Azomethine-functionalized task-specific ionic liquid for diversion of toxic metal ions in the aqueous environment into pharmacological nominates

Article abstract of DOI:10.1016/j.molliq.2020.114525

By this work, a new azomethine-supported task-specific ionic liquid (ABIIL) was fabricated based on bis-(butylimidazolium hexafluorophosphate) salicylidene Schiff base. The successful formation of ABIIL was confirmed form its microanalytical and spectral

Full text of DOI:10.1016/j.molliq.2020.114525

MOLLIQ-114525; No of Pages 10
Journal of Molecular Liquids xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Azomethine-functionalized task-specific ionic liquid for diversion of
toxic metal ions in the aqueous environment into
pharmacological nominates
W.N. El-Sayed a,b, J. Alkabli , Khalid Althumayri , Reda F.M. Elshaarawy ⁎, Lamia A. Ismail
a
c
b,d,
e
a
Department of Chemistry, College of Sciences and Arts - Alkamil, University of Jeddah, 23218 Jeddah, Saudi Arabia
Department of Chemistry, Faculty of Science, Suez University, 43533 Suez, Egypt
Department of chemistry, College of science, Taibah University, 30002 Al-Madinah Al-Munawarah, Saudi Arabia
Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine Universität Düsseldorf, Düsseldorf, Germany
b
c
d
e
Department of Chemistry, Faculty of Science, Port Said University, 42526 Port Said, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
By this work, a new azomethine-supported task-specific ionic liquid (ABIIL) was fabricated based on bis-
butylimidazolium hexafluorophosphate) salicylidene Schiff base. The successful formation of ABIIL was con-
firmed form its microanalytical and spectral results. The excellent aqueous-ethanolic solubility coupled with
the high chelating capacity of ABIIL enabled it to act as a multifunctional scavenger for removing of Cu(II) and
Fe(III) ions from aqueous environments. Not only has that, but also transformed these toxic ions into promising
pharmacological candidates. ABIIL showed an excellent scavenging efficiency, as it can uptake up to 98.9% and
Received 11 August 2020
Received in revised form 21 September 2020
Accepted 6 October 2020
Available online xxxx
(
Keywords:
96.7% of Fe(III) and Cu(II) ions, respectively, from aqueous-ethanolic effluents. Besides, it could be easily regen-
Task-specific ionic liquid
Toxic metal ions
Remediation by complexation
Antimicrobial
erated and reused for six cycles without significant loss in its efficiency. The scavenging outputs (M-ABIIL) exhib-
ited excellent and broad-spectrum antimicrobial activity, with a slight preference toward fungi than bacteria. Fe-
ABIIL is the most potent antimicrobial nominate as revealed from its MIC values (μg/mL): 16.8 (C. albicans) < 18.9
Cytotoxicity
(S. aureus) < 19.5 (A. flavus) < 23.1 (E. coli). Additionally, this complex is more cytotoxic (IC50 3.40 ± 0.53 μg/mL)
than the clinical anticancer drug (Vinblastine, VB) (IC50 3.79 ± 1.01 μg/mL) toward colon cancer cells (HTC116),
whereas it is less cytotoxic (IC50 85.66 ± 1.44 μg/mL) than VB (IC50 57.12 ± 1.95 μg/mL) to normal human cells
(HeLa). Thus, ABIIL has great potential for removing toxic Cu(II) and Fe(III) ions from aqueous environments,
converting them into chemotherapeutic agents.
©
2020 Elsevier B.V. All rights reserved.
1
. Introduction
modification their chemical constituents according to the user's needs.
For instance, they explored their specific efficiency in organic synthesis
[4], nanomaterials fabrication [5], catalysis [6], extraction [7], electro-
chemistry [8], analytical chemistry [9], active pharmaceutical ingredi-
ents (API) [10] and so far [3]. Recently, utilized as scavengers for
primary amines [11] and a turn-on pH nano-fluorosensor [12].
Previous studies demonstrated that the TSILs could offer promising
scavengers for the removal of metal ions from aqueous effluents
[13,14]. Despite there are many TAILs that have been investigated for
extraction and separation of metal ions from aqueous solutions based
upon physical interactions [13–15]; a few trials have been performed
to endow coordinating groups to the ionic liquid, rendering them
more fiercely for extraction of metal ions. These few trials involve
supporting of ionic liquid with thiourea [16], macrocyclic ethers [17],
Ionic liquids (ILs) have been categorized as eco-friendly alternatives
for traditional toxic organic solvents due to their amazing characteris-
tics such as promoted mechanical and thermal stability, high solubiliza-
tion power, reusability, tunable chemical/ physical properties, non-
volatility, non-flammability, and intrinsic conductivity [1]. Moreover,
the toxicity study revealed that most of ILs showed relatively low
toxic impacts toward several biological systems [2]. These unique fea-
tures of ILs make them the best choice for many researchers to design
and refine their chemical structures (i.e. fine-tuning the cation and/or
anion), rendering them inimitably suited for many applications [3].
These functionalized ILs often referred to as task-specific ionic liquids
(
TSILs) which have been designed, fabricated, and tuned by
2
-hydroxybenzylamine [18], ethylene glycol [19], carboxylic groups
[20], and recently aminothiazolyl Schiff bases [21] or porous organic co-
⁎
Corresponding author at: Department of Chemistry, Faculty of Science, Suez
University, 43533 Suez, Egypt.
polymer [22]. The preference of the chelating TSILs over non-chelating
ones is due to the availability of the functional group which provides
E-mail addresses: reda.elshaarawy@suezuniv.edu.eg, reel@hhu.de (R.F.M. Elshaarawy).
https://doi.org/10.1016/j.molliq.2020.114525
0167-7322/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: W.N. El-Sayed, J. Alkabli, K. Althumayri, et al., Azomethine-functionalized task-specific ionic liquid for diversion of toxic
metal ions in the aqueou..., Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2020.114525

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
them the advantage of the ability to chelate diverse metal ions with pH-
controlled selectivity and pH-dependent stability [23].
