Spectral characterization and antimicrobial activity of some schiff bases derived from 4-chloro-2-aminophenol and various salicylaldehyde derivatives

Article abstract of DOI:10.1002/cjoc.201180473

A series of N-(5-chloro-2-hydroxyphenyl)-(3/4/5-substituted)- salicylaldimines (I-XI) were synthesized using appropriate synthetic route. Their structures were characterized by FT-IR, UV-Visible, ESI-MS, ¹H and ¹³C NMR spectroscopic techniques and analytical methods. The crystal structure of N-(5-chloro-2-hydroxyphenyl)-5-bromosalicylaldimine (V) was determined by X-ray diffraction at room temperature. Relationship between the melting points and the structures of the compounds was examined. Antimicrobial activity of the compounds was evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis. Antifungal activities were reported for Candida albicans. Schiff bases showed considerable antimicrobial activity against S. aureus, S. epidermidis and C. albicans. N-(5-Chloro-2-hydroxyphenyl)-3-hydroxy- salicylaldimine (II) has the broadest and highest antimicrobial activity according to the others. A series of N-(5-chloro-2-hydroxyphenyl)-(3/4/5- substituted)-salicylaldimines (I-XI) were synthesized using appropriate synthetic route. Relationship between the melting points and the structures of the compounds was examined. Antifungal activities were reported for Candida albicans. Schiff bases showed considerable antimicrobial activity against S. aureus, S. epidermidis and C. albicans. N-(5-Chloro-2-hydroxyphenyl)-3-hydroxy- salicylaldimine (II) has the broadest and highest antimicrobial activity. Copyright

Full text of DOI:10.1002/cjoc.201180473

FULL PAPER
DOI: 10.1002/cjoc.201180473
Spectral Characterization and Antimicrobial Activity of Some
Schiff Bases Derived from 4-Chloro-2-aminophenol and
Various Salicylaldehyde Derivatives
Cinarli, Adema
Gürbüz, Demeta
Tavman, Aydin*,a
Birteksöz, A. Seherb
a Istanbul University, Faculty of Engineering, Department of Chemistry, 34320, Avcilar, Istanbul, Turkey
b Istanbul University, Faculty of Pharmacy, Department of Pharmaceutical Microbiology, 34452, Beyazit, Istanbul,
Turkey
A series of N-(5-chloro-2-hydroxyphenyl)-(3/4/5-substituted)-salicylaldimines (I—XI) were synthesized using
1
appropriate synthetic route. Their structures were characterized by FT-IR, UV-Visible, ESI-MS, H and 13C NMR
spectroscopic techniques and analytical methods. The crystal structure of N-(5-chloro-2-hydroxyphenyl)-5-bromo-
salicylaldimine (V) was determined by X-ray diffraction at room temperature. Relationship between the melting
points and the structures of the compounds was examined. Antimicrobial activity of the compounds was evaluated
against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomo-
nas aeruginosa, Proteus mirabilis. Antifungal activities were reported for Candida albicans. Schiff bases showed
considerable antimicrobial activity against S. aureus, S. epidermidis and C. albicans. N-(5-Chloro-2-hydroxy-
phenyl)-3-hydroxy-salicylaldimine (II) has the broadest and highest antimicrobial activity according to the others.
Keywords salicylaldimine, Schiff bases, X-ray diffraction, spectroscopy, antimicrobial
Introduction
These investigations led to the conception that Schiff
bases of 5-chloro-salicylaldehyde would possess poten-
tial antimicrobial properties. For example, it was re-
ported that (E)-4-chloro-2-[(4-fluorobenzylimino)-
methyl]phenol showed the most favorable antimicrobial
activity against B. subtilis, E. coli, P. fluorescence, S.
aureus and A. niger.[37]
In this study, we describe the synthesis of eleven
salicylaldimine Schiff bases (Scheme 1) derived from
4-chloro-2-aminophenol with various salicylaldehyde
derivatives and characterization of them by using ana-
lytical and spectroscopic techniques. Antibacterial and
antifungal activities of the Schiff bases were evaluated
by the disk diffusion method against six bacteria and C.
albicans as fungus.
Compounds with the structure of —C＝N— (azo-
methine group) are known as Schiff bases, which are
usually synthesized from the condensation of primary
amines and active carbonyl groups. Schiff bases are
important class of compounds in medicinal and phar-
maceutical field.[1] They are facing with growing inter-
est and they may have numerous applications, e.g. as
anticancer,[2,3] antibacterial,[4-10] antiviral,[11] antifun-
gal,[7-10,12] and about their other biological proper-
ties.[13-15] It was reported that some Schiff bases have
antitumor activity.[16,17] Demirbas et al.[18-21] prepared
some 1,2,4-triazole derivatives incorporating Schiff
base structure as antitumor agents. Also these
1,2,4-triazole derivatives have been found to possess
antimicrobial activity.[21-26] On the other hand, lots of
researchers studied on synthesis, characterization and
structure-activity relationship (SAR) of Schiff
bases.[27-30]
Experimental
Chemistry and apparatus
All chemicals and solvents are of reagent grade and
were used without further purification.
Salicylaldimines are known the o-hydroxy deriva-
tives of Schiff bases and they are of particular interest
due to an asymmetric intramolecular hydrogen bond
formed between the oxygen and nitrogen atoms.[15,31-35]
Salicylaldehyde derivatives, with one or more halo-
atoms in the aromatic ring, showed variety of biological
activities like antibacterial and antifungal activities.[36]
Elemental data were obtained with a Thermo Finni-
gan Flash EA 1112 analyzer. Melting points were deter-
mined using an Electro thermal melting-point apparatus.
