Promising Ag(I) complexes with N-acylhydrazones from aromatic aldehydes and isoniazid against multidrug resistance in tuberculosis

Article abstract of DOI:10.1016/j.molstruc.2021.130193

In the present work, synthesis, characterization and antitubercular assays of N-acylhydrazones derivatives and their corresponding silver(I) complexes are described. The compounds were characterized by elemental analysis, IR and NMR spectroscopic measurem

Full text of DOI:10.1016/j.molstruc.2021.130193

Journal of Molecular Structure 1234 (2021) 130193
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Promising Ag(I) complexes with N-acylhydrazones from aromatic
aldehydes and isoniazid against multidrug resistance in tuberculosis
Paulo Victor P. dos Santosa, Camila M. Ribeirob, Fernando R. Pavanb, Pedro P. Corbic,
Fernando R.G. Bergaminid,c, Marcos A. Carvalhoe,c, Kaique A. D’Oliveriaa, Alexandre Cuina,∗
a LQBin – Laboratory of BioInorganic Chemistry, Chemistry Department, Institute of Exact Sciences, Federal University of Juiz de Fora – UFJF, 36036-330, Juiz
de Fora, MG, Brazil
b São Paulo State University (UNESP), School of Pharmaceutical Sciences, Tuberculosis Research Laboratory Araraquara, SP, Brazil
c Institute of Chemistry, University of Campinas – UNICAMP, 13083-970, Campinas, SP, Brazil
d Laboratory of Synthesis of Bioinspired Molecules, Institute of Chemistry, Federal University of Uberlândia – UFU, Uberlândia, MG, Brazil
e Chemistry Department, Federal University of Mato Grosso – UFMT, 78060-900, MT, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present work, synthesis, characterization and antitubercular assays of N-acylhydrazones derivatives
and their corresponding silver(I) complexes are described. The compounds were characterized by elemen-
tal analysis, IR and NMR spectroscopic measurements, molar conductivity assays and powder diffraction X
Received 19 October 2020
Revised 12 February 2021
Accepted 22 February 2021
Available online 26 February 2021
ray studies. Some of the synthesized compounds have shown minimum inhibitory concentration (MIC90
)
values against M. tuberculosis H37Rv (ATCC 27294) lower than 0.098 μg/mL, while the cytotoxic activity
assays over MRC-5 cells reveled that all compounds present selectivity indexes higher than 27. Further-
more, N-acylhydrazones compounds showed promising activities even against multidrug-resistant clinical
strains of M. tuberculosis.
Keywords:
N-acylhydrazones
Silver complexes
Mycobacterium tuberculosis
Powder X-ray diffraction
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
clear need for the development of new compounds able to fight
the resistant strains and reduce the time of full treatment [2,3].
Tuberculosis (TB), also known as Bacillus of Koch, was discov-
ered by the German scientist Robert Koch in 1882. In the 1990s,
TB had major impact on the world’s population, reaching the sta-
tus of global emergency disease according to the World Health Or-
ganization (WHO). TB is a highly infectious disease since it can
be transmitted by the aerosol produced from a simple sneeze, for
example. The main symptoms of TB encompass coughing, bloody
sputum production, weakness, weight loss and fever. In 2019, an
estimated 1.2 million people died due to TB (data referring to HIV-
negative cases), with the likelihood of developing TB being higher
among people infected with HIV [1].
Isoniazid (INH) is a worldwide synthetic drug used against M.
tuberculosis [4–6] with a range of minimum inhibitory concentra-
tion (MIC) between 0.02–0.2 μg/mL [7]. The proposed mechanism
of action of INH is described in Scheme 1. Initially, INH is activated
by catalase peroxidase (KatG) enzyme, giving rise to reactive species
able to form an adduct with NAD+. The INH-NAD adduct blocks the
action of the enzyme inhA, which is responsible for fatty acid syn-
thesis type II (FASII), resulting in serious damages to mycobacteria
cell since it prevents the synthesis of mycolic acids, which is an ex-
clusive and important component of the mycobacteria cell wall. In
addition, INH has others possible targets inside bacteria increasing
its effectiveness against TB [8] as described in Scheme 2.
In most cases, treatments of TB are time-consuming, taking up
to 6 to 12 months to be completed [1]. Due to the long time of
treatment and to the fact that the symptoms may disappear in the
first weeks of treatment, many patients discontinue the treatment
prior to mycobacteria complete elimination, triggering the emer-
gence of resistant strains.
However, M. tuberculosis bacillus has already developed resis-
tance to INH by mutations in KatG and inhA enzymes. Hence, an al-
ternative is to promote the reaction of INH with other compounds,
such as aromatic aldehydes, to obtain new organic compounds in
which the pharmacophore portion of isoniazid is preserved [9].
Adducts from condensation between INH and aldehydes are
known as N-acylhydrazones, which constitute an important class of
organic compounds. N-Acylhydrazones have characteristics such as
structural versatility, relative ease synthesis and satisfactory yields.
In biological systems, the N-acylhydrazones have also shown
Since time-consuming treatments on TB and resistant strains of
M. tuberculosis are serious world public health issues, there is a
∗
Corresponding author.
E-mail address: alexandre.cuin@ufjf.edu.br (A. Cuin).
https://doi.org/10.1016/j.molstruc.2021.130193
0022-2860/© 2021 Elsevier B.V. All rights reserved.

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Scheme 1. Proposed action mechanism of INH.
Scheme 2. General procedure to obtain N-acylhydrazones from isoniazid and aldehydes.
promising results in several applications such as antibacterial,
M. tuberculosis H37Rv and also over clinical multi-drug resistant
strains, and the results are presented for the first time in this
work.
antidepressant, anti-inflammatory, anticancer, anti-HIV and anti-
diabetic, among other biological activities [10–14].
Biologically active Fe(II)-INH complexes against strains of M. tu-
berculosis resistant to traditional drugs have been reported [15–22],
as well other divalent metal complexes with INH such as Ru(II),
Zn(II) and Cu(II) [23–27]. In those cases, the biological activities of
the metal complexes were higher than free INH, probably due to
the synergism between the activities of the metal ion and the free
INH.
