Structural properties and in vitro evaluation of some Ln (III) complexes as potential selective antimicrobial and antioxidant substances

Article abstract of DOI:10.1007/s11696-021-01676-x

Rare metals have been used in pharmaceuticals and for medicinal purposes for long time. Currently, the link between some specific medicinal and biological properties of inorganic drugs has been established. [Ln(NO₃)₃] complexes with N-(2-hydroxynaphthalen-1-yl) methylene) isonicotinohydrazide Schiff base, [Ln(NHIso)₂(NO₃)₂]NO₃, complexes 1–8, were prepared and characterized using different techniques. The expected coordination for prepared complexes is ten, six from the tri-dentate NHIso ligand, and four from the two bi-dentate nitrate groups. DFT calculations on La and its cationic [La(NHIso)₂(NO₃)₂]⁺ complex were carried out at the B3LYP level of theory. The NHIso ligand and its lanthanide complexes were screened for antimicrobial activity, in vitro activity against four gram-negative bacteria Ec: Escherichia coli; Kp: Klebsiella pneumonia; Pm: Proteus mirabilis; Pa: Pseudomonas aeruginosa, with two gram-positive bacteria En: Enterococcus faecalis and Sa: Staphylococcus aureus. Complexes 1, 2, 4, 7 and 8 showed excellent and higher activity against En and Sa Gram-positive bacteria than the free ligand, especially complex 2 with a MIC value of 4 μg/mL. The reported complexes have greater and significant efficiency in quenching DPPH than that of free NHIso ligand, with a scavenging activity between 39 and 65%. Graphic Abstract: Ln (III) nitrate complexes with N-(2-hydroxynaphthalen-1-yl) methylene) isonicotinohydrazide Schiff base, [Ln(NHIso)2(NO3)2]NO3, were prepared and characterized. They showed very promising antimicrobial and antioxidant activities. Their molecular geometries have been examined using DFT calculations and the obtained results are in good agreement with the experimental data.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s11696-021-01676-x

Chemical Papers
https://doi.org/10.1007/s11696-021-01676-x
ORIGINAL PAPER
Structural properties and in vitro evaluation of some Ln (III) complexes
as potential selective antimicrobial and antioxidant substances
1
1
1
1
2
Ahmed K. Hijazi · Ziyad A. Taha · Abdellatif Ibdah · Idris M. Idris · Waleed M. Al‑Momani
Received: 27 January 2021 / Accepted: 22 April 2021
©
Institute of Chemistry, Slovak Academy of Sciences 2021
Abstract
Rare metals have been used in pharmaceuticals and for medicinal purposes for long time. Currently, the link between some
speciꢀc medicinal and biological properties of inorganic drugs has been established. [Ln(NO ) ] complexes with N-(2-hy-
3
3
droxynaphthalen-1-yl) methylene) isonicotinohydrazide Schiꢁ base, [Ln(NHIso) (NO ) ]NO , complexes 1–8, were prepared
2
3 2
3
and characterized using diꢁerent techniques. The expected coordination for prepared complexes is ten, six from the tri-dentate
+
NHIso ligand, and four from the two bi-dentate nitrate groups. DFT calculations on La and its cationic [La(NHIso) (NO ) ]
2
3 2
complex were carried out at the B3LYP level of theory. The NHIso ligand and its lanthanide complexes were screened for
antimicrobial activity, in vitro activity against four gram-negative bacteria Ec: Escherichia coli; Kp: Klebsiella pneumonia;
Pm: Proteus mirabilis; Pa: Pseudomonas aeruginosa, with two gram-positive bacteria En: Enterococcus faecalis and Sa:
Staphylococcus aureus. Complexes 1, 2, 4, 7 and 8 showed excellent and higher activity against En and Sa Gram-positive
bacteria than the free ligand, especially complex 2 with a MIC value of 4 μg/mL. The reported complexes have greater and
signiꢀcant eꢂciency in quenching DPPH than that of free NHIso ligand, with a scavenging activity between 39 and 65%.
Extended author information available on the last page of the article
Vol.:(0
1
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3

Chemical Papers
Graphic Abstract
Ln (III) nitrate complexes with N-(2-hydroxynaphthalen-1-yl) methylene) isonicotinohydrazide Schiff base,
[
Ln(NHIso)2(NO3)2]NO3, were prepared and characterized. They showed very promising antimicrobial and antioxidant
activities. Their molecular geometries have been examined using DFT calculations and the obtained results are in good
agreement with the experimental data.
Keywords Hydrazone Schiꢁ base · Lanthanides complexes · DFT · MIC · Antibacterial · Antioxidant
Introduction
due to f–f transitions. These trivalent ions are capable of
producing luminescence by photosensitization when coor-
dinated with organic ligands bearing a chromophore with
appropriate photophysical properties.
Lanthanides complexes have a diversity of applications in
bioinorganic chemistry, catalysis, luminescence and medici-
nal chemistry (Bünzli 2008; Al Momani et al. 2013; Chan-
drasekhar et al. 2013; Ghozlan et al. 2011; Taha and Hijazi
Metal complexes containing hydrazones as Schiꢁ bases
have been studied in details due to their antimicrobial and
industrial uses (Canpolat and Kaya 2004; Palai et al. 2018;
Desoky et al. 2019). The studies show, that in all cases, the
metal complexes screened against diꢁerent types of bacteria
(Gram-positive and Gram-negative) and against fungi, act
as more potent agents than their hydrazine ligands. P, S, N
and O presence as donor atoms in many Schiꢁ bases, gave
them an importance in biology by inhibiting the growth of
bacteria (Xu et al. 2010). The ones which contain (C=N)
gives delocalization associated with extended conjugation
by forming an extreme chelated ring (Abdel-Rahman et al.
2017a, b; Belicchi et al. 2001; Abu-Dief et al. 2020).
