Synthesis and characterization of azobenzene derivatives and azobenzene-imidazolium conjugates with selective antimicrobial potential

Article abstract of DOI:10.1016/j.molstruc.2021.130049

Five new non-fluorinated and fluorinated azo derivatives, as well as a new series containing five azo-imidazolium conjugates of varying alkyl chain length in the imidazolium head group were prepared and characterized using FTIR and NMR spectroscopy, and e

Full text of DOI:10.1016/j.molstruc.2021.130049

Journal of Molecular Structure 1232 (2021) 130049
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis and characterization of azobenzene derivatives and
azobenzene-imidazolium conjugates with selective antimicrobial
potential
Halimah Funmilayo Babamalea,b, Thiagarajan Sangeetha , Joo Shun Tan , WanSinn Yam
a,∗
c
c
a
School of Chemical Sciences, Universiti Sains Malaysia, 11800 Gelugor, Pulau Pinang
b
Department of Industrial Chemistry, University of Ilorin, P.M.B 1515, Ilorin Nigeria
c
School of Industrial Technology, Universiti Sains Malaysia, 11800 Gelugor, Pulau Pinang
a r t i c l e i n f o
a b s t r a c t
Article history:
Five new non-fluorinated and fluorinated azo derivatives, as well as a new series containing five azo-
imidazolium conjugates of varying alkyl chain length in the imidazolium head group were prepared and
characterized using FTIR and NMR spectroscopy, and elemental microanalysis. Antimicrobial activities of
these compounds against pathogenic Gram positive bacterium Staphylococcus aureus and Gram negative
bacteria Escherichia coli, Salmonella enterica serovar Typhimurium, as well as yeasts Candida albicans and
Saccharomyces cerevisiae were evaluated using the disc diffusion method. The azo derivatives and their
imidazolium conjugates were selectively active against the tested microorganisms with zone of inhibition
diameters ranging from 10mm-21mm. Their biological efficacy was dependent on the chain length and
level of fluorine substitution. The presence of long alkyl chains is essential for the azo derivatives to
exhibit microbial efficacy. Active azo-imidazolium conjugates on Staphylococcus aureus contained 16 and
Received 24 November 2020
Revised 27 January 2021
Accepted 28 January 2021
Available online 3 February 2021
Keywords:
Azo-imidazolium conjugates
fluorinated azo derivatives
E. coli
Staphylococcus aureus
Candida albicans
18 carbons in the alkyl chains while Gram negative strains exhibited a cut-off effect at chain length C16.
Difference in antimicrobial behavior of the azo derivatives could be due to the different cell wall between
the Gram positive and negative bacteria. Fluorination had no effect on the activity against E. coli and
Salmonella. However, a clear correlation between the level of fluorine substitution and the antimicrobial
activity against Staphylococcus aureus, Candida albicans and Saccharomyces cerevisiae was observed.
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
exhibit various biological activities such as antiseptic [6], antimi-
crobial [6–14], anti-tumor [15], antineoplastic [16], anti-androgenic
[17] and antidiabetic [18] activities. Azo compounds are known to
interact with the bacterial cell membranes. Their ability to photo-
switch enable them to modulate membrane interaction of peptides
[19], and hence they are used as photocontrollers in biological sys-
tems [20–24]. Recently, azo-amphiphiles, in particular those con-
taining a cationic ammonium head group were reported to show a
high antimicrobial potential [25]. On the other hand, heterocyclic
imidazole derivatives, a class of azole compounds play a critical
role in many biological systems and functions [26]. They constitute
a major class of compounds with medicinal and pharmacological
properties [35–38]. The biological efficacy of imidazolium deriva-
tives depends on the counter anions, the head groups and the N-
substituents on the imidazolium moiety [27]. In both azo and imi-
dazolium compounds, hydrophobicity/lipophilicity was found to in-
crease their biological efficacy [25,28]. Due to the unique chemi-
cal and physiological properties of the fluorine atom, fluorination
The emergence of multi-drug resistant microbial strains is one
of the major public health threats and hence it is essential to de-
sign and develop new, efficient and tolerant alternative antimicro-
bial drugs [1]. According to literature, the development of new
antimicrobial agents against Gram-negative bacteria is difficult as
their cell membrane forms a strong barrier that prevents the per-
meation of antibacterial agents [2]. Hence, the majority of the ex-
isting antibacterial agents for Gram positive bacteria are ineffective
against their Gram negative counterparts. Yeasts from the Candida
genus also pose serious health risks to humans due to their op-
portunistic nature [3]. Azo compounds are used in a wide range
of technological applications [4,5]. This class of compounds also
∗
Corresponding author
E-mail address: wansinn@usm.my (W. Yam).
https://doi.org/10.1016/j.molstruc.2021.130049
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
could modulate the chemical and biological properties, pharmaco-
dynamics and pharmacokinetics of organo-compounds [29]. Over
the years, research and development of fluorine-containing drugs
have progressed significantly. The presence of fluorine atom(s)
could increase drugs’ selectivity and lipophilicity, thus resulted in
increased antimicrobial activities [30]. Hence, we are interested
to investigate the antimicrobial potency of compounds compris-
ing azo, imidazolium and fluorine components. To the best of
our knowledge, there is no reports on the antimicrobial activities
of fluorinated azo compounds and azo-imidazolium conjugates.
Therefore, in the present work, our aim is to synthesize new azo
derivatives of different fluorine substitution, and azo-imidazolium
conjugates with varying chain length on the ionic imidazolium
head group. These compounds were assayed against pathogenic
Gram positive bacterium Staphylococcus aureus and Gram negative
bacteria Escherichia coli, Salmonella enterica serovar Typhimurium,
as well as yeasts Candida albicans and Saccharomyces cerevisiae to
evaluate their antimicrobial potential.
2.2. Synthesis
All azo derivatives were synthesised following the steps as de-
picted in Scheme 1 [4]
2
.2.1. Synthesis of N-[4-(decyloxy)phenyl]acetamide, 1
To a 250-ml round bottom flask, 4-acetaminophenol (5.0 g, 33.1
mmol) was dissolved in acetone (100mL). 1-Bromodecane (36.4
mmol, 8.05g), and K CO3 (59.4mmol, 13.72g) were then added. The
2
reaction mixture was refluxed for 24 hours. After the reaction was
complete, excess solvent was removed using a rotatory evapora-
tor. Excess K CO3 was removed by washing the crude product with
2
dichloromethane (DCM). The solid was filtered and the residue was
dried. The sticky, whitish solid precipitate was then purified with
n-hexane.
