Synthesis, spectral characterization and antimicrobial activity of some new azo dyes derived from 4,6-dihydroxypyrimidine

Article abstract of DOI:10.1016/j.molliq.2012.03.003

A number of new azo disperse dyes were synthesized by coupling 4,6-dihydroxypyrimidine with diazonium salts derived from 4-methoxy aniline, N-(4-amino phenyl) acetamide, 3- and 4-methyl aniline, 2-trifluoromethyl aniline, 4-flouoroaniline, 4-cyanoaniline, 4-amino acetophenone, 4-nitroaniline, 2-bromo-4-methyl aniline and 4-amino azobenzene. Spectroscopic data of these dyes, dissolved in six polar solvents, were measured. The effects of acid, base, temperature and concentration on the visible absorption spectra of the dyes are also reported. The structures of all compounds were confirmed by FT-IR spectra, electronic absorption spectra in UV and visible regions, ¹H NMR, mass spectroscopy and elemental analysis. In addition, the antimicrobial activity of the dyes was examined in detail.

Full text of DOI:10.1016/j.molliq.2012.03.003

Journal of Molecular Liquids 169 (2012) 21–26
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Synthesis, spectral characterization and antimicrobial activity of some new azo dyes
derived from 4,6-dihydroxypyrimidine
a
a
b
c
a
a
M.R. Yazdanbakhsh a, , H. Yousefi , M. Mamaghani , E.O. Moradi , M. Rassa , H. Pouramir , M. Bagheri
⁎
a
Department of Chemistry, Faculty of Sciences University of Guilan, Rasht, Iran
Department of Chemistry, Faculty of Sciences, Islamic Azad University, Lahijan, Iran
Department of Biology, Faculty of Sciences University of Guilan, Rasht, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A number of new azo disperse dyes were synthesized by coupling 4,6-dihydroxypyrimidine with diazonium salts
derived from 4-methoxy aniline, N-(4-amino phenyl) acetamide, 3- and 4-methyl aniline, 2-trifluoromethyl
aniline, 4-flouoroaniline, 4-cyanoaniline, 4-amino acetophenone, 4-nitroaniline, 2-bromo-4-methyl aniline and
4-amino azobenzene. Spectroscopic data of these dyes, dissolved in six polar solvents, were measured. The ef-
fects of acid, base, temperature and concentration on the visible absorption spectra of the dyes are also reported.
The structures of all compounds were confirmed by FT-IR spectra, electronic absorption spectra in UV and visible
regions, 1H NMR, mass spectroscopy and elemental analysis. In addition, the antimicrobial activity of the dyes
was examined in detail.
Received 10 December 2011
Received in revised form 3 March 2012
Accepted 6 March 2012
Available online 19 March 2012
Keywords:
Azo dye
Dihydroxypyrimidine
Pyrimidine dye
Solvent effect
© 2012 Elsevier B.V. All rights reserved.
Substituent effect
Antimicrobial activity
1. Introduction
NMR, mass spectroscopy and elemental analysis. In addition, the
antimicrobial activity of the dyes was examined in detail.
Due to their unique clinical applications, syntheses of pyrimidine
drugs have been intensively investigated in recent years. Pyrimidine
derivatives are highly effective as hypnotic drugs [1–3], antitumor,
antibacterial and anti-HIV agents, and in cancer detection [4–12].
Pyrimidine derivatives are also present in the structure of nucleic
acids in living cells [13]. Azo dyes are an important class of organic
colorants which contain at least a conjugated azo chromophore
(\N_N\). They are also considered as the largest and the most ver-
satile class of dyes [14–17]. Azo compounds are the most widely used
class of dyes, having applications in various fields, such as dyeing tex-
tiles, as biomedical agents, and in advanced applications in organic
synthesis. Important investigations have also been carried out on
the synthesis and optical behavior of heteroarylazo dyes by Raposo
and coworkers and other authors [18–26]. Among heterocyclic azo
dyes, pyrimidine azo dyes can be used as ligands which form com-
plexes with transition metals and produce important colorimetric
sensors for cations and anions [27–31]. In this work, a series of new
hetaryl azo dyes were synthesized through azo coupling reaction
using 4,6-dihydroxypyrimidine as coupling component (Scheme 1).
