibb’s free energy change (ΔG) of
the complex–SSDNA adduct. (The UV–visible spectra of 0.25 mM 2–4 can be seen in
figure S1 (see online supplemental material at http://dx.doi.org/10.1080/00958972.2015.
1
073269), and data for the plots B–D, in tables S1–S4 of Supplementary materials). The
calculated values of binding constants and Gibb’s free energy change (ΔG) for 1–4 are
given in table 4.
Absorbance spectra of the four complexes exhibit a single broadband with λmax at 272.4,
2
79.0, 275.2, and 274.4 nm for 1–4, respectively. The band corresponds to the π–π* transi-
tions of ligand-based aromatic moiety. The strong absorbance of these compounds in the
near-UV region (272–295 nm) is attributed to the long-living triplet excited state of the
aromatic system [8].
Incremental addition of DNA lowers the intensity of absorbance, i.e. hypochromic effect
with no prominent red shift in λmax. The hypochromism may be due to either compactness
in the structure of the complex alone or in the complex–DNA adduct. Hypochromic effect
with no prominent shift (Δλ ≤ 8 nm) indicates outside binding (groove binding) as a domi-
nant mode of interaction [32]. Groove binders induce little or no structural rearrangement in
the DNA and show binding propensity for the AT-rich DNA pockets. The AT-rich base

Cinnamate zinc(II) complexes
3647
(A)
(B)
(C)
(D)
(E)
Figure 8. (A) Absorption spectra of 0.25 mM 1 in the absence (a) and presence of 2.26 (b), 4.32 (c), 6.20 (d),
.92 (e), 9.50 (f), 10.96 (g), 12.32 (h), and 13.57 (i) μM SSDNA. The arrow direction indicates the increasing
SSDNA concentration. (B–D) Plots of A /(A − A ) vs. 1/[DNA] for 1–4, respectively. The best fit line, superim-
posed on the data according to equation (1) yielded DNA-binding constants (K) and Gibb’s free energy change
ΔG) of the complex–SSDNA adduct.
7
o
o
(
pairs not only possess H-bond acceptors (N3 of adenine and O2 of thymine), but can also
develop favorable hydrophobic interactions between the adenine C2 hydrogens and the aro-
matic rings present in the DNA-binding complexes [20, 33]. The low affinity DNA binders
5
have K < 10 [34], so among the synthesized complexes, 2 is a strong binder, while 1, 3,
b
and 4 are weak binders. Highest binding affinity of 2 can be attributed to its extended
aromatic moiety [35]. Overall, the calculated intrinsic binding constants for 1–4 are in

3
648
S.T. Hafeez et al.
Table 4. UV–visible and DNA-binding data for 1–4.
−
1
−1
Complex
λmax (nm)
K (M
)
ΔG (kJ mol )
4
5
4
4
1
2
3
4
272.4
279.0
275.2
274.4
1.18 × 10
1.26 × 10
4.64 × 10
1.89 × 10
−23.22
−29.09
−26.62
−24.39
agreement with those previously reported for Zn(II) complexes [34]. The negative value of
ΔG is indicative of the spontaneiety of the complex–DNA adduct formation.
3
.5. Viscosity measurements
The viscosity measurements are an effective tool while studying the interaction of small
molecules with DNA. The viscosity of DNA solution is sensitive to the variation in length
of DNA. Therefore, measurement of DNA viscosity is considered as a critical method for
elucidation of the complex–DNA interaction mode. Measurement of relative viscosity has
proved to be a reliable technique for DNA-binding studies. When a complex exclusively
binds in the DNA grooves, it causes a kink or bend in DNA helix thus reducing its effective
length which results in a decrease in the DNA solution’s viscosity [8, 19, 36].
−
5
A series of solutions were made keeping DNA concentration constant (4.75 × 10 M),
and concentrations of 1–4 were varied. All of the samples were allowed to equilibrate for
1
/3
1
0 min prior to the flow time measurement. The values of the relative viscosity (η/η )
o
1
/3
were calculated from (t/to) ratio for all the samples, where η, η , t, and t represent the
o
o
viscosity and time of the DNA solution in the presence and the absence of the complex,
1
/3
respectively. Plot of (η/ηo) versus (compound)/(DNA) ratio is shown in figure 9, indicat-
ing that the viscosity decreases upon addition of increasing the amount of compound in
each case, therefore, the groove-binding mode is deduced as binding mode of the
complexes with DNA. The predicted mode is in agreement with the results of UV–visible
spectroscopy.
