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Serendipitous Synthesis of Five-Coordinated Half-Sandwich Aminoimine Iridium(III) and Ruthenium(II) Complexes and Their Application as Potent Anticancer Agents.
Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Serendipitous Synthesis of Five-Coordinated Half-Sandwich
Aminoimine Iridium(III) and Ruthenium(II) Complexes and Their
Application as Potent Anticancer Agents
Qing Du, Lihua Guo,* Xingxing Ge, Liping Zhao, Zhenzhen Tian, Xicheng Liu, Fanjun Zhang,
and Zhe Liu*
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Institute of Anticancer Agents Development and Theranostic Application, The Key Laboratory of Life-Organic Analysis and Key
Laboratory of Pharmaceutical Intermediates and Analysis of Natural Medicine, Department of Chemistry and Chemical
Engineering, Qufu Normal University, Qufu 273165, China
S Supporting Information
*
ABSTRACT: Stable five-coordinated (16-electron) half-sandwich iridium(III) and ruthenium(II) complexes are rarely
reported, and their biological evaluations have not been considered to date. Herein, in an experiment designed to synthesize sixcoordinated half-sandwich iridium(III) and ruthenium(II) complexes containing N,N-chelated α-keto-β-diimine ligands, we
observed the serendipitous formation of half-sandwich aminoimine iridium(III) and ruthenium(II) complexes via solventinvolved rearrangement reaction. These unsaturated 16-electron complexes had sufficient stability in DMSO−water solution.
Moreover, no reaction with two-electron donors (CO and PPh3) and nucleobase (9-MeA and 9-EtG) was observed. Most of the
complexes show good anticancer activities toward A549, HeLa, and HepG2 cancer cells, which are higher than the clinical drug
cisplatin. The investigation of mechanism by flow cytometry showed that the complexes exert their anticancer efficacy by
inducing apoptosis or necrosis, and increasing the intracellular ROS level. In addition, fluorescence property of these complexes
makes it possible to investigate the microscopic mechanism by confocal microscopy. Notably, the complexes Ir3 and Ru1 enter
A549 cancer cells through an energy-independent pathway, and they are mainly located in mitochondria and lysosomes.
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INTRODUCTION
In recent years, there has been growing interest in the synthesis
of organometallic half-sandwich iridium(III) complexes and
ruthenium(II) complexes of the type [(η5-C5Me5)Ir(XY)Cl]0/+
and (η6-arene)Ru(XY)Cl, respectively, where XY = bidentate
ligands.1−9 These six-coordinated 18-electron complexes
predominantly provoked application in metal-based anticancer
agents and catalysis.10−18 To this end, many research groups
have focused their attention on the identity of XY, where a
large number of bidentate ligands have been considered.
Examples of six-coordinated half-sandwich iridium(III) complexes and ruthenium(II) complexes containing bidentate
anionic or neutral C,N-,4,8,10−13 N,N-,9,14,19,20 N,O-,9,21
P,P-,22,23 P,O-,2,6 and P,S-ligands24,25 have been known. The
Sadler group has reported two types of half-sandwich
iridium(III) complexes containing neutral N,N-chelated ligand
bipyridine (bpy) and anionic C,N-chelated ligand 2-phenyl© XXXX American Chemical Society
pyridine (phpy), respectively, where they showed that the
modification of bidentate ligands, the fixed ligands, and a
monodentate ligand on the metal center had a significant effect
on the chemical reactivity and biological activity (Scheme 1a, I
and II).9−12 We has also reported on a series of cationic halfsandwich iridium(III) and ruthenium(II) complexes with N,Nchelated imino-pyridyl or diimine ligands and found that
cancer cell cytotoxicity and selectivity can be tuned by both
metal ions and chelate ligands (Scheme 1a, III and IV).26−28
Nevertheless, to the best of our knowledge, stable fivecoordinated (16-electron) half-sandwich iridium(III) complexes and ruthenium(II) complexes are rarely reported, being
limited to amidinate or aminopyridinate complexes.29−31
Notably, these reported five-coordinated amidinate or aminoReceived: January 30, 2019
A
DOI: 10.1021/acs.inorgchem.9b00282
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Scheme 1. Reported Half-Sandwich Iridium(III) and Ruthenium(II) Complexes and Our Current Work
Scheme 2. Synthesis of Complexes Ir1−Ir6 and Ru1
they were fully characterized by various techniques (Scheme
1c). The proposed mechanism and roadmap of this reaction
was studied. Furthermore, these complexes have been
systematically studied for their chemical properties, cancer
cell toxicity, mechanism of actions, and molecular imaging in
live cells. To our knowledge, this work has shown for the first
time the biological activity of five-coordinated half-sandwich
iridium(III) and ruthenium(II) complexes.