DMSO‑d
6
) δ (ppm): 161.33, 158.21, 137.86, 136.22, 133.14, 132.42,
125.02, 123.07, 122.70, 118.74, 117.63, 57.62, 55.91, 54.81, 51.970,
49.02, 36.13, 32.97, 31.61, 31.09, 21.34, 19.17 and 13.61. 3 P NMR
1
Amongst toxic heavy metal ions (HMIs) popularly distributed in
aqueous environments, cupric (Cu(II)) and ferric (Fe(III)) ions were
deemed as potential toxicity sources [24,25] due to their capacity to
generate free radicals and reactive oxygen species (ROS) in the live
cells [24,26], inducing their programmed death. The major sources of
the toxic ferric ions in aqueous environments are; steel tempering, min-
ing, coal coking, and metallurgical industries [27].On the other hand, cu-
pric ions have emitted in aqueous effluents as a result of many industrial
processes, such as electroplating, metal finishing, etching, and plastics
1
9
(202 MHz, DMSO‑d
(471 MHz, DMSO‑d ) δ: −70.57 (d, J = 711.2 Hz). ESI-MS: in positive
mode peaks at m/z 568.4 ([C25
6
): δ −142.95 (hept, J = 711.2 Hz). F NMR
6
+
−
H
37
F
6
N
5
OP] , M – PF
) a.m.u. Anal. Calcd. for C25
(M = 713.53 g/mol): C, 42.08; H, 5.23; N, 9.82%. Found: C,
41.99; H, 5.31; N, 9.78%.
6
) a.m.u. and
2
+
−
211.6 ([C25
OP
H
37
N
5
O] , M – 2 PF
6
37 12
H F
N
5
2
2.3. Deprotonation constant (pKa) of ABIIL
[28]. As the Cu(II) and Fe(III) ions are very toxic metal even at low con-
centrations, therefore, the cupric- and ferric-polluted wastewater
should be remediated before discharging into the aquatic environment
The dissociation constant (pK
aqueous solution (10 M) of ionic strength of 0.04 M (KNO ) by titra-
a
) of ABIIL was estimated at 298 K in its
−4
3
[27,28].
−3
tion with an aqueous NaOH solution (1.6 × 10 M).
.4. Scavenging of Cu(II) and Fe(III) ion by ABIIL extractant
A general protocol mimic to the common solid-phase extraction
Few trials have been reported to remove cupric and ferric ions from
aqueous solutions using TSILs. For instants, imidazolium-supported
TSILs have been applied as scavengers for M(II/III) ions (M = Cu, Co,
Ni, Zn, Cd, Fe) from their respective aqueous solutions; by chelating
them [20,29]. In addition, ammonium-based TSILs showed moderate
to good effect in removing and recovering of several metal ions (Cu
2
(
(
SPE) technique [32] has been utilized for removal of heavy metal ions
HMIs) (Cu(II) and Fe(III)) from aqueous ethanolic solutions by ABIIL
(
II), Pb(II), Zn(II), Cd(II), Ni(II), Co(II), and Fe(III)) from aqueous efflu-
as an extracting agent. In brief, a solution of metal ion (0.5 mmol,
.10 g Cu(CH CO ·2H O; 0.302 g Fe(NO ·9H O) in distilled water
5 mL) was slowly added to the pale-yellow solution of ABIIL (0.71 g,
.0 mmol) in ethanol (30 mL) containing 100 μL of 0.1 M NaOHaq
Then, the reaction mixture was heated under reflux with stirring for
h. After cooling to ambient temperature, the isolated colored solids
were collected by filtration, washed with cold ethanol and diethyl
ether, (2 × 3 mL) for each, and dried in a desiccator. Samples of the ob-
tained complexes were analyzed as follow;
ents [29,30]. Recently, microcapsules composed of styrene and
divinylbenzene were used to encapsulate pyridinium TSILs for Zn(II)
and Cu(II) recovery from aqueous media [31]. Nevertheless, these re-
ported TSILs are limited and their routes of fabrication are sophisticated
and expensive.
All these aforementioned facts prompted us to design and fabricate a
new azomethine-supported bis-butylimidazolium chelating task-
specific ionic liquid (ABIIL) which will be utilized not only for the re-
moval of Cu(II) and Fe(III) ions from the aqueous solutions but also to
convert these ions to metals-based pharmacological nominates.
0
(
1
3
)
2 2
2
)
3 3
2
.
1
[
2
Cu(ABIIL) ] (Cu-ABIIL): Dark yelowish green crystals, Yield
−
1
6
1
9%. FTIR (KBr, cm ): 3125 (w, br), 1647 (m, sh), 1622 (s, sh),
549 (s, sh), 1457 (m, sh), 1336 (m, sh), 1271 (m, sh), 1150 (m,
2. Experimental part
sh), 837 (vs, sh), 643 (m, br), 525 (w, br), 478 (m, sh). ESI-MS:
+
in positive mode peaks at m/z 1315.3 ([C48
H
68CuF18
, M – 2 PF
6
N
10
O
2
P
3
]
, M
) a.m.u.,
) a.m.u., and 220.0 ([C48
). Anal. Calcd. for C48 68CuF24
M = 1460.54 g/mol): C, 39.47; H, 4.69; N, 9.59%. Found: C,
2.1. Materials and instrumentation
−
2+
−
-
3
H
PF
6
) a.m.u., 585.2 ([C48
H
68CuF12
N
10
O
2
P
2
]
3
+
−
41.6 ([C48H68CuF N O P] , M – 3PF
68CuN10
6 10 2 6
Chemicals, solvents, and practical procedures utilized in the prepa-
4
+
−
O
2
]
, M – 4 PF
6
H
10 2 4
N O P
ration of salicylaldehyde-supported butylimidazolium ionic liquids
SBIILs) (2a,b) and 1-(3-aminopropyl)-3-butyl-1H-imidazolium
(
(
3
9.42; H, 4.71; N, 9.38%.
