Synthesis, structure investigation and biological evaluation of 2-thiophene N(4)-phenylthiosemicarbazone and its three metal derivatives

Article abstract of DOI:10.1016/j.molstruc.2015.07.031

A 2-thiophene N(4)-phenylthiosemicarbazone (HL) ligand and its three metal derivatives [CuL₂ ] (1), [NiL₂] (2) and [PdL₂] (3) are synthesized and characterized by elemental analysis, IR spectra, mass spectra as well as the

Full text of DOI:10.1016/j.molstruc.2015.07.031

Accepted Manuscript
Synthesis, structure investigation and biological evaluation of 2-thiophene N(4)-
phenylthiosemicarbazone and its three metal derivatives
Zilang Wang, Yuanyuan Wu, Yan Fu, Mingxue Li, Yanxue Tai, Yanke Li
PII:
S0022-2860(15)30142-3
10.1016/j.molstruc.2015.07.031
MOLSTR 21686
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 20 April 2015
Revised Date: 12 July 2015
Accepted Date: 16 July 2015
Please cite this article as: Z. Wang, Y. Wu, Y. Fu, M. Li, Y. Tai, Y. Li, Synthesis, structure investigation
and biological evaluation of 2-thiophene N(4)-phenylthiosemicarbazone and its three metal derivatives,
Journal of Molecular Structure (2015), doi: 10.1016/j.molstruc.2015.07.031.
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ACCEPTED MANUSCRIPT
Synthesis, structure investigation and biological evaluation of
2-thiophene N(4)-phenylthiosemicarbazone and its three metal
derivatives
Zilang Wang a, Yuanyuan Wu a, Yan Fua, Mingxue Li a,*, Yanxue Tai a, Yanke Li
aHenan Key Laboratory Polyoxometalates, Institute of Molecular and Crystal Engineering,
College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, PR China
ABSTRACT A 2-thiophene N(4)-phenylthiosemicarbazone (HL) ligand and its three metal
derivatives [CuL2 ] (1), [NiL2] (2) and [PdL2] (3) are synthesized and characterized by elemental
analysis, IR spectra, mass spectra as well as the single-crystal X-ray diffraction. Compounds 1−3
have the identical architectures in which the Schiff bases L- ions act as the bibasic chelating
ligands with thiolate S and imine N atoms as the donor sites. Cytotoxic studies carried out in vitro
against human liver hepatocellular carcinoma HepG2 cells and human normal hepatocyte
QSG7701 cells show that 1 can be able to inhibit cell proliferation growth. Compound 1 promotes
a dose-dependent apoptosis in HepG2 cells. The potential structure-activity relationships among
HL and 1−3 are further investigated by Hirshfeld surface combining fingerprint plots.
Keywords: Crystal structure; Thiosemicarbazone; Cytotoxicity; Hirshfeld surface;
Structure-activity relationships
_________________________________
*Corresponding author. Tel: +86 2378 3881518, Fax: +86 2378 3881589.
E-mail address: limingxue@henu.edu.cn (M. -X. Li)
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1. Introduction
Thiosemicarbazones and their metal complexes have received considerable attentions due to
their good repeatability, various structures and beneficial pharmacological properties [1–7]. It is
reported that the biological activities of thiosemicarbazones are closely related to the parent
aldehyde or ketone group, amino-terminal substitution and metal ions [8-13]. Moreover, the
antitumour activities of thiosemicarbazones increase with their ability coordinating to the metal
ions [8–9].
Thiosemicarbazones usually coordinate to the metal ions, notable for transition metal,
through the bidentate (N, S) mode or tridentate (N, N, S) mode [14–15], which are obviously
affected by the types of the substituent group on the azomethine carbon. Their coordination
abilities are greatly influenced by the extended delocalization of electron density over the
–NH–C(S)–NH–N=C– system, which can be strengthened by the substitutions of the terminal N
atom.16 Thus, the rational design and synthesis of the specific thiosemicarbazones is still an
interesting and challenging field.
