Synthesis of new nano schiff base complexes: X-Ray crystallography, thermal, electrochemical and anticancer studies of nano uranyl schiff base complexes

Article abstract of DOI:10.4314/bcse.v32i1.8

This study presents synthesis and characterization of new nano uranyl Schiff base complexes. Electrochemistry of these complexes showed a quasireversible redox reaction without any successive reactions. Furthermore, X-ray crystallography exhibited that beside the coordination of tetradentate Schiff base, one solvent molecule (dimethylformamide) was also coordinated. According to Coats-Redfern plots the kinetics of thermal decomposition of the studied complexes was first-order in all stages. Anticancer activities of the uranyl Schiff base complexes against cancer cell lines (Jurkat) was studied and determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide) assay. The results demonstrated that the complexes with aliphatic bridging units showed less anticancer activities than those having the aromatic units.

Full text of DOI:10.4314/bcse.v32i1.8

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Bull. Chem. Soc. Ethiop. 2018, 32(1), 89-100.
 2018 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v32i1.8
ISSN 1011-3924
Printed in Ethiopia
SYNTHESIS OF NEW NANO SCHIFF BASE COMPLEXES: X-RAY
CRYSTALLOGRAPHY, THERMAL, ELECTROCHEMICAL AND ANTICANCER
STUDIES OF NANO URANYL SCHIFF BASE COMPLEXES
Fahimeh Dehghani Firuzabadi1, Zahra Asadi1* and Reza Yousefi2
1Department of Chemistry, College of Science, Shiraz University, Shiraz 71454, Iran
2Protein Chemistry Laboratory, Department of Biology, Shiraz University, 71454 Shiraz, Iran
(Received November 19, 2016; Revised January 15, 2018; Accepted January 23, 2018)
ABSTRACT. This study presents synthesis and characterization of new nano uranyl Schiff base complexes.
Electrochemistry of these complexes showed a quasireversible redox reaction without any successive reactions.
Furthermore, X-ray crystallography exhibited that beside the coordination of tetradentate Schiff base, one solvent
molecule (dimethylformamide) was also coordinated. According to Coats-Redfern plots the kinetics of thermal
decomposition of the studied complexes was first-order in all stages. Anticancer activities of the uranyl Schiff
base complexes against cancer cell lines (Jurkat) was studied and determined by MTT (3-[4,5-dimethylthiazol-2-
yl]-2,5-diphenyltetrazoliumbromide) assay. The results demonstrated that the complexes with aliphatic bridging
units showed less anticancer activities than those having the aromatic units.
KEY WORDS: Uranyl Schiff base complex, Anticancer activities, Thermal studies, Electrochemistry; X-ray
crystallography
INTRODUCTION
Studies show that Schiff bases and their complexes have many applications in the fields of
catalysis [1, 2], synthesis [3], polymerization [4], epoxidation of olefins [5], degradation of dyes
through decomposition of hydrogen peroxide and other reagents, textile industries [6],
biological [7], and photochromic applications [8]. Coordination chemistry of uranyl salts is an
area of chemistry that has been widely studied recently, especially when compared to the
interest involving coordination compounds of the lanthanides, transition metals [9] and actinides
of oxidation states +5 and +6 [10].
Unlike d-block oxo-cations, [UO2]2+ is stable over a wide pH range and can be identified in
almost all uranium(VI) oxide solids. This species has a linear O=U=O structure, and the
additional ligands coordinate to the central atom in the equatorial plane of UO22+. The number of
equatorial coordination sites varies between 3 and 6. The Schiff base ligands in uranyl Schiff
base complexes bound in a tetradentate plane. A solvent molecule occupies the fifth coordinate
site in the equatorial position [11]. The presence of the solvent can play an important role in the
activation of the substrate in catalysis for acyl transfer, Michael-type addition of thiols,
molecular recognition of urea derivatives, pyridine derivatives, amines, quinolines, nitriles, and
other anions [12]. In our previous work [13], we investigated the effect of aromatic amines on
the anticancer activity of the uranyl Schiff base complexes. Here we utilized the aliphatic
amines in the synthesis of some new uranyl Schiff base complexes to find their anticancer
activity. All the complexes were characterized by different techniques.
