Solvatochromism, spectral properties and antimicrobial activities of new azo-azomethine dyes with N2S2O2 donor set of atoms

Article abstract of DOI:10.1016/j.molstruc.2014.05.014

Six new azo-azomethine dyes, H₂Lⁿ (n = 1-6), with N₂S₂O₂ donor set of atoms have been prepared via condensation reaction of 1,10-diaza-4,7-dithiadecane, I, with substituted azo-coupled salicylaldehyde

Full text of DOI:10.1016/j.molstruc.2014.05.014

Accepted Manuscript
Solvatochromism, spectral properties and antimicrobial activities of new azo-
azomethine dyes with N2S2O2 donor set of atoms
Hamid Khanmohammadi, Maryam Pass, Khatereh Rezaeian, Gholamreza Talei
PII:
S0022-2860(14)00486-4
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.05.014
MOLSTR 20613
Reference:
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Accepted Date:
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2 April 2014
5 May 2014
Please cite this article as: H. Khanmohammadi, M. Pass, K. Rezaeian, G. Talei, Solvatochromism, spectral properties
and antimicrobial activities of new azo-azomethine dyes with N2S2O2 donor set of atoms, Journal of Molecular
Structure (2014), doi: http://dx.doi.org/10.1016/j.molstruc.2014.05.014
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Solvatochromism, spectral properties and antimicrobial
activities of new azo-azomethine dyes with N2S2O2 donor set
of atoms
Hamid Khanmohammadi∗, 1, Maryam Pass1, Khatereh Rezaeian1, Gholamreza Talei2
1-Department of Chemistry,Faculty of science, Arak University, Arak 38156-8-8349, Iran
2-Razi Herbal Medicines Research Center, Lorestan University of Medical Sciences, Khorram
Abad, Iran
Abstract
Six new azo-azomethine dyes, H2Ln (n=1-6), with N2S2O2 donor set of atoms have been prepared
via condensation reaction of 1,10-diaza-4,7-dithiadecane, I, with substituted azo-coupled
1
salicylaldehyde. The dyes were characterized by IR, UV-Vis and H NMR spectroscopic
methods as well as elemental analysis. The solvatochromic behavior of the dyes was also probed
by studying their UV-Vis spectra in four pure organic solvents of different polarities and a
meaningful correlation was observed. Furthermore, all prepared dyes were assayed for their
antibacterial and antifungal activities by disc diffusion method. The results indicated that all
prepared dyes show good inhibition against Staphylococcus epidermidis and Bacillus cereus and
did not show any antibacterial activity against Escherichia coli as compared to standard drugs.
Keywords: Antmicrobial; Azo; Dye; Schiff base; Solvatochromism.
∗
Corresponding author.h-khanmohammadi@araku.ac.ir Tel: +98-861-2777401; Fax: +98-861- 4173406.
1

1. Introduction
During the past decades, considerable attention has been drawn towards the synthesis of azo
compounds [1,2]. Azo compounds are extensively utilized in chemical industries as dyes and
pigments because of their extraordinary coloring and thermal properties [3,4]. Also, azo
compounds and their metal complexes have shown promise as indicators, radical reaction
initiators and therapeutic agents [5-7]. Moreover, attention has been also devoted to the optical
and physico-chemical properties of azo compounds for their potential applications in areas of
nonlinear optics, optical storage media, chemosensors, liquid crystals, photochemical molecular
switches and in manufacture of protective eye glasses and filters [8-16].
It is worth mentioning that spectral properties of azo compounds depend not only on the azo
groups but also on the presence of other coupling components. Among various coupled-dyes,
azo-azomethine dyes have attracted the interest of chemists owing to exhibiting several structural
properties and uses [17,18]. Recently, much effort has been devoted to the study of azo-
azomethine dyes including hydroxyl groups [19, 20]. The presence of ortho-hydroxyl groups in
this type of dyes has been regarded as one of the important elements favoring for existence of
intramolecular proton transfer. Interestingly, this process has significant effect on their electronic
structure which can be exploited for their thermochromic and/or photochromic properties and
also the design of molecular electronic devices [21]. Also, the tautomerism in polyhydroxy
derivatives of azo-azomethine dyes play key role in many fields of chemistry and especially
biochemistry [20]. The presence of azo/imino, phenol/imino and hydrazone/azo-enaminone
tautomers of these compounds may impact noticeably on their unique photo-physical and photo-
chemical properties, which is in turn strongly influenced by several factors including
temperature, the substituent structure and solvent polarity [20,21].
2