pyridinate complexes are usually synthesized by a two-step
method (Scheme 1b). First, six-coordinated complexes are
prepared by the reaction of bidentate ligands with metal
precursors. Then, the five-coordinated complex can be
obtained by the extrusion of the chloride ligand of the
corresponding six-coordinated complex with the action of
NaBArF (BArF = [3,5-(CF3)2Ph]4B).
In the present work, our initial plan was to synthesize novel
six-coordinated half-sandwich iridium(III) and ruthenium(II)
complexes bearing N,N-chelated α-keto-β-diimine ligands. We
performed this reaction according to the previously reported
experimental conditions, which were usually employed to
prepare six-coordinated half-sandwich iridium(III) and
ruthenium(II) analogues.2,9 Surprisingly, however, the product
obtained was found to be five-coordinated half-sandwich
aminoimine iridium(III) and ruthenium(II) complexes, and
■
RESULTS AND DISCUSSION
Synthesis, Characterization and Spectroscopic Properties. The synthesis of α-keto-β-diimine ligand was
performed as reported previously.32 Treatment of [(η5Cpx)IrCl2]2 (D1−D6) ((Cpx = C5(CH3)4R, R = CH3, Ph,
biphenyl, Cy, 1-methylbenzene, 1-fluorobenzene) with α-ketoβ-diimine ligand in methanol or the mixture of methanol and
B
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Figure 1. X-ray crystal structures with atom numbering schemes for (a) complex Ir2, (b) complex Ir3, and (c) complex Ru1 with the thermal
ellipsoids drawn at the 50% probability level. The hydrogen atoms have been omitted for clarity.
Scheme 3. Control Experiments and Deuterium-Labeling Study
ppm in the 13C NMR represents the signals for the OCH3 of
these complexes.
These complexes were further structurally determined by
single-crystal X-ray diffraction (Figure 1). X-ray crystallographic data are given in Tables S3 and S4. The molecular
structure of Ir2, Ir3, and Ru1 showed five-coodinated “threelegged piano-stool” half-sandwich aminoimine complexes that
are formally 16-electron species. A five-membered (NN)Ir or
(NN)Ru chelate ring was observed in these structures. In
general, the Ir−N1 and Ru−N1 bonds (1.937(5)−1.954(4) Å)
are shorter than the Ir−N2 and Ru−N2 bond distances
(2.097(4)−2.163(8) Å). The C2−N1(1.482(6) Å), C2−
N1(1.476(7) Å), and C2−N1(1.458(12) Å) distances are
consistent with C−N single bonds. The C3−N2(1.286(6) Å),
C3−N2(1.292(7) Å), and C3−N2(1.294(12) Å) distances are
CHCl3 at reflux temperature and then with NH4PF6 gives
access to five-coordinated half-sandwich aminoimine iridium(III) complexes in moderate isolated yields. It seems that the
rearrangement reaction occurs with solvent methanol as a
reactant. Subsequent experiment showed that the similar
ruthenium(II) complex could also be obtained by treating
[(η6-p-cymene)RuCl2]2 (D7) with the same ligand, indicating
that this serendipitous reaction shows great metal compatibility
(Scheme 2). These complexes were fully characterized by 1H
NMR, 13C NMR, and 2D-NMR (HSQC) spectroscopy,
elemental analysis, and mass spectrometry (Figures S6−S20
and S23−S29). In CDCl3, the characteristic peaks in the 1H
NMR for iridium(III) and ruthenium(II) complexes are at ca.