−1
Yield: 56.37 %. FTIR (KBr) ʋ/cm : 3320, 3140 (N-H), 2923, 2850
Csp3-H), 1661 (C=O), 1607 (C=C), 1236 (C-O). 1H NMR (500 MHz,
(
CDCl ) δ/ppm: 0.88 (t, 3H, J = 7 Hz, CH ), 1.35 (m, 12H, CH ), 1.46
3
3
2
(
m, 2H, CH CH ), 1.69 (m, 2H, OCH CH ), 1.87 (t, 3H, J = 7.3 Hz,
2
3
2
2
OCCH ), 3.91 (t, 2H, J = 7 Hz, OCH ), 6.84 (d, 2H, J = 8.9 Hz, Ar-H),
2. Experimentals
3
2
7.09 (s, 1H, NH), 7.36 (d, 2H, J = 10 Hz, Ar-H).
2
.1. Materials and methods
2
.2.2. Synthesis of 4-(decyloxy)aniline, 2
Reagents and chemicals used in this research were of analytical
To a 250-ml round bottom flask containing compound 1 in
grade and used as procured. A Stuart SMP10 melting point appa-
ratus was used to measure the melting points of the compounds.
FTIR spectra were recorded on a Perkin Elmer 2000 spectropho-
tometer and NMR spectra were recorded on a Bruker ADVANCE
ethanol (80ml), an aqueous solution of sodium hydroxide (22.4
equiv.) was added. The reaction mixture was refluxed for 24 h.
Subsequently, excess solvent was removed using a rotatory evap-
orator. The crude product was washed with distilled water and re-
crystallized from ethanol. Yield: 91.10 %. FTIR (KBr) ʋ/cm 1: 3381,
−
5
00MHz spectrophotometer. Elemental analyses were carried out
by using a Perkin Elmer 2400 LS series CHNS/O analyser.
3310 (N-H), 2920, 2852 (Csp3-H), 1515 (C=C), 1247 (C-O). 1H NMR
Scheme 1. Synthesis routes toward the formation of azo derivatives, 3-12.
2

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
(
500 MHz, CDCl ) δ/ppm: 0.88 (t, 3H, J = 7 Hz, CH ), 1.33 (m, 12H,
(d, 2H, J = 9 Hz, Ar-H), 7.47 (d, 2H, J = 9.05 Hz, Ar-H), 7.86 (d, 2H,
J = 9 Hz, Ar-H).
3
3
CH ), 1.44 (m, 2H, CH CH ), 1.73 (m, 2H, OCH CH ), 3.88 (t, 2H,
2
2
3
2
2
J = 7 Hz, OCH ), 6.24 (s, 2H, NH ), 6.79 (d, 4H, Ar-H).
2
2
2
.2.5. Synthesis of (E)-N-alkyl-N’-6-(4-(4’-decyloxyphenyl)
diazenyl)phenoxy)hexan-1-imidazolium bromides, 8-12
ꢀ
.2.3. Synthesis of (E)-4-((4 -(decyloxy)phenyl)
diazenyl)phenols/fluorinatedphenols, 3-5
2
To a 100 mL round bottom flask containing compound 6 (0.3g,
0
.6 mmol) in acetone (40ml), the corresponding N-alkyl-imidazole
1.0 equiv.) was added and the reaction mixture was refluxed for
8hrs. Subsequently, the reaction mixture was cooled to room tem-
A 250-mL round bottom flask containing a mixture of com-
pound 2 (3.33g, 13.4 mmol) and hydrochloric acid (3ml) in ace-
tone (100ml) was placed in an ice-water bath between 0-5 ᵒC and
stirred for 1 h. A cold aqueous solution of phenol (1.0 equiv.),
sodium carbonate (1.0 equiv.) and sodium hydroxide (1.0 equiv.)
was then added dropwise. The reaction mixture was stirred for
(
4
perature and excess solvent was removed using a rotary evapora-
tor. The crude products were recrystalised from diethyl ether to
yield compounds 8-12 in pure form.
(n = 10) yield: 68.6%. M.p.: 122-124 ˚C. FTIR (KBr) ʋ/cm 1:
−
8
1
-2 h while maintaining the temperature between 0-5 ᵒC. Subse-
3
069 (C -H), 2922, 2852 (C -H), 1601 (C=C),1499, 1473 (N=N),
sp2
sp3
quently, the ice-water bath was removed and the reaction mixture
was stirred overnight at room temperature. The reaction mixture
was then neutralized with an aqueous solution of sodium hydrox-
ide upon which a reddish brown precipitate was formed. The crude
product was filtered, washed with distilled water, and purified
using column chromatography in DCM/Petroleum Ether (80:20).
Compounds 4 and 5, were synthsised following the same proce-
dure, except that phenol was replaced with 2,6-difluorophenol or
+
1
243 (C-O), 1147 (C-N). Anal. calcd. [C41
H
BrN O ] : C = 67.84,
65
4
2
1
H = 9.03, N = 7.72; Found: C = 66.99, H = 9.05, N = 7.74.
H
NMR (500 MHz, CDCl ) δ/ppm: 0.88 (m, 6H, CH ), 1.28 (m, 26H,
3
3
CH ), 1.45 (m, 4H, OCH CH CH ), 1.57 (m, 2H, NCH CH CH ), 1.82
2
2
2
2
2
2
2
(
m, 4H,OCH CH ), 1.90 (m, 2H, NCH CH ), 1.98 (m, 2H, NCH CH ),
2 2 2 2 2 2
4
.03 (m, 4H, OCH ), 4.31 (t, 2H, J = 7.5 Hz, NCH ), 4.40 (t, 2H,
2
2
J = 7.4 Hz, NCH ), 6.97 (d, 4H, Ar-H), 7.18 (s, 1H, NCH), 7.22 (s,1H,
2
NCH), 7.87 (d, 4H, Ar-H), 10.76 (s,1H, NCH). 13C NMR (125 MHz,
2
,3,5,6-tetrafluorophenol.
: Yield: 52.9 %. M.p: 103-106 ˚C. FTIR (KBr) ʋ/cm 1: 3166 (O-
CDCl ) δ/ppm: 162.27, 161.66, 146.72, 146.01, 137.19, 125.08, 121.37,
−
3
3
121.27, 114.83, (Carom), 68.46, 67.74, 50.36, 50.16, (OCH NCH ),
2, 2
H), 2919, 2850 (Csp3-H),1600 (C=C), 1497 (N=N), 1250 (C-O), 1150
31.90, 31.85, 30.31, 30.19, 29.58-29.17, 28.99, 26.29, 26.01, 25.80,
(
C-N). 1H NMR (500 MHz, CDCl ) δ/ppm: 0.88 (t, 3H, J = 6.9 Hz,
3
2
5.17, 22.70, 22.67 (CH ), 14.14, (CH ). 9 (n = 12) yield: 80.6%. M.p.:
2
3
CH ), 1.27 (m, 12H, CH ), 1.46 (m, 2H, OCH CH CH ), 1.81 (m, 2H,
3
2
2
2
2
−1
127-129 ˚C. FTIR (KBr) ʋ/cm : 3071 (C
-H), 2922, 2851 (C
-
sp3
sp2
OCH CH ), 4.01 (t, 2H, J = 7 Hz, OCH ), 6.91 (d, 2H, J = 8.9 Hz,
2
2
2
H), 1601 (C=C), 1499, 1468 (N=N), 1243(C-O), 1147 (C-N). Anal.
