Designing of homo and heteroleptic zinc(II) carboxylates: synthesis, spectroscopic characterizations, DNA binding study, CTAB interaction and in vitro antimicrobial evaluations

Article abstract of DOI:10.1007/s13738-019-01594-6

Synthesis of two homoleptic and five heteroleptic zinc (II) carboxylate complexes with two different ligands: HL¹ = 3-chlorobenzoic acid and HL² = 2-(4-chlorophenyl) acetic acid have been reported in this paper. The general formulae of the two homoleptic complexes are: Zn(L¹)₂(1), and Zn(L²)₂(2). Similarly, the general formulae for two different types of heteroleptic complexes are: (Type-I): [(Zn)₂(L¹)₄(bipy)₂(H₂O)] (3), [Zn(L²)₂(bipy)(H₂O)] (4) and (Type-II): [ZnL¹L²] (5), [ZnL¹L²(py)] (6) and [ZnL¹L²(bipy)] (7). The synthesized complexes were characterized in the solid state by FT-IR, CHN analyses and in solution state by NMR (¹H, ¹³C) spectroscopy. Complexes 3 and 4 were also characterized by single crystal analysis where data revealed that the geometry around each Zn atom is distorted trigonal bipyramidal and octahedral, respectively. The synthesized complexes were interacted with SS-DNA and CTAB (surfactant). Interaction of the synthesized compounds with SS-DNA was studied by UV–visible spectroscopy and viscometry and intercalative mode of interaction was exhibited. Moreover, the interaction of the synthesized complexes with CTAB was studied by conductometry showing a strong binding that is evident from higher CMC and negative Gibbs free energy of micellization (ΔGm) values. The tested compounds were further screened for in vitro antibacterial and antifungal activities and were found active against the studied strains of bacteria and fungus.

Full text of DOI:10.1007/s13738-019-01594-6

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01594-6
ORIGINAL PAPER
Designing of homo and heteroleptic zinc(II) carboxylates: synthesis,
spectroscopic characterizations, DNA binding study, CTAB interaction
and in vitro antimicrobial evaluations
1
2
1
1
1
3
Kaleem Ullah · Muhammad Sirajuddin · Muhammad Zubair · Ali Haider · Saqib Ali · Faizan Ullah ·
4
4
5
Grzegorz Dutkiewicz · Maciej Kubicki · Corrado Rizzoli
Received: 13 August 2018 / Accepted: 7 January 2019
©
Iranian Chemical Society 2019
Abstract
1
Synthesis of two homoleptic and five heteroleptic zinc (II) carboxylate complexes with two different ligands: HL =3-chlo-
2
robenzoic acid and HL =2-(4-chlorophenyl) acetic acid have been reported in this paper. The general formulae of the two
1
2
homoleptic complexes are: Zn(L ) (1), and Zn(L ) (2). Similarly, the general formulae for two different types of heteroleptic
2
2
1
2
1
2
1 2
complexes are: (Type-I): [(Zn) (L ) (bipy) (H O)] (3), [Zn(L ) (bipy)(H O)] (4) and (Type-II): [ZnL L ] (5), [ZnL L (py)]
2
4
2
2
2
2
1
2
(
6) and [ZnL L (bipy)] (7). The synthesized complexes were characterized in the solid state by FT-IR, CHN analyses and in
1 13
solution state by NMR ( H, C) spectroscopy. Complexes 3 and 4 were also characterized by single crystal analysis where
data revealed that the geometry around each Zn atom is distorted trigonal bipyramidal and octahedral, respectively. The
synthesized complexes were interacted with SS-DNA and CTAB (surfactant). Interaction of the synthesized compounds
with SS-DNA was studied by UV–visible spectroscopy and viscometry and intercalative mode of interaction was exhibited.
Moreover, the interaction of the synthesized complexes with CTAB was studied by conductometry showing a strong bind-
ing that is evident from higher CMC and negative Gibbs free energy of micellization (ΔGm) values. The tested compounds
were further screened for in vitro antibacterial and antifungal activities and were found active against the studied strains of
bacteria and fungus.
Keywords Zn carboxylates · Spectroscopic characterization · DNA interaction · CTAB interaction · Antimicrobial activity
Introduction
Kaleem Ullah and Muhammad Sirajuddin have equal contribution.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01594-6) contains
supplementary material, which is available to authorized users.
At present, humongous amount of attention has been dealt
on designing and synthesis of coordination complexes due
to their interesting structures and prospective applications
in the field of biological activities, molecular magnetism
and catalysis [1–3]. The chemistry of various derivatives of
aromatic carboxylic acids such as phenyl acetic acid and ace-
tylsalicylic acids have been a subject of interest in life sci-
ences, especially for their anti-inflammatory, antipyretic and
in vitro antitumor properties [4–6]. The synthesis of metal
complexes in which carboxylic acid act as a ligand is a topic
of interest in pharmaceutical, medicinal and bioinorganic
chemistry as an approach to the discovery of new potentially
active drugs [7]. Out of the carboxylate complexes, zinc(II)
carboxylates are of particular interest because of their struc-
tural diversity caused by, first, different geometries adopted
by zinc center, and second, the attached carboxylate ligands
can bind the central zinc via different binding modes such
*
Muhammad Sirajuddin
m.siraj09@yahoo.com
1
2
3
4
5
Department of Chemistry, Quaid-i-Azam University,
Islamabad 45320, Pakistan
Department of Chemistry, University of Science
and Technology Bannu, Bannu, KPK 28100, Pakistan
Department of Botany, University of Science and Technology
Bannu, Bannu, KPK 28100, Pakistan
Department of Chemistry, Adam Mickiewicz University
in Poznan, Poznan, Poland
Dipartimento di Chimica Generale ed Inorganica,
Chimica Analitica, Chimica Fisica, Centro di Studio per la
Strutturistica Diffrattometrica del C.N.R., Università di
Parma, 43100 Parma, Italy
Vol.:(0
1
123456789)
3

