Synthesis, structure characterization and antimicrobial evaluation of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles

Article abstract of DOI:10.1016/j.saa.2012.12.074

The present article deals with the synthesis, spectral characterization and antimicrobial activity of phenylazo dyes. All of the synthesized phenylazo dyes were characterized using ATR-FTIR, FT-Raman, ¹H NMR, ¹³C NMR, elemental analy

Full text of DOI:10.1016/j.saa.2012.12.074

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, structure characterization and antimicrobial evaluation
of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles
c
Selin Kinali-Demirci a, Serkan Demirci b, , Mustafa Kurt
⇑
a Department of Chemistry, Faculty of Science, Gazi University, 06500 Ankara, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Amasya University, 05100 Amasya, Turkey
c Department of Physics, Faculty of Arts and Sciences, Ahi Evran University, 40100 Kırsehir, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
4-(Substituted phenylazo)-
3,5-diacetamido-1H-pyrazoles were
synthesized.
Phenylazo dyes were examined by
FT-IR, FT-Raman, UV, NMR
techniques and DFT.
Phenylazo dyes were screened for
their antibacterial and antifungal
activity.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 October 2012
Received in revised form 17 December 2012
Accepted 22 December 2012
Available online 4 January 2013
The present article deals with the synthesis, spectral characterization and antimicrobial activity of pheny-
lazo dyes. All of the synthesized phenylazo dyes were characterized using ATR-FTIR, FT-Raman, 1H NMR,
13C NMR, elemental analysis and mass spectroscopic techniques. Solvent effects on the UV–Vis absorp-
tion spectra of these phenylazo dyes were studied. Acid and base effects on the visible absorption max-
ima of the phenylazo dyes were also reported. The structural and spectroscopic analysis of the molecules
were carried out using Density Functional Theory (DFT) employing the standard 6-31G(d) basis set, and
the optimized geometries and calculated vibrational frequencies were evaluated via comparison with
experimental values. The antimicrobial activity of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyra-
zoles was reported against bacteria, including B. cereus (RSKK 863), S. aureus (ATCC 259231), M. luteus
(NRRL B-4375), E. coli (ATCC 11230) and the yeast C. albicans (ATCC 10239).
Keywords:
Phenylazo dyes
Solvatochromism
Vibrational spectra
DFT
Ó 2013 Elsevier B.V. All rights reserved.
Antimicrobial activity
Introduction
contain at least one nitrogen–nitrogen double bond called azo
group (N@N) [17,18]. Azo groups are relatively robust and chemi-
Azo compounds are the largest class of industrially synthesized
organic dyes and are important materials because of their versatile
applications in various fields, such as electronics, foods, drugs, cos-
metics and textiles [1–5]. Several studies describe the synthesis
[6–9], absorption spectra [10,11], solvatochromic behavior
[12,13] and theoretical investigation [14–16] of azo dyes. Azo dyes
cally stable, and therefore, extensive studies have been carried out
investigating azobenzene based structures as dyes and colorants.
The aromatic groups around the azo bond help to stabilize the
N@N group by making it part of an extended delocalized system.
The synthesis, chemical structure and methods of application for
these compounds are generally not complex.
Tautomerism is not only important to the dyestuff manufac-
turer, but it is also important in other areas of chemistry. Specifi-
cally, the azo-hydrazone tautomerism is quite interesting for
⇑
Corresponding author. Tel.: +90 358 242 1613; fax: +90 358 242 1616.
E-mail addresses: srkndemirci@gmail.com, serkan.demirci@amasya.edu.tr
theoretical studies and is also important from
a practical
(S. Demirci).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.074