The structures of all products were confirmed by IR, UV–vis and 1H-
2. Experimental
2.1. Material and methods
Solvents were removed according to standard procedures. Liquid
and solid aromatic amines were purified by distillation and recrystal-
lization, respectively. High purity 4,6-dihydroxypyrimidine was
purchased from Merck. IR spectra were recorded on a Shimadzu
8400 FT-IR spectrophotometer. 1H-NMR spectra were obtained by
FT-NMR (500 MHz) Brucker apparatus in DMSO-d6, using TMS as in-
ternal standard. The absorption spectra of the compounds were run
on a Cary UV–vis double-beam spectrophotometer (Model 100). The
mass spectra (electron impact, 70 eV) were obtained on an Agilant
Technology (HP) instrument. The elemental analysis was determined
on a Leco CHNS-900 analyzer. Melting points were recorded with an
Electro-thermal apparatus.
2.2. Synthesis of the azo dyes
2.2.1. General procedure for diazotization
Aromatic amine (2.0 mmol) was dissolved in a mixture of glacial
acetic acid and propionic acid (6 mL, 2:4) and cooled in an ice-salt
bath to −5°°C. The mixture was then added in portions during 45 min
to a cold solution of nitrosyl sulfuric acid (prepared from sodium nitrite
⁎
Corresponding author. Tel./fax: +98 131 772 0733.
E-mail address: mr-yazdan@guilan.ac.ir (M.R. Yazdanbakhsh).
0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2012.03.003

22
M.R. Yazdanbakhsh et al. / Journal of Molecular Liquids 169 (2012) 21–26
Scheme 1. Synthesis of azo dyes 1–11.
(1 g) and concentrated sulfuric acid (7 mL) at 60°°C. The mixture was
stirred for an additional 45 min at the same temperature.
was then stirred for 1 h at 0–5 °C. The progress of the reaction was fol-
lowed by TLC using ethyl acetate-petroleum ether (7:3). After comple-
tion of the reaction the pH was adjusted to 3–4 by addition of 10%
hydrochloric acid solution. The resulting solid was filtered, washed
with cold water and dried. Recrystallization from DMF-H2O gave pure
crystals of the dyes. The selected physical properties of the synthesized
dyes were measured and listed in Table 1.
2.2.2. Preparation of 5-aryl azo-4,6-dihydroxypyrimidine
When diazotization was completed, as described above, the dwww.
patoghu.coiazo liquor was added to a vigorously stirring solution of 4,6-
dihydroxypyrimidine (2.0 mmol) in sodium hydroxide (0.4 g,
10 mmol) and water (10 mL). The pH of the reaction mixture was main-
tained at 7.5–9 by adding 2.5% sodium hydroxide solution. The mixture
2.3. Determination of antimicrobial activity
The antibacterial activity of compounds synthesized was mea-
sured using Salmonella typhimurium (ST), Micrococcus luteus (ML),
Bacillus subtilis (BS) and Pseudomonas aeruginosa (PS). All media
were prepared according to manufacturers' instructions. A colony of
each organism was transferred from nutrient agar plates to nutrient
broth cultures and incubated for 18 h at 37 °C. Bacteria from nutrient
broth cultures were inoculated onto four Mueller–Hinton agar plates.
Antibacterial activity was determined using the well diffusion tech-
nique. A sterilized glass tube (5 mm diameter) was used to aseptically
remove the solid medium and create wells for addition of 35 μL sam-
ple solutions. A concentration of 125 μg/ml of sample, prepared in
DMSO, was added to these wells. After incubation at 37 °C for 24 h,
zone of inhibition was measured. Tetracycline and erythromycin
were used as positive controls.
Table 1
The physical properties of synthesized dyes.