Journal of the Iranian Chemical Society
as monodentate, bidentate and bridging [8, 9]. This struc-
tural diversity results in attractive catalytic and biological
applications where the oxidation state of zinc metal, type
of carboxylate ligands, as well as their geometry around the
zinc center are the key factors influencing the relationship
between structure and activity [10–12].
sperm DNA (SS-DNA) (Arcos) was used as received from
Fluka, Switzerland. Analytical grade ethanol, methanol and
DMSO were obtained from Merck Chemicals (Germany)
and used without further purification.
Physical measurements
DNA is the primary target for many anticancer drugs due
to its prime role in cell life. It is highly important to know
the interaction mode of the anticancer drug as DNA offers
a number of interactive sites for covalent and non-covalent
binders [13]. The synthesis of new compounds with better
binding affinity like cis-platin is the demand of the day for
nucleic acid structures [14]. The study of the interaction of
transition metal complexes with DNA has been the main
focus of recent research. Subsequent structural changes in a
DNA strands can easily be examined by a number of experi-
mental techniques [15].
Melting points of all the complexes were recorded on
Gallenkamp (UK) electrothermal melting point appara-
−
1
tus. FT-IR spectra were recorded from 4000 to 400 cm
1
13
using a Bruker FT-IR spectrophotometer. { H} and { C}
NMR spectra were recorded on a Bruker Advance Digital
300 MHz FT NMR spectrometer (Switzerland), at room
1
temperature, using DMSO as an internal reference [δ H
1
3
(DMSO) = 2.5 ppm and δ C (DMSO) = 40 ppm]. DNA-
binding interaction studies were performed with a Perkin
Elmer Lambda 20, double-beam spectrophotometer and
ubbelohde viscometer. Inolab 720 Precision Conductivity
N-donor heterocyclic ligands, such as 2,2′-bipyridine
and 1,10-phenanthroline possess good coordinating ability
due to π–π interactions and thus their use for complexation
import enhancement in various chemical and biological
properties [16, 17].
−
1
Meter with a cell constant value of 0.475 cm was used for
the measurement of electrical conductivities of CTAB and
the synthesized zinc(II) carboxylates.
Data for compound 3 was collected on a Bruker APEX-II
CCD diffractometer radiation at 294(2) K. Unit cell param-
eters were determined using the APEX2 program. Data
reduction was carried out by the SAINT program. Correc-
tion for absorption was performed using the SADABS [18]
program and SHELXT was used to solve the structure by
direct methods [19]. SHELXL2014/7 [20] was used for ani-
sotropic refinement using full matrix least-squares for all
non-H atoms.
The drugs can be transported to the targeted area via drug
carrier systems. Out of these systems, a surfactant can be a
potential drug carrier because of its property of micelle for-
mation that structurally resembles the cell membrane, creat-
ing a solubilization environment for the drug and increases
its availability to the target site. Therefore, the study of inter-
actions between coordination complexes and surfactants is
of prime importance. Stability of these complex-surfactant
systems is highly dependent upon the geometry and structure
of the complexes.
For compound 4 data were collected at 100(1) K by the
ω-scan technique on Agilent Technologies Xcalibur four-cir-
cle diffractometer with Eos CCD detector and graphite-mon-
Here, in this paper we are reporting the synthesis of
seven new homoleptic and heteroleptic [type (I) and (II)]
carboxylate complexes composed of aromatic carboxylic
acids along with the incorporation of pyridine and bipy-
ridine ligands. These complexes have been interacted with
salmon sperm DNA (SS-DNA), where the interaction stud-
ies are explored by UV–visible absorption spectroscopy and
viscometry. The interaction of these complexes with cetyl
N,N,N-trimethylammonium bromide (CTAB, surfactant) has
been investigated using conductometric method. Moreover,
these complexes have further been screened for antifungal
and antibacterial activities.
ochromated MoK radiation (λ=0.71069 Å). The data were
α
corrected for Lorentz-polarization, as well as, for absorp-
tion effects. Precise unit-cell parameters were determined
by a least-squares fit of 973 (6), 7203 (7), and 13,517 (8)
reflections of the highest intensity, chosen from the whole
experiment. The structures were solved with SIR92 [21] and
2
refined with the full-matrix least squares procedure on F by
SHELXL-2013 [20].
Synthesis of Zn(II) carboxylate complexes
Procedures for the synthesis of complexes (1–7)
1
Experimental
[Zn(L ) ] (1): The sodium salt of 3-chlorobenzoic acid
2
1
(
HL ) was prepared by a dropwise addition of aqueous
Materials
solution of sodium bicarbonate (0.252 g, 3 mmol) to the
1
suspended solution of HL (0.518 g, 3 mmol) in water with
4
-chlorophenylacetic acid, 3-chlorobenzoic acid, zinc nitrate
constant stirring at 40 °C [22]. The mixture was stirred
till the appearance of clear solution. After that, aqueous
solution of zinc nitrate hexahydrate (0.447 g, 1.5 mmol)
hexahydrate, pyridine, 2,2′-bipyridine and CTAB were
obtained from Sigma Aldrich (USA). Sodium salt of Salmon
1
3

