Synthesis, characterization and α-amylase and α-glucosidase inhibition studies of novel vanadyl chalcone complexes

Article abstract of DOI:10.1002/aoc.6042

A series of chalcone ligands and their corresponding vanadyl complexes of composition [VO (L^I–IV)₂(H₂O)₂]SO₄ (where L^I = 1,3-Diphenylprop-2-en-1-one, L^II = 3-(2-Hydroxy-phenyl)-1-phenyl-propenone, L^III = 3-(3-Nitro-phenyl)-1-phenyl-propenone, L^IV = 3-(4-Methoxy-phenyl)-1-phenyl-propenone) have been synthesized and characterized using various spectroscopic (Fourier-transform infrared, electrospray ionization mass, nuclear magnetic resonance, electron paramagnetic resonance, thermogravimetric analysis, vibrating sample magnetometer) and physico-analytic techniques. Antidiabetic activities of synthesized complexes along with chalcones were evaluated by performing in vitro and in silico α-amylase and α-glucosidase inhibition studies. The obtained results displayed moderate to significant inhibition activity against both the enzymes by vanadyl chalcone complexes. The most potent complexes were further investigated for the enzyme kinetic studies and displayed the mixed inhibition for both the enzymes. Further, antioxidant activity of vanadyl chalcone complexes was evaluated for their efficiency to release oxidative stress using 2,2-diphenyl-1-picryl-hydrazyl-hydrate assay, and two complexes (Complexes 2 and 4) have demonstrated remarkable antioxidant activity. All the complexes were found to possess promising antidiabetic and antioxidant potential.

Full text of DOI:10.1002/aoc.6042

Received: 25 July 2020
DOI: 10.1002/aoc.6042
Revised: 17 September 2020
Accepted: 17 September 2020
F U L L P A P E R
Synthesis, characterization and α-amylase and α-glucosidase
inhibition studies of novel vanadyl chalcone complexes
Mandeep Kaur
| Raj Kaushal
Department of Chemistry, National
A series of chalcone ligands and their corresponding vanadyl complexes of
composition [VO (LI–IV) (H O) ]SO (where L = 1,3-Diphenylprop-2-en-
Institute of Technology, Hamirpur, India
I
2
2
2
4
Correspondence
II
III
1
-one, L = 3-(2-Hydroxy-phenyl)-1-phenyl-propenone, L = 3-(3-Nitro-phe-
Raj Kaushal, Department of Chemistry,
National Institute of Technology,
Hamirpur, 177005 Himachal Pradesh,
India.
IV
nyl)-1-phenyl-propenone, L = 3-(4-Methoxy-phenyl)-1-phenyl-propenone)
have been synthesized and characterized using various spectroscopic (Fourier-
transform infrared, electrospray ionization mass, nuclear magnetic resonance,
electron paramagnetic resonance, thermogravimetric analysis, vibrating sam-
ple magnetometer) and physico-analytic techniques. Antidiabetic activities of
synthesized complexes along with chalcones were evaluated by performing
in vitro and in silico α-amylase and α-glucosidase inhibition studies. The
obtained results displayed moderate to significant inhibition activity against
both the enzymes by vanadyl chalcone complexes. The most potent complexes
were further investigated for the enzyme kinetic studies and displayed the
mixed inhibition for both the enzymes. Further, antioxidant activity of vanadyl
chalcone complexes was evaluated for their efficiency to release oxidative
stress using 2,2-diphenyl-1-picryl-hydrazyl-hydrate assay, and two complexes
Email: rajkaushal@nith.ac.in
(Complexes 2 and 4) have demonstrated remarkable antioxidant activity. All
the complexes were found to possess promising antidiabetic and antioxidant
potential.
K E Y W O R D S
docking, enzyme inhibition, vanadyl chalcone complexes, α-amylase, α-glucosidase
1
| INTRODUCTION
encouraged the progress of vanadium chemistry. As
2+
VO is less toxic than other oxidation states due to its
[
9]
Vanadium is a critically important element from biolog-
ical point of view, especially coordination chemistry
of Oxidation States III, IV and V that show pronounced
significance in water. Therapeutic potency of its com-
plexes is obvious from its application in nitrogen
fixation,
activity, insulin-mimetic action, cleavage and bind-
ing of DNA and antioxidant properties. This pivotal
role of vanadium in biological and chemical processes
stable bio-state condition in organs, it is being moni-
tored for its hypoglycemic effect since the 19th century
[
1]
[
10]
because of its insulin-mimetic action.
The highly
[2]
conjugated chalcone and its derivatives as ligands have
captivated scientists' attention due to its reactive car-
[
3]
[4]
[11]
used as halo-peroxidases,
antitumour
bonyl group,
varied range of biological activities,
[5]
[6]
[12]
diversity of substituents and ease of synthesis.
There-
[7]
[8]
fore, chalcones and its metal complexes have induced
broad spectrum of biological potential and have been
[
13]
used in traditional medicine for so long.
The anti-
Abbreviations: DPPH, 2,2-diphenyl-1-picryl-hydrazyl-hydrate..
diabetic activity of the chalcones was most prominent
Appl Organomet Chem. 2020;e6042.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 17
https://doi.org/10.1002/aoc.6042

