Synthesis, characterization, and biological properties of oxidovanadium(IV) complexes of acetylsalicylhydroxamic acid (N-acetyloxy-2-hydroxybenzamide) as potential antimicrobials

Article abstract of DOI:10.1177/1747519820907563

New oxidovanadium(IV) complexes of composition [VO(AcSHA)₂] 1 and [VO(acac)(AcSHA)] 2 are synthesized by reactions of VOSO₄.5H₂O and [VO(acac)₂] with acetylsalicylhydroxamic acid AcSH₂A (C₆H₄(OH)(CONHOCOCH₃)) in a 1:2 molar ratio in absolute ethanol. The compounds are characterized by the Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, electron spin resonance, and mass spectrometry along with elemental analyses, molar conductivity, and magnetic moment measurements. The infrared spectra of the complexes suggest bonding through carbonyl and phenolic oxygen atoms (O,O coordination). The magnetic moment, electron spin resonance, and mass spectra of the complexes indicate that both exist as monomers, and a distorted square pyramidal geometry around vanadium is proposed. The thermal behavior of the complexes is studied by thermogravimetry and differential thermal analysis techniques under an N₂ atmosphere, yielding VO₂ as the decomposition product. The in vitro antimicrobial assays against pathogenic Gram-positive bacteria, Gram-negative bacteria, and fungi (minimum inhibitory concentration method) show the appreciable antimicrobial potential relative to the respective standard drugs, tetracycline hydrochloride, and fluconazole.

Full text of DOI:10.1177/1747519820907563

907563CHL0010.1177/1747519820907563Journal of Chemical ResearchPriya et al.
research-article2020
Research Paper
Journal of Chemical Research
1–11
© The Author(s) 2020
Article reuse guidelines:
sagepub.com/journals-permissions
Synthesis, characterization, and biological
properties of oxidovanadium(IV) complexes
of acetylsalicylhydroxamic acid
https://doi.org/10.1177/1747519820907563
DOI: 10.1177/1747519820907563
journals.sagepub.com/home/chl
(N-acetyloxy-2-hydroxybenzamide) as
potential antimicrobials
Bhanu Priya, Abhishek Kumar and Neeraj Sharma
Abstract
New oxidovanadium(IV) complexes of composition [VO(AcSHA)2] 1 and [VO(acac)(AcSHA)] 2 are synthesized by
reactions of VOSO4.5H2O and [VO(acac)2] with acetylsalicylhydroxamic acid AcSH2A (C6H4(OH)(CONHOCOCH3)) in
a 1:2 molar ratio in absolute ethanol. The compounds are characterized by the Fourier-transform infrared spectroscopy,
ultraviolet–visible spectroscopy, electron spin resonance, and mass spectrometry along with elemental analyses, molar
conductivity, and magnetic moment measurements. The infrared spectra of the complexes suggest bonding through carbonyl
and phenolic oxygen atoms (O,O coordination). The magnetic moment, electron spin resonance, and mass spectra of the
complexes indicate that both exist as monomers, and a distorted square pyramidal geometry around vanadium is proposed.
The thermal behavior of the complexes is studied by thermogravimetry and differential thermal analysis techniques under
an N2 atmosphere, yielding VO2 as the decomposition product. The in vitro antimicrobial assays against pathogenic Gram-
positive bacteria, Gram-negative bacteria, and fungi (minimum inhibitory concentration method) show the appreciable
antimicrobial potential relative to the respective standard drugs, tetracycline hydrochloride, and fluconazole.
Keywords
acetylsalicylhydroxamic acid, biological properties, oxidovanadium(IV) complexes, spectral studies
Date received: 15 September 2019; accepted: 28 January 2020
Corresponding author:
Department of Chemistry, Himachal Pradesh University, Shimla, India
Neeraj Sharma, Department of Chemistry, Himachal Pradesh University,
Summer Hill, Shimla 171005, India.
Email: neerajsharma_univ@yahoo.co.in