EXPERIMENTAL
Chemicals and apparatus
1,2-Ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine,
1,4-butylenediamine,
uranylacetatedihydrate UO2(OAc)2.2H2O, tetrabutylammunium perchlorate (Bu4NClO4), 2-
__________
*Corresponding author. E-mail: zasadi@shirazu.ac.ir
This work is licensed under the Creative Commons Attribution 4.0 International License

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Fahimeh Dehghani et al.
hydroxy-1-naphthaldehyde, methanol, chloroform (CHCl3), dimethylformamide (DMF),
acetonitrile (CH3CN), DMSO-d6, potassium bromide (KBr) and CDCl3 were purchased
commercially and used without further purification.
The electronic absorption spectra were recorded using a Perkin-Elmer Lambda 2
spectrophotometer. FT-IR spectra were recorded by Shimadzu FTIR–8300 infrared
spectrophotometer. The 1H NMR spectra were recorded on a Bruker Avance DPX–250
spectrometer in DMSO−d6 solvent using TMS as an internal standard at 250 MHz. Elemental
microanalyses were obtained using a CHN Thermo-Finnigan Flash EA1112. BUCHI 535
instrument was used to obtain the melting point of the compounds. Thermal gravimetric
analyses were recorded on Perkin-Elmer Pyris Diamond model. Electrochemical studies were
obtained by using Auto lab 302N. A three-electrode system was utilized, i.e., a glassy carbon
working electrode, a reference electrode (Ag/Ag+ in TBAP/acetonitrile solution), and a Pt
auxiliary electrode. The measurements of CV for CH3CN solution containing uranyl complexes
(1 mM) and TBAP (0.10 M) were carried out in the potential range from 0.2 V to -1.4 V.
Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte.
Incubator and ELISA reader (Bio-Tek's ELx808, USA) were used for anticancer studies.
Transmission electron microscopy (TEM) images were obtained on a Zeiss EM10C
transmission electron microscope using ACC voltage of 60 kV. The X-ray diffraction
measurements were made on a STOE IPDS 2T diffractometer with graphite monochromated
Mo-Kα radiation.
Synthesis of the ligands
All the tetradentate Schiff base ligands were prepared by condensation of diamines (1 mmol)
and 2-hydroxy-1-naphthaldehyde (2 mmol) in methanol (25 mL). The mixture was refluxed for
about 5 h. The products were washed with methanol and diethyl ether. All the Schiff base
ligands were dried at 50 ºC under vacuum (Figure 1).
Figure 1. Structural representation of the Schiff base ligands.
H2L1: N,N'-bis(naphthalidene)-1,2-ethylenediamine. Yield: 66%, color: yellow, m.p. >250 C,
anal. found (calc.): C24H20N2O2 (368.43): C, 78.64 (78.24); H, 5.47 (5.47); N, 8.02 (7.60). IR
(KBr, cm-1): 3469 (O-H), 2953-3042 (C-H), 1637 (C=N), 1540 (C=C), 1H NMR: Schiff base was
not soluble in DMSO or CDCl3. UV-Vis (acetonitrile): λmax (nm),  (M-1cm-1) = 261 (15608),
269 (sh), 305 (11054), 400 (8629), 424 (9209).
H2L2: N,N'-bis(naphthalidene)-1,2-propylenediamine. Yield: 78%, color: yellow, m.p. = 157-
159 C, anal. found (calc.): C25H22N2O2 (394.47): C, 79.49 (79.17); H, 5.71 (5.62); N, 7.51
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Synthesis of new nano Schiff base complexes
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1
(7.10). IR (KBr, cm-1): 3433 (O-H), 2931-3031 (C-H), 1620 (C=N), 1542 (C=C), H NMR (250
e
MHz, DMSO-d6, room temperature): δ (ppm) = 1.34-1.42 (d, 3H, CH3 ), 3.94 (m, 1H, CHd),
c
4.10 (d, 1H, CH2 ), 6.67-8.03 (m, 12H, ArH), 9.10 (d, 1H, HbC=N), 9.20 (d, 1H, HaC=N), 14.20
(s, 1H, OHb), 14.46 (s, 1H, OHa). UV-Vis. (acetonitrile): λmax (nm),  (M-1cm-1) = 310 (23034),
363 (10191), 406 (13193), 426 (12655).