2
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KAUR AND KAUSHAL
from the extensive range of activities, and many key
structural features are already acknowledged in the lit-
2 | EXPERIMENTAL
[14]
erature.
Diabetes mellitus (DM) is a prevalent global
2.1 | Materials and chemicals
burden of disease now. It is the third leading cause of
[15]
mortality worldwide.
According to the World Health
Analytical reagent (AR)–grade chemicals and solvents
were employed as received for the synthesis of
organic ligands. Acetophenone, benzaldehyde, 2-hydrox-
ybenzaldehyde, 3-Nitrobenzaldehyde, 4-Anisaldehyde,
ethanol, sodium hydroxide, hydrochloric acid,
Organization report, more than 400 million people live
with diabetes worldwide. In 2016, it was the seventh
leading cause of death. Almost 90% cases of diabetes
[16]
out of total are of type 2 DM.
Chronic diabetes is
associated with many postprandial effects like prema-
ture dying, blindness, obesity, cataracts, kidney failure,
heart attack, fatty liver disease, stroke and lower limb
dimethylsulphoxide,
phosphate
buffer,
DPPH,
p-nitrophenyl-α-D-glucopyranoside, Aspergillus oryzae
α-amylase, Acarbose and α-glucosidase were purchased
from Sigma Aldrich and Himedia.
[17]
amputation.
During the ongoing Covid-19 pandemic,
it was observed that the chances of diabetic patients to
get infected with the virus are 5%–18% more than the
others. Moreover, during the SARS-CoV-1 outbreak in
2.2 | Physical measurements
2
002–2003, diabetes was the sole independent factor to
[18]
increase the complications.
Since the last few
Determination of the melting point was carried out on
paramount digital melting point apparatus. Infrared
stretching frequencies were recorded in the range
decades, diabetes status has increased from mild disor-
der to one of the foremost reason for morbidity and
[19]
−1
mortality among the population.
Now, chalcones and
400–4,000 cm . Electron paramagnetic spectroscopy
its metal complexes exert hypoglycemic properties by
targeting the different enzymes involved in the meta-
bolic and digestion processes such as tyrosine phospha-
tase, α-glucosidase α amylase, aldose reductase and
study was performed on ESR-JEOL (JES-FA200 ESR
Spectrometer with X and Q band). ESI mass spectrum
was performed with XEVO G2-XS QTOF. H-NMR spec-
1
trum was recorded on JEOL PECX 500 MHz spectrome-
ter. TGA thermogram was recorded using SDT Q600
V20.9 Build 20 facility. The molar conductivity was mea-
sured with the alpha-06 digital conductivity metre. The
biological activities were analysed using microprocessor
ultraviolet–visible (UV–Vis) spectrophotometer (double
beam LI-2800). Surface morphology was monitored by
scanning electron microscope (SEM).
[20]
dipeptidyl peptidase 4.
Actually, by retardation of the
hyperactivity of the α-cells (amylase and glucosidase),
[21]
blood glucose level is lowered.
Inhibition of these
enzymes delays the digestion of carbohydrate and slows
down the glucose absorption rate, which depresses the
[22]
postprandial hyperglycemia.
For example, acarbose,
miglitol and voglibose are few drugs already used in
clinical practice. Still, the currently available anti-
diabetic drugs do not present the desired efficacy and
are generally associated with serious adverse side
2.3 | Synthesis of chalcone ligands
[14]
effects.
As stated above, vanadium complexes and chalcones
both induces great therapeutic potential, but an area of
complexation of vanadium metal with chalcones has
Chalcones were synthesized by the classical Claisen–
[
24]
Schmidt method.
All the ligands were prepared either
by stirring or by a solvent-free grinding method as
described as follows:
[23]
been less explored. In 2017, Atlam et al.
synthesized
the vanadium complex with DMATP chalcone, and
complex was found to possess great deal of DNA bind-
ing and antimicrobial potential but did not study its
antidiabetic potential. So, in this present study, four
vanadium chalcone complexes were synthesized and
characterized using Fourier-transform infrared (FTIR),
electrospray ionization (ESI) mass, nuclear magnetic
resonance (NMR), electron paramagnetic resonance
Method A: 1,3-Diphenylprop-2-en-1-one, 3-(3-Nitro-phe-
nyl)-1-phenyl-propenone and 3-(4-Methoxy-phenyl)-
1-phenyl-propenoneligands were synthesized by stirring
ethanolic solution of acetophenone (100 mg, 8.3 mmol)
and substituted benzaldehyde in 1:1 molar ratio. NaOH
solution was added gradually till the yellow-coloured
precipitates were formed. After 5 h of stirring, the
mixture was neutralized with 0.2 N HCl solutions to
eliminate the excess base. Yellow-coloured precipitates
were vacuum-filtered, washed with ethanol and dried in
(
EPR) and thermogravimetric analysis (TGA) studies.
Additionally, their antioxidant activity is analysed on
,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH), and
2
antidiabetic potential is monitored against α-glucosidase
and α-amylase enzymes.
the open. General scheme for the synthesis of Chalcones
I–III
L
is shown in Scheme 1.

