Synthesis of Nickel(II) Complexes of Novel Naphthalimide Based Heterodipodal Schiff Base Ligands, Structure, Characterization and Application for Degradation of Pesticides

Article abstract of DOI:10.1002/ejic.202000461

To degrade the highly toxic pesticide into less harmful components, we have synthesized four nickel complexes of naphthalimide based organic ligands. These complexes catalyze the hydrolysis of phosphorothioate bonds of organophosphates in an aqueous medium. The metal complexes {[Ni(L₁)₂]–[Ni(L₄)₂]} were synthesized by the electrochemical method and characterized using single-crystal X-ray crystallography and mass spectrometry. Analytical techniques revealed that complexes are mononuclear and possess octahedral geometry. The rate of degradation of chlorpyriphos and parathion methyl was evaluated using ³¹P NMR and LC-MS chromatogram. The by-product of chlorpyriphos upon catalytic degradation with complex was confirmed from mass spectrometry. It was found that chlorpyriphos degrade into 3,5,6-trichloropyridin-2-ol after 50 minutes of incubation with catalyst. However, parathion methyl took only 20 minutes to hydrolyze into its by-product. Moreover, the inhibition assay of acetylcholinesterase was performed for pesticides in the presence of metal complex and the interesting outcome was recorded.

Full text of DOI:10.1002/ejic.202000461

European Journal of Inorganic Chemistry
Accepted Article
Title: Synthesis of Ni (II) Complexes of Novel Naphthalimide Based
Heterodipodal Schiff Base Ligands, Structure Characterization
and Application for Degradation of Pesticides
Authors: Jagpreet Singh Sidhu, Pushap Raj, Thangarasu Pandiyan,
and Narinder Singh
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000461
Link to VoR: https://doi.org/10.1002/ejic.202000461
0
1/2020

European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
Synthesis of Ni (II) Complexes of Novel Naphthalimide Based
Heterodipodal Schiff Base Ligands, Structure Characterization
and Application for Degradation of Pesticides
[a]
[a]
[b]
[a]
Jagpreet Singh Sidhu , Pushap Raj , Thangarasu Pandiyan and Narinder Singh*
[
a]
Mr, Jagpreet Sidhu, Dr. Pushap Raj, Dr. Narinder Singh
Department of Chemistry
Indian Institute of Technology Ropar
Punjab, India, 140001
E-mail: nsingh@iitrpr.ac.in
Homepage: https://sites.google.com/a/iitrpr.ac.in/iitropar-chemistry/faculty/dr-narinder-singh
Thangarasu Pandiyan
[
b]
Department of Inorganic Chemistry
National Autonomous University of Mexico,
Mexico
Supporting information for this article is given via a link at the end of the document.
Abstract: To degrade the highly toxic pesticide into less harmful
catalytical activity is required because some of the pesticides
are toxic even at the low concentration and cannot be degraded
easily. Due to their high catalytical activity and tunability at active
sites, coordination complexes have been emerging as potential
candidates for catalysis of pesticides.[9] The metal ion at the
catalytical center governs an important role in the electron
transfer process.[10] Therefore, synthesis of metal complexes is
quite interesting research area to utilize them for hydrolysis of
OPs. To synthesize such metal complexes, a green and
sustainable approach has great demand. To fulfill this demand,
components, we have synthesized four nickel complexes of
naphthalimide based organic ligands. These complexes catalyze the
hydrolysis of phosphorothioate bonds of organophosphates in an
1 2 4 2
aqueous medium. The metal complexes ([Ni(L ) ] -[Ni(L ) ]) were
synthesized by the electrochemical method and characterized using
single-crystal X-ray crystallography and mass spectrometry.
Analytical techniques revealed that complexes are mononuclear and
possess octahedral geometry. The rate of degradation of
3
1
chlorpyriphos and parathion methyl was evaluated using P NMR
and LC-MS chromatogram. The byproduct of chlorpyriphos upon
catalytic degradation with complex was confirmed from mass
spectrometry. It was found that chlorpyriphos degrade into 3,5,6-
trichloropyridin-2-ol after 50 minutes of incubation with catalyst.
However, parathion methyl took only 20 minutes to hydrolyze into its
byproduct. Moreover, the inhibition assay of acetylcholine esterase
was performed for pesticides in the presence of metal complex and
the interesting outcome was recorded.
electrochemistry is
a fascinating synthetic tool. It is a
multidisciplinary science having high applicability in various
research fields such as physical, chemical and biological
sciences.[
11]
It can be used for the synthesis of organic
compounds in both laboratory and industrial scale. In
electrosynthesis, the clean energy source such as electrons is
used as redox reagent instead of harmful chemicals.[12] The
electrons can easily be added and remove from the system
without any complication. Generally, electrosynthesis can
generate less waste in chemical reactions rather than
[13]
conventional chemical synthesis. This technique is one of the
Introduction
[14]
simplest methods to achieve reduction and oxidation.