δ 3.9 ppm and δ 4.0 ppm, respectively, corresponding to the
proton of the OCH3 group. The chemical shift at δ 56−58
C
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Scheme 4. Proposed Mechanism of the Reaction
Figure 2. (a) UV/vis spectra of complexes Ir1−Ir6 and Ru1 (20 μM) in CH2Cl2 at 298 K. Inset represents the offset spectra for clarity. (b)
Normalized emission spectra of complexes Ir1−Ir6 and Ru1 (20 μM) in CH2Cl2 at 298 K (λex = 365 nm). Inset represents the locally enlarged
spectra for clarity.
into the CH3 substituents in the α-positions of the aminoimine
framework.
On the basis of these experimental results, the possible
mechanism is proposed as shown in Scheme 4. The methanol
molecule attacks the carbonyl group (α-keto) in intermediate
A and after nucleophilic addition results in intermediate B.
Subsequently, electron transfer give access to the release of a
HCl molecule and intermediate B rearranged to the fivecoordinated complex C bearing anionic N,N-cheletad ligands
(Scheme 4a). No intermediates have been observed, but since
this is an intramolecular rearrangement reaction, it is expected
to be very fast. In addition, the migration of the H proton of
CH3OH into the CH3 substituents in the α-positions of the
aminoimine framework can be attributed to the combinatorial
action of hydrogen−deuterium exchange and imine−enamine
tautomerism (Scheme 4b).
Solution Stability and Reaction Chemistry. The
solubility of these complexes is poor in water. However, they
readily dissolve in CHCl3 and dimethyl sulfoxide (DMSO),
affording red solutions. To investigate the stability of the
complexes in aqueous solution, Ir3 and Ru1 were monitored
in 70% DMSO-d6/30% D2O (v/v) or 80% DMSO-d6/20%
D2O (v/v) solutions by 1H NMR at 298 K (Figures S33 and
S34). No additional peaks were found in the 1H NMR spectra
after 24 h, suggesting that these complexes did not suffer from
ligand dissociation or decomposition under test conditions. In
addition, complex Ir3 was added in water and stirred at 298 K
for 24 h. Subsequently, the solid sample of complex Ir3 was
recovered and dissolved in CDCl3 to repeat the 1H NMR
consistent with CN double bonds. The introduction of R
substituents on the tetramethylcyclopentadienyl ring for
iridium(II) complexes has little influence on the Ir−C
(centroid) bond distance and the Ir−N1 bond distance.
Notably, the distance between oxygen (CO) and ruthenium
atom (2.375(7) Å) is significantly shorter than that between
oxygen (CO) and iridium atom (3.337−3.341 Å), which
indicates the weak interaction between the carbonyl oxygen
atom and metal in the ruthenium(II) complex.