S. Kinali-Demirci et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
13
perspective because the two tautomers have different properties
[14]. Although many commercially available azo dyes are predom-
inantly in the hydrazone form [19], in light-sensitive studies,
including polymer [20–22] and controlled release [23], the azo
form of the dye is preferred.
geometries was confirmed by vibrational spectra calculations,
which gave positive values for all of the obtained wavenumbers.
Antimicrobial activity of phenylazo dyes
Although, the synthesis of 4-(4-substituted phenylazo)-3,5-
diacetamido-1H-pyrazoles has been reported by Elnagdi et al.
[24], to our knowledge, the antimicrobial activity, electronic spec-
tra and molecular structure of these dyes have not been studied. In
this paper, we present the synthesis of new phenylazo dyes. The
antimicrobial activity and absorption ability of these dyes that
are substituted with different groups at their o-, m- and p-position
were also examined in detail. The calculated vibrational wavenum-
bers and chemical shifts were compared with the experimental
data for the mentioned molecules.
The in vitro antibacterial activities of the phenylazo dyes were
studied using the agar well-diffusion method in the bactericidal
and fungicidal testing. The origin of the microbial strains are B. cer-
eus RSKK 863, S. aureus ATCC 259231, M. luteus NRLL B-4375, E. coli
ATCC 11230 and C. albicans ATCC 10239 as yeast. The bacterial and
yeast cultures were incubated at 37 °C for 18 h. The phenylazo
dyes were dissolved (20 lg/mL) in DMSO and stored at room tem-
perature. Mueller Hinton Agar (15 mL) that was stored at ca. 45 °C
was then poured into the petri dishes and allowed to solidify. Holes
of 12 mm in diameter were punched carefully using a sterile cork
borer, and these were completely filled with the test solutions.
The plates were incubated for 24 h at 37 °C. The mean value ob-
tained for the two holes was used to calculate the zone of growth
inhibition for each sample. DMSO was used by itself as a control
under the same conditions for the tested microorganisms. The
diameter of the inhibition zone resulting from DMSO was sub-
tracted from each case. The antimicrobial activity results were cal-
culated as the mean of three trials.
Experimental
Synthesis of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles
The synthesis of 2-(substituted phenylazo)malononitriles and
4-(substituted phenylazo)-3,5-diamino-1H-pyrazoles was carried
out according to the methods in the literature [24]. Equimolar
amounts of 4-(substituted phenylazo)-3,5-diamino-1H-pyrazoles
and acetic acid were refluxed for 24 h [24]. After the reaction
was complete, the reaction mixture was chilled in an ice bath.
The precipitated product was filtered off and recrystallized from
an appropriate solvent. The crystalline product was dried over-
night under a vacuum at room temperature (Scheme 1). The
appearance, yield, crystallization solvent, melting point and ele-
mental analysis of the phenylazo dyes are given in Table 1.
Physical measurements
The melting points were determined on a Barnstead Electro-
thermal 9200 melting point instrument. Mass spectra were taken
on an Agilent 1100 MSD instrument. The elemental analyses (C,
H and N) were performed on a Leco CHNS-932 type elemental ana-
lyzer. Fourier Transform Infrared (ATR-FTIR) spectra of the 4-
(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles were ob-
tained using a Thermo Nicolet 6700 spectrometer with a Smart Or-
bit attenuated total reflection attachment. The FT-Raman spectra
of the samples were recorded in the 50–3500 cmÀ1 region on a
Bruker FRA 106/S FT-Raman instrument using 1064 nm excitation
from an Nd:YAG laser. The detector is a liquid nitrogen cooled Ge
detector. NMR spectra were recorded on a Bruker-Spectrospin
Avance DPX 400 Ultra-Shield NMR spectrometer with chemical
shifts in ppm (for CDCl3, tetramethylsilane was used an as internal
standard). The absorption spectra were measured on a Unicam
UV2-100 spectrophotometer at the wavelength of maximum
Computational details
Calculations for the electronic structure and geometry optimi-
zation of the phenylazo dyes were performed using the Gaussian
09 program [25] package and the Gauss-View molecular visualiza-
tion program [26]. The molecular structures of the phenylazo dyes
were optimized using the DFT/B3LYP level with the 6-31G(d)
basis set [27]. The optimized structural parameters were used
in the vibrational wavenumbers. The stability of the optimized
Scheme 1. Synthesis of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles.

