synthesis, characterization and antibacterial
TRANSCRIPT
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Ajibulu et al. World Journal of Pharmacy and Pharmaceutical Sciences
SYNTHESIS, CHARACTERIZATION AND ANTIBACTERIAL
ACTIVITY OF SCHIFF BASE, N, N1- BIS(4-NITROBENZYLIDENE)
ETHYLENEDIAMINE, METAL(II) COMPLEXES
K. E. Ajibulu*, A. E. Okoronkwo and J. B. Owolabi
Department of Chemistry, Federal University of Technology, P.M.B.704 Akure, Ondo State,
Nigeria.
ABSRACT
The Schiff base ligand, N,N1-bis(4-nitrobenzylidene) ethylenediamine,
has been synthesized by stirring ethylenediamine and 4-
nitrobenzaldehyde in ratio 1:2 at room temperature. The ligand was
characterized using (FT-IR, UV-vis) spectroscopies, (1H,
13C) NMR
spectrum, Mass Spectrum, TGA/DTA and magnetic moments.
Matal(II) complexes of the ligand were synthesized in a ratio of 1:2,
M:L, and characterized. From elemental analysis data, the metal
complexes formed had the general formulae [M(L)2], where L = Schiff
base ligand (C16H14N4O4) and M = Mn, Ni and Co. On the basis of FT-
IR, and NMR data “N” donor atoms of the Schiff base ligand
participated in coordination with metal (II) ions, and thus, a four
coordinated tetrahedral geometry for the complexes of Mn and Ni while six coordinated
octahedral geometry proposed for Co respectively. The free ligand and its metal complexes
have been screened for biological activity against Gram-positive and Gram-negative bacteria.
KEYWORDS: Schiff base, ethylenediamine, antibacterial, metal(II) complex.
1. INTRODUCTION
The condensation of an amine with aldehyde or ketone, forming what is called a Schiff base
is one of the oldest reactions in chemistry.[1-2]
Schiff base ligands coordinate to a metal
through the imine nitrogen and another group, usually oxygen.[3-7]
Bidentate Schiff bases with
N,N donor atoms are well known to coordinate with various metal ions and have attracted a
great deal of interest in recent years due to their rich coordination chemistry.[8-10]
Schiff base
WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES
SJIF Impact Factor 7.632
Volume 10, Issue 9, 2059-2072 Review Article ISSN 2278 – 4357
*Corresponding Author
K. E. Ajibulu
Department of Chemistry,
Federal University of
Technology, P.M.B.704
Akure, Ondo State, Nigeria.
Article Received on
24 July 2021,
Revised on 13 Aug. 2021,
Accepted on 02 Sept. 2021,
DOI: 10.20959/wjpps20219-19563
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ligands are potentially capable of forming stable complexes with metal ion.[11-15]
The
azomethine (-HC=N-) linkage present in Schiff base ligand and its metal(II) complexes show
a wide range of biological activity and are of useful industrial application.[16-22]
In this article,
we present the synthesis, characterization and thermal analysis of Co(II), Ni(II), and Mn(II)
complexes containing bidentate Schiff base ligand, N,N1-bis(4-nitrobenzylidene)
ethylenediamine, and to examine their biological activity against Escherichia coil,
Staphylococcus aureu, Klebsiella pnuemoniae and bascillus substillis
2. EXPERIMENTAL
2.1 MATERIALS AND METHODS
The chemicals and solvents used in this research work were of analytical grade source from
Sigma-Adrich Chemical Company. Synthesis of Schiff Base ligand was carried out in pure
solvent. FT-IR spectra of synthesized compounds (in a KBr) were recorded in
400-500/400 cm-1
region on infrared spectrometer Varian 660 MidIR Dual/MCT/DTGS
Bundle with ATR. The 1H and
13C NMR spectra of the Schiff base ligand are recorded in