2. Experimental
2.1. Materials and methods
The starting compounds isoniazid (99%), salicylaldehyde (98%),
o-vanillin (2-hydro xy-3-methoxybenzaldehyde) (99%), m-vanillin
(3-hydroxy-4-methoxybenzaldehyde, 99%), vanillin (4-hydroxy-3-
methoxybenzaldehyde, 99%) and silver nitrate (98%) were pur-
chased from Sigma-Aldrich Co. and used without further purifica-
tion. Elemental analyses of C, H and N were performed on CHNS-O
EA 1110 Analyzer, CE Instruments. The infrared (IR) spectra were
recorded on Bruker ALPHA FTIR spectrophotometer in the range
4000–400 cm−1 and samples were prepared as KBr pellets. The 13C
and 1H NMR data for IZoVA and AgIZoVA samples were recorded
on Bruker Avance III 500 MHz, while IZSAL, AgIZSAL, IZmVA, Ag-
IZmVA, IZVAN and AgIZVAN compounds were recorded on Bruker
Avance 400 MHz. Tetramethylsilane was used as the internal stan-
dard. The NMR samples were prepared in deuterated dimethyl-
sulfoxide solutions – DMSO-d6. Conductivity measurements were
performed using a HMCDB-150 HIGH MED conductivity meter.
Dimethylsulfoxide (DMSO) solutions at 1.0 × 10−3 mol/L of com-
pounds were used.
Silver is widely used due to its high biological activity [28].
Compounds containing silver in metallic form mainly in nanopar-
ticles, or their respective salts, have been explored in Medicine
for a long time since metallic silver or its compounds are able to
overcome or prevent infections in burns and wounds. Our research
group has recently focused on Ag(I) complexes against TB [26–37].
Nowadays, bacterial resistance to Ag(I) ions is rare and often tran-
sient, except for a description in the literature in which a strain of
Pseudomonas stutzeri showed resistance [41].
Recently, a silver(I) complex with INH of molecular formula
AgC6H7N3O•NO3 was described in the literature. Coordination of
INH to silver was suggested to occur in a bidentate mode by the
nitrogen of the NH2 group and by the oxygen atom of the C=O
group. The complex presented a minimal inhibitory concentration
(MIC90) of 0.78 μg/mL against M. tuberculosis H37Rv strain [42].
In this paper, synthesis and characterization of N-
acylhydrazones, obtained by isoniazid with salicylaldehyde (IZSAL),
o-vanillin (IZoVA), m-vanillin (IZmVA) or vanillin (IZVAN) and their
respective Ag(I) complexes are presented. Besides the analytical,
spectroscopic and structural studies, biological assays were per-
formed to evaluate the activity of the compounds against standard
2.2. X ray powder diffraction
The powder of the organic compounds and silver(I) complexes
were gently grounded in an agate mortar. The grounded powders
2

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Table 1
Crystallographic data of AgIZoVA
Empirical formula
Formula weight
T(K)
C28H28AgN7O10
730.09
298
˚
λ(CuKα) (A)
1.5418
Crystal System
Space Group
Triclinic
P-1
˚
a(A)
7.739(3)
6.990(2)
16.652(1)
82.09(4)
103.38(5)
126.74(2)
702.21(6)
1
˚
b(A)
˚
c(A)
α(o)
β(o)
γ (o)
3
˚
V (A )
Z
dcalc(g cm−3
)
1.722(2)
6.43(1)
352
μ (mm−1
)
Fig. 1. IZoVA molecule and its respective torsion angles numbered from τ1 to τ7
.
F(000)
In the SA step, only τ3 to τ7 angles were used. All torsion angles, rotation and
Number of Parameters
44
translation variables were left free in the final refinement procedure.
Rbragg / Rwp / GOF
0.026 / 0.013 / 11.0
were deposited in the hallow of thin glass slide, which served as
sample holder with nearly zero-background. Diffractograms of each
compound were obtained by accumulating signal for 2 to 3 hours
in the range of 4 to 55° 2θ, with step of 0.02° (2θ), with time
of 0.2s in each step. Typically, DS (Divergent Slit) of 0.6 mm is
used. For the ligands and the complex AgIZSAL, in which the crys-
tal structures have already been reported, the experimental cell
parameters found were in accordance with described in the lit-
erature. Basic crystallographic data are described in the Table 5
[43–47].
niazid and streptomycin were solubilized in water and filtered at
0.22 μm to ensure sterility.
All stock solutions were prepared at 1.0 g/L and diluted accord-
ing to the standardized concentrations in the assay (the range used
was 25 to 0.098 μg/mL) in a 96 well microplate at the volume of
100 μL (serial dilution 1:2). To determine MIC90, the REMA (Re-
sazurin Microtiter Plate Assay) method was used [52]. Mycobac-
terium tuberculosis H37Rv (ATCC 27294) was cultured in 7H9 cul-
ture medium supplemented with OADC (oleic acid, albumin, dex-
trose and catalase) for 7-10 days at 37°C until turbidity of 1 Mc-
farland scale was reached (the densitometer DEN1, Biosan, wave-
The crystal model of AgIZoVA complex was solved using pow-
der diffraction method. Initially, new and long measurements were
performed, (15 hours in the range of 3 to 105° 2θ with step 0.02°).
Then, 21 first reflections were identified followed by indexing pro-
cedure [48] and the approximate parameters of the unit cell were
performed through the methods [49] available in TOPAS Academic
[50]. The crystal model of AgIZoVA was solved using a Simulated
Annealing process (SA)[49]. In this process, a rigid body model for
organic moiety [45], idealized as Cartesian coordinates, with free
rotation, translation and flexible at few torsion angles (see Fig.1)
was used.
length = 565
15 nm) and then diluted in the same culture
medium to achieve the concentration of 2 × 105 colony form-
ing units (CFU)/mL for use in the experiment. Finally, 100 μL of
the inoculum were added to 100 μL of drug diluted at different
concentrations. Plates were incubated at 37°C for seven days. Af-
ter this incubation period, 30 μL of the 0.01% resazurin solution
in sterile distilled water was added to all wells of the microplate
and incubated for 24h at 37°C. Resazurin is an oxidoreduction in-
dicator able to show cell viability. Plate readings were proceeded
after 24h at wavelength of 530/570 nm (emission/excitation) in a
spectrophotometer (Cytation 5 Cell Imaging Multi-Mode Reader).
Fluorescence readings indicate bacterial growth, where the posi-
tive control is 100% growth and the negative control is 0% growth.
MIC90 is defined as the lowest concentration of the drug able to
inhibit 90% growth of the inoculum compared to the positive con-
trol. The experiments were performed in biological triplicate and
the outcomes are presented in the form of the mean obtained from
the results and the standard deviation.