14
S. Kinali-Demirci et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
Table 1
The appearance, yield, crystallisation solvent, melting point and elemental analysis of phenylazo dyes.
Dye
Appearance
Yield (%) Crystallization solvent Melting point (°C) Molecular formula (mol. wt) C% calc. (exp.) H% calc. (exp.) N% calc. (exp.)
2Cl-PDP
3Cl-PDP
4Cl-PDPa
2Nt-PDP
3Nt-PDP
4Nt-PDPa
2Me-PDP
3Me-PDP
Brown
Yellow
Dark yellow 58
Orange
Brown
Brown
Yellow
Yellow
57
75
Toluene
292–293
235–237
276–278
220–221
244–246
211–213
238–239
217–219
183–185
C
C
C
13H13ClN6O2 (320.7)
13H13N7O4 (331.3)
14H16N6O3 (316.3)
48.68 (48.65)
47.13 (47.08)
53.16 (53.10)
4.08 (4.04)
3.95 (3.89)
5.10 (5.02)
26.20 (26.22)
29.60 (29.55)
26.57 (26.49)
Ethanol/H2O
Ethanol/H2O
Toluene
Ethanol/H2O
Toluene
Toluene
Toluene
Toluene
82
97
52
55
73
97
4Me-PDPa Red
a
Literature [24].
absorption (kmax) in a range of solvents, including DMSO, DMF,
methanol, acetonitrile, acetic acid and chloroform, at various con-
centrations (10À6–10À8).
Similarly, the azo stretching of the phenylazo dyes shifted to lower
wavenumbers in the experimental Raman spectra (Fig. 2).
The experimental chemical shifts of phenylazo dyes are pre-
sented in Table S2 (Supplementary information). Two broad peak
approximately 11.0 and 9.0 ppm are assigned to N-H proton. The
multiplet between 7.9 and 7.1 ppm are assigned to aromatic ring
protons [28,29], and the singlet approximately 2.3 ppm are as-
signed to acetate (ACOCH3) protons for all of the phenylazo dyes.
In 1H NMR spectra of the Me-PDP, singlet at 3.9 ppm belongs to
methoxy protons (AOCH3) [29]. In 13C NMR spectra, peak at
153.2 ppm belongs to two C3 atoms and peak at 72.4 ppm corre-
sponds to C4 carbon atom (pyrazole ring). Carbonyl, C2 has the
highest chemical shifts and observed at 169.8 ppm. The peak of
the acetate carbons (ACOCH3) appeared at 22.5 ppm for all of the
phenylazo dyes. Aromatic carbon peaks are shown to be at approx-
imately 100–140 ppm depends on the substituted positions. Meth-
oxy carbon peak was observed at about 55.6 ppm for Me-PDP.
Results and discussion
Vibrational analysis
The structures of the phenylazo dyes were elucidated using
spectroscopic methods. The experimental ATR-FTIR spectral data
for the dyes are shown in Fig. 1. The experimental ATR-FTIR spectra
of the phenylazo dyes showed a band at 3450–3200 cmÀ1, which
was assigned to the ANAH stretching. The C@O stretching bands
of the dyes are located at 1700–1680 cmÀ1 in all of the experimen-
tal spectra for the phenylazo dyes. The theoretical wavenumbers
for the phenylazo dyes were calculated using the density func-
tional B3LYP/6-31G(d) method with a scaling factor of 0.9613
[27], and the selected wavenumbers are summarized in Table S1
(Supplementary information). The calculated wavenumbers for
the ANAH and C@O stretching are shown at 3500–3300 cmÀ1
and 1750–1700 cmÀ1, respectively. There were 10–50 cmÀ1 shifts
to lower wavenumbers observed for the NAH and C@O stretching
bands of the experimental ATR-FTIR spectra compared with the
theoretical FTIR spectra. This observation strongly supports the
idea that a hydrogen bond can form between the ANAH and
C@O groups. The characteristic band (N@N) of the phenylazo dyes
appeared at 1400 cmÀ1 in the theoretical FTIR spectra. However, in
the experimental FTIR spectra of the dyes, the N@N stretching
shifted to a lower wavenumber (1390–1370 cmÀ1) and depended
on the neighbouring group and intermolecular hydrogen bonding.
UV–Vis spectra of phenylazo dyes
The UV–Vis absorption spectra of the phenylazo dyes were re-
corded between 300 and 700 nm using a variety of solvents and
concentrations (10À6–10À8 M), and the results are shown in
Fig. 4. The absorption maxima of the dyes were found to be inde-
pendent of the solution phase and did not have a correlation with
the dielectric constants of the solvents. Each of the phenylazo dyes
gave a single dominant absorption peak. Additionally, as outlined
in Table 2, there was no significant change observed with the use
of chloroform, acetic acid, DMSO, DMF, acetonitrile and methanol.
The absorption maxima of the phenylazo dyes in the correspond-
ing solvents are similar. We observed that in DMSO and DMF,
Fig. 1. The experimental FT-IR spectrums of phenylazo dyes.