H2L3: N,N'-bis(naphthalidene)-1,3-propylenediamine. Yield: 77%, color: yellow, m.p. = 209-
211 C, anal. found (calc.): C25H22N2O2 (382.46): C, 78.76 (78.51); H, 5.74 (5.80); N, 7.75
1
(7.32). IR (KBr, cm-1): 3446 (O-H), 2941-3039 (C-H), 1622 (C=N), 1541 (C=C), H NMR (250
b
MHz, DMSO-d6, room temperature): δ (ppm) = 2.06-2.21 (m, 2H, CH2 ), 3.74-3.76 (t, 4H,
a
CH2 ), 6.71-8.07 (m, 12H, ArH), 9.14 (s, 2H, HC=N), 14.17 (s, 2H, OH). UV-Vis (acetonitrile):
λmax (nm),  (M-1cm-1) = 262 (sh), 270 (sh), 309 (19057), 410 (13682), 424 (14659).
Synthesis of the nano uranyl Schiff base complexes
The complexes were prepared by slow addition of uranyl acetate (0.40 mmol, 0.17 g), which
was dissolved in about 50 mL of methanol, into a hot 50 mL methanolic solution of stirred H2L
(0.38 mmol, 0.15 g). The addition of uranyl acetate was prolonged for about 24 h. The mixture
was then refluxed for another 24 h. The precipitated solids were slowly cooled, filtered and
washed with methanol and ether. TEM image showed nano-particles with sizes between 19-32
nm (Figure 2).
Figure 2. TEM image of nano-particles of [UO2(L2)(MeOH)].
[UO2(L1)(MeOH)]. Yield: 60%, color: orange, m.p. >250 C, anal. found (calc.): C25H22N2O5U
(668.49): C, 45.34 (44.92); H, 3.10 (3.32); N, 4.18 (4.19). IR (KBr, cm-1): 3358 (O-H) (MeOH),
2734-3051 (C-H), 1619 (C=N), 1540 (C=C), 885 (U=O), 644 (U-N). 1H NMR (250 MHz,
DMSO-d6, room temperature): δ (ppm) = 3.14 (d, 3H, MeOH), 4.07 (q, 1H, MeOH), 4.74 (s,
4H, CH2), 7.24-8.37 (m, 12H, ArH), 10.33 (s, 2H, HC=N). UV-Vis (acetonitrile): λmax (nm), 
(M-1cm-1) = 243 (69032), 355 (sh), 394 (sh), 315 (17609).
[UO2(L2)(MeOH)]. Yield: 70%, color: red, m.p. >250 C, anal. found (calc.): C26H24N2O5U
(682.52): C, 46.19 (45.76); H, 3.53 (3.54); N, 4.51 (4.10). IR (KBr, cm-1): 3417 (O-H) (MeOH),
2916-3070 (C-H), 1612 (C=N), 1550 (C=C), 902 (U=O), 547(U-N). 1H NMR (250 MHz, DMSO-
e
d6, room temperature): δ (ppm) = 1.42-1.45 (d, 3H, CH3 ), 3.14 (d, 3H, MeOH), 4.08 (q, 1H,
c
MeOH), 4.67- 4.74 (d, 2H, CH2 ), 5.15 (m, 1H, CHd), 7.24-8.37 (m, 12H, ArH), 10.18 (s, 1H,
HbC=N), 10.33 (s, 1H, HaC=N). UV-Vis (acetonitrile): λmax (nm),  (M-1cm-1) = 316 (sh), 365
(8732).
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Fahimeh Dehghani et al.
[UO2(L3)(MeOH)]. Yield: 49%, color: red, m.p. >250 C, anal. found (calc.): C26H24N2O5U.
0.7H2O (695.12): C, 44.52 (44.93); H, 3.18 (3.68); N, 4.17 (4.03). IR (KBr, cm-1): 3417 (O-H
)
1
(MeOH), 2931-3039 (C-H), 1612 (C=N), 1542 (C=C), 902 (U=O), 555 (U-N). H NMR (250
b
MHz, DMSO-d6, room temperature): δ (ppm) = 2.65 (s, 2H, CH2 ), 3.14 (d, 3H, MeOH), 4.09
a
(q, 1H, MeOH), 4.42-4.47 (m, 4H, CH2 ), 7.22-8.24 (m, 12H, ArH), 10.09 (s, 2H, HC=N).