The water molecule and the nitrate ion were also used as rigid
bodies but idealized as Z-matrix formalism. Translation and rota-
tion variables were left free for the water molecule. A single Ag(I)
ion was fixed in special position at the origin as a symmetry point.
In the case of the nitrate ion, the nitrogen atom is also fixed at a
special position (0.5 × 0.5y 0.0z). The oxygen atoms of the nitrate
ion have shown disorder, where each oxygen was placed at 60° to
each other and all oxygen atoms are on the same plane [1 1 0]
with 50% of occupancy. In the final refinement carried out by the
Rietveld method [51], the rigid bodies used in SA step were main-
tained.
The clinical strains assays were performed using microdilution
in 96-well plates, according to the MycoTB Plate method, with 8
clinical strains of M. tuberculosis, which are strain 1: CF 169, strain
2: CF 93, strain 3: CF 112, strain 4: CF 107, strain 5: CF 108, strain
6: CF 16, strain 7: CF 89 and strain 8: CF 168 [53].
Crystal data and data collection parameters are presented in
Table 1. AgIZoVA final Rietveld refinement plot is supplied as Sup-
plementary Materials (SM).
Unfortunately, the crystal models for AgIZVAN and AgIZmVA
were not solved at the moment, even after many experimental ef-
forts to obtain single crystals or trying to solve the crystal struc-
tures from powder diffraction method.
2.3.2. In vitro cytotoxic activity assays
The cytotoxicity assay was performed on MRC-5 cells (human
lung fibroblast – ATCC CCL–171) in plates with 96-well, using the
microdilution technique and using resazurin as an indicator of cell
viability. The experiments were performed in triplicate [54].
2.3. Antibacterial activity assays
2.3.1. Determination of minimal inhibitory concentration (MIC)
The IZSAL, AgIZSAL, IZoVA, AgIZoVA, IZmVA, AgIZmVA, IZVAN
and AgIZVAN compounds and the standard drugs used as an ex-
perimental control (moxifloxacin, rifampicin and ofloxacin), were
solubilized in dimethylsulfoxide and the antibiotics amikacin, iso-
2.3.3. Selectivity index (SI)
The selectivity index (SI) was calculated by dividing the
IC50/MIC90 values, which demonstrates how much a compound
is selective in killing the microorganism without causing cellular
3

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Table 2
:1H NMR assignments for IZoVA and AgIZoVA.
Assignments (ppm)
Compound
NH
OH
H1
N=CH
H2
H7
H9
H8
OCH3
AgIZoVA
IZoVA
12.27(s)
12.25(s)
+0.02
10.67(s)
10.70(s)
-0.03
8.80(d)
8.79(dd)
+0.01
8.70(s)
8.70(s)
0
7.86(dd)
7.84(dd)
+0.02
7.21(dd)
7.20(dd)
+0.01
7.05(dd)
7.05(dd)
0
6.87(t)
6.87(t)
0
3.82(s)
3.82(s)
0
ꢀδ (ppm)
s: singlet; d: duplet; dd: doublet duplet; t: triplet
Table 3
13 C NMR assignments for IZoVA and AgIZoVA.
Assignments (ppm)
Compound
C=O
C1
C5
C6
N=CH
C3
C2
C9
C4
C8
C7
OCH3
AgIZoVA
IZoVA
161.25
161.52
-0.27
150.56
150.47
+0.09
148.84
149.07
-0.23
147.98
148.09
-0.11
147.16
147.30
-0.14
140.22
140.13
+0.09
121.66
120.33
120.60
-0.27
119.15
119.29
-0.14
118.99
119.05
-0.06
113.99
114.09
-0.10
55.85
55.94
-0.09
121.64
ꢀδ (ppm)
+0.02
Table 4
mL) of salicylaldehyde were slowly added. Catalytic amount of
glacial acetic acid was added, and the mixture was stirred at 70 °C
for 2h. The yellow precipitate formed was collected by filtration,
washed with ethanol and stored in desiccator under silica. Yield
40%. Melting point (Mp): 254-256°C. MW 241.25 gmol−1. Anal.
Calc. for C13H11 N3O2: C, 64.72%; H, 4.60%; N, 17.42%. Found: C,
64.68%; H, 4.57%; N, 17.40%. Selected IR bands (KBr, cm−1): ν(OH)
3432; ν(NH) 3193; ν(C–H) 3006; ν(C=O) 1682; ν(C=N) 1624. 1H-
NMR (DMSO-d6) (ppm): 12.28 (s, 1H, NH); 11.08 (s, 1H, OH); 8.81
(dd, 2H, J= 4.6Hz, H1); 8.68 (s, 1H, N=CH); 7.85 (dd, 2H, J= 4.5Hz,
H2); 7.60 (dd, 1H, J= 7.6Hz, H9); 7.32 (m, 1H, H8); 6.93 (m, 2H,
H6/H7). 13C-NMR (DMSO-d6) (ppm): 161.34 (C=O); 157.47 (C5);
150.39 (C1); 148.95 (N=CH); 139.99 (C3); 131.74 (C7); 129.20 (C9);
121.50 (C2); 119.43 (C8); 118.69 (C4); 116.44 (C6).
Molar conductivity in DMSO
Ag(I) complexes
1
×
10−3 mol/L of
Complex
Molar conductivity (μScm2mol−1
)
AgIZSAL
AgIZoVA
AgIZmVA
AgIZVAN
34.4
34.6
8.97
56.8
Table 5
Crystallographic data for synthesized ligands and Ag(I) complexes. Crystallography
data of AgIZoVA have been described in Table 1.
Crystallographic data
3
˚
˚
˚
˚
˚
Compound
Space Group
a(A)
b(A)
c(A)
β(A)
V(A )
[38]
IZmVA
P21/n
P21/n
P21/c
P21/c
P21/c
9.16
11.48
6.52
13.88
16.00
10.88
10.74
18.57
93.68
1459.9
1379.0
1273.0
1165.9
2661.8
IZVAN[39]
IZoVA[40]
IZSAL[41]
13.34
7.67
98.42
3.1.2. (2-Hydroxy-3-methoxybenzaldehyde)isonicotinoylhydrazone
(IZoVA)
16.26
15.56
12.64
110.41
121.14
104.73
8.14
AgIZSAL[42]
11.71
The IZoVA was synthesized following the procedure to IZSAL.