2
Journal of Chemical Research 00(0)
Introduction
The ever-increasing research interest in oxidovanadium(IV)
complexes is due to their prodigious biological and medici-
nal properties,1–4 such as insulin-mimetic,5–8 DNA binding
and cleavage activity,9–11 anticancer,12 antioxidant,13–15
antitrypanosomiasis,16,17 antileishmaniasis,18 antiamebia-
sis,19 antituberculosis,20 and anti-HIV21 activity inducing
apoptosis, inhibiting cell proliferation and preventing the
metastasis of cancer against various cell lines.22–24 The
model studies related to vanadium biochemistry providing
information on vanadium metabolism, toxicity, detoxifica-
tion, and catalytic activity have been reported.25 The
bis(maltolato) (BMOV), bis(ethylmaltolato) (BEOV), and
bis(allixinato)oxidovanadium(IV) are some of the most
studied insulin-enhancing oxidovanadium(IV) com-
plexes.26–28 A drug containing vitamin A and vanadium(IV)
salt having insulin-mimetic antidiabetic properties has been
reported.8 Oxidovanadium(IV) complexes as YopH tyros-
ine phosphatase inhibitors, a virulence factor produced by
pathogenic species of Yersinia, have also been described.29
The exponential progress in the medicinal chemistry of bio-
logically relevant vanadium complexes for therapeutic
applications is evident from numerous reports.30–33
On the contrary, hydroxamic acids with the functionality
RCC(O)N(RN)OH (RC =alkyl/aryl; RN =H or alkyl/aryl) are
an important and key class of weak organic acids that have
been well studied as bioligands. The distinctive chelating
ability34,35—due to keto–enol tautomerism exhibited by the
hydroxamic and hydroximic forms36—and the vast spectrum
of pharmacological, toxicological, and pathological proper-
ties of hydroxamic acids have fascinated researchers in the
design of new complexes of biological relevance.37–39
Biologically significant acetylated hydroxamic acids
synthesized from salicylhydroxamic acid using various
acetylating agents and different methodologies have been
reported.40,41 The reaction of salicylhydroxamic acid with
acetyl chloride in the presence of pyridine and ethyl acetate
forms acetylsalicylhydroxamic acid (AcSH2A) where
AcSH2A= C6H4(OH)(CONHOCOCH3), and the acetyl
group is located on the hydroxamic acid group. The vana-
dium hydroxamate complexes derived from acetohy-
droxamic acid (aceto-HAha), benzohydroxamic acid
(HBha), N-phenylbenzohydroxamic acid, 2-hydroxypyri-
dine N-oxide,42 nicotinohydroxamato, 4-nitrobenzohydrox-
amate, and 2-chloro-4-nitrobenzohydroxamate ligands are
also well-documented.43,44
As a part of our continuing work on vanadium hydroxa-
mates,45–47 we herein report the synthesis of new
bis(acetylsalicylhydroxamato) and the mixed-ligand (acety-
lacetonato)(acetylsalicylhydroxamato)oxidovanadium(IV)
complexes using two different vanadium precursors along
with their characterization by the Fourier-transform infrared
spectroscopy (FTIR), ultraviolet–visible spectroscopy
(UV-Vis), electron spin resonance (ESR), and mass spectral
techniques. The electrochemical and thermal behavior of
the complexes has also been studied. The antimicrobial and
antioxidant potential of the complexes has been assayed
against some pathogenic bacteria and fungi by minimum
inhibitory concentration (MIC) method and DPPH
Scheme 1. Synthesis of oxidovanadium(IV) complexes.
(1,1-diphenyl-2-picrylhydrazyl) free radical scavenging
method, respectively.
Results and discussion
The reactions of VOSO4.5H2O and VO(acac)2 with 2 equiv.
of AcSH2A in absolute ethanol in separate experiments
gave dark blue complexes of composition [VO(AcSHA)2]
1 and [VO(acac)(AcSHA)] 2, respectively, in quantitative
yields and are consistent with their elemental analysis
(Scheme 1).
The molar conductance values of the complexes meas-
ured in methanol were 3.92 and 3.90Scm2 mol−1, respec-
tively, suggesting their non-electrolytic nature.48 At the
room temperature, magnetic moment of 1.70 and 1.72BM
(Bohr magneton) for complexes 1 and 2 is well within
the range reported for monomeric oxidovanadium(IV)
complexes.49
Infrared spectra
A comparison of the infrared (IR) spectra of the complexes
with that of the ligand supports their formation. Free
AcSH2A exhibited bands due to ν(OH)phenolic, ν(N–H),
ν(C=O)acetyl, ν(C=O)hydroxamic, ν(C–N), and ν(N–O) modes
at 3423, 3345, 1773, 1645, 1348, and 954cm−1, respec-
tively, whereas the complexes [VO(AcSHA)2] and
[VO(acac)(AcSHA)] displayed the respective bands at
3274, 1770, 1603, 1371, and 907cm−1 and 3392, 1770,
1660–1626, 1348–1342, and 917cm−1, as presented in
Tables 1 and 2, respectively.
The nonobservance of the band due to the ν(OH) mode
in complexes 1 and 2 is indicative of deprotonation of the
phenolic hydrogen, involving bonding through the phenolic
oxygen. The ν(C=O)hydroxamic mode in complex 1 shifted to
a lower wavenumber by 42cm−1 and the ν(C–N) mode
shifted to a higher wavenumber by 23cm−1 as compared to
the ligand. The absorption band due to ν(C=O)acetyl occurred
at 1770cm−1, showing an insignificant shift from the ligand
and suggesting the nonparticipation of the acetyl group in
bonding (see Figure S1(a)–(c) in the supporting informa-
tion). The shift in the ν(N–O) mode to a lower wavenumber
by 47cm−1 is contrary to earlier reports wherein the ν(N–O)
mode shifts to a higher wavenumber upon complexation.
The occurrence of the ν(N–H) mode is suggestive of its
retention upon complexation. The absorption bands due to
the ν(V=O) mode occurred at 970 and 957cm−1, respec-
tively. However, this observation is in contrast to those for
Co(II), Ni(II), Cu(II), and Zn(II) complexes of AcSH2A
wherein tridentate bonding behavior of ligand has been
reported.40