Moreover, reaction setup is quite convenient reaction and there
is easy accessibility of power supply, electrodes and cells.
The main use of electrosynthesis lies in oxidation and reduction
reaction in organic reaction.[16] However, the number of
Organophosphates (OPs) represent the largest class of
pesticides, insecticides as well as herbicides which are useful to
protect agricultural products from pest, insects and weeds.[1] It is
well documented that the use of pesticides helps to protect the
[15]
electrochemical methods for synthesis of inorganic and
organometallic compounds is less explored; in spite of huge
physiochemical information available on the behavior of
inorganic and organometallic compounds on electrodes. The
synthesis of coordination complexes from organic ligands, which
have a weak acid group such as OH, NH, amide or thiol needs
deprotonation of the ligand. The limitation of this method lies in
the production of some undesired products and waste.
Therefore, it is a time of need to explore green synthetic
methods that are highly efficient for the synthesis of metal
complexes. In this context, the electrochemical synthesis has
3
3% of global cultivation products.[2] Although, the unused
pesticide residue left in the environment can contaminate the
food products and also disturb the ecosystem.[3] The general
toxicity associated with pesticides consumption is the inhibition
of the acetylcholinesterase activity (AChE).[4] AChE is an
essential enzyme which hydrolyze the parasympathetic
neurotransmitter acetylcholine to choline and acetic acid in
neuromuscular junction.[5] It is an important reaction in the
nervous system which permits the cholinergic neuron to return
its resting position after activation.[6] The inhibition mechanism
proceeds through the irreversible binding of OPs with the
catalytical site of the enzyme.[7] Therefore, the degradation of
pesticides to less toxic components has great demand
nowadays. As per literature reports, various metalloenzyme and
metal oxide nanoparticles were explored for catalytical
considerable
utility
over
other
classical
methods.
Electrochemical techniques utilize a simple apparatus and pure
starting reactants. Additionally, this approach allows the only
selective transformation of specific groups in ligands or
coordination
complexes
under
normal
experimental
[8]
degradation of pesticides. However, more improvement in the
1
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
conditions.[17] In last two decades, Dolomanov and Puschmann,
research group have been given tremendous efforts for the
electrochemical synthesis of transition metal complexes by a
metal anode in a solution containing ligands of weak acid (OH,
triplet at 4.39 and 3.14 ppm in HNMR confirmed the structure of
S-81. Moreover, the peak at 40.28, 31.91 ppm confirmed the
1
1 4
alkylic carbon peak of the structure. The final products (HL -HL )
were synthesized by condensation reaction between amine and
corresponding aldehydes in ethanol solvent at reflux condition.
The final structures were characterized by 1HNMR, CNMR,
NH, SH).[18] Besides this,
a variety of other coordination
13
complexes of O, N, S, P donor sites ligands have been
synthesized by electrochemical approach with different metal
ions includes Ni (II), Cu(II), Zn (II), Co(II), Fe (II/III), Cd (II), Pb
1
HRMS and single crystal XRD data (Figure S1-S18). In H NMR
spectrum, the characteristics Schiff base peak of ligands lies in
the region of 8.5 to 8.9 ppm and 13C NMR spectrum exhibiting
characteristics peak 153 to 165 ppm. Further, the ligands were
characterized using HRMS and each ligand gave its M+H m/z
peak in mass spectrum. The m/z value for HL
HL was recorded at 453.1250 [M+H], 503.1422 [M+H],
498.1098 [M+H] and 469.1219 [M+H] respectively.
Synthesis of Metal Complexes: The synthesis of nickel metal
complexes was achieved by electrochemical oxidation of NiNO
in an electrolytic cells containing acetonitrile solution of particular
ligand. For the electrochemical reactions, a electrolytic cells
equipped with anode and cathode electrode was employed. The
voltage difference was remained in between 5-8 mV. The
electrochemical efficiency (Ef) calculated for nickel metal ions
and it was lies in the range of 0.4-0.6 mol F-1 for each metal
complex solution. During the reaction the release of hydrogen
gas at cathode and oxidation of metal ion at anode is as:
(
II) and Sn (II). In this context, we have utilized the
electrochemistry approach to synthesize the nickel-metal
complexes. To synthesize the metal complexes, naphthalimide
as a basic organic structural motif having π electronic system
was selected. As per the literature reports, these electronic
configuration helps in structure extensions through π-anion, π-π
and π-solvent interactions. These interactions can be utilized to
built extended network.[19] Moreover, easy synthetic modulation
makes naphthalimide an interesting candidate for metal complex
synthesis.
