Microwave assisted one-pot synthesis, photophysical and physicochemical studies of novel biologically active heterocyclic Donor (D)-π-Acceptor (A) chromophore

Article abstract of DOI:10.1016/j.bioorg.2021.104964

A donor-π-acceptor (D-π-A) chromophore, 2-amino-4-(9-ethyl-9H-carbazol-3-yl)-8-methoxy-5,6-dihydrobenzo[h]quinoline-3-carbonitrile (AEDQ) was synthesized from the condensation of 6-methoxy-3,4-dihydronaphthalen-1(2H)-one, 9-ethyl-9H-carbazole-3-carbaldehyde, malononitrile and NH₄OAc in ethanol. Spectroscopic techniques and elemental analysis were employed to establish the structure of AEDQ. Photophysical parameters and fluorescence quantum yield were calculated in the different polarity solvents to evaluate the interactions of the solvent with AEDQ chromophore. Further, the interaction of the AEDQ with cationic and anionic surfactants (CTAB, SDS) were also evaluated by using fluorescence spectroscopy techniques. The intensity of the fluorescence spectrum increased as the concentration of surfactants increased, suggesting that strong interaction occurs between AEDQ with surfactants, and this interaction arises from electrostatic forces. As a result, the AEDQ chromophore could be used to determine the CMC of surfactants. The disc diffusion and minimal inhibitory concentration (MIC) technique were used to test in-vitro antibacterial activity against Gram +ve and Gram ?ve bacteria, and the results are compared with the standard drug, tetracycline. AEDQ also showed good ADMET, pharmacokinetics and drug-likeness properties, which are desirable for a good drug candidate. The molecule also fits well in the DNA gyrase A active pocket site with the binding free energy of ?17.92 kcal/mol, which testifies its good antibacterial activity.

Full text of DOI:10.1016/j.bioorg.2021.104964

Bioorganic Chemistry 112 (2021) 104964
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Microwave assisted one-pot synthesis, photophysical and physicochemical
studies of novel biologically active heterocyclic Donor (D)-
π
-Acceptor
(
A) chromophore
a
,
*
a
a
a
b
Salman A. Khan , Qasim Ullah , Salahuddin Syed , Alimuddin , Abdulraheem S.A. Almalki ,
c,
*
d
d
e
f
Sanjay Kumar , Rami J. Obaid , Meshari A. Alsharif , S.Y. Alfaifi , Humaira Parveen
a
Physical Section, School of Sciences, Maulana Azad National Urdu University (MANUU), Hyderabad 500032, Telangana, India
b
Department of Chemistry, Faculty of Science, Taif University, Taif 210974, Saudi Arabia
c
Department of Chemistry, Multani Mal Modi College Patiala 147001, Punjab, India
d
Chemistry Department, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia
e
Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
f
Department of Chemistry, Faulty of Science, University of Tabuk, Tabuk, Saudi Arabia
A R T I C L E I N F O
A B S T R A C T
A donor- -acceptor (D-
Keywords:
π
π
-A) chromophore, 2-amino-4-(9-ethyl-9H-carbazol-3-yl)-8-methoxy-5,6-dihydrobenzo[h]
One-pot
quinoline-3-carbonitrile (AEDQ) was synthesized from the condensation of 6-methoxy-3,4-dihydronaphthalen-1
2H)-one, 9-ethyl-9H-carbazole-3-carbaldehyde, malononitrile and NH OAc in ethanol. Spectroscopic techniques
Quinoline
(
4
Stokes shift
Antibacterial
Molecular docking
and elemental analysis were employed to establish the structure of AEDQ. Photophysical parameters and fluo-
rescence quantum yield were calculated in the different polarity solvents to evaluate the interactions of the
solvent with AEDQ chromophore. Further, the interaction of the AEDQ with cationic and anionic surfactants
(
CTAB, SDS) were also evaluated by using fluorescence spectroscopy techniques. The intensity of the fluores-
cence spectrum increased as the concentration of surfactants increased, suggesting that strong interaction occurs
between AEDQ with surfactants, and this interaction arises from electrostatic forces. As a result, the AEDQ
chromophore could be used to determine the CMC of surfactants. The disc diffusion and minimal inhibitory
concentration (MIC) technique were used to test in-vitro antibacterial activity against Gram +ve and Gram ꢀ ve
bacteria, and the results are compared with the standard drug, tetracycline. AEDQ also showed good ADMET,
pharmacokinetics and drug-likeness properties, which are desirable for a good drug candidate. The molecule also
fits well in the DNA gyrase A active pocket site with the binding free energy of ꢀ 17.92 kcal/mol, which testifies
its good antibacterial activity.
1
. Introduction
ICT characteristics are dependent on the band gap of molecules [3]. Due
to these photophysical properties, the donor- -acceptor chromophores
π
Organic compounds with electron-donating (OCH
3
, N-CH
3
, OH) and
found applications in the field of material science like OLEDs, laser dye,
optical or electro-optical devices, sensor materials and dye-sensitized
solar cell etc. [4]. Therefore, to obtain excellent photophysocal prop-
erties, approaches such as enhanced donor to acceptor intramolecular
charge transfer and insertion of suitable substituents on the conjugated
chain of the chromophores have been used [5].
electron-withdrawing (CN, NO
2
, C=O) groups are known as donor-
π
-acceptor (D- -A) chromophores, usually displaying charge split-up
π
from donor to acceptor upon photoexcitation and the phenomenon is
known as intramolecular charge transfer (ICT) [1]. The electron
donating and withdrawing groups are localized in separate parts of the
molecule leading to charge transfer and is responsible for their photo-
physical properties [2]. The photophysical properties (viz. Stokes shift,
molar extinction coefficients, oscillator strength, transition dipole mo-
ments), fluorescence lifetime, fluorescence quantum yield and especially
N-Alkyl carbazole, a polycyclic nitrogen-containing heterocyclic ar-
omatic compound, exhibits an extensive -bond conjugated system and
π
broad application profile in the field of organic, electrical, and optical
materials [6]. When linked with an acceptor group, the N-alkyl
*
Corresponding authors.