UV-Vis (acetonitrile): λmax (nm),  (M-1cm-1) = 316 (sh), 365 (sh).
[UO2(L4)(MeOH)]. It was synthesized by template method. Yield: 60%, color: orange, m.p.
>250 C, anal. found (calc.): (C27H26N2O5U). 2NO3. 1H2O (838.57): C, 38.46 (38.67); H, 3.42
(3.37); N, 6.26 (6.68). IR (KBr, cm-1): 3456 (O-H), 2939-3047 (C-H), 1628 (C=N), 1543 (C=C),
902 (U=O), 470 (U-N). 1H NMR (250 MHz, DMSO-d6, room temperature): δ (ppm) = 4.08 (m,
b
a
4H, CH2 ), 4.37 (m, 4H, CH2 ), 7.13-8.19 (m, 12H, ArH), 10.13 (s, 2H, HC=N). UV-Vis
(acetonitrile): λmax (nm),  (M-1cm-1) = 243 (24181), 330 (14974), 441 (sh).
X-ray structural determination of [UO2(L3)DMF]
Crystals of [UO2(L3)DMF] were obtained in good yield by slow evaporation of a DMF solution
of [UO2(L3)MeOH] at room temperature. The red crystal was mounted on a glass fiber and used
for data collection. The data collection and reduction were performed by X-AREA program
[14]. The multi-scan absorption correction was performed by MULABS routine [15]. The
structure was solved by direct methods using SHELXS97 [16] and subsequent difference
Fourier map and then refined by a full-matrix least-squares on F2 by SHELXL97 in SHELXTL
package [16]. The non-hydrogen atoms were refined anisotropically. All of the H atoms were
positioned geometrically and constrained to ride on their parent atoms with Uiso(H) = 1.2 or
1.5Ueq(C). All refinements were performed using the SHELXTL crystallographic software
package. All calculations were done using PLATON [17].
Cell culture and MTT assay for analysis of anticancer properties of the complexes
The cancer cells were cultured in RPMI 1640 Medium (HiMedia, Mumbai, India) supplemented
with 10% Fetal Calf Serum (FCS) (Biochrom, Germany). Also 100 IU/mL of penicillin and 100
mg/mL of streptomycin were added to the medium as antibiotics to control the growth of
contaminating microorganisms. The cells were cultured in 96-well cell culture plates (Greiner,
USA), and kept at 37 °C in a humidified atmosphere of 5 percentage CO2, in a CO2 incubator.
All the experiments were performed using Jurkat cancer cell line of 10-15 passage. The growth
inhibitory effect of uranyl complexes (L1-L4) toward the cancer cells was measured using 3-
(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay. Briefly, the cleavage
and conversion of the soluble yellowish MTT to the insoluble purple formazan by active
mitochondrial dehydrogenase of living cells has been used to develop an assay system
alternative to other assays for measurement of cell proliferation [18]. The drug treatment was
performed as the harvested cells were seeded into the 96-well plate (2.5 × 104 cells/well) with
varying concentrations of the sterilized uranyl complexes (0-100 μM) and incubated for 24 and
48 h. Four hours to the end of incubations, 25 μL of MTT solution (5 mg/mL in PBS) was added
to each well containing fresh and cultured media. At the end, the insoluble formazan produced
was dissolved in solution containing 10% SDS and 50% DMF (left for 1 h at 37 °C in dark
conditions) and optical density (OD) was read against reagent blank with multi well scanning
spectrophotometer (ELISA reader, Bio-Tek's ELx808, USA) at a wavelength of 570 nm. The
absorbance is a function of concentration of the converted dye. The OD value of study groups
was divided by the OD value of untreated control and presented as percentage of control (as
100%). Also the values of IC50 (the concentrations required for 50% growth inhibition), after 24
h of incubation with the complexes were calculated. Cisplatin was used as a positive control on
this study just to see that cytotoxic assay system is working well. The IC50 value of cisplatin
Bull. Chem. Soc. Ethiop. 2018, 32(1)