4
3
3
3
3
3
2
2
2
.0
.8
.6
.4
.2
.0
.8
.6
.4
Complex 1
Complex 2
Complex 3
Complex 4
3
5
85
135
r = [COMPLEX]/[DNA]
Figure 9. Effect of increasing concentration of 1–4 on relative viscosity of SSDNA.

Cinnamate zinc(II) complexes
3649
Figure 10. ALP inhibition profile of ligand and its Zn(II) complexes (1–4).
3.6. ALP inhibition study
The effect of varying concentration of synthesized zinc(II) complexes on the activity of the
enzyme; ALP was studied for hydrolysis of p-NPP (p-nitrophenylphosphate). ALP catalyzes
the transfer of phosphate groups to alcohol (transphosphorylation) or water (hydrolysis) using
a variety of phosphor-monoesters and are characterized by a high-pH optima and a broad
range of substrate specificity [37]. The concentration of p-NPP is directly related to the
activity of inhibitor and was monitored spectrophotometrically. Here, we have observed that
the ligand itself was inactive against ALP. For 1–4, observed maximum values of %
inhibition were 100, 80.6, 100, and 90.54, respectively, at 1.11 mM concentration (figure 10).
A comparison of inhibition activities of ligand and its complexes indicates that these might
2
+
be the Zn responsible for deactivation of enzyme. Zinc ions decrease enzyme’s activity by
2
+
2+
occupying Mg -binding sites, in addition to Zn -binding sites, thus rendering the enzyme’s
active sites blocked [6].
4
. Conclusion
Four new zinc(II) complexes of 4-methyl trans-cinnamate as a main ligand and
,10-phenanthroline, 2,2′-bipyridine, and ethylenediamine as co-ligands have been synthe-
1
sized and characterized by FT-IR and NMR spectroscopy. Distorted square-pyramidal struc-
ture for 3 and octahedral for 4 were confirmed by single-crystal XRD. DNA-binding
studies by UV–visible spectroscopy and viscometry illustrated groove-binding mode of the
complexes with SSDNA. Negative ΔG values indicate spontaneity of binding with SSDNA.
ALP inhibition studies revealed that the complexes are inhibitors of ALP and inhibition is
concentration dependant.
Supplementary material
Crystallographic data for the crystal structures reported in this article have been deposited with
the Cambridge Crystallographic Data Center, CCDC # 1042909 (3) and 1042910 (4). Copies
of this information may be obtained free of charge from the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ [Fax: +44(1223)336–033 or Email: deposit@ccdc.cam.ac.uk].

3
650
S.T. Hafeez et al.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[
[
[
1] D. Dobrzyńska, T. Lis, L.B. Jerzykiewicz. Inorg. Chem. Commun., 8, 1090 (2005).
2] V. Zeleňák, M. Sabo, W. Massa, P. Llewellyn. Inorg. Chim. Acta, 357, 2049 (2004).
3] S. Adisakwattana, W. Sompong, A. Meeprom, S. Ngamukote, S. Yibchok-anun. Int. J. Mol. Sci., 13, 1778
(
2012).
[
[
[
[
[
[
4] V. Zeleňák, I. Císařová, P. Llewellyn. Inorg. Chem. Commun., 10, 27 (2007).
5] S. Caglar, S. Demir, Z. Heren, O. Büyükgüngör. Polyhedron, 30, 1389 (2011).
6] R.L. Dean. Biochem. Mol. Biol. Educ., 30, 401 (2002).
7] M. Sirajuddin, S. Ali, N.A. Shah, M.R. Khan, M.N. Tahir. , Spectrochim. Acta, Part A, 94, 134 (2012).
8] M. Sirajuddin, S. Ali, A. Haider, N.A. Shah, A. Shah, M.R. Khan. Polyhedron, 40, 19 (2012).
9] Y.-G. Sun, K.-L. Li, Z.-H. Xu, T.-Y. Lv, S.-J. Wang, L.-X. You, F. Ding. J. Coord. Chem., 66, 2455 (2013).
[
10] F. Asghar, A. Badshah, A. Shah, M.K. Rauf, M.I. Ali, M.N. Tahir, E. Nosheen, Z. Rehman, R. Qureshi.