3
Fe(ABIIL) (H O)(NO )] (Fe-ABIIL): Dark purple powder, Yield
5%. FTIR (KBr, cm ): 3453 (m, br), 3122 (w, br), 1620 (s, sh),
549 (s, sh), 1458 (m, sh), 1336 (s, sh), 1272 (m, sh), 1151 (m,
hexafluorophosphate (5) coupled with the instrumentation used for
the comprehensive characterization of prepared compounds were de-
scribed in the online electronic supplementary information (ESI†).
[
2
2
−
1
6
1
sh), 839 (vs, sh), 653 (m, br), 506 (w, br), 458 (w, br). ESI-MS:
2
.2. Synthesis of ABIIL
+
in positive mode peaks at m/z 1387.6 ([C48
70
2+
6 3
H F18FeN11O P ] ,
−
−
M – PF
u., 365.7 ([C48
6
) a.m.u., 621.2 ([C48
FeN11
, M – 4 PF
M = 1532.86 g/mol): C, 37.61; H, 4.60; N, 10.05%. Found: C, 37.52;
H
70
F
12FeN11
O
6
P
2
]
, M – 2 PF
) a.m.u., and 238.1
). Anal. Calcd. for C48
6
) a.m.
Into a 100 mL round-bottomed flask (RBF), a solution of SBIIL (2b)
H
70
F
6
O
6 6
P]3 , M – 3 PF
+
−
(
1.62 g, 4 mmol) in ethanol (35 mL) was gradually added to an ethanolic
4
+
−
(
[C48H70FeN11
O
6
]
6
70 6 4
H F24FeN11O P
solution (25 mL) of the aminopropyl derivative (5) (1.31 g, 4 mmol)
containing a catalytic amount of glacial acetic acid (three drops) under
stirring. Then, the reaction mixture was heated under reflux and contin-
uous stirring for 3–5 h (TLC was used to monitor the completion of re-
action). After reaction completion, the solvent was partially
evaporated followed by cooling of the content of RBF to ambient tem-
perature. The precipitated product was filtered, washed with cold etha-
nol and ether, (3 × 5 mL) for each, dried, and then recrystallized from
aqueous ethanol to give ABIIL as yellow fine crystals. Yield (2.49 g,
(
H, 4.63; N, 9.98.
2.5. Regeneration of ABIIL scavenger
An aqueous solution containing a mixture of HCl (1.0 M, 3 mL) and
thiourea (4% w/v) was added to the extracting products (M-ABIIL com-
plexes) (100 mg). Thereafter, these mixtures have subjected to ultra-
sonic irradiation for 30 min. The color change of the reaction solution
from colorless to yellow color was an indication of the progress of the
ABIIL-recovering process. After reaction completion, the reaction mix-
8
2
1
9%), mp 98–99 °C. FTIR (KBr, cm−1): 3336 (m, br), 3079 (m, br),
982 (m, sh), 2959 (m, sh), 2889 (m, sh), 1631 (vs, sh), 1567, 1549,
466 (s, sh), 1335 (m, sh), 1279 (s, sh), 1150 (s, sh), 965(m, sh), 836
1
(
vs, sh), 735 (m, sh). H NMR (200 MHz, DMSO‑d
6
) δ (ppm): 10.19 (s,
3
ture was neutralized with an aqueous NaHCO solution (1.0 M) which
1H), 9.43 (s, 1H), 9.12 (s, 1H), 9.04 (s, 1H), 8.11–7.96 (m, 2H),
7.82–7.76 (m, 2H), 7.39 (d, 1H, J = 7.1 Hz), 7.06–7.01 (m, 2H), 5.69 (s,
2H), 5.10 (t, 2H, J = 6.9 Hz), 4.26 (t, 2H, J = 7.2 Hz), 4.11 (t, 2H, J =
6.9 Hz), 3.99 (t, 2H, J = 6.8 Hz), 2.25–2.09 (m, 6H), 1.96–1.81 (m, 4H),
0
.93 (t, J = 7.2 Hz, 3H), 0.85 (t, J = 7.3 Hz, 3H). 13C NMR (125 MHz,
leads to the precipitation of the parent scavenger (ABIIL). The recovered
ligand (ABIIL) was collected by filtration, washed several times with
Milli-Q water to remove the undesired byproducts (M-thiourea com-
plexes). Then, this scavenger was dried under reduced pressure and
can be used for a further removal process.