Biologically active species bonded to metal ions have
enhanced the activities of the synthesized complexes. Many
research groups showed the synthesis of a variety of Ln(III)
complexes containing mono-, bi- and tri-dentate hydrazones,
which have interesting biological and therapeutic activities
2
021). Literature studies show that Ln(III) complexes have
higher antibacterial and antioxidant activities than their cor-
responding Schiꢁ base ligands (Kumar et al. 2009; Hijazi
et al. 2017a, b; Taha et al. 2018; Ameen et al. 2018; Jin et al.
2
017). Ameen et al. revealed that their synthesized Pr(III)
complexes can act as good antibacterial and mild antifungal
substances. Hijazi et al. showed that their lanthanide com-
plexes derived from N-(2-hydroxynaphthalen-1-yl) methyl-
ene) nicotinohydrazide Schiꢁ base have moderate activities
against diꢁerent strains of bacteria.
These type of complexes have luminescent properties
which make them useful substances in a variety of applica-
tions, such as: liquid crystals, light emission diodes, bio-
physics and optical systems (Gao et al. 2018; Wang et al.
2
019; Singh et al. 2007; Cai et al. 2021; Andres and Chauvin
020). Luminescent Ln(III) ions have unique emission bands
2
1
3

Chemical Papers
(
Khan and Sharma 2008; Agarwala et al. 1990). Acylhydra-
zones belong to Schiꢁ base family with keto-type structure
–O=C–N–N=C–) contain π-bonds and a variety of heter-
spectra, respectively. Tetramethylsilane (TMS) was used as
an internal standard for measuring the chemical shifts in
(
deuterated dimethylsulphoxide (DMSO-d ). Molar conduc-
6
−
4
oatoms. These types of complexes have been studied due to
their biological activity. They have been reported to possess,
antimalarial, antitubercular, analgesic, anti-inꢃammatory,
antibacterial, antifungal, antiviral, antiplatelet, antioxidant
and antitumoral activities (Taha et al. 2015; Avaji et al.
tivities were measured at 298 K, 10 M concentration, in
DMSO solution, using WTW LF 318 conductivity meter
(Jenway Company, United Kingdom). UV–Visible spectra
−
6
were recorded at 298 K, 10 M concentration, in DMSO
solution, using a UV-2550 spectrophotometer (Schimadzu
Corporation, Japan). Edinburgh FS900SDT spectrometer
was used to record luminescent spectra in DMSO solution
with 1.0 cm quartz cell. Scanning of the emission is carried
out at wavelength that varied from 200 to 700 nm. Ther-
mal analysis was performed on a PCT-2A thermo-balance
analyzer (B.R.A.H.M.S GmbH, Germany) in the range of
20–900 °C operating at a heating rate of 10 °C/min under
2
009; Aziz et al. 2014; Bayrak et al. 2009). Of the most
widely used drugs for the treatment of tuberculosis, are the
ones that contain isoniotinic acid hydrazide and pyrazina-
mide (Gudasi et al. 2007; Gulerman et al. 2000).
A wide range of hydrazones and their derived compounds
have been reported for their antibacterial activities against
diꢁerent types of bacteria (Kuriakose et al. 2007; Hijazi
et al. 2017a).
N . Scanning electron microscope images (SEM) were per-
2
It is hypothesized that there is a strong link and correla-
tion between Schiꢁ bases and complexes derived from them,
containing transition metals and lanthanides, as inorganic
drugs, and their medicinal and biological properties (anti-
bacterial and antioxidant). In this paper, the preparation,
characterization, luminescence, density functional theory
formed using Quanta FEG 450 microscope equipped with
Everhart Thornley Detector (FEI company, United States).
Preparation of complexes
The Ln(III) complexes were synthesized according the fol-
lowing procedure: 30 mL acetonitrile solution of 0.2 g (0.68
mmol) of NHIso, was charged to 30 mL ethyl ethanoate
solution of 0.34 mmol of Ln(NO ) ·xH O salts. The overall
(
DFT) and biological studies and activities of eight novel
Ln(III) nitrate complexes with isonicotinohydrazide Schiꢁ
base is reported. The antioxidant, antibacterial, lumines-
cence and DFT properties have been studied. This present
work is considered a continuation study, of our research
group, on the lanthanides and transition metals chemistry
3
3
2
solution was stirred for 120 min., at room temperature. Fil-
tration was used to separate the formed precipitate. It was
washed many times with acetonitrile and ethyl ethanoate
(
Taha et al. 2017a, b; Ajlouni et al. 2018, 2019; Taha et al.
018, 2020; Hijazi et al. 2020, 2021; Taha et al. 2017a, b).
(
50:50) solution mixture using a Buchner funnel with a sin-
2
tered glass disk for puriꢀcation. The precipitate was dried,
under normal atmosphere at room temperature, for 24 h.
Experimental
[La(NHIso) (NO ) ]NO complex 1
2
3 2
3
The NHIso ligand was prepared according to literature
For C H LaN O (1057.87), Calcd. (%): C, 45.00; H,
44 56 9 13
(
[
[
[
Khan and Sharma 2008). Analytical grade solvents,
2.89; N, 13.89; La, 15.31. Found (%): C, 44.89; H, 2.95; N,
−
1
−1
−1
Sm(NO ) ·6H O], [La(NO ) ·6H O], [Nd(NO ) ·6H O],
13.76; La, 15.26. Λ = 88.7 Ω cm mol . Selected IR
3
3
2
3 3
2
3 3
2
m
−
1
−
Pr(NO ) ·6H O], [Er(NO ) ], [Gd(NO ) ·6H O],
(KBr, cm ): ν(OH) 3433, ν(C=N) 1613, ν(NO ) 1384,
3
3
2
3
3
3
3
2
3
1
Dy(NO ) ·H O], [Eu(NO ) ·5H O], 2-hydroxy-1-naph-
ν(M–N) 432, ν(M–O) 411. H-NMR: δ (OH) 12.55 ppm,
3
3
2
3 3
2
1
3
thaldehyde and isonicotinic hydrazide, were purchased
from Merck (Germany) and used as received. Flash 2000
elemental analyzer (Thermo Fischer Scientiꢀc, Germany)
was used to perform elemental analyses of C, H and N. The
complexes lanthanides content was determined by titration
with Ethylenediaminetetraacetic acid disodium salt (EDTA)
using an indicator (xylenol orange) and a buꢁer (acetic acid)
purchased from Merck (Germany). Bruker ALPHA spectro-
photometer (Bruker, Germany) was used to record FT-IR
(CH=N) 8.84 ppm, (C=N) 9.47 ppm. C-NMR: δ (C=O)
160.94 ppm, (C=N) 139.75 ppm. Yield: 85%.