However, o-vanillin was used instead salicylaldehyde. Yellow crys-
talline solid was obtained in 85% yield. Mp: 237-239°C. MW 271.28
gmol−1. Anal. Calc. for C14 H13N3O3: C, 61.99%; H, 4.83%; N, 15.49%.
Found: C, 62.08%; H, 4.65%; N, 15.57%. Selected IR bands (KBr,
cm−1): ν(OH) 3460; ν(NH) 3200; ν(C–H) 3005; ν(C=O) 1690;
ν(C=N) 1627. 1H-NMR (DMSO-d6) (ppm): 12.25 (s, 1H, NH); 10.70
(s, 1H, OH); 8.79 (dd, 2H, J= 4.4Hz, H1); 8.70 (s, 1H, N=CH); 7.84
(dd, 2H, J= 4.4Hz, H2); 7.20 (dd, 1H, J= 7.9Hz, H7); 7.05 (dd, 1H, J=
8.1Hz, H9); 6.87 (t, 1H, J= 7.9Hz, H8); 3.82 (s, 3H, OCH3). 13C-NMR
(DMSO-d6) (ppm): 161.52 (C=O); 150.47 (C1); 149.07 (C5); 148.09
(C6); 147.30 (N=CH); 140.13 (C3); 121.64 (C2); 120.60 (C9); 119.29
(C4); 119.05 (C8); 114.09 (C7); 55.94 (OCH3).
damage, in which a promising value is SI >10 [54]. The SI values
of the compounds are listed in the Table 6.
3. Synthesis
3.1. Synthesis of N-acylhydrazones
3.1.1. (2-Hydroxybenzaldehyde)isonicotinoylhydrazone (IZSAL)
In a round bottom flask, 3.8 mmol (0.521 g) of isoniazid dis-
solved in 40.0 mL ethanol were first added. Then, 3.8 mmol (0.40
Table 6
Results of MIC90, MRC-5 cells assays and SI for N-acylhydrazones and its Ag(I) complexes.
Compound
MW (g.mol−1
)
MIC90(average
SD) (μg/mL)
MIC90(μmol/L)
IC50(average
SD) (μg/mL)
SI
IZSAL
241.25
670.39
271.28
730.44
289.28
441.15
289.28
712.42
137.06
822.95
361.37
585.61
581.57
401.43
0.581
0.550
2.41
>100
>172
>48.2
>230
27.26
>1020
42.70
>952
109.38
>5102
AgIZSAL
IZoVA
< 0.098
0.434
< 0.146
1.60
4.722
>100
8.397
>100
7.045
>100
13.344
>500
0.118
0.344
0.075
AgIZoVA
IZmVA
0.308
0.422
< 0.339
0.374
0.363
0.171
0.715
0.119
1.057
0.958
0.475
1.557
1.241
1.048
1.888
< 0.098
0.165
AgIZmVA
IZVAN
0.023
0.012
0.042
0.105
AgIZVAN
Isoniazid
Rifampicin
Ofloxacin
Amikacin
Streptomycin
Moxifloxacin
0.122
< 0.098
< 0.098
0.382
0.169
0.165
0.091
0.024
0.561
0.276
0.625
MW=Molar Weight; SD: Standard Deviation
4

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Scheme 3. General procedure to the synthesis of silver(I) complexes. R1 to R3 codes are described in the Scheme 2
3.1.3. (3-Hydroxy-4-
3.2.1. [Ag(IZSAL)2(H2O)]NO3 (AgIZSAL)
methoxybenzaldehyde)isonicotinoylhydrazonemonohydrate
(IZmVA)
The AgIZSAL was synthesized as described by Ghammamy [47].
Briefly, a solution of 5.0 mL of acetonitrile containing silver ni-
trate (0.5 mmol, 0.085g) was added to IZSAL (1.0 mmol, 0.241
g) previously dissolved in 30 mL of methanol. The final solu-
tion was stirred for 2.5h, at 60°C, in the dark. The Ag(I) com-
plex was obtained as a green polycrystalline solid, which was sep-
arated by simple filtration and stored in desiccator under silica.
Yield 60%. Mp: 250-252°C. MW 670.39 gmol−1. Anal. Calc. for
[Ag(C13H11 N3O2)2(H2O)]NO3 C, 46.58%; H, 3.61%; N, 14.63%. Found:
C, 46.50%; H, 3.57%; N, 14.59%. Selected IR bands (KBr, cm−1):
ν(OH) 3443; ν(NH) 3193; ν(C–H) 3006; ν(C=O) 1684; ν(C=N)
1624; νsim(N-O(NO3)) 1384. 1H-NMR (DMSO-d6) (ppm): 12.32 (s,
2H, NH); 11.05 (s, 2H, OH); 8.80 (d, 4H, J= 5.9Hz, H1); 8.69 (s, 2H,
N=CH); 7.88 (dd, 4H, J= 4.6Hz, H2); 7.61 (dd, 2H, J= 7.7Hz, H9);
7.31 (m, 2H, H8); 6.93 (m, 4H, H6/H7). 13C-NMR (DMSO-d6) (ppm):
161.23 (C=O); 157.47 (C5); 150.58 (C1); 149.01 (N=CH); 140.31
(C3); 131.81 (C7); 129.11 (C9); 121.75 (C2); 119.45 (C8); 118.70 (C4);
116.44 (C6).
The IZmVA was synthesized following the same procedure as
described to IZSAL. However, 3-hydroxy-4-methoxybenzaldehyde
was used instead of salicylaldehyde. A yellow crystalline solid was
obtained in 70 % yield. Mp: 235-237°C. MW 289.28gmol−1 Anal.
Calc. for C14 H13N3O3•H2O: C, 58.13%; H, 5.23%; N, 14.53%. Found: C,
57.40%; H, 5.20%; N, 14.25%. Selected IR bands (KBr, cm−1): ν(OH)
3415; ν(NH) 3245; ν(C–H) 3085; ν(C=O) 1650; ν(C=N) 1606. 1H-
NMR (DMSO-d6) (ppm): 11.90 (s, 1H, NH); 9.36 (s, 1H, OH); 8.77
(dd, 2H, J= 4.5Hz, H1); 8.31 (s, 1H, N=CH); 7.80 (dd, 2H, J= 4.5Hz,
H2); 7.29 (d, 1H, J = 1.9Hz, H5); 7.08 (dd, 1H, J= 8.3Hz, H9); 6.98
(d, 1H, J= 8.3Hz, H8); 3.81 (s, 3H, OCH3). 13C-NMR (DMSO-d6)
(ppm): 161.42 (C=O); 150.34 (C1); 150.12 (C7); 149.27 (C6); 146.96
(N=CH); 140.70 (C3); 126.87 (C4); 121.54 (C2); 120.68 (C9); 112.45
(C5); 111.92 (C8); 55.63 (OCH3).