2

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
2
.6. Pharmacological performance study
The positive mode electrospray ionization mass spectra (ESI-MS) of
ABIIL displayed four distinctive peaks at m/z 568.4 and 211.6 corre-
sponding to the successive departure of hexafluorophosphate counter
2.6.1. Antimicrobial activity
−
+
The antimicrobial performance for the scavenging products (Cu(II)-/
anions to generate a single-charged [M – PF
6
]
and double-charged
−
2+
Fe(III)-ABIIL complexes) was assessed in comparison to the native scav-
enger (ABIIL) and clinical drugs (antibacterial, ampicillin; antifungal,
amphotericin B), against different microbial strains including Staphylo-
coccus aureus (S. aureus, ATCC-25923) as a Gram-positive bacterium,
Escherichia coli (E. coli, ATCC-25922) as a Gram-negative bacterium,
and Aspergillus flavus (A. flavus) & Candida albicans (C. albicans, NCIM
No. 3100) as fungal species. This study was performed according to
the usual antimicrobial evaluation protocol followed in our earlier re-
ported works [11,33]. The diameter of zone of inhibition (ZOI, mm)
and minimum inhibitory concentration (MIC) were used as antimicro-
bial activity indices for the tested compounds.
6
[M – 2 PF ]
cations. Also, these data agree with the molecular for-
mula proposed by the elemental analyses.
The appearance of two sets of absorption bands (characteristic for
AEBI and SBIIL) and vanishment of others along with the emergence
of new ones in the spectrum of the new scavenger (ABIIL) (see Fig. S1,
ESI) confirms its successful fabrication. Just to name few, the two main
−1
peaks centered at 3336 and 1279 cm are assigned to the vibration
of hydroxyl and aryl-O fragments of the phenolic group in the SBIIL seg-
−
1
ment. However, absorption bands noticed at 1466, 965, and 836 cm
−
are ascribed to the vibration of imidazolium and PF
ionic liquids terminals in the AEBI and SBIIL segments. On the other
hand, vanishment of the stretches of the NH group (at 3501 and
in AEBI spectrum) and aldehyde moiety (at 2820 and
6
fragments of
2
−1
2.6.2. Anticancerl activity
3398 cm
−1
The anticancer efficacy of the scavenging products was evaluated in
1658 cm in SBIIL spectrum), coupled with the growth of new stretch
−1
comparison to a clinical anticancer drug (Vinblastine, VB) against two
human cell lines; colon carcinoma (HCT116) and normal cells (Hela).
Again, this work was carried out using the standard MTT protocol described
in our previous study [34]. The cell viability% and IC50 values were utilized
as cytotoxicity activity markers for the examined compounds.
at 1631 cm (assignable for the vibration of azomethine group) in the
spectrum of ABIIL; proves the successful formation of the new scaven-
ger (ABIIL) by Schiff base condensation of the amino group of AEBI
with an aldehyde moiety of SBIIL.
1
The coexistence of two groups of NMR signals in the H NMR spec-
trum of ABIIL (Fig. 1) confirms the successful condensation of AEBI
with SBIIL to form ABIIL. (See Scheme 1.)
3
. Results and discussion
As shown in Fig. 1, the first set of 1H NMR peaks are centered at
chemical shift values of 10.19, 9.04, 8.11–7.96, 5.10, 4.26, and
3.1. Synthesis of new scavenger (ABIIL)
3
.99 ppm (distinctive for the aminoethyl butyl imidazolium (AEBI)
The synthesis of new task-specific ionic liquid (TSIL) based on
salicylidene moiety and butylimidazolium ionic liquids (BIILs)
terminals involves seven chemical reactions. Initially, quaternization of
part); while the other group which is positioned at 9.12, 7.82–7.01,
5.69, and 4.11 ppm are characteristic for SBIIL segment. Interestingly,
the emergence of a new singlet at δ 9.43 ppm corresponding to the res-
onance of azomethinic proton, coupled with the downfield shift of the
phenolic (–OH) proton to δ 10.19 ppm are ascribed to the intramolecu-
1
1
-butylimidazole with N-(2-bromoethyl)phthalimide (1) to generate
n
-(2-(phthalamido)ethyl)- 3- butylimidazolium bromide (2a), which
..
is readily transformed into the corresponding hexafluorophosphate salt
through an anion metathesis reaction using an aqueous HPF . Then, the
rd step involves a dephthaloylation of compound 2b by the traditional
lar H-bonding (O-H• N) between the azomethine (-CH=N-) and ortho-
hydroxyl groups in ABIIL.
6
3
Additionally, the 13C NMR technique provides informative structural
insight concerning the carbon-atoms distribution map in the skeleton of
ABIIL scavenger. The 13C NMR spectrum of ABIIL revealed the presence
of C-atoms distinctive for both AEBI and SBIIL segments (see Fig. 2A).
Noteworthy, this spectrum exhibited two characteristic peaks at δ
161.33 and 158.21 ppm due to the nuclear resonances of phenolic
(C\\O) and azomethinic (-CH=N) carbon atoms, respectively. Powerful
evidence for anchoring of ionic liquids on the terminals of ABIIL is the ap-
pearance of a septet signal (centered at δ −142.95 ppm, J = 711.2 Hz)
hydrazinolysis reaction using hydrazine monohydrate in an ethanolic
medium followed by simple extraction with dichloromethane (DCM),
filtration, and evaporation of solvent to separate a pure 1-(2-
aminoethyl)-3-butyl-imidazolium hexafluorophosphate (AEBI, 3).
Other sets of reactions were dedicated for the preparation of
salicylaldehyde-supported butylimidazolium ionic liquids (SBIILs); in
the fourth reaction, a bromomethylation process was performed on
salicylaldehyde to obtain 5-(bromomethyl) salicylaldehyde (4) which
is utilized as an alkylating agent for the quaternization of 1-buty
limidazole to produce salicylaldehyde-based butylimidazolium bromide
31
and a doublet peak (centered at δ −70.57 ppm, J = 711.2 Hz) in the
P
(Fig. 2B) and 19F NMR (Fig. 2C) spectra of ABIIL, respectively.