[
Pr(NHIso) (NO ) ]NO complex 2
2 3 2 3
For C H PrN O (1059.87), Calcd. (%): C, 44.90; H, 2.88;
44
56
9
13
N, 13.86; La, 15.49. Found (%): C, 44.72; H, 2.96; N, 13.94;
−1
−1
−1
La, 15.50. Λ =113.2 Ω cm mol . Selected IR (KBr,
m
−1
−
cm ): ν(OH) 3432, ν(C=N) 1613, ν(NO ) 1384, ν(M–N)
−
1
3
spectra in the region of 4000–400 cm . Bruker Avance
00 MHz and 100 MHz spectrometer (Bruker Corpora-
4
31, ν(M–O) 412.Yield: 86%.
4
1
13
tion, United States) was used to record the H and C NMR
1
3

Chemical Papers
[
Nd(NHIso) (NO ) ]NO complex 3
of bacteria [Gram-negative bacteria: Escherichia coli (Ec);
Klebsiella pneumonia (Kp); Proteus mirabilis (Pm); Pseu-
domonas aeruginosa (Pa); Gram-positive bacteria: Entero-
coccus faecalis (En); Staphylococcus aureus (Sa)] (Hijazi
et al. 2017a). A stock solution of DMSO of each antibac-
terial was prepared according to NCCLS guidelines . The
MIC was done in standard sterile 96 well ꢃat bottom plates
and the layout was designed so that each row covered the
antibacterial dilution of 16–0.015 μg/mL with one control
well with no chemical. Using sterilized pipette, a 40 μL of
each antibacterial with the wanted concentration was added
to each well and another well was ꢀlled with the same con-
trol volume [DMSO (− ve control) and Oxytetracycline
(+ve control)]. About 150 μL of Mueller Hinton medium
was added to all wells, followed by a 10 μL of the bacterial
culture. After sealing the plates, incubation at 310 K under
normal conditions was done. After 24 h incubation, Eliza
reader was used to read the microtitre plates.
2
3 2
3
For C H NdN O (1063.20), Calcd. (%): C, 44.73; H,
4
4
56
9
13
2
.87; N, 13.81; La, 15.80. Found (%): C, 44.80; H, 2.85;
−
1
−1
−1
N, 13.70; La, 15.87. Λ =113.7 Ω cm mol Selected
m
.
−
1
−
IR (KBr, cm ): ν(OH) 3432, ν(C=N) 1614, ν(NO ) 1384,
3
ν(M–N) 432, ν(M–O) 411. Yield: 73%.
[Sm(NHIso) (NO ) ]NO complex 4
2 3 2 3
For C H SmN O (1069.32), Calcd. (%): C, 44.44; H,
4
4
56
9
13
2
1
.85; N, 13.81; La, 16.36. Found (%): C, 44.57; H, 2.86; N,
−
1
−1
−1
3.66; La, 16.50. Λ = 90.5 Ω cm mol Selected IR
m
.
−
1
−
(
(
KBr, cm ): ν(OH) 3432, ν(C=N) 1613, ν(NO ) 1384, ν
3
M–N) 432, ν(M–O) 413. Yield: 70%.
[
Eu(NHIso) (NO ) ]NO complex 5
2 3 2 3
For C H EuN O (1070.92), Calcd. (%): C, 44.36; H,
4
4
56
9
13
2
.85; N, 13.69; La, 16.51. Found (%): C, 44.24; H, 2.76;
Antioxidant activities
−
1
−1
−1
N, 13.73; La, 16.36. Λ =111.9 Ω cm mol Selected
m
.
−
1
−
IR (KBr, cm ): ν(OH) 3432, ν(C=N) 1614, ν(NO ) 1383,
The antioxidant activities of NHIso and its prepared com-
plexes, 1–8, were measured and tested according to litera-
ture (Hijazi et al. 2017a), using a UV-2401PC UV–Visible
3
ν(M–N) 431, ν(M–O) 412. Yield: 71%.
−
4
[Gd(NHIso) (NO ) ]NO complex 6
spectrophotometer. 5×10 M solutions of all tested sam-
ples and Diphenyl-1-picrylhydrazyl (DPPH) were prepared
in DMSO. A 500, 1000, 1500, 2000 and 2500 μL of each
tested compound and 400 μL of DPPH solution was added
to ꢀll up volume of 4 mL to get ꢀnal concentration of 62.5,
125, 187.5, 250 and 312.5 μM of tested compound and 50
μM of the DPPH as a control, 400 μL from DPPH solution
was diluted using DMSO to 4.0 mL.
2
3 2
3
For C H GdN O (1076.21), Calcd. (%): C, 44.11; H,
4
4
56
9
13
2
1
.83; N, 13.62; La, 16.98. Found (%): C, 44.24; H, 2.78; N,
−
1
−1
−1
3.79; La, 17.04. Λ = 95.0 Ω cm mol Selected IR
m
.
−
1
−
(
KBr, cm ): ν(OH) 3433, ν(C=N) 1612, ν(NO ) 1383,
3
ν(M–N) 432, ν(M–O) 411. Yield: 73%.
Dy(NHIso) (NO ) ]NO complex 7
[
2
3 2
3
Computational method
For C H DyN O (1081.46), Calcd. (%): C, 43.85; H,
4
4
56
9
13
2
.81; N, 13.54; La, 17.45. Found (%): C, 43.69; H, 2.89;
Computations were carried out using the DFT (B3LYP)
calculation in GAUSSIAN 03 program using the 6-31G(d)
basis set for all atoms except for La LANL2TZ eꢁective
core potential basis set with f polarization functions has been
used. The structure was veriꢀed to be minimum through cal-
culating hessian vibrational frequencies at the same level of
theory and basis sets that are used for optimization.