Journal of the Iranian Chemical Society
was added dropwise to the reaction mixture and stirred
data (calculated value/found value): C (51.37/51.82), H
(2.80/2.89), N (3.0/3.10).
1
at 40 °C for 3–4 h. The white precipitates of [Zn(L ) ]
2
1
2
1
2
therefore formed were filtered, washed with distilled water
[ZnL L (bipy)] (7): Sodium salts of HL and HL
and then air dried.
(1.5 mmol each) were prepared separately as described for
complex 3 and 4, respectively. The methanolic solution of
zinc nitrate hexahydrate (0.447 g, 1.5 mmol) was added
Yield: 70%; M.P: 241–243 °C; molecular weight: 376.5;
molecular formula: C H Cl O Zn; elemental data (calcu-
1
4
8
2
4
1
lated value/found value): C (44.66/44.32), H (2.14/2.20).
dropwise to the HL solution followed by the addition of
2
2
[
Zn(L ) ] (2): Complex 2 was synthesized using a similar
HL solution. Then 2,2′-bipyridine (1.5 mmol) was added
2
procedure as described for complex 1 except sodium salt
in stoichiometric amount (1.5 mmol) to the above reaction
mixture. After 24 h of stirring at 40 °C, the clear solution so
formed was rotary evaporated. The solid product obtained
was washed with distilled water and air dried.
2
of 2-(4-chlorophenyl) acetic acid (HL ) was used instead
1
of HL .
Yield: 75%; M.P: 254–255 °C; molecular weight: 404.6;
molecular formula: C H Cl O Zn; elemental data (calcu-
Yield: 75%; M.P: 188–190 °C; molecular weight: 546.7;
molecular formula: C H Cl O N Zn; elemental data (cal-
1
6
12
2
4
lated value/found value): C (47.50/48.0), H (2.99/3.04).
2
5
18
2
4
2
1
1
[
(Zn) (L ) (bipy) (H O)] (3): Sodium salt of HL was
culated value/found value): C (54.92/55.02), H (3.32/3.50),
2
4
2
2
synthesized as described in the synthesis procedure of com-
plex 1, except solvent media for the ligand was methanol,
however that for sodium bicarbonate was water. Then the
methanolic solution of zinc nitrate hexahydrate (0.447 g,
N (5.12/5.01).
DNA interaction assay by UV–visible spectroscopy
1
.5 mmol) was added to the solution of sodium salt of
In distilled water 2 mg DNA was dissolved and stirred for
overnight to give the DNA solution. From the UV-absorb-
ance data at 260 and 280 nm the nucleotide–protein ratio
(N/P ratio) of 1.8 was obtained showing that DNA is free of
protein. The DNA concentration (ε=6600 M) was calculated
1
HL , followed by the addition of 2,2′-bipyridine (0.235 g,
1
4
.5 mmol). The reaction mixture was stirred for 3–4 h at
0 °C. The solvent mixture was rotary evaporated and the
dried product was recrystallized in methanol.
−
5
Yield: 78%; M.P: 219–221 °C; molecular weight: 1083.3;
molecular formula: C H Cl N O Zn ; elemental data (cal-
via absorption spectroscopy and was found 4.15×10
M
[23, 24]. The concentration of the compound was kept con-
stant while that of DNA was varied. To abrogate the concen-
tration of DNA, same amount of DNA was added both to the
reference and sample solutions. Compound-DNA solutions
were allowed to incubate for about 10 min at room tempera-
ture before measurements were made. Absorption spectra
were recorded using cuvettes of 1 cm path length at room
temperature (25± 1 °C).
48
34
4
4
9
2
culated value/found value): C (53.17/53.0), H (3.14/3.23).
2
[
Zn(L ) (H O)(bipy)] (4): Complex 4 was synthesized
2
2
using a similar procedure as described for complex 3 except
2
1
HL was used instead of HL .
Yield: 72%; M.P: 234–236 °C; molecular weight: 580.8;
molecular formula: C H Cl O N Zn; elemental data (cal-
2
6
24
2
5
2
culated value/found value): C (53.77/53.62), H (4.17/4.02),
N (4.82/4.91).
1
2
1
2
[
ZnL L ] (5): Sodium salts of HL and HL (1.5 mmol
DNA interaction assay by viscosity measurements
each) were prepared separately as described for complex 1
and 2, respectively. An aqueous solution of zinc nitrate hexa-
Ubbelohde viscometer was used to find the viscosity at a
room temperature (25± 1 °C). Flow time was measured with
a digital stopwatch and each sample was measured three
times to calculate the average flow time. Data were presented
1
hydrate (0.447 g, 1.5 mmol) was added dropwise to the HL
2
solution followed by the addition of HL solution. The reac-
tion mixture (solution A) was stirred for 24 h at 40 °C. The
final product was filtered and washed with distilled water
and was air dried.
1
/3
as (η/η ) vs complex–DNA ratio, [complex]/[DNA]. The
o
viscosity of DNA in the presence and absent of compound
Yield: 76%; M.P: 240–242 °C; molecular weight: 390.5;
molecular formula: C H Cl O Zn; elemental data (calcu-
are represented by η and η , respectively. From the observed
o
flow time of DNA containing solutions. Viscosity values
1
5
10
2
4
lated value/found value): C (46.13/47.02), H (2.58/2.60).
were calculated [25].
1
2
[
ZnL L (py)] (6): Complex 6 was synthesized using a
similar procedure as described for complex 5, except pyri-
dine was also added in stoichiometric amount (1.5 mmol) to
the solution A. This reaction mixture was further stirred for
Complex–CTAB interaction study by conductance
The conductance of compound-surfactant solutions was
measured using LR 01/T cell coupled to a Microprocessor
Precision Conductivity Meter LF 3000 (WTW) calibrated
with KCl solution before measurements, to determine the
critical micelle concentration (CMC) values. Circulating
2
4 h at 40 °C. The product formed was filtered and washed
with distilled water.
Yield: 75%; M.P: 268–270 °C; molecular weight:
4
67.6; molecular formula: C H Cl O NZn; elemental
20 13 2 4
1
3

Journal of the Iranian Chemical Society
thermostated liquid was used for maintaining the tempera-
ture of the cell constant (± 0.01 K). During conductance
measurement the concentration of the CTAB was varied
while that of the compound was kept constant. The repro-
ducibility of conductance measurements was estimated to be
12 mg/mL in (DMSO) was transferred to a non-solidified
SDA and the tubes were then allowed to solidify in slant-
ing position at room temperature. Each tube was inoculated
with 4 mm diameter piece of inoculum from 7 days old
fungal culture. The media supplemented with DMSO and
Terbinafine (200 µL/mL) were used as negative and positive
controls, respectively. The tubes were incubated at 28 °C
for 7 days and growth was determined by measuring linear
growth (mm) and growth inhibition was calculated with ref-
erence to the negative control.
±
0.5%. The uncertainty in the composition and temperature
−
1
was estimated as ± 0.0005 mol and ± 0.1 K in the molar
concentration and temperature, respectively.
Antibacterial assay
Agar well-diffusion method [26] was used for the evaluation
of bacterial activity of the tested compounds against four
bacterial strains: Staphylococcus aureus, Enterobacter aero-
Results and discussion
genes, Escherichia coli and Bacillus subtilis. Broth culture
FT‑IR results
6
(
0.75 mL) containing ca, 10 colony forming units (CFU)
per mL of the test strain was added to 75 mL of nutrient
agar medium at 45 °C, mixed well, and then poured into a
The FT-IR data for the selected peaks are shown in Table 1
while a representative spectrum is given in Suppl. Fig.
S1. The binding of carboxylate ligands in complexes 1–7
is confirmed by the presence of Zn–O absorption bands
1
4 cm sterile Petri plate. The media was allowed to solidify
and 8 mm wells were dug with a sterile metallic borer. Then
a DMSO solution of test sample (100 mL) at 1 mg/mL was
added to the respective wells. DMSO served as negative con-
trol, and the standard antibacterial drugs Kanamycin Sulfate
−
1
observed at 426, 418, 415, 416, 427, 428 and 415 cm ,
respectively and the shifting of C=O absorption bands
towards lower wavenumber value compare to that of free
ligands [27]. The binding and monodentate mode of the
carboxylate moiety was determined from the difference
of symmetric and asymmetric stretching frequencies
(
1 mg/mL) was used as the positive control. Triplicate plates
of each bacterial strain were prepared which were incubated
aerobically at 37 °C for 24 h. The activity was determined
by measuring the diameter of zone showing complete inhi-
bition (mm).
(Δν) [28]. In complexes 1 and 2 the νOCO
vibrations
asym
−
1
appeared at 1575 and 1580 cm while νOCO
vibra-
sym
−
1
tions appeared at 1389 and 1400 cm , respectively. The
Antifungal assay
difference between asymmetric and symmetric vibra-
−
1
tions (Δν) for 1 and 2 are 186 and 180 cm , receptively,
indicating bidentate mode of coordination of ligands
with the zinc atom in solid state (compare to respec-
Agar tube dilution method [26] was used for the evaluation
of fungal activity of the tested compounds against three fun-
gal strains: Aspergillus Niger, Aspergillus flavus, Aspergillus
fumigatus. 4 mL sabouraud dextrose agar (SDA) medium
was taken in screw caped test tubes which were autoclaved
for 15 min at 121 °C and were then allowed to cool at 50 °C.
After that 66.6 µL of compound from the stock solution
1
1
2
−
tive NaL and NaL with Δ(COO ) values of 250 and
−
215 cm , respectively) [29, 30]. According to the lit-
erature, a comparison of the Δ value of the carboxylate
complex with Δ value of its sodium salt is governed as:
−
−
if Δ(COO )
<< Δ(COO )
then the
studied complex
sodium salt
−
1
Table 1 FT-IR data (cm ) of
Comp. no.
ν(OCO)
Asym
Δν=νasym − νsym
ν(OH)
ν(Zn–O)
ν(Zn–N)
1
2
ligands (HL and HL ) and their
Zn(II) complexes
Sym
1
NaL
1680
1705
1575
1580
1553, 1736
1559, 1737
1553
1556
1557
1470
1490
1389
1400
1390, 1378
1398, 1380
1389
1399
1388
250
215
186
180
163, 358
161, 357
164
157
169
2800–3100
3270
–
3350–2460
–
3400–2400
–
–
–
–
–
–
–
–
–
499
516
–
510
499
2
NaL
1
2
3
4
5
6
7
426
418
415
416
427
428
415
Numbering of the compounds is accordance to Scheme 1
1
3