On the other hand, Schiff bases derived from salicylaldehyde have long been considered as
polydentate ligands to form very stable complexes with transition metal ions [22]. They have
been reported to show a variety of biological actions involving antibacterial, antifungal,
anticancer and herbicidal activities [23-26].
In view of the foregoing discussion, our present work manifests the synthesis and
characterization of six new acyclic azo-azomethine dyes containing N2S2O2 donor set of atoms,
H2Ln (n=1-6), derived from condensation reaction of 1,10-diaza-4,7-dithiadecane, I, with 5-(4-
substituted-phenyl)-azo-salicyladehyde, 1-6, Figure 1. All prepared title compounds are air stable
solids, intensely colored, soluble in DMF and DMSO and indicated dye characteristic since the
molar extinction coefficients (ε) were over 11,000 M−1 cm−1 in DMSO [27]. The solvatochromic
behavior and substituent effect of the newly prepared compounds were examined in various
solvents with different polarities. Moreover, antimicrobial activity of the dyes was evaluated by
using in vitro assays.
Figure 1
2. Experimental
2.1. Materials
All of the reagents and solvents involved in synthesis were of analytically grade and used as
received without further purification. Salycilaldehyde, 4-nitroaniline, 4-chloroaniline, 4-
ethylaniline, 4-bromaniline, 4-methylaniline and 4-flouroaniline were obtained from Aldrich and
Merck. Azo-coupled precursors, 1-6, were prepared according to the well-known literature
procedure [28].
3

2.2. Instrumentation
1
The structure of all synthesized compounds was confirmed by H NMR spectra, recorded on
Bruker AV 300 MHz and Bruker AV 400 MHz spectrometers. FT-IR spectra were recorded as
pressed KBr discs, using Unicom Galaxy Series FT-IR 5000 spectrophotometer in the region of
400–4000 cm-1. Melting points were determined on Electrothermal9200 apparatus. C. H. N.
analyses were performed on a Vario EL III elemental analyzer. Electronic spectral measurements
were carried out using Optizen 3220 UV spectrophotometer in the range 200–700 nm.
2.3. Synthesis
2.3.1. Synthesis of 1,10-diaza-4,7-dithiadecane, I
1,10-diaza-4,7-dithiadecane was prepared according to modified previously reported method [29,
30]. A mixture of 2-aminoethanthiol hydrochloride (11.36 g, 0.1 mol) and sodium hydroxide
(4.12 g, 0.103 mol) in deionized water (60 mL) was heated to reflux for 30 min. The solution
was allowed to cool to 60-65 °C and then 1,2-dibromoethane (9.39 g, 0.05 mol) was added
dropwise over a period of 30 min and the mixture was heated to reflux for 2 h. After cooling to
room temperature, the mixture was extracted with chloroform. The organic layer was dried over
anhydrous MgSO4 and then evaporated to dryness in vacuo. The residue was further washed
thoroughly with diethyl ether and dried under vacuo at room temperature.
2.3.2. General procedure for synthesis of azo-azomethine dyes, H2Ln (n=1-6)
A solution of diamine I (0.28 g, 1 mmol) in absolute EtOH (10 mL) was added to a stirring
solution of azo-coupled precursors, 1-6, (2 mmol) in absolute EtOH (50 mL) during a period of
30 min at 50 °C. The solution was then heated in water bath for 4 h at 80 °C with stirring. The
mixture was filtered whilst hot and the obtained solid was washed with hot ethanol (three times)
and then with diethyl ether. The resulted product was dried in air.
4