−
1
−1
−1
N, 13.43; La, 17.46. Λ =111.7 Ω cm mol Selected
m
.
−
1
−
IR (KBr, cm ): ν(OH) 3433, ν(C=N) 1614, ν(NO ) 1384,
3
ν(M–N) 432, ν(M–O) 411. Yield: 73%.
[
Er(NHIso) (NO ) ]NO complex 8
2 3 2 3
For C H ErN O (1086.22), Calcd. (%): C, 43.63; H,
4
4
56
9
13
2
.80; N, 13.47; La, 17.87. Found (%): C, 43.72; H, 2.74;
−
1
−1
−1
N, 13.87; La, 17.76. Λ =113.3 Ω cm mol Selected
Results and discussion
m
.
−
1
−
IR (KBr, cm ): ν(OH) 3423, ν(C=N) 1612, ν(NO ) 1384,
3
ν(M–N) 431, ν(M–O) 412. Yield: 80%.
In this work, the NHIso ligand was synthesized by conven-
tional one step reaction of 2-hydroxy-1-naphthaldehyde with
Isonicotinic Hydrazide in a 1:1 molar ratio following same
procedure as described in the literature (Khan and Sharma
2008). The ligand was characterized using diꢁerent spectro-
scopic techniques. The NHIso ligand was found to be soluble
in DMSO and DMF.
Antibacterial activities
The antibacterial activities of NHIso and the prepared
complexes, 1–8, were measured using micro‐broth dilution
minimum inhibition concentration against diꢁerent strains
1
3

Chemical Papers
N
N
H
C H OH
H
2
5
N
O
H
N
N
N
+
H
reflux, 30 min.
OH
O
O
OH
2
-hydroxy-1-naphthaldehyde
isonicotinohydrazide
Schiff base ligand
NHIso
L
a
c
n
e
(
t
N
O
o
O
n
N
i
3
t
)
r
3
i
.
l
n
N
e
,
H
R
2
O
O
H
O
.
T
.
O
O
HN
N
NO
3
N
Ln
NH
O
O
H
O
O
N
N
O
[
Ln = La (III), Pr (III), Nd (III), Sm (III),
Dy (III), Eu (III), Gd (III), and Er (III)]
Scheme 1 Synthesis of NHIso ligand and its Ln(III) complexes
Table 1 FT-IR values of the NHIso ligand and complexes 1–8
Complex
ν(OH)
ν (N–H)
ν(C=O)
ν(C=N)
ν(NO −
)
ν (M–N)
ν(M–O)
3
ν1
ν2
ν3
ν4
ν1–ν4
ν0
NHIso
3440
3433
3432
3432
3432
3432
3433
3432
3423
3222
3222
3221
3220
3222
3221
3222
3222
3222
1692
1620
1614
1613
1613
1614
1614
1612
1614
1612
–
–
–
–
–
–
–
–
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
–
–
–
–
–
–
–
–
1463
1464
1464
1463
1463
1464
1463
1462
1031
1032
1032
1031
1033
1032
1032
1032
815
816
815
815
815
817
816
815
1284
1284
1285
1284
1285
1285
1284
1285
179
180
179
178
179
178
179
177
1384
1384
1382
1384
1383
1383
1384
1384
433
432
433
433
432
433
433
435
411
412
411
413
412
411
411
412
Complexes 1–8 were synthesized by reacting the NHIso
Molar Conductance
ligand with lanthanide nitrate hydrate (Ln(NO ) nH O,
3
3.
2
where Ln: La(III), Sm(III), Gd(III), Pr(III), Nd(III), Er(III),
Dy(III) and Eu(III), in 2:1 mol ratio, in an acetonitrile-
ethyl ethanoate solution at room temperature. A group of
complexes that correspond to the molecular formula of
Molar conductivities of NHIso ligand and all complexes are
listed in the experimental part. The molar conductivity val-
ues for complexes 1–8 in DMSO solution are in the range
−
1
−1
−1
88.7–113.7 Ω cm mol at room temperature. They are
in accordance with reported for 1:1 electrolyte (Geary 1971).
Molar conductivity data suggest that two nitrates are coordi-
nated directly to the Ln metal ions through the inner sphere,
while the third exist at the outer coordination sphere.
[
Ln(NHIso) (NO ) ]NO , complexes 1–8, were obtained,
2
3 2
3
Scheme 1. All prepared complexes, 1–8, are soluble in
DMSO and DMF, non-hygroscopic and stable in normal
laboratory atmosphere.
1
3

Chemical Papers
Table 2 Spectral data of NHIso and complexes 1–8
Complex
λmax (nm)
Absorbance
Band Assignments
NHIso
326
0.091
0.091
0.092
0.122
0.057
0.081
0.098
0.229
0.241
0.251
0.195
0.230
0.241
0.189
0.221
0.227
0.165
0.221
0.249
0.233
0.248
0.256
0.136
0.155
0.155
0.158
0.204
0.214
π→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
π→π*
π→π*
n→π*
3
3
4
28
49
16
c
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
314
3
3
28
69
313
3
3
28
68
315
b
3
3
28
68
314
3
3
28
68
316
3
3
28
68
a
313
328
1800
1600
1400
1200
1
1000
-
Wavenumber/ cm
3
69
314
Fig. 1 FT-IR spectra of (a) NHIso; (b) complex 1; (c) complex 4
3
3
28
68
314
Fourier transform infrared (FT‑IR) spectroscopy
3
3
28
68
Table 1 summarizes the important FT-IR spectral data of
the NHIso ligand and complexes 1–8. The characteristic
bands of the Schiꢁ base ligand along with the expected shifts
due to complexation with the Ln(III) ions are displayed in
the spectra. The IR spectrum of NHIso shows the stretch-
bands, with diꢁerent intensities, were observed in the spec-
tra of complexes 1–8, that were not present in the spectrum
of the NHIso. These new bands are characteristic for the
stretching vibration of M–N and M–O, respectively (Pandey
et al. 1987).
