Spectral characterization and antimicrobial activity of some Schiff bases derived from 4-methyl-2-aminophenol

Article abstract of DOI:10.1002/cjoc.201100237

A series of N-(5-methyl-2-hydroxyphenyl)-(2/3/4/5-substituted)- benzaldimines (I-XIII) 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-methyl-2-hydroxyphenyl)-3,4-dimethoxybenzaldimine (XIII) was determined by X-ray diffraction at room temperature. Relationship between the melting points and the structures of the compounds were examined. Antibacterial activities of the compounds were evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis. Antifungal activities were reported for Candida albicans. Some of the Schiff bases showed considerable antimicrobial activity against S. aureus and C. albicans. Copyright

Full text of DOI:10.1002/cjoc.201100237

FULL PAPER
DOI: 10.1002/cjoc.201100237
Spectral Characterization and Antimicrobial Activity of Some
Schiff Bases Derived from 4-Methyl-2-aminophenol
Gürbüz, Demeta
Cinarli, Adema
Tavman, Aydin*,a
Birteksöz, A. Seherb
a Department of Chemistry, Faculty of Engineering, Istanbul University, 34320, Avcilar, Istanbul, Turkey
b Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Istanbul University, 34452,
Beyazit, Istanbul, Turkey
A series of N-(5-methyl-2-hydroxyphenyl)-(2/3/4/5-substituted)-benzaldimines (I—XIII) were synthesized us-
ing 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-methyl-2-hydroxyphenyl)-
3,4-dimethoxybenzaldimine (XIII) was determined by X-ray diffraction at room temperature. Relationship between
the melting points and the structures of the compounds were examined. Antibacterial activities of the compounds
were evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumo-
niae, Pseudomonas aeruginosa and Proteus mirabilis. Antifungal activities were reported for Candida albicans.
Some of the Schiff bases showed considerable antimicrobial activity against S. aureus and C. albicans.
Keywords Schiff bases, methylhydroxyphenyl, spectroscopy, X-ray diffraction, antimicrobial
Introduction
agents.[25-30]
In this study, keeping in view the facts mentioned
Schiff bases are some of the most widely used or-
ganic compounds. They are used as pigments and dyes,
catalysts, intermediates in organic synthesis, and as
polymer stabilizers.[1,2] They are also used as substrates
in the preparation of a number of industrial and bio-
logically active compounds via ring closure, cycloaddi-
tion, and replacement reactions.[3,4]
above, we synthesized thirteen benzaldimine Schiff
bases (Scheme 1) derived from 4-methyl-2-amino-
phenol with various salicyl- and dimethoxy-benzal-
dehyde derivatives and characterized them by using
analytical and spectroscopic techniques. Antibacterial
and antifungal activities of the Schiff bases were evalu-
ated by the disk diffusion method against six bacteria
and C. albicans as fungus.
Schiff bases are widely applicable in analytical de-
termination, using reactions of condensation of primary
amines and carbonyl compounds in which the azome-
thine bond is formed (determination of compounds with
an amino or carbonyl group); using complex formation
reactions (determination of amines, carbonyl com-
pounds and metal ions); or utilizing the variation in their
spectroscopic characteristics following changes in pH
and solvent.[5-9] They exhibit a broad range of biological
activities, including antifungal, antibacterial, antimalar-
ial, antiproliferative, anti-inflammatory, antiviral, anti-
pyretic, and herbicide properties.[1,10,11] On the other
hand, it was reported that some Schiff bases have anti-
tumor activity.[12-20] Imine or azomethine groups are
present in various natural, natural-derived, and
non-natural compounds. The imine group present in
such compounds has been shown to be critical to their
biological activities.[21-24] Schiff bases have also been
extensively used as ligands in coordination chemistry
because of their excellent donor abilities and chelating
Experimental
Chemistry and apparatus
All chemicals and solvents are of reagent grade and
were used without further purification. Elemental data
were obtained with a Thermo Finnigan Flash EA 1112
analyzer. Melting points were determined using an
1
Electro thermal melting-point apparatus. H NMR and
13C NMR spectra were run on a Varian Unity Inova 500
NMR spectrometer. The residual DMSO-d6 signal was
also used as an internal reference. FT-IR spectra were
recorded in KBr disks on a Mattson 1000 FT-IR spec-
trometer. UV-Visible spectra were performed on a
Perkin Elmer Lambda 25 UV/Visible Spectrometer. The
Electron Spray Ionization-Mass Spectrometry (ESI-MS)
analyses were carried out in positive ion modes using a
Thermo Finnigan LCQ Advantage MAX LC/MS/MS.
*
E-mail: atavman@istanbul.edu.tr.; Tel.: ＋90 212 473 7070; Fax: ＋90 212 473 70 79
Received August 19, 2011; accepted November 7, 2011.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc201100237 or from the author.
970
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Chin. J. Chem. 2012, 30, 970—978

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
Scheme 1
120.25 (C-1'); IR (KBr) ν: 3426, 2909, 1632, 1622,
1523, 1490, 1284, 1231, 1191, 1145, 1009, 823, 770,
OH
－
1
3
2
6
561 cm ; UV-vis (MeOH) λmax: 446, 354, 350, 269,
231, 220 nm; MS (70 eV) m/z (%): 228 ([M＋1]＋, 100),
229 ([M＋2]＋, 15.1). Anal. calcd for C14H13NO2: C
74.00, H 5.77, N 6.16; found C 73.82, H 5.86, N 6.28.