KAUR AND KAUSHAL
3 of 17
Method B: synthesis of 3-(2-Hydroxy-phenyl)-1-phenyl-
propenone was carried out by grinding 1-Phenylethanone
and 2-Hydroxy benzaldehyde in 1:1 molar ratio using
mortar and pestle with NaOH for 10–15 min till the mass
thickens. Then, the solidified mass was dissolved in water
and neutralized with 0.2 M HCl, and precipitates of
IV
chalcone (L ) were vacuum-filtered, washed with etha-
SCHEME 1 General reaction scheme for the synthesis of
Chalcones L , L
[25]
nol and dried in air.
Scheme 2.
The reaction scheme is shown in
I
III-IV
I
2
.3.1 | 1,3-Diphenylprop-2-en-1-one (L )
ꢀ
−1
Yield:74.56, m.p.: 57 C; FTIR spectrum (KBr; ῡ cm ):
2.3.4 | 3-(2-Hydroxy-phenyl)-1-phenyl-
propenone (L )
1
II
3
062 ( CH), 1,662 (C O); H NMR (H O-d , 500 MHz) δ
ppm): 7.83 (d, 1H, J = 15.8 Hz; H ), 7.52 (d, 1H,
J = 15.8 Hz; H ), Ring A, 8.03 (t, 2H), 7.65 (m, 2H), 7.58
2
2
(
A
ꢀ
−1
Yield: 86.72, m.p.: 125 C; FTIR spectrum (KBr; ῡ cm ):
B
13
1
(
t, 1H), Ring B, 7.50 (t, 2H), 7.42 (m, 3H); C NMR
H O-d , 500 MHz) δ (ppm): 190.5 (C O), 144.7 (C )
3,565 ( OH), 3,053 ( CH), 1,668 (C O); H NMR (H O-
2
(
1
1
d , 500 MHz) δ (ppm): 10.03 (1H, S, OH, D O exchange-
2
2
A
2
2
+
22.7 (C ); ESI mass (m/z %): 209.10 (MH , 100), 191.09,
able), 8.22 (d, 1H, J = 15.8 Hz; H ), 7.97 (d, 1H,
B
A
52.07.
J = 6.9 Hz; H ), 7.64–7.20 (m, 5Hs of Ring A), 6.67–6.51
B
13
(
m, 4Hs of Ring B); C NMR (H O-d , 500 MHz) δ
2
2
(
ppm): 194 (C O),174 (C OH), 146 (C ), 123 (C ); ESI
A
B
+
2
.3.2 | 3-(3-Nitro-phenyl)-1-phenyl-
mass (m/z %): 225.10 (MH ), 207, 183, 165.
III
propenone (L )
ꢀ
−1
Yield: 80.69, m.p.: 155 C; FTIR spectrum (KBr; ῡcm ):
,073 ( CH), 1,605 (C O), 1,568 (NO ν ), 1,366 (NO ν );
2.4 | Synthesis of vanadyl chalcone
I-IV
3
complexes [VO (L ) (H O) ]SO (1–4)
2
as
2 s
2
2
2
4
1
H NMR (H O-d , 500 MHz) δ (ppm): 7.9 (d, 1H,
2
2
J = 8.25 Hz; H ), 7.86 (d, 1H, J = 15.8 Hz; H ), Ring A,
Vanadyl chalcone complexes were prepared according to
A
B
[
23]
8
.11 (d, 2H), 7.56 (t, 2H), Ring B, 8.52 (s,1H), 8.28 (d, 1H);
method reported by Atlam et al.
with certain modifica-
1
3
C NMR (H O-d , 500 MHz) δ (ppm): 189.6 ( C O),
tions. The ethanolic solution of VOSO .xH O (0.0012
2
2
4
2
+
I-IV
1
41.6 (C ), 122.3 (C ); ESI mass (m/z %): 254 (MH ,
moles) was mixed with the ethanolic solution of L
A
B
1
00), 230, 209, 176.
(0.0024 moles) in a 1:2 molar ratios with continuous stir-
ring followed by dropwise addition of 20 ml of 0.1 M
solution of NaOH. Then, the reaction mixture was
refluxed for about 10 h. During the course of reaction, a
green-coloured precipitate of the complex was separated
out. The precipitates of the desired complex were filtered
under vacuum and washed with ethanol for three–four
times. The reaction can be rationalized in the form of
chemical equation as represented in Scheme 3.
2
.3.3 | 3-(4-Methoxy-phenyl)-1-phenyl-
IV
propenone (L )
ꢀ
−1
Yield: 72.34, m.p.: 92 C; FTIR spectrum (KBr; ῡ cm ):
,063 ( CH), 2,954 ( CH), 1,660 (C O), 1,163
3
1
(C O C); H NMR (H O-d , 500 MHz) δ (ppm): 7.08
2
2
(
d, 1H, J = 15.8 Hz; H ), 7.43 (d, 1H, J = 15.1 Hz; H ),
A
B
Ring A- 8.02 (t, 2H), 7.62 (m, 3H), Ring B- 7.51 (t, 2H),
13
I
6
.95 (t, 2H), 3.86 (s, 3H); C NMR (H O-d , 500 MHz)
2.4.1 | [VO (L ) (H O) ]SO (1)
2
2
2
2
2
4
δ (ppm): 190.5 (C O), 144.7 (C ), 119.7 (C ), 55.3
A
B
+
ꢀ
Yield (%): 69.33, m.p.: >300 C; paramagnetic; FTIR
(
OCH ); ESI mass (m/z %): 239 (MH , 100), 237, 189.
3
−1
spectrum (KBr; ῡcm ): 3,483 (OH), 1,615 (C O),
,119, 616 (SO ), 966 (V O), 513 (V O), 674 (Coord.
1
4
H O). ESI mass (m/z %): 615 (molar mass),
2
I
+
2 2 2 7 5
1
5
(
41 ([VO (L ) (H O) ]Na , 453 ([VO(L )(C H O)
+
1
I
1
+
H O) ]K , 274 (VO(L ), 230 (L )Na, 209 (L H );
2 2
ʌM = 54.15 Ω− cm mol in mM solution of DMSO;
1
2
−1
SCHEME 2 Reaction scheme for the synthesis of
II
3
-(2-Hydroxy-phenyl)-1-phenyl-propenone (L )
giso = 1.9978.

4
of 17
KAUR AND KAUSHAL
[
26]
assay method with some changes.
In brief, fixed vol-
ume of 0.1 mM solution of DPPH in ethanol was added
to different concentrations (5, 20, 50, 80, 100, 150, and
300 μM) of the prepared ligand and vanadyl chalcone
complexes (1–4) in dark. Then, the solution was incubated
for 1 h at room temperature for reaction completion.
Absorbance was recorded for each dilution at 517 nm
against reference control (ascorbic acid) at the same
wavelength. A graph was plotted between concentration
(on the abscissa) and % inhibition (on the ordinate) to
calculate IC50 value. The % inhibition for DPPH radical
was evaluated according to the following equation:
SCHEME 3 General reaction scheme for the synthesis of
I-IV
[
VO (L
2 2 2 4
) (H O) ]SO complexes (1–4)
II
A0−A1
A0
2
.4.2 | [VO (L ) (H O) ]SO (2)
2 2 2 4
DPPH radical scavenging activity orð%Þ inhibition =
× 100,
ꢀ
ð1Þ
Yield (%): 76.30, m.p.: >300 C; paramagnetic; FTIR spec-
−
1
trum (KBr; ῡcm ): 3,447 (OH), 1,589 (C O), 1,120,
19 (SO ), 970 (V O), 519(V O), 705 (Coord. H O). ESI
6
where A0 = absorbance of control reaction and
4
2
II
mass (m/z %): 646 (molar mass), 480 ([VO (L )
A = absorbance in presence of test sample.
1
+
2 2 9 7 2 2 7 5
II
+
(
4
3
H O) (C H O)]Na , 470 ([VO (L )(H O) (C H O)]K ,
II
+
II
30 ([VO (L )(H O) (C H O)]H , 308 (([VO (L )(H O)],
2 2 7 5 2
II
+
II
+
II
13 [VO (L )]Na , 263 (L )K , 207 (L -OH);
2.6 | Antidiabetic activity
ʌM = 89.32 Ω− cm mol in mM solution of DMSO;
1
2
−1
giso = 1.9869.
2.6.1 | Alpha-glucosidase inhibition assay
The synthesized complexes were evaluated for
α-glucosidase inhibitory activity against α-glucosidase
extracted from yeast. The investigation was carried out
III
2
.4.3 | [VO (L ) (H O) ]SO (3)
2 2 2 4
ꢀ
Yield (%): 62.59, m.p.: >300 C; paramagnetic; FTIR spec-
according to a previously reported pNPG method incor-
−
1
[27]
trum (KBr; ῡcm ): 3432 (OH), 1,598 (C O), 1,113,
21 (SO ), 957 (V O), 528 (V O), 775 (Coord. H O). ESI
porating few modifications.
In short, 10 μl of
6
α-glucosidase enzyme solution of 5 U/ml prepared in ice-
cold phosphate buffer (pH 6.9) was added to different
concentrations (3, 6, 10, 15, 20, and 50 μM) of the ligands
4
2
III
mass (m/z %): 679 for [VO (L ) (H O) ]SO+ Na, 342 for
VOL )Na ,276for(L )+Na ;ʌ =50.32Ω cm mol
2
2
2
III
+
III
+
−1
2
−1
(
M
in mM solution of DMSO; giso = 1.9856.
and their vanadyl chalcone complexes and incubated for
ꢀ
20 min at 37 C. After incubation, the addition of 200 μL
of 1 mM pNPG solution was carried out to the solution
followed by the incubation for 30 min at 37 C. The reac-
IV
ꢀ
2
.4.4 | [VO (L ) (H O) ]SO (4)
2
2
2
4
tion was ceased off by pouring 200 μL of Na CO into the
2
3
ꢀ
Yield (%): 48.21, m.p.: >300 C; paramagnetic; FTIR spec-
reaction vessel. UV–Vis spectrophotometer used to record
the absorbance of yellow colour solution due to the liber-
ation of p-nitrophenol at wavelength 405 nm and % inhi-
bition was calculated using Equation 2. IC50 values were
computed from the plot of concentration v/s % inhibition.
Acarbose was taken as the standard reference.
−
1
trum (KBr; ῡ cm ): 3,465 (OH), 1,639(C O), 1,115,
12 (SO ), 965 (V O), 528 (V O), 783 (Coord. H O). ESI
6
4
2
IV
+
IV
+
mass (m/z %): 239 (for L + H ), 274 (for L - 3H) + K ,
IV
IV
3
40 [for VO (L )(H O) ], 540 (for [VO (L )
2 2
+
−1
2
−1
(H O) (C1 H O )]K , ʌ = 53.29 Ω cm mol in mM
2
2
0
9
2
M
solution of DMSO; giso = 1.9993.
ꢀ
ꢁ
Ab−As
Ab
Inhibition activity ð%Þ =
× 100,
ð2Þ
2.5 | Antioxidant activity
I-IV
Synthesized chalcones ligands (L
)
and their
respective vanadyl complexes of chemical composition
where A and A correspond to the absorbance of the
sample under investigation, blank (with no sample),
respectively.
s
b
I-IV
[
VO (L ) (H O) ]SO (1–4) were evaluated for their
2
2
2
4
antioxidant activity using the DPPH radical scavenging