−
1
ing vibration of (C=N) group at 1620 cm , while showing
−
1
a strong C=O stretching band at 1692 cm , Fig. 1. Upon
complexation, the C=O band disappeared in the spectra of
all complexes 1–8, strongly suggesting enolization process
is taking place during complexation (Biradar and Kulkarni
Coordination of the nitrate ligand to the metal ion may
occur in three types, mono-dentate and bi-dentate ligand
within the inner coordination sphere, or as uncoordinated
ion in the outer coordination sphere (Hunter et al. 2007) The
change in frequency separation |ν −ν | between symmetric
1
971). The spectrum of the free NHIso shows a vibration
−
1
band at 3440 cm which is attributed to the –OH group,
−1
which shifts slightly, after complex formation, to 3432 cm .
The band of the –NH group of the free ligand is observed
1
4
−
and asymmetric stretching of the NO group can be used
3
−
1
at 3222 cm , still un-shifted after complexation. This may
be attributed to the coordination through –OH, C=O and
C=N groups.
to diꢁerentiate between these biding states. The spectrum of
−
1
complex 1 displays several intense bands at 1463 cm (υ ),
1
−
1
−1
−1
1031 cm (υ ), 815 cm (υ ) and 1284 cm (υ ) which
2
3
4
The IR spectra of complexes 1–8 indicate that a coordina-
tion bond and chelation occur through the C=N group of the
ligand due to the shift in the wavenumber of this group to a
lower one as seen clearly in Table 1, (Abdel-Rahman et al.
may be assigned to the coordinated nitrate ion (C ), Fig. 1.
2v
All complexes give a |ν − ν | separation in the range
1
4
−
1
−
177–180 cm which suggests that all NO ions in the com-
3
plexes coordinate to the metal ion as bi-dentate ligand (Yan
−
1
2
016a, b, 2017a; Sengupta et al. 1998; Donia and El-Boraey
et al. 2007). The band at 1384–1383 cm in the spectra of
the complexes indicates that a free nitrate group is present in
−1
2
002). In the range 432–435 cm−1 and 411–413 cm new
1
3

Chemical Papers
the outer sphere. The measured values of molar conductivi-
ties of all complexes strongly support the results obtained
from the FT-IR data.
DTGA
1
00
80
1H‑NMR characterization
60
1
4
0
0
0
The H-NMR spectra of the NHIso and complexes 1–8 were
recorded in the range 0–15 ppm in deuterated dimethylsul-
TGA
2
phoxide, DMSO-d solution. For the ligand, the proton of
6
the hydroxyl group (OH) is assigned to the peak observed
at 12.57 ppm. At 9.48 ppm and 8.84 ppm, two singlet peak
are observed and assigned to the protons of the azomethine
1
00 200 300 400 500 600 700 800 900
o
Temperature/ C
(
CH=N) group, and of the NH group, respectively. The pro-
Fig. 3 TGA–DTGA thermo-grams for complex 1
tons of the aromatic rings of the NHIso ligand are assigned
in the range of δ = 7.25–7.98 ppm. Complex 1 spectrum
shows a slight shift in the singlet peak of the hydroxyl (OH)
group with a value of 12.55 ppm. This shift is considered
a slight high shift and group (Li et al. 2007). The peak due
to azomethine proton appears at 9.44 ppm indicating the
coordination of nitrogen atom azomethine (C=N) with the
metal ion. The peak of NH group did not shift at all after
complexation, which means that no coordination occurred
between the La ion and NH group. All signals observed, in
the spectrum, of the protons of the aromatic rings remained
unchanged after complexation. This indicates that coordina-
tion occurred without deprotonation of the hydroxyl (OH).
All Signal peaks present in the region δ=114–136 ppm are
due to aromatic carbons.
Ultraviolet–visible (UV–vis) spectroscopy
UV–vis spectra of the NHIso ligand and complexes 1–8
were carried out at room temperature in DMSO. The wave-
length (λ ) values for all prepared substances are tabu-
max
lated in Table 2. The absorption spectrum of the free NHIso
ligand, shows four maxima at 326, 328, 347 and 416 nm.
The bands observed at λ =326 nm and λ =328 nm are
max
max
attributed to the π – π* transitions of the aromatic ring. A π
13C‑NMR characterization
1
3
C-NMR spectra of the NHIso and its complexes were
recorded in DMSO-d . Two signals were observed at 164.97
6
and 143.74 ppm assigned to carbonyl (C=O) carbon and
the azomethine carbon (C=N), in the spectrum of the free
ligand, respectively. After complexation, the signal of C=O
was shifted to 160.94 ppm, while the signal of C=N was
shifted to 139.75 ppm. These shifts are a strong evidence of
the coordination between these two groups with the La ion.
Ligand
Complex 6
Complex 5
Complex 7
Complex 4
DTGA
100
80
60
40
20
0
TGA
4
00 450 500 550 600 650 700
100 200 300 400 500 600 700 800 900
o
Temperature/ C
Wavelength (nm)
Fig. 2 TGA–DTGA thermo-grams for NHIso
Fig. 4 Photoluminescence spectra of the ligand and complexes 4–7
1
3

Chemical Papers
–
π* transition of the azomethine group C=N may be attrib-
uted to the absorption band that exists at λ =347 nm. The
max
presence of the lone pair of electrons of p- orbital of N-atom
in C=N will cause conjugation between them. This conjuga-
tion will cause a transition between n – π*, appearing as a
band with low energy at λ =416 nm.
max
The recorded spectra of complexes 1–8 are diꢁerent from
that of the ligand, suggesting coordination with metal ions.
Two important changes were observed in the spectra due
to complexation process between the ligand and the metal
ions. In UV–vis region (300–650 nm) π→π* n and →π*
absorption bands upon coordination, the two lower energy
bands in NHIso are overlapped in a single band and shifted
to shorter wavelength region (blue shift) (Keshavan et al.