Dye
X
mp(°C)
λmax
(nm, DMSO)
Color
Yield%
1
2
3
4
5
6
7
8
p-OCH3
p-NHCOCH3
p-CH3
m-CH3
o-CF3
p-F
p-CN
p-COCH3
p-NO2
o-Br, p-CH3
p-N_N\Ph
188–189
216–217
198–199
223–224
199–200
199–200
265–266
211–212
241–242
232–233
295–296
375, 404s
397, 406s
379
Orange
Orange
Yellow
67
83
90
88
85
82
87
81
90
85
72
373
Yellow
385, 409s
367, 391s
380, 420s
371, 400s
390–506s
385, 415s
406
Orange
Golden yellow
Yellow
Yellow
Brown
9
10
11
Yellow
Orange
Scheme 2. Possible tautomeric forms for azo dyes 1–11.

M.R. Yazdanbakhsh et al. / Journal of Molecular Liquids 169 (2012) 21–26
23
Table 2
Characterization data for the synthesized dyes.
Dye IR (cm−1, KBr)
1H NMR (DMSO-d6, ppm)
1
2
3370, 3330, 1710, 1508, 1415, 817
3410, 3350, 1720, 1650, 1440, 840
3.17 (s, 3H), 6.97 (d, J=8.5 Hz, 2H), 7.68 (d, J=8.5 Hz, 2H), 9.18 (d, J=9.5 Hz, 0.25H), 9.14 (d, J=8.4 Hz, 0.75H),
10.93 (d, J=8.4 Hz, 0.75H), 12.38 (d, J=9.5 Hz, 0.25H), 13.80 (OH), 14.75 (NH)
3.03 (s, 3H), 7.59 (d, J=8.9 Hz, 2H), 7.69 (d, J=8.9 Hz, 2H), 9.18 (d, J=10.0 Hz, 0.33H), 9.15 (d, J=9.4 Hz,.0.66H),
10.0 (s, 1H), 10.98 (d, J=9.4 Hz,.0.66H), 12.39 (d, J=10.0 Hz,.0.33H), 13.77 (OH), 14.73 (NH)
3
4
3370, 3320, 1710, 1508, 1415, 817
3300, 3300–3200, 1710, 1650, 1520,
1420, 1225, 805
2.18 (s, 3H), 7.01 (d, J=8.4 Hz, 2H), 7.05 (d, J=8.4 Hz, 2H), 9.16 (d, J=9.7 Hz, 1H), 11.28 (d, J=9.7 Hz, 1H), 13.72 (OH)
2.35 (s, 3H), 6.99 (d, J=7.8 Hz, 1H), (t, J=7.78 Hz, 1H), 7.62 (s, 1H), 9.18 (d, J=10.0 Hz, 0.33H), 9.15 (d, J=9.4 Hz, 0.66H),
11.02 (d, J=9.4 Hz, 0.66H), 11.42 (d, J=10.0 Hz, 1H), 13.61 (OH)
5
3410, 3350, 1715, 1660, 1510, 1220–1120 7.30–7.75 (m, overlapped, 3H), 8.42 (d, J=8.4 Hz, 1H), 9.20 (d, J=9.2 Hz, 0.2H), 9.15 (d, J=9.8 Hz, 0.8H), 11.28
(d, J=9.2 Hz, 0.2H), 12.42 (d, J=9.8 Hz, 0.8H), 14.28 (OH), 15.30 (NH)
6
3400, 3000, 2920, 1725, 1500, 1430, 1150 7.24 (dd, 4J=8.8 Hz, 3J=8.5 Hz, 2H), 7.61–7.81 (m, overlapped, 2H), 9.18 (d, J=9.1 Hz, 0.2H), 9.14 (d, J=9.8 Hz, 0.8H),
11.12 (d, J=9.1 Hz, 0.2H), 12.38 (d, J=9.8 Hz, 0.8H), 13.65 (OH), 14.85 (NH)
7
3400, 3320, 2238, 1670, 1600, 1500, 825 7.71 (d, J=8.8 Hz, 2H), 7.77 (d, J=8.8 Hz, 2H), 9.18 (d, J=9.2 Hz, 0.3 H) 9.15 (d, J=9.5 Hz, 0.7H), 10.93