1 2 3
, HL , HL and
4
3
Naphthalimde based receptor having electron rich atom
(
nitrogen/sulfur) can donate an electrons to electron deficient
metal ions and thus forms metal chelates. Owing to their
catalytical activity, coordination complexes have significant
applicability in OPs degradation. Herein, we report the
naphthalimide based nickel complexes for catalytical
degradation studies of a series of pesticides namely chlorpyrifos
and parathion methyl. The degradation studies revealed that all
nickel complexes exhibit good catalytical activity for pesticide
degradation. LC-MS chromatogram was used to investigate the
degradation studies of OPs.
-
+ L2e-
H
2
L + 2e → ↑ H
2
Ni → Ni + 2e-
L indicate the ligand
All the metal complexes were obtained with practical yield of 65-
5% in single-step reaction. The yield was calculated after
2+
7
successful drying the solid residues. Thus synthesized complex
were characterized from mass spectrometry. The mass spectra
of the metal complex showed the 2:1 stoichiometry which were
further confirmed with single crystal XRD. The structure revealed
that nickel metal ion form six coordinate with nitrogen, sulphur
and oxygen of two lignd.
1 4
Figure 1: Chemical structure of ligands HL -HL and their potential binding
sites for metal ions highlight with blue colors.
Results and Discussion
1 4
Scheme 1: Synthetic scheme for Ligands HL -HL
Synthesis of Ligands: The naphthalimide based heterdipodal
Schiff base ligands HL1-4 (Figure 1) were synthesized by
multistep reaction as shown in scheme 1. The synthesis process
started with the substitution reaction of 3-bromoethylphtalimide
with 2-aminothiophenol in acetonitrile solvent under nitrogen
atmosphere. As synthesized S-79 was treated with hydrazine
hydrate and refluxed. Precipitated residues were filtered out and
the filtrate was collected to get S-80. The S-80 was yellowish-
brown oil and used as it is in the next reaction without any
further purification. Thus synthesized amine was refluxed with
Photophysical Properties of Metal Complexes: The
photophysical properties of ligands and their metal complexes
were recorded using UV-vis absorption spectroscopy in
1
acetonitrile solvent. The absorption spectra of HL (Figure2A)
revelaed that the absorption band at 260 nm was
correspondence to the π-π* transitions while the absorption
band of 345 nm dictate the n- π* transitions of the naphthalimide
moiety.[20] The ligand HL
behavior than HL . It showed the two absorption band at 460
and 360 nm which are correspondence to n-π* and π- π*
exhibited different UV-absorption
2
1
1
,8-naphthalic anhydride in ethanol and pale yellowish
precipitates were collected after filtration. The presence of two
2
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
transitions respectively of aromatic conjugation system.[19b]
1
Crystal Structure Description: Ligand HL crystallized in
Moreover, HL
spectrum to HL
3
exhibited a similar type of UV-vis absorption
in the same solvent system. It showed the π-π*
triclinic crystal system with space group of P-1 (CCDC No.
1977048). The asymmetric unit of crystal contains one moiety of
1
transitions absorption maxima at 340 nm. The absorption band
at 333 nm for HL
was also observed.[21] Further, the change in
the absorption profile of ligands was recorded upon the
successive addition of NiNO (0-10 µM) in ligand solution. To
confirm the binding of a metal ion with the co-ordination sphere
of ligands, a titration experiment study was recorded for each
ligand. As shown in Figure 2A, a new abs band at 430 nm has
emerged while 267 nm absorption band showed a hyperchromic
shift upon addition of metal ion solution. Such changes in the
absorption spectra indicates the modulation of energy gap due
27 20 2 3
ligand, C H N O S. The Ortep diagram along with atom
4
numbering scheme is given in Figure 3A. The ligand crystal is
stabilized by O−H···N hydrogen bonding between hydroxyl and
imine linkage of the naphthalimide ligand. Crystal lattice of
ligand exhibits C-H···O and C-H···S type of interactions with the
different moieties of ligand as shown in Figure S19-S20. The
bond length and bond angle of the crystal is given in Table
S1and S2.
3
2
to ligand to metal charge transfer band. The ligand HL showed
a different absorption profile with isosbestic point at 423 nm. The
absorption band at 460 nm shows the hyperchromic shift with a
hypsochromic shift of 20 nm was observed in absorption band of
3
90 nm. The broadening of the absorption band at 460 nm may
indicate the d-d transitions of nickel metal complex (Figure 2B).
Similarly, significant changes in absorption spectra of HL3 was
observed upon the successive addition of nickel metal ions as
shown in Figure 2C. Titration experiment confirmed the binding
affinity of Ni2+ metal ion to the lsynthesized receptor molecules
Figure 3: (A) Ortep diagram of Ligand HL
(color codes: C = black, N = blue, S = yellow, O = red).