Journal of the Iranian Chemical Society
Synthesis of sodium salts of ligands
Cl
Cl
O
O
C
3
7
4
H O
2
1
2
-
+
C
HL1
OH
NaHCO3
+ H O + CO
+
5
O Na
2
2
6
NaL1
O
O
H O
9
8
2
-
+
Cl
CH C OH + NaHCO
HL2
3
Cl
CH
2
C
O Na
+
H O + CO
2 2
2
1
3
10
11
NaL2
1
2
Synthesis of Homolyptic Zn(II) complexes (1-2)
H O
2
1
2
2
NaL + Zn(NO ) .6H O
1
3
2
2
Zn(L ) + 2NaNO
2
3
4
4
-5 hr stirring
at 40-50 °C
Complex-1
H O
2
2
2
NaL + Zn(NO ) .6H O
3
2
2
Zn(L ) + 2NaNO
2
3
-5 hr stirring
at 40-50 °C
Complex-2
Synthesis of Heterolyptic type (I) Zn(II) complexes (3-4)
H O/CH OH
2
3
1
1
2
NaL + Zn(NO ) .6H O + bipy
3 2 2
[(Zn) (L ) (bipy) (H O)] + 2NaNO
2 4 2 2 3
4
-5 hr stirring
at 40-50 °C
Complex-3
H O/CH OH
2
2
3
2
NaL + Zn(NO ) .6H O + bipy
2
3
2
2
[Zn(L ) (H O)(bipy)] + 2NaNO
2
2
3
4
-5 hr stirring
at 40-50 °C
Complex-4
Synthesis of Heterolyptic type (II) Zn(II) complexes (5-7)
H O
1
2
2
1 2
NaL + NaL + Zn(NO ) .6H O
ZnL L + 2NaNO
3
3
2
2
4
-5 hr stirring
at 40-50 °C Complex-5
1
2
H O/CH OH
2 3
NaL + NaL + Zn(NO ) .6H O + py
1 2
3
2
2
[ZnL L (py)] + 2NaNO
3
4
-5 hr stirring
at 40-50 °C Complex-6
1
2
H O/CH OH
2
3
1 2
NaL + NaL + Zn(NO ) .6H O + bipy
3
2
2
[ZnL L (bipy)] + 2NaNO
3
4
-5 hr stirring
at 40-50 °C Complex-7
py = pyridine and bipy = bipyridine
1
2
Scheme 1 Synthesis of complexes 1–7. Numbering of NaL and NaL is for NMR interpretation
binding mode of the carboxylate moiety will be bidentate
then the binding mode of the carboxylate moiety will be
monodentate [30].
−
−
chelating; if Δ(COO )
≤Δ(COO )
then
sodium salt
studied complex
the binding mode of the carboxylate moiety will be bidentate
Interestingly, for heteroleptic type I complexes, i.e., 3 and
4, two types of bands regarding asymmetric and symmetric
−
−
bridging and if Δ(COO )
>>Δ(COO )
studied complex
sodium salt
1
3