Ar-H), 6.98 (d, 2H, J = 9 Hz, Ar-H), 7.81 (d, 2H, J = 8.9 Hz, Ar-
H), 7.83 (d, 2H, J = 9 Hz, Ar-H). 4: Yield: 80.3%. M.p: 87-90 ˚C.
sp3
+
calcd. [C43
H
BrN O ] : C = 68.50, H = 9.22, N = 7.43; Found:
69
4
2
1
C = 68.35, H = 9.56, N = 7.32. H NMR (500 MHz, CDCl ) δ/ppm:
−1
3
FTIR (KBr) ʋ/cm : 3374(O-H), 2920, 2852 (C -H), 1604 (C=C),
0
.87 (m, 6H, CH ), 1.28 (m, 30H, CH ), 1.46 (m, 4H, OCH CH CH ),
3 2 2 2 2
1
1
501 (N=N), 1249 (C-O), 1147 (C-N), 1021 (C-F). H NMR (500
1
.58 (m, 2H, NCH CH CH ), 1.82 (m, 4H, OCH CH ), 1.89 (m, 2H,
2 2 2 2 2
MHz, CDCl ) δ/ppm: 0.88 (t, 3H, J = 7 Hz, CH ), 1.29 (m, 12H,
3
3
NCH CH ), 1.90 (m, 2H, NCH CH ), 4.03 (m, 4H, OCH ), 4.31 (t, 2H,
2
2
2
2
2
CH ), 1.46 (m, 2H, OCH CH CH ), 1.81 (m, 2H, OCH CH ), 4.03
2
2
2
2
2
2
J = 7.5 Hz, NCH ), 4.40 (t, 2H, J = 7.4 Hz, NCH ), 6.98 (d, 4H, Ar-
2
2
(
t, 2H, J = 6.6 Hz, OCH ), 6.99 (d, 2H, J = 9 Hz, Ar-H), 7.53 (d,
2
H), 7.17 (s, 1H, NCH), 7.21 (s,1H, NCH), 7.89 (d, 4H, Ar-H), 10.76
s,1H, NCH). 13C NMR(125 MHz, CDCl ) δ/ppm: 161.28, 160.98,
J = 8.6 Hz, 2H, Ar-H), 7.86 (d, J = 9 Hz, 2H, Ar-H). 5: Yield: 73%.
sp3
(
−
1
3
M.p.: 97-100°C. FTIR (KBr) ʋ/cm : 3383(O-H), 2920, 2853(C
-
146.93, 146.80, 137.89, 124.35, 121.51, 121.39, 114.69, (Carom), 68.37,
H), 1603(C=C), 1509 (N=N), 1252 (C-O), 1155 (C-N), 1019 (C-F). 1H
67.85, 50.24, 50.03, (OCH NCH ), 31.90, 30.29, 30.23, 29.59-29.22,
2, 2
NMR (500 MHz, CD OD) δ/ppm: 0.91 (t, 3H, J = 7 Hz, CH ), 1.32
3
3
2
8.99, 28.87, 26.28, 26.03, 25.88, 25.46, 22.68, (CH ),14.13 (CH ).
2
3
−1
(
(
m, 12H, CH ), 1.49 (m, 2H, CH CH ),1.79 (m, 2H, OCH CH ), 4.07
2 2 3 2 2
1
0 (n = 14) yield: 50.6%. M.p: 129-132 ˚C. FTIR (KBr) ʋ/cm
:
t, 2H, J = 8 Hz, OCH ), 7.03 (d, 2H, J = 9.1 Hz, Ar-H), 7.77 (d, 2H,
2
3
073 (C -H), 2920, 2850 (C -H), 1601(C=C), 1499, 1467 (N=N),
sp2
sp3
J = 9 Hz, Ar-H).
1243 (C-O), 1148 (C-N). Anal. calcd. [C45
H
BrN O ]+: C = 69.12,
73
4
2
H = 9.41, N = 7.16; Found: C = 69.31, H = 9.72, N = 7.18.
1
2
.2.4. Synthesis of (E)-N-(4-bromohexyl)oxy)phenyl)-N’-decyloxy)
H NMR (500 MHz, CDCl ) δ/ppm: 0.87 (m, 6H, CH ), 1.30 (m,
3
3
phenyl/substitutedphenyl) diazenes, 6,7
34H, CH ), 1.46 (m, 4H, OCH CH CH ), 1.56 (m, 2H, NCH CH CH ),
2 2 2 2 2 2 2
In a 250mL round bottom flask, compound 3 (3g, 8.5mmol) and
1.82 (m, 4H, OCH CH ), 1.87 (m, 2H, NCH CH ), 1.98 (m, 2H,
2 2 2 2
1
,6-dibromohexane (7 equiv.) were dissolved in acetone (80ml).
NCH CH ), 4.03 (m, 4H, OCH ), 4.31 (t, 2H, J = 7.5 Hz, NCH ), 4.40
2
2
2
2
Potassium carbonate (3.0 equiv.) was then added and the reaction
mixture was refluxed for 7 h. Subsequently, the solvent was re-
moved using a rotary evaporator and the crude product was re-
crystalized from methanol to yield compound 6. Compound 7 was
synthsised following the same procedure, except compound 3 was
replaced with compound 4.
(t, 2H, J = 7.4 Hz, NCH ), 6.98 (d, 4H, Ar-H), 7.17 (s, 1H, NCH),
2
13
7.21 (s,1H, NCH), 7.93 (d, 4H, Ar-H), 10.74 (s,1H, NCH). C NMR
(125 MHz, CDCl ) δ/ppm: 161.24, 160.94, 146.99, 146.87, 137.85,
3
124.32, 121.52, 121.41, 114.67, (Carom), 68.35, 67.83, 50.29, 50.09,
(OCH NCH ), 31.93, 31.90, 30.31, 30.29, 30.23, 29.69-29.00, 28.87,
2
,
2
26.28, 26.03, 25.90, 25.47, 22.70, (CH ), 14.14 (CH ). 11 (n = 16)
2
3
Yield: 53.42%. M.p.: 96-99 ˚C. FTIR (KBr) ʋ/cm 1: 2919,
−
yield: 48.7%. M.p: 122-124 ˚C. FTIR (KBr) ʋ/cm : 3073 (C
−1
-H),
sp2
6
2
850(Csp3-H), 1603 (C=C), 1497 (N=N), 1246(C-O), 553 (C-Br).