3.1.4. (4-Hydroxy-3-
methoxybenzaldehyde)isonicotinoylhydrazonemonohydrate
(IZVAN)
3.2.2. [Ag(IZoVA)2NO3] H2O (AgIZoVA)
The AgIZoVA was synthesized following the same procedure of
AgIZSAL. The green polycrystalline solid obtained using the IZoVA
ligand was separated by simple filtration and stored in desicca-
tor under silica. Yield 60%. Mp: 234-236°C. MW 730.44 gmol−1
The IZVAN was synthesized as described to IZSAL. However,
vanillin was used instead of salicylaldehyde. A green crystalline
solid was obtained in 75 % yield. Mp: 234-236°C. MW 289.28
gmol−1. Anal. Calc. for C14 H13N3O3•H2O: C, 58.13%; H, 5.23%; N,
14.53%. Found: C, 58.21%; H, 5.27%; N, 14.62%. Selected IR bands
(KBr, cm−1): ν(OH) 3517; ν(NH) 3446; ν(C–H) 3063; ν(C=O) 1666;
ν(C=N) 1605. 1H-NMR (DMSO-d6) (ppm): 11.90 (s, 1H, NH); 9.64
(s, 1H, OH); 8.76 (dd, 2H, J= 4.5Hz, H1); 8.34 (s, 1H, N=CH); 7.80
(dd, 2H, J= 4.4Hz, H2); 7.36 (d, 1H, J= 1.8Hz, H9); 7.12 (dd, 1H, J=
8.2Hz, H5); 6.86 (d, 1H, J= 8.1Hz, H6); 3.83 (s, 3H, OCH3). 13C-NMR
(DMSO-d6) (ppm): 161.61 (C=O); 150.43 (C1); 149.81 (C7); 149.44
(C6); 148.23 (N=CH); 140.80 (C3); 125.52 (C4); 122.67 (C9); 121.65
(C2); 115.59 (C8); 109.23 (C5); 55.71 (OCH3).
.
Anal. Calc. for [Ag(C14 H13N3O3)2NO3]H2O: C, 46.04%; H, 3.86%; N,
13.42%. Found: C, 46.42%; H, 3.84%; N, 13.30%. Selected IR bands
(KBr, cm−1): ν(OH) 3432; ν(NH) 3192; ν(C–H) 3023; ν(C=O) 1675;
ν(C=N) 1603; νsim(N-O(NO3)) 1384. 1H-NMR (DMSO-d6) (ppm):
12.27 (s, 2H, NH); 10.67 (s, 2H, OH); 8.80 (d, 4H, J= 4.5Hz, H1);
8.70 (s, 2H, N=CH); 7.86 (dd, 4H, J= 6.0Hz, H2); 7.21 (dd, 2H,
J= 7.8Hz, H7); 7.05 (dd, 2H, J= 8.1Hz, H9); 6.87 (t, 2H, J= 7.9Hz,
H8); 3.82 (s, 6H, OCH3). 13C-NMR (DMSO-d6) (ppm): 161.25 (C=O);
150.56 (C1); 148.84 (C5); 147.98 (C6); 147.16 (N=CH); 140.22 (C3);
121.66 (C2); 120.33 (C9); 119.15 (C4); 118.99 (C8); 113.99 (C7);
55.85 (OCH3).
3.2. Synthesis of silver(I) complexes
3.2.3. [Ag(IZmVA)]NO3 (AgIZmVA)
The general procedures of synthesis of the silver(I) complexes
The AgIZmVA was synthesized following similar procedure of
AgIZSAL. However, the IZmVA was used as ligand instead IZSAL and
with N-acylhydrazones are described in Scheme 3.
5

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Fig. 2. 1H NMR spectra of AgIZoVA(red) and IZoVA(black).
it was used an equimolar ratio of silver nitrate. The green polycrys-
talline solid obtained was separated by simple filtration and stored
in desiccator under silica. Yield 50%. Mp: 234-236°C. MW 441.15
gmol−1. Anal. Calc. for [Ag(C14 H13N3O3)]NO3: C, 38.12%; H, 2.97%;
N, 12.70% Found: C, 39.71%; H, 3.32%; N, 12.35%. Selected IR bands
(KBr, cm−1): ν(OH) 3465; ν(NH) 3263; ν(C–H) 3026; ν(C=O) 1648;
ν(C=N) 1602; νsim(N-O(NO3)) 1389. 1H-NMR (DMSO-d6) (ppm):
11.97 (s, 1H, NH); 9.35 (s, 1H, OH); 8.78 (dd, 2H, J= 5.6Hz, H1);
8.32 (s, 1H, N=CH); 7.86 (dd, 2H, J= 4.6Hz, H2); 7.29 (d, 1H, J=
1.9Hz, H5); 7.10 (dd, 1H, J= 8.3Hz, H9); 6.98 (d, 1H, J= 8.4Hz,
H8); 3.81 (s, 3H, OCH3). 13C-NMR (DMSO-d6) (ppm): 161.24 (C=O);
150.74 (C1); 150.19 (C7); 149.57 (C6); 146.94 (N=CH); 141.11 (C3);
126.71 (C4); 121.91 (C2); 120.71 (C9); 112.50 (C5); 111.92 (C8);
55.64 (OCH3).
4. Results and discussion
4.1. IR spectroscopy
The spectra of free N-acylhydrazones are similar to the spec-
tra of the respective Ag(I) complexes. The assigned bands to ν(OH)
are found in the range 3517-3415 cm−1 for the ligands while the
same bands are observed at 3517-3432 cm−1 for the complexes.
The ν(N
̶ H) vibration band did not change when IR spectra of
ligands and complexes are compared. This vibration band is ob-
served at 3446-3193 cm−1 for ligands and at 3443-3192 cm−1 for
the complexes. The aromatic ν(C ̶ H) vibration band is marked in
the range 3085-3006 cm−1, and it appears unchanged when the
ligands and complexes are compared. The stretching vibration of
CO i.e. ν(C=O) is identified at 1690-1650 cm−1 for the ligands. The
same vibration band is observed at 1684-1648 cm−1 in the respec-
tive complexes. The ν(C=N) absorption band is assigned in the re-
gion 1627-1605 cm−1 for the ligands and it appears at 1624-1601
cm−1 in the complexes. The M-L bands, such as ν(Ag-N), could not
be observed, since these bands fall at low energies and, probably,
they were overlapped by the organic moiety vibration bands.