1H and 13C NMR spectra were run on a Varian Unity
Inova 500 NMR spectrometer. The residual DMSO-d6
*
E-mail: atavman@istanbul.edu.tr.; Tel.: ＋90 212 473 7070; Fax: ＋90 212 473 70 79
Received March 10, 2011; accepted September 6, 2011.
Chin. J. Chem. 2012, 30, 449—459
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Cinarli et al.
FULL PAPER
Scheme 1 Chemical diagram of the Schiff bases under study
(SIR92) and expanded using Fourier techniques. The
non-hydrogen atoms were refined anisotropically. H
atoms were treated as riding, with C—H＝0.95(6) Å
and Uiso(H)＝1.2Ueq(C). All calculations were per-
formed using the CrystalStructure crystallographic
software package.[38] Coordinate parameters of the
structure were deposited with the CSD, deposition
number is CCDC 701403.
OH
3
2
HO
R1
2'
4
N
3'
1
R2
6
1'
4'
5
Cl
6'
5' R3
Compound
R1
R2
H
R3
H
I
H
Determination of antimicrobial activity
II
OH
CH3
H
H
H
Antimicrobial activities against Staphylococcus
aureus ATCC 6538, Staphylococcus epidermidis ATCC
12228, Escherichia coli ATCC 8739, Klebsiella pneu-
moniae ATCC 4352, Pseudomonas aeruginosa ATCC
27853, Proteus mirabilis ATCC 14153 and Candida
albicans ATCC 10231 were determined by the micro
broth dilutions technique strictly following the National
Committee for Clinical Laboratory Standards (NCCLS)
recommendations.[39,40] Mueller-Hinton broth for bacte-
ria and RPMI-1640 medium buffered to pH 7.0 with
MOPS for yeast strain were used as the test medium.
Serial two-fold dilutions ranging from 5000 to 4.9
μg/mL were prepared in medium. The inoculum was
prepared using a 4—6 h broth culture of each bacteria
and 24 culture of yeast strains adjusted to a turbidity
equivalent to a 0.5 McFarland standard, diluted in broth
media to give a final concentration of 5×105 cfu/mL
for bacteria and 0.5×103 to 2.5×103 cfu/mL for yeast
in the test tray. The trays were covered and placed in
plastic bags to prevent evaporation. The trays containing
Mueller-Hinton broth were incubated at 35 ℃ for 18—
20 h and the trays containing RPMI-1640 medium were
incubated at 35 ℃ for 46—50 h. The minimum in-
hibitory concentrations (MIC) were defined as the low-
est concentration of compound giving complete inhibi-
tion of visible growth. Antimicrobial effects of the sol-
vents were investigated against test microorganisms.
According to values of the controls, the results were
evaluated.
III
IV
V
H
H
OH
H
H
H
Br
Cl
VI
VII
VIII
IX
X
H
H
H
H
OH
CH3
NO2
Cl
H
H
H
H
Br
Cl
H
XI
H
Cl
signal was also used as an internal reference. FT-IR
spectra were recorded in KBr disks on a Mattson 1000
FT-IR spectrometer. UV-Visible spectra were per-
formed on a Perkin Elmer Lambda 25 UV/Visible
Spectrometer. The Electron Spray Ionization-Mass
Spectroscopy (ESI-MS) analyses were carried out in
positive ion modes using a Thermo Finnigan LCQ Ad-
vantage MAX LC/MS/MS.
Synthesis of the Schiff bases
The Schiff bases were prepared by condensation re-
action of 4-chloro-2-aminophenol (1.44 g; 10 mmol)
with appropriate salicylaldehyde (e.g. 2,3-dihydroxy-
benzaldehyde for II, 1.38 g; 10 mmol) in 20 mL of
ethanol. This mixture was then refluxed with stirring for
3 h and the solution was allowed at the room tempera-
ture to crystallize the Schiff bases.
The structures of the compounds were confirmed by
1
FT-IR, H NMR, 13C NMR and Mass spectral data and
Results and discussion
elemental analyses.
The analytical data and physical properties of the
Schiff bases are summarized in Table 1. As can be seen
from Table 1, II, IV and VII are structurally isomers.
Also, there are two structural isomers consisting of III
and VIII with the molecular formula C14H12ClNO2.
Crystallography
Diffraction measurements were carried out at (20±1)
℃ on a Rigaku RAXIS RAPID imaging plate area de-
tector with graphite monochromated Mo Kα radiation
(μ＝0.71070 Å), with a distance of 127.40 mm between
the crystal and the detector (Istanbul University Ad-
vanced Analyses Laboratory).
For the structure solution, 147514 reflections were
collected, 4297 were unique (Rint＝0.065); equivalent
reflections were merged. An empirical absorption cor-
rection was applied which resulted in transmission fac-
tors ranging from 0.52 to 1.00. The data were corrected
for Lorentz and polarization effects.