To probe the mechanism, the following control experiments
were carried out. First, the progress of the reaction was
monitored by thin-layer chromatography (TLC). The reaction
of α-keto-β-diimine ligand with [(η5-Cpx)IrCl2]2 in CH3OH
gave one new point on the TLC plates. In contrast, no new
product was observed by replacing CH3OH with CHCl3
(Scheme 3a). Additionally, α-keto-β-diimine ligand did not
react with CH3OH in the absence of [(η5-Cpx)IrCl2]2 (Scheme
3a). These results were also confirmed by 1H NMR timedependent analysis of the reaction mixture in a NMR tube
(Figures S30 and S31) and suggested that the combinatorial
action of the metal and CH3OH are involved in this
rearrangement reaction, which results in the formation of the
five-coodinated products. Second, a deuterium-labeling study
was conducted using CD3OD and CH3OD as solvent,
respectively (Scheme 3b). From the 1H NMR spectrum of
the isolated products, deuterium-labeled complexes Ir7 and Ir8
were obtained, respectively (Figure S32), indicating that the
OCH3 group in these complexes was from the solvent
methanol. In addition, the H proton of CH3OH migrated
D
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Table 1. IC50 Values of Complexes Ir1−Ir7 and Ru1 Tested toward Cancer and Normal Cell Lines and Comparison with
Cisplatin
IC50 (μM)
Complex
A549
HeLa
HepG2
BEAS-2B
16HBE
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
Ru1
cisplatin
14.5 ± 1.5
5.1 ± 0.6
3.0 ± 0.1
5.6 ± 0.1
4.5 ± 1.5
2.4 ± 0.1
4.6 ± 0.2
3.1 ± 0.1
21.3 ± 1.7
12.3 ± 0.1
4.9 ± 0.9
4.2 ± 1.3
3.1 ± 0.01
4.4 ± 0.4
2.2 ± 0.1
4.6 ± 1.0
5.2 ± 0.6
7.5 ± 0.2
3.2 ± 0.2
3.6 ± 0.4
3.8 ± 0.4
5.8 ± 0.1
3.2 ± 0.1
2.1 ± 0.1
3.4 ± 0.1
3.9 ± 0.4
22.7 ± 1.1
11.9 ± 0.3
3.2 ± 0.01
3.4 ± 0.04
3.5 ± 1.0
4.7 ± 0.9
1.9 ± 1.1
4.4 ± 1.7
1.5 ± 0.2
13.7 ± 0.5
5.8 ± 0.4
4.7 ± 0.1
4.8 ± 0.4
5.9 ± 0.6
3.0 ± 0.8
5.8 ± 0.2
2.5 ± 0.7
Figure 3. Cell cycle analysis of A549 cells after 24 h of exposure to complexes Ir3 and Ru1 at 310 K. Concentrations used were 0.25, 0.5, and 1
equipotent concentrations of IC50. Cell staining for flow cytometry was carried out using PI/RNase. (a) FL2 histogram for the negative control
(untreated cells), Ir3, and Ru1 with 0.25, 0.5, and 1 equipotent concentrations of IC50. (b) Cell populations in each cell cycle phase for control, Ir3,
and Ru1. Data are quoted as mean ± SD of three replicates.
spectra (Figure S35). There was also no change in the 1H
NMR spectra, indicating that the complexes were stable when
a high content of water was employed. These complexes were
also monitored over 8 h by UV/vis spectroscopy in 50%
DMSO/50% H2O (v/v) or 60% DMSO/40% H2O (v/v)
solutions to further estimate the stability of these complexes
(Figure S36). There were no obvious changes in the
absorption spectra of these complexes, which was consistent
with the NMR analysis. Overall, these studies suggest that all of
E
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Figure 4. Apoptosis analysis of A549 cells after 24 h of exposure to complexes Ir3 and Ru1 at 310 K determined by flow cytometry using annexin
V-FITC vs PI staining. (a) A549 cells were left untreated (control) or treated with different concentrations of Ir3 and Ru1 for 24 h: lower left,
living cells; lower right, early apoptotic cells; upper right, late apoptotic cells; upper left, necrotic cells. (b) Histogram showing populations for A549
cells in four stages treated by Ir3 and Ru1. Data are quoted as mean ± SD of three replicates.
The emission spectra display a strong resemblance for these
complexes Ir1−Ir6 and Ru1 among each other, indicating that
the Cpx perturbations and metal center exhibit little variation
on the emission wavelength of these complexes. Notably, the
fluorescent complexes can help researches to real-time track
the accumulation, uptake, and distribution of the anticancer
agents in living cells.33−36 Thus, the rich fluorescent properties
of the five-coordinated half-sandwich iridium(III) and
ruthenium(II) complexes in this system represent a big
advantage, and this was able to provide a tool for exploring
the mechanism of actions (MoAs) of these anticancer
complexes.