1 3
(B) Ortep diagram of Ligand HL
(
1 4
HL -HL ). It showed that a significant absorption band at 390
nm was developed upon aliquot of metal addition and
hypochromic shift in band at 330 was recorded. The isobestic
Ligand HL
system with space group of P2
Asymmetric unit of ligand HL exhibits moiety formula of
S. Ortep diagram along with atom is given in Figure
3
:
Ligand HL
3
crystallized in monoclinic crystal
point in absorption spectra of HL
Similar results were obtained for ligand HL
3
was recorded at 352 nm.
upon bind with Ni2+
1
/c (CCDC No. 1977052).
4
3
ions as shown in Figure 2D. Aliquot addition of Ni2+ to ligand
solution showed the formation of new absorption band at 458
nm while the absorption band of 333 nm showed a hypochromic
shift. In this spectra, three isobestic points were recorded at 392,
27 19 3 5
C H N O
3B. In solid-state, the crystal was stabilized by intramolecular
hydrogen bonding between imine and phenolate ion (enol form)
of the ligand. The packing analysis of ligand revealed C-H···O
and C-H···S type of interactions in naphthalimide unit as shown
in Figure S20. The bond length and bond angle of the crystal is
given in Table S3 and S4.
3
67 and 314 nm. All these absorption spectra designate the
binding affinity of Ni2+ with the coordination sphere of ligands.
2 2 2 2
) ] : Complex [Ni(L )
]2+ crystallized in triclinic
2
+
Complex [Ni(L
crystal system with space group of P-1 (CCDC No. 1977051).
The asymmetric unit of the complex consists of one unit of Ni2+
NiO
. The Ni2+ is mononuclear as well as octahedral
,
C
62
H
42
N
4
6 2
S
2
+
geometry and contains two molecules of ligands. The Ni is
coordinated to two nitrogen atoms (imine linkage), two oxygen
atoms (phenolate group) and two Sulphur atoms of the ligands.
The Ortep diagram and atom numbering scheme is given in
Figure 4 and Figure S13. Ni2+ complex is octahedral in geometry
with bond length of Ni1−S1, Ni1−N1 and Ni1−O1 are of
2
.4851(11), 2.018(3) 1.990(3) Å respectively, which is equal to
Ni1−S2, Ni1−N2 and Ni1−O2. The selected bond length and
bond angle is given in Table S5-6. Packing diagram of complex
exhibits C-H···O and C-H···C type of interactions between
different moieties of naphthalimide ligands as shown in Figure
S21-S22. The crystal refinement parameters of ligands and
complex are given in Table S7. The stoichiometry of complexes
(
2:1) was determined by job plot analysis (Figure S24). The
Figure 2: UV-Vis absorption spectra of ligands upon addition of metal ions (0-
result shows that nickel complexes exhibit 2:1 stoichiometry
between ligand and metal ions.
2
+
1
0 µM) (A) UV-vis absorption spectra of HL1+ Ni (B) UV-vis absorption
2
2+
+ Ni2+ (D) UV-vis
Ni2+
+ . The concentration of ligand solutions
4
spectra of HL + Ni
(C) UV-vis absorption spectra of HL
3
absorption spectra of HL
remained same (10 µM)
3
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
profile of parathion methyl. (C) Rate of hydrolysis upon increasing substrate
concentration. (D) Lineweaver-Burk plot. All these studies were performed
]2+ metal complex.
3 2
using [Ni(L )
As shown in Figure 5A, the absorbance intensity at 407 nm
increased with time upon incubation of parathion methyl with
2
+
2 2
complex [Ni(L ) ] . The absorbance enhancement was
observed only upto 24 minutes and plateau phase was reached
above this time. It indicated that the hydrolysis of parathion
methyl completed within 24 minutes. Further, the Michaelis-
Menten plot was drawn to investigate the effect of substrate
concentration on its rate of hydrolysis. As shown in Figure 5C,
the rate of hydrolysis shows linear relationship with substrate
concentration upto 240 µM and then attained saturation phase. It
indicated that metal complex binds with specific number of a
2 2
Figure 4: ORTEP diagram of complex [Ni(L )
]2+ (color codes:
C = black, N = blue, S = yellow, O = red, green = Ni2+).
Catalytical Degradation Activity of Organophosphorus
Pesticides: In the previous years, transition metal complexes
were utilized for the phosphatase activity.[20] Most of these
metals are cobalt, zinc and copper which were used for the
catalytic degradation of OPs.[22] As per our best knowledge, very
few reports available that utilized nickel metal complexes for
hydrolysis of phosphoester bonds of OPs. Therefore, we
explored the nickel metal complexes for the hydrolysis of highly
toxic parathion methyl and chlorpyriphos to less toxic
components. For the control experiment, UV-Vis absorption
spectra of parathion methyl was recorded in the presence of 3
substrate molecule to hydrolyze it. K
line-Weaver Burk plot as shown in Figure 5D. The comparison
of Vmax and K for different complexes is shown in table 1. All the
m
value was calculated from
m
complexes show comparable kinetic parameters. No significant
differences were observed.