KAUR AND KAUSHAL
5 of 17
2.6.2 | Alpha-amylase inhibition assay
where Vmax is the maximal velocity, [S] is the substrate
concentration and K is the Michalis constant.
m
α-amylase inhibition assay was performed in vitro by
using iodine starch method as described in the study of
[
28]
Zhang and Kim amending slightly.
To prepare the
2.7 | In silico α-amylase and α-glucosidase
inhibition studies of vanadyl chalcone
complexes
reaction mixture, 10 μl of 20 u/ml of α-amylase (extracted
from A. oryzae) was dissolved in 10 mM phosphate buffer
pH 6.9, NaCl 6 mM) and mixed with varying concentra-
(
tions of the test sample. The reaction mixture was then
incubated for 30 min at 37 C. After incubation, 100 μl of
The binding modes of α-amylase and α-glucosidase
enzyme with synthesized complexes (1–4) were investi-
gated with the help of molecular docking using autodock
tool 1.5.6. The 3D structure of the chalcones and their
vanadyl complexes were obtained from ACD/chemsketch
in MDL molfiles (V2000) format. The 3vx0.pdb and 3w37.
pdb files were downloaded from Protein data bank for
the structure of α-amylase and α-glucosidase, respec-
tively. These files were processed for energy minimiza-
tion using Swiss-Pdb viewer 4.1.0. and got it ready for
docking. The autodock input files were created using
autodock tool 1.5.6 software. The docked files were
processed using cygwin64 software, and UCSF Chimera
software was employed to visualize the docked poses.
ꢀ
1
2
1
% starch solution was poured into it and incubated for
0 min at 37 C. The reaction was terminated by adding
00 μl of 1 M HCl to the reaction mixture, and 200 μl of
ꢀ
iodine solution was added afterwards. The quantification
of the colour imparted to the reaction mixture by iodine
solution (as yellow colour of iodine changes to deep blue
colour if starch if present) was done spectrometerically at
6
20 nm wavelength. Percentage inhibition of activity was
calculated from the following equation:
ꢂ
ꢃ
As−Ab
Ac−Ab
%
inhibition activity =
× 100,
ð3Þ
where A = absorbance of the test sample, A = absor-
bance of the blank (excluding starch and test sample)
3 | RESULTS AND DISCUSSION
s
b
and A = absorbance of the control (excluding α-amylase
and test sample).
3.1 | Synthesis, characterization of
chalcone and their vanadium complexes
c
A graph was plotted between the concentration of the
test sample and its inhibitory activity (%) to determine
the IC50 value and compared with the standard reference
acarbose (commercially used α-amylase inhibitor).
The synthesis of vanadium chalcone complexes was car-
ried out as the scheme presented in Scheme 3. Complexes
were dark green-coloured fine powder of amorphous
nature and are stable at standard temperature and pres-
sure. The related analytical and physical data are summa-
rized in Table 1 and discussed in the following sections.
2.6.3 | Enzyme kinetics and mode of
inhibition
Kinetics studies for α-glucosidase and α-amylase were per-
formed in order to determine the mode of inhibition
followed by vanadyl complex inhibitors. Different
3.1.1 | FTIR spectral data
The resultant FTIR spectral data of complexes
(Figures S5–S8) are reported after comparing with their
respective ligands (Figures S1–S4). FTIR spectra of syn-
thesized vanadyl chalcone complexes show the appear-
ance of the strong but broad absorption band in the
range of 3,483–3,432 cm− due to νOH stretching vibration
concentrations
of
substrate
(p-nitrophenyl-α-D-
glucopyranoside for α-glucosidase and starch for α-amylase)
were used in the presence of different concentrations of the
test sample with the best IC50 value. A test sample of
control (0 μM), 10 μM concentration was used for
α-glucosidase and for α-amylase. Michaelis–Menten equa-
tion (Equation 4) and Lineweaver–Burk double-reciprocal
plot (1/V v/s 1/[S]) was employed to discern the Vmax, Kmax
1
[
30]
of the H O molecule in the complexes.
Bonding mode
2
of the water molecule was further verified by the pres-
−
1
ence of an absorption band in range 650–800 cm ,
[29]
and mode of inhibition.
which appears due to the coordinated mode of a water
[
31]
molecule.
TGA analysis was further carried out to
1
V
Km
1
establish the presence of water molecule in coordination
sphere. From the graph in Figure 1, 4.9% weight loss was
observed at 142 C temperature, which was assigned to
=
+
,
ð4Þ
Vmax½Sꢁ Vmax
ꢀ