Priya et al.
3
Table 1. IR spectral data of the ligand (AcSH2A) and the complexes 1 and 2.
Ligand/complex
(AcSH2A)
Bands (cm−1)
3423, 3345, 3189, 3071, 1773, 1645, 1625, 1596, 1537, 1486, 1348, 1307, 1244, 1141, 1123, 1030, 954,
864, 748, 675, 637, 578, 502, 445, 419
[VO(AcSHA)2]
3274, 3050, 2941, 2866, 2729, 2583, 1770, 1603, 1463, 1371, 1308, 1231, 1185, 1156, 1097, 1051, 1031,
970, 907, 857, 782, 744, 688, 596, 546, 461, 422
[VO(acac)(AcSHA)]
3392, 3182, 3071, 2793, 2464, 1770, 1660, 1626, 1596, 1490, 1348, 1342, 1213, 1154, 1119, 1032, 1012,
957, 917, 867, 748, 676, 578, 504, 444
Table 2. Important IR frequencies (cm−1) of the ligand (AcSH2A) and the complexes 1 and 2.
Ligand/complex
ν(OH)hydroxamic
ν(N–H)
ν(C=O)acetyl
ν(C=O)hydroxamic
ν(C–N)
ν(N–O)
(AcSHA)
3423
–
–
3345
3274
3392
1773
1770
1770
1645
1603
1660–1626
1348
1371
1348–1342
954
907
917
[VO(AcSHA)2]
[VO(acac)
(AcSHA)]
Table 3. UV-Vis spectral data of the ligand (AcSH2A) and the
complexes 1 and 2.
Table 4. Mass spectral data of the complex [VO(AcSHA)2] 1.
Complex
m/z
Intensity (%)
Ligand/complex
Λ (nm)
[VO(AcSHA)2 +Na]+
[VO(AcSHA)2 −6H]+
[2AcSHA]
479
451
390
354
262
234
218
4.3
21.7
8.6
60.8
34.7
20
(AcSH2A)
[VO(AcSHA)2]
[VO(acac)(AcSHA)]
319
270, 308, 478, 735
305, 316, 425, 720
[2(AcSHA)−2CH3 −4H]+
[VO(AcSHA)]+
[AcSHA+K]+
[AcSHA+Na]+
100
Electronic spectra
The UV-Vis spectra of the ligand (AcSH2A) recorded in
absolute ethanol displayed an absorption band at 319nm
attributed to an intra-ligand π→π* transition. Complexes 1
and 2 exhibited bands at 270, 308, 478, and 735nm and
305, 316, 425, and 720nm in the UV-Vis region, respec-
tively (Table 3). The high-energy intra-ligand bands at 270
and 308nm and 305 and 316nm occurred in complexes 1
and 2, respectively, are contrary to previous reports.49,50
The bands appeared in the visible region may be assigned
[VO(acac)+K+ −3H]+, respectively (Scheme 3) (see
Figure S3 in the supporting information).
ESR spectra
At the room temperature, X-band ESR spectra of com-
plexes 1 and 2 displayed the well-resolved typical eight
lines due to the interaction of an unpaired electron of the
vanadium(IV) center with its own nucleus, that is, I=7/2
indicative of the mononuclear oxidovanadium(IV). The
nuclear magnetic quantum numbers analogous to these
lines are −7/2, −5/2, −3/2, −1/2, +1/2, +3/2, +5/2, and
+7/2 from low to high field. The complex 1 showed
g‖=1.94 and A‖ (×10−4 cm−1)=163 and g┴=1.98 and A┴
(×10−4 cm−1)=65. The complex 2 exhibited g‖=1.96 and
A‖=161 and g┴=1.98 and A┴=67. The giso values calcu-
lated from the spectra for complexes 1 and 2 of same mag-
nitude 1.96 are close to the spin-only value (free electron
value of 2.0023; Table 6).
2
2
to B2 →2A1 (3dxy→3dz2) and B2 →2E (3dxy→3dxz,
3dyz) d–d transitions, respectively, and a plausible square
pyramidal geometry around vanadium is proposed.51,52
Mass spectra
The electrospray ionization (ESI) mass spectrum of com-
plex 1 exhibited a molecular ion peak at m/z (%), that is,
479 (4.3), corresponding to [VO(AcSHA)2 +Na]+. The
most abundant peak at 218 (100) corresponded to
[AcSHA+Na]+, which is presented in Table 4.
The other structurally important fragment ions at
m/z (%) 451 (21.7), 390 (8.6), 354 (60.8), 262 (34.7), and
234 (20) corresponded to [VO(AcSHA)2 −6H]+,
[2AcSHA], [2AcSHA−2CH3 −4H]+, [VO(AcSHA)]+, and
[AcSHA+K]+, respectively, as clearly shown in Scheme 2
(see Figure S2 in the supporting information).
The observed order A‖>A┴ and g┴>g‖ suggests that
the unpaired electron lies in the dxy orbital corresponding to
the square pyramidal geometry around vanadium in com-
plexes 1 and 2 in agreement with the reports on
oxidovanadium(IV) chelates.53,54
The mass spectrum of complex 2 displayed the molecu-
lar ion and the base peak at m/z (%) 360 (18) and 302 (100)
corresponding to [VO(acac)(AcSHA)] and [VO(acac)
(AcSHA)−OCOCH3 −H]+, respectively (Table 5).
Cyclic voltammetry
The free ligand (AcSH2A) displayed one reductive wave
and one oxidative wave at −0.61 and −0.51V, respectively.
The complex 1 exhibited two reduction waves at −0.48 and
The other fragment ions at m/z (%) 230 (25.4) and
202 (21.8) corresponded to [AcSHA+K+ −4H]+ and

4
Journal of Chemical Research 00(0)
Scheme 2. Mass spectral fragmentation pattern of complex 1.
Table 5. Mass spectral data of complex [VO(acac)(AcSHA)] 2.
transfer process and also adjudged from the peak current
ratio Ipa/Ipc. The electrode process can be represented as
Complex
m/z
Intensity (%)
IV
V




VO L
VO L
→




[VO(acac)(AcSHA)]
360
302
230
202
18
100
25.4
21.8
[VO(acac)(AcSHA)−OCOCH3 −H]+
[AcSHA+K+ −4H]+
The E1/2 value of 519mV may be assigned to metal-cen-
tered oxidation of VIV to VV lying within the range reported
for related complexes.55 Based upon physicochemical and
various spectral techniques, a distorted square pyramidal
geometry in both the mononuclear complexes has been pro-
[VO(acac)+K+ −3H]+
+0.69V and one oxidation wave at −0.551V. The complex posed around the vanadium (Figures 4 and 5).
[VO(acac)(AcSHA)] 2 exhibited reductive and oxidative
waves at +0.62 and −0.26V, respectively (Table 7 and
Figures 1–3).
Thermogravimetric studies
The peak-to-peak separation value (ΔEp =79mV) is The complexes 1 and 2 have shown the thermal stability up
indicative of a single-step pseudo-reversible one-electron to 60°C and 85°C, respectively, after which these