2.3.2.1. bis-(2-((ethylimino)methyl)-4-((4-nitrophenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L1
Yield: 41.22%, m.p. 252-253oC.1H NMR (DMSO-d6, 400 MHz, ppm): δ 2.80(s, 4H), 2.94(t, 4H,
H
J=6.42 Hz), 3.83(t, 4H, J=6.42 Hz), 6.76(d, 2H, J=9.23 Hz), 7.93(m, 6H), 8.09(d, 2H, J=2.4 Hz),
8.35(d, 4H, J=8.8 Hz), 8.71(s, 2H). IR (KBr, cm-1): 1633(C=N/C=C), 1433(N=N), 1587(phenol
ring), 1516(NO2), 1338(NO2), 1288(C-O). Anal. Calcd. For C32H30N8O6S2: C, 55.96; N, 16.32;
H, 4.40; S, 9.34. Found: C, 55.46; N, 16.69; H, 4.12; S, 9.85 %. λ
(nm) (ε (M-1cm-1)): 260
max
(33200), 415 (28200) and 460 (27250) in DMSO.
2.3.2.2. bis-(2-((ethylimino)methyl)-4-((4-flourophenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L2
o
1
Yield: 78.79%, m.p. 168-171 C. H NMR (DMSO-d6, 400 MHz, ppm): δ 2.80(s, 4H), 2.93(t,
H
4H, J=6.4 Hz), 3.82(t, 4H, J=6.4 Hz), 6.88(d, 2H, J=8.8 Hz), 7.38(t, 4H, J=8.8 Hz), 8.09(m, 6H),
8.02(d,2H, J=2.4), 8.72(s, 2H), 14.1(br, 2H). IR (KBr, cm-1): 1635(C=N/C=C), 1500(N=N),
1595(phenol ring), 1286(C-O). Anal. Calcd. for C32H30F2N6O2S2: C, 60.74; N, 13.28; H, 4.78; S,
10.14 %. Found: C, 60.43; N, 13.86; H, 4.37; S, 10.61 %. λmax (nm) (ε (M-1cm-1)): 266 (84200)
and 369 (20800) in DMSO.
2.3.2.3. bis-(2-((ethylimino)methyl)-4-((4-chlorophenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L3
1
Yield: 74.54%, m.p. 197-200oC. H NMR (DMSO-d6, 400 MHz, ppm): δ 2.80(s, 4H), 2.93(t,
H
4H, J=6.4 Hz), 3.82(t, 4H, J=6.4 Hz), 6.86(d, 2H, J=9.2 Hz), 7.75(d, 4H, J=8.8 Hz), 7.80(d, 4H,
J= 8.8 Hz), 7.90(dd, 2H, J=9.2, J=2.4Hz), 8.03(d, 2H, J=2.4 Hz), 8.71(s, 2H), 14.1(br, 2H). IR
(KBr, cm-1): 1635(C=N/C=C), 1493(N=N), 1575(phenol ring), 1284(C-O). Anal. Calcd. for
C32H30Cl2N6O2S2: C, 57.74; N, 12.63; H, 4.54; S, 9.63. Found: C, 57.43; N, 12.71; H, 4.16; S,
9.85 %. λmax (nm) (ε (M-1cm-1)): 264 (93950) and 379 (48450) in DMSO.
5