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-3-meth-
ylbenzaldimine; N-(5-methyl-2-hydroxyphenyl)-3-
methylsalicylaldimine (II): m.p. 181 ℃; color: dirty
R1
R2
4
2'
N
3'
1
1'
5
R3
CH
4'
H3C
6'
5'
R4
1
Compound
R1
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
R2
H
R3
H
R4
Yield/% m.p./℃
yellow; H NMR (DMSO-d6, 500 MHz) δ: 9.47 (s, 1H,
I
H
H
60
90
165
181
185
203
214
174
185
261
253
238
98
OH), 8.93 (s, 1H, CH＝N), 7.40 (d, br, J＝7.8 Hz, 1H,
H-6'), 7.25 (d, br, J＝7.3 Hz, 1H, H-6), 7.18 (d, br, J＝
1.5 Hz, 1H, H-4'), 6.92 (dd, J＝8.3, 1.9 Hz, 1H, H-4),
6.84 (m, 2H, H-3＋H-5'), 2.24 (s, 3H, 5-CH3), 2.20 (s,
3H, 3'-CH3); 13C NMR (DMSO-d6, 125 MHz) δ: 162.33
(CH＝N), 134.21 (C-4'), 130.76 (C-6'), 129.10 (C-4),
120.51 (C-6), 118.82 (C-5'), 177.10 (C-3), 20.86
(5-CH3), 15.98 (3'-CH3), 159.96 (C-2'), 149.52 (C-2),
135.00 (C-1), 129.00 (C-5), 125.81 (C-3'), 119.29 (C-1');
IR (KBr) ν: 3426, 3032, 2915, 1614, 1546, 1514, 1293,
II
CH3
H
H
III
IV
V
H
CH3 81
OCH3
H
H
H
88
76
65
73
86
94
80
66
OCH3
H
H
VI
VII
VIII
IX
X
H
Cl
Br
Cl
Cl
Br
H
H
H
Cl
H
Br
H
－
1
1232, 1039, 813, 761 cm ; UV-vis (MeOH) λmax: 452,
354, 270, 262, 218, 212 nm; MS (70 eV) m/z (%): 242
([M＋1]＋, 31.0), 241 ([M]＋, 100). Anal. calcd for
C15H15NO2: C 74.67, H 6.27, N 5.81; found C 74.96, H
6.41, N 5.70.
OCH3
H
H
XI
XII
XIII
OCH3
H
OCH3
H
OCH3
OCH3 55
80
72
H
OCH3 OCH3
H
137
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-5-meth-
ylbenzaldimine; N-(5-methyl-2-hydroxyphenyl)-5-
methylsalicylaldimine (III): m.p. 185 ℃; color: dark
orange; UV-vis (MeOH) λmax: 458, 359, 326, 269, 262,
213 nm; 1H NMR (DMSO-d6, 500 MHz) δ: 13.44 (s, 1H,
OH-2'), 9.41 (s, 1H, OH), 8.87 (s, 1H, CH＝N), 7.38 (d,
J＝1.9 Hz, 1H, H-6'), 7.18 (dd, J＝8.3, 1.9 Hz, 1H,
H-4'), 7.13 (d, J＝1.5 Hz, 1H, H-6), 6.91 (dd, J＝8.3 Hz,
1H, H-3'), 6.82 (m, 2H, H-3＋H-4), 2.26 (s, 3H, 5-CH3),
2.23 (s, 3H, 5'-CH3); 13C NMR (DMSO-d6, 125 MHz) δ:
162.06 (CH＝N), 134.18 (C-4'), 132.70 (C-6'), 129.03
(C-4), 120.64 (C-6), 117.17 (C-3), 117.06 (C-3'), 20.86
(5-CH3), 20.66 (5'-CH3), 159.17 (C-2'), 149.47 (C-2),
135.46 (C-1), 128.99 (C-5), 127.90 (C-5'), 119.93 (C-1');
IR (KBr) ν: 3426, 2915, 1635, 1522, 1502, 1466, 1285,
Synthesis of the Schiff bases
The Schiff bases were prepared by condensation re-
action of 4-methyl-2-aminophenol (246 mg; 2 mmol)
with appropriate salicylaldehyde (e.g. 3-methylsalicylal-
dehyde for II, 272 mg; 2 mmol) in 10 mL of ethanol.
This mixture was then refluxed with stirring for 3 h and
the solution was allowed at the room temperature to
crystallize the Schiff bases. The crystalline product was
dissolved in ethanol and filtered for recrystallization.
The filtrate was kept at room temperature for 2—3 d to
slow evaporation. After this period the crystals suitable
for X-ray diffraction study were formed. The single
crsytals were filtered and dried at room temperature.
The structures of the compounds were confirmed by
－
1
1252, 1200, 1168, 1108, 1095, 822, 592 cm ; MS (70
eV) m/z (%): 242 ([M＋1]＋, 100). Anal. calcd for
C15H15NO2: C 74.67, H 6.27, N 5.81; found C 74.56, H
6.38, N 5.94.
1
FT-IR, UV-vis, H NMR and 13C NMR, mass spec-
trometry techniques and elemental analysis. The com-
pounds I—V and VIII—XIII are the new compounds
(except VI and VII) and IR, UV and NMR spectra of
the compounds are given as Supporting Information.
N-(5-methyl-2-hydroxyphenyl)-2-hydroxybenzaldi-
mine; N-(5-methyl-2-hydroxyphenyl)-salicyl-aldimine
(I): m.p. 165 ℃ ; color: orange-red; 1H NMR
(DMSO-d6, 500 MHz) δ: 13.78 (s, 1H, OH-2'), 9.43 (s,
1H, OH), 8.94 (s, 1H, CH＝N), 7.59 (dd, J＝1.6, 7.3 Hz,
1H, H-6'), 7.36 (dt, br, J＝1.6, 7.3 Hz, 1H, H-4'), 7.16
(d, J＝1.6, 1H, H-6), 6.93 (m, 3H, H-4＋H-3'＋H-5'),
6.84 (d, J＝7.8 Hz, H-3), 2.24 (s, 3H, CH3); 13C NMR
(DMSO-d6, 125 MHz) δ: 162.07 (CH＝N), 133.42
(C-4'), 132.93 (C-6'), 129.15 (C-4), 120.57 (C-6),
119.37 (C-5'), 117.37 (C-3), 117.09 (C-3'), 20.85 (CH3),
161.47 (C-2'), 149.51 (C-2), 135.22 (C-1), 129.01 (C-5),
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-3-meth-
oxybenzaldimine; N-(5-methyl-2-hydroxyphenyl)-3-
methoxysalicylaldimine (IV): m.p. 203 ℃; color: or-
1
ange-red; H NMR (DMSO-d6, 500 MHz) δ: 14.07 (s,
1H, OH-2'), 9.49 (s, 1H, OH), 8.93 (s, 1H, CH＝N),
7.18 (s, br, 1H, H-6), 7.16 (d, J＝7.8 Hz, 1H, H-6'), 7.05
(d, J＝7.8 Hz, 1H, H-4), 6.92 (d, br, J＝8.3 Hz, 1H,
H-4'), 6.84 (s, br, 1H, H-5'), 6.82 (d, J＝7.8 Hz, 1H,
H-3), 3.79 (s, 3H, OCH3), 2.23 (s, 3H, CH3); 13C NMR
(DMSO-d6, 125 MHz) δ: 161.89 (CH＝N), 129.16
(C-4), 124.47 (C-6), 120.42 (C-6'), 118.54 (C-3), 117.07
(C-5'), 115.88 (C-4'), 56.56 (OCH3), 20.86 (CH3),
152.69 (C-2'), 149.38 (C-3'), 148.9 (C-2), 134.67 (C-1),
129.02 (C-5), 119.94 (C-1'); IR (KBr) ν: 3450, 2927,
Chin. J. Chem. 2012, 30, 970—978
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Gürbüz et al.