On the other hand, a strong band in 1389-1384 cm−1 appears
only in the spectra of the complexes and it was assigned to the
symmetric stretching mode of ν(N-O), confirming the presence of
nitrate ion in all silver(I) complexes.
3.2.4. [Ag(IZVAN)2]NO3 (AgIZVAN)
The synthesis of AgIZVAN was the same as described to Ag-
IZSAL. The light green polycrystalline solid obtained was sepa-
rated by simple filtration and stored in desiccator under silica.
Yield 60%. Mp: 227-229°C. MW 712.42 gmol−1. Anal. Calc. for
[Ag(C14 H13N3O3)2]NO3: C, 47.21%; H, 3.68%; N, 13.76%. Found: C,
47.54%; H, 3.64%; N, 13.69%. Selected IR bands (KBr, cm−1): ν(OH)
3517; ν(NH) 3443; ν(C–H) 3065; ν(C=O) 1649; ν(C=N) 1601;
νsim(N-O(NO3)) 1387. 1H-NMR (DMSO-d6) (ppm): 11.99 (s, 2H,
NH); 9.68 (s, 2H, OH); 8.78 (m, 4H, H1); 8.36 (s, 2H, N=CH); 7.85
(dd, 4H, J= 4.5Hz, H2); 7.36 (d, 2H, J= 1.5Hz, H9); 7.13 (dd, 2H, J=
8.2Hz, H5); 6.85 (d, 2H, J= 8.1Hz, H6); 3.83 (s, 6H, OCH3). 13C-NMR
(DMSO-d6) (ppm): 161.38 (C=O); 150.77 (C1); 150.06 (C7); 149.51
(C6); 148.17 (N=CH); 141.08 (C3); 125.28 (C4); 122.69 (C9); 121.92
(C2); 115.57 (C8); 109.23 (C5); 55.68 (OCH3).
All FTIR spectra of the free ligands and their respective Ag(I)
complexes are depicted as Supplementary Material.
4.2. 1H and 13 C NMR analysis
The assignments of the NMR signals were based in literature
[55,56].The 13C and 1H spectra of Ag(I) complexes were analyzed
6

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Fig. 3. Crystal structure of AgIZoVA drawn using Schakal [63]. The Ag(I) ions are placed at special position and they act as pivot to IZoVA molecules. The atoms of asymmetric
unit were labeled (except hydrogen atoms). Color codes: Carbon (gray), Hydrogen (white), Silver (pink), Nitrogen (blue) and Oxygen (red).
−
Fig. 4. Crystal structure of AgIZoVA showing the disorder of nitrate ions.The NO3 ions connect different [AgIZoVA] ions, making 2D polymer. The atomic labels of non-
hydrogen atoms present in the asymmetric unit were described in the Figure 3.
in comparison to NMR spectra of the free ligands. The NMR spectra
of IZoVA and AgIZoVA are shown in Fig. 2 and the corresponding
assignments are presented in Table 2 and Table 3, while the 1H
and 13C NMR spectra of the other free ligands and Ag(I) complexes
are presented as Supplementary Material.
trogen atom of pyridine ring, even though it has a 1:1 metal:ligand
proportion.
4.3. Conductivity measurements
It was observed in the 1H and 13C NMR spectra of all silver
complexes that the signals assigned as the hydrogen atoms H1 and
H2 and the carbon atoms C1 and C2 atoms in pyridine ring are
shifted downfield, suggesting that the Ag(I) ions are coordinated
by the nitrogen atom of the pyridine ring.
The molar conductivities of complexes AgIZSAL, AgIZoVA, Ag-
IZmVA and AgIZVAN were obtained in 1 × 10−3 mol/L DMSO so-
lutions and the results are shown in Table 4.
Conductivity data fall in the range 8.97 to 56.8 μScm2mol−1 in
DMSO. The molar conductivity of AgIZVAN, of 56.8 μScm2mol−1
is typical for a 1:1 electrolyte compound [57]. On the other hand,
the complex AgIZmVA showed low molar conductivity of 8.97
μScm2mol−1. It means that the nitrate anion is still present in the
inner-coordination sphere of the complex probably in the chelate
mode (O,O’), as−occurs in some non-electrolyte metal complexes
containing NO3 [58,59]. The values found for AgIZSAL and AgI-
ZoVA were lower than the conductivity level associated to 1:1 elec-
Furthermore, the crystalline structure of AgIZSAL were reported
by single X-ray diffraction [47], where the coordination of Ag(I) ion
occurs by the nitrogen atom of the pyridine ring (see Scheme 3).
From this data and considering that the compounds are analogous,
it can be inferred that the coordination in the AgIZoVA and AgIZ-
VAN complexes occurs in a similar way. In the AgIZmVA complex
the ligand IZmVA appears coordinated to Ag(I) ion only by the ni-
7

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Table 7
trans fashion. The nitrate ion is also bonded to Ag(I), but the oxy-
gen atoms of nitrate showed disorder and appear like a star in the
Critical concentration for classification of
first- and second-lines drugs resistant.
˚
crystal structure, see Fig. 4. The bond distance of Ag-O6 is 2.121A
Drug
Concentration (μg/mL)
˚
while Ag-O5 is 2.629A. Taking into account the nitrate ion with-
out disorder, the geometry around Ag(I) ions is better described as
T-form, where the angle N-Ag-O6 is 85.2o. The structure of AgI-
ZoVA complex has strong intramolecular interactions between the
phenolic hydroxyl and the imino nitrogen (N3), where the dis-
Amikacin
4.0
Streptomycin
Rifampicin
Isoniazid
2.0
2.0∗
0.5∗∗
5.0
Ethionamide
Moxifloxacin
˚
2.0∗
tance O2…N3 is 2.594A and the H2b…N3 distance is estimated as
˚
1.829A. Even in disorder, there are hydrogen bonds between oxy-
∗0.5–2.0μg/mL, it is considered borderline
because has an acceptable variation of the
result of MIC due to the method used.
gen atoms of nitrate ions and water molecule (see Fig. 3) along b
˚
axis in the crystalline lattice ranging from 2.395 to 2.624A, as well
∗∗
˚
the N3…O1, with 2.833A has intermolecular interaction expanding
0.125–0.50 μg/mL, it is considered border-
line because has an acceptable variation of
the result of MIC due to the method used.
the supramolecular structure on the a, b plane. Details of intra and
intermolecular interactions, hydrogen bonds, distance and angle
bonds, atomic positional parameters, the packing of the structure
AgIZoVA along axes a, b and c, are presented as Supplementary
Materials.
trolyte in DMSO solution, but these values are too high for non-
−
electrolyte compounds. Some metal complexes containing NO3 as
counter ion or even coordinated to metal ion as monodentate lig-
and have been reported with similar conductivities values as found
in case of AgIZSAL and AgIZoVA complexes, supporting that the ni-
trate ions present in its crystal structures could be partially disso-
ciated in DMSO solution [30, 57, 60–62].