(d, J=8.4 Hz, 0.7 H), 12.38 (d, J=9.5 Hz, 0.3 H), 13.91 (OH), 14.85 (NH)
8
3400, 3300, 1670, 1650, 1510, 1400,
1200, 810
3400, 1720, 1590, 1527, 1415, 825
2.56 (s, 3H), 7.80 (d, J=8.5 Hz, 2H), 7.97 (d, J=8.5 Hz, 2H), 9.18 (d, J=9.0 Hz, 0.33H), 9.15(d, J=9.0 Hz, 0.66H),
11.23 (d, J=9.0 Hz, 0.66H), 12.33 (d, J=9.2 Hz, 0.33H), 13.42 (OH), 14.37 (NH)
7.90 (d, J=8.5 Hz, 2H), 8.20 (d, J=8.5 Hz, 2H), 9.19 (d, J=7.15 Hz, 0.2H), 9.14 (d, J=7.70 Hz, 0.8H), 11.35
(d, J=7.70 Hz, 0.8H), 12.23 (d, J=7.15 Hz, 0.2H), 13.92 (OH), 14.76 (NH)
9
10
3400, 3250, 2900, 1680, 1520, 1470,
1300, 817
2.32 (s, 3H), 7.20 (d, J=8.5 Hz 1H), 7.52 (s, 1H), 8.13 (d, J=8.5 Hz, 0.66H), 8.19 (d, J=8.5 Hz, 1H), 9.18
(d, J=10.0 Hz, 0.33H), 9.14 (d, J=9.3 Hz, 0.66H), 11.22 (d, J=9.3 Hz, 0.66H), 12.44 (d, J=10.0 Hz, 0.33H), 14.10 (OH),
15.03 (NH)
11
3430, 3300–3250, 1670, 1590, 1540, 1370 7.54–7.61 (m, 4H), 7.75 (d, J=8.9 Hz,1H), 7.87 (d, J=7.5 Hz,2H), 7.90 (d, J=7.5 Hz, 2H), 9.22 (d, J=9.4 Hz, 1H), 11.40
(d, J=9.4 Hz, 1H), 13.82 (OH)
3. Results and discussion
The infrared spectra (KBr) of all the compounds showed strong
absorption bands at 3000–3410 cm−1 for the hydroxy group and
1670–1720 cm−1 for the carbonyl group. It can be suggested that
these dyes exist as the azo-keto-enol forms (T2–T4) in solid state. The
IR spectra also showed bands at 3084–3020 cm−1 (aromatic C\H),
1500–1520 cm−1 (N_N), 1118–1315 cm−1 (C\F, dyes 5 and 6),
2238 cm−1 (CN, dye 7) and 1527 cm−1 (NO2, dye 9).
3.1. Structure identification of azo-dyes
As shown in Scheme 1 the hydroxy pyrimidine dyes 1–11 were
prepared by coupling of 4,6-dihydroxypyrimidine with diazotized
aromatic amines. The dyes may exist in six possible tautomeric
forms, namely azo-dienol (T1), azo-keto-enol (T2), azo-enol-keto
(T3), azo-keto-enol (T4), hydrazo-diketo (T5) and hydrazo-diketo
(T6) (Scheme 2).
The 1H NMR spectra of all the dyes in DMSO-d6 showed a multiplet
at 6.97–8.23 ppm for aromatic protons, doublets at 9.13–9.16 ppm
and 9.18–.9.21 ppm for the major isomer and its minor tautomer
Table 3
Elemental analysis and mass spectral data of the synthesized dyes.