2.3.2.4. bis-(2-((ethylimino)methyl)-4-((4-bromophenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L4
1
Yield: 94.95%, m.p. 213-215oC. H NMR (DMSO-d6, 400 MHz, ppm): δ 2.80(s, 4H), 2.93(t,
H
4H, J=6.4 Hz), 3.82(t, 4H, J=6.4 Hz), 6.85(d, 2H, J=9.2 Hz), 7.74(m, 6H), 7.9(m, 2H), 8.03(d,
2H, J=2.8 Hz), 8.71(s, 2H), 14.1(br, 2H). IR (KBr, cm-1): 1635(C=N/C=C), 1493(N=N),
1572(phenol ring), 1282(C-O). Anal. Calcd. for C32H30Br2N6O2S2: C, 50.94; N, 11.14; H, 4.01;
S, 8.50. Found: C, 50.67; N, 11.21; H, 3.48; S, 9.11%. λmax (nm) (ε (M-1cm-1)): 261 (75100) and
380 (49700) in DMSO.
2.3.2.5. bis-(2-((ethylimino)methyl)-4-((4-methylphenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L5
o
1
Yield: 94.74%, m.p. 146-148 C. H NMR (DMSO-d6, 400 MHz, ppm): δ 2.37(s, 6H), 2.79(s,
H
4H), 2.92(t, 4H, J=6.3 Hz), 3.81(t, 4H, J=6.3 Hz), 6.90(d, 2H, J=9 Hz), 7.34(d, 4H, J=8.1 Hz),
7.71(d, 4H, J= 8.1 Hz), 7.89(dd, 2H, J=9, J=3Hz), 8.00(d, 2H, J=3 Hz), 8.70(s, 2H),14.1(br, 2H).
IR (KBr, cm-1): 1635(C=N/C=C), 1491(N=N), 1581(phenol ring), 1284(C-O). Anal. Calcd. for
C34H36N6O2S2: C, 65.36; N, 13.45; H, 5.81; S, 10.26. Found: C, 65.73; N, 12.94; H, 5.56; S,
10.54 %. λmax (nm) (ε (M-1cm-1)): 260 (68050) and 375 (48300) in DMSO.
2.3.2.6. bis-(2-((ethylimino)methyl)-4-((4-ethylphenyl)diazenyl)phenol)ethane-1,2-dithiol, H2L6
o
1
Yield: 32.78%, m.p. 164-167 C. H NMR (DMSO-d6, 400 MHz, ppm): δ 1.22(t, 6H, J=7.6 Hz
H
), 2.68(q, 4H, J=7.6 Hz ), 2.80(s, 4H), 2.93(t, 4H, J=6.4 Hz), 3.82(t, 4H, J=6.4 Hz), 6.90(d, 2H,
J=9.2 Hz), 7.38(d, 4H, J=8.4 Hz), 7.73(d, 4H, J= 8.4 Hz), 7.90(dd, 2H, J=9.2, J=2.4Hz), 8.02(d,
2H, J=2.4 Hz), 8.72(s, 2H), 14.1(br, 2H).IR (KBr, cm-1): 1635(C=N/C=C), 1491(N=N),
1581(phenol ring), 1284(C-O). Anal. Calcd. for C36H40N6O2S2: C, 66.23; N, 12.87; H, 6.18; S,
9.82. Found: C, 65.84; N, 12.30; H, 5.39; S, 10.39 %. λmax (nm) (ε (M-1cm-1)): 260 (93750) and
371 (52500) in DMSO.
6

2.4. Antimicrobial activity studies
2.4.1. Antibacterial assessment
Antibacterial evaluation was carried out against six standard bacteria including Staphylococcus
aureus ATCC25923, Escherichia coli ATCC 25922, Staphylococcus epidermidis ATCC 12228,
Proteus mirabilis ATCC29906, Pseudomonas aeruginosa ATCC27853, Bacillus cereusanda yeast
Candida albicans ATCC10231. Bacillus cereus and Candida albicans strain were originally
isolated from rice and patient, respectively and used along with standard strain. The bacteria
were grown on the Muller Hinton broth or agar (Merck, Germany) for experimental study.
2.4.2. Antimicrobial testing
The compounds were dissolved in DMSO at the concentration of 1000, 500, 100 µg/mL and
used for antibacterial evaluation. The solution was UV-sterilized and used for disk diffusion.
Paper discs (6.5 mm) were impregnated with 40 mL of the sample and the solvent was
evaporated under a safety cabinet at room temperature. Bacterial suspension s turbidity was
compared and equalized with the Mac Farland 0.5 standard. Then, the suspension spread over a
Muller Hinton agar plate by sterile swab and Penicillin, Gentamicin and Amphotericin B
o
antibiotics were used as positive controls. The plates were incubated at 35 C overnight and the
inhibition zone (IZ) was measured [31].
3. Result and discussion
Six new azo-azomethine dyes, H2Ln (n=1-6), were synthesized via condensation reaction of 5-(4-
X-phenyl)-azo-salicyladehyde (X= NO2, Et, Cl, Br, Me and F) with 1,10-diaza-4,7-dithiadecane
1
in ethanol which were easily identified by their IR and HNMR spectra. All prepared dyes are
intensely colored and soluble in DMF and DMSO. The existence of –N=N– and –C=N– moieties
7