In Vitro Cytotoxicity. The cytotoxic activities of all
complexes against the lung cancer A549 cells line, the human
HeLa cervical cancer cells line and hepatoma cells line were
examined by the MTT assay (Table 1) with cisplatin for
comparison. Very interestingly, all of the complexes are highly
potent toward these three types of cancer cell lines with IC50
values (concentration at which 50% of the cell growth is
inhibited) in the range 2.2−14.5 μM. The IC50 values of most
of the complexes in this system are much lower than the values
obtained with cisplatin against A549 cells, HeLa cells and
HepG2 cells. Ir6 was the most cytotoxic complex against three
types of cancer cell lines, indicating that the anticancer activity
can be enhanced by the introduction of the fluorinated
substituents in the η5-Cpx ring for these complexes. In addition,
the introduction of the extended phenyl rings onto the
tetramethylcyclopentadienyl ring also increased the anticancer
activity of the complexes against A549 cells and HeLa cells,
which is consistent with the reported six-coordinated C,N and
N,N-chelated half-sandwich Ir(III) complexes.9,12 On the
other hand, the presence of deuterium-labeled substituents
only slightly changed the anticancer activity of the complexes
(Ir7 vs Ir3). The cytotoxic activities of complexes Ir1−Ir7 and
Ru1 were further evaluated against BEAS-2B and 16HBE
the complexes in this system have sufficient stability for further
investigation of biological activity and chemical reactivity.
Previously studies have shown that the reactions of
unsaturated 16-electron amidinate or aminopyridinate iridium(III) and ruthenium(II) complexes with a series of twoelectron donors can produce stable compounds containing 18
valence electrons.30,31 When CO atmosphere or PPh3 was
introduced in a NMR tube containing a CDCl3 solution of Ir1,
no additional 1H NMR peaks were observed over a period of
20 h, indicating that CO and PPh3 did not react with Ir1
(Figures S37 and S38). The very stable nature of these
complexes may arise from the above-mentioned weak
coordination between oxygen (CO) and metal atom.
Thus, the binding of model nucleobases 9-methyladenine
(9-MeA) and 9-ethylguanine (9-EtG) with complex Ir3 was
examined using the 1H NMR technique. 1.0 molar equiv of 9MeA or 9-EtG was added to solution of complex Ir3 in 70%
DMSO-d6/30% D2O (v/v) at 310 K (Figures S39 and S40).
No new 1H NMR peaks were observed over a period of 24 h,
suggesting that the reaction between model nucleobases and
Ir3 did not occur. Also, nucleobase adduct of this complex was
not detected by mass spectrometry. These results suggested
that DNA may not be the major target for this type of fivecoordinated complexes.
Spectroscopic Studies. Absorption spectra of complexes
Ir1−Ir6 and Ru1 were recorded in CH2Cl2 solution (final
DMSO concentration, 1% v/v) to study their spectroscopic
properties (Figures 2a and S41). Complexes Ir1−Ir6 show
intense bands between 289 and 334 nm and broad and less
intense bands at 440−452 nm, respectively. In contrast, only
weak and broad absorption bands at approximately 525 nm are
observed for Ru1.
The emission spectra of Ir1−Ir6 and Ru1 in CH2Cl2
solutions are obtained at 298 K (Figure 2b). Upon excitation
at 365 nm, Ir1−Ir6 and Ru1 emit purple (408−435 nm) light.
F
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Figure 5. Analysis of ROS level by flow cytometry after A549 cells were treated with complexes Ir3 and Ru1 at the 0.25 and 0.5 equipotent
concentrations of IC50 for 24 h and stained with H2DCFDA. Data are quoted as mean ± SD of three replicates.
necrosis rather than the apoptotic pathway for complex Ir3. As
a result, iridium(III) complexes in this system showed a
different mechanism of action from the that of the
corresponding ruthenium(II) complexes.