Melting points
It is expected that there are inter- and intramolecular
hydrogen bonding in the all compounds in this study. It
is known that intermolecular hydrogen bonding plays an
important role in high melting points of Schiff bases. It
is noticed that the compound I has the lowest melting
point among all the compounds (Table 1). This observa-
tion shows that the substituents also increase the melting
points of the other compounds (II—XI) in respect to
The structure of V was solved by direct methods
450
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 449—459

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
Table 1 Analytical data and physical properties of the compounds I—XI
Found (calcd)/%
H
Compound
Yield/%
70
m.p./℃
157
232
220
221
201
203
238
173
268
271
279
Color
Light brown
Orange
C
N
I
C13H10ClNO2
II
C13H10ClNO3
III
C14H12ClNO2
IV
C13H10ClNO2
V
C13H9BrClNO2
VI
C13H9Cl2NO2
VII
C13H10ClNO3
VIII
C14H12ClNO2
IX
62.65 (63.04)
4.18 (4.07)
4.01 (3.82)
4.83 (4.62)
3.84 (3.82)
3.28 (2.78)
3.41 (3.22)
4.01 (3.82)
4.51 (4.62)
3.26 (3.10)
2.19 (2.32)
2.74 (2.55)
5.78 (5.66)
58.77 (59.22)
64.20 (64.25)
58.89 (59.22)
47.82 (47.81)
54.17 (55.34)
58.77 (59.22)
64.34 (64.25)
53.44 (53.35)
43.40 (43.25)
49.18 (49.32)
5.54 (5.31)
5.42 (5.35)
5.50 (5.31)
4.56 (4.29)
5.08 (4.96)
5.54 (5.31)
5.11 (5.35)
9.74 (9.57)
3.70 (3.88)
4.56 (4.42)
85
97
Light orange
Dark yellow
Yellow-orange
Orange
73
90
96
66
Brick red
85
Orange
74
Yellow-orange
Orange
C13H9ClN2O4
X
C13H8BrCl2NO2
XI
93
95
Orange
C13H8Cl3NO2
compound I in addition to intermolecular hydrogen
bonding. On the other hand, it is observed that the
melting point of VIII is relatively lower (173 ℃) due
to electron donating of the electropositive methyl group
on the salicyl ring. The methyl group weakens the in-
termolecular hydrogen bonding and as a result of this,
the melting point and thermal stability of the compound
VIII is lower according to the others except the com-
pound I.[32,41,42] Also it can be concluded that methyl
group at the 5'-position strengthens the keto-enol
tautomerism.
of the hydrogen bonding.[32-35,43]
FT-IR spectra
FT-IR spectral data of the compounds are given in
Table 2. Also, brief information of hydrogen bonding
existence in the compounds according to the IR spectra
is presented in Table 2.
Figure 1 Comparison of the IR spectra of the Schiff bases in-
cluding two hydroxy groups.
The broad bands between 2800 and 2400 cm－1 in the
spectra of all the compounds demonstrate the formation
of the OH…N intramolecular hydrogen bond between
OH and N atom of the Schiff base.[32,43]
The IR spectra of the Schiff bases show medium or
strong intensity absorption bands between 1600 and
1650 cm－1 assigned to C＝N stretching mode (Table 2).
The presence of aromatic rings has been identified by
their characteristic ring vibrations at 1500—1400, 1200
Figure 1 shows the changes of intramolecular hy-
drogen bonding in II, IV and VII compounds. The
common property of these three compounds is that they
have two hydroxyl groups: The second OH group is
located at the 3, 4 and 5-positions, for II, IV and VII,
respectively (Scheme 1). It is observed that hydrogen
bonding is strengthening in the order VII＞IV＞II. The
band at 3481 cm－1 of II can be assigned to ν(OH). This
band disappears in the spectra of IV and VII. The broad
—1100 and 930—700 cm－ regions. The absence of
1
bands characteristic of ν(C＝O) and primary amine
ν(NH) confirms the formation of the proposed Schiff
base framework.
The C—O stretching vibrations appear in the 1200—
1250 cm－1 range as strong bands.[44] The C—Cl stretch-
ing vibration is seen in the range 600—700 cm－ as
1
characteristics of the bands in the 3000—2500 cm－
1
medium or weak bands for all of the compounds.[45] In
range in the spectra of IV and VII are related to strength
the IR spectra of IX, the strong or medium bands at
Chin. J. Chem. 2012, 30, 449—459
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Cinarli et al.
FULL PAPER
Table 2 FT-IR spectral data for the compounds I–XI
H-bonding
－
1
Compound
Frequency/cm , KBr pelletsa
in the IR spectra
3040 m, 2919 m, 2854 m,br, 2547 m,br, 1639 m, 1621 s, 1498 s, 1428 m, 1237 m, 1201 s, 1139 m,
1030 m, 902 m, 811 m, 766 s, 657 w
Considerable
H-bonding
I
3483 m ν(OH), 3036 m,br, 2925 m, 2854 m,br, 2693 m,br, 1634 s, 1464 m, 1436 m, 1288 m, 1230 s,
1170 m, 755 m, 657 w
Considerable
H-bonding
II
3071 m,br, 2920 m, 2673 m,br, 2562 m,br, 1624 s, 1595 sh, 1441 m, 1232 s, 1162 m, 1036 m, 817 m,
762 m, 662 w
Considerable
H-bonding
III
IV
V
3178 m,br ν(OH), 3072 m,br, 2926 m, 2553 m,br, 1637 s, 1592 m, 1269 s, 1228 s, 1131 m, 989 m, 915
m, 849 m, 790 m, 662 w
Considerable
H-bonding
3071 m,br, 2925 m,br, 2854 m,br, 2587 m, 1628 m, 1607 w, 1504 s, 1288 m, 1231 m, 1177 m, 1123 m,
816 m, 656 m, 525 w
Considerable
H-bonding
3072 m,br, 2926 m,br, 2542 m,br, 1628 s, 1452 m, 1208 m, 1154 m, 1093 m, 1018 m, 910 m, 831 s,
698 w
Strong hydrogen
bonding
VI
VII
VIII
IX
3063 m,br, 2923 m,br, 2847 m,br, 2689 m,br, 1646 s, 1603 m, 1470 s, 1434 m, 1285 m, 1199 s, 1147
m, 1027 m, 917 m, 836 m, 761 m, 664 m
Considerable
H-bonding
Weak hydrogen
bonding
3428 m, 2925 m, 1631 s, 1585 m, 1508 s, 1438 m, 1294 m, 1240 m, 1162 m, 922 m, 822 m, 656 w
3066 m, 2925 m,br, 2774 m,br, 2557 m,br, 1649 s, 1623 s, 1446 m, 1391 m, 1296 s, 1238 m, 1192 m,
1151 m, 1100 m, 1038 m, 901 m, 837 m, 755 m, 639 m
Considerable
H-bonding
3214 m,br, 3059 m,br, 2925 m,br, 1628 s, 1499 s, 1438 m, 1305 m, 1226 s, 1145 m, 1021 m, 915 m,
845 m, 739 m, 664 m
Weak hydrogen
bonding
X
XI
Considerable
H-bonding
3164 m,br, 3063 m,br, 2921 m, 1628 s, 1508 s, 1438 m, 1217 s, 1149 m, 1034 m, 854 m, 761 m, 660 w
a m, medium; s, strong; sh, shoulder; w, weak; br, broad.