Journal of the Iranian Chemical Society
stretching vibrations of carboxylate ligands were observed
signal (observed in 1H of ligand) and the upfield shifting of
methylene protons (complexes 2, 4–7) confirmed the forma-
tion of all complexes.
−1
which are νOCO
(1553, 1736 cm ) and νOCO (1390,
sym
asym
−
1
1
1
4
378 cm ) for complex 3, whereas, νOCO
(1559,
asym
−
1
−1
1
737 cm ) and νOCO (1398, 1380 cm ) for complex
The { H} NMR spectra of heteroleptic type I complexes
sym
−1
. The respective Δν values are (163 and 358 cm ) for com-
(3 and 4) do not support the observed solid state geome-
try of ligands around Zn atom. If the observed geometry
remained intact in solution, magnetically non-equivalent
protons for the phenyl groups of attached ligands should
had been observed, however, the observations were vice
versa. Therefore, the geometry of ligands in solution
changed from bidentate to monodentate mode of binding
−
1
plex 3, whereas (161 and 357 cm ) for complex 4, suggest-
ing both bidentate and monodentate type of bonding modes
of ligands co-existing in solid state of heteroleptic type I
complexes [30, 31]. The attachment of 2,2′-bipyridine group
in both complexes was observed by the appearance of peaks
−
1
at 499 and 516 cm attributed to Zn–N absorption bands.
−
1
13
Moreover, broad bands in the region of 3600–3400 cm
[32]. This has further been confirmed by “{ C} NMR”.
also suggested the attachment of water molecules. Further-
more, the of water molecule is also evident from XRD data.
For heteroleptic type II complexes, i.e., 5, 6 and 7, there
should be separate peaks for the carboxylate symmetric and
asymmetric vibrations with different Δν values. But here we
got a single peak each carboxylate symmetric and asymmet-
ric vibrations. The differently coordinated –COO moieties
have very difference in energies of the vibrational energy
levels which cause the overlapping of bands [14, 30]. The
respective Δν values are calculated and are in the range of
Peaks at 7.35–7.85 ppm were assigned to the phenyl pro-
tons, whereas those at 7.50–8.67 ppm were assigned to the
protons of 2,2′-bipyridine moiety. The peak observed at
3.24–3.41 ppm confirms the coordination of water molecule.
In heteroleptic type (II) complexes (5, 6 and 7) two differ-
ent carboxylate ligands are attached together with zinc metal
atoms. Their attachment with zinc metal is confirmed by
the appearance of methylene protons at 3.45 ppm, 3.47 ppm
and 3.52 ppm values for complexes 5, 6 and 7, respectively
2
1
(for L which is absent in L ) and the co-existence of phenyl
protons of both ligands in the region of 7.25–8.61 ppm.
−
1
1
57–169 cm confirming bidentate mode of coordination
around the Zn atom. Furthermore, the attachment of pyridine
group in complex 6, whereas, attachment of 2,2′-bipyridine
group in complex 7 was observed by the appearance of peaks
1
3
{ C} NMR
−1
13
at 510 and 499 cm respectively, attributed to Zn–N absorp-
tion bands [14, 30]. These observations have been further
The positioning of carboxylate carbon in { C} NMR is sen-
sitive to the geometry around the metal center and is indica-
1
13
13
confirmed by H and C-NMR data.
tive of complexation. The representative { C} NMR spectra
for complexes 1, 2 and 4 are given in Suppl. Figs. S2–S4.
The signals at 167.0–173.8 ppm is assigned to the C1 of the
carboxylate carbon in the free ligands, showing a down field
shift in the range of 170.4–179.4 ppm upon complexation
with Zn atom (Table 3). For heteroleptic type I complexes
NMR results
{1H} NMR
1
1
1
The { H} NMR spectra of the carboxylate ligands (HL ,
(3 and 4) it has already been found by “{ H} NMR” that the
2
HL ) and their respective complexes were recorded in
solid state structures for both complexes do not remain intact
in solution and the geometry of ligands around Zn atom has
changed. This can be further proved by the explanations;
DMSO-d as solvent. The detailed data are given in Table 2.
6
1
In the H-NMR of 1–7 complexes, the disappearance of O–H
1
1
2
Table 2 { H} NMR data (ppm) of ligands (HL and HL ) and their respective Zn(II) complexes
H. #
L1
L2
1
2
3
4
5
6
7
H1
H3
H5
H6
10.40 (s)
7.94 (s)
7.8 (d)
7.57 (m)
–
–
–
–
–
–
–
–
–
–
–
–
7.75 (s)
7.45 (d)
7.32 (m)
7.75 (d)
7.83 (s)
7.46 (d)
7.79 (s)
7.47 (d)
7.89 (s)
7.42 (d)
8.61 (s)
7.47 (d)
7.56 (m)
7.93 (d)
8.5 (s)
8.2 (d)
7.8 (m)
7.89 (d)
7.42 (m) 7.35 (m) 7.53 (m)
7.8 (d)
H7
7.9 (d)
–
7.75 (d)
7.8 (d)
H8
H9
H11 H12
Hwater
–
–
–
–
10.9 (s)
3.56 (s)
7.21–7.30 (m)
–
–
–
–
–
–
–
–
–
–
–
3.43 (s)
7.23–7.32 (m)
–
3.45 (s)
3.47 (s)
3.52 (s)
7.25–7.32 (m) 7.26–7.32 (m) 7.27–7.39 (m)
–
3.41 (s)
3.24 (s)
–
–
Numbering of the compounds is accordance to Scheme 1
1
3

Journal of the Iranian Chemical Society
1
3
Table 3 { C} NMR data (ppm)
13
L1
L2
C
1
2
3
4
5
6
7
1
2
of ligands (HL and HL ) and
their Zn(II) complexes
C1
C2
C3
C4
C5
C6
C7
C8
167.0
132.5
129.7
134.1
134.2
129.2
127.6
–
–
–
–
–
–
–
–
–
–
–
–
170.4
131.2
129.6
133.2
137.5
130.5
128.5
–
–
–
–
–
–
–
–
–
–
–
–
170.7
132.4
129.9
134.9
136.5
130.0
128.3
–
–
–
–
–
–
–
–
–
–
170.3
131.2
130.5
137.5
137.0
129.6
128.5
176.7
42.2
131.0
131.6
128.3
133.5
170.6
132.3
129.5
134.2
134.6
129.1
127.9
176.7
42.2
131.3
131.4
128.2
134.0
172.8
131.2
131.0
137.2
137.6
129.1
128.5
179.4
42.4
130.2
132.4
127.5
133.6
–
173.2
39.8
130.7
132.5
128.2
133.4
176.6
42.5
130.9
131.6
128.3
137.0
176.7
42.5
130.9
131.5
128.2
137.1
C9
C10
C11
C12
C13
–
–
–
Numbering of the compounds is accordance to Scheme 1
(
a) one carbonyl peak appeared at 170.7 ppm for complex
to each zinc atom in a monodentate mode of coordina-
tion. Moreover, each of the two 2,2′-bipyridine ligands are
coordinated to zinc atoms via Zn–N bonds in a bidentate
fashion. The geometry around zinc atom can be defined
by structural distortion index, i.e., τ value and is given as:
τ = (β − α)/60. The first and second largest basal angles
around the Zn atom are represented by β and α, respec-
tively. It is well reported that τ values of 0 and 1 corre-
spond to a perfect square-pyramidal and a perfect trigonal-
bipyramidal geometries, respectively [33, 34]. The τ value
calculated for complex 3 is 0.65 that suggests a distorted
trigonal bipyramidal geometry arrangement around zinc
atoms. A distorted trigonal bipyramidal coordination
geometry has registered for each Zn(II) cation, with bipy-
ridine at the apex giving the axial coordination. The tetra
A bridging framework constituted by tetra carboxylate can
accommodate metal–metal separation up to 3.452 Ǻ, the
Zn—Zn separation in the present case is 4.006 Ǻ [29]. The
water molecule that can be seen in Fig. 2 is disordered over
two sets of sites about a twofold axis with site occupancies
of 0.5. Moreover, the O4 oxygen atom of a carboxylate
group is also disordered over two orientations with site
occupancies of 0.5. The H atoms of water molecule were
located in a difference Fourier map and refined with the
O–H and H…H distances constrained to be 0.82 (1) and
3
and at 176.7 ppm for complex 4, (b) magnetically equiva-
lent carbons for the phenyl groups of attached ligands were
observed.
The formation of heteroleptic type (II) complexes was
confirmed by the presence of all respective signals of both
1
3
ligands in { C} NMR spectra and can be further justified
1
2
as: (a) HL and HL carbonyl peaks appears at 167.0 ppm
and 173.8 ppm, respectively, while after complexation the
peaks shifted at relatively higher ppm values of 170.26 ppm
13
and 176.71 ppm, respectively. The { C} NMR spectrum for
complex 5 is shown in Suppl. Fig. S5. The appearance of
methylene C9 carbon and its downfield shift upon complexa-
tion (39.8 ppm → 42.2–42.4 ppm) and (c) the appearance
of carbon signals of phenyl rings of both ligands at down-
field ppm values of 127.5–137.5 ppm. Moreover, the char-
acteristic signals of 2,2′-bipyridine and pyridine appeared
in the region of 122.5–150.6 ppm and 130.4–149.5 ppm,
respectively.
X‑ray crystallographic study
The crystallographic data for complexes 3 and 4 with
their selected bond lengths and bond angles are shown in
Tables 4, 5 and 6, respectively.
1
.296 (2) Å, respectively. The disordered water molecule
Crystal structure of complex 3
in complex 3 plays an important role in bridging (Fig. 2)
by utilizing both hydrogen atoms for joining the two mol-
ecules via H-bonding. The partial packing diagram of
complex 3 (Fig. 3) gives the formation of the 3D network
via hydrogen bonds (dashed lines). Only one position of
the disordered O4 oxygen atom is shown. All the hydrogen
atoms which are not involved in hydrogen bonding are
omitted for clarity purpose.
The complex 3 has a monoclinic crystal system with C2/c
space group. It can be seen from Fig. 1 that complex is
a binuclear system and is composed of two zinc metal
atoms, four carboxylate and two 2,2′-bipyridine ligands.
The two zinc metal atoms are linked by two carboxylate
ligands via oxygen atoms (as bridging mode of binding),
whereas the other two carboxylate ligands are attached
1
3