In the past few decades, many transition metal complexes likely Co(II) [17], Ni(II) [18–19],
Cu(II) [20], Zn(II) [21], Pd(II) [22-24], Ag(I) [25], Au(I) [26] and Pt(II) [26] related to
thiosemicarbazones have been prepared and their cytotoxic activities have been investigated using
different cell line cultures. However, the mechanism of action is still controversial in many
respects and has not been completely identified including ribonucleotide reductase inhibition,
metal dependent radical damage, DNA binding, and inhibition of protein synthesis, etc. Therefore,
the discovery and development of new metal-based drugs remain an evergrowing area in the
medicinal inorganic chemistry as usual.
In recent years, we have been working on the structural and biological properties of
thiosemicarbazones and their metal complexes [17, 21, 25, 27–33]. We focus our mind on the
optimization of thiosemicarbazones and the selective preference of metal ions in order to
effectively enhance biological activities and reduce the potential toxicity. We have previously
reported the synthesis, crystal structure and biological activities of 2-thiophene
N(4)-methylthiosemicarbazone and its Ag(I) complex [25], which has taken on the better
biological activities. To continue this research, herein 2-thiophene N(4)-phenylthiosemicarbazone
(HL) is prepared, in which a phenyl is introduced to replace methyl with the aim of altering the
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delocalization of electron density over the –NH–C(S)–NH–N=C– system and adjusting its
coordination ability. Furthermore, we attempt to increase the interaction area of the non-covalent
bond binding like groove binding and intercalative binding with the substrate molecule. Ultimately,
their pharmacological properties can be improved and optimized. In this paper, three transition
metal complexes [CuL2] (1), [NiL2] (2) and [PdL2] (3) (Scheme 1) are successfully synthesized
via HL. They are carried out in vitro against HepG2 cells and normal QSG7701 cells. The effect
of 1 on cell apoptosis in HepG2 is studied. The possible reasons for the activity differences among
HL and 1-3 are further analyzed by Hirshfeld surface combing fingerprint plots.
Scheme 1. The reaction scheme for the synthesis of 1−3.
2. Experimental
2.1. Materials and physical measurements
All solvents and reagents were commercially available and used without further purification.
Melting points were determined with a X-5 Micro Processor Melting-point Apparatus. C, H and N
elemental analyses were performed on a Perkin-Elmer 240C elemental analyzer. The mass spectra
(MS) were taken out on an Esquire 3000 LC-MS mass spectrometer. The infrared spectrum was
recorded from KBr pellets on a Nicolet 170SXFT-IR spectrometer in the range of 400-4000 cm-1.
2.2. Synthesis of 2-thiophene N(4)-phenylthiosemicarbazone (HL)
N(4)-phenylthiosemicarbazide (0.50 g, 3 mmol) is added dropwise to an ethanol solution (30
mL) of 2-thiophene (0.34 g, 3 mmol) with five drops of acetic acid as catalyst. After refluxed for 2
h, the resultant solution is filtered. Yellow powders separated on cooling are washed with ethanol
and dried over P4O10 in vacuo, yield 81%. Melting point: 203−204 °C. Elemental analysis calcd
(%) for C12H11N3S2: C 55.14%, H 4.24%, N16.08%. Found: C 55.36%, H 4.47%, N 15.92%.
ESI-MS. Found: m/z 284.0 [HL + Na+]. Calcd: m/z 284.0. Colorless crystals suitable for X-ray
studies are obtained by slow evaporation of its ethanol solution.
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2.3. Synthesis of [CuL2] (1)
An ethanol solution containing Cu(ClO4)2·6H2O (0.074 g, 0.2 mmol) is added dropwise to an
ethanol solution (20 mL) of 2-thiophene N(4)-phenylthiosemicarbazone (0.105 g, 0.4 mmol) and
NaOAc (0.034 g, 0.4 mmol). After refluxing with stirring for 2 h, the resultant solution is filtered.