Intracellular ROS Levels Determination. Previous
studies showed that both iridium complexes and ruthenium
complexes can promote cancer cell death through the
generation of ROS.41,42 Thus, when A549 cancer cells were
exposed to Ir3 and Ru1 for 24 h, the effects of complexes Ir3
and Ru1 on intracellular ROS levels were analyzed by flow
cytometry (Figure 5). Concentration-dependent and increased
ROS total levels in the cells were observed. As a result,
induction of ROS may also contribute to the anticancer activity
of these iridium and ruthenium complexes.
Cellular Localization. Due to luminescent properties of
these complexes, we subsequently tried to detect images of Ir3
and Ru1 in A549 cells. As expected, clear confocal microscopy
images were observed for Ir3 and Ru1 at λex = 488 nm (Figure
6). The intense and punctate green fluorescence was observed
in the cytoplasm, indicating that the Ir3 and Ru1 can
effectively penetrate into A549 cells after 1 h incubation. The
A549 cells were dual-stained with Ir3 and Ru1, and the
commercially available organelle-specific probes MitoTracker
Deep Red (MTDR) or LysoTracker Deep Red (LTDR),
respectively. Medium Pearson correlation coefficients (PCC)
of 0.71 (MTDR) and 0.61 (LTDR) in the merged image were
observed for Ir3, indicating that Ir3 can localize in the
mitochondria and lysosome to a certain extent. However, less
overlap was observed for complex Ru1 with PCC values of
0.46 (MTDR) and 0.54 (LTDR), respectively.
Cellular Uptake. Generally, small molecules can enter cells
through energy-independent (endocytosis and active transport) or energy-dependent (facilitated diffusion and passive
diffusion) transport pathways.43−45 As a result, the cellular
uptake mechanisms of Ir3 and Ru1 were also investigated
through confocal microscopy (Figure S41). Incubation of
(human bronchial epithelial cell lines). Unfortunately, no
selectivity was observed for normal cells versus cancer cells
with these five-coordinated complexes (Table 1).
Cell-Cycle and Apoptosis Studies. To further elucidate
the MoAs of the iridium(III) and ruthenium(II) complexes,
complexes Ir3 and Ru1 on cell cycle progression in A549 cells
were investigated (Figure 3, Tables S5 and S6). We chose Ir3
and Ru1 because modification of substituents is carried out
around Ir3, i.e., Ph vs CH3, Ph vs Cy, Ph vs biphenyl, 1methylbenzene, and 1-fluorobenzene, and two types of metal
centers (Ir and Ru) were studied. Cell cycle analysis was
performed by flow cytometry in propidium iodide (PI) stained
cells after treatment with Ir3 and Ru1 at different
concentrations for 24 h. Treating of A549 cells with complexes
Ir3 and Ru1 at 0.25, 0.5, and 1 × IC50 concentration led to the
negligible change of the cell cycle progression compared to
untreated cells. However, the percentages of cells at sub-G1
phase showed an increase from 0.3% to 9.5% after treatments
with 1 × IC50 of complex Ru1.
A large amount of metal-based anticancer agents have been
shown to promote cellular death by activating apoptosis, which
often leads to many related protein expressions.37−40 Thus,
A549 cancer cells were treated with complexes Ir3 and Ru1 at
0.5, 1, 2, and 3 equipotent concentrations of IC50 for 24 h and
analyzed by flow cytometry (Figure 4, Tables S7 and S8).
Obviously, a concentration-dependent apoptosis population
was detected for complex Ru1. When Ru1 is at 3 equipotent
concentrations of IC50, a total of 71.8% of early apoptotic
(14.2%) and late apoptotic (57.6%) cells were undergoing
enhanced apoptosis compared with the negative control
(11.0%). This was also supported by the detection of sub-G1
fraction on cell cycle progression for Ru1. In contrast, complex
Ir3 induced negligible changes on the apoptosis against A549
cells. When A549 cells were incubated with Ir3 at 3 × IC50
concentration, a total of 78.3% of cells were nonviable,
indicating that cell death is induced predominantly through
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were trackable in cells by confocal microscopy. Ir3 and Ru1
can be quickly and effectively taken into A549 cancer cells
through an energy-independent pathway, and they were mainly
localized to mitochondria and lysosome. This work seems to
be the first demonstration of one-step synthesis and biological
evaluation of stable five-coordinated (16-electron) halfsandwich iridium and ruthenium complexes.