Dye
Molecular
formula
C%
H%
N%
EIMS (70 eV) m/z
Rel (intensity)
Caled
Found
Caled
Found
Caled
Found
1
2
3
4
5
6
7
8
C11H10N4O3
53.65
52.74
57.39
57.39
46.97
51.28
54.77
55.81
45.97
42.85
60.00
53.52
53.02
57.12
57.61
46.83
51.33
54.87
55.69
46.12
42.89
59.81
4.06
4.02
4.34
4.34
2.49
3.00
2.90
3.87
2.68
2.92
3.75
4.18
4.11
4.35
4.21
2.55
2.97
3.03
3.74
2.65
3.03
3.81
22.76
25.64
24.34
24.34
19.92
23.93
29.04
19.85
26.68
18.18
26.25
22.34
25.61
24.41
24.36
20.01
24.91
28.91
20.05
26.72
18.02
26.44
246 (M+;15), 220 (25), 191 (32), 142 (26), 121 (100), 95 (31)
277 (M+;10), 247 (25), 218 (34), 176 (36), 120 (79), 148 (100)
230 (M+;18), 204 (30), 174 (43), 119 (42), 105 (100), 80 (46)
230 (M+;21), 204 (29), 174 (47), 120 (39), 105 (100), 81 (49)
281 (M+;17), 256 (23), 225 (33), 184 (31), 170 (100)
233 (M+;14), 207 (29), 179 (34), 136 (84), 109 (100), 83 (74)
242 (M+;19), 216 (28), 185 (46), 130 (44), 116 (100), 94 (39)
258 (M+;22), 232 (36), 202 (35), 119 (82), 147 (100)
261 (M+;20), 235 (36), 207 (42), 164 (39), 135 (100)
308 (M+;26), 282 (35), 253 (29), 197 (37), 183 (100)
320 (M+;12), 294 (22), 230 (51), 195 (100), 80 (46)
C
C
C
C
C
C
C
C
C
C
12H11N5O3
11H10N4O2
11H10N4O2
11H7N4O2F3
10H7N4O2F
11H7N5O2
12H10N4O3
10H7N5O4
11H10N4O2Br
16H12N6O2
9
10
11
Table 4
Influence of solvent on λmax of dyes 1–11.
Dye
MeOH/OH−
DMSO
DMF
Acetonitrile
Chloroform
Methanol
Acetic acid
MeOH/H+
1
2
3
4
5
6
7
8
392
372
375
356
348,420s
356, 389s
414, 355s
369, 429s
469, 376s
372, 401s
401, 496s
375, 404s
397, 406s
379
373, 402s
378, 400s
377
385
386, 399s
370
367
355, 390s
365
355, 380s
373, 399s
382, 500s
363
384
378
370
368
355, 386s
373, 380s
356
373
376
392
368
361
361
355
363
355
369
373
359
397
388
386
374
367
361
377
355
375
377
371
397
392
362
360
361
355
378
356
374
373
369
396
373
374
385, 409s
367, 391s
380, 420s
371, 400s
390, 506s
385, 415s
406
380, 404s
367, 390s
378, 417s
372, 400s
386, 506s
383, 413s
405
9
10
11
377
400
399
s: Shoulder.

24
M.R. Yazdanbakhsh et al. / Journal of Molecular Liquids 169 (2012) 21–26
2
1.6
1.2
0.8
0.4
0
assigned to the tautomeric hydrazone proton (_N\NH\). These re-
6
2
sults show that the dyes may exist as a mixture of tautomeric azo and
hydrazone forms, although dyes 3, 4 and 11 only showed a broad
peak at 13.61–13.82 ppm, which is related to the azo form
(Scheme 2). Tables 2 and 3 present the characteristic data of dyes 1–11.
1: MeOH
2: Acetonitrile
3: Chloroform
4: DMSO
5: DMF
6: Acetic acid
5
3
1
3.2. Solvent effects
4
Absorption spectra of azo dyes 1–11 were recorded in various sol-
vents at a concentration of ~10−6 M and the results are summarized
in Table 4. The visible absorption spectra of the dyes did not show
regular variation with the polarity of solvents.
Dyes 3, 4 and 11 showed one absorption maxima in all of the used
solvents, which means they are present in only one tautomeric form.