The obtained solid product is recrystallized from ethanol and dried over P4O10 in vacuo. Yield,
68%. Melting point: 199−201 °C. Elemental analysis calcd (%) for C24H20CuN6S4: C 49.34%, H
3.45%, N 14.38%. Found: C 49.28%, H 3.59%, N 14.20%. ESI-MS. Found: m/z 585.7
[Cu(L)(HL)]+. Calcd: m/z 585.3.Violet crystals suitable for X-ray studies are obtained by slow
evaporation of its ethanol solution.
2.4. Synthesis of [NiL2] (2)
The procedure is the same as that for 1 except that Cu(ClO4)2·6H2O (0.074 g, 0.2 mmol) is
replaced by Ni(ClO4)2·6H2O (0.073 g, 0.2 mmol). Yield, 60%. Melting point: 212−214 °C.
Elemental analysis calcd (%) for C24H20NiN6S4: C 49.75%, H 3.48%, N 14.50%. Found: C
50.02%, H 3.56%, N 14.31%. ESI-MS. Found: m/z 578.9 [Ni(L)(HL)]+. Calcd: m/z 579.0. Red
crystals suitable for X-ray studies are obtained by slow evaporation of its ethanol solution.
2.5. Synthesis of [PdL2] (3)
The procedure is the same as that for 1 except that Cu(ClO4)2·6H2O (0.074 g, 0.2 mmol) is
replaced by PdCl2 (0.035 g, 0.2 mmol). Yield, 55%. Melting point: 198−200 °C. Elemental
analysis calcd (%) for C24H20PdN6S4: C 45.96%, H 3.21%, N 13.40%. Found: C 45.28%, H 3.39%,
N 13.20%. ESI-MS. Found: m/z 629.3 [Ni(L)(HL)]+. Calcd: m/z 628.1. Orange crystals suitable
for X-ray studies are obtained by slow evaporation of its ethanol solution.
2.6. X-ray crystallography
Single crystal X-ray data collection are performed on a Bruker SMART APEX CCD
area-detector diffractometer equipped with a graphite-monochromated MoK
α radiation (λ =
0.71073 Å) at 293 (2) K. The intensities are corrected for Lorentz and polarization effects and for
empirical absorption. The structure is solved by direct methods and refined by full-matrix
least-squares techniques based on F2 using SHELXS–97 and SHELXL–97 programs [34],
respectively. All non-hydrogen atoms are refined anisotropically. All remaining H atoms were
positioned geometrically. A summary of the crystal data and refinement results are listed in Table
1. Selected bond lengths are given in Table 2.
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Table 1 Summary of crystal data and refinement results for HL and 1−3.
HL
1
2
3
Empirical formula
Formula weight
Crystal size /mm
Crystal system
Space group
T /K
C12H11N3S2
261.36
C24H20CuN6S4
584.29
C24H20NiN6S4
C24H20PdN6S4
627.10
579.41
0.58×0.40×0.07
Triclinic
P−1
0.46×0.34×0.07
Monoclinic
P2(1)/c
0.56×0.49×0.11
Orthorhombic
Pbca
0.48×0.37×0.08
Orthorhombic
Pbca
296(2)
296(2)
296(2)
296(2)
a /Å
5.724(11)
10.09(19)
11.56(2)
629.6(2)
72.374(3)
81.929(4)
88.249(4)
1.379
7.105(4)
7.507(4)
24.771(14)
1291.7(12)
90.00
9.8627(15)
7.8100(12)
32.299(5)
2487.9(7)
90.000
10.0707(10)
7.7048(7)
32.526(3)
2523.7(4)
90.00
b /Å
c /Å
V Å 3
α (°)
β (°)
102.143(18)
90.00
90.000
90.00
γ (°)
90.000
90.00
Dc /g cm−3
Z
1.502
1.547
1.650
2
2
4
4
µ /mm−1
θ (°)
0.403
1.194
1.142
1.093
1.87–26.00
272
2.84–25.00
598
2.42–25.00
1192
2.38–25.00
1264
F000
Index ranges
−6 ≤ h ≤ 7,
−12 ≤ k ≤ 9,
−14 ≤ l ≤ 13
3472
−8 ≤ h ≤ 8,
−8 ≤ h ≤ 8,
−18 ≤ l ≤ 29,
6206
−11 ≤ h ≤ 11,
−9 ≤ k ≤ 9,
−17 ≤ l ≤ 38
10379
−11 ≤ h ≤ 11,
−7 ≤ h ≤ 9,
−38 ≤ l ≤ 34,
11795
Refl. collected
Refl. unique
2432
2248
2168
2212
Rint
0.0538
0.0894
0.1230
0.0767
Parameters
154
160
161
160
R1,wR2 [I ≥ 2σ (I)]
R1,wR2 (all date)
Goodness-of-fit on F2
0.0595, 0.1602
0.0919, 0.1739
0.856
0.0807, 0.1845
0.1198, 0.1949
0.873
0.0509, 0.1095
0.0979, 0.1335
0.744
0.0309, 0.0491
0.0644, 0.0538
0.756
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Table 2 Selected bond lengths (Å) and bond angles (°) for HL and 1−3 a.