3
equivalent of NiNO . There is no change in absorption spectra
was recorded upto 30 minutes. It indicated that metal ion alone
is not able to hydrolyze the OPs into its byproducts. Further, to
predict the degradation productivity of catalyst, the fixed
concentration of given OPs (10 equivalent) was incubated with
1
0 µM solution of complex. To avoid the interference of metal
complex in UV-absorption profile, the hydrolysed product was
extracted with chloroform from aqeous solution and the
absorption profile of organic layer was recorded to monitor the
hyrolysis rate. As the hydrolysis reaction was proceeded, the
absorbance intensity at 407 nm started increasing.
Enhancement in absorbance was recorded to measure the
hydrolysis of parathion methyl in the presence of metal complex.
Upon catalytic hydrolysis, the p-nitrophenoxide released from
parathion methyl which results into lone pair of oxygen engaged
in conjugation with aromatic ring.[20b] Thus generated p-
nitrophenoxide showed enhancement in absorbance at 407 nm.
Figure 6: LC-MS chromatogram of Chlorpyriphos upon hydrolysis with metal
complex [Ni(L )
3 2
]2+
Further, to prove the hyrolysis of parathion methyl and
chlorpyriphos by metal complexes, phosphorus NMR was
recorded in DMSO (Figure S23). At 0 min of incubation with
metal complex, the 31P NMR was recorded as a pure sample.
Change in the original OPs NMR peak with time intimate the
degradation of the original structure to its byproducts. Parathion
methyl exhibited a peak at  = 65 ppm. Upon incubation with
2
+
catalyst [Ni(L
3
)
2
]
, the peak at 65 ppm started to diminish while
new peak at 52 ppm was emerged. In NMR titration study,
parathion methyl took 20 minutes to completely hydrolyzed into
its by-products. Further, the NMR titration study was also
performed with chlorpyriphos. The pure chlorpyriphos 31P NMR
peak at  value of 60 ppm took 50 minutes to diminish
completely. The generation of a new peak at 54 ppm with the
disappearing of 60 ppm peaks showed
response. After 50 of incubation of chlorpyriphos with [Ni(L ) ] ,
a time-dependent
2
+
3 2
the new hydrolyzed product of chlorpyriphos was observed
(Figure S24).
Figure 5: (A) UV-Vis absorption spectra of parathion methyl after hydrolysis
with metal complex. It indicated that p-nitrophenoxide generated upon
hydrolysis of parathion methyl. (B) Time denedent change in the absorption
4
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
Acetyl choline esterase Activity: OPs are the irreversible
inhibitor of the acetylcholinesterase which leads to an increase
in the acetylcholine level in blood upon poising.[7a, 23] Therefore,
monitoring the acetylcholinesterase activity is an important factor
to identify the efficiency of metal catalyst to hydrolyze the OPs.
AchE hydrolyze the acetylcholine into thiocholine which is thiol-
containing reactive species.[24] Free thiol group easily reduce the
Table 1. Kinetic parameter for hydrolysis of parathion methyl using different
metal complex
-
1
Complex
Pesticide
V
max (ms )
m
K (M)
[
[
[
[
Ni(L
Ni(L
Ni(L
Ni(L
1
2
3
4
)
2
]2+
Parathion methyl
Parathion methyl
Parathion methyl
Parathion methyl
5.5X10-4
1.5X10-4
]2+
5.6X10-4
1.45X10-4
)
2
disulfide linkage of dithiobisnitro-benzoate also called Ellman
)
2
]2+
]2+
5.6X10-4
5.5X10-4
1.35X10-4
1.55X10-4
reagent and gives
a
thiobisnitro-benzoate.
[25]
Thiobisnitro-
benzoate is highly yellow-colored UV-light absorbing chemical
reagent. Therefore, we employed Ellman reagent to monitor the
enzymatic hydrolysis of acetylcholine into thiocholine in the
presence of metal complex. To avoid the interference from
nitrophenol as generated from the
)
2
For a more detailed investigation of hydrolysis reaction of
chlorpyriphos, the LCMS chromatogram was recorded. As
shown in Figure 6, the chlorpyriphos exhibited retention time of
3
.06 minutes at 0 minutes of incubation. After 25 minutes of
hydrolysis
of
parathion
methyl,
we
employed
2
+
diethylcynophosphate as an irreversible inhibitor of acetylcholine
esterase. The diethylcynophosphate (100 µM) was treated with
each metal complex (10 µM) for 30 minutes and after every 3
3 2
incubation with [Ni(L ) ] , a new peak at 2.50 minutes has
appeared and peak at 3.06 minutes reduced. Further, after 50
minutes, the peak corresponding to 3.06 minutes was
completely disappeared and new peak at 2.50 was obtained.