Fig. 6 SEM image of complex 2
2
000). This shift is suggested to occur due to the electrons
The thermal curves for complexes indicate that the com-
pounds start losing mass with partial evaporation of organic
lone pair donation of the ligand’s N-atom to the metal ions,
which is consistence with that observed earlier (Keshavan
et al. 2000). It was diꢂcult to identify the absorption band
due to the f–f transition of the Ln(III) metal ions in the vis-
ible region of all complexes, because transitions of f–f orbit-
als are very weak, and the strong charge transfer transition
of the ligand will obscure the bands corresponding to these
transitions (Raman et al. 2001).
st
nd rd
th
ligand (1 step). The 2 , 3 and 4 steps involve the loss of
one nitrate (NO ) molecule from the outer sphere, two NO
3
3
molecules from the inner sphere and other part of the ligand,
as shown in Fig. 3 for complex 1.
Luminescence properties
The ꢃuorescent properties of NHIso and complexes 4–7
were recorded in methanol at room temperature, Fig. 4.
Pure NHIso demonstrates an intense emission band at
548 nm. This band could be assigned due to π → π* tran-
sitions of the p electrons of the aromatic rings as well
as n → π* transitions of the C=O and C=N groups. The
emission spectra of complexes 4–7 display only the ligand
characteristic emission peaks with an obvious blue shift
and a signiꢀcant decrease in the ꢃuorescence intensity.
This indicating that NHIso is coordinated with lanthanide
ions and cannot transfer the absorbed energy onto Ln(III)
excited states.
Thermo‑gravimetric analysis
Thermo-gravimetric (TG) and diꢁerential thermo-gravi-
metric (DTG) analysis were done under N ꢃow within the
2
temperature range 25–900 °C. The ligand is considered
thermally stable in the range 25–265 °C as shown from the
TGA–DTG curve. The decomposition occurs in one step
between 265 and 450 °C, Fig. 2, at maximum temperature of
3
15 °C, accompanied by a mass loss of 95.11%. The remain-
ing weight may correspond to some ashes. All prepared
complexes do not possess solvent molecules and/or water
molecules according to their TGA–DTGA curves. These
reported curves suggest that decomposition of the synthe-
sized complexes, 1–8, proceeds with four consecutive steps.
Fig. 5 SEM image of NHIso
Fig. 7 SEM image of complex 7
1
3

Chemical Papers
Table 3 MIC of NHIso and
complexes 1–8 against a
number of bacteria (μg/mL)
Tested compounds
Gram-negative bacteria
Gram-positive
bacteria
Ec
Kp
Pm
Pa
Sa
En
NHIso
N
N
N
N
N
N
N
N
N
N
2
N
N
N
N
N
N
N
N
N
N
4
N
N
N
N
N
N
N
N
N
N
8
N
N
N
N
N
N
N
N
N
N
2
16
8
4
16
8
16
16
8
32
16
4
32
16
32
32
16
16
N
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
16
N
8
DMSO (−ve control)
Oxytetracycline(+ve control)
8
Ec Escherichia coli; Kp Klebsiella pneumonia; Pm Proteus mirabilis; Pa Pseudomonas aeruginosa; En
Enterococcus faecalis; Sa Staphylococcus aureus
N None active compound
Scanning electron micrographs (SEM)
aureus (Sa). No activity toward any of the Gram-negative
bacteria have been recorded. Comparing these results with
the N-(2-hydroxynaphthalen-1-yl) methylene) nicotinohy-
drazide Schiꢁ base (Hijazi et al. 2017a), it is clear that the
reported isonicotinohydrazide ligand (NHIso) is selective
toward Gram-positive bacteria with better MIC values (16
and 32 μg/mL than that for nicotinohydrazide (MIC values
for Sa and En are 64 and 256 μg/mL, respectively). Many
groups may play an important role in the activity against
diꢁerent strains of bacteria, two groups present in the inves-
tigated NHIso ligand are the hydroxyl and azomethine, their
presence is the cause of the promising activity of the ligand
against Gram-positive bacteria (Azza et al. 2009). All syn-
thesized complexes were selective toward Gram-positive
bacteria only and possessed excellent antibacterial activi-
ties against Staphylococcus aureus and Enterococcus fae-
calis, especially complex 2, which showed the highest value
of 4 μg/mL. All complexes showed no activity toward the
tested Gram-negative bacteria. Complexes 1, 2, 4, 7 and 8
showed higher activities against Gram-positive bacteria than
SEM for NHIso, complex 2 and complex 7 are shown in
Figs. 5, 6 and 7, respectively. NHIso image shows that it
exists as almost cylindrical rods. Clear and obvious changes
in the structures morphology of complexes 2 and 7 exist
compared to NHIso, which indicates the formation of com-
plexes. The SEM images of both complexes are almost the
same.
Antimicrobial activity
The bactericidal screening results of NHIso and the synthe-
sized complexes are recorded in Table 3. MIC was deꢀned as
the minimal concentration that has optical density less than
that of the Oxytetracycline which is the positive control.