1553 and 1322 cm－ can be assigned to the symmetric
1
and asymmetric ν(NO2), respectively. The C — Br
stretching vibrations are seen at 525 and 506 cm－ as
1
weak bands for the compounds V and X.[46]
UV-visible spectra
The UV-visible spectral data of the compounds are
presented in Table 3. The UV-visible spectra of the
compounds III and X are shown in Figure 2 as sample.
Table 3 UV-visible spectral data of the compounds
Compound
Wavelength (λmax/nm) in MeOH (10－4 mol/L)
449 sha, 354 m,br, 262 m, 214 s
Figure 2 UV-visible spectra of compounds III and X in the
range of 200—500 nm.
I
II
451 w, 349 m,br, 281 m,br, 262 m, 215 s
452 w,br, 352 m,br, 269 m,br, 215 s
422 m,br, 352 m,br, 269 m, 228 sh, 212 s
456 sh, 364 m,br, 262 m, 214 s
The UV-visible absorption spectra were obtained in
methanol at room temperature. The electronic spectra of
the compounds exhibit intense bands in the 200—400
nm region, which may be assignable to n→π* and
π→π* transitions. The 210—300 nm bands are due to
the π→π* transitions of the aromatic rings. The 300—
350 nm bands involve π→π* transitions of the C＝N
group. The longer wavelength band over ca. 400 nm can
be assigned to an intramolecular charge transfer interac-
tion.[47-51]
III
IV
V
VI
VII
VIII
IX
X
452 w,br, 364 m,br, 269 m, 234 sh, 215 s
477 sh, 375 m,br, 349 sh, 269 m, 213 s
451 w,br, 359 m,br, 269 m, 237 sh, 214 s
461 sh, 426 m,br, 350 m,br, 269 m, 262 m, 211 s
462 w,br, 440 sh, 367 m,br, 269 m, 211 s
463 m,br, 437 sh, 365 m,br, 269 m, 213 s
XI
UV-visible spectroscopy is known to be a very sen-
sitive method for studying tautomeric equilibrium in
a sh, shoulder; m, medium; br, broad; s, strong; w, weak.
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
Schiff bases. The two long-wave bands observed in the
electronic spectra of the compounds have been assigned
to the OH and NH forms.[48-54] The bands at ca. 350 nm
observed in spectra of the Schiff bases can be assigned
to the OH-form. The bands above 370 nm can be as-
signed to the NH-forms.[48] A lot of compounds such as
I, II, III, IV and VIII, have the characteristic OH band,
whereas some of them, e.g. VII, X and XI, have char-
acteristic NH band. The UV-visible spectra of the Schiff
bases having the NH band indicate the existence of the
proton transfer equilibrium.
isotopic patterns in the spectra of the compounds in-
cluding more than one chlorine atom (VI, X and XI)
and a bromine atom together with one (V) and two chlo-
rine atoms (X). Considering all the compounds, the
most isotopic patterns are observed in the spectra of the
compound X that includes one bromine and two chlo-
rine atoms as expected (Table 4, Figure 3). The peak
with 100% relative abundance of the compound IV may
be assigned to a dimer molecule for IV, in which a hy-
droxy group is out.
NMR spectra
Mass spectra
1H NMR spectral data and their assignments are
presented in Table 5. The OH protons of 5-chloro-2-hy-
droxyphenyl ring appear in the δ 9.93—10.41 range,
whereas NMR signal values of the salicylaldimine ring
OH protons (at 2'-position) that form intramolecular
hydrogen bonding with the C＝N nitrogen atom, vary
between δ 12.55 and 15.09. The NMR signals of the
second OH protons of the salicylaldimine rings at the
compounds II (3'-position), IV (4'-position) and VII
(5'-position) are seen below δ 10: δ 9.06, 9.95 and 9.04
for II, IV and VII, respectively.
The ESI-MS spectral data of the compounds are
given in Table 4 as molecular ions with the relative
abundance.