Priya et al.
5
complexes went decomposition in two steps. The mass as well as the role of the ligand in various redox and uptake
loss of 45% in the first step in complex 1 in the tempera- processes, wherein the active species formed depend upon
ture range of 60°C–427°C analogous to the dissociation of the thermodynamic stability of vanadium complexes and
one
acetylsalicylhydroxamate
ligand
yielding the potential of ligand to cross the cell membrane in bodily
[VO(AcSHA)] as the likely unstable intermediate. The fluids at physiological pH.57–69 The oxidovanadium(IV)
mass loss of 36.9% in the second step, between 427°C and hydroxamates43,45–47,70,71 have drawn considerable attention
646°C, accounted for the decomposition of another owing to their interesting biological activity over the last
AcSH2A ligand to yield VO2 as the final residue. The for- few years. In pursuit of new vanadium-based antimicrobi-
mation of VO2 as thermolyzed product of vanadium(IV) als, the antimicrobial activity of the complexes 1 and 2 has
hydroxamate complexes has been authenticated by record- been assayed.
ing the IR spectra of the residue. The sharp absorption
bands appeared at ~992cm−1 due to ν(V=O) mode and the Antibacterial activity. The uncoordinated ligand (AcSH2A)
other bands appeared at 675, 658, 620, 520, and 322cm−1 showed inhibitory effects against the test bacteria at MIC
are in line with earlier reports on the IR spectra of VO2.56 125µg/mL. The complex 1 affected the growth inhibition
The thermal decomposition pattern of complex 1 is pre- of Bacillus cereus and Escherichia coli at MIC 31.25µg/
sented in Scheme 4.
mL, while that of Staphylococcus aureus, Pseudomonas
A broad exothermic peak at 556.0°C in differential ther- aeruginosa, and Salmonella typhi occurred at 15.63µg/mL,
mal analysis (DTA) curve corroborated thermal decompo- which may be attributed to the difference in the diffusion of
sition in thermogravimetry. The mass loss of 57.73% in the complex through the cell wall of these bacteria. The
complex 2 in the first step in the temperature range of complex 2 has been found to be quite effective against E.
85°C–400°C accounted for the removal of one acetylsali- coli and S. typhi at MIC 31.25µg/mL compared to B.
cylhydroxamate ligand yielding [VO(acac)] as the probable cereus, P. aeruginosa, and S. aureus at 62.5µg/mL. The
unstable intermediate. The mass loss of 27.57% in the sec- reference drug tetracycline hydrochloride inhibited test
ond step, between 400°C and 617°C corresponded to the bacteria at MIC 3.90–15.63µg/mL (Table 9 and Figure 8).
decomposition of the acetylacetonate ligand to yield VO2
as the final residue. The thermal decomposition pattern of teria and highly effective against B. cereus better than the
complex 2 is presented in Scheme 5. standard drug. The growth inhibition by complex 1 is
The complex 1 is quite effective against all the test bac-
The two-step decomposition in the thermogravimetric prominent against S. aureus (Gram-positive) and S. typhi
analysis (TGA) is accompanied by an exothermic inflection (Gram-negative) relative to the free ligand and the complex
at 133°C and a broad peak at 577°C in the DTA curve 2. The enhanced inhibitory activity of the complexes can be
(Table 8 and Figures 6 and 7).
ascribed to the reduction of the polarity in the metal ion and
increased delocalization of π electrons over the whole che-
late ring, thereby increasing the lipophilicity and allowing
efficient diffusion of the complex into the bacterial cell
Biological studies
Literature contains numerous reports on the transport of the wall.72,73
pharmacologically active vanadium(IV) and (V) complexes
Antifungal activity. The antifungal activity of the free ligand
and the complexes 1 and 2 has been studied against Rhizoc-
tonia solani and Fusarium sambucinum. The ligand
(AcSH2A) inhibited these fungi with MIC values of 62.5
and 15.62μg/mL, respectively. The complexes 1 and 2
have shown enhanced inhibitory effects against the test
fungi at MIC values of 7.81, 15.62, and 31.25μg/mL,
respectively (Table 10 and Figure 9). The standard drug
fluconazole inhibited these fungi at MIC 3.90μg/mL.
Antioxidant activity. The antioxidant activity of the free
ligand and the complexes 1 and 2 studied by the DPPH
method showed a low scavenging potential (∼4.9%–
26.3%) for the ligand, which was significantly enhanced
(∼29.4%–45.3% and ∼10.4%–43.28%) in complexes
through the oxidation of V(IV)O2+ to V(V)O+. The
Scheme 3. Mass spectral fragmentation pattern of complex 2.
Table 6. ESR spectral data of oxidovanadium(IV) complexes 1 and 2.
2g ⊥ +g
‖
Complex
g‖
g┴
∆g=g┴−g‖
A‖ (×10−4 cm−1)
A┴ (×10−4 cm−1)
giso
=
3
[VO(AcSHA)2]
[VO(acac)(ACSHA)]
1.94
1.96
1.98
1.97
0.04
0.01
1.96
1.96
163
161
65
67

6
Journal of Chemical Research 00(0)
Table 7. Cyclic voltammetric data of ligand (AcSH2A) and
oxidovanadium(IV) complexes 1 and 2.
Ligand/complex Epa (V) Epc (V) ΔE (V) Ipa (A) Ipc (A) Ipa/Ipc
(AcSH2A)
−0.51 +0.61
1.110 0.85 3.83 0.22
[VO(AcSHA)2] −0.551 +0.690 −1.250 1.25 4.01 0.31
[VO(acac)
(AcSHA)]
−0.260 +0.62 −0.880 3.30 5.09 0.65
Figure 1. Cyclic voltammogram of the free ligand (AcSH2A).
Figure 4. Chemcraft structure of the complex 1
[VO(AcSHA)2].
Figure 5. Chemcraft structure of the complex 2 [VO(acac)
(ACSHA)].
Figure 2. Cyclic voltammogram of the complex 1
[VO(AcSHA)2].
Figure 3. Cyclic voltammogram of the complex 2 [VO(acac)
(ACSHA)].
complex 1 exhibited high activity compared to the free
ligand and the complex 2 (Table 11).
This is in agreement with the fact that large conjugated
systems upon chelation with metal ions promote the
Scheme 4. Thermal decomposition pattern of complex 1.