FULL PAPER
1614, 1510, 1461, 1457, 1349, 1208, 1172, 1047, 813,
3447, 3076, 2911, 1638, 1611, 1522, 1445, 1413, 1381,
－
－
1
1
745, 721, 576 cm ; UV-vis (MeOH) λmax: 460, 355,
309, 268, 262, 230, 213 nm; MS (70 eV) m/z (%): 257
([M]＋, 100). Anal. calcd for C15H15NO3: C 70.02, H
5.88, N 5.44; found C 70.02, H 5.96, N 5.42.
1252, 1168, 1124, 1031, 922, 878, 814, 685, 548 cm ;
UV-vis (MeOH) λmax: 458, 363, 268, 262, 242, 213 nm;
MS (70 eV) m/z (%): 306 ([M]＋, 100), 307 ([M＋1]＋,
18.0), 308 ([M＋2]＋, 97.1), 309 (9.3, [M＋3]＋), 311
([M＋4]＋, 9.6). Anal. calcd for C14H12BrNO2: C 54.92,
H 3.95, N 4.58; found C 55.07, H 4.01, N 4.45.
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-4-meth-
oxybenzaldimine; N-(5-methyl-2-hydroxyphenyl)-4-
methoxysalicylaldimine (V): m.p. 214 ℃; color: dark
yellow; 1H NMR (DMSO-d6, 500 MHz) δ: 14.41 (s, 1H,
OH-2'), 9.46 (s, 1H, OH), 8.82 (d, J＝1.6 Hz, 1H, CH＝
N), 7.43 (d, J＝8.8 Hz, 1H, H-6'), 7.16 (d, J＝1.6 Hz,
1H, H-6), 6.88 (dd, J＝8.8, 1.6 Hz, 1H, H-4), 6.82 (d,
J＝8.3 Hz, 1H, H-3), 6.44 (dd, J＝8.8, 2.6 Hz, 1H,
H-5'), 6.37 (d, J＝2.6 Hz, 1H, H-3'), 3.78 (s, 3H, OCH3),
2.23 (s, 3H, CH3); 13C NMR (DMSO-d6, 125 MHz) δ:
160.24 (CH＝N), 134.51 (C-6'), 128.39 (C-4), 120.03
(C-6), 116.93 (C-3), 107.17 (C-5'), 101.77 (C-3'), 56.04
(OCH3), 20.90 (CH3), 166.51 (C-4'), 164.50 (C-2'),
148.80 (C-2), 134.15 (C-1), 129.04 (C-5), 113.73 (C-1');
IR (KBr) ν: 3440, 2938, 1625, 1609, 1523, 1486, 1457,
1315, 1290, 1237, 1221, 1127, 1022, 797, 609, 569
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-3,5-di-
chlorobenzaldimine; N-(5-methyl-2-hydroxyphenyl)-
3,5-dichlorosalicylaldimine (VIII): m.p. 261 ℃; color:
dark yellow; 1H NMR (DMSO-d6, 500 MHz) δ: 9.94 (s,
1H, OH), 9.07 (s, 1H, CH＝N), 7.64 (d, J＝2.4 Hz, 1H,
H-4'), 7.60 (d, J＝2.9 Hz, 1H, H-6'), 7.33 (s, 1H, H-6),
7.00 (dd, J＝8.3, 1.5 Hz, 1H, H-4), 6.89 (d, J＝8.3 Hz,
1H, H-3), 2.26 (s, 3H, CH3); 13C NMR (DMSO-d6, 125
MHz) δ: 159.25 (CH＝N), 133.03 (C-4'), 130.98 (C-4),
130.32 (C-6'), 119.87 (C-6), 117.25 (C-3), 20.89 (CH3),
160.54 (C-2'), 149.31 (C-2), 131.28 (C-1), 129.29 (C-5),
123.81 (C-5'), 120.41 (C-3'), 120.06 (C-1'); IR (KBr) ν:
3210, 2922, 1638, 1622, 1506, 1350, 1277, 1211, 1148,
1016, 853, 814, 754, 671; UV-vis (MeOH) λmax: 466,
364, 303, 268, 262, 246, 216 nm; MS (70 eV) m/z (%):
296 ([M]＋, 100), 297 ([M＋1]＋, 6.5), 298 ([M＋2]＋,
72.0), 299 ([M＋3]＋, 18.3), 300 ([M＋4]＋, 9.9), 301
([M＋5]＋, 15.1), 302 ([M＋6]＋, 4.9). Anal. calcd for
C14H11Cl2NO2: C 56.78, H 3.74, N 4.73; found C 56.64,
H 3.61, N 4.68.
－
1
cm ; UV-vis (MeOH) λmax: 452, 425, 357, 342, 309,
256, 214 nm; MS (70 eV) m/z (%): 257 ([M]＋, 100).
Anal. calcd for C15H15NO3: C 70.02, H 5.88, N 5.44;
found C 69.90, H 5.84, N 5.50.