deuterated DMSO (Internal Standard TMS) on Bruker spectrometer. The electronics spectra
of the synthesized compounds were recorded on a Spectrumlab 752S spectrophotometer in
the 0-400, 400-900 range for ligand and complexes. Magnetic susceptibility measurements of
the metal complexes were determined on Gouy balance at room temperature using
Swissmake-H-1640 with maximum capacity 80g and precision ±0.01 mg. Melting point were
recorded on a gallenkamp apparatus and are uncorrected. The TGA/DTG were recorded on
Shimadzu TGA - Q50 thermo balance. For each sample analysed by TGA the run starts in
Nitrogen and ramps the temperature up to 8000C, 10
0C min
-1. The synthesized compounds
were screened in vitro for their antibacterial activities against Gram positive and Gram
negative bacterials using the plate diffusion method.[23]
2.2 Synthesis of Schiff Base Ligand: N, N1-bis(4 nitrobenzylidene) ethylenediamine
The ligand (L) (Scheme 1) was prepared according to the literature.[23]
Ethylenediamine
(0.012mol, 0.7g) with 4-nitrobenzaldehyde (0.002mol, 3.54g) in a 50ml round bottom flask
was stirred in 20ml ethanol at room temperature for 3 hours, two drops of conc. H2SO4 was
added to the mixture to adjust its PH to ≈ 6. The resulting milk coloured precipitate formed
was separated by filtration and purified by recrystalization from ethanol (and dried overnight
in air). Yield: 76%, 3.2lg, colour: milk, m.p: 189– 2010C. Elemental analysis for C16H14N4O4
(FW = 326.31) found: C, 58.62%; H, 4.27%; N,17.12% calculated: C, 58.89%; H, 4.29%; N,
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17.17%. MW:326g. FT-IR (KBr, disc cm-1
): 1118v(C-N), 1635.3 v(HC=N), UV-Vis
(acetonitrite) & max (nm) 275, 298. 1HNMR (ppm d6 – DMSO, 400 MHZ): 8.6(S, 1H, CH =
N), 8.4 (S, 2H, N-CH2), 8.0 – 8.4(Ar H). 13
CNMR (ppmd6 - DMSO):161(HC = N), 129-
124(Ar, C=C). MS: m/z 326[m+ + 1].
2.3. Synthesis of the Schiff Base Metal Complexes
The Schiff base Metal (II) Complexes (Scheme 1) were prepared by reacting the Schiff base
with the metal (II) ions according to the literature methods.[23, 24]
Metal (II) salts of Co, Ni and Mn were used to complex the ligand, 0.02mole of Schiff base
was dissolved in 20ml ethanol in around bottom flask. To this solution, 0.01 mole of metal
salt solution was added. The mixture was magnetically stirred and reflux for 3 hours at
500C. The precipitate formed was filtered, washed with cold water to remove unreacted
Schiff base ligand and its metal (II) Salts.
O2N CH O + H2N NH2+ CH NO2O
Stir in EtOH, rt. for 3hrs
O2N CH N N CH NO2
Refluxed in EtOH
for 31/2 hrs
O2N CH N N CH NO2
O2N CH N N CH NO2
M
= =
==
= =
==
MX.nH2O
Where M = Co (II), Ni (II) and Mn (II).
Figure 1: Synthesis of the Schiff base ligand and its metal (II) complexes.
2.3.1. Mangnese (II) Complex: Yield, 66.5%, M.W 821g, Colour: deep brown, m.p = 3100C.
Elemental analysis data for C32H30SMnN8O13 found: C, 46.53%; H, 3.63%; N, 13.61%
calculated: C, 46.77%; H, 3.60%; N, 13.64%. FT-IR (KBr Disc Cm-1
): 1632 v(HC=N), 1113
v(C-N), 527v(M-N), UV-Vis (acetonitrite) λ max (nm) 336, 400. MS: m/z 822[M+ + 1]
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2.3.2. Cobalt (II) complex: Yield: 55.2% Colour: Indian Red, M.P: ˃3000C, MW =
780g. Elemental analysis data for C32H28 Cl2CoN8O8 found: C, 49.16%; H, 3.46%; N, 14.38%
calculated: C, 49.23%; H, 3.59%, N, 14.36%. FTIR: 1597 v(HC = N), 588.08 v(H20), 542.50
v(M-N), 1132 v(C-N). UV-vis (acetonitrite) λ max (nm), 481, 611, 662. MS: m/z 780[M+ +
1].