Priya et al.
7
trapping of free radicals, which results in discoloration the ν(C=O)hydroxamic, and a shift of the ν(N–O) and ν(C–N)
from the purple DPPH radical solution to a yellow solution modes to a higher frequency, without any significant change
showing scavenging of DPPH radicals by hydrogen in ν(C=O)acetyl. This indicates that the acetylsalicylhy-
donation.
droxamic acid acts as a bidentate chelating ligand involving
bonding through carbonyl and phenolic oxygen atoms
(O,O). From spectral studies, a distorted square pyramidal
geometry may tentatively be proposed around vanadium.
The complexes are electrochemically active and exhibit
single-step pseudo-reversible one-electron transfer pro-
cesses. The thermal behavior of complexes 1 and 2 studied
by the thermogravimetric technique and showed a two-step
decomposition to yield VO2 as the residue. The in vitro
antibacterial assay of the free ligand and the complexes 1
and 2 has shown that the growth inhibition by complex 1 is
prominent against S. aureus (Gram-positive) and S. typhi
(Gram-negative) relative to the free ligand and the complex
2. The in vitro antifungal activity of the ligand and com-
plexes evaluated against R. solani and F. sambucinum
showed that the complex 1 exhibits good inhibitory effects
against both the fungi in contrast to complex 2. The results
reveal these new complexes as promising antimicrobial
agents to be explored further for medicinal applications. It
has been further elucidated that the complex 1 exhibited
high antioxidant activity compared to the free ligand and
the complex 2.
Conclusion
The oxidovanadium(IV) complexes of composition
[VO(AcSHA)2] and [VO(acac)(AcSHA)] derived from
acetylsalicylhydroxamic acid [C6H4(OH)CONHOCOCH3]
have been synthesized and thoroughly characterized by
various physicochemical and spectroscopic techniques
(FTIR, UV-Vis, ESR) and mass spectrometry. IR data
showed the disappearance of the ν(OH)phenolic, lowering of
Experimental details
Materials and methods
All chemicals of reagent grade were used. Vanadyl sulfate
(VOSO4.5H2O; Merck) was used as procured. [VO(acac)2]
and
acetylsalicylhydroxamic
acid
[C6H4(OH)
CONHOCOCH3] were synthesized by reported meth-
ods,74,75 and characterized by microanalyses and IR spec-
troscopy. The vanadium content in the complexes was
Scheme 5. Thermal decomposition pattern of complex 2.
Figure 6. TGA and DTA curves of complex 1 [VO(AcSHA)2].

8
Journal of Chemical Research 00(0)
Figure 7. TGA and DTA curves of complex 2 [VO(acac)(ACSHA)].
Table 8. Thermal data of oxidovanadium(IV) complexes 1 and 2.
Complex
Initial
Stages of
Observed
Decomposition
Peak nature in
Decomposition
decomposition decomposition mass loss (%) temperature range
DTA (exothermic, product
°C)
temperature
60°C
(°C)
60–427
[VO(AcSHA)2]
I
45
–
[VO(AcSHA)]
II
I
II
36.9
57.73
27.57
427–646
85–400
400–617
556
133
577
VO2
[VO(acac)]
VO2
[VO(acac)(AcSHA)] 85°C
DTA: differential thermal analysis.
solution in methanol) of the complexes was obtained
using a conductivity bridge (Type CM-82T; Elico) at
25°C±0.1°C. At the room temperature, magnetic suscep-
tibility was measured by Gouy’s method,76 using
Hg[Co(NCS)4] as a calibrant. The IR spectra were
recorded as KBr pellets using a FTIR spectrophotometer
(PerkinElmer). Electronic spectra were recorded using a
100 Bio UV-Vis spectrophotometer (Varian Cary) in abso-
lute ethanol. ESI mass spectra were recorded using a
Micromass Quattro-TOF (Waters), with a mass range of
4000amu in quadrupole and 20,000amu in Tandem time-
of-flight (TOF). At the room temperature, powder X-band
ESR spectra were recorded using an E112 ESR spectrom-
eter (Varian). The cyclic voltammetric measurements
were performed at 25°C on an Autolab Potentiostat 128N
electrochemical analyzer using a single compartmental
cell of volume 10–15mL, comprising a three-electrode
system of a Pt-disk as the working electrode, Pt-wire as an
auxiliary electrode, and Ag/AgCl electrode as the refer-
ence electrode. Potassium chloride (KCl; 0.4M) was used
as the supporting electrolyte in the methanol/H2O (5:95)
electrolyte system. Thermograms (TGA and DTA curves)
of the complexes were recorded using a Diamond TG/
DTA thermogravimetric analyzer (PerkinElmer) at a
Figure 8. Bar diagram showing the in vitro antibacterial activity
studies of the free ligand and the complexes 1 and 2.
determined as V2O5 by decomposing the complex with a
mixture of concentrated H2SO4 and concentrated HNO3.
The carbon, hydrogen, and nitrogen analyses were
obtained using the CHN elemental analyzer (FLASH
2000; Thermo Scientific). The molar conductance (10−3 M