in structure of the dyes has caused them to show specific spectral properties and antimicrobial
activity against the tested Gram-positive bacteria.
3.1. Infrared spectra
To clarify the position of the most important bands in the IR spectra of 1-6 and H2Ln (n=1-6),
their assignments based on broad data available for related compounds [10,12,21] are presented
in Table 1. A strong band observed in the IR spectra of 1-6 in the region of 1653-1672 cm−1 can
be assigned to the υ(C=O) group. The total absence of υ(C=O) band in the IR spectra of H2Ln
(n=1-6) together with appearance of new υ(C=N) band in the range of 1633-1635 cm−1 clearly
denoted that new Schiff-base compounds had formed in each case. The symmetric N=N
stretching mode, in the IR spectra of H2Ln (n=1-6), leads to a medium band at 1433–1500 cm−1,
while the υ(C-O) stretching mode gives an intense band within the range of 1282–1288 cm−1.
The IR spectra of 1 and related azo-azomethine dye, H2L1, indicate strong bands at 1338 and
1516cm-1 assigned to the NO2 groups [32].
Table 1
3.2. 1H NMR Spectra
n
1
The H NMR spectra of 1-6 and H2L (n=1-6), recorded at ambient temperature in DMSO-d6,
exhibit a group of signals corresponding to the hydrogens of each molecule. The slightly broad
1
signal at δ 11.47–11.61 ppm in the H NMR spectra of 1-6 is attributed to the OH protons, as
H
was confirmed by deuterium exchange when D2O was added to DMSO-d6 solution. The OH
protons of H Ln (n=1-6) exhibit a slightly broad resonance at δ 14.10 ppm. The CH=N protons
H
2
8

of H Ln (n=1-6) exhibit a singlet resonance at δ 8.70-8.72 ppm. Also, the 1H NMR spectra of the
H
2
dyes show a doublet (δ 7.39-7.93 ppm) and also a doublet (δ 7.74-8.36 ppm) assigned to the
H
H
para-substituted aromatic ring. The doublet pattern of δ 7.74-8.36 ppm signal is simplified after
H
irradiation at 7.39-7.93 ppm. The ratio Δδ/J for para-substituted aromatic ring in H2L4 is equal to
zero, it means that the chemical shift difference, Δδ, between the coupled protons becomes zero,
the middle peaks coalesce to give a single peak, and the end peaks vanish. This situation is
encountered with equal chemical shifts for two set of para-substituted aromatic ring protons in
H2L4 and AA′XX′ system changes into an A4 system.
3.3. Electronic absorption spectra and substituent effects
The UV-Vis absorption spectra of H2Ln (n=1-6), recorded in DMSO at room temperature,
exhibit main bands at 260-266, 369-415 and 445-460 nm (Figure 2 and Table 1).The intense
band located at 260-266 nm can be assigned to the moderate energy (π→π*) transition of the
aromatic rings while the broad absorption band at 369-415 nm is due to low energy (π→π*)
transition involving the π-electrons of the azo and azomethine groups [33]. It is worth to note
that the position of π→π* band is highly influenced by the nature of the para-substituent, R. It
acquires a red shift in λ
along with the increase in the electron-accepting ability of the
max
substituent in the sequence of F< Et< Me< Cl Br< NO2. This manner can be explained on the
basis of the expected high delocalization of the electrons in the para-substituted dye with nitro
group which enhances the delocalization of conjugated system [34]. In addition, the low energy
π→π* band of azo–azomethine dyes is more red shifted than related azo-coupled precursors, 1-6,
because of extended π-resonance system. The observed red shift in o-hydroxy substituted azo-
9