Journal of the Iranian Chemical Society
Table 4 Crystal data and
refinement parameters for
complexes 3 and 4
Parameter
3
4
Empirical formula
Mr
Temperature (K)
Crystal system
Space group
a (Å)
C H Cl N O Zn
1083.33
294 (2)
Monoclinic
C2/c
27.163 (5)
9.6100 (17)
22.611 (4)
C H Cl N O Zn
578.72
298 (2)
Monoclinic
4
8
34
4
4
9
2
26 22
2
2
5
P2 /n
1
12.29279 (17)
13.38893 (17)
15.9704 (2)
b (Å)
c (Å)
α, β, γ (°)
V (Å )
Z
90, 129.086 (2), 90
4581.5 (14)
4
1.571
1.342
90, 103.2087 (14), 90
2558.98 (6)
4
1.502
1.2089
3
3
ρcalcg (cm )
1
µ (mm )
F(000)
Radiation
2200.0
1184
MoKα (λ=0.71073)
3.722 to 50.992
−30≤h≤32, −11≤k≤11,
MoKα (λ=0.71073)
6.06 to 56.608
2
θ range for data collection (°)
Index ranges
−15≤h≤16,
−
27≤l≤27
−17≤k≤17,
−
21≤l≤21
Reflections collected
18,998
58,743
R , R
0.0390, 0.0327
4267/3/324
1.041
0.0277, 0.0178
6026/0/413
1.041
int
sigma
Data/restraints/parameters
S
R1, wR2
0.0356, 0.0834
0.57/−0.54
1,584,356
0.0343, 0.0800
0.46/−0.47
1,571,691
Δρmax/Δρmin (e Å−3
)
CCDC deposition number
Table 5 Selected bond lengths for complexes 3 and 4
Complex 3 Complex 4
4 is composed of zinc center bonded with a water mol-
ecule, 2,2′-bipyridine and two carboxylate ligands (one in a
monodentate mode and the other in bidentate mode of coordi-
nation). The longer Zn–O2 (2.23 Å) and shorter Zn–O1 bonds
Atom
Atom
Length (Å)
Atom
Atom
Length (Å)
(
2.061 Å) show the asymmetric coordination of two carboxy-
Zn1
Zn1
Zn1
Zn1
Zn1
Cl1
O1
O2
O2
O3
O4A
O4B
O3
O1
N2
O2
N1
C4
C1
C1
1.9528 (16)
1.9793 (14)
2.0930 (18)
2.1617 (16)
2.1856 (19)
1.734 (2)
1.259 (2)
1.254 (3)
2.1617 (16)
1.236 (3)
1.372 (5)
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Cl1
C9
O1
O2
O3
O4
O1
O3
O4
O5
N1
N2
C6
C10
C1
C1
C9
C9
2.0474 (13)
2.2016 (15)
2.2390 (15)
2.0621 (14)
2.1594 (15)
2.1028 (15)
1.743 (2)
1.512 (3)
1.255 (2)
1.236 (2)
1.258 (2)
lates to the zinc center. The longer Zn–O bond distances are
accompanied by shorter C–O bond distances and vice versa.
Therefore, zinc center is six coordinated adopting distorted
octahedral geometry. The electron pair repulsion and steric
effects induced by carboxylate ligands are mainly responsible
for the distortion of the octahedral environment around Zn
atom. The crystal lattice also contains water molecules which
is involved in intramolecular hydrogen bond (vide infra) play-
ing a vital role in the development of supramolecular structure:
as it creates the centrosymmetric, hydrogen-bonded dimers
H···O 1.86 (3) Å, O···O 2.728 (2) Å, O–H···O 173 (3)°, (Fig. 5).
1
Zn11
C8
C8
C8
1.240 (4)
1.242 (2)
1
1−X, +Y, 3/2−Z
Compound–CTAB interaction study
Crystal structure of complex 4
The formation of surfactant micelles has an important affect
on the moieties present in drug at the site of action. In case
of oral administration of drug with a surfactant, CMC has
large impact. A high value of CMC of a surfactant is a good
The complex 4 has a monoclinic crystal system with P2 /n
1
space group. From Fig. 4, it can be seen that the complex
1
3