S. Kinali-Demirci et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
15
Fig. 2. The experimental Raman spectrums of phenylazo dyes.
the kmax of the 4Nt-PDP dye bathochromically shifted with respect
to the kmax in other solvents (e.g., for 4Nt-PDP kmax is 443 nm in
DMSO, 427 nm in DMF and ꢀ394 nm in other solvents).
The effects of the substituents on the dyes were also studied.
The differences in the absorption spectra for the dye solutions
can be assessed in terms of the dye structures. Details of the visible
absorption spectra of the azopyrazole dyes that contain electron
accepting substituents and electron donating substituents are
shown in Table 2. When the substituents were in the p- and o-posi-
tions of the benzene rings, the kmax of the dyes showed significant
bathochromic shifts in all of the solvents. Greater bathochromic
shifts were observed for o-substituted benzene rings than for p-
substituted benzene rings, except for nitro groups. Whereas the
p- and o-substituents showed electron withdrawing or donor prop-
erties owing to their inductive effects and resonance effects, the
m-substituents showed only inductive effects. As a result of these
greater electronic effects, the dispersion of electrons was more
affected. The AOCH3 and ANO2 groups that possess greater
resonance effects, showed significant bathochromic shifts in the
p- and o-positions of the benzene rings. The results we obtained
were in accord with these electronic effects.
Fig. 3. Absorption spectra of 4-(methoxyphenylazo)-3,5-diamino-1H-pyrazoles
and 4-(methoxyphenylazo)-3,5-diacetamido-1H-pyrazoles.
the phenylazo dyes are given in Table 3. The results indicate that
the phenylazo dyes are in the azo form in the gas phase, and the
stability of phenylazo dyes increases as the substitution number
of the azo dye increases from 2 to 4.
The phenylazo dyes can exist in four possible tautomeric forms,
namely the azo-amine form (a), the hydrazo-amine form (b), the
azo-imine form (c) and the hydrazo-imine form (d), as shown in
Scheme 2. The hydrazo form of the compounds, which has hydro-
The effects of acid, base and concentration on the absorption of
the dye solutions were investigated, and the results are shown in
Table 2. As seen in the table, the absorption spectra kmax of the dyes
in concentrated methanol are similar to the absorption spectra of
the dyes in diluted methanol. When acetic acid (0.1 M) and piper-
idine (0.1 M) were added to the dye solutions in diluted methanol,
the absorption spectra of kmax of the dyes did not significantly shift.
gen atoms present in the a- and b- positions, is more stable. There-
fore, we expected that the phenylazo dyes are present in the
hydrazo-amine (b) and hydrazo-imine (d) forms. The UV spectra
of the 4-(substituted phenylazo)-3,5-diamino-1H-pyrazoles pro-
duced a shoulder; however, this shoulder disappeared when all
of the phenylazo dyes were acetylated (Fig. 3). This result suggests
that the phenylazo dyes are present as a single tautomeric form in
all of the solvents used.
The dyes can exist in the hydrazo and azo tautomeric forms, but
the spectroscopic and optimized structural parameter results sug-
gest that these phenylazo dyes are predominantly in the azo
(Scheme 2c) form in solution and in the solid state.
Molecular geometry
The optimized structural parameters of the phenylazo dyes
were calculated using the DFT-B3LYP level with the 6-31G(d) basis
set. The optimized structures for the phenylazo dyes are shown in
Fig. S1 (Supplementary information). 4-(substituted phenylazo)-
3,5-diacetamido-1H-pyrazole is comprised of a two-rings (phenyl
and pyrazole) system, and the rings are connected to each other
by the azo group (N@N). The N@N bond length is 1.252 Å, and
the average length of the N@N bonds in the phenylazo dyes vary
from 1.2779 to 1.2791 Å. The lengthened N@N distance of the
phenylazo dyes is the result of intramolecular hydrogen bonds
[30] and conjugation in the two rings [16]. The length of the
N@N bonds in the phenylazo dyes is longer than the N@N bonds
in 4-(phenylazo)-3,5-diasetamido-1H-pyrazole [16] because of ste-
ric hindrance. The total energies of the azo and hydrazo forms of
Antimicrobial activity of phenylazo dyes
The synthesized phenylazo dyes were tested for their antimi-
crobial activity against bacterial strains: B. cereus RSKK 863, S. aur-
eus ATCC 259231, M. luteus NRLL B-4375, E. coli ATCC 11230 and