NHIso ligand and its complexes showed various degree of
MIC on the growth of the bacterial strain tested. Results indi-
cated that the ligand showed a signiꢀcant antibacterial activ-
ity against Enterococcus faecalis (En) and Staphylococcus
N
Scheme 2 Scavenging activity
N
proposed mechanism for NHIso
N
N
O
N-
O
+
HN
NH
+
HN
O
2
N
NO
2
N
N
2
O N
NO
2
OH
O-
NO
2
NO
2
1
3

Chemical Papers
Fig. 8 DPPH scavenging activ-
ity of NHIso and complexes 1–8
Table 4 Antioxidant scavenging
activity results of NHIso and
complexes 1–8
Complex
DPPH scavenging activity (%)
Concentration (µM)
62.50
125.0
187.5
250.0
312.5
NHIso
30.2± 0.2
41.5± 0.3
47.1± 0.9
41.1± 1.3
41.3± 1.1
44.5± 1.5
44.7± 0.5
39.6± 0.1
39.1± 0.9
41.9± 0.9
42.5± 0.6
56.1± 0.6
46.6± 1.0
48.8± 1.1
51.9± 0.2
44.7± 0.3
56.6± 0.6
44.2± 0.2
44.8± 0.4
49.4± 0.5
57.8± 0.8
49.7± 1.5
54.0± 0.3
58.7± 0.7
57.9± 0.1
58.3± 1.5
47.2± 0.5
51.9± 0.2
50.0± 0.2
60.0± 0.2
54.2± 1.1
58.8± 1.4
61.1± 0.3
62.7± 0.7
60.8± 0.7
62.5± 0.4
60.2± 0.4
63.7± 0.4
61.3± 1.3
65.5± 0.5
61.5± 1.0
61.9± 0.1
63.9± 1.2
64.9± 0.1
62.9± 0.6
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
the NHIso free ligand. Their previously reported nicotino-
hydrazide complexes (Hijazi et al. 2017a) showed diꢁerent
and variable activities toward Gram-negative and Gram-pos-
itive bacteria. It is obvious that the currently reported com-
plexes, 1–8, have showed selective and much better activities
against Gram-positive bacteria, Sa & En, ranging from 4 to
3
2 μg/mL, than that of their nicotinohydrazide analogues
with a MIC values between 16 and 256 μg/mL. The activity
enhancement is due to the reduction of the polarity of the
lanthanide ions. This reduction may arise from the partial
sharing of the positive charge on the Ln ions with the N and
O donor atoms and may be because of the electron delocali-
zation over the entire system (Abdel-Rahman et al. 2016a,
b; Abdel-Rahman et al. 2020). The central atom lipophilic
nature will increase, which increases the complexes penetra-
tion into the lipid membrane of the microorganism cell wall.
This penetration process may raise the complex activity,
restricting further growth of the organism. In Gram-negative
+
Fig. 9 Optimized ground state geometry of [La(NHIso) (NO ) ]
2
3 2
1
3

Chemical Papers
bacteria, and on their surfaces, Lipopoly Saccharide (LPS)
is found to be one of the major components, in addition to
peptidoglycan layer. Lipopolysaccharide is critical in main-
taining the barrier function preventing the passive diꢁusion
of hydrophobic solutes. In contrast, Gram-positive bacteria,
lack an outer lipid membrane, but contain a cytoplasmic
membrane bordered by a layer of peptidoglycan.
30 and 60%, while the nicotinohydrazide showed activi-
ties between 13 and 22% only. These numbers could be
attributed to the fact that DPPH radical scavenging assay
is an electron transfer (ET)-based method with mechanism
of Hydrogen Atom Transfer (HAT) (Cao et al. 1996; Prior
et al. 2005).
DFT calculations
Antioxidant activity
The optimized ground state str ucture of
+
Determination of the NHIso ligand and complexes 1–8 as
free radical scavengers, is performed using DPPH. The
DPPH test is based on the ability of the stable 2, 2-diphenyl-
[La(NHIso) (NO ) ] cation at B3LYP level of theory
2
3 2
(Fig. 9) are in a good agreement with the expected experi-
mental data. It shows that Lanthanum has 10 coordina-
tion number. The two nitrate ligand has 4 coordination.
Each nitrate acts as bi-dentate ligand through two oxy-
gen atoms with La–O bond distance 2.56 Å and 2.60 Å.
The other 6 coordination came from the two Schiꢁ base
ligands in which the bond length in La–O=C, La–OH–C
and La–N=N are 2.54 Å, 2.68 Å and 2.89 Å, respectively,
for one of the Schiꢁ base ligand. For the other one, the
bond lengths are 2.54 Å, 2.65 Å, and 2.87 Å. The vibration
1
-picrylhydrazyl free radical to react with hydrogen donors
(
Inoue et al. 2005; Fahey and Stephenson; 2002). As stable
nitrogen-centered free radical, DPPH is characterized by the
delocalization of spare electron over the molecule, giving a
strong absorption maximum at 517 nm in purple color. By
mixing a free radical scavenging antioxidant substance with
the used free radical, which can donate a hydrogen atom,
DPPH-H will form from the pairing of the odd electron of
the radical with hydrogen from the substance investigated
as an antioxidant. This process is accompanied by a change
in color from purple to yellow, scheme 2. Figure 8 shows
the plots of DPPH scavenging activity percent for NHIso
and complexes 1–8. The scavenging activity was calculated
using the following equation:
−
1
−1
frequency of C=N is 1620 cm and 1615 cm for the ꢀrst
and second ligand. The vibrational frequency of the two
−
1
−1
C=O are 1637 cm and 1639 cm . The decreasing of the
vibration frequency of the C=N and C=O as result of the
coordination agrees with the experiments and support the
proposed structure of the complex.
ꢀ
ꢁ × 100%
A − A
o
s
%
Scavenging Activity =
,
A
o
Conclusion
·
where A is the absorbance of the DPPH in the absence
o
of the tested samples and after shaking (control) and A
s
In this work, N-(2-hydroxynaphthalen-1-yl) methylene)
Isonicotinohydrazide, NHIso, Schiꢁ base ligand and its
synthesized lanthanide complexes 1–8 characterized using
diꢁerent techniques. The ligand was concluded to be a bi-
dentate chelate being coordinated to the central lanthanide
ion in a 2:1 stoichiometric ratio by the two azomethine
nitrogen atoms and the two carbonyl oxygen atoms. The
molar conductance values showed that one nitrate group
is coordinated through the outer coordination sphere for
·
is the absorbance of the DPPH in the presence of tested
compound.