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-5-chloro-
benzaldimine; N-(5-methyl-2-hydroxyphenyl)-5-chloro-
1
salicylaldimine (VI): m.p. 174 ℃; color: orange; H
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-3-bromo-
5-chlorobenzaldimine; N-(5-methyl-2-hydroxyphenyl)-
3-bromo-5-chlorosalicylaldimine (IX): m.p. 253 ℃;
color: orange; 1H NMR (DMSO-d6, 500 MHz) δ: 9.95 (s,
1H, OH), 9.05 (s, 1H, CH＝N), 7.77 (d, J＝2.9 Hz, 1H,
H-6'), 7.64 (d, J＝2.4 Hz, 1H, H-6), 7.33 (d, J＝1.5 Hz,
1H, H-4'), 7.00 (dd, J＝8.3, 1.9 Hz, 1H, H-4), 6.89 (d,
J＝8.3 Hz, 1H, H3), 2.26 (s, 3H, CH3); 13C NMR
(DMSO-d6, 125 MHz) δ: 159.19 (CH＝N), 135.88
(C-4'), 131.65 (C-6'), 130.34 (C-4), 119.90 (C-6),
117.25 (C-3), 20.89 (CH3), 161.37 (C-2'), 149.32 (C-2),
131.19 (C-1), 129.30 (C-5), 120.85 (C-5'), 119.79 (C-1'),
113.83 (C-3'); IR (KBr) ν: 3449, 3238, 2915, 1640,
1617, 1501, 1346, 1277, 1208, 1138, 1016, 854, 815,
NMR (DMSO-d6, 500 MHz) δ: 13.81 (s, 1H, OH-2'),
9.51 (s, 1H, OH), 8.94 (s, 1H, CH＝N), 7.70 (d, J＝2.4
Hz, 1H, H-6'), 7.38 (dd, J＝8.8, 2.7 Hz, 1H, H-4'), 7.16
(s, br, 1H, H-6), 6.94 (m, 2H, H-4＋H-3'), 6.84 (d, J＝
8.2 Hz, 1H, H-3), 2.24 (s, 3H, CH3); 13C NMR
(DMSO-d6, 125 MHz) δ: 160.29 (CH＝N), 132.94
(C-4'), 131.52 (C-6'), 129.64 (C-4), 120.41 (C-6),
119.44 (C-3), 117.16 (C-3'), 20.85 (CH3), 160.36 (C-2'),
149.71 (C-2), 134.71 (C-1), 129.03 (C-5), 122.71 (C-5'),
121.43 (C-1'); IR (KBr) ν: 3426, 3068, 2916, 1632,
1609, 1516, 1469, 1397, 1254, 1231, 1177, 1128, 1035,
－
1
869, 823, 690, 651, 608 cm ; UV-vis (MeOH) λmax
:
458, 364, 268, 26, 232, 216 nm; MS (70 eV) m/z (%):
260 ([M-1]＋, 100), 261 ([M]＋, 7.1), 262 ([M＋1]＋,
723, 643, 583 cm ; UV-vis (MeOH) λmax: 490, 468,
366, 304, 255, 218, 210 nm; MS (70 eV) m/z (%): 338
([M－2]＋, 6.85), 339 ([M－1]＋, 5.2), 340 ([M]＋, 69.2),
341 ([M＋1]＋, 13.9), 342 ([M＋2]＋, 100), 343 ([M＋
3]＋, 14.2), 344 ([M＋4]＋, 22.3). Anal. calcd for
C14H11BrClNO: C 49.37, H 3.26, N 4.11; found C 49.29,
H 3.51, N 4.08.
－
1
＋
25.5), 263 ([M ＋ 2] , 12.8). Anal. calcd for
C14H12ClNO2: C 64.25, H 4.62, N 5.35; found C 64.17,
H 4.71, N 5.18.
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-5-bromo-
benzaldimine; N-(5-methyl-2-hydroxyphenyl)-5-bromo-
1
salicylaldimine (VII): m.p. 185 ℃; color: orange; H
NMR (DMSO-d6, 500 MHz) δ: 13.85 (s, 1H, OH-2'),
9.52 (s, 1H, OH), 8.94 (s, 1H, CH＝N), 7.83 (d, J＝1.9
Hz, H-6'), 7.49 (tt, J＝8.8, 1.9, 1.0 Hz, 1H, H-4'), 7.16
(s, 1H, H-6), 6.94 (d, br, J＝7.8 Hz, 1H, H-4), 6.89 (d,
J＝8.8 Hz, 1H, H-3'), 6.84 (d, J＝7.8 Hz, 1H, H-3),
2.24 (s, 3H, CH3); 13C NMR (DMSO-d6, 125 MHz) δ:
160.28 (CH＝N), 135.75 (C-4'), 134.48 (C-6'), 129.64
(C-4), 120.39 (C-6), 119.90 (C-3), 117.51 (C-3'), 20.86
(CH3), 160.75 (C-2'), 149.71 (C-2), 134.68 (C-1),
129.03 (C-5), 122.06 (C-1'), 110.03 (C-5'); IR (KBr) ν:
N-(5-Methyl-2-hydroxyphenyl)-2-hydroxy-3-meth-
oxy-5-bromobenzaldimine; N-(5-methyl-2-hydroxy-
phenyl)-3-methoxy-5-bromosalicylaldimine (X): m.p.
1
238 ℃; color: dark yellow; H NMR (DMSO-d6, 500
MHz) δ: 9.61 (s, 1H, OH), 8.93 (s, 1H, CH＝N), 7.38
(m, 1H, H-6'), 7.20 (s, br, 1H, H-6), 7.14 (d, br, J＝1.9
Hz, 1H, H-4'), 6.94 (d, br, J＝1.0 Hz, 1H, H-4), 6.84 (dd,
J＝8.3, 1.0 Hz, 1H, H-3), 3.81 (s, 3H, OCH3), 2.24 (s,
3H, CH3); 13C NMR (DMSO-d6, 125 MHz) δ: 159.97
(CH＝N), 129.57 (C-4), 125.81 (C-6), 120.13 (C-6'),
972
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Chin. J. Chem. 2012, 30, 970—978

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
117.89 (C-3), 117.11 (C-4'), 56.87 (OCH3), 20.87 (CH3),
153.40 (C-3'), 150.40 (C-2'), 149.37 (C-2), 133.65 (C-1),
129.09 (C-5), 120.61 (C-1'), 108.72 (C-5'); IR (KBr) ν:
3426, 3071, 2916, 1634, 1622, 1500, 1470, 1360, 1295,
1212, 1016, 876, 824, 777, 591; MS (70 eV) m/z (%):
334 ([M－2]＋, 100), 335 ([M－1]＋, 7.1), 336 ([M]＋,
89.2), 337 ([M＋1]＋, 7.1); UV-vis (MeOH) λmax: 469,
381, 358, 312, 268, 262, 212 nm. Anal. calcd for
C15H14BrNO3: C 53.59, H 4.20, N 4.17; found C 53.45,
H 4.29, N 4.30.