(5a). Thereafter, a bromide exchange in compound 6a with
hexafluorophosphate anion was performed to prepare compound 5b.
Eventually, a classical Schiff base condensation was carried out between
the amino component (3) and SBIIL (5b) in ethanolic solution to fabri-
cate the desired scavenger, 1-butyl-3-(3-(((2-(1-butyl-midazolium-3-
yl)ethyl)imino)methyl)-4-hydroxybenzyl)-imidazolium
3.3. pH-potentiometry
As the chelating capacity of any protic ligand is strongly correlated to
the extent of its ionization and the stability of its ionizable form at differ-
ent pH values, so, it is of importance to examine the deprotonation pro-
cess and dissociation constant of ABIIL. In this context, the dissociation
performance of ABIIL was examined by a pH-potentiometric method
in an aqueous ethanolic solution at ambient temperature. Moreover,
the stability of ABIIL in aqueous media was inspected by a pH-
hexafluorophosphate (ABIIL). It was obtained in an excellent yield with
high purity and structurally characterized based on the elemental analy-
1
13 19 31
sis and spectroscopic methods (FTIR, UV–Vis, NMR ( H, C, F, P) and
ESI-MS).
−
4
potentiometric titration of its solution (10
M) against NaOH
−
3
3.2. Structural characterizations of new scavenger (ABIIL)
(10 M) (Fig. S2, ESI†). This titration curve showed a single abrupt
change corresponding to the departure of one proton form ABIIL with-
out losing its identity at a wide pH-range (4.8–10.5). The average num-
Regarding solubility, ABIIL is insoluble in water (Solubility in water =
9.7 g/L) and methanol but soluble in ethanol and has aqueous stability in
ber of acidic protons in ABIIL (n̄A) was calculated at serial pH values
basic and neutral solutions (pH = 10–5); while it is readily decomposed,
by dissociation of azomethine bond, at low pH values (pH < 4) like the
behavior of most Schiff bases [35]. The elemental analysis of new scaven-
ger (ABIIL) gave satisfactory results which in good consistent with the
suggested molecular formula of it (see experimental part).
according to Irving–Rossotti equation (Eq. (1)) [36]:
V1N °
−
n
¼ Y−
ð1Þ
A
ðV1 þ V Þ T
°
l
3

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Fig. 1. 1H NMR spectra of AEBI (3), salicylaldehyde-supported butylimidazolium hexafluorophosphate (5b), and ABIIL scavenger in d
-DMSO at 300 MHz.
6
Y = number of dissociable protons; V
1
= volume of NaOH added;
complexes, [M(ABIIL)
2 3 x 2
(NO ) (H O)y] (M = Cu(II), x = y = 0; M =
V
o
= initial volume (25 mL); N° = concentration of NaOH
Fe(III), x = y = 1) (see Scheme 2).
−3
(
1.6 × 10 M).
Alteration of the physicochemical properties of the scavenging prod-
ucts (M(II/III) ABIIL complexes) in comparison to the reaction inputs,
(Cu(II)/ Fe(III) ions and ABIIL), along with the structural characterization
of these outputs based upon their elemental and spectral analysis con-
firms the success of our scavenging protocol. Interestingly, the uptake of
metal ions by the ABIIL molecule can reach up to 98.9% (see Table 1).
Plots of the nA vers pH values (Fig. S3, ESI†) show a maximum
at n̄A = ~1, proving that the ABIIL contains one ionizable acidic
proton. The acid dissociation constant (pKa) of ABIIL was esti-
mated within the studied pH-range using half method (HM)
(
(
pKa = 7.35) and further verified by the least square method
LSM) (pKa = 7.34). In summary, ABIIL behaves as a monoprotic
ligand [37].
3.5. Optimization of ABIIL recovering conditions
3.4. Conversion of toxic metal ions into pharmacological nominates
The regeneration of the scavenger is an important and crucial issue to
The ability of bis-(butylimidazolium) salicylidene (ABIIL) to scav-
minimize operating costs and increase the feasibility of this process
investment. In this context, recovering of ABIIL from its scavenging prod-
ucts was carried out under different conditions using various metal-
enge the toxic metal ions (Cu(II) and Fe(III)) from their respective aque-
ous ethanolic solutions, coupled with their conversion into
pharmacological nominates, was investigated using our previous proto-
col. Initially, the optimum conditions for this remediation process were
determined by studying the scavenging of Cu(II) ions by ABIIL from cu-
pric acetate solution under different experimental conditions. Only
7.3% of Cu(II) ions have been removed by ABIIL and converted into
the corresponding complex (Cu(II)ABIIL) by heating under reflux for
h. On the other hand, the addition of NaOH to the remediation
3
desorbing agents (HCl–thiourea, HNO –thiourea, HCl–thiosulfate,
HNO –thiosulfate), according to our earlier work [21], to determine the
3
best conditions or regeneration of ABIIL scavenger. Again and in the
consistent with our previous study, HCl-thiourea mixture (1 M HCl con-
taining 4% (w/v) thiourea) was proven to be the ideal metal-desorbing
agent for the regeneration of native scavenger (ABIIL). The total recovery
ratio of ABIIL from scavenging products (Cu(II)-/Fe(III)-ABIIL) and its
further reuse without significant loss in its efficacy is remarkably high
as revealed from Fig. 3. After six cycles, the ABIIL still sustained 94% and
92% of its initial scavenging ability for Cu(II) and Fe(III) ions, respectively.