4.5. Antibacterial activity assays and selectivity index
The N-acylhydrazones and its Ag(I) complexes have been eval-
uated against M. tuberculosis H37Rv and the results are listed in
Table 6. The synthesized compounds showed high activity against
M. tuberculosis, to which one shall emphasize the activities of IZ-
VAN, AgIZmVA and AgIZVAN (0.105, 0.165 and 0.122 μg/mL) as
well as AgIZSAL and IZmVA that presented MIC90 lower than 0.098
μg/mL, being more effective than some commercial antitubercular
drugs.
4.4. X-ray diffraction studies
The crystallographic parameters of some compounds studied in
the present work are summarized in Table 5.
The crystal structures of ligands and the AgIZSAL complex were
already reported and their crystallographic parameters experimen-
tally obtained fit well with those ones early published [38–42].
As previously stated, the AgIZoVA crystal structure was solved
and refined by powder diffraction methods. The AgIZoVA com-
plex crystallizes in triclinic space group P-1. Fig. 3 shows the crys-
tal structure for AgIZoVA. Since Ag(I) ions lie on inversion center
they act as pivot for the IZoVA ligand where Ag(I) ions were sur-
rounded by two neutral ligands. Each ligand bonds to Ag(I) ions
As showed in Table 6 the synthesized compounds substituted at
1,3 (meta) and 1,4 (para) positions on the aromatic ring had greater
impact on the biological activity against tuberculosis than the sub-
stituted compounds in the position 1,2 (ortho) [64]. Also, the selec-
tivity indexes of N-acylhydrazone compounds are higher than 25.
For IZmVA, for example, the SI value is higher than 1000.
The low MIC values of N-acylhydrozone compounds and their
Ag(I) complexes, described in Table 6, encouraged us to evalu-
ate the compounds against 8 clinical strains. It is worth noting
that clinical strains may be resistant to different commercial drugs
through several mechanisms [65]
˚
by nitrogen atom from pyridine moiety in 2.234A and, as expected
by crystallographic imposition, the angle N-Ag-N is 180o, and in
Table 8
MIC of N-acylhydrazones, its Ag(I) complexes and antibiotics used for the treatment of TB against clinical strains 1 to 4 of M.tuberculosis
Compound
CF 169
CF 93
CF 112
CF 107
Clinical Strain 1
Clinical Strain 2
Clinical Strain 3
Clinical Strain 4
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
IZSAL
>25
>103.6
>37.29
>92.16
>34.23
>92.16
>56.67
>86.42
>35.09
28.97
>25
>103.6
>37.29
>92.16
>34.23
>92.16
>56.67
>86.42
>35.09
9.77
>25
>103.6
>37.29
>92.16
>34.23
>92.16
>56.67
>86.42
>35.09
1.32
23.90
11.56
>25
0.32
0.90
99.07
17.24
>92.16
>34.23
77.53
>56.67
>86.42
>35.09
5.23
AgIZSAL
>25
>25
>25
IZoVA
>25
>25
>25
AgIZoVA
IZmVA
>25
>25
>25
>25
>25
>25
>25
22.43
>25
0.23
AgIZmVA
IZVAN
>25
>25
>25
>25
>25
>25
>25
AgIZVAN
Streptomycin
Amikacin
Rifampicin
Isoniazid
Ethionamide
Moxifloxacin
Classification
>25
>25
>25
>25
16.85
0.20
6.61
0.03
5.68
0.55
0.87
0.77
0.82
0.30
>25
>25
0.26
0.09
0.29
0.29
3.04
1.30
0.35
0.33
<0.10
1.24
2.66
0.34
2.26
3.86
1.40
0.003
0.36
0.02
2.22
< 0.10
5.21
< 0.12
38.02
<0.10
>25
<0.12
0.36
0.43
0.89
>182.3
>150.4
<0.24
>182.3
>150.4
0.64
2.41
> 25
< 0.10
> 150.4
<0.24
>25
<0.60
3.09
<0.10
0.20
0.06
Resistant to Streptomycin,
Isoniazid and Ethionamide
Resistant to Streptomycin,
Isoniazid and Ethionamide
Resistant to Isoniazid and
Ethionamide
Resistant to Streptomycin and
low resistance to moxifloxacin∗
and isoniazid∗∗
MIC (μg/mL) = Average; SD= Standard Deviation;
∗0.5 – 2.0 μg/mL, it is considered borderline because has an acceptable variation of the result of MIC due to the method used;
∗∗0.125 – 0.50 μg/mL, it is considered borderline because has an acceptable variation of the result of MIC due to the method used.