E-mail addresses: sahmad_phd@yahoo.co.in (S.A. Khan), sanjay2002@gmail.com (S. Kumar).
https://doi.org/10.1016/j.bioorg.2021.104964
Received 17 August 2020; Received in revised form 27 March 2021; Accepted 3 May 2021
Available online 5 May 2021
0
045-2068/© 2021 Elsevier Inc. All rights reserved.

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
Scheme 1. Synthesis of 9-ethyl carbazole-3-carboxaldehyde.
substituted carbazole framework generates an excellent donor-
-acceptor chromophore [7]. Recently, quinoline derivatives with
CH Aromatic, J = 6.8 Hz), 7.63 (dd, 1H, CH Aromatic, J = 5.6, 4.2 Hz),
7.53 (dd, 1H, CH Aromatic, J = 3.4, 4.2 Hz), 7.48 (s, 1H, CH Aromatic),
7.32 (d, 1H, CH Aromatic, J = 7.4 Hz), 7.26 (s, 1H, CH Aromatic), 7.09
(d, 1H, CH Aromatic, J = 7.6 Hz), 6.96 (d, 1H, CH Aromatic, J = 7.4 Hz),
π
excellent photophysical properties, like blue emission and good fluo-
rescence quantum yield, have been reported [8]. Quinoline derivatives
are of continued interest for synthetic organic chemistry as well as
medicinal chemistry [9]. Polysubstituted quinolines are significant
heterocyclic compounds due to their diverse biological activities like
anti-cancer [10], antibacterial [11], anti-HIV [12], antimalarial and
anti-inflammatory [13]. In addition, quinoline derivatives have also
been used in the electronic and optoelectronic field because of their
attractive electrical, optical and mechanical properties [14]. Therefore,
5
.12 (s, 2H, NH
2
), 4.06 (q, 2H, N-CH
), 2.79–2.74 (m, 2H, CH ), 2.68–2.61 (m, 2H, –CH
) δ: 161.43, 158.93,
2
-CH
3
, J = 6.8 Hz), 3.66 (s, 3H, O-
CH
CH
3
3
2
2
), 1.21 (t, 3H,
13
-CH
2
-N, J = 6.2 Hz); C NMR (125 MHz, CDCl
3
1
1
57.20, 154.29, 153.56, 151.24, 149.12, 145.87, 142.92, 128.63,
25.12, 124.96, 123.21, 121.98, 119.34, 116.54, 114.12, 112.96 56.12
(
O-CH
3
), 38.56 (CH
3
-CH
2
2 2 3
-N), 28.28 (CH ), 25.96 (CH ), 16.21 (CH -
CH
2
-N); Anal. Calc. for C29 H N
24 4
O: C, 78.36, H, 5.94, N, 12.60, Found:
we have developed a novel heterocyclic donor- -acceptor chromophore
π
C, 78.31, H, 65.89, N, 12.56.
with promising photophysical characteristics and biological profile with
the integration of the carbazole and quinolines units.
2
2
.4. Antibacterial activity of the heterocyclic chalcone
2
. Experimental
.4.1. Media and strains
The synthesized compound was tested with bacterial strains (Gram-
2
.1. Chemicals and reagents
positive and Gram-negative), namely Staphylococcus aureus (FNCC
047), Bacillus substilis (FNCC 0041), Eschericia coli (FNCC 0091) and
0
Chemical reagents and solvents were obtained from commercial
Shigella flexnerri (ATCC 12022). Nutrient medium (Peptone 5 g/L; beef
sources (Sigma-Aldrich/Merck) and were used as such. For UV–visible
absorption spectra, and fluorescence spectra measurements, HPLC grade
solvents were used. Carbazole-3-carbaldehyde was prepared (Scheme 1)
according to the reported procedure [15].
◦
extract 3 g/L; pH = 7.0) and incubation time 24 h at 37 C was used to
subculture the bacteria.
2
.4.2. Disc-diffusion evaluation
Disc-diffusion technique was applied to evaluate the antibacterial
2
.2. Instrumentation
activity of newly synthesized heterocyclic quinoline-3-carbonitrile
AEDQ). The method was performed as described earlier with insignif-
(
Reaction progress was monitored using pre-coated aluminium sheets
icant alteration [17].
(
Silica gel 60F254) for TLC from Merck. Melting point (m.p.) of the
Briefly, the entire bacterial cells were developed in BHI medium for
◦
5
synthesized compounds was measured in open capillary tubes using
Stuart scientific apparatus. Perkin-Elmer 100FT-IR spectrophotometer
the period of 24 h at 37 C. After incubation, about 10 CFU/ml bacterial
◦
load were inoculated on sterile nutrient agar at 40 C in laminar flow
1
was used to obtain the FTIR spectrum while HNMR (600 MHz) and
hood. On these nutrient agar plates with bacterial strains, paper discs
1
3
CNMR (125 MHz) spectrum of the heterocyclic quinoline-3-
carbonitrile (AEDQ) was recorded in CDCl on Bruker spectrometer.
(diameter = 6.0 mm) treated with 10, 20, 25, 50, 100
μ
g/mL solution of
3
heterocyclic quinoline-3-carbonitrile (AEDQ) in DMSO were applied.
Elementar Analysensysteme GmbH VarioEL elemental analyzer was
employed for the elemental analysis of quinoline-3-carbonitrile. Shi-
madzu UV-16550PC UV–Visible and RF-5301PC was employed to get
the UV–visible and fluorescence spectra of quinoline-3-carbonitrile
DMSO as negative control and tetracycline (30
antibiotic drug was used.