6
of 17
KAUR AND KAUSHAL
I-IV
TABLE 1 Important infrared-spectrum bands (ῡ cm−1) of chalcones (L ) and [VO (L
I-IV
2 2 2 4
) (H O) ]SO (1–4) complexes
Ligand/complexes
OH
-
C O
1,662
V O
V O
Coordinated H
2
O
4
SO ion
I
L
-
-
-
-
-
-
-
II
L
3,665
-
1,668
1,605
1,660
1,615
1,589
1,598
1,639
-
-
-
III
L
-
-
-
IV
L
-
-
-
-
I
[
[
[
[
VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
]SO
]SO
]SO
4
(1)
(2)
3,483
3,447
3,432
3,465
966
970
957
965
513
519
528
535
674
705
775
778
1,119, 616
1,120, 619
1,113, 621
1,115, 612
II
VO (L )
III
2
(H
2
2
4
VO (L
)
2
(H
2
2
4
(3)
IV
VO (L )
2
(H
2
2
4
(4)
[23,32]
1
13
the loss of coordinated water molecule.
Theoreti-
3.1.2 | H and C NMR spectral data for
cally calculated weight loss for water molecule was calcu-
lated to be 5.01%. So, both the experimental and
theoretical values are in close agreement. The peak
shifting of C O group of free chalcones in 1,600–1,700
region to lower frequency in complexes vouch for the
ligands
Formation of all the synthesized ligands was further
characterized using H NMR (Figures S9–S12) and
NMR (Figures S13-S16) spectral technique. The appear-
ance of peculiar doublet for the newly formed olefinic
bond was observed at 7.83 and 7.52 ppm for L , at 8.22
and 7.97 ppm for L , at 7.9 and 7.86 ppm for L and at
7.08 and 7.43 ppm for L . In C spectrum, distinct peaks
appeared corresponding to Olefinic C C bond and C O
functional at 122.7, 144.7 and 190.5 ppm for Group L ; at
123.6, 138.3 and 194.3 ppm for L ; 122.3, 141.7 and
189.6 ppm for L ; 119.7, 144.7 and 190.5 for L . In H
NMR spectra, appearance of singlet peaks at 10.03 ppm
and 3.86 ppm due to hydroxyl proton of L ligand and
1
13
C
[
23]
coordination of ligand to metal through C O group,
which was further confirmed by appearance of M O
I
−
1 [33,34]
II
III
peak in region 520–550 cm .
The presence of sul-
IV
13
phate ion was supported by the emergence of two promi-
nent peaks around wavelengths 1,100 and 600. Further,
the nonsplitted nature of the vibrational band at
I
−
1
II
1
,110–1,120 cm
nature of the sulphate group.
complexes show their characteristic V O band at
in complexes supported the ionic
[35]
III
IV
1
The oxido-vanadium
−
1
[36]
I
9
50–980 cm in the spectrum.
The appearance and
IV
shifting of IR spectral peaks in the complexes are given
in Table 1.
methoxy protons of L respectively were the few charac-
teristic peaks along with the other important peaks
(
as given in above section in synthesis part) which con-
I-IV
firmed the synthesis of the ligands L
.
3.1.3 | Mass spectral data
The mass spectral data of the ligands (Figures S17–S20)
and complexes (Figures S21–S24) have further supported
the formation of vanadyl chalcone complexes. The
I-IV
recorded mass spectrum of ligands (L ) displayed the
+
(
M + H ) ion peak at m/z 209, 225, 254 and 239, respec-
tively. Further, series of fragmented ion peaks for the
ligands were observed according to their general frag-
[
37]
mentation pattern
as given as follows in Scheme 4.
+
Molecular ion peak for Complex 1 (M + K ) was
observed at m/z value 654. Series of daughter ions peaks
1
+
at 543 (for complex-SO + Na), 429 (for VO(L )(C H O )),
4
9
7
+
1
1
2
74 (for VO(L ), 207 (L ) and 144 (C H O + K ). For
7 5
Complex 2, the following daughter ion peaks were
II
+
III
FIGURE 1 Thermogravimetric analysis curve of [VO (L
O) ]SO (3)
)
2
observed: 480 ([VO (L ) (H O) (C H O)]Na , 470 ([VO
1 2 2 9 7
II
+
II
(
H
2
2
4
(L ) (H O) (C H O)]K , 430 ([VO (L ) (H O) (C H O)]
1 2 2 7 5 1 2 2 7 5

KAUR AND KAUSHAL
7 of 17
3.1.5 | EPR data
The X-band EPR spectrum for powdered vanadium
IV) complexes was measured at room temperature. EPR
study of powder sample gives valuable information
(
[
40]
regarding the structure of the complex.
EPR spectra
for all the 4 complexes are given in Figure 2. The spec-
trum consists of a broad anisotropic curve as a character-
[
41]
istic peak without any hyperfine splitting.
The giso
value was calculated from the spectra using the following
equation:
SCHEME 4 General pattern of fragmentation of chalcone
molecule into daughter ions
h × f
mB × B
g =
,
ð5Þ
34
where h = Planck's constant (6.62× 10− J. S), f = fre-
+
II
II
+
II
H , 308 (([VO (L ) (H O) ], 313 [VO (L )]Na , 263 (L )
quency (Hz), B = magnetic field (in Tesla) and m : Bohr
1
2
1
B
+
II
+
−24
K and 207 (L -OH). For Complex 3, molecular ion M is
magneton = 9.2740154 10
J/T
at 704 m/z value. The fragmented ions at few m/z values
The observed lower giso value than g value for the free
III
may be inferred as at 679 for [VO (L ) (H O) ]SO+ Na,
electron (g = 2.0023) supports the fact that the complex
2
2
2
III
e
III
+
+
4
2
6
2
74 for [VO (L ) (C H O)]Na , 342 for (VOL )Na and
76 for (L ) + Na . Similarly, for Complex 4, M was at
is axially symmetrical (Table 3). The lowering in g values
may be associated with a spin–orbit interaction of
1
9
7
III
+
+
[
41]
74. The mass spectrum shows distinctive peaks at
ground-state and low-lying excited states.
Garribba and Micera
The study of
IV
+
IV
[42]
39 (for L + H ), 340 [for VO (L )(H O) ] and 540 (for
showed that geometry of metal
2
2
IV
+
[
VO (L )(H O) (C1 H O )]K daughter ion.
with less-than-half-filled electronic configuration always
has lower values of giso than that of a free electron. More-
over, giso value indicated that a complex molecule was
2
2
0
9 2
[
36]
3.1.4 | Conductance measurement and
displaying a square pyramidal geometry.
gravimetric analysis for complexes [VO
I-IV
(L
) (H O) ]SO (1–4)
2
2
2
4
3
.1.6 | Geometry of the complexes
Molar conductance measurement gives valuable informa-
tion about the electrolytic behaviour of the complexes.
The position of the sulphate ion group in the complex
can further be verified firmly by measuring molar
The electronic spectrum (Figure S25) of Complex 3 dis-
play bands at 308 and 342 nm which were assigned to
ligand–metal charge transfer transition in the complex.
Absorption of bands at 390 and 559 nm were assigned to
[38]
conductance in mM solution of DMSO (Table 2).
Mol-
2
2
2
2
ar conductance values were in the range of
spin allowed to B ! A and B ! B transitions,
2
1
2
1
1
−1
−1
5
0–90 Ω− cm mol , which indicates 1:1 electrolytic
respectively. This pattern of absorption corroborates for
[
39]
[43]
behaviour.
This validates the presence of sulphate ion
the square pyramidal geometry of the complex,
as
in ionization sphere. Also gravimetrically, all the com-
plexes give white-coloured precipitates of barium sul-
phate when treated with barium chloride solution as
presented in Scheme 5.
described in EPR spectrum data analysis. The TGA ther-
mogram (as illustrated in Figure 1) showed the decompo-
sition steps. Weight loss of 4.9% was observed at 142 C
ꢀ
temperature, which was assigned to the loss of
TABLE 2 Physical properties of metal chalcone complexes
1
2
Sr. No.
Complexes
Melting point
% yield
69.33
76.30
62.59
48.21
Molar conductance (Ω− cm mol−1)
I
ꢀ
1.
2.
3.
4.
[VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
]SO
]SO
]SO
4
(1)
(2)
>300 C
54.15
89.32
50.32
53.29
II
[VO (L )
III
2
(H
2
2
4
[VO (L
)
2
(H
2
2
4
(3)
(4)
IV
[VO (L )
2
(H
2
2
4