J. Organomet. Chem., 717, 1 (2012).
[
[
[
[
[
[
11] M. Jiang, Y.-T. Li, Z.-Y. Wu. J. Coord. Chem., 65, 1858 (2012).
12] H. Wu, Y. Bai, J. Yuan, H. Wang, G. Pan, X. Fan, J. Kong. J. Coord. Chem., 65, 2839 (2012).
13] D.-D. Li, Z.-W. Tao. J. Coord. Chem., 66, 4237 (2013).
14] K. Pothiraj, T. Baskaran, N. Raman. J. Coord. Chem., 65, 2110 (2012).
15] C.V. Sastri, D. Eswaramoorthy, L. Giribabu, B.G. Maiya. J. Inorg. Biochem., 94, 138 (2003).
16] G.M. Sheldrick. SHELXS-97, Program for X-ray Crystal Structure Solution, Göttingen University, Göttingen
(
1997).
[
17] G.M. Sheldrick. SHELXS-97, Program for X-ray Crystal Structure Refinement, Göttingen University,
Göttingen (1997).
[18] J. Liu, T. Zhang, T. Lu, L. Qu, H. Zhou, Q. Zhang, L. Ji. J. Inorg. Biochem., 91, 269 (2002).
[19] J. Lu, H. Guo, Y. Zhang, J. Jiang, Y. Liu, L. Zang, J. Huang. J. Coord. Chem., 65, 1765 (2012).
[20] M. Sirajuddin, S. Ali, A. Badshah. J. Photochem. Photobiol., B, 124, 1 (2013).
[21] R.A. Hussain, A. Badshah, M.N. Tahir, B. Lal, I.A. Khan. Aust. J. Chem., 66, 626 (2013).
[22] A.K. Asatkar, S. Nair, V.K. Verma, C.S. Verma, T.A. Jain, R. Singh, S.K. Gupta, R.J. Butcher. J. Coord.
Chem., 65, 28 (2012).
[
[
[
[
[
[
[
[
[
23] Y.-F. Chen, M. Liu, J.-W. Mao, H.-T. Song, H. Zhou, Z.-Q. Pan. J. Coord. Chem., 65, 3413 (2012).
24] T. Koike, E. Kimura. J. Am. Chem. Soc., 113, 8935 (1991).
25] W.H. Chapman Jr., R. Breslow. J. Am. Chem. Soc., 117, 5462 (1995).
26] S.T. Hafeez, S. Ali, M.N. Tahir, M. Iqbal, K.S. Munawar. J. Coord. Chem., 67, 2479 (2014).
27] N. Ali, M.N. Tahir, S. Ali, M. Iqbal, K.S. Munawar, S. Perveen. J. Coord. Chem., 67, 1290 (2014).
28] V. Zeleňák, Z. Vargová, K. Györyová. Spectrochim. Acta, Part A, 66, 262 (2007).
29] Z. Rehman, S. Shahzadi, S. Ali, G.-X. Jin. Turk. J. Chem., 31, 435 (2007).
30] Z. Rehman, N. Muhammad, S. Ali, A. Meetsma. Acta Crystallogr., E63, m89 (2007).
31] A. Shah, E. Nosheen, S. Munir, A. Badshah, R. Qureshi, Z. Rehman, N. Muhammad, H. Hussain.
J. Photochem. Photobiol., B, 120, 90 (2013).
[
[
[
32] S.S. Kalanur, U. Katrahalli, J. Seetharamappa. J. Electroanal. Chem., 636, 93 (2009).
33] I. Haq. Arch. Biochem. Biophys., 403, 1 (2002).
34] G. Barone, A. Terenzi, A. Lauria, A.M. Almerico, J.M. Leal, N. Busto, B. García. Coord. Chem. Rev., 257,
2848 (2013).
[
[
[
35] S. Anbu, M. Kandaswamy. Polyhedron, 30, 123 (2011).
36] J. Lu, X. Liao, B. Wu, P. Zhao, J. Jiang, Y. Zhang. J. Coord. Chem., 66, 1574 (2013).
37] M.R. Malik, V. Vasylyeva, K. Merz, N. Metzler-Nolte, M. Saleem, S. Ali, A.A. Isab, K.S. Munawar,
S. Ahmad. Inorg. Chim. Acta, 376, 207 (2011).