μ
g/mL) as reference
The efficacy of different concentration of heterocyclic quinoline-3-
carbonitrile (AEDQ) on the bacteria was evaluated with the zone of in-
◦
(
AEDQ), respectively.
hibition after incubation period of 24 h at 37 C.
2
.3. Synthesis of 2-Amino-4-(9-ethyl-9H-carbazol-3-yl)-8-methoxy-5,6-
2.4.3. Antibacterial activity by MIC assay
dihydrobenzo[h]quinoline-3-carbonitrile (AEDQ)
Minimum Inhibitory concentration (MIC) was also determined to
evaluate antibacterial efficiecy of the quinoline-3-carbonitrile (AEDQ)
by broth dilution assay. Heterocyclic quinoline-3-carbonitrile (AEDQ)
was dissolved in DMSO, and different concentration (512, 256, 128, 64,
AEDQ was synthesized by the condensation of 6-methoxy-3,4-dihy-
dronaphthalen-1(2H)-one (5.67 mmol, 1.0 g), 9-ethyl-3-carbazole-
carboxaldehyde (5.67 mmol, 1.26 g), malononitrile (5.67 mmol, 0.36 g),
32, 16, 8, 4, 2 and 1 g/mL) of the compound were prepared from the
μ
and NH
normal microwave oven (at 210 W, MW power) for 7 min. TLC (Silica gel
0F254) was used to monitor the progress of the reaction. After com-
4
OAc (5.67 mmol, 2.58 g), in absolute alcohol was heated in
stock solution by serial dilution. These serial dilutions of the heterocy-
clic quinoline-3-carbonitrile (AEDQ) were added in each test tube with
1 mL of bacterial cultures (approximately 105 CFU/ mL) standard
inoculant. The MIC of the heterocyclic quinoline-3-carbonitrile (AEDQ),
6
plete consumption of reactants, ice-water was added to the mixture,
filtered the solid thus obtained, and recrystallized from ethanol [16].
◦
was evaluated after incubation at 37 C for 24 h. DMSO and Tetracycline
ꢀ
1
Orange crystals, %yield: 87.50%; FT-IR (
ν
, cm ): 3432 (NH
2
), 3092
was used as negative and positive controls [18].
(
C-H stretching), 2932 (C-H stretching), 1561 (C = C aromatic stretch-
–
1
ing), 1253 (C
–
N), H NMR (600 MHz CDCl
3
) δ:8.09 (d, 1H, CH Aro-
matic, J = 7.2 Hz), 7.89 (d, 1H, CH Aromatic, J = 8.4 Hz), 7.71 (d, 1H,
2

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
Scheme 2. Synthesis of quinoline derivative ((AEDQ).
Scheme 3. Tentative mechanism of the formation of heterocyclic quinoline-3-carbonitrile (AEDQ).
maximum of ten conformers were considered during docking process.
2
.5. Docking studies
The images were visualized using PyMoL.
3. Result and discussions
3.1. Chemistry
The heterocyclic quinoline-3-carbonitrile (AEDQ) 2D structure was
drawn with ChemDraw Ultra 16.0. Total drug score was predicted with
OSIRIS (ADMET based Java library layer) and energy minimization of
the molecules is done on Dundee PRODRG2 server [19,20]. The opti-
mized structure was used as input for docking simulation in Auto-
Dock4.2 to find the appropriate protein binding site [21]. Finally
optimized structures were saved in pdbqt format. For a compound
Heterocyclic quinoline-3-carbonitrile (AEDQ) has been prepared by
the reaction of 9-ethyl-3-carbazolecarboxaldehyde, 6-methoxy-1-
3

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
Table 1
Physicochemical parameters and fluorescence quantum yield of AEDQ in different solvents.
N
T
ꢀ 1
ꢀ 1
ꢀ 1
Δv (cmꢀ 1)
Solvent
Δf
E
E
T
(30Kcal mol
λ
ab(nm)
λ
em(nm)
ε
M
cm
f
μ
12 Debye
Φ
f
st
DMSO
DMF
0.263
0.274
0.305
0.308
0.217
0.255
0.274
0.148
0.0014
0.441
0.404
0.654
0.762
0.259
0.472
0.164
0.210
0.0002
45.1
43.8
51.9
55.4
39.1
41.1
45.6
36.0
31.1
380
379
376
377
375
374
373
372
369
418
416
420
421
410
409
407
405
400
26,890
24,182
19,210
20,150
19,890
19,820
20,180
20,820
18,000
0.26
0.23
0.21
0.22
0.18
0.18
0.18
0.18
0.15
4.47
4.29
4.12
4.22
3.79
3.77
3.71
3.76
3.43
2392
2347
2786
2773
2276
2288
2239
2190
2100
0.62
0.60
0.47
0.24
0.68
0.64
0.69
0.53
0.22
EtOH
MeOH
CHCl
3
CH
CH
2
Cl
CN
2
3
Dioxane
n-Hexane
9
7
6
4
3
1
00
78
50
00
50
00
50
0
7
6
DMSO
DMF
EtOH
MeOH
74
CHCl
3
E
E
a
f
CH Cl
2
2
7
7
6
2
0
8
CH CN
3
Dioxane
n-Hexane
4
00
450
500
550
600
3
0
35
40
45
50
55
Wavelength (nm)
-1
Fig. 1. Emission spectra of AEDQ (1 × 10ꢀ 5 M).