2.3.3. Nikel (II) Complex: Yield: 68.8%. Colour: Orange green, M.p: 2650C, MW = 807g. El
emental analysis data for C32H28SNiN8O12 found: C, 47.52%; H,3.45%;N, 13.36% calculated:
C, 47.58%; H, 3.47; N, 13.88%. FT-IR: 1601 v(HC=N), 1130 v(C-N) 521.13v(M-N). UV-
Vis (acetonitrite) λ max (nm), 506, 612, 721.MS: m/z 807[M+ + 1].
2.4 ANTIMICROBIAL ACTIVITIES
Susceptibility of two Gram-positive and two Gram-negative bacteria isolate to metal
complexes and ligands was determined following the BSAC Diffusion Method for
Antimicrobial Susceptibility Testing Version 9.1.[25]
This test was carried out to determine
the antimicrobial ability of the metal complexs and ligands to inhibit the growth of the test
bacteria isolates that were collected from Microbiology Department, Adekunle Ajasin
University, Akungba Akoko. The plate diffusion technique was used for the antibiotic
sensitivity test. Overnight cultures of the organisms were swabbed on sterile Muller Hilton
solidified Agar plates using sterile swab sticks. 8mm sized cork borer was used to bore hole
on the agar surface at equidistance. The well was filled with 50 μg/ml of metal complexes
and ligands, Amoxicillin was used as positive control while 30% DMSO used in diluting and
dissolving into solutions as negative control. All the plates were incubated at 370C to 24
hours. The zones of inhibition generated by the antibiotics were measured to the nearest
millimetres (mm) and interpreted as sensitive (S), intermediate (I), and resistant (R). The
zones of inhibition were measured and interpreted according to.[23]
3.0 RESULT AND DISCUSSION
The Schiff base ligand in this study was first synthesized by.[8]
using the reflux method. In
this research, the ligand was prepared using room temperature method. The Schiff base
ligand is soluble in DMSO. The metal complexes are colured solids which are stable in air.
The complexes are soluble in DMSO and water.
The melting points of the complexes were higher than that of the Schiff base ligand,
indicating that the complexes are more stable than the ligand. The chemical equation showing
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the preparation of the Schiff base ligand and its metal (II) complexes are represented in
scheme 1.
3.1 FT-IR Spectral Analysis. The formation of Schiff base ligand and metal complexes was
determined by comparing the FT-IR spectrum of the free ligand with the spectra of the metal
(II) complexes. The stretching frequency of the azomethine HC=N bound, v(C-N) were
observed at 1635 and 1188 cm-1
for the free ligand. The HC=N stretching frequencies in
metal (II) complexes were observed at 1597, 1601 and 1632cm-1
for Cobalt(II), Nikel(II) and
Maganese(II), respectively, shift to lower wave members. This indicated coordination of
Schiff base through the azomethine nitrogen.[8, 24]
The appearance of weak band in the region
529-588cm-1 attribute to v(M-N).[8, 27]
confirmed complexation. This shows that the Schiff
base ligand coordinated to the metal via “N” atoms.
3.2 NMR Spectral Analysis. The 1H and
13C NMR spectra of the Schiff base ligand and its
metal (II) complexes were recorded in DMSO-d6 as shown in figure 1 (a) and (b). The 1H
NMR spectrum of the Schiff base showed a single peak at δ=8.6ppm corresponding to the
azomethine proton (HC=N-) confirmed the formation of Schiff base during condensation
reaction. The observed peak at δ = 161.24ppm in the 13
C NMR specturum was further proof
that the ligand was successfully synthesized.[4,27]
3.3 ELECTRONIC SPECTRAL ANALYSIS
The electronic spectral data of the Schiff base ligand and its metal (II) complexes are given in
the experimental section. The Schiff base ligand exhibit two bands at 275 and 298nm
respectively.