Priya et al.
9
Table 9. Antibacterial activity data determined by the MIC method.
Ligand/complex
MIC±SD (μg/mL)
Gram-positive
B. cereus
Gram-negative
S. aureus
E. coli
125±0.2
31.25±0.05
62.5±0.5
P. aeruginosa
S. typhi
125±0.4
15.63±0.05
62.5±0.5
(AcSH2A)
[VO(AcSHA)2]
[VO(acac)(AcSHA)]
Tetracycline hydrochloride
125±0.3
3.90±0.2
62.5±0.45
7.84±0.02
125±0.5
15.63±0.4
31.25±0.02
15.63±0.01
125±0.04
15.63±0.3
62.5±0.2
7.84±0.4
15.63±0.03
15.63±0.2
MIC: minimum inhibitory concentration; SD: standard deviation.
solution. After cooling to 0°C, acetyl chloride (2.4mL,
34mmol) was added. The mixture was stirred at 0°C for
30min, followed by stirring at room temperature.75,77 To this
solution, ethyl acetate (30mL), 5% HCl (90mL), and a satu-
rated solution of sodium chloride (120mL) were added. The
aqueous phase was separated from the organic phase through
separating funnel and dried over magnesium sulfate. The sol-
vent was removed using a rotary evaporator to afford a
cream-colored solid that was recrystallized from ethyl
acetate.
Yield=2.2g (32%). Decomposition Temp.=135°C. The
formation of acetylsalicylhydroxamic acid [N-(acetoxy)-2-
hydroxybenzamide] was established by the elemental anal-
ysis, IR, and 1H nuclear magnetic resonance (NMR)
spectroscopy. Anal. calcd for [C6H4(OH)CONHOCOCH3]:
C, 55.20; H, 4.90; N, 7.28; found: C, 54.85; H, 4.65; N,
7.00%. IR (KBr disk): 1805, 1795, 1650, 1620, 1200cm−1.
1H NMR (MHz CDCl3): δ 2.45 (s, 3H, CH3) and 7–8 (m,
4H, ArH).
Figure 9. Bar diagram showing the in vitro antifungal activity
studies of the free ligand and the complexes 1 and 2.
Table 10. Antifungal activity determined by the MIC method.
Synthesis of [VO(AcSHA)2] from VOSO4.5H2O. To a solu-
tion of VOSO4.5H2O (1 g, 3 mmol) in absolute ethanol
(10 mL) was added 2 equiv. of AcSH2A (1.5 g, 7 mmol)
dissolved in absolute ethanol (10 mL). The reaction mix-
ture was stirred for 1 h and then refluxed for 8–10 h. The
excess solvent was removed by distillation. To the con-
centrate was added petroleum ether (20 mL), and the
product was dried under vacuum. A dark blue solid was
obtained.
Yield=1.2g (67%), Decomposition Temp.=145°C,
Mol. Mass [C18H16N2O9V]=457, Anal. calcd for
[C18H16N2O9V]: C, 50.05; H, 4.35; N, 3.29; V; 14.32;
found: C, 49.56; H, 4.00; N, 3.00; V, 13.98%. ΛM (MeOH):
3.92Scm2 mol−1; µeff (293K): 1.70BM.
Ligand/complex
MIC±SD (μg/mL)
R. solani
F. sambucinum
(AcSH2A)
62.5±0.3
7.81±0.01
31.25±0.5
3.90±0.2
15.62±0.04
15.62±0.2
31.25±0.3
3.90±0.01
[VO(AcSHA)2]
[VO(acac)(AcSHA)]
Fluconazole
MIC: minimum inhibitory concentration; SD: standard deviation.
Table 11. Antioxidant activity data of the free ligand and the
complexes 1 and 2 using DPPH.
Ligand/complex
Scavenging potential (%)
(AcSH2A)
[VO(AcSHA)2]
[VO(acac)(AcSHA)]
~4.9–26.3
~29.4–45.3
~10.4–43.28
Synthesis of [VO(acac)(AcSHA)] from [VO(acac)2]. To a solu-
tion of VO(acac)2 (0.5g, 1mmol) in absolute ethanol
(10mL) was added 2 equiv. of AcSH2A (1g, 5mmol) dis-
solved in absolute ethanol (10mL). The reaction mixture
was stirred for 1h and then refluxed for 8–10h. The excess
solvent was removed by distillation. To the concentrate was
added petroleum ether (20mL), and the product was dried
under vacuum whereupon a dark blue complex was formed.
Yield=0.50g (72%), Decomposition Temp.=157°C,
Mol. Mass [C14H15NO7V]=360, Anal. calcd for
[C14H15NO7V]: C, 50.40; H, 4.27; N, 3.25; V; 14.50; found:
C, 50.06; H, 3.95; N, 3.05; V, 13.90%. ΛM (MeOH):
3.90Scm2 mol−1; µeff (293K): 1.72BM.
heating rate of 10°C/min from ambient temperature to
800°C under an N2 atmosphere.
Synthesis
Synthesis of (AcSH2A). To pyridine (15mL) was added sali-
cylhydroxamic acid (5g, 32.7mmol), and the reaction mix-
turewasstirredatroomtemperaturetoformanorange-colored

10
Journal of Chemical Research 00(0)
517nm. All the tests were carried out in triplicate. Ascorbic
acid was used as a standard or positive control. The ability
to scavenge the DPPH radical was calculated using the fol-
lowing equation
Biological assay
Antibacterial activity. The free ligand AcSH2A and the
oxidovanadium(IV) complexes [VO(AcSHA)2] and
[VO(acac)(AcSHA)] were screened in vitro for the antibac-
terial and antifungal activity against the selected Gram-
positive bacteria (S. aureus and B. cereus), Gram-negative
bacteria (E. coli, P. aeruginosa, and S. typhi), and fungi (R.
solani and F. sambucinum) at different concentrations in
dimethyl sulfoxide (DMSO) employing the MIC
method.78,79 The MIC is the lowest concentration of the
antimicrobial agent that prevents the development of visi-
ble growth of microbes after overnight incubation. The
samples were tested in triplicate.
A
control − Asample