azomethine compounds may be inferred from (i) selective solvation, (ii) the ability of the solvent
to form stronger intermolecular H-bonds with a particular tautomeric form, Figure 3, and (iii) the
intramolecular hydrogen bonding between C=N and/or N=N with OH groups [22,34]. The very
broad band located at longer wavelength, 460 nm, is attributed to the n→π* transition of azo and
azomethine chromophores and also intramolecular charge transfer involving the whole of
molecule [22, 34].
Figure 2
Figure 3
3.4. Solvatochromic behavior
The electronic transitions of azo-azomethine dyes strongly depend on the nature of media [33].
To achieve this, the electronic absorption spectra of 2× 10-5 M solution of the prepared dyes in
four organic solvents with different polarity were recorded at room temperature. The polarity and
hydrogen bonding properties of the used solvents in the present investigation, indicated by the
Kamlet–Taft parameters (α, β, and π*) [3,34,35], Eq. 1, are given in Table 2.
(νa- νf) =(νa- νf)0 + a.α + b.β +s.π* (1)
α is a scale of solvent hydrogen bond donor (HBD) acidities which refer to the donation of the
proton. β is a scale of solvent hydrogen-bond acceptor (HBA) basicities which refers to the
acceptance of the proton of a hydrogen bond. π* is a scale of solvent dipolarity/polarizability
which refer to the ability of solvent to stabilize a charge or a dipole by virtue of its dielectric
effect. The π* value is correlated with the solvatochromic behavior values. The solvatochromic
behavior of a dye is the shift of the π→π* band wavelength due to the presence of solvent with
10

different polarity, which is due to the interaction between the solute and solvent molecules
[35,36]. We found that the absorption band at 369-415 nm generally shows bathochromic shift
(positive solvatochromism) as the polarity of solvent was increased. The influence of solvents for
the prepared dyes increases in the order DMSO>DMF>CHCl3>CH3CN. This positive
solvatochromism may be due to the effect of dipole moment changes of the excited state and/or
changes in the hydrogen bonding strength in polar solvents [35,36]. In addition, it is worth
mentioning that the n→π* band appears only in DMSO and DMF solvents (in DMF is
overlapped with π→π* band) and this band vanishes completely in CHCl3 and CH3CN. This fact
can be explained in according to β parameter which is high for DMSO and DMF, Table 2. As the
β parameter increases, the ability of the solvent for accepting the proton of OH-group is
increased, too. Conclusively, the generation of hydrazone and enaminone tautomers is expected
in DMSO and DMF solutions. The absorption spectra of H2L1 in various solvents are shown in
Figure 4 (For other dyes see supporting information).
Table 2
Figure 4
3-5- Evaluation of antibacterial activity of azo precursors, 1-6, and azo-azomethine dyes, H2Ln
(n=1-6)
The disk- diffusion method was carried out to evaluate the antibacterial activity of azo
precursors, 1-6, and azo-azomethine dyes, H2Ln (n=1-6), using Penicillin (10µg/D), Gentamicin
(10µg/D) and Amphotericin B (10µg/D) as the control antibiotics. All the compounds were
tested against different Gram- positive bacteria namely S. aureus, S. epidermidis and B. cereus,
11