16
S. Kinali-Demirci et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
Fig. 4. Absorption spectra of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles in chloroform (1), acetic acid (2), DMSO (3), DMF (4), acetonitrile (5) and methanol (6).
Table 2
Influence of solvent on kmax (nm) of azo dyes.
Dye
DMSO DMF Acetonitrile Methanol Acetic acid Chloroform Methanol (10À6 M) Methanol (10À8 M) Methanol (acid) Methanol (base)
2Cl-PDP
3Cl-PDP
4Cl-PDP
2Nt-PDP
3Nt-PDP
4Nt-PDP
2Me-PDP 389
3Me-PDP 361
4Me-PDP 371
382
363
371
376
371
443
378
363
370
378
369
427
386
360
371
371
358
361
370
360
396
383
358
370
369
351
362
371
361
396
382
355
369
370
354
356
371
354
386
383
357
368
371
357
361
383
360
394
385
357
370
369
351
362
371
361
396
382
355
369
369
355
363
371
359
394
381
355
369
367
353
359
371
355
393
383
356
365
369
354
357
371
359
411
380
356
365
Table 3
yeast; C. albicans ATCC 10239 by the disk diffusion method. The
antimicrobial activity results are given in Table 4. The best results
were obtained for compound 2Cl-PDP against the microorganisms,
and a similar effect was noted for 4Cl-PDP. Generally, the 2Cl-PDP
and 4Cl-PDP dyes were the most active, but 3Cl-PDP showed no
inhibition in the growth of the microorganisms. The Nt-PDP dyes
had higher antibacterial activity than Me-PDP dyes, but they had
lower activity than Cl-PDP. Antibacterial effect of some antibiotics
was investigated as detailed elsewhere [31–35]. Compared to anti-
biotics, phenylazo dyes showed lower activity except for 2Cl-PDP
and 4Cl-PDP against E.coli, S. aureus, M. luteus and B. cereus. Anti-
bacterial activity of 2Cl-PDP and 4Cl-PDP dyes is very close to some
antibiotics such as ampicillin [32], tetracycline [31] and erythro-
mycin [35] against E. coli and B. cereus.
Calculated total energies (E) of the azo and hydrazo form of azo dyes.
Dye
Tautomer
Azo
Hydrazo
2Cl-PDP
3Cl-PDP
4Cl-PDP
2Nt-PDP
3Nt-PDP
4Nt-PDP
2Me-PDP
3Me-PDP
4Me-PDP
À1442.35195822
À1442.35209481
À1442.35224307
À1187.24791636
À1187.25653618
À1187.25767314
À1097.27051341
À1097.27770344
À1097.28002072
À1442.31132906
À1442.32615779
À1442.32661301
À1187.20887164
À1187.21438208
À1187.23180144
À1097.22872347
À1097.24264651
À1097.25352025
The Cl atoms play a vital role in various metabolic systems in
these microorganisms. Moreover, the position of Cl atoms is
particularly important. The Me-PDP and Nt-PDP dyes show varying
degrees of inhibition of the growth of the microorganisms. These

S. Kinali-Demirci et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 12–18
17
Scheme 2. Molecular structure and tautomers of phenylazo dyes with different R substituents.
Table 4
Antimicrobial activities of azo dyes.
Dye
Inhibition zone diameter (mm)
E coli ATCC 11230
S aureus ATCC 259231
M luteus NRRL B-4375
B cereus RSKK 863
C albicans ATCC 10239
2Cl-PDP
3Cl-PDP
4Cl-PDP
2Nt-PDP
3Nt-PDP
4Nt-PDP
2Me-PDP
3Me-PDP
4Me-PDP
24/26/28
–
16/16/16
8/8/8
4/4/4
–
10/12/12
8/10/12
18/22/20
6/6/6
–
14/14/14
6/6/6
8/8/8
–
8/10/10
–
–
10/10/10
–
18/20/20
4/6/6
20/20/20
–
16/16/16
6/4/4
10/10/12
8/10/10
10/10/10
–
12/12/8
–
20/22/18
20/18/18
4/2/4
16/18/18
–
16/12/16
6/6/6
10/10/8
–
–
–
–
10/8/10
dyes (Table 4) have a more profound effect upon the growth of
E. coli, B. cereus and C. albicans. Unfortunately, there was no rela-
tionship between the position of the substituents and antimicro-
bial activity for the phenylazo dyes.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.12.074.
Conclusions
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