2921, 2851 (Csp3-H), 1601(C=C), 1499, 1473 (N=N), 1250 (C-O),
1
+
H NMR (500 MHz, CDCl ) δ/ppm: 0.88 (t, 3H, J = 6.92 Hz,
1144 (C-N). Anal. calcd. [C
H
47 77
BrN O ] : C = 69.69, H = 9.58,
3
4
2
1
CH ), 1.33 (m,12H, CH ), 1.47 (m, 2H, CH CH CH Br), 1.53 (t, 4H,
N = 6.92; Found: C = 69.78, H = 10.00, N = 7.08. H NMR
(500 MHz, CDCl ) δ/ppm: 0.88 (m, 6H, CH ), 1.24 (m, 38H, CH ),
3
2
2
2
2
OCH CH CH ), 1.82 (m, 4H, OCH CH ), 1.91 (m, 2H, CH CH Br),
2
2
2
2
2
2
2
3
3
2
3
4
.43 (t, 2H, J = 6.8 Hz, CH Br), 4.03 (m, 4H, OCH ), 6.97 (d,
1.47 (m, 4H, OCH CH CH ), 1.57 (m, 2H, NCH CH CH ), 1.81 (m,
2 2 2 2 2 2
2
2
H, Ar-H), 7.87 (d, 4H,Ar-H). 7 Yield: 50.5%. M.p.: 60- 62 ˚C.
4H, OCH CH ), 1.91 (m, 2H, NCH CH ), 1.97 (m, 2H, NCH CH ),
2 2 2 2 2 2
−1
FTIR (KBr) ʋ/cm : 2919, 2850 (Csp3-H), 1604 (C=C), 1470 (N=N),
4.04 (m, 4H, OCH ), 4.32 (t, 2H, J = 7.5 Hz, NCH ), 4.40 (t,
2
2
1
259 (C-O), 1031 (C-F), 569 (C-Br).. 1H NMR (500 MHz, CDCl )
2H, J = 7.4 Hz, NCH ), 6.99 (d, 4H, Ar-H), 7.17 (s, 1H, NCH),
3
2
13
δ/ppm: 0.88 (t, 3H, J = 6.9 Hz, CH ), 1.31 (m,12H, CH ), 1.47
7.21 (s,1H, NCH), 7.91 (d, 4H, Ar-H), 10.74 (s,1H, NCH). C NMR
3
2
(
m, 2H, CH CH CH Br), 1.53 (m, 4H, OCH CH CH ), 1.81 (m, 4H,
(125 MHz, CDCl ) δ/ppm: 161.61, 161.32, 147.01, 146.31, 138.14,
2
2
2
2
2
2
3
OCH CH ), 1.90 (m, 2H, CH CH Br), 3.43 (t, 2H, J = 6.8 Hz, CH Br),
124.67, 121.38, 121.32, 114.81, (Carom), 68.43, 67.91, 50.34, 50.13,
(OCH NCH ), 31.94, 31.91, 30.30, 30.24, 29.71-29.20, 28.99, 28.84,
2
2
2
2
2
4
.03 (t, 2H, J = 6.6 Hz, OCH ), 4.21 (t, 2H, J = 6.4 Hz, OCH ) 6.98
2
2
2,
2
3

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
peak at 553 cm 1 confirmed the formation of compounds 6 and
−
2
6.29, 26.02, 25.89, 25.46, 22.70, (CH ) 14.14 (CH ). 12 (n = 18)
1
2
3
−
yield:46.25%. M.p: 104-106 ˚C. FTIR (KBr) ʋ/cm : 3070 (C -H),
7 as shown in Fig. 1(b). The successful incorporation of the imida-
sp2
2
919, 2850 (Csp3-H), 1601 (C=C),1499, 1467 (N=N), 1244 (C-O),
zolium moiety into the latter was confirmed by the appearance of
+
−1
1148 (C-N). Anal. calcd. [C49
H
BrN O ] : C = 70.22, H = 9.74,
the characteristic C-N peak at 1144-1155 cm
in the FTIR spec-
81
4
2
1
N = 6.68; Found: C = 70.02, H = 10.02, N = 6.46. H NMR (500
MHz, CDCl ) δ/ppm: 0.87 (m, 6H, CH ), 1.27 (m, 42H, CH ), 1.45
tra of the azo-imidazolium conjugates, compounds 8-12, which
3
3
2
conformed to the reported values [24]. Stretching vibrations of
the para-substituted phenyl rings was observed around 845 cm 1.
−
(
m, 4H, OCH CH CH ), 1.56 (m, 2H, NCH CH CH ), 1.80 (m, 4H,
2 2 2 2 2 2
OCH CH ), 1.91 (m, 2H, NCH CH ), 1.96 (m, 2H, NCH CH ), 4.03
Fig. 1(c) shows the diagnostic peaks in compound 8.
2
2
2
2
2
2
(
m, 4H, NCH ), 4.31 (t, 2H, J = 7.5 Hz, OCH ), 4.41 (t, 2H, J = 7.4 Hz,
2
2
OCH ), 6.97 (d, 4H, Ar-H), 7.18 (s, 1H, NCH), 7.23 (s,1H, NCH), 7.87
2
(
d, 4H, Ar-H), 10.65 (s,1H, NCH). 13C NMR (125 MHz, CDCl ) δ/ppm:
3.2. NMR Spectroscopy
3
162.09, 161.38, 147.86, 147.29, 138.61, 124.80, 121.29, 121.23, 114.86,
(
Carom), 68.47, 67.96, 50.37, 50.16, (OCH NCH ), 31.93, 31.90, 30.32,
In order to further elucidate the molecular structures of the
synthesised compounds, the 1H-and 13C NMR spectroscopy were
employed. Similar spectral characteristics were observed in the
1H NMR spectra of compounds 3, 4 and 5. The following discus-
sion was based on compound 3. The NMR spectrum with peak
integrations (in red) which reveal the ratio of the numbers of
chemically different hydrogen atoms in compound 3 is shown in
Fig. 2. A triplet at 0.88 ppm (J = 7.0 Hz) could be assigned to
the methyl protons. Signals corresponded to the methylene pro-
tons were observed as three mutiplets within 1.27 ppm-1.82 ppm.
The oxymethylene protons in these compounds were observed as
one triplet at 4.02 ppm (J = 7 Hz). Due to electron withdrawing
effect of the oxygen atoms, these protons are more deshielded and
hence, their signals are shifted downfield as compared to that of
other methylene protons in the terminal chains. In compound 3,
signals attributable to the aromatic protons were observed as four
doublets, each integrated to two protons, at 6.90 ppm (J = 8.9 Hz),
6.98 ppm (J = 9 Hz), 7.80 ppm (J = 8.9 Hz) and 7.84 ppm (J = 9
Hz). However, in the difluorinated and tetrafluorinated analogues,
compounds 4 and 5, respectively, the same type of protons gave
rise to three doublets at 6.98 ppm (J =9 Hz), 7.52 ppm (J = 8.6 Hz)
and 7.85 ppm (J = 9 Hz) in the former, and two doublets at 7.03
ppm (J = 9 Hz), and 7.79 ppm (J = 9 Hz) in the latter. Similar spec-
tral characteristics in terms of chemical shift values and splitting
patterns as those discussed for compounds 3 and 4 were observed
in the 1H NMR spectra of the alkylated analogues compounds 6
and 7, except for an additional triplet at 3.43 ppm (J = 6.8 Hz)
which could be assigned to the protons attached to the brominated
2
,
2
3
0.26, 29.71-29.00, 28.90, 28.83, 26.30, 26.01, 25.90, 25.46, 22.70,
(
CH ), 14.12 (CH ).