6
5
media has significantly improved the Cu(II) uptake to 96.7% during
only 1 h at ambient temperature. The scavenging outputs for the toxic
metal ions (Cu(II) and Fe(III)) using ABIIL are the corresponding
4

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Scheme 1. The stepwise schematic protocol for the preparation of 1-(2-aminoethyl)-3-butyl-imidazolium hexafluorophosphate (AEBI, 3), salicylaldehyde-supported butylimidazolium
ionic liquids (SBIILs), and ABIIL scavenger.
Fig. 2. (A) 13C NMR (126 MHz); (B) 31P NMR (202 MHz); and (C) 19F NMR (471 MHz) spectra of the ABIIL scavenger in d
6
-DMSO.
5

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Scheme 2. Scavenging of toxic metal ions (Cu(II) and Fe(III)) by ABIIL and conversion into the corresponding complexes.
Table 1
3
.6. Structural features of the scavenging products
Removing of the target metal ions by the new scavenger (ABIIL); in comparison with
reported ones.
a
The micro-analytical analysis of the scavenging products (Cu(II)-/Fe
III)-ABIIL) agrees with their proposed molecular formulas, [Cu(ABIIL)
Scavenger
Metal ions Operating conditions
Uptake (%) Ref.
(
2
]
pH
T (°C) Time (min)
2 2 3
and [Fe(ABIIL) (H O)(NO )], (see Experimental section). On the other
hand, the structural formulas of these complexes could be deduced
based on spectral analysis (IR and UV–Vis). FTIR is essential to predict
the ABIIL binding sites with metal ions and the coordination sphere
for each metal ion, as well. Synchronous changes in the intensities
and/or the positions of the absorption bands recorded in the FTIR spec-
tra of the scavenging products (M-ABIIL) in comparison to those in the
spectrum of scavenger (ABIIL) (cf. Fig. S1, ESI); coupled with the emer-
gence of new absorptions bands, confirms the success of chelation of
metal ion by ABIIL. Moreover, based on these changes we can propose
the most reasonable M-ABIIL chelation mode. For instance, the phenolic
ABIIL
Cu(II)
Fe(III)
Cu(II)
Fe(III)
6.4
6.4
6–7 78
6–7 78
6–7 37
1.5
6
6
2–3 20
8
8
5.3
5
25
25
60
60
120
120
40–60
20
96.7
98.9
87.2
94.3
90.3–95.6
53
91.4
94.6
44.3
96.6
95.3
98.9
88.1
74.3
91.2
83.5
94.1
94.5
This work
This work
[21]
[21]
[38]
[39]
[38]
[38]
[40]
[41]
[41]
[38]
[42]
[42]
[38]
[43]
[44]
[44]
HATPS
Activated C Cu(II)
Fe(III)
Fly ash
GO
20
40
20
Cu(II)
Cu(II)
Fe(III)
Cu(II)
Fe(III)
Cu(II)
Cu(II)
Fe(III)
Cu(II)
Fe(III)
Cu(II)
Cu(II)
90
24 h
10 h
5
GO-NH
2
25
25
20
65
65
20
37
25
25
5
GO/ Fe
Zeolite
2
O
3
24 h
120
120
300
180
150
30
−1
(
-OH) absorption band (at 3336 cm in the spectrum of ABILL) was
5
4.5
7
8
8
disappeared in the spectra of complexes, confirming of its de-
protonation to form phenolate anion that chelates metal ions. Addition-
ally, shifting in the wavenumber of the C\\O peak (Δν = − (9–14)
CS
PSCSB
PISCSB
−1
cm ) in the spectra of M-ABIIL complexes as compared to the native
ABIIL along with the emergence of a weak peak at the rang of
a
Scavening conditions for ABIIL; ABIIL (0.5 × 10−3)/Metal ion (0.5 × 10−3) solutions,
ethanol (10 mL) containing 100 μL of 0.1 M NaOHaq, stirring 60 min/25 °C. GO = Graphene
oxide; GO-NH = Amine-functionalized graphene oxide; CS = Chitosan; PSCSB = poly
salicylidene) chitosan Schiff base; PISCSB = poly(ionic-salicylidene) chitosan Schiff base.
−1
6
54–547 cm (distinctive for M-O stretching vibration), offer more ev-
idence for sharing of the phenolic (OH) group in chelation of metal ions
[45,46]. The band due to the azomethine group (-C=N) was negatively
2
(
Fig. 3. Scavenging efficiency of the ABIIL for (A) Cu(II) ions and (B) Fe(III) ions after six consecutive scavenging (sorption)–regeneration (desorption) cycles.
6

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
1
.82 BM which agrees with the presence of odd electron on Cu(II) ion
in a square-planar geometry environment [50]. On the other hand, the
solution of the Fe-ABIIL complex displayed a characteristic peak at
6
3
43 nm due to the spin-forbidden A1g → T2g transition of a high-spin
5
Fe(III) ion (d ) in an octahedral field. However, the high-spin octahedral
Fe(III) complexes usually show a very weak spin-forbidden d-d transi-
tion that hasn't appeared in their UV–Vis spectra. Also, the magnetic
moment of the Fe-ABIIL complex (5.62 BM) proposed the high-spin
5
configuration of the Fe(III) ion (d configuration) in an octahedral envi-
ronment [51].
The stability of the scavenger (ABIIL) and its complexes was checked
beneath the physiological conditions (pH = 7.4, T = 36.5–37.5 °C) by
−3
storing a solution (10 M) of each sample in a PBS-DMSO buffer for
2 h; observing the physicochemical changes and recoding the UV–Vis
7
spectra of each stock solution at time intervals (every 24 h). Noteworthy
that no physicochemical changes such as color alteration or formation of
precipitates as evidence no aggregation of ABIIL or its complexes in their
respective solutions. Meanwhile, no significant changes were noticed in
the UV–Vis spectra of ABIIL or its complexes during the storing time
(
Fig. S4, ESI), confirming our earlier suggestion.