(a) (b)
Fig. 1: (a) 1H NMR spectrum of ligand (L
1), (b)
13C NMR spectrum of ligand (L
1)
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The band at 275nm is assigned to the π–π* in benzene.[24]
The band appearing at 298nm is
assigned to n - π* transition of nonbonding electrons present on the nitrogen of the
azomethine group (C = N); upon complexation, π–π* transition of ligand shift to a longer
wavelength.
In Co(II) complex, three bands were observed at 481, 611 and 662.nm. This observed
transition are due to d-d transition assigned to 4T1(g)(F)
4T2(g)(F)(v1),
4T1(g)(F)
4A2(g)(F) (v2),
4T1(g)(F)
4T1(g)(P)(V3), respectively suggesting octahedral geometry
around the Co(II) ion.[27-29]
The electronic spectra of Ni(II) complex exhibited three bands, 506, 612,and 721nm
respectively. This bands are assigned to transition, 3A2(F)
3T1(F)(v1),
3A2(F)
3T2(F)(v2),
3A2(F)
3T1(P)(V3).
The observed magnetic susceptibility, 3.78 B.M (normal range for tetrahedral complexes is
3.7-4.0) is an indicative of tetrahedral geometry.[30]
Electronic spectra of Mn(II) complexes
gives two bands, 336, 400. The band 336nm may be attributed to ligand-metal charge
transfer, while 400nm band is assigned to transition, 6A1 4T2 which suggest tetrahedral
geometry around Mn(II) ion.[28, 31, 32]
3.4 CONDUCTIVITY MEASUREMENT
The molar conductivity of the synthesised compounds were measure at room temperature in
10-3
M water, acetone and methanol. The values of molar conductivity of the synthesized
compounds range between 119-127 Ohm-1
.Cm2. Mol
-1 for Ni(II) and Mn(II) complexes
indicating their electrolytic nature, while 85 Ohm-1
.Cm2.Mol
-1 for Co(II) indicating
nonelectro lytic nature.[33]
It suggested that there were anions present outside the coordination
sphere of Ni(II) and Mn(II) complexes.
3.5 THERMAL ANALYSIS
Thermal data and metal ligand (L) of the complexes are given in Table 1. The analysis
of TG/DTG curves of the ligand Fig. 2, showed that thermal decomposition occurs through
four steps. The first degradation step began at 20oC-152
oC may be accounted for loss of
(CH2-CH2), assigned to 8.2%(Obs.), 8.6%(Calc.). This step combined with two different
processes, the first is exothermic with TDTG at 80oC and the second endothermic process with
TDTG at 151oC. The second step in the temperature range 152
oC-394
oC can be attributed to
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the loss of (C6H4) group, assigned to 23.5% (Obs.), 23.31% (Calc.). The degradation is
exothermic process (TDTG) peak at 165oC. The third decomposition at 394
oC-600
oC broad
exothermic process (TDTG) peak at 449oC and broad endothermic (TDTG) peak at 559
oC is
attributed to loss of NO2 group assigned to 15.4%(Obs.), 14.11%(Calc.). The forth
degradation in the temperature range of 670oC-800
oC with sharp-long exothermic (TDTG)
peak at 750oC is attributed to the loss of [C6H4, NO2, (CH=N)2], assigned to 51.40% (Obs.),
48.62% (Calc.).
(a) (b)
(c) (d)
Figure 2: (a) TG curve of Ligand L (b) TG curve of complex L(Co) (c) TG curve of
complex L(Mn) (d) TG curve of complex L(Ni)
The analysis studies of TG/DTG curve [Ni(L)2]
complex, Figure 2(d) revealed that thermal decomposition occurs through three steps. The
first step observed at 20oC-175
oC with endothermic effect TDTG at 47
oC, 9.2% Obs.),
9.04% (Calc.) mass loss due to removal of [CH2, 4H, NO2]. The second step may be
accounted for the loss of [(C6H6)2, (NO2)2] at temperature range 175oC-349
oC with two
processes, sharp endothermic (TDTG) peak at.
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Table 1: TG/DTG Data of Ligand and its Complexes with Decomposition Steps.
Compound Step
Temp.
Range
(oC)
DTG
Max
(oC)
Thermal
Effect
Mass loss.
