Microwave solid phase synthesis, characterization and antimicrobial activities of bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine-zinc(II)

Article abstract of DOI:10.14233/ajchem.2016.19242

One mononuclear complex (1) has been designed and synthesized by bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine (L) with Zn(CH₃COO)₂·2H₂O in microwave radiation assistance. The complex was characterized by X-ray cry

Full text of DOI:10.14233/ajchem.2016.19242

Asian Journal of Chemistry; Vol. 28, No. 1 (2016), 207-210
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19242
Microwave Solid Phase Synthesis, Characterization and Antimicrobial Activities of
Bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine-Zinc(II)
*
SUO-PING XU and XUE YANG
Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 221116, P.R. China
*Corresponding author: Fax: +86 516 83500366; Tel: +86 516 83403165; E-mail: xsp62@jsnu.edu.cn
Received: 14 April 2015;
Accepted: 25 May 2015;
Published online: 5 October 2015;
AJC-17576
One mononuclear complex (1) has been designed and synthesized by bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine (L) with
Zn(CH3COO)2·2H2O in microwave radiation assistance. The complex was characterized by X-ray crystallography, confirming that the
central zinc(II) was coordinated by two oxygen atoms, two nitrogen atoms from L. The complex was assayed for in vitro antibacterial (B.
subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli and E. cloacae) activities and showed better antimicrobial activity against Gram-
positive strains than Gram-negative strains.
Keywords: Bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine, Mononuclear zinc(II) complex, Antibacterial activity.
performed on a CHN-O-Rapid instrument and were within
0.4 % of the theoretical values. Melting points were measured
a Boetius micro melting point apparatus.
INTRODUCTION
Salicylaldehyde type’s Schiff base and the metal comp-
lexes thereof show a wide spectrum of antimicrobial properties
[1-7]. A number of researchers studied the synthesis, charac-
terization and structure-activity relationship (SAR) of Schiff
bases [5,8-11]. Although these methods synthesize reliable
routes for the preparation of Schiff base type’s complexes, most
of them follow lengthy procedures and time. Therefore, the
development of direct and efficient procedures for these classes
of compounds from materials has been the target of synthetic
organic chemistry. In this paper, one mononuclear complex
(1) was synthesized by bis(5-chloro-2-hydroxybenzaldehyde)-
ethane-1,2-diamine (L) with Zn(CH3COO)2·2H2O in microwave
radiation assistance. The complex was assayed for antibacterial
activities against three Gram-positive bacterial strains (Bacillus
subtilis, Staphylococcus aureus and Streptococcus faecalis)
and three Gram-negative bacterial strains (Escherichia coli,
Pseudomonas aeruginosa and Enterobacter cloacae) by the
3-(4,5-dimethyl-2-triazyl)-2,5-diphenyl-2H-tetrazolium
bromide (MTT) method.
Preparation of 5-chloro-2-hydroxybenzaldehyde and
ethane-1,2-diamine in ethanol (L) and its zinc(II) complex
(1): Compound Lwas designed and synthesized from 5-chloro-
2-hydroxybenzaldehyde and ethane-1,2-diamine in ethanol.
The ligand and Zn(CH3COO)2·2H2O were mixed together and
microwave radiated 6 min in 150 W. The yellow powder was
dissolved in ethanol/DMF (1/1) and afforded bis(5-chloro-2-
hydroxybenzaldehyde)ethane-1,2-diamine-zinc (1) (Scheme-I).
Preparation of L:A mixture of 5-chloro-2-hydroxyben-
zaldehyde (20 mmol) and ethane-1,2-diamine (10 mmol) in
20 mL ethanol was refluxed for 1 h.After filtration, the yellow
solid was washed with ethanol and water, dried and recrys-
tallized from ethanol. Yield: 76 %, m.p.: 125-128 °C. UV (λ
nm): 375; 253. Selected IR data (KBr, νmax, cm-1): 2960(m),
1638(s), 1595(m), 1524(s), 1455(s), 1378(s), 1332(m),
1309(s), 1241(m), 1175(s), 1138(m), 1089(s), 1052(m), 970(s),
834(m), 706(m); 1H NMR (CDCl3) δ ppm: 11.65 (s, 2H), 8.24
(s, 2H), 7.48 (d, J = 7.2 Hz, 2H), 7.20 (d, J = 5.4 Hz, 2H),
6.82 (m, J = 12.6 Hz, 2H), 4.06 (s, 4H). Anal. Calcd. for
C16H14N2Cl2O2 (%): C, 56.99; H, 4.18; N, 8.31. Found (%): C,
57.06; H, 4.21; N, 8.27.
EXPERIMENTAL
All chemicals were of reagent grade and used as received.
UV spectra were recorded on a U-3000 spectrophotometer.
IR spectra were recorded on a Nexus 870 FT-IR. H NMR
spectra were recorded on a Bruker DPX 300 model spectrometer
(Bruker Bioscience, USA) in CDCl3. Elemental analyses were
Complex1:CompoundL(10mmol)andZn(CH3COO)2·2H2O
(10 mmol) were mixed together and microwave radiated 6 min
in 150 W. The yellow powder was dissolved in ethanol/DMF
(1/1). After standing for 7 days, the single crystals of 1 were
1