Gram- negative P. aeruginosa, P. mirabilis and E. coli. Antifungal activity was tested against C.
albicans.
Among the azo precursors, 2 and 6 showed the strong activity against Gram– positive bacteria S.
epidermidis and B. cereus (See supporting information). While, weak activity was observed on
S. aureus (See supporting information). The moderate inhibitory effect was also observed for the
azo precursors against P. mirabilis. In addition, the azo precursors have low activity against E.
coli and P. aeroginosa (See supporting information). Furthermore, it can be found that the azo
precursors have shown moderate effect on C. albicans (See supporting information).
Also H2Ln (n=1-6), like the azo precursors, had the strongest activity against S. epidermidis
(Table 3) and the greatest inhibition zone belonged to H2L4 and H2L6. However, the moderate
effect on S. aureus and P. mirabilis was exhibited for the azo-azomethine dyes. In addition, all
azo-azomethine dyes showed moderate effect on C. albicans, Table 4.
Table 3
Table 4
In short, we found that azo precursors, 1-6, and the dyes, H2Ln (n=1-6), showed some biological
activities to different extend. A few were significantly strong and impressive. It is noteworthy
that the activities were mostly against Gram-positive rather than Gram-negative bacteria and
especially against S. epidermidis and B. cerus. Simultaneous presence of two functional groups,
N=N and C=N, in the examined compounds may explain the strong antimicrobial activity of
those [37, 38]. Therefore, the result indicated that these compounds have strong biological
activities which require further research and study to make useful application in different
industries like textile.
12

Conclusion
New azo-azomethine dyes have been synthesized via condensation reaction of 5-(4-X-phenyl)-
azo-salicyladehyde (X= NO2, Et, Cl, Br, Me and F) with 1,10-diaza- 4,7-dithiadecane in ethanol.
All prepared dyes showed positive solvatochromic behavior as the polarity of solvent was
increased. Antibacterial and antifungal activity of azo precursors and also azo-azomethine dyes
were done in comparison with standard antibiotic. Among the 7 selected strains of bacteria and
fungi including S. aureus, E. coli, S. epidermidis, P. mirabilis, P. aeruginosa, B. cereus, and a
yeast C. albicans, Gram-positive bacteria exhibited more sensitivity to all compounds.
Supplementary data
Supplementary data associated with this article can be obtained free of charge via….
Acknowledgements
We are grateful to Arak University for financial support of this work. We also would like to
thank Razi Herbal Medicines Research Center, Lorestan University of Medical Sciences on
antimicrobial studies.
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16

Figure legends:
Figure 1: The synthesized azo-azomethine dyes.
Figure 2: Electronic absorption spectra of H2Ln (n=1-6) (2×10-5 mol L-1) in DMSO.
Figure 3: Structures of Imino-phnol, hydrazone and enaminone tautomers for azo-azomethine
dyes.
Figure 4: Electronic spectra of H2L1 in various solvents.
17

Table 1: Tentative assignments of some selected IRa frequencies (cm-1) and UV-Vis data of the
prepared azo-azomethine dyes and their azo precursors
ν(phenol
λ
max (nm) (ε (M-1cm-1)) in
Compounds ν(C-O) ν(C=O) ν(C=C) ν(C=N) ν(NO2)
ν(N=N)
ring)
DMSO
1525,
1346
246 (4500), 382(12700), 551
(1850)
1
2
3
4
5
6
1288
1286
1286
1286
1287
1277
-
-
-
-
-
-
1575
1595
1572
1572
1576
1581
1479
1479
1477
1475
1481
1479
1666
1608
260 (14650), 341 (25253), 461
(5022)
-
-
-
-
-
1672
1668
1620
1622
256 (6490), 410 (7850),
466(9345)
260 (9320), 349 (18700), 456
(7049)
1668
1620
260 (7580), 344 (23400), 437
(3720)
1668
1653
-
1620
1602
1614
260 (7360), 347 (16314),
447(3120)
1516,
1338
260 (33200), 415 (28200), 460
(27250)
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
1288
1633
1587
1433
1286
1284
1282
1284
1284
-
-
-
-
-
1603
1605
1607
1600
1602
1635
1635
1635
1635
1635
-
-
-
-
-
1595
1575
1572
1581
1581
1500
1493
1493
1491
1491
266(84200), 369 (20800)
264 (93950), 379 (48450)
261 (75100), 380 (49700)
260 (68050), 375 (48300)
260 (93750), 371 (52500)
aKBr discs
18