The antioxidant activity of all tested complexes was
found to be concentration dependent and as the concen-
trations of the tested compounds increase, the scaveng-
ing ratio increases in required range, Table 4. The NHIso
free ligand was found to have an activity between 30 and
6
0% within investigated concentration range due to the
key role of the functional group, OH, by forming stable
macromolecular radicals when reacting with used radical
by the H-abstraction. It is clear that complexes 1–8 have
more eꢂciency in quenching DPPH than that of character-
ized by virtue of delocalization of spare electron their free
NHIso ligand, with activities between 39 and 65%, Table 4
and Fig. 8. These activities are higher than the reported
ones for the nicotinohydrazide complexes, ranging from
all complexes. IR spectral data also reveal that the two
−
nitrate NO groups coordinated to lanthanide metal ions
3
bi-dentately in all complexes. So, coordination number
ten is suggested for metal ion in all prepared complexes.
The antimicrobial activities of complexes 1–8 were stud-
ied against diꢁerent strains of bacteria, (Gram-negative
bacteria) and (Gram-positive bacteria). Complexes 1, 2,
4
, 7 and 8 showed signiꢀcant and higher activity against
1
3 to 60%. The eꢂciency of NHIso ligand in quenching
DPPH is much better that it’s N-(2-hydroxynaphthalen-
-yl) methylene) nicotinohydrazide Schiꢁ base analogue
Hijazi et al. 2017a ). NHIso showed activities between
En: Enterococcus faecalis and Sa: Staphylococcus aureus
Gram-positive bacteria than the NHIso ligand, especially
complex 2 with a MIC value of 4 μg/mL. The antioxi-
dant activities of all prepared complexes are concentration
1
(
1
3

Chemical Papers
dependent and the scavenging values increase with the
increase in sample concentration in the tested range show-
ing much more eꢂciency in quenching DPPH than the
NHIso ligand, with a scavenging activity between 39 and
of therapeutic potentials under in vitro conditions of Pd(II), Ag(I)
and Cu(II) complexes of 5-diethyl amino-2-({2-[(2-hydroxy-
benzylidene)-amino]-phenylimino}-methyl)-phenol. Molecules.
https://doi.org/10.3390/molecules25215089
Abu-Dief AM, Abdel-Rahman LH, Abdel-Mawgoud AAH (2020) A
robust in vitro anticancer, antioxidant and antimicrobial agents
based on new metal-azomethine chelates incorporating Ag(I), Pd
6
5%. Future work must focus on the synthesis of new
Schiꢁ bases containing diꢁerent functional groups, which
may improve the activities of the compounds. The antimi-
crobial studies should be conducted in vivo, as well as the
study of antimalarial, antifungal, anti-inꢃammatory and
antiviral properties of the synthesized complexes.
(
II) and VO (II) cations: probing the aspects of DNA interaction.
Appl Organomet Chem. https://doi.org/10.1002/aoc.5373
Agarwala BV, Hingorani S, Nagana Gowda GA (1990) Synthetic and
physicochemical studies of uranium complexes with semicarba-
zone and hydrazine. Inorg Chim Acta 176:149–154. https://doi.
org/10.1016/S0020-1693(00)85106-3
Ajlouni AM, Taha ZA, Hijazi AK, Al Momani WM (2018) A Series
of lanthanide complexes with 2-ꢃuoro-N’-(furan-2-ylmethylene)
benzohydrazide ligand: synthesis, characterization, luminescent
properties and biological evaluation. Appl Organomet Chem.
https://doi.org/10.1002/aoc.4536
Authors contribution AKH involved in conceptualization, investiga-
tion, methodology, project administration, resources, roles/writing—
original draft and writing—review and editing. ZAT participated in
data curation, formal analysis and writing—review and editing. IMI
involved in investigation and formal analysis. AI participated in soft-
ware, data curation and formal analysis. WMAl-M involved in inves-
tigation and methodology.
Ajlouni AM, Hijazi AK, Taha ZA, Al Momani W, Okour A, Kühn FE
(2019) Synthesis, characterization and biological and catalytic
activities of propionitril: ligated transition metal complexes with
[B(C
F ) ] as counter anion. Cat Lett 149:2317–2324. https://doi.
6
5 4
org/10.1007/s10562-019-02804-9
Funding Deanship of Scientiꢀc Research, Jordan University of Sci-
ence and Technology is acknowledged for ꢀnancial support (project
no. 110/2017).
Al Momani W, Taha ZA, Ajlouni AM, Shaqra Q, Zoubi M (2013) A
study of in vitro antibacterial activity of lanthanides complexes
with a tetradentate schiꢁ base ligand. Asian J Trop Biomed 3:367–
3
70. https://doi.org/10.1016/S2221-1691(13)60078-7
Ameen I, Tripathi AK, Mishra RL, Siddiqui A, Tripathi UN (2018) A
study on enhancing the quantum yield and antimicrobial activ-
ity of Pr(III) by varying the coordination environment. RSC Adv
Data availability The datasets generated during and/or analyzed during
the current study are available from the corresponding author.
8
:8412–8425. https://doi.org/10.1039/c7ra13035j
Declarations
Andres J, Chauvin AS (2020) Colorimetry of luminescent lanthanide
complexes. Molecules. https://doi.org/10.3390/molecules251740
22
Conflict of interest The authors declare no conꢃict of interest.
Avaji PG, Kumar CHV, Patil SA, Shivananda KN, Nagaraju C (2009)
Synthesis, spectral characterization, in vitro microbiological eval-
uation and cytotoxic activities of novel macrocyclic bis hydra-
zone. Eur J Med Chem 44:3552–3559. https://doi.org/10.1016/j.
ejmech.2009.03.032
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Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional aꢂliations.
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8:1907–1918. https://doi.org/10.1007/s11224-017-0975-2
Authors and Aꢀliations
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Ahmed K. Hijazi · Ziyad A. Taha · Abdellatif Ibdah · Idris M. Idris · Waleed M. Al‑Momani
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*
Ahmed K. Hijazi
Department of Basic Medical Sciences, Faculty of Medicine,
Yarmouk University, Irbid, Jordan
akhijazi@just.edu.jo
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Department of Chemical Sciences, Faculty of Science
and Arts, Jordan University of Science and Technology, P.O.
Box 3030, Irbid 22110, Jordan
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