E (30) kcal mol
T
Fig. 2. Plot of absorption energy (E
a f T
) and emission energy (E ) versus E (30)
4
tetralone, malononitrile and NH OAc in absolute alcohol upon irradia-
for AEDQ.
tion in domestic microwave oven (Scheme 2). The tentative mechanism
for the synthesis of heterocyclic quinoline-3-carbonitrile has been
depicted in Scheme 3. Firstly, Knoevenagel condensation between
carbazole aldehyde and malononitrile produced intermediate A that
upon addition of 3-methoxy-1-tetralone generate B. Addition of
ammonia from ammonium acetate to B and loss of a water molecule led
to the formation of C, which upon autooxidation produce final product,
AEDQ. The structure of AEDQ was established using spectral analysis.
displayed a broad, intense absorption band with a red shift (11 nm) with
the increase in solvent polarity from n-hexane (369 nm) to DMSO (380
nm) (Table 1). This shift may be accredited to intermolecular charge
transfer (ICT) for the transition due to the electron-donating (N-CH
2
-
CH ) group [22]. Solvent polarity also affected the molar absorption
3
coefficients, see Table 1. Upon excitation at 375 nm, emission spectra of
AEDQ also exhibited red shift (ca. 18 nm) with a change in solvent
polarity from hexane (400 nm) to DMSO (418 nm) (Fig. 1). Photoin-
duced intramolecular charge transfer (PICT) from N-alkyl carbazole in
the excited state may be attributed to the red shift [23]. In the alcoholic
solvent like MeOH and EtOH, the intermolecular hydrogen bonding of
AEDQ with alcoholic solvent may also be contributing to the red shift.
ꢀ
1
ꢀ 1
The absorption band at 3432 cm and 1253 cm in the IR spectrum,
due to amino (NH
2
) and conjugated C=N group, respectively. The
ꢀ 1
carbonyl absorption at 1655 cm of 6-methoxy-1-tetralone of reactant
also disappeared in the product indicating the formation of AEDQ
molecule. The 1H NMR spectra in CDCl
3
of the AEDQ displayed well-
determining signals. The characteristic peak for NH as a singlet at
.12 ppm, indicating the formation of AEDQ. Ten aromatic protons of
2
The correlation of absorption (E
quinoline-3-carbonitrile (AEDQ) in various solvents with Dimroth
empirical polarity parameters E (30) of corresponding solvents [24] is
depicted in Fig. 2, and a direct correlation (Eqs. (1) and (2)) between
energies (E and E ) and E (30) is obtained.
a f
) and emission energy (E ) of the
5
the AEDQ appered in the range δ8.09-6.96 ppm and two multiplets at
δ2.79–2.74 ppm and δ2.68–2.61 ppm for benzyl protons (C5-H and C6-H
correspondingly. Furthermore, the configuration of the heterocyclic was
auxiliary obeyed by 13C NMR spectrum, which exhibited usual signals of
T
a
f
T
the carbon atoms in the aromatic rings and showed two signals at
E
a
= 76.33 ꢀ 0.010 × E
T
(30)
(1)
(2)
1
3
δ28.28 ppm and δ25.92 ppm for the benzyl carbons. The details of
C
NMR spectrum of the AEDQ have been given in the experimental
E = 66.95 ꢀ 0.072 × E (30)
f
T
section.
3
.3. Determination of transition dipole-moments and stokes shift
The solvent polarity strongly affected the physicochemical parame-
3
.2. Physicochemical properties of the AEDQ
The heterocyclic quinoline-3-carbonitrile (AEDQ) absorption spectra
ters (viz. Stokes shift, oscillator strength, transition dipole moments) of
were recorded in solvents of varying polarity, i.e. MeOH. EtOH, DMSO,
DMF, CHCl , CH Cl , CH CN, THF, 1,4 dioxane, and n-hexane. The
absorption spectra of the heterocyclic quinoline-3-carbonitrile (AEDQ)
heterocyclic quinoline-3-carbonitrile (AEDQ). The change in diploe-
3
2
2
3
moments of excited state and ground state (Δ
μ
=
μ
e
–μ
g
) of the hetero-
cyclic quinoline-3-carbonitrile (AEDQ) in different solvents were
4

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
2
2
2
2
2
2
2
400
350
300
250
200
150
100
0
0
0
.7
.6
.5
0.4
0.3
0
.2
3
0
35
40
45
50
55
-1
E (30) Kcal mol
T
0
.00 0.05 0.10 0.15 0.20 0.25 0.30
Fig. 4. Plot of Φ
f T
versus E (30) of AEDQ in the solvents of different polarity.
f
Equation (7) is used to calculate the oscillator strength of heterocy-
Fig. 3. Plot of Δf versus Stoke’s shift.
clic quinoline-3-carbonitrile (AEDQ) in the solvents [29].
∫
determined [25].
f = 4.32 × 10ꢀ 9
ε
(v)dv
(7)
Physicochemical parameters of the heterocyclic quinoline-3-
carbonitrile (AEDQ) in the solvents were calculated using Lippert-
Mataga equation [26].
is wavenumber (in cm 1) and
ꢀ
ε
is molar absorption coefficient
where,
υ
(
M
1cm ).
ꢀ ꢀ 1
2
2Δμ
hca
From the values of oscillator strength (f) of the heterocyclic
Δvst = vabs ꢀ vem
=
Δf + Const.
(3)
3
quinoline-3-carbonitrile (AEDQ) in various solvents (Table 1), it was
inferred that oscillator strength (f) directly relates to solvent polarity.
where (Δvst) is the Stokes shift; the Stokes shift vary with the solvent
polarity, representing the effect of polarity on the excited state, a is
cavity radius, c and h are velocity of light and the Plank’s constant,
respectively. Δf is solvent orientation polarizability and is calculated by
the following equation (4)
3
.4. Fluorescence quantum yields of the AEDQ
The fluorescence quantum yield (Φ
f
) of quinoline-3-carbonitrile
(
AEDQ) was determined with the comparative method (standard refer-
Δf = ε
ꢀ 1
+ 1
η2 ꢀ 1
ence, Quinine Sulphate Φ
r
= 0.55 in 0.1 M H SO
2 4
) using the following
(8)
ꢀ
(4)
2
equation (8). [30]
2ε
2η
+ 1
2
I × A
r
r
×
η
where
ε
is molar absorption coefficient, and
η
is refractive index of the
f
Φ = Φ
2
I
r
× A × η
r
respective solvent.