149.74 (C-3'), 149.65 (C-2), 138.12 (C-1), 130.22 (C-5),
128.71 (C-1'); IR (KBr) ν: 3423, 3056, 2938, 2855,
1624, 1597, 1515, 1465, 1422, 1385, 1276, 1247, 1138,
1023, 884, 808, 613 cm ; UV-vis (MeOH) λmax: 373,
350, 315, 282, 269, 262, 235, 214 nm; MS (70 eV) m/z
(%): 270 ([M－1]＋, 100). Anal. calcd for C16H17NO3: C
70.83, H 6.32, N 5.16; found C 70.79, H 6.42, N 5.08.
－
1
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, 28178 reflections were
collected, 1394 were unique (Rint＝0.032); equivalent
reflections were merged. An empirical absorption cor-
rection was applied which resulted in transmission fac-
tors ranging from 0.73 to 0.99. The data were corrected
for Lorentz and polarization effects.
The structure of XIII was solved by direct methods
(SIR92) and expanded using Fourier techniques.[31,32]
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.[33] Coordinate parameters of the
structure were deposited with the CSD, deposition
number is CCDC 825167.
N-(5-Methyl-2-hydroxyphenyl)-2,4-dimethoxyben-
1
zaldimine (XI): m.p. 98 ℃; color: milky brown; H
NMR (DMSO-d6, 500 MHz) δ: 8.81 (s, 1H, OH), 8.55
(s, 1H, CH＝N), 8.15 (d, J＝8.3 Hz, H-6'), 6.87 (s, 1H,
H-6), 6.82 (d, J＝8.3 Hz, H-5'), 6.73 (d, J＝7.8 Hz, 1H,
H-4), 6.64 (s, 1H, H-3'), 6.62 (d, J＝8.8 Hz, 1H, H-3),
3.88 (s, 3H, 2'-OCH3), 3.84 (s, 3H, 4'-OCH3), 2.21 (s,
3H, CH3); 13C NMR (DMSO-d6, 125 MHz) δ: 154.00
(CH＝N), 129.53 (C-6'), 127.74 (C-4), 119.83 (C-6),
116.22 (C-3), 107.11 (C-5'), 98.64 (C-3'), 56.53
(2'-OCH3), 56.22 (4'-OCH3), 20.88 (CH3), 164.20 (C-4'),
161.36 (C-2'), 149.37 (C-2), 139.12 (C-1), 128.80 (C-5),
118.20 (C-1'); IR (KBr) ν: 3426, 3086, 2980, 2914,
1621, 1590, 1508, 1469, 1383, 1300, 1277, 1214, 1168,
－
1
1112, 1040, 947, 825, 802 cm ; UV-vis (MeOH) λmax
:
358, 321, 280, 270, 240, 216, 210 nm; MS (70 eV) m/z
(%): 270 ([M－1]＋, 100). Anal. calcd for C16H17NO3: C
70.83, H 6.32, N 5.16; found C 70.78, H 6.44, N 5.04.
N-(5-Methyl-2-hydroxyphenyl)-3,5-dimethoxyben-
1
zaldimine (XII): m.p. 72 ℃; color: light brown; H
NMR (DMSO-d6, 500 MHz) δ: 8.72 (d, J＝1.9 Hz, 1H,
OH), 8.62 (s, 1H, CH＝N), 7.21 (d, J＝1.9, 2H, H-2'＋
H-6'), 7.02 (s, 1H, H-6), 6.88 (dd, J＝8.8, 1.0, 1H, H-4),
6.77 (d, J＝8.3 Hz, 1H, H-3), 6.62 (t, J＝2.4, 2.4 Hz,
1H, H-4'), 3.81 (s, 6H, 2×OCH3), 2.22 (s, 3H, CH3);
13C NMR (DMSO-d6, 125 MHz) δ: 159.33 (CH＝N),
128.70 (C-4), 119.93 (C-6), 116.54 (C-3), 107.23 (C-2'
＋C-6'), 104.24 (C-4'), 56.12 (2×OCH3), 20.89 (CH3),
161.30 (C-3'＋C-5'), 149.75 (C-2), 139.20 (C-1), 137.73
(C-1'), 128.76 (C-5); IR (KBr) ν: 3393, 3087, 2932,
2839, 1625, 1599, 1506, 1463, 1430, 1377, 1347, 1291,
1238, 1215, 1158, 1062, 923, 837, 814, 684 cm ;
UV-vis (MeOH) λmax: 369, 348, 279, 269, 262, 233, 217,
210 nm; MS (70 eV) m/z (%): 270 ([M－1]＋, 100), 271
([M]＋, 11.2). Anal. calcd for C16H17NO3: C 70.83, H
6.32, N 5.16; found C 70.90, H 6.34, N 5.10.
N-(5-Methyl-2-hydroxyphenyl)-3,4-dimethoxyben-
zaldimine (XIII): m.p. 137 ℃; color: golden yellow;
1H NMR (DMSO-d6, 500 MHz) δ: 8.61 (s, 1H, OH),
8.58 (s, 1H, CH＝N), 7.73 (d, J＝1.9 Hz, 1H, H-2'),
7.44 (dd, J＝8.3, 1.9 Hz, 1H, H-6'), 7.05 (d, J＝8.3 Hz,
1H, H-4), 7.00 (d, J＝1.5 Hz, 1H, H-6), 6.85 (dd, J＝
8.3, 1.5 Hz, 1H, H-3), 6.76 (d, J＝8.3 Hz, 1H, H-5'),
3.85 (s, 3H, 3'-OCH3), 3.82 (s, 3H, 4'-OCH3), 2.22 (s,
3H, CH3); 13C NMR (DMSO-d6, 125 MHz) δ: 158.91
(CH＝N), 128.09 (C-4), 124.83 (C-6'), 119.62 (C-6),
116.28 (C-3), 111.88 (C-2'), 110.62 (C-5'), 56.33
(3'-OCH3), 56.31 (4'-OCH3), 20.93 (CH3), 152.38 (C-4'),
Determination of antimicrobial activity
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.[34,35] 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 cultures 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 plas-
tic 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
inhibitory concentrations (MIC) were defined as the
lowest concentration of compound giving complete in-
hibition of visible growth. Antimicrobial effects of the
－
1
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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973

Gürbüz et al.