HL
1
2
3
S(1)-C(7)
N(1)-C(7)
N(1)-C(6)
N(2)-C(7)
N(2)-N(3)
N(3)-C(8)
C(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
1.673(4)
1.336(5)
1.433(5)
1.341(5)
1.378(4)
1.288(5)
1.373(5)
1.376(6)
1.360(6)
1.382(6)
92.6(2)
Cu(1)-N(3)#1
Cu(1)-N(3)
Cu(1)-S(1)
Cu(1)-S(1)#1
S(1)-C(7)
1.978(7)
1.978(7)
2.265(3)
2.265(3)
1.741(9)
1.359(10)
1.424(11)
1.308(10)
1.388(8)
1.311(9)
180.0(3)
96.9(2)
Ni(1)-N(3)
Ni(1)-N(3)#1
Ni(1)-S(1)#1
Ni(1)-S(1)
S(1)-C(7)
1.882(4)
1.882(4)
2.1679(15)
2.1679(15)
1.727(5)
1.361(6)
1.413(6)
1.301(6)
1.403(5)
1.299(6)
180.0(1)
94.74(14)
Pd(1)-N(3)#1
Pd(1)-N(3)
Pd(1)-S(1)#1
Pd(1)-S(1)
S(1)-C(7)
2.011(3)
2.011(3)
2.2929(10)
2.2929(10)
1.747(3)
1.366(4)
1.403(4)
1.299(4)
1.394(3)
1.296(4)
180.00(11)
N(1)-C(7)
N(1)-C(6)
N(2)-C(7)
N(2)-N(3)
N(3)-C(8)
N(1)-C(7)
N(1)-C(6)
N(2)-C(7)
N(2)-N(3)
N(3)-C(8)
N(1)-C(7)
N(1)-C(6)
N(2)-C(7)
N(2)-N(3)
N(3)-C(8)
C(12)-S(2)-C(9)
C(7)-N(1)-C(6)
C(7)-N(2)-N(3)
C(8)-N(3)-N(2)
C(1)-C(6)-N(1)
C(5)-C(6)-N(1)
N(3)#1-Cu(1)-N(3)
N(3)#1-Cu(1)-S(1)
N(3)-Cu(1)-S(1)
N(3)-Ni(1)-N(3)#1
N(3)-Ni(1)-S(1)#1
N(3)#1-Pd(1)-N(3)
N(3)#1-Pd(1)-S(1)#1 82.59(9)
127.6(3)
120.6(3)
116.9(3)
121.1(4)
118.4(3)
83.1(2)
N(3)#1-Ni(1)-S(1)#1 85.26(14)
N(3)-Pd(1)-S(1)#1
N(3)#1-Pd(1)-S(1)
N(3)-Pd(1)-S(1)
97.41(9)
97.41(9)
82.59(9)
180.0
N(3)#1-Cu(1)-S(1)#1
N(3)-Cu(1)-S(1)#1
S(1)-Cu(1)-S(1)#1
83.1(2)
N(3)-Ni(1)-S(1)
N(3)#1-Ni(1)-S(1)
S(1)#1-Ni(1)-S(1)
85.26(14)
94.74(14)
180.0
96.9(2)
180.00(6)
S(1)#1-Pd(1)-S(1)
a Symmetry transformations used to generate equivalent atoms: −x+1, −y+1, −z; −x+2, −y, −z+1; −x+1, −y, −z+1
for 1−3, respectively.