The dependability of the Stokes shift (Δvst) on polarizability is
where Φ
tensity and absorbance of the reference (Quinine Sulphate), respec-
tively. Similarly, Φ , I, and A is fluorescence quantum yield, fluorescence
intensity and absorbance of the heterocyclic quinoline-3-carbonitrile
AEDQ), respectively, and is refractive index of the solvent.
The solvent polarity also affected the emission spectra of heterocyclic
azomethine AEDQ, as shown by variations in Φ values (Table 1). The
effect seems to be due to polarizability and hydrogen bonding with the
versus E (30) shows
r r r
, I and A is the fluorescence quantum yield, fluorescence in-
indicated by its linear correlation (Fig. 3) with orientation polarizability
(
Δf) [27].
The dipole moment of ground and excited state of heterocyclic
f
quinoline-3-carbonitrile (AEDQ) was calculated using Lippert-Matga
equation (3), where cavity radius (a) of the heterocyclic quinoline-3-
carbonitrile (AEDQ) was determined using equation (5) [28].
(
η
f
(
)
1/3
3
M
4Nπd
a =
(5)
electron donor and acceptor groups. The plot of Φ
f
T
that as the solvent polarity increased, the fluorescence quantum yield
increased (Fig. 4) [31]. However, in highly polar solvents (viz. methanol
and ethanol), the positive solvatokinetic effect negatively impacts the
where N is Avogadro’s constant, d is density and M is molecular mass of
heterocyclic quinoline-3-carbonitrile (AEDQ). The dipole moment of
AEDQ found to be 4.32D as determined from the slope of Stokes shift
plot with polarizability (Fig. 3). The value indicated the strong inter-
action of AEDQ molecules with adjoining medium to cause solvent
reformation due to photoinduced ICT and dipole creation.
Φ
f
, compared to less polar solvents. The interaction between AEDQ and
solvent increases as the polarity of the solvent increases, but in proton
donor solvents, hydrogen bonding interactions between the solvent and
AEDQ molecule result in a decrease in fluorescence quantum yield (Φ
f
)
The values of the transition dipole moments of the heterocyclic
quinoline-3-carbonitrile (AEDQ) in different solvents (Table 1), calcu-
lated using equation (6), indicated that dipole-moments increases with
an increase in solvent polarity.
[32].
3.5. Effect of the surfactants on the emission spectrum of AEDQ
Cationic surfactant (CTAB, cetyl trimethylammonium bromide) and
anionic surfactant (SDS, sodium dodecylsulphate) were used to probe
their effect on the emission spectrum of AEDQ. To evaluate the in-
teractions, the emission spectra of AEDQ were oabtained in the absence
of surfactants and at the varying concentrations of surfactants (for
CTAB, 2.0 × 10ꢀ to 1.8 × 10ꢀ 3 M and for SDS, 2.0 × 10ꢀ 3 to 1.8 × 10ꢀ 2
f
μ2
=
(6)
4
.72 × 10ꢀ 7Emax
where, Emax is energy of absorption maximum and f is oscillator
strength.
4
5

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
1
25
00
130
1
1
1
20
10
00
CMC
1
75
50
25
9
8
7
6
5
0
0
0
0
0
0
40
3
50
400
450
500
550
600
0.0000 0.0004 0.0008 0.0012 0.0016 0.0020
-3
A
[
CTAB] mol dm
Fig. 5. Emission spectra of AEDQ (1 × 10ꢀ 5 M mol dm ) with different
ꢀ 3
f
Fig. 7. Plot of I versus CTAB concentration.
concentration of CTAB, (with increasing emission intensity, the concentration
of CTAB is 0.0, 2.0 × 10 , 4.0 × 10 , 6.0 × 10ꢀ 4, 8.0 × 10ꢀ 4, 1.0 × 10ꢀ 3, 1.2
ꢀ 4
ꢀ 4
ꢀ 3
ꢀ 3
ꢀ 3
ꢀ 3
×
10 , 1.4 × 10 , 1.6 × 10 , 1.8 × 10 M).
1
1
10
00
1
05
9
7
6
4
3
1
0
5
0
5
0
5
9
8
7
6
5
0
0
0
0
0
0
.000
0.004
0.008
0.012
-3
0.016
0.020
0
3
[
SDS] mpl dm
50 375 400 425 450 475 500 525 550 575 600
Wavelength (nm)
f
Fig. 8. Plot of I versus SDS concentration.
Fig. 6. Emission spectra of AEDQ (1 × 10ꢀ 5 M mol dm ) with different
ꢀ 3
concentration of SDS (with increasing emission intensity, the concentration of
Table 2
SDS is 0.0, 2.0 × 10 , 4.0 × 10 , 6.0 × 10ꢀ 3, 8.0 × 10ꢀ 3, 1.0 × 10ꢀ 2, 1.2 ×
ꢀ
3
ꢀ 3
Antibacterial activity of AEDQ (zone inhibition, in mm) and MIC.
ꢀ 2
ꢀ 2
ꢀ 2
ꢀ 2
1
0
, 1.4 × 10 , 1.6 × 10 , 1.8 × 10 M).