8
of 17
KAUR AND KAUSHAL
SCHEME 5 Gravimetric analysis
of vanadium chalcone complexes
FIGURE 2 Experimental X-Band electron paramagnetic resonance spectra of complexes: (a) Complex 1, (b) Complex 2, (c) Complex
and (d) Complex 4
3
ferromagnetic component. The value of magnetic
moment measured from the hysteresis curve was found
to be 1.56 B.M., which also favourably validates the
square pyramidal geometry of V (IV) complex with one
TABLE 3
giso values of the complex molecules
Complexes
g
iso
I
[
[
[
[
VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
]SO
]SO
]SO
4
(1)
(2)
1.9978
1.9869
1.9856
1.9993
[
44]
II
unpaired electron.
From the spectrum, it has been
VO (L )
III
2
(H
2
2
4
observed that magnetization decreases to zero with the
decrease in magnetic field, and loop closes at 1.48 T. On
application of magnetic field in reverse direction, nega-
tive values of magnetization appear, and loop closes at
VO (L
)
2
(H
2
2
4
(3)
(4)
IV
VO (L )
2
(H
2
2
4
−
1.48 T. This positive slope of loop or curve shows the
[
45]
coordinated water molecule, 12.85% weight loss (calcd.
paramagnetic nature of complex.
Based on the evalu-
ꢀ
ꢀ
1
3.04%) in range 420 C–480 C for loss of NO of ligands
ated data from the characterization techniques, tentative
structure of the complexes is given as follows in
Scheme 7.
2
ꢀ
and 14.2% weight loss (calcd. 13.8%) at 584 C for the SO
4
[23,32]
ꢀ
group.
The higher char value even at 800 C repre-
sents the high thermal stability of the complex. The
decomposition steps are shown in Scheme 6.
Further, magnetic nature and magnetic moment of
the complex were measured from the hysteresis loop of
vibrating sample magnetometer spectrum (Figure 3) at
room temperature. The magnetic hysteresis loop of Com-
plex 3 displays a characteristic pattern of dominant para-
magnetic component along with little impurity of
3.1.7 | Surface morphology
SEM was employed to monitor the surface morphology
of the ligands and their vanadyl complex. The resulting
images are shown in Figures 4 and 5 for ligands (L
and their vanadyl complexes (1–4), respectively. From
I-IV
)

KAUR AND KAUSHAL
9 of 17
SCHEME 6 Decomposition steps of
Complex 3 according to thermogravimetric
analysis thermogram
FIGURE 3 Vibrating sample
magnetometer spectrum of Complex 3
S4), which show the presence of all the functional groups
in complexes viz Vanadium, sulphur, oxygen, carbon and
nitrogen. However, percentage of elements present can-
not be conferred correctly as EDX cannot detect hydro-
[
48]
gen atom.
3
3
.2 | Biophysical evaluation
.2.1 | Antioxidant capacity
SCHEME 7 Purposed structure of synthesized complexes
Formation of reactive free radicals and oxygen species
increases due to the hyperglycemic conditions in diabe-
tes, which depresses the antioxidant system of the body,
[
46]
the figures, ligands displayed a platelet-like structure.
[
49]
These platelet-like structures got agglomerate upon com-
plexation with vanadyl sulphate and is compacted in
appearance than that in case of ligands. On comparing
the SEM images of ligands and complexes, a significant
change in surface morphology has been observed viz
compactness of the structure, fewer void spaces and
This confirmed
the coordination of ligands to the vanadium metal. It was
further supported by the energy dispersive X-ray analysis
hence increases cellular damage.
DPPH radical scav-
enging assay was used to monitor the antioxidant capac-
ity of vanadyl chalcone complexes. A literature study
showed that the efficiency of a particular complex to
behave as an antioxidant agent depends upon its ability
to donate hydrogen/electron to reduce the DPPH as it is
[47]
[50]
reduction in soft and spongy nature.
a stable nitrogen-centred free radical.
Among all the
II
ligands, only L with hydroxy derivative was found
to be an effective antioxidant agent with IC50
273.26 μg/ml. Among all complexes, [VO (L ) (H O) ]
II
(
EDX) data of complexes (Figures S26–S29; Tables S1–
2
2
2