■
ASSOCIATED CONTENT
S Supporting Information
*
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00282.
Details of the Experimental Section, Figures S1−S44
,and Tables S1−S8 (PDF)
Figure 6. Determination of intercellular localization of complexes Ir3
and Ru1 by confocal microscopy. (a) The green and red fluorescence
represent Ir3 and mitochondria or Ru1 and mitochondria,
respectively. (b) The green and red fluorescence represent Ir3 and
lysosome or Ru1 and lysosome, respectively. Scale bar: 20 μm.
Accession Codes
CCDC 1842508, 1842524, and 1872742 contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
A549 cells with Ir3 or Ru1 at 4 °C or in the presence of
various inhibitors (the metabolic inhibitor carbonyl cyanide 3chlorophenylhydrazone (CCCP) and chloroquine) did not
lead to the decrease of cellular uptake levels compared with
control cells incubated at 37 °C. Thus, it seems that the
cellular uptake of Ir3 and Ru1 mainly relies on the energy
independent transport mechanism, such as endocytosis and
active transport.
In general, hydrophobicity is a factor relevant for cell uptake
and anticancer activity. Therefore, the octanol/water partition
coefficient (log P) was determined by the shake-flask method
(Figures S42 and S43). Complex Ir3 displays a log P value of
1.30, higher than that for complex Ru1 (0.72). Since
lipophilicity has often correlated with the cell uptake and
cytotoxicity, the total cellular accumulations of complexes Ir3
and Ru1 were also studied by ICP-MS after 12 h of exposure
to these complexes (5 μM). Complex Ir3 showed a higher
cellular accumulation than complex Ru1 (103 ppb per 1 × 105
cells vs 69 ppb per 1 × 105 cells, Figure S44). These results
suggested that Ir3 gives rise to an increased hydrophobicity
compared to Ru1. However, the trend cellular accumulation
does not correlate with their cytotoxicity. Thus, the effect of
lipophilicity cannot fully explain the difference in IC50 values
between these complexes in this system.
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail: guolihua@qfnu.edu.cn (L.G.).
*E-mail: liuzheqd@163.com (Z.L.).
ORCID
Lihua Guo: 0000-0002-0842-9958
Xicheng Liu: 0000-0002-5932-7206
Zhe Liu: 0000-0001-5796-4335
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
We thank the Shandong Provincial Natural Science Foundation (ZR2018MB023), the National Natural Science Foundation of China (Grant No. 21671118) and the Taishan Scholars
Program for support.
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CONCLUSIONS
In this work, we have uncovered a serendipitous synthesis of
five-coordinated half-sandwich aminoimine iridium(III) and
ruthenium(II) complexes by the solvent-involved rearrangement reaction, presumably via an electron-transfer process.
The structures of these complexes were determined by X-ray
crystallography. This type of unsaturated 16-electron complex
showed good stability in aqueous solution. The complexes did
not react with CO and PPh3 to afford 18-electron adducts. In
addition, no interaction with the nucleobases (9-MeA and 9EtG) was observed. All of the complexes displayed high
potency toward A549, HeLa, and HepG2 human cancer cells.
The MoAs study showed that iridium(III) complexes were
attributed to cell necrosis, while the ruthenium(II) complex
was associated with apoptosis induction. Furthermore, the
increase of ROS level also contributes to the anticancer activity
of these iridium(III) and ruthenium(II) complexes. On the
basis of fluorescence property of these complexes, Ir3 and Ru1
H
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