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2.7. Cytotoxicity assay [27]
The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay is carried
out to evaluate cytotoxicity. Cells are plated into 96-well plates at a cell density of 1 × 104 cells
per well and allowed to grow in a CO2 incubator. After 24 h, the medium is removed and replaced
by fresh medium containing the tested compounds which are dissolved in DMSO at 0.01 M and
diluted to various concentrations with phosphate-buffered saline (PBS) before the experiment, and
the final concentration of DMSO is lower than 1%. After 24 h of incubation, cultures are
incubated in 100 µL of medium with 10 µL of 5 mg mL−1 MTT solution for 4 h at 37 °C. The
medium with MTT is removed, and 100 µL of DMSO was added to each well to dissolve the
formazan. The absorbance at 570 nm is measured using a microplate reader (Bio-Tek ELX800,
USA). The inhibitory percentage of each compound at various concentrations is calculated, and
the IC50 value is determined.
2.8. Apoptosis analysis [27]
To examine whether the cytotoxicity of 1 is due to apoptosis, cell apoptosis is determined by
morphologic observation and Annexin V-FITC. For morphologic observation, cells are stained
with acridine orange (AO) and ethidium bromide (EB) and assessed by fluorescence microscopy.
Briefly, 1 µL of a stock solution (100 µg mL−1 AO and EB) was added to 25 µL of a cell
suspension. EB-negative cells with nuclear shrinkage, blebbing, and apoptotic bodies are counted
as apoptotic cells.
3. Result and discussions
3.1. Structural features of HL and 1–3
Molecular structures of the title compounds HL and 1–3 are shown in Fig. 1. For HL,
thiolate S(1) atom is trans to imine N(3) atom so that HL is not propitious to combine a metal ion
as chelating ligand. Relevant N(3)–C(8) 1.288(5) Å, N(2)–N(3) 1.378(4) Å and C(7)–S(1) 1.673(4)
Å bond lengths show that –N(2)H–N(3)=C(8)– and –C(7)=S(1) modes exist in HL as observed in
other free unsubstituted thiosemicarbazides [14, 35]. HL at (x, y, z) and the other molecule at (−x,
−y+1, −z+1) are linked together through a pair of N(2)–H···S(1) hydrogen bonds building a R2 (6)
2
ring, which helps to stabilize the structure packing.
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Fig.1. Molecular structures of compounds HL and 1−3, showing the atom numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms not involved in hydrogen
bonding have been omitted for clarity. Symmetry codes (a): – x+1, – y+1, – z in 1; – x+2, – y, –
z+1in 2; – x+1, – y, – z+1 in 3.
Through HL, three compounds 1-3 having the identical structures are successfully
synthesized. H atom bound to N(2) finally separate resulting in a L- anion in 1-3. Compound 1 has
an inversion center at Cu2+ site, which is coordinated by two L- anions through two N(3) atoms
[Cu(1)–N(3) 1.978(7) Å] and two S(1) atoms [Cu(1)–S(1) 2.265(3) Å] forming a regular
parallelogram. After L- ion coordinating to Cu2+ ion, the related C(7)=S(1) and C(7)–N(2) bond
modes in HL are obviously changed to C(7)–S(1) and C(7)=N(2) bond modes in 1, which can be
proved by the obvious changes of the corresponding bond lengths. For 2, bond distances round
Ni2+ ion are Ni(1)–N(3) 1.882(4) Å and Ni(1)–S(1) 2.1678(15) Å, respectively. The corresponding
C(7)–S(1) and C(7)–N(2) bond lengths are 1.728(5) and 1.299(6) Å. For 3, Pd(1)–N(3) and
Pd(1)–S(1) bond lengths are 2.011(3) and 2.2929(10) Å, respectively. Additionally, the related
C(7)–S(1) and C(7)–N(2) bond distances are 1.747(3) and 1.299(4) Å. These results fully indicate
the related C(7)=S(1) and C(7)–N(2) bond modes in HL are also changed to C(7)–S(1) and
C(7)=N(2) bond modes in 2–3.