The m/z value corresponding to 2.50 minutes was found to be
1
2
minutes, the
diethylcynophosphate solution added to the
enzymatic solution. Enzyme was incubated for 5 minutes with
each addition of metal complex treated OPs solution followed by
the addition of Ellman reagent. The change in the absorbance
spectra of Ellman reagent was recorded.
97.94 which represents the M+H peak of 3,5,6-trichloropyridin-
-ol (Figure. S25). As obtained result indicate the breakage of
phophoester bond the chlorpyriphos in the presence of metal
complex and release the 3,5,6-trichloropyridin-2-ol as
a
byproduct. From the above-mentioned results, it was predicted
that the metal complex has coordination number 6; two ligands
bind with nickel through sulfur, nitrogen, and oxygen atom.
Spectral chemical series indicate that the binding ability these
atoms are in order S>N>O. It is interesting to mention here that
sulfur and nitrogen bind with nickel through strong irreversible
bond, where as the bond between oxygen and nickel is
reversible. Therefore, due to strong Infinity of pesticides to bind
with nickel, the bond between oxygen and nickel break
reversibly, the oxygen of naphthalene subgroup may attack at
phosphorus center result into degradation of OPs.Hence, high
electrophilic character of the phosphorus group is more to
hydrolysis in the aqueous system which leads to its degradation
via phosphoester bond breakage. In conclusion, we can say that
such metal complex enhances the hydrolysis of OPs in the
alkaline aqueous medium through enhancing electrophilicity
character to phosphorus group. The structure of OPs and
corresping byproducts is shown in Figure 7.
Figure 8: Acetylcholinesterase assay
As shown in Figure 8, the absorbance at 412 nm was enhanced
due to the hydrolysis of Ellman reagent by free thiocholine.
Enhanced absorbance is the result of the hydrolysis of
acetylcholine into thiocholine by AchE. It indicated that the
inhibition efficiency of OPs was reduced upon treatment with
metal complexes. These outcomes dictated that the metal
complex hydrolyzed the OPs which results in no inhibition of
AchE and more free thiocholine has been generated from acetyl
choline. Thus generated thiocholine reduced the Ellman reagent
and therefore, enhancement in absorption spectra of Ellman
reagent correlated with hydrolytic efficiency of metalcomplex.
Moreover, we found that all the metal complexes showed
comparable results to reduce the inhibition of AchE. However,
3 2
complex [Ni(L )
]2+ is more effective to hydrolyze the OPs than
Figure 7: Chemical structure of OPs and their hydrolysed product in the
presence of metal complex.
others.
5
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
(m, 2H), 4.33 (s, b, 2H), 3.16 – 3.12 (m, 2H). 13C NMR (100 MHz, CDCl3)
δ 164.19, 148.12, 135.41, 134.13, 131.63, 131.40, 129.64, 128.27,
Conclusion
1
27.01, 122.57, 118.72, 117.23, 115.04, 40.28, 31.91.
The naphthalimide based heteropodal receptor containing
nitrogen, sulfur and oxygen as a hetero atom were synthesized.
Thus synthesized receptors were characterized using NMR,
mass spectrometry and single crystal XRD. The nickel metal
complexes of these receptors were prepared by electrochemical
method and characterized using single crystal XRD and mass
spectrometry. These analytical tools revealed that the receptor
formed the mononuclear complexes with metal ions with 2:1
stoichiometery. Further, these complexes were employed for the
degradation of parathion methyl and chlorpyriphos. The
degradation mechanism was predicted with LC-MS and NMR
spectroscopy. Additionally, the complexes were utilized the
assay of acetylcholine esterase activity. All the complexes were
showed comparable activity to hydrolyze the OPs.
Ligand HL1: The Ligand HL1 was synthesized via a condensation
reaction between S-81 (348 mg, 1 mmol) and 2-hydroxybenzaldehyde
(122 mg, 1 mmol) in methanol. A yellow color solid was separated out
after two hours of refluxing. The solid was washed and recrystallized in
methanol to get pure product. Yield: 90%, 1 H NMR (400 MHz in CDCl3) δ
(ppm) = 13.15 (s, 1H), 8.59 (s, 1H), 8.57 (d, J = 7.3 Hz, 2H), 8.19 (d, J =
8.2 Hz, 2H), 7.77 (d, J = 7.8 Hz, 1H), 7.72 (t, J = 7.8 Hz, 2H), 7.39 – 7.35
(m, 2H), 7.33-7.29 (m, 1H), 7.18 (t, J = 7.5 Hz, 1H), 7.11 (d, J = 7.2 Hz,
1H), 6.99 (d, J = 8.2 Hz, 1H), 6.92 (t, J = 7.4 Hz, 1H), 4.46 – 4.42 (m, 2H),
3
.33 – 3.27 (m, 2H).13C NMR (100 MHz in CDCl3) δ (ppm): 164.17,
162.06, 161.27, 146.45, 134.19, 133.38, 132.39, 132.05, 131.65, 131.44,
128.28, 127.76, 127.48, 127.01, 126.36, 122.54, 119.34, 119.07, 117.73,
117.54, 39.79, 28.91. HR-ESI-MS: m/z calcd (C27H20N2O3S, [M+H]),
453.1279; found, 453.1250 [M+H].