10 of 17
KAUR AND KAUSHAL
FIGURE 4 Scanning electron
microscope photographs of Ligands I–IV
IV
SO (2) and [VO (L ) (H O) ]SO (4) were found to be
enzyme completely, all the complexes have shown a
potent inhibition against α-glucosidase with IC50 value
ranging in 7.35, 9.15, 3.26 and 8.51 μg/ml for Complexes
1–4, respectively. Among all the complexes, Complex
4
2
2
2
4
most potent antioxidant agents in comparison with
respective free ligands with IC50 39.58 μg/ml and
2.62 μg/ml values, respectively. This enhancement in
the activity of complexes comparative with the ligands
can be attributed to the formation of large conjugated
3
III
3 with nitro group derivative on L at m-position dem-
onstrated the best inhibitory activity with 3.26 μg/ml IC50
value. So, introduction of electron withdrawing group
enhanced the inhibition activity of the complex. As vana-
dium complexes possess square pyramidal geometry, they
may bind to the α-glucosidase at active or allosteric site
through vacant (sixth) coordination position on vana-
dium ion. After binding, the establishment of hydrogen
and hydrophobic interactions stabilize the inhibitor coop-
(
IV) 2+
(V) +
system and oxidation of V
O
to V
O in the sys-
[36]
II
tem.
The presence of the hydroxy group in L may be
the active factor for its antioxidant potential. The % inhi-
bition data for ligand and complexes in given Table 4 and
shown by the bar graph in Figure 6.
[
51]
3
3
.3 | Biological evaluation
eratively as explained in the study of Misra.
Further,
mode of inhibition was monitored for the complex with
the best IC , and it displayed the mixed type inhibition.
.3.1 | α-glucosidase inhibition assay
50
The % inhibition of α-glucosidase enzyme activity by the
synthesized complexes was evaluated by the method
3.3.2 | α-amylase inhibition assay
[27]
described in a report of Ain et al.
The IC50 value for
1
IV
all the complexes and standard acarbose was determined
from the graph between % inhibition v/s concentrations
and are given in Table 5. In studies, a continuous
decrease was observed in the activity of α-glucosidase
with increasing concentration of the sample in solution.
Although % inhibition activity of the complexes was less
than that of the standard acarbose which inhibits the
In the present study, ligands (L –L ) and complexes
(1–4) were screened for the inhibition activity against
α-amylase. The calculated % inhibition and IC50 value
for the ligands and complexes have been presented in
Table 6. The inhibition pattern for both ligands and
complexes was ascertained to be dose-dependent; viz
with the increase of inhibitor concentration,
%

KAUR AND KAUSHAL
11 of 17
FIGURE 5 Scanning electron microscope photographs for Complexes 1–4
inhibition increased. From in vitro studies of ligands,
hypoglycemic agent with 302 μg/ml IC50 value, even
better than standard acarbose which IC50 value was
found to be 388 μg/ml. The reason behind the better
activity of the complexes is may be due to extra struc-
tural advantage (increased conjugation and Π-cloud).
From the literature studies, it has been established that
the active site on the surface of the α-amylase enzyme
is located in V-shaped depression. The predicted square
pyramidal geometry of the complexes may bind the
I
no hypoglycemic activity was observed for L and the
IV
highest activity for L with 164 μg/ml IC50 value. IC50
values were calculated from the plot % inhibition v/s
concentration (in μM) to measure the half maximal
inhibitory concentration. All the complexes have shown
a remarkable and better inhibition activity than ligands
against the α-amylase enzyme. Among the complexes,
II
Complex 2 with L was detected to be the most potent
TABLE 4 Percentage (%) DPPH
radical scavenging activity
Concentration (μM)
Ligand/complexes
5
20
50
80
100
150
IC50 μg/ml
I
L
-
-
-
-
-
-
-
II
L
42.97 43.96 44.53 44.6
45.5
47.09 273.23
III
L
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
IV
L
-
I
[
[
[
[
VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
]SO
]SO
]SO
4
(1)
(2)
-
II
VO (L )
III
2
(H
2
2
4
44.74 46.81 50.87 54.07 61.07 64.52
39.58
-
VO (L
)
2
(H
2
2
4
(3)
-
-
-
-
-
-
IV
VO (L )
2
(H
2
2
4
(4) 39.91 45.43 45.92 56.43 59.31 64.14
32.62
Ascorbic acid
86.96 97.18 97.29 97.30 97.82 98.03

12 of 17
KAUR AND KAUSHAL
FIGURE 6 2,2-diphenyl-1-picryl-
hydrazyl-hydrate scavenging activity of
II
ligand (L ) and their vanadyl complexes
(2 and 4)
active site or at some other site near active sites
through hydrogen bonds or other hydrophobic interac-
tions. Thus, block the access to active site of the
enzyme or changes the shape or environment around it
due to allosteric interaction. So, the enzyme is no lon-
ger active for the hydrolysis of the polysaccharide
3.3.3 | Enzyme kinetics and mode of
inhibition
The inhibitors can approach the enzyme in many ways to
[
53]
prevent its activity in the metabolism.
So, the mecha-
nism of inhibition followed by the complex inhibitors for
the enzyme was discerned using the Lineweaver–Burk
[52]
molecule.
I-IV
TABLE 5 Percentage (%) α-glucosidase inhibition activity of [VO (L
2 2 2 4
) (H O) ]SO (1–4) complexes
Concentration (μM)
Complexes
3
6
10
15
20
50
IC50 (μg/ml)
7.35
I
%
%
%
%
inhibition for [VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
4
(1)
(2)
3.58
8.05
47.80
51.91
72.33
18.81
71.42
59.18
93.67
49.82
76.79
60.23
97.31
93.21
98.75
71.81
98.44
94.95
99.11
88.12
98.71
97.58
II
inhibition for [VO (L )
III
2
(H
2
2
]SO
4
9.15
inhibition for [VO (L
)
2
(H
2
2
]SO
4
(3)
(4)
27.09
15.66
3.26
IV
inhibition for [VO (L )
2
(H
2
2
]SO
4
8.51
I-IV
I-IV
TABLE 6 Percentage (%) α-amylase inhibition activity of chalcones (L ) and [VO (L
)
2
(H
2
O)
2
]SO
4
(1–4) complexes
Concentration (μM)
Complexes
20
50
80
100
150
300
500
IC50 (μg/ml)
I
%
%
%
%
%
%
%
%
inhibition for L
inhibition for L
inhibition for L
inhibition for L
-
-
-
-
-
-
-
II
1.58
9.82
12
8.55
12.38
11.15
29.52
9.85
8.44
10.20
7.58
14.66
12.54
41.76
16.01
11.38
10.27
11.64
18.71
12.71
47.79
20.91
11.97
26.11
12.33
24.71
23.24
57.65
36.55
53.60
37.46
34.30
38.07
38.96
76.18
92.29
62.70
53.27
63.14
663
III
IV
10.41
13.8
9.52
4.29
5.37
5.92
707.59
164.06
302.52
369.42
443.18
412.13
I
inhibition for [VO (L )
2
(H
2
O)
O)
O)
O)
2
]SO
4
(1)
(2)
6.38
0.94
4.17
3.90
II
inhibition for [VO (L )
III
2
(H
2
2
]SO
4
inhibition for [VO (L
)
2
(H
2
2
]SO
4
(3)
(4)
IV
inhibition for [VO (L )
2
(H
2
2
]SO
4