I(%)=
×100
Acontrol
where Acontrol is the absorbance of the control, and Asample is
the absorbance of the sample.
Acknowledgements
The authors thank the IIT Mandi for recording Fourier-transform
infrared spectroscopy (FTIR), mass spectra, and elemental analy-
ses. The authors gratefully acknowledge the support of the
Department of Biotechnology, Himachal Pradesh University,
Shimla, for providing laboratory facilities to carry out biological
studies.
Method. A sterile flat bottom 96-well microtiter plate was
labeled as 1–7, in which wells 1–5 are allotted for the test
sample, 6 for the positive control (broth+standard antibi-
otic (2μL)+microorganism), and 7 for the negative con-
trol (broth+microorganism). Then, 30µL of media was
added to each well, including the positive and negative con-
trols. A stock solution of the sodium salt of Resazurin dye
as an indicator (0.02% (wt/mol); Sigma Aldrich)80 was pre-
pared in distilled water, filtered, sterilized, and stored at
4°C for 1week. This dye (5µL) was added to each well.
The test samples were added in twofold dilution to wells
(1–5). The plates were then wrapped with aluminum foil
and incubated at 37°C for 24h in the case of bacteria and at
28°C for 72h for fungi. A change in color in the wells of the
positive control indicated the proper growth of the isolate,
and no change in color of wells of the negative control indi-
cated the absence of contaminants. The results were com-
pared with the standard antibacterial drug tetracycline
hydrochloride and the antifungal drug fluconazole.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
ORCID iD
Neeraj Sharma
https://orcid.org/0000-0002-5410-6674
Supplemental material
Supplemental material for this article is available online.
References
Statistical analysis. Statistical analysis was performed using
the standard t-test, and p<0.05 was considered significant.
The data are represented as standard deviation.
1. Wai-Yin Sun R, Ma D-L, Wong EL-M, et al. Dalt Trans
2007; 4884.
2. Rehder D. Inorganica Chim Acta 2017; 455: 378–389.
3. Pessoa JC, Etcheverry S and Gambino D. Coord Chem Rev
2015; 301–302: 24–48.
Antioxidant activity. The free radical scavenging activity of
the complexes is measured in terms of hydrogen donation
or radical scavenging ability using the stable DPPH radical
as described by Blois.81 DPPH is usually used as a substrate
to evaluate antioxidant activity. DPPH (1,1-diphenyl-2-pic-
rylhydrazyl) having an unpaired electron displays a strong
absorption band at 517nm, which decreases stoichiometri-
cally upon pairing of the electron.82,83 A change in the
absorbance produced in the reaction is widely used to test
the ability of molecules to act as free radical scavengers.
The newly synthesized oxidovanadium complexes in +4
oxidation state can donate an electron to reduce the DPPH
radical to DPPH (α,α-diphenyl-β-picrylhydrazine), and the
VO(IV) ion is oxidized to VO(V). The stock solutions of
the complexes (0.001g/mL) were prepared in DMSO, from
which different concentrations (20–100µL) being pre-
pared. A solution of DPPH (0.1mmol) in methanol was
prepared, and 1mL of this solution was added to each of the
test solutions. The mixture was shaken vigorously and
incubated for 30min. The absorbance was measured at
4. Rehder D. Dalt Trans 2013; 42: 11749.
5. Crans DC. J Org Chem 2015; 80: 11899–11915.
6. Kiss T, Enyedy ÉA and Jakusch T. Coord Chem Rev 2017;
352: 401–423.
7. Sanna D, Buglyó P, Micera G, et al. JBIC J Biol Inorg Chem
2010; 15: 825–839.
8. Adam AMA, Naglah AM, Al-Omar MA, et al. Int J
Immunopathol Pharmacol 2017; 30: 272–281.
9. Devi RKB, Devi SP and Singh RKH. Spectrosc Lett 2012;
45: 93–103.
10. Sasmal PK, Saha S, Majumdar R, et al. Inorg Chem 2010;
49: 849–859.
11. Butenko N, Tomaz AI, Nouri O, et al. J Inorg Biochem 2009;
103: 622–632.
12. Evangelou AM. Crit Rev Oncol Hematol 2002; 42: 249–265.
13. Martínez Medina JJ, Naso LG, Pérez AL, et al. J Inorg
Biochem 2017; 166: 150–161.
14. Naso LG, Lezama L, Valcarcel M, et al. J Inorg Biochem
2016; 157: 80–93.
15. Savithri K and Revanasiddappa HD. Bioinorg Chem Appl
2018; 2018: 1–12.