Journal of the Iranian Chemical Society
Table 6 Selected bond angles
for complexes 3 and 4
Complex 3
Atom
Complex 4
Atom
Atom
Atom
Angle (˚)
Atom
Atom
Angle (˚)
O3
O3
O1
O3
O1
N2
O3
O1
N2
O2
C1
C1
C8
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
O1
O1
N2
N2
116.39 (7)
102.87 (7)
140.64 (6)
90.42 (7)
90.66 (6)
91.74 (6)
106.81 (7)
89.44 (7)
76.17 (7)
160.67 (7)
118.31 (13)
127.86 (13)
121.29 (16)
126.50 (17)
O1
O1
N2
O5
O1
N1
O5
N2
N1
O1
O5
N2
N1
O3
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
Zn1
O5
O3
O1
N2
N1
N2
O3
O3
O3
O4
O4
O4
O4
O4
92.78 (6)
97.21 (6)
93.96 (6)
104.10 (6)
170.55 (6)
76.59 (6)
98.07 (6)
154.60 (6)
91.53 (6)
92.50 (5)
156.61 (6)
98.25 (5)
89.00 (6)
58.64 (5)
1
O2
1
O2
1
O2
N1
N1
N1
N1
Zn1
Zn1
Zn1
Zn1
1
1
O2
O3
N1
C15
1
1−X, +Y, 3/2−Z
Fig. 1 ORTEP view of complex 3
indicator for bioavailability of drug upon dilution. While a
low value of CMC of a surfactant is an indicator of low bio-
availability of drug and will remain in micelles system [35].
The binding of the heteroleptic carboxylates with CTAB
was explored by conductometric method. Solutions of 1 mM
of each complex were prepared in methanol and their spe-
cific conductance was measured in the presence of various
aqueous conc. of CTAB (0–7 mM) to study the interaction
between the compound and CTAB. A constant concentra-
tion of the compound was used while that of CTAB ranged
from 0 to 7 mM. With increase in the concentration of the
CTAB, an increase in the conductance was observed and an
inflection point was observed (different for each compound)
at different molar concentrations. The CTAB monomers
combination point giving to shape a structure is known as
micelle and the concentration at which this point is achieved
1
3

Journal of the Iranian Chemical Society
Fig. 2 Bridging role of the disordered water molecule in complex 3. Symmetry code: (1) 1/2−x, 3/2−y, 1−z
Fig. 3 Partial packing diagram of complex 3 showing the formation of the 3D network via hydrogen bonds (dashed lines). Only one position of
the disordered O4 oxygen atom is shown. Hydrogen atoms not involved in hydrogen bonding are omitted
1
3

Journal of the Iranian Chemical Society
Fig. 4 Perspective view of
complex 4
Fig. 6 Graph between CTAB–complex vs specific conductance for
complex 4. At 0.0034 M conc. Micelles form
−
mainly due to the movement of Br from the surface of one
micelle to another [36]. In the presence of the compound
a higher value of CMC of CTAB was observed at higher
concentration as compared to its aqueous solution, which
Fig. 5 Centrosymmetric dimer created by the hydrogen-bonded com-
plexes 4. Hydrogen bonds are shown as dashed blue lines
+
is due to strong binding of compound–CTAB monomers.
The compound reduces the charge density by decreasing
the repulsion between the positively charged N atoms of
is known as critical micelle concentration (CMC) of CTAB.
During the addition of CTAB, the major ions formation
responsible for the reduction of the surface tension of aque-
+
CTAB monomers. The entropy of compound–CTAB is
increased due to the lowering of CTAB monomer combi-
nation rate in the presence of the compound.
+
ous media and enhancement of the conductance are CTAB
−
and Br ions [36]. There is a little interaction among these
Figure 6 shows a CMC value of 0.0034 M for the com-
pound 4-CTAB system which is higher than that of the
aqueous free CTAB surfactant (0.0009 mol/L) [37]. The
increase in CMC confirms the strong binding of compound
to the CTAB resulting in high bioavailability of the drug to
the biological system. CMC values for the complexes (3,
5–7)–CTAB system are shown in Fig. 7.
ions due to their small size and fast movement. A sharp
increase in conductance in pre-micellar concentration
region is observed while in post-micellar concentration
region the rate of increase in conductance is lowered as
the free monomers are utilized in the micelle formation.
In post-micellar concentration region, the conductance is
1
3

Journal of the Iranian Chemical Society
Fig. 7 Graph between CTAB–complex vs specific conductance for complexes
ΔGm = 2.303(1 + ꢀ) RT log Xcmc
Table 7 Different parameters data for CTAB-complex interactions for
complex 3–7
ꢀ
= 1 − ꢁ
Complexes
Parameters
ꢁ = S ∕S
2
1
–
ΔG (kJ/mol) con-
CMC (M)
−lnXcmc
ductometry
The extent of the counter ion binding is shown by β while
the extent of ionization or dissociation which is calculated
before and after CMC from the ratio of plots is shown by α.
Slopes of conductivity–concentration plots before and after
CMC are shown by S and S , respectively. X be calculated
3
4
5
6
7
42.40
44.13
39.50
42.69
40.76
0.0033
0.0034
0.0029
0.0024
0.0026
9.73
9.70
9.86
10.05
9.98
1
2
cmc
as X = cmc/55.55.
cmc
A negative value of ΔGm is the indication of spontaneous
solubilization of the compound in surfactant micelles system
because of the interaction between the positive parts of sur-
factant interaction with compound which lead to the achieve-
ment of a stable system of compound–CTAB.
Numbering of the compounds is accordance to Scheme 1
A higher CMC value of the tested compounds with
CTAB is responsible for good bioavailability to the bio-
DNA binding study by UV–visible spectroscopy
logical system. Table 7 represents the CMC, -lnX
and
cmc
–
ΔG (kJ/mol) values of the screened compounds.
The binding of compounds with SS-DNA was elaborated by
UV–Vis. spectroscopy. Spectra of compounds 3 and 4 are
given in Figs. 8 and 9, respectively as representatives (For
complexes 1, 2, 5–7, see Suppl. Figs. S6–S10). During the
ΔGm is the free energy for the micellization process
and is the difference of G values at the highest concen-
tration of surfactant and without surfactant which can be
calculated by the equation
1
3