Effect of AEDQ on bacterial stains
S. aureus
B. substilis
E. coli
S. flexneri
M). The heterocyclic quinoline-3-carbonitrile (AEDQ) emission intensity
increases with the increase in the concentration of the surfactants
AEDQ (Disc)
AEDQ (MIC)
Tetracycline (Disc)
Tetracycline (MIC)
DMSO
15.4 ± 0.5
22.3 ± 0.5
10.8 ± 0.2
12.6 ± 0.2
16
16
64
32
(
Figs. 5 and 6). Such enhancement of the fluorescence may be due to the
overtone mechanism of the heterocyclic quinoline-3-carbonitrile
AEDQ) with CTAB and SDS [33]. The fluorescence intensity showed a
13.0 ± 0.5
20.0 ± 0.5
12.0 ± 0.5
14.0 ± 0.5
32
32
32
32
(
–
–
–
–
ꢀ
4
ꢀ 3
rapid rise at surfactant concentrations of 8.72 × 10 and 6.25 × 10
ꢀ 1
mol L for CTAB and SDS, respectively (see Fig. 7 and Fig. 8). These
concentrations were found to be remarkably close to critical micellar
concentrations (CMC) of respective surfactants [34]. As a result, AEDQ
may be a good candidate for estimating the CMS of the surfactants (see
Figs. 7 and 8).
diffusion method. The zone of inhibition (see Table 2) demonstrated the
antibacterial activity of heterocyclic quinoline-3-carbonitrile (AEDQ)
and results inferred that AEDQ is a promising antibacterial agent
(
Table 2).
3
.6.2. Minimum inhibitory concentration (MIC)
3
3
.6. Antibacterial activity
The MIC assessment was carried out by the broth dilution assay
(
referenced by NCCLS), and the assessment revealed that heterocyclic
.6.1. Disc diffusion assay
quinoline-3-carbonitrile (AEDQ) is an effective antibacterial agent
against both type of bacterial strains (see Table 2). The quinoline-3-
The heterocyclic quinoline-3-carbonitrile (AEDQ) was tested for its
efficacy against Gram-positive and Gram-negative bacteria by disc
6

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
Table 3
ADMET and Lipinski’s filters for drug likeness.
#
a
Compound
M.Wt
ClogP*
LogD
HBA
HBD
PSA
Ro5 (Y/N)
AEDQ
444.53
331.34
444.15
5.93
6.18
5
6
9
2
2
6
74.64
72.88
181.62
Y
Y
Y
#
Ciprofloxacin(Control)
Tetracycline
1.32
ꢀ 1.13
ꢀ 3.49
ꢀ 0.89
*
At pH 7.4.
#
Calculated using ChemAxon LogD predictor.
a
HBA- hydrogen bond acceptor, HBD- hydrogen bond donor, PSA - polar surface area (obtained using Marvin Sketch 5.1). Ro5 (Y/N): Rule of five followed or not; Y:
Yes; N: No.
Fig. 9. Docking poses of the compound (AEDQ) inside the active site pocket of DNA gyrase A.
carbonitrile (AEDQ) exhibited excellent efficacy against S. aureus (MIC
were docked with the quinoline-3-carbonitrile (AEDQ). The molecule
was found to interact with various residues inside the active site of DNA
gyrase A, but not with those within the active site pocket of DNA gyrase
B. With DNA gyrase A, the binding free energy was found to be ꢀ 17.92
kcal/mol, suggesting that the inhibitor binds well within the active site
pocket (see Fig. 9). The molecule also showed hydrogen bonding, hy-
drophobic, and other interactions with the target, explaining its good
antibacterial activity.
1
6
μ
g/mL), B. substilis (MIC 16
μ
g/mL) and E. flexneri (MIC 32 g/mL).
μ
3
.6.3. ADMET and pharmacokinetic studies
The ADMET and pharmacokinetic properties of the synthesized
heterocyclic quinoline-3-carbonitrile (AEDQ) were tested with pkCSM
Cambridge online source) to ensure that it has drug potential and
(
validated using MedChem DesignerTM software version 3.0 [35]. The
predicted values revealed that the molecule has high solubility poten-
tial, ꢀ 7.167 (log mol/L) in water and 0.247 (log Papp in 10 cm/s) in
Caco-2 cells while skin permeability is ꢀ 2.735 and intestinal absorption
4. Conclusion
(
(
human) is 96.872% (log Kp). The permeability of the BBB is ꢀ 0.38
logBBB) and the permeability of the CNS is ꢀ 1.353. (logPS). The AEDQ
An efficient one-pot synthesis for the heterocyclic quinoline-3-
carbonitrile (AEDQ) has been described. Physicochemical parameters
(Stoke’s shift, molar extinction coefficient, fluorescence quantum yield)
of the heterocyclic quinoline-3-carbonitrile (AEDQ) were studied by
using solvents of varying polarity. The results showed that these pa-
rameters vary with the polarity of solvent. The excited state energy of
heterocyclic quinoline-3-carbonitrile (AEDQ) was affected strongly with
solvent polarity compared to ground state energy, indicating the intra-
molecular charge transfer during excitation. Also, AEDQ could be used
to determine the CMC of the surfactants. In addition, the in-vitro anti-
bacterial activity of heterocyclic molecule showed that it is active
against gram positive and negative bacteria tested. This compound also
showed good ADMET properties and followed Lipinski’s filters, which
are requisites for a molecule to show drug-like properties. The molecule
also fits well in DNA gyrase A active site with a binding free energy of
ꢀ 17.92 kcal/mol, which strongly supports the in-vitro antibacterial
results.
inhibit CYP3A4 and CYP2C19, indicated that it would prevent xenobi-
otics from being metabolized in the body. The clearance value of AEDQ
is quite favorable (0.855 log mL/min/kg). This value signifies that it
does not accumulate in the body and therefore is non-toxic. The LD50 for
oral rat acute toxicity was 2.618 mol/kg, and the LOAEL for oral rat
chronic toxicity was 0.913 (log mg/kg bw/day). These findings show
that the compound possesses good ADMET properties, required for a
molecule to exhibit drug-like properties.