Fig. 4. UV–Vis spectra of ABIIL scavenger and its scavenging products (Cu-ABIIL and
Fe-ABIIL).
3
3
.7. Pharmacological study
.7.1. Antimicrobial study
To assess the suitability of scavenging products (M-ABIIL com-
shifted from 1631 cm−1, in free ligand to 1621 ± 1 cm−1 (Δν =
−
1
−
11 cm ), in complexes, as indicative of the coordination of the
plexes) for application as antibiotics, the capacity of these complexes
to suppress the growth of common medically-relevant microbes such
as S. aureus (ATCC-25923) (Gram-positive (G ) bacterium), E. coli
azomethinic N atom with metal ions [21,46]. This is consistent with
−1
+
the growth of a new absorption band at the rang of 465–442 cm as-
signable for M–N vibration. Thus, ABIIL act as a monoanionic bidentate
−
(ATCC-25922) (Gram-negative (G ) bacterium), A. flavus, and
(
NO) chelating ligand. The broad band observed at 3453 cm−1 in the
C. albicans (NCIM No. 3100) (fungi) were in vitro investigated in com-
parison to the native scavenger (ABIIL) and clinical drugs (Antibacterial,
Streptomycin (ST), and Tetracyclin (TC); Antifungal, Ketoconazole
(KCZ)) (see Fig. 5). It is worth that the scavenging products (Cu(II)-/
Fe(III)-ABIIL complexes) are more efficient than the native scavenger
(ABIIL) in suppressing the growth of all tested microbial species; with
efficacies higher than the clinical drugs, as revealed from the values of
ZOIs (Fig. 5). Notably, S. aureus is more susceptible to the biocidal effects
of the M-ABIIL complexes than E. coli (Fig. 5, left). Where the MIC values
of Cu(II)-/Fe(III) complexes against S. aureus and E. coli are 25.4/
18.9 μg/mL and 41.2/23.1 μg/mL, respectively (i.e the activity of the
spectrum of Fe(III)-ABBIL complex, characteristic for the O\\H group,
emphasizes the involvement of a water molecule in the coordination
sphere for Fe(III) ion [21].
The UV–Vis spectra of the solutions of ABIIL scavenger and its metal
−
3
complexes in DMSO (10 M) were measured within a wavelength
range of 200–500 nm at ambient temperature (Fig. 4). The electronic
spectrum of ABIIL is dominated by three main maxima at 337, 249,
and 221 nm attributable for the n → π∗ and π → π∗ transitions
implicated in the azomethine, phenolic, and imidazolium moieties,
respectively [47,48]. UV–visible spectroscopy is a very helpful tool in
predicting the geometries of complexes on the basis of the identities
of d–d transitions. For example, the electronic spectrum of the Cu-
ABIIL complex showed a new peak at 397 nm which can be assigned
+
scavenging products against G -bacterium is 1.3–1.6 times higher
than G -bacterium). This, in turn, means Fe-ABIIL is more potent than
−
Cu-ABIIL in fighting the tested bacterial pathogens; with efficacies
higher and clinical drugs, streptomycin (MICS. aureus/ E. coli = 50.6/
27.5 μg/mL) and tetracycline (MICS. aureus/ E. coli = 37.5/43.2 μg/mL).
The promoted antibacterial performance of scavenging products (M-
ABIIL) in comparison to the native scavenger (ABIIL) could be explained
as
superimposed B1g → B2g and 2B1g → E
transitions) that distinctive
g
d → π∗ metal-ligand charge-transfer (MLCT) transitions
2
2
2
(
for the distorted square-planar geometry of Cu(II) complexes [47,49].
The measured magnetic moment for this complex was found to be
Fig. 5. Graph of the zone of inhibition (ZOI, mm) for the native scavenger (ABIIL) and scavenging products (Cu-/Fe-ABIIL complexes) against different medically relevant microbial
pathogens. Insets are the micrographs for ZOI of tested compounds against bacterial strains.
7

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
based on the chelation theory [52] and Overtone's concept [53]. Gener-
ally, the chelating ligands can form highly stable five-/six-membered
metallocyclic rings (chelate rings) upon binding to the metal ions. This
metallocyclic ring offer template for the delocalization of p-electrons
of metal ion, therefore, reduces its polarity and increases the lipophilic-
ity of the whole complex to a larger extent. This increased lipophilicity
promotes the penetration of the metal complex into the phospholipid
membrane of the microbial cell, causing either collapse of the perme-
ability barrier [54] or inducing malfunction in metal-binding sites of en-
zymes of this cell [55]. Meanwhile, as the size and/or the number of
metallocyclic rings increases; the polarity of metal ion decreases and
the lipophilic character of complex increases, which in turn enhances
the interaction between complex and the lipid layer in the outer mem-
brane of the microbial cell [56].
and C. albicans. Plus, the MIC values (μg/mL) for Fe-ABIIL against micro-
bial species were found to be: 18.9, S. aureus; 23.1, E. coli; 19.5, A. flavus;
and 16.8, C. albicans.