3.2. Infrared spectra study
The characteristic vibrational bands of HL and 1–3 corresponding to the important functions
in the system are presented in Table 3. The free ligand HL shows two bands at 3300 and 3141
cm-1 assigned to N−H stretching vibrations, which are observed at 3379, 3381 and 3381 cm-1 in
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complexes 1–3 [27], respectively. A strong absorption at 1546 cm-1 is attributed to ν(C=N) in HL.
The decrease in frequency of ν(C=N) band for three compounds compared to that in HL
indicating that the coordination is through imine N atom. The obviously increase in frequency of
ν(N–N) band from 1204 cm-1 in HL to 1245, 1250, 1247 cm-1 in 1–3 further support the
coordination of imine N atom. A band appeared at 854 cm-1 is assigned to ν(C=S) in HL, which
has been shifted to lower frequency 823, 830 and 830 cm-1 in 1–3 suggesting that the coordination
of thiolate S atom through –C–S–Metal mode after enolization followed by deprotonation on
sulfur [3, 14].
Table 3 IR spectral assignment for HL and 1−3 (cm-1).
Compounds
ν
(C=N)
1546
1525
1502
1496
ν
(N−N)
1204
1245
1250
1247
ν
(C=S)
854
ν
(N−H)
HL
1
3300, 3141
3379
823
2
3381
830
3
3381
830
3.3. Cytotoxicity assay
The ability of Cu(ClO4)2·6H2O, HL and three metal compounds to inhibit growth of HepG2
and QSG7701 cells are tested. Herein Mitoxantrone is used as the reference compound for
comparison. Comparison of the cytotoxic activities indicates 1 has much lower IC50 value (12.71 ±
1.22, 13.12 ± 0.53 µM) with the better cytotoxicity (Fig. 2). Cu(ClO4)2·6H2O, HL and 2–3 have
no antitumor activity at all. For 1, it is necessary to make embedded study in the mechanism of
action
Fig. 2. The cytotoxicity of Cu(ClO4)2, HL and 1-3 on tumor cells and normal cells. Mitoxantrone
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(Mito) is used as reference.
3.3.1 Effect of 1 on cell apoptosis
Green live cells with normal morphology are observed in control group (Fig. 3). Green early
apoptotic cells with nuclear margination and chromatin condensation and orange later apoptotic
cells with fragmented chromatin and apoptotic bodies are observed after 1 treatment. The results
suggest that 1 can induce liver cancer cells apoptosis in vitro.
Fig. 3. Morphologic observation of HepG2 cell apoptosis is determined by AO/EB staining with
the indicated concentrations of 1 for 48 h.
3.4. Hirshfeld surface analysis
Hirshfeld surfaces combining fingerprint plots generated by the Crystalexplorer 2.1 software
36
can identify the types and regions of intermolecular interactions and the proportion of this
interaction to the total Hirshfeld surfaces area. Molecular Hirshfeld surfaces in crystal structure
are constructed from the electron distribution. The normalized contact distances (dnorm) based on
both de, di and the vdw radii of the atom are listed in the following equation. The 2D fingerprint
plot is the combination of de and di [37–39].
vdw
dnorm = (di – rivdw)/ rivdw + (de – revdw)/re
Hirshfeld surfaces for HL and 1–3 have been mapped over dnorm, shape index and curvedness (Fig.