The predicted pharmacokinetic parameters and other physico-
chemical properties, often known as Lipinski’s filters, are essential for in
silico as well as in vitro assessment of drug-like characteristics of a
molecule [36,37]. A molecule that lacks good pharmacokinetic param-
eters and does not obey Lipinski’s filters fails in the later stages of drug
development. From the predicted pharmacokinetic parameters and after
applying Lipinski’s filters (shown in Table 3) it appears that the mole-
cule shows good drug-likeness properties and could be a promising drug
candidate for further studies.
Declaration of Competing Interest
3
.7. Molecular docking studies
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
To further confirm the experimental findings, molecular docking
analysis of the heterocyclic quinoline-3-carbonitrile (AEDQ) was con-
ducted. The 2D structure of molecule was transformed to an energy-
minimized 3D structure, which was then used for docking. S. aureus
DNA gyrase A (PDB-2XCT) and DNA gyrase B (PDB-3G75) active sites
Acknowledgements
Taif university researchers supporting project number (TURSP-
7

S.A. Khan et al.
Bioorganic Chemistry 112 (2021) 104964
2
020/44) Taif University, Taif, Saudi Arabia.
[19] S. Mouilleron, M.A. Badet-Denisot, B. Gollinelli-Pimpaneau, Ordering of C-terminal
loop and glutaminase domains of glucosamine-6-phosphate synthase promotes
sugar ring opening and formation of the ammonia channel, J. Mol. Biol. 377 (2008)
References
1
174–1185.
[
20] T. Sander, J. Freyss, M. Korff, J.R. Reich, C. Rufener, OSIRIS, an entirely in-house
developed drug discovery informatics system, J. Chem. Inf. Model 49 (2009)
232–246.
[
[
[
[
1] C.M. Yruela, J. Garin, J. Orduna, S. Franco, E. Quintero, J.T.L. Navarrete, B.
E. Diosdado, B. Villacamp, J. Casado, R. Andreu, Dꢀ π–A compounds with tunable
intramolecular charge transfer achieved by incorporation of butenolide nitriles as
acceptor moieties, J. Org. Chem. 80 (2015) 12115–12128.
[21] O. Trott, A.J. Olson, AutoDock Vina: Improving the speed and accuracy of docking
with a new scoring function, efficient optimization, and multithreading, J. Comput.
Chem. 31 (2010) 455–461.
2] M. Jia, X. Ma, L. Yan, H. Wang, Q. Guo, X. Wang, Y. Wang, X. Zhan, A. Xia,
Photophysical properties of intramolecular charge transfer in two newly
[22] S.M. Khopde, K.I. Priyadarsini, D.K. Palit, T. Mukherjee, Effect of solvent on the
excited-state photophysical properties of curcumin, Photochem. Photobiol. 72
(2000) 625–631.
synthesized tribranched Donor–
2010) 7345–7352.
3] J. Kulhanek, F. Bures, O. Pytela, F. Pippig, M. Danko, T. Mikysek, Z. Padelkova,
M. Ludwig, Quadrupolar D- -A- -D chromophores with central tetrafluorobenzene
π–Acceptor chromophores, J. Phys. Chem. A 114
(
[23] L. Reynolds, J.A. Gardecki, S.J.V. Frankland, M.L. Hornig, M. Maroncelli, Dipole
solvation in non-polar solvents: experimental studies of reorganization energies of
solvation dynamics, J. Phys. Chem. 100 (1996) (1996) 354.
π
π
acceptor and two peripheral N, N-dimethylamino and methoxy donors, J Fluor.
Chem. 161 (2014) 15–23.
[24] F.S. Shirazi, B. Hemmateenejad, A.M. Mehranpour, Determination of the empirical
solvent polarity parameter ET(30) by multivariate image analysis, Anal. Methods 5
(2013) 891–896.
4] S. Shalini, R. Balasundaraprabhu, T.S. Kumar, N. Prabavathy, S. Senthilarasu,
S. Prasanna, Status and outlook of sensitizers/dyes used in dye sensitized solar cells
(
DSSC): a review, Int. J. Energy Res. 40 (2016) 1303–1320.
[25] F. Schluter, K. Riehemann, N.S. Kehr, S. Quici, C.G. Daniliuc, F. Rizzo, A highly
fluorescent water soluble spirobifluorene dye with a large Stokes shift: synthesis,
characterization and bio-applications, Chem. Commun. 54 (2018) 642–645.
[26] E.G. Demissie, E.T. Mengesha, G.W. Woyess, Modified solvatochromic equations
for better estimation of ground and excited state dipole moments of p-
aminobenzoicacid (PABA): Accounting for real shape over hypothetical spherical
solvent shell, J. Photochem. Photobiolo. A 337 (2017) 184–191.
[27] E.A. Nikitina, A.V. Odinokov, F.V. Grigoriev, M.V. Basilevsky, A.A. Khlebunov, V.
A. Sazhnikov, M.V. Alfimov, Molecular simulation of solvent-induced stokes shift
in absorption/emission spectra of organic chromophores, J. Phys. Chem. B 111
(2007) 3953–3959.
[
[
5] J. Kulh a´ nek, F. Bures, Imidazole as a parent
π
-conjugated backbone in charge-
transfer chromophores, Beilstein J. Org. Chem. 8 (2012) 25–49.
6] P. Thongkasee, A. Thangthong, N. Janthasing, T. Sudyoadsuk, S. Namuangruk,
T. Keawin, S. Jungsuttiwong, V. Promarak, Carbazole-dendrimer-based
Donor–
of the carbazole dendritic donor, ACS Appl. Mater. Interfaces 6 (2014) 8212–8222.
7] K. Srinivas, C.R. Kumar, M.A. Reddy, K. Bhanuprakash, V.J. Rao, L. Giribabu, D- -A
organic dyes with carbazole as donor for dye-sensitized solar cells, Synth. Met. 161
π–Acceptor type organic dyes for dye-sensitized solar cells: effect of the size
[
[
[
π
(
2011) 96–105.