Ligand HL2: Ligand HL2 was synthesized by similar procedure as
adopted in ligand HL1. Yield: 90%, 1H NMR (400 MHz in CDCl3) δ (ppm)
Experimental Section
=
15.29 (s, 1H), 9.36 (s, 1H), 8.53 (d, J = 7.5 Hz, 2H), 8.14 (t, J = 9.3 Hz,
3
7
1
H), 7.77 (t, J = 8.5 Hz, 2H), 7.68 (dd, J = 15.1, 7.6 Hz, 3H), 7.51 (t, J =
.7 Hz, 1H), 7.37-7.29 (m, 2H), 7.25-7.24 (m, 2H), 7.04 (d, J = 9.1 Hz,
H), 4.45 – 4.42 (m, 2H), 3.33 – 3.30 (m, 2H).13C NMR (100 MHz in
Nickel nitrate, 2-Aminothiophenol, hydrazine hydrate and potassium
carbonate were purchased from Avra Synthesis. All the aldehyde,
chlorpyriphos, parathion methyl and 1,8-naphthalic anhydride were
provided by Sigma-Aldrich. All the chemicals were used as it is without
any further purification. The OPs are highly toxic in nature, therefore
precautions were taken during experiments as mentioned on data safety
sheet. The deuterated solvents were purchased from Sigma-Aldrich.
CDCl3) δ (ppm): 168.08, 164.15, 155.39, 145.40, 136.27, 134.13, 133.20,
1
1
31.61, 131.40, 130.31, 129.41, 128.25, 128.05, 127.55, 127.20, 126.96,
23.61, 122.51, 121.66, 119.19, 117.76, 109.31, 39.73, 29.70. ESI-MS:
m/z calcd (C31H22N2O3S, [M+H]), 503.1429; found, 503.1422 [M+H].
1HNMR and 13CNMR was recorded on Jeol instruments operated at 400
and 100 MHz respectively. 31P NMR was recorded using magnetic field
Ligand HL3: Ligand HL3 was synthesized above reported method. Yield:
90%, 1H NMR (400 MHz in CDCl3) δ (ppm) = 14.23 (s, 1H), 8.67 (s, 1H),
8.56 (d, J = 7.3 Hz, 2H), 8.37 (d, J = 2.7 Hz, 1H), 8.24-8.19 (m, 3H), 7.79
(d, J = 7.9 Hz, 1H), 7.73 (t, J = 7.8 Hz, 2H), 7.35 (t, J = 7.5 Hz, 1H), 7.21
(d, J = 7.4 Hz, 1H), 7.15 (d, J = 7.7 Hz, 1H), 7.02 (d, J = 9.2 Hz, 1H), 4.46
– 4.42 (m, 2H), 3.33 – 3.29 (m, 2H). 13C NMR (100 MHz in CDCl3) δ
(ppm): 166.69, 164.21, 162.15, 160.09, 145.27, 140.00, 134.29, 132.29,
131.67, 131.48, 128.79, 128.45, 128.29, 127.05, 126.81, 122.48, 118.51,
of 160 MHz. The chemical shift was defined in ppm with reference to
tetramethyl silane as an internal standard. UV-vis absorption titration of
ligands with metal ions was performed using UV-2600 Shimadzu
spectrophotometer. The path length of UV cuvette was 10 cm made up of
quartz. HRMS of ligands and metal complexes was recorded on XEVO
G2-XS QTOF. The concentration and degradation mechanism of OPs
was recorded using LC-MS chromatogram.
1
4
18.39, 117.84, 39.67, 29.37. ESI-MS: m/z calcd (C27H19N3O5S, [M+H]),
98.1124; found, 498.1098 [M+H].
Synthesis of Ligands: Naphthalimide based heterodipodal Schiff base
ligands was synthesized by multistep reaction as shown in Scheme 1.
Ligand HL4: Ligand HL4 was synthesized above reported method. Yield:
9
7
0%. 1 H NMR (400 MHz in CDCl3) δ (ppm) = 13.60 (s, 1H), 8.56 (d, J =
.7 Hz, 3H), 8.19 (d, J = 8.2 Hz, 2H), 7.77-7.70 (3, 3H), 7.31 (t, J = 7.5
Synthesis of S-79: 2-Aminothiophenol was dissolved in dry acetonitrile.
To this solution K2CO3 (1 eq) was added and refluxed for 1h under inert
atmosphere. Solution of N-(2-Bromoethyl)phthalimide in dry acetonitrile
was added to the solution of 2-Aminothiophenol drop-wise over the
period of 40 minutes. The mixture was further refluxed for 7 h and then
filtered off while hot to get brownish oily S-79.