Journal of the Iranian Chemical Society
A
∈G
∈G
0
1
=
+
⋅
A − A0
∈H−G − ∈G
∈H−G − ∈G K[DNA]
where A and A are absorbance of pure complex and com-
0
plex–DNA adduct, respectively, K is binding constant, ∈
G
and ∈
molar absorption coefficient of complex and
H−G
complex–DNA adduct, respectively. Binding constants for
the complexes were calculated from the plot 1/[DNA] along
the abscissa and A /A–A along the ordinate. The calculated
0
0
values of binding constants are given in Table 8. The bind-
ing constants values are comparable to that of other zinc
complexes determined [40–43]. The Gibb’s free energy was
calculated using the following equation.
Fig. 8 Compound 3–DNA spectrum (λ =273 nm) in the absence
max
ΔG = − RT ln(K)
(
a) and presence of 7 (b), 14 (c), 21 (d), 28 (e), 35 (f) and 42 (g) µM
−
1
−1
−1
Here R is general gas constant (8.314 J M K ) and T is
absolute temperature (298 k). The calculated values of ΔG
are negative which indicates spontaneity of the reaction.
DNA solution. The inside plot of Ao/A–Ao vs 1/[DNA] (µM) was
used for K and ΔG values
Viscometry method for compound–DNA interaction
1
/3
Viscometry data were plotted between (η/η ) and concen-
o
tration ratio (compound/DNA) as given in Fig. 10. As it is
evident from the graph, an increase in the relative viscos-
ity of DNA with the addition of increasing concentration
ratio was observed which is the sign of intercalative mode.
Furthermore the intercalative mode of interaction was also
confirmed by comparing the test compounds with a famous
classical intercalator, ethidium bromide (EB), like that
increases the relative viscosity of DNA by lengthening the
DNA-helix [44–46].
Fig. 9 Compound 4–DNA spectrum (λ =273 nm) in the absence
Antibacterial results
max
(
a) and presence of 7 (b), 14 (c), 21 (d), 28 (e), 35 (f), 42 (g) and
4
8 (h) µM DNA solution. The inside plot of Ao/A–Ao vs 1/[DNA]
−1
Four different strains of bacteria viz. Staphylococcus
aureus, Enterobacter acrogens, Escherichia coli and
(
µM) was used for K and ΔG values
DNA–compound binding study two phenomenons were
observed: hypochromism and minor red shift of 2–3 nm. The
existence of these two phenomenons indicates that the com-
pounds interact with the DNA via intercalative binding mode
Table 8 Different parameters data of UV–visible spectroscopy for
complexes 1–7
Comp. no.
Parameters
[38].
–
ΔG (kJ/mol)
K (M−1) UV–vis
λmax(nm)
For the tested compounds there were two major peaks
UV–vis
in their spectra which are due to two types of transitions:
prominent peak due to π–π* transition and a shoulder peak
due to n–π* transition. The π–π* transition corresponds to
the aromatic moiety of compound while the n–π* transition
is due to carbonyl functionality. The significant absorbance
of these complexes in the near-UV area is ascribed to the
aromatic system (having triplet excited state). Benesi–Hilde-
brand equation was used to calculate the binding parameters
3
1
2
3
4
5
6
7
18
20
19
21, 19
20
21
20
1.29×10
2.6×10
1.29×10
269
276
273
294–306
275
252
292
3
3
3
3
3.9×10 , 2.9×10
3
3.6×10
4.6×10
3.0×10
3
3
[
39]:
Numbering of the compounds is accordance to Scheme 1
1
3

Journal of the Iranian Chemical Society
lipid layer beneath the cell wall which inhibits the penetra-
tion of drugs to the cell.
Antifungal activity
Three different strains of fungi were used for exploring the
antifungal activity of the tested compounds via agar well
diffusion method using terbinafine as a standard drug and
DMSO as a vehicle control. The antifungal activity was
expressed in terms of percent growth inhibition as; for
significant activity>70% growth inhibition, for good inhi-
bition activity > 60–70% growth inhibition, for moderate
activity > 50–60% growth inhibition, for non-significant
activity < 50% growth inhibition [50]. It is evident from
Table 10 that the antifungal activity of two ligands fall in
the non-significant category while the activity of some of
the complexes fall in the categories of good to moderate
comparable to that of standard drug. The enhancement in
the activity of the ligands is coordination to metal (compl-
exation) that actually increase their hydrophilic solubility
inside the cell that permit them to cross the cell membrane
and thus easily reach the target.
Fig. 10 Interaction of DNA with compounds 1–7 and EB by viscom-
etry
Bacillus subtilis were used for the exploration of antibac-
terial potential of the evaluated compounds using Kana-
mycin sulfate as a standard drug and DMSO as a vehi-
cle control. The antibacterial activity was expressed in
terms of zone inhibition in mm and the data is presented
in Table 9. The criteria of antibacterial activity refers to
Davis and Stout and Ambarwati who classified it into: low
(
< 5 mm), moderate (5–10 mm), strong (10–19 mm) and
Conclusions
very strong (> 20 mm) [47–49]. It is evident from Table 9
that the screened compounds have exhibited good to strong
activity comparable to that of standard, while high activity
than free ligand particularly against Gram-positive (Staph-
ylococcus aureus) bacterial strain. Less activity against
Gram-negative bacteria is due to the presence of portative
Two new homoleptic and five heteroleptic (type-I and type-
II) zinc(II) carboxylate complexes were successfully synthe-
sized and characterized by FT-IR, elemental analyses (C, H,
1
13
N), single crystal XRD and by { H} and { C} NMR spec-
troscopy. The structures of the heteroleptic type-I complexes
(
3 and 4) were also characterized by single crystal X-ray
1
2
Table 9 Antibacterial activity of HL , HL and their Zn(II) com-
plexes 1–7
1
2
Table 10 Antifungal activity of HL , HL and their Zn(II) complexes
–7
1
Comp. No
Zone of inhibition (mm)
Comp. No
Inhibition (%) in linear growth of fungal strains
Entero-
bacter
aerogenes
Escheri- Staphy-
Bacillus
subtilis
chia
coli
lococcus
aureus
Aspergillus
niger
Aspergillus
flavus
Aspergillus
fumigatus
HL1
9
7
5
8
6
9
8
7
HL
1
27
29
51
51
53
49
58
48
29
100
31
27
65
59
35
52
61
46
34
100
18
21
56
65
42
60
63
38
2
2
HL
HL
1
2
3
4
5
6
7
14
15
12
11
13
12
8
11
11
15
13
12
9
19
17
14
13
17
14
13
28
18
15
11
12
19
11
12
22
1
2
3
4
5
6
11
27
7
41
100
a
a
Kanamycin sulfate 26
Terbinafine
Numbering of the compounds is accordance to Scheme 1
Standard drug
Numbering of the compounds is accordance to Scheme 1
Standard drug
a
a
1
3

Journal of the Iranian Chemical Society
diffraction analysis showing a distorted trigonal bipyrami-
dal geometry around each Zn atom in complex 3, whereas a
distorted octahedral geometry around Zn atom in complex
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9. G.M. Sheldrick, Acta Cryst. A71, 3 (2015)
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with CTAB resulting in a negative value of ΔGm that sug-
gest in micelles the compounds solubilized spontaneously
as a result of attractive interactions between compound and
positively charged micelles resulting in a stable CTAB–com-
pound system. Moreover, higher critical micelles concentra-
tion values indicate a good bioavailability of drugs. Inter-
action of the screened compounds with DNA results in an
intercalative mode of binding as confirmed by UV–visible
spectroscopy and viscometric techniques. The evaluation
of the screened compounds for their antibacterial and anti-
fungal activities has shown good to strong activity against
the studied bacterial strains and good to moderate fungal
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