Dyes 1, 2 and 5 to 10 exhibit two absorption maxima in some sol-
vents, which indicate the presence of two tautomeric forms. It was
also observed that the absorption spectra of the dyes in various sol-
vents did not significantly change except for dyes 5, 7, 9 and 10
(Fig. 1). The λmax of dyes 5, 7, 9 and 10 shifted considerably in
DMSO and DMF with respect to λmax in other solvents (Table 4).
Strong evidence that dyes 5, 7, 9 and 10 exist in equilibrium is provid-
ed by the two absorption maxima and isobestic points in the visible
spectra of, for example, dye 9 in different solvents (Fig. 2). This equi-
librium may exist between tautomeric and anionic forms.
It was also observed that the absorption curves of the dyes were a
little sensitive to acid. The absorption maxima values of all dyes in
methanol, when 0.1 M HCl was added, being nearly the same as
those observed in acetic acid. This indicates that all of them have a
single tautomeric form in these conditions. But they are very sensitive
to bases, except dyes 1, 2 and 4. λmax of the dyes showed a large bath-
ochromic shift when a small amount of 0.1 M KOH was added to their
methanolic solutions. In the case of dyes 5, 7, 8, 9, 10 and 11, adding
0.1 M KOH to their methanolic solutions, did not significantly change
the maximum absorption at the shorter wavelengths; however, a
maximum at longer wavelengths appeared. It can be suggested that
these dyes are predominantly in two tautomeric forms in basic
media (Fig. 3).
300
350
400
450
500
wavelenght (nm)
Fig. 1. Absorption spectra of dye 4 in various solvents.
3
2.5
2
2
1: DMSO
2: MeOH
3
6
3: Chloroform
4: DMF
4
5: Acetonitrile
6: Acetic acid
5
1.5
1
1
0.5
0
300
400
500
600
700
wavelength (nm)
Fig. 2. Absorption spectra of dye 9 in various solvents.
Many authors have examined the effects of temperature and con-
centration on the tautomeric equilibria of arylazo dyes in solutions
and found that the equilibria change with decreasing temperature
[32–34]. In this study, diluted and concentrated solutions of dyes 1–
11 in chloroform, acetonitrile, methanol, DMSO and DMF were exam-
ined in the temperature range 25–70 °C. The λmax values of synthe-
sized dyes did not change significantly by altering the dye
concentration in chloroform, acetonitrile, methanol, DMSO and
DMF, except for dyes 1 and 7 in methanol, in which a red shift
emerged due to an increase in concentration. It is of interest to note
respectively (dyes 1, 2 and 5–10), related to pyrimidine ring proton
(N_CH\NH). Dyes 3, 4 and 11 exhibited only one doublet at 9.16–
9.22 ppm for this proton (Table 3). The spectra also showed a singlet
at 3.17 (\CH3, 1), 3.03 (\CH3, 2), 2.18 (\CH3, 3), 2.35 (\CH3, 4),
2.56 (\CH3, 8) and 2.32 (\CH3, 10) ppm. For all the dyes except 3, 4
and 11, the broad peak at 13.42–14.32 ppm was assigned to the tauto-
meric phenol proton (C_C\OH) and the spectra of all mentioned
dyes showed another broad peak at 14.37–15.30 ppm, which was
Table 5
Influence of temperature and sample concentration on absorption maxima of dyes 1–11.
Dye
DMSO conc.
(25 °C)
DMSO dil.
(25 °C)
DMSO
(70 °C)
DMF conc.
(25 °C)
DMF dil.
(25 °C)
DMF
(70 °C)
λ
max(nm)
A. nitrile dil.
(25 °C)
Meth. conc.
(25 °C)
Meth. dil.
(25 °C)
Chl. conc.
(25 °C)
Chl. dil.