Table 2: Selected physical and solvatochromic parameters (α, β, and π*) for used solvents
Solvent
α
β
π*
ε
μ/D
CH3CN
DMSO
0.19
0.00
0.40
0.76
0.66
1.00
35.94
46.45
3.94
4.09
DMF
0.00
0.20
0.69
0.10
0.88
0.69
36.71
4.89
3.81
1.15
CHCl3
19

Table 3: Antibacterial activity of H2Ln (n=1-6).
Staphylococcus Staphylococcus Bacillus
Proteus Pseudomonas
Compound
H2L1
Concentration
E.coli
aureus
epidermidis
cereus
mirabilis
aeruginosa
11
8
8
-
16
14
13
18
18
17
16
14
11
21
16
14
13
11
11
20
18
12
18
14
11
19
17
14
21
20
18
17
13
13
16
15
14
18
24
15
-
-
16
11
-
8
8
40µ g/D
20µ g/D
5µ g/D
-
8
-
20
18
14
18
14
10
12
12
-
8
40µ g/D
20µ g/D
5µ g/D
H2L2
-
-
8
-
-
8
12
15
-
8
10
11
-
8
40µ g/D
20µ g/D
5µ g/D
H2L3
H2L4
H2L5
H2L6
10
10
8
-
40µ g/D
20µ g/D
5µ g/D
-
-
8
-
-
8
10
8
-
-
-
8
40µ g/D
20µ g/D
5µ g/D
-
-
8
-
-
10
10
12
12
-
-
11
9
40µ g/D
20µ g/D
5µ g/D
-
-
-
-
-
DMSO
Penicillin
Gentamicin
-
-
34
-
-
15
-
-
28
-
-
-
21
-
-
20
-
-
17
10µ g/D
10µ g/D
20

Table 4: Antifungal activity of H2Ln (n=1-6) against Candida albicans.
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
40µ g/D
20µ g/D
5µ g/D
12
12
14
17
19
19
11
12
11
12
15
17
13
12
10
13
12
11
* Inhibition zone for Amphotericin B(10µ g/D):24mm
21

S
S
S
S
R
H
H
N
N
H
HO
NH2 H2N
OH
(I)
N
N
O
N
N
N
N
OH
R
R
R
1
NO2
F
H2Ln (n=1-6)
2
3
4
5
6
Cl
Br
CH3
Et
Figure 1
22

Figure 2
23

S
S
N
N
Imino- phenol
HO
OH
N
N
N
N
R
R
R
R
S
S
HN
NH
Enaminone
O
O
N
N
N
N
R
S
S
N
N
Hydrazone
O
O
N
N
HN
NH
R
Figure 3
24

Figure 4
25

Hamid Khanmohammadi , Maryam Pass, Khatereh Rezaeian, Gholamreza Talei
J. Mol. Struct. xxx (2014) xxx
Solvatochromism, spectral properties and antimicrobial activities of new azo-azomethine dyes with
N S O donor set of atoms:
2
2
2
New azo-azomethine dyes have been prepared via condensation reaction of 1,10-diaza-4,7-dithiadecane
with substituted azo-coupled salicylaldehyde. The UV-Vis spectra of the dyes in pure organic solvents of
different polarities and their antimicrobial activities have been investigated.
S
S
H
H
N
N
HO
OH
N
N
N
N
R
R
R= NO2, F, Cl, Br, Me, Et
26

Research highlights:
>New bisiminated water insoluble azo-azomethine dyes have synthesized> Solvatochromic
properties of the dyes in various organic solvents have been investigated> Aantimicrobial
activities of the prepared dyes have been reported.
27