208 Xu et al.
Asian J. Chem.
Cl
Cl
Cl
O
N
N
NH2
H2N
+
OH
OH
HO
L
Cl
Cl
Cl
Cl
N
N
MW 150W
6 min
N
N
Zn(OAc)2.2H2O
+
Zn
O
O
OH
HO
1
Scheme-I: Synthesis of ligand and compound 1
obtained, separated by filtration, washed with ethanol thrice
and dried.Yield: 80 %, m.p.: > 300 °C. UV (λ nm): 386; 253.
Selected IR data (KBr, νmax, cm-1): 1618(s), 1596(m), 1524(s),
1455(s), 1378(m), 1309(s), 1241(m), 1175(m), 1139(s),
1089(m), 1052(s), 970(m), 835(m), 792(m), 743(m), 707(s).
Anal. calcd. for C16H12N2O2ZnCl2 (%): C, 47.98; H, 3.02; N,
6.99. Found (%): C, 47.76; H, 3.05; N, 7.03.
Crystal structure determinations and refinements: The
crystallographic date for 1 was collected on a Bruker Smart
1000 CCD area detector diffractometer equipped with MoKα
(λ = 0.71073 Å) radiation using ω-scan mode. Empirical absor-
ption correction was applied to the data. Unit cell dimensions
were obtained with least-squares refinements and all structures
were solved by direct methods with SHELXL-97. All non-
hydrogen atoms were located from the trial structure and then
refined anisotropically. All hydrogens were generated in
idealized positions. All calculations were performed with
SHELXL-97 programs [12]. Other relevant parameters of the
crystal structure are listed in Table-1.
aeruginosa, E. coli and E. cloacae using MTT medium. The
MICs of the test complexes were determined by a colorimetric
method using the dye MTT [13]. A stock solution of the
synthesized complex (50 µg/mL) in DMSO was prepared and
graded quantities of the test complexes were incorporated in
specified quantity of sterilized liquid medium. A specified
quantity of the medium containing the complex was poured
into microtitration plates. Suspension of the microorganism
was prepared to contain approximately 105 cfu/mL and applied
to microtitration plates with serially diluted complexes in
DMSO to be tested and incubated at 37 °C for 24 h for bacterial.
After the MICs were visually determined on each of the micro-
titration plates, 50 µL of PBS (phosphate buffered saline 0.01
mol/L, pH 7.4: Na2HPO4·12H2O 2.9 g, KH2PO4 0.2 g, NaCl
8.0 g, KCl 0.2 g, distilled water 1000 mL) containing 2 mg/mL
of MTT was added to each well. Incubation was continued at
room temperature for 4-5 h. The content of each well was removed
and 100 µL of isopropanol containing 5 % 1 mol/L HCl was
added to extract the dye.After 12h of incubation at room tempe-
rature, the optical density (OD) was measured with a micro-
plate reader at 570 nm. The observed MICs were presented in
Table-2.
TABLE-1
CRYSTALLOGRAPHIC AND EXPERIMENTAL
DATA FOR COMPOUND 1
Empirical formula
Formula weight
C16H12N2O2ZnCl2
400.55
RESULTS AND DISCUSSION
The complex of the formula C16H12N2O2ZnCl2 was
prepared in moderate yield (80 %). IR spectra of L show four
bands in 2960 cm-1 and 1638 cm-1 region, characteristic of the
mixed modes of vibrations arising from normal coordinates
having contributions from ν(OH) and ν(C=N) [14]. The infrared
spectra of complex 1 (KBr pellets) display an intense absorp-
tion band at about 1618 cm-1 attributable to the ν(C=N) shifted
about 20 cm-1 lower wave-number compared with 1638 cm-1
of L. The UV spectra of the complex display an intense absorp-
tion peak at 253 nm (π→π*) and 386 nm (n→π*). The structure
of complex 1 was confirmed by a single-crystal X-ray diffrac-
tion and shown in Figs. 1 and 2. The crystal structure consists
of mononuclear complex. The molecular structure of complex
1 crystallize in triclinic with space group P-1; bond distances
and angles are provided in Table-3. The complex 1 is electro-
nically neutral mononuclear compound. The central metal (Zn),
on an inversion center, are in octahedral coordination geometry
with oxygen and nitrogen donors from L. The general Zn-O
and Zn-N bond lengths are in the range 1.963(14)-2.006(13)
Å and 2.121(19)-2.123(15) Å, unexceptional and similar to
the corresponding bonds in other manganese Schiff base
complexes [15].
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
Triclinic
P-1
4.7669(9)
12.690(4)
27.505(5)
90.211(11)
92.277(6)
90.095(5)
1662.5(7)
4
296(2)
1.600
1.807
808
7683 / 0 / 415
1.48 to 28.50
21608 / 7683
0.0393
R1 =0.0408, wR2 = 0.1089
0.624 and -0.198
γ (°)
V (Å3)
Z
T (K)
Density (g/cm3)
µ (mm-1)
F(000)
Data/restrains/parameters
θ range (°)
Reflections collected/ unique
Rint
Final R indices [I > 2σ(I)]
(∆ρ)max, (∆ρ)min (e/Å3)
aR= Σ||Fo|-|Fc|/∑|Fo|, bwR = [Σ[w(Fo2-Fc2)2]/Σ[w(Fo2)2]]1/2
Antimicrobial activity: The antibacterial activity of L
and 1 was tested against B. subtilis, S. aureus, S. faecalis, P.