FULL PAPER
solvents were investigated against test microorganisms.
According to values of the controls, the results were
evaluated.
The C—O stretching vibrations appear in the
1200—1250 cm－ range as strong bands.[37] The C—Cl
1
stretching vibration is seen in the range 600—700 cm－
1
as medium or weak bands for VI, VIII and IX. The
C—Br stretching vibrations are seen at 548, 583 and
591 cm－1 as weak bands for the compounds VII, IX and
X.[38]
Results and Discussion
The analytical data and physical properties of the
Schiff bases are given in Experimental section. As can
be seen from Scheme 1, XI, XII and XIII are structur-
ally isomers. Also, II with III and IV with V are iso-
mers. Considering the yields, it can be said that the sub-
stituents increase the yields of the compounds II—XIII
(except XII) in respect to I. The high yields of the
compounds VIII and IX, which have two electronega-
tive groups at R2 and R4, are remarkable. Also, the
methyl groups at R2 or R4 positions increase the yield of
the compounds II and III.
A considerable strong H-bonding is observed in the
compounds I—X with salicyl OH group (weak and
－
1
broad bands between 2800 and 2400 cm ), whereas
weak H-bonding in the compounds XI—XIII does not
include salicyl OH group, as expected.
UV-Visible spectra
The UV-visible spectral data of the compounds are
presented in Experimental section. The UV-visible ab-
sorption 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.
UV-visible spectroscopy is known to be a very sensi-
tive method for studying tautomeric equilibrium in
Schiff bases. The two long-wave bands observed in the
electronic spectra of the compounds have been assigned
to the enol and keto forms (Scheme 2).[39-45] The bands
between 350 and 400 nm can be assigned to the enol
form whereas the bands above 400 nm are assigned to
the keto form.[46-51] According to this, much of the
compounds such as I—X, which have salicyl OH group,
have the characteristic keto form band, whereas the oth-
ers, XI—XIII, have characteristic enol form band in
methanol. The UV-visible spectra of the Schiff bases
having the keto form band indicate the existence of the
proton transfer equilibrium.
Melting points
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 (165 ℃, see Experimental section)
among the compounds including salicyl group (except
XI—XIII). Accoding to this observation it can be said
that the substituents increase the melting points of the
compounds II—X in respect to the compound I in addi-
tion to intermolecular hydrogen bonding. The melting
points of the compounds VIII, IX and X are higher than
those of the others: 261, 253 and 238 ℃, respectively:
These compounds contain two electronegative groups
with a salicyl ring; Cl, Cl (VIII); Br, Cl (IX) and OCH3,
Br (X). This may mean that Br, Cl and OCH3 substitu-
ents on the salicyl ring cause stronger hydrogen bonding
according to the others and consequently, they increase
the melting points considerably. It is remarkable that the
dimethoxy derivatives (XI—XIII) have lower melting
point than the others. These compounds include only
one OH group and they have weaker intermolecular
hydrogen bonding, and consequently, their melting
points decrease.
Scheme 2
OH
OH
N
H
HO
Br
Cl
O
Br
Cl
The melting points of the Schiff bases in this study
are lower than those of 4-chloro-2-aminophenol deriva-
tive analogues.[36] This observation leads us to conclude
that methyl substituent on hydroxyphenyl ring decreases
the melting point of Schiff bases.
N
CH
CH
H3C
H3C
In the UV-visible spectra above 400 nm, the absorp-
tion values of the compounds VIII, IX and X, are
higher than the others: 466, 468 and 469 nm, respec-
tively (also, they have higher meting points than the
others: see Melting Points section). On the other hand,
the salicyl OH protons of these three compounds could
FT-IR spectra
FT-IR spectral data of the compounds are given in
Experimental section. The bands at around 3400 cm–1
can be assigned to ν(OH) in the IR spectra of the all
compounds. The medium or strong intensity absorption
bands between 1610 and 1640 cm－1 are assigned to C＝
N stretching mode. The presence of aromatic rings has
been identified by their characteristic ring vibrations at
1
not be detected in their H NMR spectra. This situation
can be explained as follows: These compounds include
two electronegative groups at 5-methyl-2-hydroxy-
phenyl ring. Probably, the strong electronegative groups
(Cl, Br, OCH3) of the hydroxyphenyl ring strengthen the
keto form, acidic character of the NH proton is in-
creased and consequently, the absorption maximum
1500—1400, 1200—1100 and 930—700 cm－ regions.
1
The absence of bands for characteristic of ν(C＝O) and
primary amine ν(NH) confirms the formation of the pro-
posed Schiff base framework.
974
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Chin. J. Chem. 2012, 30, 970—978

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
It is observed that azomethine proton of V gives a
doublet by far interacting with H(6) (J＝1.6 Hz). OH
proton of XII appears as a doublet as a result of far in-
teraction with H(2') (J＝1.9 Hz).
The compounds XI, XII and XIII have two methoxy
groups. The NMR spectral data show that the methoxy
carbon atoms of the compound XII are magnetically
equivalent. Two methoxy group protons of XII give
only a signal at δ 3.81 (6H). At the same time, methoxy
carbons give only one peak at δ 56.12 in the 13C NMR
spectra. According to the APT spectral data, C(2') and
C(6') are also magnetically equivalent to each other:
They exhibit a single signal at δ 107.23.
Figure 1 UV-visible spectra of the compounds VIII and XI in
the range of 225—500 nm.
13C NMR (APT) spectral data are given in Experi-
mental section with their assignments. All of the carbon
atoms were observed and APT spectra of the com-
pounds are straightforward. APT spectrum of IV is pre-
sented in Figure 2. Azomethine carbons of the com-
pounds appear between δ 154.00 and 162.3. The carbon
atoms bonded to the OH group [C(2)] at
methyl-hydroxyphenyl ring give signals at the lower δ
value (near δ 149) than the carbon atoms that bonded to
the other OH group, C(2') (at around δ 160). The methyl
carbons of 5-methyl-2-hydroxyphenyl rings are ob-
served near δ 20.9.
shifts to the higher wavelength.