All of the mole peaks of the Schiff bases are deter-
mined. It is known that chlorine and bromine have two
isotopes: These isotopes, their percent abundance and
approximately relative proportions are as the follows:
35Cl (75.8%)∶37Cl (24.2%) (3∶1); 79Br (50.7%)∶81Br
(49.3%) (1∶1). There are isotopic patterns in the
ESI-MS spectra of all the compounds because of pres-
ence of chlorine atom. Besides, it is observed a lot of
Table 4 ESI-MS data of the compounds I—XI
Compound and MW (g/mol) Molecular ions (m/z) with relative abundance (%)
I; C13H10ClNO2; 247.68
II; C13H10ClNO3; 263.67
III; C14H12ClNO2; 261.70
248.2 (100, [M＋1]＋), 249.4 (15.1, [M＋2]＋), 250.2 (43.2, [M＋3]＋)
264.5 (31.0, [M＋1]＋), 263.6 (10.5, [M]＋), 262.6 (100, [M－1]＋)
262.6 (100, [M＋1]＋), 263.5 (30.7, [M＋2]＋)
264.5 (38.0, [M＋1]＋), 265.8 (17.2, [M＋2]＋), 509.3 (100, [2M－OH]), 511.3 (71.9), 525.5 (56.7), 526.5
IV; C13H10ClNO2; 263.67
(20.8), 527.5 (22.0)
V; C13H9BrClNO2; 326.57 324.6 (38.0, [M－2]＋), 325.4, 326.7, 327.5, 328.6, 329.7,
280.6 (100, [M－2]＋), 281.7 (11.7, [M－1]＋), 282.5 (65.6, [M]＋), 283.6 (8.1, [M＋1]＋), 284.5 (9.6, [M＋
2]＋)
VI; C13H9Cl2NO2; 282.12
VII; C13H10ClNO3; 263.67 264.5 (31.0, [M＋1]＋), 263.7 (10.5, [M]＋), 262.6 (100, [M－1]＋)
VIII; C14H12ClNO2; 261.70 262.5 (31.6, [M＋1]＋), 261.6 (10.5, [M]＋), 260.6 (100, [M－1]＋)
IX; C13H9ClN2O4; 292.67
290.3 (100, [M－2]＋), 292.4 (65.7, [M]＋), 293.5 (29.3, [M＋1]＋), 294.5 (28.6, [M＋2]＋)
358.8 (41.4, [M－2]＋), 359.9 (6.0, [M－1]＋), 360.8 (100, [M]＋), 361.7 (15.9, [M＋1]＋), 362.5 (49.7, [M＋
1]＋), 363.2 (43.0, [M＋2]＋), 364.1 (9.8, [M＋3]＋), 364.8 (11.7, [M＋4]＋), 365.7 (5.0, [M＋5]＋)
314.7 (87.2, M＋－2), 316.6 (100, [M]＋), 317.7 (14.6, [M＋1]＋), 318.6 (31.5, [M＋2]＋), 319.5 (5.4, M＋＋
3), 320.5 (4.4, M＋＋4)
X; C13H8BrCl2NO2; 361.02
XI; C13H8Cl3NO2; 316.57
Table 5 1H NMR spectral data of the compounds (δH in DMSO-d6)
Chloro-hydroxyphenyl protons
Salicylaldimine protons
Compound
CH＝N
H3
H4
H6
OH
OH
H3'
H4'
H5'
H6'
7.61 dd
7.45 d
J＝2.7
7.50 dd
7.39 dt, br
J＝1.4; 8.5
6.90 dd
7.15 dd
6.95 m
6.95 d
9.95 s
8.97 s 13.39 s 6.95 m
8.95 s 13.74 s 9.06 sa
8.97 s 13.87 s 2.20 sb
6.95 m
I
J＝1.9; 7.8
7.15 dd
J＝2.5; 8.5
7.04 dd
6.74 t
J＝7.8
6.86 t
10.05 s
10.00 s
II
J＝8.8 J＝2.7; 8.5 J＝1.0; 1.5
J＝1.5; 7.8
7.29 dd, br
J＝7.6;1.3
7.42 dd, br
6.96 d
7.15 dd
7.48 d
III
J＝8.8 J＝2.4; 8.8
J＝2.6
J＝7.3; 1.0 J＝7.3; 7.8 J＝7.6; 1.2
Chin. J. Chem. 2012, 30, 449—459
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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453

Cinarli et al.
FULL PAPER
Continued
Chloro-hydroxyphenyl protons
Salicylaldimine protons
Compound
H3
CH＝N
H4
H6
OH
OH
H3'
H4'
H5'
H6'
6.36 dd
J＝2.2; 8.8
7.84 d
6.91 d
7.08 dd
6.24 d
J＝1.9
6.92 d
9.95
7.38 d
J＝8.8
7.37 s
10.20 s, br 8.79 s 13.85 s
IV
J＝8.8 J＝2.5; 8.8
6.96 d 7.52 dd
J＝9.1 J＝2.3; 8.7
6.97 d 7.43 dd
J＝8.8 J＝2.9; 8.8
6.93 d 6.76 dd
J＝8.9 J＝8.9; 2.9
6.94 d 7.14 dd
J＝8.6 J＝2.4; 8.6
6.98 d 7.22 dd
J＝8.6 J＝2.5; 8.6
7.00 d 7.21 dd
s, bra
7.16 dd
7.43 d
J＝2.7
6.96 d
J＝2.9
6.99 d
J＝2.9
7.42 d
J＝2.6
7.61 d
J＝2.6
7.81 dd
10.01 s
8.96 s 13.36 s
—
—
V
VI
J＝8.7 J＝2.3; 8.7
J＝2.7
7.72 d
13.34 7.41 d
7.17 dd
10.02 s, br 8.96 s
s, br
J＝8.6 J＝2.6; 8.6
J＝2.6
7.42 d
6.84 d
J＝8.6 J＝8.6; 2.6
6.84 d 7.21 dd
J＝8.3 J＝2.2; 8.3
7.00 d 8.20 dd
7.12 dd
9.88 s
9.93 s
8.85 s 12.55 s
8.91 s 13.06 s
9.25 s 15.09 s
9.05 s 15.08 s
9.07 s 14.97 s
9.04 sa
2.26 sb
—
VII
VIII
IX
J＝2.6
7.41 d, br
J＝1.9
8.59 d
10.41 s
10.36 s
10.36 s
J＝9.2 J＝9.3; 2.9
J＝2.9
7.66 d
7.58 d
X
—
—
J＝8.6 J＝8.6; 2.6 J＝2.6, 0.6
J＝2.6
J＝2.6
7.62 d
7.00 d
7.22 dd
7.69 d
7.57 d
XI
—
—
J＝8.6 J＝8.6; 2.6
J＝2.6
J＝2.6
J＝2.6
a OH; b 3H (CH3).