2 3
2
.3. Disc Diffusion Method
The non-fluorinated and fluorinated azo derivatives, 3-7 and the
azo-imidazolium conjugates, 8-12 were examined for their antimi-
crobial activities against five pathogenic microorganisms using the
agar well diffusion method. All the pathogenic bacteria were inoc-
ulated in nutrient broth and incubated at 37°C for 12-14 hours. The
inoculated microbes were spread, and wells were produced on the
nutrient agar. The wells were filled with 100 μL of each sample.
Agar well diffusion agar was used to assess the antibacterial and
antifungal potentials of the synthesized compounds. The tested
pathogenic microorganisms Staphylococcus aureus, Escherichia coli,
Salmonella enterica serovar Typhimurium, Candida albicans and Sac-
charomyces cerevisiae were inoculated into the Brain Heart Infusion
(
BHI) broth and incubated at 37°C for 16 h. The cultures were then
diluted with sterile 0.9 % saline solution to achieve turbidity of 0.5
McFarland standard. The Mueller Hinton agar was then inoculated
by streaking the test microorganisms using a sterile swab over the
entire agar surface. 20 μl of each sample as well as the positive
and negative controls were pipetted respectively onto each ster-
ile paper discs (7 mm) which were placed on the agar and the
plates were incubated at 37°C for for 24 hours. The zone of in-
hibition was measured and recorded after the incubation period.
Samples at concentrations ranging from at 0.5-2.5mg/mL were pre-
pared by dissolving 0.5-2.5mg of each sample in 1 mL of methanol,
except for compounds 7 and 8 which were dissolved in chloro-
form. The positive controls Vancomycin, ampicillin, streptomycin
sulphate and chloramphenicol were prepared at 300 μg/mL. As
positive controls, 300 μg/mL vancomycin was used for Staphylococ-
cus aureus, 300 μg/mL ampicillin for Escherichia coli and Salmonella
enterica serovar Typhimurium and 300 μg/mL streptomycin sul-
phate as well as chloramphenicol was used for Candida albicans
and Saccharomyces cerevisiae, respectively.
carbon, (-CH Br).
2
Due to close structural resemblance, similar splitting patterns
and chemical shift values were observed in the 1H-NMR spectra of
compounds 8-12. The following discussion was based on the spec-
tral data of compound 8 as a representative homologue. Compound
8 showed similar spectral characteristics as those discussed for
compound 6. However, a singlet corresponded to the acidic pro-
ton at C2 at 10.76 ppm, two additional triplets at 4.30 (J = 7.5 Hz),
and 4.38 ppm (J = 7.4 Hz) ascribable to the methylene protons ad-
jacent to the N1 and N3 as well as two singlets at 7.18 ppm and
7.22 ppm attributable to the N-CH of the imidazolium moiety were
observed in compound 8 (see Fig. 3 with peak integration in red).
The formation of the azo-imidazolium conjugates, compounds
3
. Results and Discussion
3
.1. FTIR Spectroscopy
8
-12 was further confirmed using the 13C NMR spectroscopy. Com-
Diagnostic peaks in compounds 3-12 were observed within the
pound 8 contained 43 carbons but only 29 signals were observed
in its 13C NMR spectrum as some of the peaks were overlapped
(Fig. 4). The aromatic carbons of the azobenzene moiety were ob-
served within 162.27 ppm – 114.83 ppm. The acidic carbon, C2 of
the imidazolium ring was seen at 137.19 ppm while that of the
alkenyl carbons were seen at 121.37 ppm and 121.27 ppm. Peaks
at 68.46 ppm and 67.74 ppm could be assigned to the oxymethy-
lene carbons, while the two nitrogenated carbons were observed at
50.36 ppm and 50.16 ppm. Other methylene carbons in the alkyl
chains and spacer were observed within 31.90 ppm-22.67 ppm.
The methyl carbons were observed at 14.14 ppm which was in
good agreement with that reported in the literature [34–36].
expected regions: v (Csp3-H) at 2919 and 2850 cm 1, v (C=C) aro-
−
−
1,
−1
matic within 1583-1604 cm
v (N=N) within 1497-1523 cm
−1
and v (C-O) ether within 1243-1259 cm . The disappearance of
−
1
the N-H peak at 3381 cm
and the appearance of O-H peak as
well as the N=N peak at 3166 cm− and 1497 cm , respectively
indicated the successful formation of the azo derivatives, com-
pounds 3, 4 and 5 (see Fig.1(a)). The formation of compounds 4
1
−1
and 5 was substantiated by the C-F peak at 1021 cm 1, similar
to that reported by Pilati et al. and Gurumurthy et al. [31,32]. On
the other hand, upon alkylation of compounds 3 and 4, the O-H
−
−1
peak at 3166 cm disappeared [33] and the presence of the C-Br
4

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
Fig. 1. FTIR spectra of compounds (a) 3, (b) 6 and (c) 8.
Fig. 2. 1H NMR spectrum of compound 3 (in CDCl3).
3
.3. Antimicrobial Activity
In this study, the potency of these compounds was influenced by
the hydrocarbon chain length in the cationic imidazolium head
group and level of fluorine substitution on the azo moeity. Long
alkyl chains and multiple fluorination are essential in inhibiting
the growth of Gram positive bacterium Staphylococcus aureus. For
azo derivatives, only those with two alkyl chains, compounds 6
The inhibitory effects of azo derivatives and the azo-
imidazolium conjugates showed selective activities against the
tested microorganisms at 1mg/mL are shown in Table 1. The re-
sults were expressed as zones of inhibition as illustrated in Fig. 5.
5

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
Fig. 3. 1H NMR spectrum of compound 8 (in CDCl3).
Fig. 4. 13 C NMR spectrum of compound 8 (in CDCl3).
Table 1
Zones of inhibition diameters (mm) for compounds 3-12 on tested pathogenic Microorganisms.