The UV-visible spectra of the compounds VIII and
XI are shown in Figure 1 to compare Schiff bases which
have keto and enol forms, respectively.
Mass spectra
The ESI-MS spectral data of the compounds are
given in Experimental section 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, their percent abundance and approximately
relative proportions are as follows: 35Cl (75.8%): 37Cl
(24.2%) (3∶1); 79Br (50.7%):81Br (49.3%) (1∶1).
There are a lot of isotopic patterns in the ESI-MS spec-
tra of the compounds VI—X because of presence of
chlorine or bromine atoms. Considering all the com-
pounds, the most isotopic patterns are observed in the
spectra of the compounds VIII (includes two chlorine
atoms) and IX (includes a chlorine and a bromine at-
oms).
Figure 2 13C NMR spectrum, obtained with Attached Proton
Test (APT) technique, of the compound IV between δ 115 and
165 range.
NMR spectra
1H NMR spectral data and their assignments are
present in Experimental section. The OH protons of
5-methyl-2-hydroxyphenyl ring appear in the δ
8.61—9.95 range, whereas NMR signal values of the
salicylaldimine ring OH protons (I—X, at 2'-position)
that form intramolecular hydrogen bonding with the
C＝N nitrogen atom, vary between δ 13.44 and 14.41.
Salicyl OH proton of II, VIII, IX and X is not detected
1
in their H NMR spectra: It can be said that OH proton
of these compounds has more acidic character than the
others and consequently, it cannot be detected because
of its dissociation.
Azomethine proton appears between δ 8.82 and 9.07
in the compounds I—X whereas it shifts to higher field,
δ 8.55—8.62 range, in the compounds XI—XIII.
Shielding of azomethine proton of the compounds
XI—XIII is increased according to the other com-
pounds because of lack of the salicyl OH group (shifting
to the high field). Similarly, also OH protons of the
compounds XI—XIII shift to the higher field because
of shielding.
Figure 3 A molecular drawing (ORTEP 3) of the asymmetric
unit of the compound XIII, showing 50% probability displace-
ment ellipsoids and the atom-numbering scheme. Broken line
shows intra-molecular hydrogen bond.
X-ray analysis
The crystal data of the compound XIII and the de-
tails of data processing are given in Table 1. Table 2
Chin. J. Chem. 2012, 30, 970—978
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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975

Gürbüz et al.
FULL PAPER
Table 1 Crystal and experimental data for the compound XIII
OH groups because of steric strain. Also, there is inter-
moleculer hydrogen bonding between H(17) and O(3)
atoms (2.177 Å). H(17) forms hydrogen bonding with
two electronegative atoms [N(1) and O(3)] as in similar
molecules reported,[52,53] and it is closer to O(3) atom
according to N(1). The crystal structure is stabilized by
intermolecular hydrogen bonds.
Empirical formula
Formula weight
Temperature
C16H17NO3
271.32
293 K
Crystal system
Space group
monoclinic
P21
a＝7.4750(5) Å,
b＝7.7954(7) Å
c＝12.6696(8) Å,
β＝98.475(4)º
730.20(9) Å3
Table 3 Selected bond lengths (Å) and angles (°) for XIII
Unit cell dimensions
O(1)—C(1)
O(2)—C(12)
O(3)—C(14)
N(1)—C(8)
C(4)—C(6)
C(9)—C(10)
C(11)—C(13)
1.358(3) O(2)—C(11)
1.420(3) O(3)—C(13)
1.432(3) N(1)—C(2)
1.262(3) C(4)—C(5)
1.377(4) C(8)—C(9)
1.410(3) C(9)—C(16)
1.408(3)
1.370(2)
1.357(2)
1.422(2)
1.506(4)
1.462(3)
1.383(3)
Cell volume
Z, Calculated density
Absorption coefficient
(Mo Kα)
2, 1.234 g/cm3
0.85 cm－
1
F(000)
288
Crystal size
0.30 mm×0.20 mm×0.10 mm
C(11)-O(2)-C(12) 118.6(2) C(13)-O(3)-C(14) 117.2(2)
Linear absorption
coefficient (μ)
No. of observations
[I＞3.00σ(I)]
0.9 cm－
1
C(2)-N(1)-C(8)
C(7)-C(1)-O(1)
C(9)-(C8)-N(1)
119.7(2) C(2)-C(1)-O(19)
118.2(2) N(1)-C(2)-C(1)
121.9(2)
116.1(2)
1372
123.6(2) C(13)-C(11)-O(2) 113.9(2)
Refinement method
Full-matrix least-squares on F
O(2)-C(11)-C(10) 125.4(2) C(15)-C(13)-O(3) 125.1(2)
O(3)-(C13)-C(11) 114.9(2)
Goodness of fit indicator
1.287
－8≤h≤8,
－8≤k≤9,
－15≤l≤15
3.0º—25.0º
Index range
Table 4 Selected torsion angles (°) for XIII
C(12)-O(2)-C(11)-C(10)
C(14)-O(3)-C(13)-C(11)
C(8)-N(1)-C(2)-C(1)
C(2)-N(1)-C(8)-C(9)
O(1)-C(1)-C(2)-C(3)
N(1)-C(8)-C(9)-C(10)
O(2)-C(11)-C(13)-O(3)
O(3)-C(13)-C(15)-C(16)
C(12)-O(2)-C(11)-C(13)
C(14)-O(3)-C(13)-C(15)
C(8)-N(1)-C(2)-C(3)
O(1)-C(1)-C(2)-N(1)
O(1)-C(1)-C(7)-C(6)
N(1)-C(8)-C(9)-C(16)
O(2)-C(11)-C(13)-C(15)
－0.8(3)
172.6(2)
148.4(2)
176.4(2)
－178.4(2)
4.3(4)
θ range for data collection
Data collection
CRYSTALCLEAR
0.050
R (I＞3σ(I))
Rw (I＞3σ(I))
0.033
Largest diff. peak and hole
0.14 and －0.17 e－/Å3
－1.1(3)
－179.4(2)
179.3(2)
－7.3(3)
－35.8(3)
－2.4(4)
178.6(2)
－175.3(3)
178.8(2)
Table 2 Hydrogen-bond geometry [Å, (°)] for XIIIa
D—H···A D—H H···A D···A D—H···A
O(1)—H(17)···N(1)1 0.882(2) 2.397(2) 2.734(3) 103.1(2)
O(1)—H(17)···O(3)2 0.882(2) 2.177(2) 2.852(2) 133.0(1)
a Symmetry code: 1: ＋x,＋y, ＋z; 2: －x, 1/2＋y,＋1－z.
contains the hydrogen bond geometry parameters. Se-
lected bond lengths and angles are given in Table 3;
some torsion angles are given in Table 4. ORTEP-III
view of the molecular structure of XIII is given in Fig-
ure 3. The unit cell of XIII is shown in Figure 4.