Hz, 1H), 7.19 (t, J = 7.6 Hz, 1H), 7.13 (d, J = 7.8 Hz, 1H), 7.01 (d, J = 7.8
Hz, 1H), 6.95 (d, J = 7.8 Hz, 1H), 6.81 (t, J = 7.7 Hz, 1H), 5.77 (s, 1H),
4.48-4.44 (m, 2H), 3.34 – 3.31 (m, 2H). ESI-MS: m/z calcd (C27H19N3O5S,
[
M+H]), 469.1222; found, 498.1219 [M+H].
Electrochemical Synthesis of Metal complexes:
Synthesis of S-80: Hydrazine hydrate (2 eq) was added to a suspension
of S-79 (1 eq) in ethanol and mixture was refluxed for one hour. Then aq.
HCl (2.0 M) was added and the reaction mixture was refluxed for a
further one hour. After this, the reaction mixture was cooled to 4 °C and
the phthalyl hydrazide was precipitated out and removed by filtration. The
solvent was removed in vacuo and residue was re-dissolved in aqueous
solution (pH 15) of NaOH (2.0 M). The aqueous solution was then
extracted by diethyl ether (5X) and dried over sodium sulphate. The
solvent was removed by vacuum to give product S-80 as a brownish oil.
[Ni(L1)2]2+: Ligand (30 mg) dissolved in acetonitrile and 5 mg of metal
salt (NiNO3) was added into it. Reaction mixture was electrolyzed for 2 h
at 5 V and 3 mA The nickel metal started to dissolve at anode, Ef = 0.4
mol F-1 and after 1 h of reaction process, the yellowish-green precipitates
were collected. The precipitates were collected after filtration and washed
with water (3X). Synthesized metal complex was characterized using
+
HRMS. Yield: 68%. ESI-MS: m/z calcd (C54H38N4NiO6S2, [M ]), 961.15;
+
found, 961.13 [M ]. Elemental analysis found for C54H38N4NiO6S2: C,
6
8.54; H, 4.2; N, 5.83; Ni, 6.9.
Synthesis of S-81: Naphthalic anhydride (1 mmol) was dissolved in
ethanol in round bottom flask. To the ethanolic solution of naphthalic
anhydride, S-80 (1.3 mmol) was added and refluxed at 60 0C for 3 hour.
After 3 h S-81 was precipitated out and collected by vacuum filtration.
Solid product was washed with ethanol and dried under vacuum to get
pure pale yellowish solid compound. 1H NMR (400 MHz, CDCl3) δ 8.55 (d,
[Ni(L2)2]2+: Synthesized as reported for [Ni(L1)2] . Yield: 65%. ESI-MS:
2+
+
+
m/z calcd (C62H42N4NiO6S2, [M ]), 1061.1977; found, 1061.1977 [M ].
Single crystal of complex was obtained from acetonitrile:methanol (1:1)
solution. Elemental analysis found for C62H42N4NiO6S2: C, 71.1; H, 4.2; N,
5.9; Ni, 5.9.
J = 7.3 Hz, 2H), 8.19 (d, J = 8.3 Hz, 2H), 7.72 (t, J = 7.8 Hz, 2H), 7.45 (d,
J = 9.5 Hz, 1H), 7.01 (t, J = 8.4 Hz, 1H), 6.65 – 6.62 (m, 2H), 4.40 – 4.37
6
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
FULL PAPER
2+
[
Ni(L3)2]2+: Synthesized as reported for [Ni(L1)2] . Yield: 73%. ESI-MS:
[6]
[7]
[8]
L. W. K. Moodie, M. C. Žužek, R. Frangež, J. H. Andersen, E. Hansen,
E. K. Olsen, M. Cergolj, K. Sepčić, K. Ø. Hansen, J. Svenson, Org.
Biomol. Chem. 2016, 14, 11220-11229.
+
+
m/z calcd (C54H36N6NiO10S2, [M ]), 1051.1366; found, 1051.1207 [M ].
Elemental analysis found for C54H36N6NiO10S2: C, 62.16; H, 3.85; N,
8
.56; Ni, 5.98.
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[
+
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[
9]
Photophysical Properties: The UV-vis absorption spectroscopic studies
were performed at room temperature. The stock solution of ligands (10
µM) were prepared in 30% acetonitrile in water. The metal solution (1
mM) was prepared in distilled water and sonicated for 15 minutes. The
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7
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European Journal of Inorganic Chemistry
10.1002/ejic.202000461
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Entry for the Table of Contents
Insert graphic for Table of Contents here.
The Nickel metal complexes of naphthalimide schiff base were synthesized using electrochemistry and utilized as a catalyst for
hydrolysis of organophosphates.
Organophosphate Hydrolysis*
8
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