3.7.2. Cytotoxicity study
The cytotoxic impacts of scavenging products (Cu-ABIIL and Fe-
ABIIL) toward two human cell lines (Colon carcinoma cells, HTC116;
Normal cells, HeLa) were in vitro assessed as compared to a clinical an-
ticancer drug (Vinblastine, VB) using MTT assay. The cell viability ratio
(Fig. 7) and the half-maximal inhibitory concentration (IC50) were
used as cytotoxicity indices. Generally, the scavenging products are
more cytotoxic than the clinical drug (VB) toward cancer cell lines
(HTC116), whereas they are less cytotoxic to the normal human cells
(HeLa), as shown in Fig. 7. Just to name a few, remediation of HTC116
and HeLa cell lines with Fe-ABIIL complex (50.0 μg/mL) can reduce
their viabilities ratio of HTC116 and HeLa cells by 91.97% and 37.54%, re-
spectively. Whereas, if such treatments were performed using VB, the
reduction in cell viability ratios was 87.74% and 51.39%, for HTC116
and HeLa cells respectively. Thus, Fe-ABIIL complex is more active and
better safe as anti-colon cancer agent (IC50 values: 3.40 ± 0.53 μg/mL
toward HCT116; 85.66 ± 1.44 μg/mL against HeLa) than the clinical an-
ticancer drug (VB) (IC50 values: 3.79 ± 1.01 μg/mL and 57.12 ±
1.95 μg/mL for HCT116 and HeLa cell lines, respectively).
As shown in Fig. 6, ABIIL can form two highly stable six-membered
metallocyclic rings which significantly diminishes the polarity of Cu
(
II) and Fe(III) ions and greatly elevates the lipophilic character of
their respective complexes, increasing the mutual interactions between
complexes and the outer lipid layer of the microbial cell wall to a larger
extent. This may lead to a breakdown of the permeability barrier of the
cell, resulting in malfunction of normal biological processes of microbial
cells. Several structural features can be proposed as the potential rea-
sons for the preferable antimicrobial activity of Fe-ABIIL complex as
compared to Cu(II) complex such as; (i) The octahedral geometry and
charge distribution around the Fe-ABIIL complex are more compatible
with those around pores of the bacterial cell-wall, making it more able
to penetrate this wall and induce more toxic reaction within the pores
Again, Fe-ABIIL complex (IC50 = 3.40 ± 0.53 μg/mL) exhibit better
anticancer activity than Cu(II) complex against HCT116 cells (IC50
=
3.58 ± 0.77 μg/mL), and this enhanced cytotoxicity could be ascribed
to the same reasons (complex geometry, Fe(III)-DNA interactions, addi-
tional HBA and HBD sites) of the promoted antimicrobial activity of Fe-
ABIIL complex in comparison to Cu-ABIIL (see Antimicrobial Study
section).
[57]. (ii) Releasing of Fe(III) ions from the Fe-ABIIL complex inside the
microbial cell which can highly interact with DNA, more than Cu(II)
ions, disordering its functions and replication [58,59]. (iii) Apart from
this, the mode of action of the Fe-ABIIL complex may also invoke H-
bonding through additional H-bond donor/acceptor (HBD/ HBA) sites
4. Conclusion
2 2
(H O, ONO ), absent in the Cu-ABIIL complex, with the active centers
of biomolecules in the microbial cell, resulting in dysfunction in their bi-
ological processes [60].
As shown in Fig. 5 (right), the M- ABIIL complexes displayed slightly
higher fungicidal activity than their bactericidal efficacy, as revealed
from the values of their respective inhibition zones against A. flavus
Aminoethyl-butylimidazolium hexafluorophosphate and salicylalde
hyde-butylimidazolium hexafluorophosphate were used as key starting
materials for fabrication of a new task-specific ionic liquid (ABIIL) based
on bis-(butylimidazolium hexafluorophosphate) supported an azome
thine group. The microanalytical and spectral results confirm the
2 2 2 2
Fig. 6. The proposed structural formula of the scavenging products, [Cu(II)(ABIIL) ] (Cu-ABIIL) and [Fe(II)(ABIIL) (ONO )H O] (Fe-ABIIL), showing the differences in their structural
features and additional H-bonding active sites in Fe-ABIIL (HBD/HBA, H O; HBA, ONO
2
2
).
8

W.N. El-Sayed, J. Alkabli, K. Althumayri et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Fig. 7. Cell viability of two human cell lines (A) Colon carcinoma cells (HTC116); (B) Normal cells (HeLa) after 24 h of treatment with serial concentrations of scavenging products (Cu-
ABIIL and Fe-ABIIL) and a clinical anticancer drug (Vinblastine, VB).
successful formation of ABIIL. The resultant material (ABIIL) exhibited
excellent solubility in aqueous-ethanolic media, which was useful for
extracting of heavy metal ions (HMIs) aqueous-ethanol. The new scav-
enger (ABIIL) displayed excellent scavenging efficiency for tested HMIs,
as it can uptake up to 98.9% and 96.7% of Fe(III) and Cu(II) ions, respec-
tively, from aqueous-ethanolic effluents. Besides, it could be easily re-
generated and reused without a significant loss of its efficiency even
after six consecutive scavenging–regeneration cycles. The physico-
chemical features, FTIR, and UV–vis spectral results of the scavenging
products indicated that the removal process occurs by the chelation of
the anionic form of ABIIL with HMIs. Where the pH-potentiometric
studies revealed that ABIIL behaves as a monobasic bidentate (N,O) li-
gand. The new chelating ionic liquid (ABIIL) underwent a color-
change from pale yellow to a yellowish-green and reddish-brown
when bound Cu(II) and Fe(III) ions, respectively, to form scavenging
products (Cu-/Fe-ABIIL). The pharmacological assessment for the scav-
enging outputs (M-ABIIL) showed that they have excellent and broad-
spectrum antimicrobial activity, with slightly better effectiveness as
fungicides than act as bactericides. For instance, the MIC values
Methodology, Data curation, Validation, Visualization, Writing - Original
Draft,
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.molliq.2020.114525.
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