Figure 3 ESI-MS spectra of the compound X.
Scheme 2 Keto-enol tautomerism of the compound IX
The chemical shift of the salicylaldimine OH proton
for VII, δ 12.55, is lower than those of the other Schiff
bases. This difference means that the salicylaldimine
OH proton of VII has less acidic character and, conse-
quently, has weaker intermolecular hydrogen bonding
according to the others. This OH proton shows the
highest shift at IX, X and XI: δ 15.09, 15.08 and 14.97,
respectively. Namely, salicylaldimine OH protons of
these three Schiff bases exhibit higher acidic character
than the others. In other words the keto-enol tautomer-
ism is dominant at IX, X and XI in DMSO (Scheme 2).
OH
OH
HO
O
N
NH
Cl
Cl
NO2
NO2
1H NMR spectra of X and XI are very similar to
each other due to their structural similarities (Figures 4
and 5).
13C NMR (APT) spectral data are given in Table 6
454
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 449—459

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
with their assignments. All of the carbon atoms were
observed and APT spectra of the compounds are
straightforward. APT spectrum of IV is presented in
Figure 6. Azomethine carbons of the compounds appear
between δ 161.4 and 164.1. The carbon atoms bonded to
the OH group (C2) at chloro-hydroxyphenyl ring give
signals at the lower δ value (between δ 150.4 and 151.0)
than the carbon atoms that bonded to the other OH
group (δ 151.4—170.3). The carbon atoms bonded to
the chlorine atom (C5) of all the compounds appear at ca.
δ 124.[48,54] The carbon atoms bonded to the second OH
oxygen atom of the salicylaldimine ring, C3', C4' and C5'
for the compounds II, IV and VII, appear at δ 146.6,
163.3 and 150.4, respectively. The methyl carbons of
III and VIII are observed at δ 15.9 and 20.6, respec-
tively.
The asymmetric unit of V consists of two independ-
ent molecules (Figure 7). The molecules are closely
similar except that they are inverted with respect to each
other. There are two independent molecules in the unit
cell and they are related by a non-crystallographic in-
version center. The inversion center is located at the cell
origin; each cell corner is surrounded by four oxygen
atoms.
Many Schiff bases have N—H…O type intramo-
lecular hydrogen bond in the literature. For example,
Popovic et al.[32] investigated the crystal structure of
N-(2-hydroxyphenyl)-5-methoxysalicylaldimine and
they found that this Schiff base has N—H…O type in-
tramolecular hydrogen bond (N—H and H…O distances
are 0.95 and 1.73 Å, respectively). In this study, it is
observed that O(2)—H(16) bond length (O—H) is
0.950(9); O(3)—H(18) bond length (O—H) is 0.95(1)
and N(1)—H(16) and N(2)—H(18) distances (C＝N…
H—O) are 1.80(1) and 1.87(1) Å, respectively (Table 8).
This shows an N…H—O type strong intramolecular
hydrogen bonding in the molecule. It is probable that
X-ray analysis
The crystal data and details of data processing are
given in Table 7. Table 8 contains the hydrogen bond
geometry parameters. Selected bond lengths and angles
are given in Table 9.
Figure 4 1H NMR spectrum of compound X between δ 6.9 and 7.9.
Figure 5 1H NMR spectrum of compound XI between δ 6.9 and 7.7.
Chin. J. Chem. 2012, 30, 449—459
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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455

Cinarli et al.
FULL PAPER
Table 6 13C NMR spectral (APT) data of the compounds (δC in DMSO-d6)
Chloro-hydroxyphenyl carbons
C2 C3 C4 C5
Salicylaldimine carbons
C2’ C3’ C4’ C5’
Compound
C1
N＝CH
C6
C1’
C6’
I
II
IIIa
IV
V
137.0 150.8 118.5 128.0 123.8 120.0
136.4 150.7 118.4 127.9 123.8 119.9
136.8 150.9 118.5 128.0 123.8 119.9
137.0 150.4 118.3 127.0 123.8 119.5
136.6 151.0 118.6 128.4 123.8 119.9
136.7 151.0 118.6 128.4 123.8 119.9
137.5 150.8 118.4 127.8 123.8 119.9
137.3 150.8 118.5 127.9 123.8 119.8
138.8 150.6 118.7 129.1 124.0 120.1
134.0 150.9 118.7 129.1 123.9 119.7
134.1 150.9 118.7 129.1 123.9 119.7
163.7
163.5
164.1
162.5
161.9
162.0
163.5
163.7
161.4
161.4
161.4
119.6 161.3 110.0 117.4 120.1 133.2
119.8 151.4 146.6 119.3 119.6 123.4
119.2 159.8 125.9 131.1 119.1 134.7
112.9 164.8 103.2 163.3 108.4 135.1
122.0 160.4 119.8 134.6 110.3 136.1
123.0 160.0 119.4 133.4 121.4 131.7
120.1 154.1 121.8 117.9 150.4 117.7
119.8 159.1 117.2 132.9 128.1 134.7
118.3 170.3 119.6 129.3 133.6 130.1
122.1 159.4 112.8 131.8 120.5 135.9
120.7 158.5 123.1 131.1 121.7 133.1
VI
VII
VIIIb
IX
X
XI
a δ 15.9 (CH3); b δ 20.6 (CH3).