Zone of Inhibition diameter (mm)
∗
Sample
3
4
5
6
7
8
9
10
11
12
Positive control
Negative control
0.3
Concentration (mg/mL)
Gram-Positive bacterial
Staphylococcus aureus
Gram-Negative Bacteria
Escherichia coli
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.3
NA
NA
11
14
11
NA
NA
NA
10
11
16a
NA
10
10
NA
NA
NA
NA
13
12
14
12
10
10
11
10
10
10
NA
NA
NA
NA
22b
25b
NA
NA
Salmonella
Yeast
Candida albicans
NA
14
20
16
21
21
NA
14
NA
13
NA
17
NA
14
NA
15
NA
15
16
13
17c
24d
NA
NA
Saccharomyces cerevisiae
Note: NA = Not activities; a = vancomycin; b = ampicillin; c = streptomycin sulphate;
d = chlorampenicol
and 7, as well as the tetrafluorinated analogue, compound 5 were
found to be active against this bacteria. On the other hand, the
active azo-imidazolium conjugates, compounds 11 and 12 con-
tained 16 and 18 carbons in the alkyl chain, respectively. It was
reported that antibacterial activity is enhanced by hydrophobic-
ity [37]. Molecules that contain hydrophobic alkyl chains are be-
lieved to disrupt the cell membranes of microorganisms. The ex-
tent of this membrane disruption is affected by chain length.
Longer chains may be incorporated into the lipid bilayers of the
plasma membrane of bacteria [38].
for the azo-imidazolium conjugates, compounds 8-12. Compounds
11 and 12 with long alkyl chains were inactive. Difference in an-
timicrobial behavior of the azo derivatives could be due to the dif-
ferent cell wall between the Gram positive and negative bacteria.
The cell wall of Gram-positive bacteria is simple. It is composed of
large fractions of negatively charged phospotidylglycerol. The at-
traction between the cationic head groups of the azo-imidazolium
conjugates and the negatively charged bacterial membrane and the
integration of the long alkyl chains into the lipid bilayer of the
cell membrane could lead to perturbation of plasma membrane
and induced cell death. On the other hand, the cell wall of Gram
negative bacteria is more complex. It is made up of a cytoplas-
mic membrane and an outer membrane [39]. The latter contains
lipopolysaccharides cross-bridge by divalent cations which stabilize
the membrane, and creates a barrier that prevents the permeation
However, an opposite trend was observed for E. coli and
Salmonella, the two tested Gram negative bacteria in this study.
Fluorination had no effect on the activity against these bacteria.
No activities were observed in compounds 4 and 5. These organ-
isms exhibited a cutoff effect at long alkyl chain length as observed
6

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
Fig. 5. Agar plates showing the growth inhibitory effect of compounds 3, 6, and 12 on selected pathogenic microorganisms at different concentrations: a = 0.5 mg/mL;
b = 1.0 mg/mL; c = 2.5mg/mL.
of lipophilic molecules [38]. Therefore, it could partially prevent
the azo molecules from reaching and inducing the disruption of
the inner plasma membrane, and thus resulting in lower or loss of
antibacterial activities of the these compounds as observed in the
present study.
rinated azo derivatives, compounds 4 and 5 were active against
this fungus. At the same concentration, the antifungal activities of
the fluorinated azo compounds were higher (inhibition zone di-
ameters 20mm and 21mm, respectively) as compared to that of
Streptomycin sulphate, the positive control (inhibition zone diam-
eter 17mm). Among all the azo-imidazolium conjugates, only com-
pound 12 with 18 carbons in the alkyl chain length on the imida-
zolium head group was active. On the other hand, all azo deriva-
tives and azo-imidazolium conjugates were active against Saccha-
romyces cerevisiae with inhibition zone diameters ranging from
Similar to Staphylococcus aureus, the growth inhibition of the
tested fungus Candida albicans and Saccharomyces cerevisiae is in-
fluenced by long alkyl chains and fluorination. Non-fluorinated
and short-chain azo derivatives and azo-imidazolium conjugates,
showed no activities against Candida albicans. However, the fluo-
7

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
1
3mm to 21mm. The tetrafluorinated azobenzene derivative, 5 was
thank the University of Ilorin, Ilorin Nigeria for the TETfund Inter-
vention Sponsorship for staff training and development.
the most potent against both fungi. The plasma membranes of fun-
gal cells are similar to neutral eukaryotic membranes that contain
zwitterionic phospholipids and ergosterol. According to literature,
imidazolium derivatives (azole class) interact directly and damage
the fungal cell membrane. They inhibit fungus growth by altering
the cell membrane structure via inhibition of ergosterol biosynthe-
sis [40,41].
References
[1] P. Klahn, Cannabinoids-Promising Antimicrobial Drugs or Intoxicants with Ben-
efits? Antibiotics 96 (2020) 297 1-27, doi:10.3390/antibiotics9060297.
[2] H. Nikaido, Multidrug efflux pumps of gram-negative bacteria, Journal of bac-
teriology 17820 (1996) 5853, doi:10.1128/jb.178.20.5853-5859.1996.
Fluorination had no effect on the activity against Gram nega-
tive bacteria E. coli and Salmonella (Table 1). However, a clear cor-
relation between the level of fluorine substitution and the antimi-
crobial activity against Staphylococcus aureus, a Gram positive bac-
terium and yeasts was observed. The presence of the highly elec-
tronegative and hydrophobic fluorine atoms enhanced lipophilic-
ity of the azo compounds. Replacing the hydrogen with fluorine
atoms resulted in little steric alterations as both elements are sim-
ilar in size. It facilitated the interactions of fluorinated azo com-
pounds with the receptor sites and the permeation into the fungal
cell membrane [42], which resulted in enhanced antifungal activi-
ties as observed in the present study.
[3] G.C. de Oliveira Santos, C.C. Vasconcelos, A.J. Lopes, M.d.S.de Sousa Cartágenes,
F.R. do Nascimento, R.M. Ramos, E.R. Pires, M.S. de Andrade, F.M. Rocha, C. de
Andrade, Monteiro Candida infections and therapeutic strategies: mechanisms
of action for traditional and alternative agents, Frontiers in microbiology 9
(2018) 1351, doi:10.3389/fmicb.2018.01351.
[4] B.
Sunil,
W.S.
Yam,
G.
Hegde,
Photoresponsive
behavior
of
hydrophilic/hydrophobic-based novel azobenzene mesogens: synthesis,
characterization and their application in optical storage devices, RSC Advances
969 (2019) 40588–40606, doi:10.1039/C9RA08211E.
[5] S. Benkhaya, S. M’rabet, A. El Harfi, Classifications, properties, recent synthesis
and applications of azo dyes, Heliyon 61 (2020) e03271, doi:10.1016/j.heliyon.
2
020.e03271.
[6] M.P.B. Piste, D.P. Indalkar, D.N. Zambare, P.S. Mundada, Synthesis and an-
timicrobial activity of substituted p-amino azobenzene with thymol moiety-a
green protocol, International Journal of Chemistry Research (2012) 25–29.
[
[
[
7] M. Yazdanbakhsh, H. Yousefi, M. Mamaghani, E. Moradi, M. Rassa, H. Pouramir,
M. Bagheri, Synthesis, spectral characterization and antimicrobial activity of
some new azo dyes derived from 4, 6-dihydroxypyrimidine, Journal of Molec-
ular Liquids 169 (2012) 21–26, doi:10.1016/j.molliq.2012.03.003.