(25 °C)
A. nitrile conc.
(25 °C)
1
2
3
4
5
6
7
8
375, 405s
395, 404s
381
374, 406s
397, 406s
381
375, 404s
398, 403s
378
373, 402s
376, 397s
379
373, 400s
378, 401s
377
375, 400s
377, 398s
380
383
386, 399s
371
368
354, 389s
364
358, 382s
371, 399s
379, 500s
363
385
385, 399s
370
366
353, 390s
362
355, 380s
373, 399s
382, 501s
363
405
368
362
361
358
362
366
368
372
360
396
392
368
365
361
355
363
355
369
373
359
395
384
376
372
366
351, 388s
372, 381s
358
373
378
384
380
370
368
353, 386s
373, 381s
356
373
378
373
373
373
375
375
374
382, 406s
368, 392s
377, 420s
372, 402s
390, 506s
388, 416s
406
385, 409s
367, 392s
378, 419s
373, 404s
391, 508s
388, 417s
406
385, 410s
367, 391s
379, 418s
373, 402s
392, 507s
387, 415s
406
382, 403s
369, 389s
380, 415s
372, 400s
386, 502s
381, 412s
403
381, 404s
367, 390s
378, 417s
369, 399s
384, 504s
383, 415s
405
380, 404s
365, 392s
377, 415s
370, 400s
386, 506s
382, 415s
405
9
10
11
375
401
377
399
399
398
Chl.: chloroform, Meth.: methanol, A. nitrile.: acetonitrile, conc.: concentrated, dil.: diluted, s.: shoulder.

M.R. Yazdanbakhsh et al. / Journal of Molecular Liquids 169 (2012) 21–26
25
1: Acetic acid
1.4
1.2
1
standard antibiotics (15 μg/well for erythromycin and 30 μg/well for
tetracycline). Nevertheless, the dyes at these lower concentrations
seem to have similar levels of antibiotic activity against these two
bacteria. It is also noteworthy that S. typhimurium was much more
sensitive to all the dyes than to either of the two control antibiotics.
2: MeOH
3: MeOH + HCl
4: MeOH + KOH
3
2
0.8
0.6
0.4
0.2
0
4
1
4. Conclusions
300
350
400
450
500
550
600
In this paper, 11 new azo disperse dyes were prepared by classical
method of azo coupling reaction. The synthesized dyes were charac-
terized by IR, 1H NMR, UV–vis, elemental analysis and mass spectros-
copy. The substituents and solvent effects on the electron absorption
spectra of these dyes were also evaluated. The absorption data of the
synthesized dyes revealed that for some of these compounds, tauto-
meric species exist in equilibrium. On the other hand, in the case of
azo hydroxypyrimidine disperse dyes, tautomeric equilibrium needs
to be considered. Furthermore, measurement of antibacterial activity
demonstrated that electron accepting groups (dyes 5–11), compared
to electron donating groups (dyes 1–4) were more active against the
tested bacteria. The dyes, at lower concentration, showed similar ac-
tivities against B. subtilis and P. aeruginosa as those shown by the con-
trol antibiotics and were far more active against S. typhimurium. The
effect of the dyes on microbes needs further examination.
Wavelength (nm)
Fig. 3. Absorption spectra of dye 11 in acidic and basic solution.
that the results indicated little change in λmax values of dyes 1–11 on
raising the temperature (Table 5). These findings support the occur-
rence of a dissociation equilibrium related to proton-donating or
proton-accepting solvents in which no change in energy is involved.
3.3. Substituents effects
As is apparent from Table 4, the introduction of an electron-
donating methoxy group to the benzene ring results in a bathochro-
mic shift in all solvents with respect to electron-accepting acetyl,
fluoro and cyano groups (for dye 1 Δλ=29 nm relative to dye 6,
Δλ=31 nm relative to dye 7 for spectra in methanol). These results
can be attributed to the electron withdrawing nature of the hydroxy-
pyrimidine moiety of the dyes.
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1
2
3
4
5
6
7
8
4.38
4.38
4.38
4.38
4.38
4.38
4.38
4.38
4.38
4.38
4.38
15
16
18
19
21
30
24
22
26
29
–
10
10
14
14
15
16
11
18
16
16
18
10
16
–
–
–
–
–
–
–
–
12
13
12
11
–
13
17
18
12
15
–
9
10
11
Stda
Stdb
13
13
12
14
12
10
18
15
30
7
8
–: Resistant.
b
Erythromycin is used as standard.
Tetracycline is used as standard.
a

26
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