Kabak et al. reported the crystal structure of the
compound I.[52] They investigated tautomeric properties
and conformations of I, and they showed that in-
tramolecular hydrogen bonds occur between the pairs of
atoms N(1) and O(1), and N(1) and O(2); the H atom is
essentially bonded to the N atom.
In this study, it is observed that O(1)—H(17) bond
length (O—H) is 0.882(2) Å and the distance between
N(1) and H(17) atoms (C＝N···H—O) is 2.397(2) Å
(Table 2). This shows that there is a weak interaction
(intramolecular hydrogen bonding) between C＝N and
C-N-C bond angle is 119.7(2)° for the C(2)-N(1)-
C(8) and C＝N bond [C(8)-N(1)] length is 1.262(3) Å.
These data are in line with the literature data.[54-58] Ac-
cording to the C(2)-N(1)-C(8)-C(9) torsion angle,
176.4(2)°, the molecule is non-planar and twisted
around C—N single bond.
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 5.
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Chin. J. Chem. 2012, 30, 970—978

Spectral Characterization and Antimicrobial Activity of Some Schiff Bases
have antibacterial and antifungal activities.[61-65]
It is observed that the compounds I, II and XII have
no any activity on the test microorganisms. On the other
hand, all of the compounds did not show significant
activity (or they have very low activity) toward S. epi-
dermidis, E. coli, P. aeruginosa and P. mirabilis.
Conclusions
It is known that salicylaldimines have strong intra-
molecular hydrogen bonding between azomethine
(HC ＝N) nitrogen and salicyl OH hydrogen at-
oms.[54,55,66-69] In this study the intramolecular hydrogen
bonding is proved by spectroscopic methods. For exam-
ple, the weak or broad bands between 2800 and 2400
cm － in the IR spectra of the compounds I—X
1
Figure 4 A packing diagram (view along the b axis) of the
compound XIII. Hydrogen bonds are shown as dashed lines.
demonstrate the formation of intramolecular hydrogen
bonding between salicyl OH hydrogen and C ＝N
nitrogen atoms of the Schiff bases. Appearing of the
NMR signal of the benzaldimine OH hydrogen above δ
12.50 is related with the intramolecular hydrogen
bonding. In UV-visible spectra, the bands between 350
and 400 nm indicate enol form and the absorptions
above 400 nm show keto form.
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.[70] In our previous studies some
N-(5-chloro-2-hydroxyphenyl)-phenylaldimines includ-
ing methoxy group and some N-(5-chloro-2-hydroxy-
Table 5 In vitro antimicrobial activities of the compounds
I—XIII (MIC, µg/mL)
Microorganismsa
Compound
Sa
Kp
Ca
—
b
III
156
—
—
IV
312
—
—
V
—
156
156
625
312
312
78
VI
—
—
VII
156
—
—
VIII
—
IX
19.5
—
—
X
—
XI
156
156
0.125
—
312
—
—
XIII
—
phenyl)-(3/4/5-substituted)-salicylaldimines
showed
Ciprofloxacin
Cefuroxime sodium
Ceftazidime
Clotrimazole
0.0625
—
—
considerable activity toward S. aureus, S. epidermidis
and C. albicans.[36,71] In this study, some of the Schif
bases show similar antimicrobial activity to those of the
literature. For example, it is observed that most of the
compounds are effective on two microorganisms men-
tioned above (S. aureus and C. albicans).
The crystal structure of N-(5-methyl-2-hydroxy-
phenyl)-3,4-dimethoxybenzaldimine (XIII) is deter-
mined by X-ray diffraction at room temperature. It
crystallizes in monoclinic system, and space group P21.
Unit-cell dimensions are as follows: a＝7.4750(5) Å,
b＝7.7954(7) Å, c＝12.6696(8) Å, V＝730.20(9) Å3,
Z＝2. Non-planar title compound has a weak intra-
molecular hydrogen bonding between C＝N nitrogen
and OH hydrogen atoms.
—
—
4.9
—
—
—
4.9
1.0
Fluconazole
—
—
a
Sa: Staphylococcus aureus ATCC 6538 (Gram＋). Kp: Kleb-
siella pneumoniae ATCC 4352 (Gram－). Ca: Candida albicans
ATCC 10231. b —: Antimicrobial activity was not detected.
At a glance of Table 5, it can be seen that most of the
compounds are effective toward S. aureus and C. albi-
cans. This observation can be evaluated as a selective
activity.
It is observed that the compounds IX (includes Br
and Cl substituents) and X (includes Br and OCH3) have
a little better antimicrobial activity according to the oth-
ers. It is possible to say that this activity is caused by
bromine atom. It is known that some compounds that
contain bromine substituent have various biological
activities. For example, bronopol (2-bromo-2-nitropro-
pane-1,3-diol) has a broad spectrum of antibacterial and
antifungal activities and is widely used as a preserva-
tives in drugs and cosmetics.[59,60] There are a lot of
studies that reported bromine containing compounds
As a conclusion, it can be said that the moderate and
selective antimicrobial activities of the Schiff bases
against S. aureus, K. pneumoniae and C. albicans en-
couraged further investigation on similar compounds.
Supplementary Material
Crystallographic data for the structure reported in
this paper have been deposited at the Cambridge Crys-
tallographic Data Centre (CCDC 825167). Copies of the
Chin. J. Chem. 2012, 30, 970—978
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
977

Gürbüz et al.
FULL PAPER
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Acknowledgements
This work was supported by the Research Fund of
Istanbul University (No. 1519).
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(Lu, Y.)
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