8] S. Pillai, M. Kozlov, S.A.E. Marras, L.N. Krasnoperov, A. Mustaev, New cross-
linking quinoline and quinolone derivatives for sensitive fluorescent labeling,
J Fluoresc. 22 (2012) 1021–1032.
[28] A.M. Asiri, M.M. Al-Amari, Q. Ullah, S.A. Khan, Ultrasound-assisted synthesis and
photophysical investigation of a heterocyclic alkylated chalcone: a sensitive and
3
+
9] R.A. Mekheimer, M.A. Al-Sheikh, H.Y. Medrasib, K.U. Sadeka, Advancements in
the synthesis of fused tetracyclic quinoline derivatives, RSC Adv. 10 (2020) 19867.
selective fluorescent chemosensor for Fe in aqueous media, J. Coord. Chem. 73
(2020) 2987–3002.
[
10] M.R. Selim, M.A. Zahran, A. Belal, M.S. Abusaif, S.A. Shedid, A.B.M. Mehany, G.A.
M. Elhagali, Y.A. Ammar, Hybridized quinoline derivatives as anticancer agents:
design, synthesis, biological evaluation and molecular docking anticancer agents,
Med Chem 19 (2019) 439–452.
[29] S.A. Khan, Q. Ullah, A.S.A. Almaliki, S. Kuamr, R.J. Obaid, M.A. Alsharif, S.
Y. Alfafi, A.A. Hashmi, Synthesis and photophysical investigation of (BTHN) Schiff
2
+
base as off-on Cd fluorescent chemosensor and its live cell imaging, J. Mol. Liq.
328 (2021) 115407.
[
[
[
[
11] D. Insuasty, O. Vidal, A. Bernal, E. Marquez, J. Guzman, B. Insuasty, J. Quiroga,
L. Svetaz, S. Zacchino, G. Puerto, R. Abonia, Antimicrobial activity of quinoline-
based hydroxyimidazolium hybrids, Antibiotics (Basel). 8 (2019) 239.
12] N. Ahmed, K.G. Brahmbhatt, S. Sabde, D. Mitra, I.P. Singh, K.K. Bhutani, Synthesis
and anti-HIV activity of alkylated quinoline 2,4-diols, Bioorg. Med. Chem. 15
[30] S.A. Khan, Q. Ullah, H. Parveen, S. Mukhtar, K.A. Alzahrani, M. Asad, Synthesis
and photophysical investigation of novel imidazole derivative an efficient
multimodal chemosensor for Cu(II) and fluoride ions, J. Phtochem Photobiol. A
406 (2021) 113022.
[31] C. Reichardt, Solvatochromic dyes as solvent polarity indicators, Chem Rev (1994)
2319–2358.
(
2010) 2872–2879.
13] X. Wen, S. Wang, D. Liu, G. Gong, Z. Quan, Synthesis and evaluation of the anti-
inflammatory activity of quinoline derivatives Med, Chem. Rese. 24 (2015)
[32] M. Shaikh, J. Mohanty, P.K. Singh, A.C. Bhasikuttan, R.N. Rajule, V.S. Satam, S.
R. Bendre, V.R. Kanetkar, H. Pal, Contrasting solvent polarity effect on the
photophysical properties of two newly synthesized aminostyryl dyes in the lower
and in the higher solvent polarity regions, J. Phys. Chem. A 114 (2010) 4507.
[33] E.D. Vendittis, G. Palumbo, G. Parlato, V. Bocchini, A fluorimetric method for the
estimation of the critical micelle concentration of surfactants, Analy. Biochem. 115
(1981) 278–286.
2
591–2603.
14] M. Khalida, M.A. Ullah, M. Adeel, M.U. Khan, M.N. Tahird, A.A.C. Bragae,
Synthesis, crystal structure analysis, spectral IR, UV–Vis, NMR assessments,
electronic and nonlinear optical properties of potent quinoline based derivatives:
Interplay of experimental and DFT study, J. Saudi Chem. Soci. 23 (2019) 546–560.
15] S.A. Khan, Multi-step synthesis, photophysical and physicochemical investigation
[
[34] A. Dominguez, A. Fernandez, N. Gonzalez, E. Iglesias, L. Montenegro,
Determination of critical micelle concentration of some surfactants by three
techniques, J. Chem. Educ. 74 (1997) 1227.
of novel pyrazoline a heterocyclic D-
π
-A chromophore as a fluorescent
3
+
chemosensor for the detection of Fe metal ion, J. Mol. Struc. 12115 (2020)
28084.
1
[35] N.A. Meanwell, Improving drug candidates by design: A focus on physicochemical
properties as a means of improving compound disposition and safety, Chem. Res.
Toxicol. 24 (2011) 1420–1456.
[
[
[
16] S.A. Khan, Green synthesis, spectrofluorometric characterization and antibacterial
activity of heterocyclic compound from chalcone on the basis of in vitro and
quantum chemistry calculation, J. Fluoresc. 27 (2017) 929–937.
[36] E.H. Kearns, L. Di, Drug-like Properties: Concepts, Structure Design and Methods,
Elsevier, USA, 2008.
17] A.M. Asiri, S.A. Khan, Synthesis, characterization, and in vitro antibacterial
activities of macromolecules derived from bis-chalcone, J. Heterocyclic Chem. 49
[37] M.P. Gleeson, Generation of a set of simple, interpretable ADMET rules of thumb,
J. Med. Chem. 51 (2008) 817–834.
(
2012) 1434–1438.
18] S.A. Khan, A.M. Khan, Synthesis and spectroscopic studies of Ru(II) complexes of
steroidal thiosemicarbazones by multi step reaction: As antibacterial agents,
Steroids 124 (2017) 23–28.
8