8] S. Concilio, P. Iannelli, L. Sessa, R. Olivieri, A. Porta, F. De Santis, R. Pantani,
S. Piotto, Biodegradable antimicrobial films based on poly (lactic acid) matrices
and active azo compounds, Journal of Applied Polymer Science 13233 (2015)
1–8, doi:10.1002/app.42357.
4. Conclusion
Five new non-fluorinated and fluorinated azo derivatives, as
well as a new series containing five azo-imidazolium conjugates
of varying alkyl chain length in the imidazolium moiety were pre-
pared and characterized using FTIR and NMR spectroscopy, and
elemental microanalysis. These compounds were assayed against
pathogenic Gram positive bacterium Staphylococcus aureus and
Gram negative bacteria Escherichia coli, Salmonella enterica serovar
Typhimurium, as well as yeasts Candida albicans and Saccha-
romyces cerevisiae using the disc diffusion method. The azo deriva-
tives and their imidazolium conjugates were selectively active
against the tested microorganisms with zone of inhibition diam-
eters ranging from 10mm-21mm. Their biological efficacy was de-
pendent on the chain length and level of fluorine substitution. It
can be concluded that in the present study, Gram positive bac-
terium preferred the more hydrophobic molecules than their Gram
negative counterparts. Fluorination had no effect on the activity
against Gram negative bacteria. However, a clear correlation was
observed between the level of fluorine substitution and the an-
timicrobial activity against Gram positive bacterium and yeasts.
These azo derivatives and azo-imidazolium conjugates may repre-
sent new alternatives to fabricate selective and effective biocides.
9] S. Piotto, S. Concilio, L. Sessa, P. Iannelli, A. Porta, E.C. Calabrese, M.R. Galdi,
L. Incarnato, Novel antimicrobial polymer films active against bacteria and
fungi, Polymer composites 349 (2013) 1489–1492, doi:10.1002/pc.22410.
[10] S. Piotto, S. Concilio, L. Sessa, A. Porta, E.C. Calabrese, A. Zanfardino, M. Var-
camonti, P. Iannelli, Small azobenzene derivatives active against bacteria and
fungi, European journal of medicinal chemistry 68 (2013) 178–184, doi:10.
1016/j.ejmech.2013.07.030.
[11] L. Sessa, S. Concilio, P. Iannelli, F. De Santis, A. Porta, S. Piotto, Antimicrobial
azobenzene compounds and their potential use in biomaterials, in: AIP Con-
ference Proceedings, AIP Publishing LLC, 2016, doi:10.1063/1.4945973.
[
12] V. Hopsu-Havu, S. Laiho, E. Lundell, A colour test for yeasts based on stain-
ing of the colonies with aromatic diazonium salts, Mycoses 101 (1966) 23–26,
doi:10.1111/j.1439-0507.1966.tb02786.x.
[
13] A.M. Khedr, M. Gaber, E.H. Abd El-Zaher, Synthesis, Structural Characteriza-
tion, and Antimicrobial Activities of Mn (II), Co (II), Ni (II), Cu (II) and Zn (II)
Complexes of Triazole-based Azodyes, Chinese Journal of Chemistry 296 (2011)
1124–1132, doi:10.1002/cjoc.201190211.
[
14] N. Parekh, K. Maheria, P. Patel, M. Rathod, Study on antibacterial activity for
multidrug resistance stain by using phenyl pyrazolones substituted 3-amino
1H-pyrazolon (3, 4-b) quinoline derivative in vitro condition, Int. J. Pharm Tech
Res 3 (2011) 540–548.
15] K.G. Samper, S.C. Marker, P. Bayón, S.N. MacMillan, I. Keresztes, Ò. Palacios,
J.J. Wilson, Anticancer activity of hydroxy-and sulfonamide-azobenzene plat-
inum (II) complexes in cisplatin-resistant ovarian cancer cells, Journal of inor-
ganic biochemistry 174 (2017) 102–110, doi:10.1016/j.jinorgbio.2017.06.003.
[
Authors Contribution
[16] P. Verwilst, J. Han, J. Lee, S. Mun, H.-G. Kang, J.S. Kim, Reconsidering azoben-
zene as component of small-molecule hypoxia-mediated cancer drugs:
theranostic case study, Biomaterials 115 (2017) 104–114, doi:10.1016/j.
a
A
Please indicate the specific contributions made by each author
biomaterials.2016.11.023.
(
list the authors’ initials followed by their surnames, e.g., Y.L. Che-
[17] H. Takahashi, T. Ishioka, Y. Koiso, M. SODEOKA, Y. HASHIMOTO, Anti-
androgenic activity of substituted azo-and azoxy-benzene derivatives, Biolog-
ical and Pharmaceutical Bulletin 2311 (2000) 1387–1390, doi:10.1248/bpb.23.
ung). The name of each author must appear at least once in each
of the three categories below.
1
387.
[18] H. Garg, C. Prakash, Potential antidiabetics. 11. Preparation of 4-arylazo-3,
-disubstituted-(2H)-1, 2, 6-thiadiazine 1, 1-dioxides, Journal of medicinal
Conception and design of study: W.S. Yam acquisition of data:
H.F. Babamale, S. Thiagarajan analysis and/or interpretation of data:
W.S. Yam, J.S. Tan
5
chemistry 154 (1972) 435–436.
[
19] J. Salta, R.I. Benhamou, I.M. Herzog, M. Fridman, Tuning the Effects of Bacterial
Membrane Permeability through Photo-Isomerization of Antimicrobial Cationic
Amphiphiles, Chemistry–A European Journal 2352 (2017) 12724–12728, doi:10.
Drafting the manuscript: W.S. Yam, H.F. Babamale, J.S. Tan, S.
Thiagarajan revising the manuscript critically for important intel-
lectual content: W.S. Yam
1002/chem.201703010.
[
20] D.J. Warner, K.S. Keane, C.J. Saint-Louis, S.C. Blackstock, in: Bridged Azoben-
zenes and Their Biological Applications, PATAI’S Chemistry of Functional
Groups, 2009, pp. 1–35, doi:10.1002/9780470682531.pat0982.
Declaration of Competing Interest
[
21] O. Sadovski, A.A. Beharry, F. Zhang, G.A. Woolley, Spectral tuning of azoben-
zene photoswitches for biological applications, Angewandte Chemie Interna-
tional Edition 488 (2009) 1484–1486, doi:10.1002/anie.200805013.
None.
[
22] S. Samanta, A.A. Beharry, O. Sadovski, T.M. McCormick, A. Babalhavaeji,
V. Tropepe, G.A. Woolley, Photoswitching azo compounds in vivo with red
light, Journal of the American Chemical Society 13526 (2013) 9777–9784,
doi:10.1021/ja402220t.