Figure 6 APT spectrum of the compound IV between δ 100 and 170 range.
Table 7 Crystal and experimental data for the compound V
Continued
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
C13H9BrClNO2
326.57
θ range for data collection/(º)
Data collection
2.6—30.0
CRYSTALCLEAR
0.130
293
R [I＞3σ(I)]
0.71070
Rw [I＞3σ(I)]
－
Largest diff. peak and hole/(e•Å )
0.070
3
Orthorhombic
1.84 and －1.28
Pnma
a＝14.8085(3),
b＝6.07160(10)
c＝28.4266(4),
β＝90
Table 8 Hydrogen-bond geometry [Å, (°)] for V
D—H…A D—H H…A D…A D—H…A
O(2)—H(16)…N(1) 0.950(9) 1.80(1) 2.55(1) 133.1(9)
O(3)—H(18)…N(2)
0.95(1) 1.87(1) 2.59(1) 130.4(9)
Unit cell dimensions/(Å, °)
Cell volume/Å3
2555.87(8)
－
Z, Calculated density/(g•cm )
3
8, 1.697
Absorption coefficient (Mo Kα) 34.26 cm–1
the electronegative Cl and Br atom substitutions on the
N-aryl and the salicyl parts, respectively, cause the N…
H—O type intramolecular hydrogen bonding.[55]
F(000)
1296
Crystal size/mm3
0.30×0.20×0.20
The C—C bond lengths for carbons near electro-
negative atoms on the N-aryl and the salicyl rings are
shorter than the phenolic C—C length. For example,
C(21)—C(26), C(24)—C(25), C(5)—C(6) and C(16)—
C(17) bond lengths are 1.23, 1.34, 1.33 and 1.35 Å, re-
spectively. There are many similar observations in the
literature.[56-58] Consequently, some C—C bond lengths
are longer than the phenolic C—C length such as C(1)
Linear absorption coefficient
(μ/cm )
34.3
－
1
No. of observations [I＞3.00σ(I)] 3634
Refinement method
Full-matrix least-squares on F
Goodness of fit indicator
1.167
－20≤h≤20, －8≤k≤8,
－40≤l≤40
Index ranges
456
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 449—459

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
Table 9 Selected bond lengths (Å) and angles (º) for V
Br(1)—C(5)
Cl(1)—C(10)
O(1)—C(13)
O(3)—C(22)
N(1)—C(8)
N(2)—C(14)
C(1)—C(2)
C(3)—C(4)
C(5)—C(6)
C(10)—C(11)
1.90(1)
1.753(9)
1.29(1)
1.28(1)
1.45(1)
1.37(1)
1.36(1)
1.37(2)
1.33(1)
1.38(1)
Br(2)—C(25)
Cl(2)—C(16)
O(2)—C(2)
O(4)—C(19)
C(22)—C(23)
N(2)—C(20)
C(1)—C(6)
1.87(1)
1.72(1)
1.30(1)
1.38(1)
1.45(1)
1.31(1)
1.51(1)
1.42(2)
1.45(2)
1.34(2)
C(14)—C(19)
C(16)—C(17)
C(18)—C(19)
N(1)—C(7)
1.41(1)
1.35(1)
1.39(2)
1.29(1)
1.37(1)
1.34(1)
1.46(1)
1.40(2)
1.23(1)
1.41(2)
C(14)—C(15)
C(24)—C(25)
C(1)—C(7)
C(4)—C(5)
C(20)—C(21)
C(21)—C(26)
C(12)—C(13)
C(8)—C(9)
C(11)—C(12)
C(7)-N(1)-C(8)
C(3)-C(2)-O(2)
O(2)-C(2)-C(1)
Br(1)-C(5)-C(4)
C(9)-C(8)-N(1)
O(1)-C(13)-C(8)
C(15)-C(14)-N(2)
O(4)-C(19)-C(14)
C(21)-C(20)-N(2)
C(23)-C(22)-O(3)
128.1(8)
122.6(9)
119.1(8)
119.6(7)
117(1)
C(14)-N(2)-C(20)
Br(2)-C(25)-C(24)
C(6)-C(5)-Br(1)
N(1)-C(7)-C(1)
125.6(8)
118.2(8)
120.4(8)
119.3(7)
115(1)
C(13)-C(8)-N(1)
O(1)-C(13)-C(12)
C(19)-C(14)-N(2)
O(4)-C(19)-C(18)
C(22)-C(21)-C(20)
O(3)-C(22)-C(21)
117(1)
126(1)
127.5(8)
116(1)
115.8(8)
123.2(9)
109.5(9)
125(1)
129.7(8)
119.5(9)
around C—N single bond. The C(8)-N(1)-C(7)-C(1)
and C(14)-N(2)-C(20)-C(21) moieties have cis confor-
mation with torsion angles of 176.4° and －176(1)°,
respectively.
Antimicrobial activity
The results concerning in vitro antimicrobial activity
of the compounds together with MIC values of com-
pared antibiotic and antifungal reagents are presented in
Table 10.