Cal. (Obs)
(%)
Assignment Metallic
Residue
L
1st
2nd
3rd
4th
20 – 152
152 – 394
394 – 600
600 – 800
80
165
449
670
Exo
Exo
Exo
Exo
8.60 (8.20)
23.31 (23.50)
14.11 (15.40)
48.62 (51.40)
CH2 = CH2
C6H6
NO2
C6H4, NO2, (CH = N)2
Ni(L)2
1st
2nd
3rd
20 – 175
175 – 349
369 – 565
47
275
400
Endo
Endo
Exo
9.04 (9.20)
34.32 (34.5)
33.80 (33.60)
CH2, 2H, NO2
(C6H6)2, (NO2)2
(CH=N)2, (CH2 = CH2,), C6H4
NiO
Mn(L)2
1st
2nd
3rd
47 – 150
150 – 327
327 – 500
98
228
400
Exo
Exo
Endo
14.2 (14.14)
28.01 (27.8)
40.02 (40.80)
CH2, 2H, (CH2=N)2,
H2O, C2H42(C6H4), NO2
(C6H4)2, (NO2)2
MnO
Co(L)2
1st
2nd
3rd
4th
22 – 170
170 – 352
294 – 598
598 – 800
47
190
400
___
Endo
Endo
Endo
___
15.47 (15.80)
18.0 (17.80)
16.59 (17.20)
____
CH2, 4H CH2 = CH2, (NO2)2
(C6H4CH=N)2, NO2
C4H6, NO2
CoO
(a) (b)
(c) (d)
Fig. 3: (a) Mass spectrum of ligand (L1), (b) Mass spectrum of complex Ni(L2), (c) Mass
spectrum of complex Co(L2), (d) Mass spectrum of complex Mn(L2).
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200oC and broad exothermic (TDTG) peak at 275
oC assigned to 34.5% (Obs.), 34.32% (Calc.).
The third decomposition step involves the removal of [(CH=N)2, (CH2-CH2)2, C6H4] at
369oC-565
oC with sharp exothermic effect (TDTG) peak at 400
oC, 33.6% (Obs.), 33.8%
(Calc.) mass loss. The possible remaining products (theoretically calculated 25.4%) may be
assigned to Ni(II) Nitrobenzene residues [C6H4O-NiON]. Lack of mass lose due to water
molecule confirms absence of water molecule in the environment of the complex.[4, 27]
The Mn(II) complex degrade in three steps Figure 2(c). The first loss in temperature range
47oC-150
oC, with broad exothermic process (TDTG) peak at 98
oC, may account for the loss
[H2O, (CH=N)2, C2H4] assigned to 14.2% (Obs.), 14.14% (Calc.) mass loss. The second
decomposition is characterized by three short exothermic effects with (TDTG) peaks at 170oC,
198oC, 300
oC and two short endothermic effects with (TDTG) peaks at 176
oC, 228
oC with
mass loss at 150oC-327
oC assigned to 27.8% (Obs.), 28.01% (Calc.). The third step involved
the removal of [(C6H4)2 (NO2)2] at 327oC-500
oC with long-sharp endothermic effect, (TDTG)
peak at 400oC, assigned to 40.8% (Obs.), 40.02% (Calc.). The final decomposition at 500
oC-
800oC corresponded to the formation of metal oxide of [C4H6N2] residue.
The Co(II) complex degrade in three steps Figure 2. The first step at 22oC-170
oC may
account for loss of [CH2, 4H, CH2=CH2, (NO2)2] of short endothermic effect with (TDTG)
peak at 47oC and broad exothermic with (TDTG) peak at 148
oC, assigned to 15.8% (Obs.),
15.47% (Calc.). Second decomposition step was recorded at temperature range of 170oC-
352oC, 17.8% (Obs.), 18.0% (Calc.) mass loss, may be assigned to decomposition of [(C6H4-
CH=N)2] and [NO2] parts, with weak endothermic and exothermic effect (TDTG) peak at
1900C and 294
0C. The third decomposition at 294
0C - 598
0C with long-sharp endothermic
process (TDTG) peak at 4000C account for loss [C4H6, NO2], assigned to 17.2% (Obs.),
16.59% (Calc.). The last step of pyrolysis at 598oC-800
oC account for loss of organic moiety
leaving CoO as residue.[8]
The results of thermal decomposition related to Co(II) and Ni(II) complexes were in
agreement with Irving-Williams series. The order of stability, Co(II) < Ni(II).[4]
3.6 Mass Spectra
The recorded mass spectrum of ligand and its metal (II) complexes with molecular ion peak
have been used to confirm the proposed structures.