8

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Table 9
MIC of N-acylhydrazones, its Ag(I) complexes and antibiotics used for the treatment of TB against clinical strains 5 to 8 of M.tuberculosis
Compound
CF 108
CF 16
CF 89
CF 168
Clinical Strain 5
Clinical Strain 6
Clinical Strain 7
Clinical Strain 8
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
MIC (μg/mL)
SD
MIC (μM)
IZSAL
24.22
15.52
>25
0.92
6.16
100.39
23.15
>92.16
>34.23
>92.16
>56.67
>86.42
>35.09
9.72
20.56
>25
0.33
85.22
18.40
5.99
9.33
0.24
76.27
8.93
>25
>103.6
>37.29
>92.16
>34.23
>92.16
>56.67
>86.42
>35.09
0.55
AgIZSAL
>37.29
36.01
>25
IZoVA
9.77
22.76
>25
5.17
1.50
>25
>92.16
>34.23
70.87
50.01
83.17
9.17
>25
AgIZoVA
IZmVA
>25
31.16
>25
>25
>25
>92.16
>56.67
>86.42
>35.09
2.87
20.50
22.06
24.06
6.53
0.41
0.90
1.32
>25
AgIZmVA
IZVAN
>25
>25
>25
>25
>25
>25
AgIZVAN
Streptomycin
Amikacin
Rifampicin
Isoniazid
Ethionamide
Moxifloxacin
Classification
>25
>25
0.66
>25
5.65
2.32
<0.10
0.36
<0.10
1.08
0.89
1.67
0.72
<0.10
6.87
>25
0.03
1.37
0.02
0.26
2.36
0.32
0.63
>25
4.33
5.56
0.13
0.05
0.08
0.17
0.01
0.001
3.96
0.03
1.23
1.31
2.24
1.08
<0.12
2.63
<0.12
50.12
<0.10
0.35
<0.12
2.55
>30.38
31.59
5.88
0.005
0.02
0.17
1.01
0.62
0.05
<0.60
2.69
>150.4
<0.25
0.11
0.66
33.45
<0.10
2.46
6.13
0.32
Resistant to Streptomycin and
low resistance to Moxifloxacin∗
and Isoniazid∗∗
Resistant to Isoniazid and
Ethionamide
Resistant to Moxifloxacin and
low resistance to Isoniazid∗∗
Resistant to Rifampicin,
Isoniazid and Ethionamide
MIC (μg/mL) = Average; SD= Standard Deviation;
∗0.5 – 2.0 μg/mL, it is considered borderline because has an acceptable variation of the result of MIC due to the method used;
∗∗0.125 – 0.50 μg/mL, it is considered borderline because has an acceptable variation of the result of MIC due to the method used.
4.5.1. Multidrug-resistant clinical strains of M. tuberculosis
The critical concentration used for the definition of resistant
strains is presented in Table 7, according to Method MycoTB Plate
[53,66].
tion of the ligands to Ag(I) ions by the N atom of the pyridine
ring. Structure model of AgIZoVA solved and refined belongs to
triclinic space group P-1. Biological tests in vitro were performed
for all compounds synthesized against M. tuberculosis H37Rv (ATCC
27294). By means of the MIC values, it can be stated that all tested
compounds showed remarkable anti-M. tuberculosis activities. The
AgIZSAL and IZmVA showed MIC90 lower than 0.098 μg/mL, such
as marked drugs used in the anti-TB therapy. Indeed, the results of
the assays over 8 clinical M. tuberculosis multidrug-resistant strains
evidenced that the compounds IZSAL showed activity for clinical
strains 4, 5, 6 and 7 about 20 μg/mL and AgIZSAL showed be ac-
tivity against strains 4, 5 and 7 with MIC values 11.56; 15.52; and
5.99 μg/mL, respectively.
The MIC values obtained for the N-acylhydrazones, its Ag(I)
complexes and antitubercular market drugs against eight clinical
strains are presented in Tables 8 and 9. The Clinical strains 1, 2,
3 and 8 proved to be resistant to all ligands and complexes, since
they showed MIC values above the limit range of 25 μg/mL. Clinical
strains 4 and 5, resistant to streptomycin, were sensitive to IZSAL
and AgIZSAL. The strain 7, which is resistant to moxifloxacin, was
sensitive to IZSAL and AgIZSAL, where the AgIZSAL complex pre-
sented MIC lower than 6.00 μg/mL. Indeed, the IZSAL also showed
activity against strain 6, which is resistant to isoniazid and ethion-
amide. The IZmVA has shown activity against strains 4 and 7. The
strain 7 is also sensitive to AgIZmVA, IZVAN and AgIZVAN, where
the AgIZVAN complex presented antitubercular activity lower than
6.53 μg/mL.
Author contributions
Paulo Victor P. dos Santos and Alexandre Cuin: PhD. Con-
ceptualization of the project; Funding acquisition; Investigation;
Methodology; Experimental work;
The clinical strain 6 showed a different behavior from the
other resistant strains since it is also resistant to isoniazid and
ethionamide. However, the compounds IZSAL, IZoVA and AgIZoVA
showed anti-TB activity.
Camila M. Ribeiro and Fernando R. Pavan: Biological tests;
Pedro P. Corbi, Fernando R. G. Bergamini and Marcos A. Car-
valho: Spectroscopic and analytical measurements;
Kaique A. D’Oliveria and Alexandre Cuin: measurements and
analyses of powder X-ray diffraction data.
Among the tested compounds, the IZSAL showed to be a potent
substance since it presents antitubercular activity against strains
resistant to streptomycin and low resistance to moxifloxacin and
isoniazid (strain 4 and 5), resistant to isoniazid and ethionamide
(strain 6) and resistant to moxifloxacin and low resistance to iso-
niazid (strain 7).
Supplementary materials
CCDC 1992187 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.
uk/data_request/cif. Detailed bond distances, angles and dihedrals
are reported in supplementary material.
5. Conclusion
New silver(I) complexes with N-acylhydrazones derivatives
were obtained. The AgIZSAL, AgIZoVA and AgIZVAN complexes pre-
sented a 1:2 M:L composition, while for AgIZmVA complex the
molar composition was 1:1. All compounds were analyzed by an-
alytical methods and spectroscopic techniques such as 1H and 13C
NMR and IR. Crystal structure of the AgIZoVA complex was solved
and refined by powder X-ray diffraction state-of-art. The Ag(I) coor-
dination of all synthesized complexes occurs by the nitrogen atom
of the pyridine ring, and even considering the absence of crystal-
lography model for AgIZmVA and AgIZVAN complexes, the IR and
1H and 13C NMR spectroscopic results corroborate the coordina-
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgments
This work was supported by grants from FAPEMIG (APQ-
00481/17), CNPq (304275/2020-4 and 303830/2017-4), FAPESP (São
9

P.V.P. dos Santos, C.M. Ribeiro, F.R. Pavan et al.
Journal of Molecular Structure 1234 (2021) 130193
Paulo State Research Foundation-Brazil, Grant # 2018/12062-4 for
Pedro P. Corbi, Grant # 2018/00163-0 for Fernando R. Pavan) and
Pró-Reitoria de Pesquisa/UNESP (PROPE ref. Process: 0102/004/43).
This study was also financed in part by the Coordenação de Aper-
feiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Fi-
nance Code 001.
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