Priya et al.
11
16. Fernández M, Becco L, Correia I, et al. J Inorg Biochem 51. Stoklosa HJ, Wasson JR and McCormick J. Inorg Chem
2013; 127: 150–160.
1974; 13: 592–597.
17. Fernández M, Varela J, Correia I, et al. Dalt Trans 2013; 42: 52. Cheng SH, Sheen SR, Cheng CP, et al. Inorganica Chim
11900.
Acta 1990; 171: 21–24.
18. Scalese G, Benítez J, Rostán S, et al. J Inorg Biochem 2015; 53. Raman N, Raja SJ, Joseph J, et al. Russ J Coord Chem 2007;
147: 116–125.
33: 7–11.
19. Machado P, de A, Mota VZ, et al. Acta Trop 2015; 148: 120– 54. Sheela A, Sarada NC and Vijayaraghavan R. Med Chem Res
127.
2013; 22: 2929–2937.
20. Maurya MR, Haldar C, Khan AA, et al. Eur J Inorg Chem 55. Kianfar AH and Mohebbi S. J Iran Chem Soc 2007; 4: 215–
2012; 2012: 2560–2577.
220.
21. Correia I, Adão P, Roy S, et al. J Inorg Biochem 2014; 141: 56. Botto I, Vassallo M, Baran E, et al. Mater Chem Phys 1997;
83–93.
50: 267–270.
22. D’Cruz OJ and Uckun FM. J Appl Toxicol; 21: 317–22.
23. Chien P-S, Mak O-T and Huang H-J. Biochem Biophys Res
Commun 2006; 339: 562–568.
57. Levina A, Crans DC and Lay PA. Coord Chem Rev 2017;
352: 473–498.
58. Levina A and Lay PA. Chem—Asian J 2017; 12: 1692–1699.
24. Chakraborty T, Swamy AHMV, Chatterjee A, et al. J Cell 59. Gonçalves G, Tomaz I, Correia I, et al. Dalt Trans 2013; 42:
Biochem 2007; 101: 244–258.
11841.
25. Baran EJ. J Braz Chem Soc 2003; 14: 878–888.
26. Winter PW, Al-Qatati A, Wolf-Ringwall AL, et al. Dalt
Trans 2012; 41: 6419.
60. Costa Pessoa J, Gonçalves G, Roy S, et al. Inorganica Chim
Acta 2014; 420: 60–68.
61. Costa Pessoa J. J Inorg Biochem 2015; 147: 4–24.
27. Peters KG, Davis MG, Howard BW, et al. J Inorg Biochem 62. Le M, Rathje O, Levina A, et al. JBIC J Biol Inorg Chem
2003; 96: 321–330.
2017; 22: 663–672.
28. Thompson KH, Lichter J, LeBel C, et al. J Inorg Biochem 63. Doucette KA, Hassell KN and Crans DC. J Inorg Biochem
2009; 103: 554–558.
2016; 165: 56–70.
29. Martins PGA, Mori M, Chiaradia-Delatorre LD, et al. ACS 64. Jakusch T, Costa Pessoa J and Kiss T. Coord Chem Rev
Med Chem Lett 2015; 6: 1035–1040.
2011; 255: 2218–2226.
30. Treviño S, Díaz A, Sánchez-Lara E, et al. Biol Trace Elem 65. Jakusch T and Kiss T. Coord Chem Rev 2017; 351: 118–126.
Res 2019; 188: 68–98.
66. Sanna D, Micera G and Garribba E. Inorg Chem 2009; 48:
5747–5757.
67. Sanna D, Ugone V, Micera G, et al. Dalt Trans 2017; 46:
8950–8967.
68. Sanna D, Palomba J, Lubinu G, et al. J Med Chem 2019; 62:
654–664.
69. Mehtab S, Gonçalves G, Roy S, et al. J Inorg Biochem 2013;
121: 187–195.
70. Gaballa AS, Teleb SM, Asker MS, et al. J Coord Chem
2011; 64: 4225–4243.
71. Hassan LR, Ramasamy K, Lim SM, et al. J Teknol 2018; 80:
6.
72. Chohan ZH, Supuran CT and Scozzafava A. J Enzyme Inhib
Med Chem 2004; 19: 79–84.
73. Chohan ZH, Mahmood-ul-Hassan Khan KM and Supuran
CT. J Enzyme Inhib Med Chem 2005; 20: 183–188.
74. Rowe RA and Jones MM. In: Inorganic Syhtheses, 1957, p.
114.
31. Sharma D, Revanasiddappa HD, Kumar BCV, et al.
Biointerface Res Appl Chem 2019; 9: 3776–3782.
32. La M, Wang P-P and Xue L-W. Inorg Nano-Metal Chem
2019; 1–5.
33. Lima S, Banerjee A, Mohanty M, et al. New J Chem 2019;
43: 17711–17725.
34. Edwards DC and Myneni SCB. J Phys Chem A 2005; 109:
10249–10256.
35. Agarwal YK and Sharma CK. Indian J Chem 2007; 46A:
1772–1777.
36. Bauer L and Exner O. Angew Chemie Int Ed English 1974;
13: 376–384.
37. Muri EMF, Nieto MJ, Sindelar RD, et al. Curr Med Chem
2002; 9: 1631–1653.
38. Senger J, Melesina J, Marek M, et al. J Med Chem 2016; 59:
1545–1555.
39. Ugwu DI, Ezema BE, Eze FU, et al. Am J Org Chem 2014;
4: 26–51.
75. O’Brien EC, Le Roy S, Levaillain J, et al. Inorganica Chim
Acta 1997; 266: 117–120.
76. Hilal OM and Fredericks GE. J Chem Soc 1954; 785.
40. Veysel T and Yılmaz FY. Transit Met Chem 1999; 24: 726–
729.
41. Loll PJ, Sharkey CT, O’Connor SJ, et al. Mol Pharmacol 77. Traynham JG and Pascual OS. J Org Chem 1956; 21: 1362–
2001; 60: 1407–1413.
1365.
42. Dessì A. J Inorg Biochem 1992; 48: 279–287.
43. Sharma S and Sharma N. Der Chem Sin 2013; 4: 108–119.
44. Sharma S and Sharma N. Der Chem Sin 2013; 4: 87–96.
45. Sharma N, Kumar V, Sharma R, et al. Bull Chem Soc Jpn
2011; 84: 855–861.
46. Kumar A, Priya B, Thakur A, et al. Adv Sci Eng Med 2018;
10: 27–37.
47. Priya B, Sharma M, Sood S, et al. Adv Sci Eng Med 2018; 10:
129–136.
78. Greenwood D, Slack R, Peutherer JF, et al. Medical microbi-
ology: A guide to microbial infections: Pathogenesis, immu-
nity, laboratory diagnosis and control. Churchill Livingstone,
2007.
79. Mackie TJ, Collee JC and McCartney JE. Practical medical
microbiology. Edinburgh: Churchill Livingstone, 1989.
80. Khalifa RA, Nasser MS, Gomaa AA, et al. Egypt J Chest Dis
Tuberc 2013; 62: 241–247.
81. Blois MS. Nature 1958; 181: 1199–1200.
82. Ilhan-Ceylan B, Tuzun E, Kurt Y, et al. J Sulfur Chem 2015;
36: 434–449.
83. Ibrahim MM, Mersal GAM, Ramadan A-MM, Shaban SY,
et al. J Mol Struct 2017; 1137: 742–755.
48. Geary WJ. Coord Chem Rev 1971; 7: 81–122.
49. Figgis BN. Introduction to ligand fields. London; New York:
John Wiley & Sons Ltd, 1966.
50. Ballhausen CJ and Gray HB. Inorg Chem 1962; 1: 111–122.