Vol. 28, No. 1 (2016)
Compound
Synthesis of Bis(5-chloro-2-hydroxybenzaldehyde)ethane-1,2-diamine-Zinc(II) 209
TABLE-2
MINIMUM INHIBITORY CONCENTRATIONS (MICs) OF THE SYNTHETIC COMPOUNDS
Microorganisms MICs (µg/mL)
Gram-positive
Gram-negative
B. subtilis
S. aureus
S. faecalis
6.25
12.5
P. aeruginosa
E. coli
E. cloacae
3.125
25
6.25
12.5
6.25
25
12.5
25
12.5
12.5
1
L
Penicillin
Kanamycin
1.562
0.39
1.562
1.562
1.562
3.125
6.25
3.125
6.25
3.125
3.125
1.562
TABLE-3
SELECTED BOND LENGTHS (Å) AND BOND ANGLES (°) OF COMPLEX 1
Bond
Zn(1)-O(1)
Zn(1)-N(2)
O(2)-C(33)
Cl(2)-C(48)
Angle
Distance
2.006(13)
2.121(19)
1.31(2)
1.75(3)
(°)
Bond
Zn(1)-O(2)
Cl(1)-C(35)
N(1)-C(28)
N(2)-C(37)
Angle
Distance
1.963(14)
1.67(3)
1.25(3)
1.26(3)
(°)
Bond
Zn(1)-N(1)
O(1)-C(19)
N(1)-C(9)
N(2)-C(47)
Angle
Distance
2.123(15)
1.30(2)
1.46(3)
1.42(2)
(°)
O(2)-Zn(1)-O(1)
O(2)-Zn(1)-N(1)
C(19)-O(1)-Zn(1)
C(9)-N(1)-Zn(1)
C(37)-N(2)-C(47)
N(1)-C(28)-C(24)
N(2)-C(37)-C(22)
C(45)-C(35)-Cl(1)
96.9(5)
O(2)-Zn(1)-N(2)
O(1)-Zn(1)-N(1)
C(33)-O(2)-Zn(1)
O(1)-C(19)-C(24)
C(37)-N(2)-Zn(1)
O(2)-C(33)-C(22)
N(2)-C(47)-C(9)
C(39)-C(48)-Cl(2)
87.0(6)
86.5(7)
132.3(11)
127.3(19)
125.1(14)
124.3(17)
112(2)
O(1)-Zn(1)-N(2)
N(2)-Zn(1)-N(1)
C(28)-N(1)-C(9)
O(1)-C(19)-C(32)
C(47)-N(2)-Zn(1)
O(2)-C(33)-C(40)
C(20)-C(35)-Cl(1)
C(10)-C(48)-Cl(2)
154.5(6)
78.3(7)
122.9(18)
121.5(18)
111.1(15)
116.6(17)
125(2)
150.4(7)
123.1(12)
114.0(15)
124(2)
130.7(19)
128(2)
119.8(19)
125(3)
114(2)
From MIC values (Table-2), the complex was more toxic
towards Gram-positive strains than Gram-negative strains when
compared to the positive controls penicillin and kanamycin,
respectively. The reason may be the difference in the structures
of the cell walls. The walls of the Gram-negative cells are more
complex than those of Gram-positive cells. Lipopolysaccha-
rides form an outer lipid membrane and contribute to the
complex antigenic specificity of Gram-negative cells. Anti-
microbial activity of complexes is due to either killing the
Fig. 1. Crystal structure of complex 1, showing 30 % probability
displacement ellipsoids (arbitrary spheres for the H atoms)
Fig. 2. Packing structure of complex 1

210 Xu et al.
Asian J. Chem.
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The work was co-financed by grants from a Project Funded
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