Acknowledgements
The authors wish to thank the Universiti Sains Malaysia for
the research facilities and financial support through the RUI re-
search grant 1001/PKIMIA/8011094 and Babamale H.F wishes to
[
23] M. Dong, A. Babalhavaeji, S. Samanta, A.A. Beharry, G.A. Woolley, Red-shifting
azobenzene photoswitches for in vivo use, Accounts of chemical research 4810
(2015) 2662–2670, doi:10.1021/acs.accounts.5b00270.
8

H.F. Babamale, T. Sangeetha, J.S. Tan et al.
Journal of Molecular Structure 1232 (2021) 130049
[
24] A. Abbaszad Rafi, N. Hamidi, A. Bashir-Hashemi, M. Mahkam, Photo-Switchable
Nanomechanical Systems Comprising a Nanocontainer (Montmorillonite) and
Light-Driven Molecular Jack (Azobenzene-Imidazolium Ionic Liquids) as Drug
Delivery Systems; Synthesis, Characterization, and in Vitro Release Stud-
ies, ACS Biomaterials Science & Engineering 41 (2018) 184–192, doi:10.1021/
acsbiomaterials.7b00621.
[33] E. Madiahlagan, B. Sunil, Z. Ngaini, G. Hegde, Synthesis, liquid crystalline
properties and photo switching properties of coumarin-azo bearing aliphatic
chains: Application in optical storage devices, Journal of Molecular Liquids 292
(2019) 111328, doi:10.1016/j.molliq.2019.111328.
[34] K. Stappert, J. Muthmann, E.T. Spielberg, A.-V. Mudring, Azobenzene-based or-
ganic salts with ionic liquid and liquid crystalline properties, Crystal Growth &
Design 159 (2015) 4701–4712, doi:10.1021/acs.cgd.5b01024.
[35] Q. Zhang, C. Shan, X. Wang, L. Chen, L. Niu, B. Chen, New ionic liquid crys-
tals based on azobenzene moiety with two symmetric imidazolium ion group
substituents, Liquid Crystals 3511 (2008) 1299–1305.
[
25] A. Franche, A. Fayeulle, L. Lins, M. Billamboz, I. Pezron, M. Deleu, E. Léonard,
Amphiphilic azobenzenes: Antibacterial activities and biophysical investigation
of their interaction with bacterial membrane lipids, Bioorganic Chemistry 94
(
2020) 103399, doi:10.1016/j.bioorg.2019.103399.
[
26] S.N. Riduan, Y. Zhang, Imidazolium salts and their polymeric materials for bio-
logical applications, Chemical Society Reviews 4223 (2013) 9055–9070, doi:10.
[36] Q. Zhang, L. Jiao, C. Shan, P. Hou, B. Chen, X. Xu, L. Niu, Synthesis and
characterisation of novel imidazolium-based ionic liquid crystals with ap-
nitroazobenzene moiety, Liquid Crystals 356 (2008) 765–772, doi:10.1080/
02678290802130264.
[37] Z. Zheng, Q. Xu, J. Guo, J. Qin, H. Mao, B. Wang, F. Yan, Structure–antibacterial
activity relationships of imidazolium-type ionic liquid monomers, poly (ionic
liquids) and poly (ionic liquid) membranes: effect of alkyl chain length and
cations, ACS Applied Materials & Interfaces 820 (2016) 12684–12692, doi:10.
1021/acsami.6b03391.
1039/C3CS60169B.
[
27] R.T. Huang, K. Peng, H. Shih, G. Lin, T. Chang, S. Hsu, T.S. Hsu, I.J. Lin, Antimi-
crobial properties of ethoxyether-functionalized imidazolium salts, Soft Matter
718 (2011) 8392–8400, doi:10.1039/C1SM05759F.
[
28] D. Demberelnyamba, K.-S. Kim, S. Choi, S.-Y. Park, H. Lee, C.-J. Kim, I.-D. Yoo,
Synthesis and antimicrobial properties of imidazolium and pyrrolidinonium
salts, Bioorganic & medicinal chemistry 125 (2004) 853–857, doi:10.1016/j.bmc.
2
004.01.003.
[38] C.R. Birnie, D. Malamud, R.L. Schnaare, Antimicrobial evaluation of N-alkyl be-
taines and N-alkyl-N, N-dimethylamine oxides with variations in chain length,
Antimicrobial agents and chemotherapy 449 (2000) 2514–2517, doi:10.1128/
AAC.44.9.2514-2517.2000.
[
29] P. Yadav, K. Lal, L. Kumar, A. Kumar, A. Kumar, A.K. Paul, R. Kumar, Synthesis,
crystal structure and antimicrobial potential of some fluorinated chalcone-1,
2
, 3-triazole conjugates, European Journal of Medicinal Chemistry 155 (2018)
63–274, doi:10.1016/j.ejmech.2018.05.055.
2
[39] N. Malanovic, K. Lohner, Gram-positive bacterial cell envelopes: The impact
on the activity of antimicrobial peptides, Biochimica et Biophysica Acta (BBA)-
Biomembranes 18585 (2016) 936–946, doi:10.1016/j.bbamem.2015.11.004.
[40] S. Slassi, A. Fix-Tailler, G. Larcher, A. Amine, A. El-Ghayoury, Imidazole and azo-
based schiff bases ligands as highly active antifungal and antioxidant compo-
nents, Heteroatom Chemistry (2019) 2019, doi:10.1155/2019/6862170.
[41] H.-L. Cheah, V. Lim, D. Sandai, Inhibitors of the glyoxylate cycle enzyme ICL1
in Candida albicans for potential use as antifungal agents, PloS one 94 (2014)
e95951, doi:10.1371/journal.pone.0095951.
[
30] A.A. Mahmood, M.A. Al-Iraqi, F.T. Abachi, Fluorine important element in new
drugs synthesis: Review Study, Iraqi Journal of Pharmacy 151 (2018) 37–
4
5.
[
31] M. Saccone, G. Terraneo, T. Pilati, G. Cavallo, A. Priimagi, P. Metrangolo,
G. Resnati, Azobenzene-based difunctional halogen-bond donor: towards the
engineering of photoresponsive co-crystals, Acta Crystallographica Section B:
Structural Science, Crystal Engineering and Materials 701 (2014) 149–156,
doi:10.1107/S205252061302622X.
[
32] S. Gan, A. Yuvaraj, M. Lutfor, M. Mashitah, H. Gurumurthy, Synthesis, liquid
crystal characterization and photo-switching studies on fluorine substituted
azobenzene based esters, RSC Advances, 59 (2015) 6279–6285, doi:10.1039/
C4RA13700K.
[42] D. Giménez, C. Andreu, T. Varea, D. Diaz, G. Asensio, The introduction of fluo-
rine atoms or trifluoromethyl groups in short cationic peptides enhances their
antimicrobial activity, Bioorganic & medicinal chemistry 1420 (2006) 6971–
6978, doi:10.1016/j.bmc.2006.06.027.
9