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3.6 Antimicrobial Activity. The antimicrobial activity test were conducted according to the
standard procedure.[2]
The result are shown in Table 2.
All the bacteria showed an intermediate to sensitive reaction to all the metal complexes and
the ligand tested. The inhibitory ability of the Schiff base ligand and its metal (II) complexes
were compared to that of known standard antimicrobial drug, Amoxicillin, Ligand (L) and
Mn(II) showed maximum inhibition zone against Escherichia coil while Ni(II) complex
showed maximum inhibition zone against Klebsiella pnuemoniae. The Co(II) complex had
the highest activity against Staphylococcus aureu.
Table 2: Antibacterial sensitivity test of Schiff base ligand and its metal (II) complexes.
Name of
organism L(mm) Ni(mm) Mn(mm) Co(mm) Amoxicillin(mm)
30%
DMSO(mm)
Klebsiella
pnuemoniae
22.00
21.00
19.00
18.00
19.00
16.00
14.00
16.00
15.00
14.00
12.00
13.00
30.00
27.00
28.00
0.00
Staphylococcus
aureus
16.00
15.00
16.00
14.00
13.00
13.00
14.00
14.00
12.00
13.00
15.00
14.00
35.00
32.00
33.00
0.00
Escherichia
coil
28.00
27.00
28.00
18.00
17.00
16.00
16.00
15.00
17.00
18.00
17.00
17.00
34.00
31.00
34.00
0.00
Bacillus
subtillis
24.00
23.00
21.00
17.00
16.00
17.00
14.00
13.00
14.00
15.00
14.00
13.0
32.00
31.00
32.00
0.00
Sensitive (S) ≥ 14, Intermediate (I) 13≤ 9 and resistant (R) ≤ 9
Name of organism L(mm) Ni(mm) Mn(mm) Co(mm) Amoxicillin(m
m)
30%D
MSO
Klebsiella pnuemoniae 20.67±1.528b 17.67±1.528
b 15.00±1.000
a 13.00±1.000
a 28.53±1.528
a 0
Staphylococcus aureus 15.67±0.577a 13.33±0.577
a 13.33±1.155
a 14.00±1.000
a 33.33±1.1528
b 0
Escherichia coil 27.67±1.0.577c 17.00±1.000
b 16.00±1.000
b 17.33±0.577
b 33.00±1.732
b 0
Bacillus subtillis 22.67±1.528b 16.67±0.577
b 13.67±0.577
a 14.00±1.000
a 31.67±0.577
b 0
Value are mean ± standard deviation of three replicates. Values in the same column with
different superscript are significantly different at P < 0.05
4.0 CONCLUSIONS
The Schiff base ligand N, N1-bis(4-nitrobenzylidene) ethylenediamine (C16H14N4O4) and its
metal(II) complexes of Co(II), Ni(II) and Mn(II) were successfully synthesized and
characterised. The Schiff base ligand coordinated to the metal (II) ion through azomethine
nitrogen resulting to the formation of stable complexes, two tetrahedral Ni(II), Mn(II) and
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one (Co(II)) octahedral geometry. The proposed geometries were based on the electronic
spectra and their molar conductivity. Ni(II) and Mn(II) were found to be electrolytic while
Co(II) non electronic in nature. All the tested compounds showed significant effects on the
tested organisms but, the Schiff base ligand exhibited better antimicrobial properties than the
metal (II) complexes. The TG/DTG analysis shows that the ligand and its complexes are
stable.
ACKNOWLEDGMENT
The authors wish to appreciate the Laboratory Scientists at the Department of Chemistry,
Federal University of Technology Akure for their support during this research work.
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