KAUR AND KAUSHAL
13 of 17
FIGURE 7 Lineweaver–Burk plot for
kinetics studies of α-glucosidase inhibition
FIGURE 8 Lineweaver–Burk plot for
kinetic studies of α-amylase inhibition
plot as given in Figures 7 and 8. The double reciprocal
plot between 1/[S] v/s 1/[V] gives a linear relationship,
where [S] is a concentration of substrate and [V] is the
reaction velocity. From the graph, the value of Vmax was
calculated from the ordinate intercept as it is equal to
graph, complexes showed mixed inhibition for both
enzymes α-glucosidase enzyme and α-amylase. Literature
studies revealed that mixed inhibition (i.e., mixture of
competitive and uncompetitive inhibition) does not
depend whether the substrate is already bound to the
enzyme or not. Likewise, the value of Km can increase or
decrease with the increase in concentration of the inhibi-
tor. From the graphs shown in Figures 5 and 6, it is
1
/Vmax, whereas negative abssica intercept is equal to
[
−1/K ]. The acquired K and Vmax values for both
m
m
enzymes are presented in Table 7. As observed from the
TABLE 7 Kinetic parameters and mode of enzymatic inhibition
Enzyme
Concentration (μM)
Control 10
V
max
K
m
Type of inhibition
Mixed
α-amylase
α-glucosidase
0.1743 0.1505
0.2953 0.1113
0.0004 0.0023
0.0128 0.0134
Control 10
Mixed

14 of 17
KAUR AND KAUSHAL
TABLE 8 Mode of interaction and interacting residues for enzymatic inhibition (where UNL = ligand LI–IV
)
Enzyme
Complex 1
Complex 2
Complex 3
Complex 4
α-amylase
-
H-Asp297, H-Asp340,
N-Arg344 with O-UNL
N-Gln35 with O-UNL
-
α-glucosidase
H-Asp232, H-Asp568 with O-UNL
O-Asp232 with
O V
O-Asp630, O-Lys506,
and O-Asp232
-
with O-NO
2
TABLE 9 In silico kinetic parameters of enzymatic inhibition
Energy of binding
(kcal/mol)
Inhibition
Electrostatic energy
(kcal/mol)
Torsional free energy
(kcal/mol)
Enzyme
Complex
constant (Ki)
242.29 nM
4.99 nM
α-amylase
1
2
3
4
1
2
3
4
−9.03
−11.33
−9.91
−7.21
−8.13
−8.84
−10.02
−6.46
−0.03
−0.44
−0.04
−3.11
+0.22
+0.10
+0.06
−0.46
+3.84
+4.39
+4.39
+4.39
+3.84
+4.39
+4.39
+4.39
54.82 nM
5.15 μM
α-glucosidase
1.09 μM
328.72 nM
45.49 nM
18.33 μM
FIGURE 9 Molecular docking model for complexes with α-glucosidase: (a) Complex 1, (b) Complex 2, (c) Complex 3 and
d) Complex 4
(

KAUR AND KAUSHAL
15 of 17
FIGURE 10 Molecular docking model for complex with α-amylase. (a) Complex 1, (b) Complex 2, (c) Complex 3 and (d) Complex 4
evident that there was a decrease in value of Vmax while
Km value increased with the increase in concentration of
inhibitor, which means it mimics the competitive
binding mode.
with Asp232 (2.61 Å), Asp568 (1.80 Å); Complex 2 have
shown H-bond with Asp232 (3.52 Å) respectively, whereas
no H-bond interaction has been seen for Complex 4
(Figure 8). Apart from H-bonding, many other hydrophobic
interactions viz van der Waals' interaction; Π-Π interac-
tions may be working inside the target cavity. Similarly,
docking studies with α-amylase enzyme were performed
to obtain the activity order of the complexes. Complex
2 with hydroxy group displayed the best and highest
binding energy at −11.33 kcal/mol. It formed an H-bond
with Asp297 (1.87 Å), Asp340 (2.08 Å) and Arg344
(3.22 Å) residues. Complex 3 showed H-bond with
Gln35 (2.65 Å), whereas Complexes 1 and 4 have not
shown any H-bonding. All the corresponding interactions
are displayed in Figures 9 and 10 for α-glucosidase and
α-amylase pdb files, respectively.
3.3.4 | In silico studies
In silico studies were performed using Autodock and
visualized in Chimera to determine the theoretically
binding mode between enzymes and complexes. The
interacting residues and free energy of binding of every
complex corresponding to the respective enzyme are
given in Tables 8 and 9, respectively. On the basis of
molecular docking results with α-glucosidase, the best Etotal
value was obtained for Complex 3 at −10.02 kcal/mol.
These results are the manifestation of the results of in vitro
α-glucosidase enzyme inhibition assay. Complex 3 has
adopted a stable conformation inside the binding pocket of
the target and displayed stable hydrogen bond between
O-atom of nitro group of complex and the O-atom of the
Asp630 amino acid residue with 2.92 Å bond lengths. Apart
from this, the possibility for H-bond with Lys506 (2.68 Å)
and Asp232 (2.85 Å) amino acids has been seen. The
activity order (in terms of Energy of binding values) was
followed by Complex 1, which have shown the H-bonds
4 | CONCLUSION
For concluding remarks, a series of chalcones and their
vanadyl complexes have been synthesized and evaluated
for α-amylase and α-glucosidase inhibitory activity.
Synthesized complexes were characterized using various
spectroscopic techniques and physical measurements
and found to display a square pyramidal geometry.

16 of 17
KAUR AND KAUSHAL
From in vitro studies, all the complexes found to pos-
sess promising activity against the α-amylase and
α-glucosidase enzyme with IC50 in range 3–9 μg/ml
and greater than 100 μg/ml against α-glucosidase and
α-amylase enzyme, respectively. These results were also
supported by the docking studies, and the investigation
revealed that the complex molecules interact with the
target enzyme through noncovalent H-bonding, van der
Waals' and hydrophobic interaction. In addition, DPPH
assay was performed to investigate the antioxidant
potential of the complexes. From the results, two
complexes (Complexes 2 and 4) have shown good anti-
oxidant potential. So, the vanadyl chalcone complexes
as expected have promising antidiabetic and antioxidant
agents.
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2
Mandeep Kaur: Conceptualization; data curation;
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DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
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5
ORCID
Mandeep Kaur https://orcid.org/0000-0003-4672-4787
Raj Kaushal https://orcid.org/0000-0003-0198-581X
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How to cite this article: Kaur M, Kaushal R.
Synthesis, characterization and α-amylase and
α-glucosidase inhibition studies of novel vanadyl
chalcone complexes. Appl Organomet Chem. 2020;
e6042. https://doi.org/10.1002/aoc.6042
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