4a-c), respectively. As shown in Fig. 4a, deep red areas are corresponding to the metal–N and
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metal–S bonds. The interactions between thiolate S atom and H atoms bound to N are shown as
pale red areas in the Hirshfeld surfaces. Visible spots are attributed to the H···H contacts. The
intermolecular N–H···S interactions with 23.6%, 20.5%, 17.2% and 16.3% contribution to the
total Hirshfeld surface for HL and 1–3 appear as two distinct spikes in the 2D fingerprint plots
(Fig. 5a-b). The lower spike attributes to S atoms interacting with H atoms bound to the nitrogen
atoms, the upper spike being N–H atoms interacting with S atoms. C···H/H···C contacts constitute
24.2%, 24.7%, 27.6% and 26.7% (Fig. 5a, c) of the total Hirshfeld surface attributing to the
C–H···π interactions for HL and 1–3, which can also be seen from the pairs of typical ‘wings’
appear at the top left and bottom right of the two-dimensional fingerprint plots. The scattered
points spread up to di = de ≈ 1.0 Å are corresponding to the H···H interactions (contribution
comprising: 38.1%, 33.0%, 32.1% and 32.7% for HL and 1–3) in the fingerprint plots (Fig. 5a). In
these compounds, π-π interactions are not observed because the adjacent red and blue triangles are
not present in the shape index surface. Additionally, π-π interactions are not evident on the
curvedness as a large flat region across the molecule [39]. After HL ligands are converted into
metal coordination complexes 1-3, the proportion of N–H···S and H···H interaction comprising
slightly decrease and C–H···π interaction constituting increase slightly, which suggest
metal-chelating has little influence on the shape and flexibility of HL ligand.
Fig. 4. Hirshfeld surface: (a) dnorm, (b) shape index and (c) curvedness for HL and 1−3.
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Fig. 5. Fingerprint plots of HL and 1−3: (a) full and involving (b) S···H/S···H and (c)
C···H/H···C contacts showing the proportion of contacts contributing to the total Hirshfeld
surface area of molecules.
3.5. Structure–activity relationships
Under the same experiment condition, Cu(ClO4)2·6H2O and HL have no cytotoxicity at all. For
1–3, although they have the identical structures, only 1 embodies the better biological activities.
On the one hand, coordination plays an important role in cytotoxic dose reduction. On the other
hand, the types of metal ion play key roles in the growth inhibitory activity [40]. Therefore, the
perfect matching between HL and transition metal results in their finally biological activity.
The investigation results of Hirshfeld surface analysis combining fingerprint plots and cytotoxic
studies signify that the action between 1 and the substrate molecule is not the non-covalent bond
binding like electrostatic binding, groove binding and intercalative binding, et al. We deduce the
mode may be covalent bond binding or other way. Tetrahedral Cu2+ having the poorer stability in
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the solution can be easily interacted by other donor atoms and changed into square pyramid or
octahedron resulting in the biological activity. In the future, it is necessary to make further
biological evaluation in vivo.
4. Conclusions
In summary, 2-thiophene N(4)-phenylthiosemicarbazone (HL) ligand and its three relevant
metal derivatives [CuL2 ] (1), [NiL2] (2) and [PdL2] (3) have been successfully synthesized and
characterized. Cytotoxic studies are carried in vitro against HepG2 cells and normal QSG7701
cells, which illustrates that original ligand HL has no biological activity. For its three coordination
compounds having identical structures, only 1 is able to inhibit cell proliferation growth. The
results indicate the better matching between HL and metal ion determines their final biological
activity. The apoptotic mechanism for 1 is evaluated in HepG2 cells. The structure-activity
relationships for HL and 1−3 have been deeply investigated by Hirshfeld surface combing
fingerprint plots, which shows that the action mode between 1 and the substrate molecule is not
the non-covalent bond binding. In this paper, inactive HL has been successfully transformed into
an active coordination compound. Unfortunately, 1 cannot well distinguish HepG2 cells from
QSG7701 cells. So, this problem will need to be further gone into.
Appendix A.Supplementarymaterial
CCDC numbers 1023272−1023275 for complexes HL and 1−3, respectively. These
crystallographic data for this paper can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China
(21071043) and the Natural Science Foundation of Henan Province (132300410146) and the
Natural Science Foundation of the Educational Department of Henan Province (14B150028).
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>Heterocyclic thiosemicarbazone>Cytotoxic studies>Hirshfeld surface >Fingerprint plots