At a glance Table 10, it can be seen that the com-
pounds II and VII have the broadest activities among
all the compounds. Common feature of the compounds
II and VII is that they have two OH groups at the sali-
cylaldimine part. It would suggest that the compound II
[N-(5-chloro-2-hydroxyphenyl)-3-hydroxy-salicylaldi-
mine] has the broadest and highest activity according to
the others. It is observed that most of the compounds are
effective on S. epidermidis and C. albicans. Generally,
the antifungal effect of the compounds (on C. albicans)
is higher than their antibacterial effects (on S. epider-
midis). For example, MIC values of the compound VI
are 19.5 and 78 µg/mL on C. albicans and S. epider-
midis, respectively (lower MIC value means higher an-
timicrobial effect). The compound III did not show any
activity on all the microorganisms, similarly the com-
pound VIII exhibited weak antimicrobial activity on S.
epidermidis only. It may be deduced that methyl group
decreases the antimicrobial activity considering the
Figure 7 A molecular drawing of the asymmetric unit of the
compound V, showing 50% probability displacement ellipsoids
and the atom-numbering scheme. Broken line shows intra-mo-
lecular hydrogen bond.
—C(6) (1.51 Å) and C(21)—C(22) (1.62 Å) (Table 9).
C-N-C bond angles are 133.1(9)° and 130.4(9)º for
the C(7)-N(1)-C(8) and C(14)-N(2)-C(20) bonds, for the
molecules A and A', respectively. C＝N bond lengths
are 1.31 [C(20)—N(2)] and 1.29 [C(7)—N(1)] Å, and
they are in line with the literature data.[32,34,58,59]
According to the C(20)-N(2)-C(14)-C(15) and
C(7)-N(1)-C(8)-C(9) torsion angles, 2(1)° and 9(1)°
respectively, the molecules are non-planar and twisted
Chin. J. Chem. 2012, 30, 449—459
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www.cjc.wiley-vch.de
457

Cinarli et al.
FULL PAPER
Table 10 In vitro antimicrobial activity of the compounds I—
XI (MIC, µg/mL)
ing methoxy group were more effective especially on S.
epidermidis and C. albicans.[37] In this study, it is ob-
served that some Schiff bases (I, II, V and IX) are also
effective on S. aureus besides S. epidermidis and C.
albicans.
The crystal structure of N-(5-chloro-2-hydroxy-
phenyl)-5-bromosalicylaldimine (V) is determined by
X-ray diffraction at room temperature. It crystallizes in
orthorhombic system, and space group Pnma. Unit-cell
dimensions are as follows: a ＝ 14.8085(3) Å, b ＝
6.07160(10) Å, c＝28.4266(4) Å, V＝2555.87(8) Å3,
Z＝8. Non-planar title compound has N…H—O type
intramolecular hydrogen bonding. Two independent
Microorganisma
Compound
Sab Seb Ecc
Kpc Pac Pmc Ca
d
78 78
—
—
—
—
—
—
—
312
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
39
19.5
—
I
II
39 78 156
III
IV
V
—
—
—
—
—
—
—
156
312
19.5
19.5
78
78 78
VI
VII
VIII
IX
X
—
—
—
78
39 156
molecules in the unit cell are related by
a
non-crystallographic inversion center. Some phenolic C
—C lengths are shorter or longer than the expected be-
cause of the electronegative group substitutions on the
N-aryl and the salicyl parts.
As a conclusion, it can be said that the considerable
antimicrobial activities of the Schiff bases against S.
aureus, S. epidermidis and C. albicans warranted further
investigation on similar compounds.
156
—
—
—
—
—
62.5 125
—
—
—
125
–
19.5
3.9
—
XI
Ciprofloxacin 0.125 156 0.0625 0.0625 2.00 0.0312
Fluconazole
—
—
—
—
—
—
1.0
a
Sa: Staphylococcus aureus ATCC 6538, Se: Staphylococcus
epidermidis ATCC 12228, Ec: Escherichia coli ATCC 8739, Kp:
Klebsiella pneumoniae ATCC 4352, Pa: Pseudomonas
aeruginosa ATCC 1539, Pm: Proteus mirabilis ATCC 14153, Ca:
Candida albicans ATCC 10231. Gram(＋). Gram(－). An-
timicrobial activity was not detected.
Supplementary material
Crystallographic data for the structure reported in
this paper have been deposited at the Cambridge Crys-
tallographic Data Centre (CCDC 701403). Copies of the
data can be obtained free of charge upon application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[e-mail: deposit@ccdc.cam.ac.uk].
b
c
d
common points of III and VIII are to have a methyl
group. It is an important observation that compound XI,
including three chlorine atoms, showed considerable
antifungal activity (MIC＝3.9 µg/mL). It is observed
that all the compounds did not show significant activity
(or they have very low activity) toward K. pneumoniae,
P. aeruginosa and P. mirabilis.
Acknowledgement
This work was supported by the Research Fund (No.
1519) of Istanbul University. The authors thank N. Gül-
şah Deniz for her useful comments on crystallographic
discussions.
Conclusions
It is known that salicylaldimines have strong in-
tramolecular hydrogen bonding between C＝N and OH
groups.[31-35,43] In this study the intramolecular hydrogen
bonding is proved by spectroscopic methods. For exam-
ple the broad bands between 2800 and 2400 cm－1 in the
IR spectra of all the compounds demonstrate the
formation of intramolecular hydrogen bonding between
OH hydrogen and C＝N nitrogen atoms of the Schiff
bases. Appearing of the NMR signal of the
salycilaldimine OH hydrogen above δ 12.50 is related
with the intramolecular hydrogen bonding.
Our study results are in line with the literature al-
though there are very limited studies on antimicrobial
activities of similar compounds. For example, it was
reported that (E)-4-chloro-2-[(4-fluorobenzylimino)-
methyl]phenol showed the most favorable antimicrobial
activity against B. subtilis, E. coli, P. fluorescence, S.
aureus and A. niger.[38] In our previous study some
N-(5-chloro-2-hydroxyphenyl)-phenylaldimines includ-
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(E1103107 Zhao, X.)
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