Highly Selective Detection of Hypochlorous Acid by a Bis-heteroleptic Ru(II) Complex of Pyridyl-1,2,3-triazole Ligand via C(sp2)-H Hydroxylation

Article abstract of DOI:10.1021/acs.inorgchem.9b01125

A Ru(II) complex (Ru-1) of a substituted pyridyl-1,2,3-triazole ligand (BtPT) for highly selective "light-up" detection of hypochlorous acid is presented. An unusual anti-Markovnikov HOCl addition to the C=C bond of 1,2,3-triazole and a highly specific C(sp²)-H hydroxylation over epoxidation made Ru-1 a highly selective luminescent HOCl probe. The abnormal regio- and stereoselective HOCl addition and subsequent hydroxylation mechanism in detail is supported by the combination of ESI-MS, ¹H/¹³C NMR spectroscopy, and ¹H NMR titration. The hydroxylation at the C5 center in 1,2,3-triazole increases the electron density and makes BtPT a better σ-donor as well as π-donor, which in turn increases the ³MC-³MLCT energy gap and inhibits the nonradiative decay from the excited state of Ru-1 and is the key reason for luminescence light-up. Most importantly, the exogenous and endogenous HOCl imaging in the living HEK293T cells is also demonstrated. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell-imaging experiments revealed rapid staining of the extranuclear region of HEK293T cells which clearly indicates the presence of cytoplasmic HOCl. The endogenous HOCl generation and imaging, stimulated by lipopolysaccharides (LPS) and paraquat in the HEK293T cells, is also demonstrated.

Full text of DOI:10.1021/acs.inorgchem.9b01125

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Highly Selective Detection of Hypochlorous Acid by a Bis-
heteroleptic Ru(II) Complex of Pyridyl-1,2,3-triazole Ligand via
C(sp2)−H Hydroxylation
Bhaskar Sen,† Sanjoy Kumar Sheet,† Sumit Kumar Patra,† Debaprasad Koner,‡ Nirmalendu Saha,‡
and Snehadrinarayan Khatua*,†
‡
†Centre for Advanced Studies, Department of Chemistry, Department of Zoology, North Eastern Hill University, Shillong,
Meghalaya-793022, India
S
* Supporting Information
ABSTRACT: A Ru(II) complex (Ru-1) of a substituted
pyridyl-1,2,3-triazole ligand (BtPT) for highly selective “light-
up” detection of hypochlorous acid is presented. An unusual
anti-Markovnikov HOCl addition to the CC bond of 1,2,3-
triazole and a highly specific C(sp2)−H hydroxylation over
epoxidation made Ru-1 a highly selective luminescent HOCl
probe. The abnormal regio- and stereoselective HOCl
addition and subsequent hydroxylation mechanism in detail
1
is supported by the combination of ESI-MS, H/13C NMR
spectroscopy, and 1H NMR titration. The hydroxylation at the
C5 center in 1,2,3-triazole increases the electron density and
makes BtPT a better σ-donor as well as π-donor, which in
turn increases the 3MC−3MLCT energy gap and inhibits the nonradiative decay from the excited state of Ru-1 and is the key
reason for luminescence light-up. Most importantly, the exogenous and endogenous HOCl imaging in the living HEK293T cells
is also demonstrated. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell-imaging
experiments revealed rapid staining of the extranuclear region of HEK293T cells which clearly indicates the presence of
cytoplasmic HOCl. The endogenous HOCl generation and imaging, stimulated by lipopolysaccharides (LPS) and paraquat in
the HEK293T cells, is also demonstrated.
bond, leading to the formation of the corresponding aldehyde
(Table S1).8
INTRODUCTION
■
Reactive oxygen species (ROS) are produced mainly in
mitochondria by ATP assisted oxidative phosphorylation in a
series of electron-transport process in living cells and control
various biological events in the human body.1,2 Among various
ROS, hypochlorous acid/hypochlorite (HOCl/ClO−), gen-
erated from H2O2 and Cl− by myeloperoxidase (MPO)-
catalyzed reaction, constructs an innate host defense system
against various types of pathogens in living organisms.3 An
appropriate HOCl level helps normal functioning of the
cellular system, but abnormal HOCl production has been
linked to cardiovascular disease, neurodegeneration, and
cancers.4 Thus, a highly selective and sensitive detection and
imaging of endogenous HOCl has received a great importance
in chemistry and biology.5
The existing HOCl probes are mostly based on rhodamine,
fluorescein, BODIPY, pyrene, cyanine, and metal complexes,6,7
where most of them used HOCl/ClO− promoted spirolactam
ring opening, oxidation of the B−H bond, pyrrole ring, p-
methoxyphenol, chalcogenides, and deoximation reactions for
sensing (Table S1).5−7 Apart, few probes have also been
established for HOCl via epoxidation of the acyclic CC
Recently, C−H functionalization has shown great potential
to form new chemical bonds.9 Metal-catalyzed C−O bond
formation is more challenging compared to C−C and C−X (X
= heteroatom) bonds.10 From an economic and environmental
viewpoint, C(sp2)−H hydroxylation with an inexpensive
oxidant is highly desirable and remains a very challenging
task.11 Despite that reports on catalytic C−H functionalization
of 1,2,3-triazoles at the 5-position exit,12 to date, there are no
reports on luminescent ROS detection via C−H hydroxylation.
The photochemistry of d6-metal complexes containing a
1,2,3-triazole ligand has been expansively studied, but the
sensing field is quiet unexplored.13 We have developed few
Ru(II) and Ir(III) based probes of the 1,2,3-triazole ligand for
sensing and bioimaging based on C-H analyte interaction.14
Ru(II) polypyridyl complexes have been extensively used as
sensors, PDT agents, and bioimaging due to the excellent
photochemical properties, stability in aqueous media, and good
cell permeability.15,16 While a few Ru(II) based HOCl selective
Received: April 17, 2019
© XXXX American Chemical Society
A
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Scheme 1. Schematic Representation of HOCl Detection by Previous8 and Our Approach
a
Scheme 2. Synthesis of BtPT Ligand and Probe Ru-1
a
(Inset) Chemical structure of Ru-2, used for control experiment.
probes via oxidation of hydrazide-derived linker and sulfur
containing heterocycles have been reported,17 a metal complex
based HOCl specific probing by new protocol will need to be
developed.
Herein, for the first time, we demonstrate HOCl specific
luminescent detection via C(sp2)−H hydroxylation in a bis-
heteroleptic Ru(II) complex (Ru-1) of a benzothiazole
substituted pyridyl-1,2,3-triazole ligand (BtPT) (Scheme 1).
Extensive NMR study furnishes a detailed picture of the
hydroxylation mechanism. The ability of Ru-1 for endogenous
HOCl imaging, stimulated by lipopolysaccharides (LPS) and
paraquat in the HEK293T cells, is also demonstrated.
Figure 1. Perspective view of Ru-1·2CHCl3 with 30% thermal
ellipsoid probability. Only non-carbon and non-hydrogen atoms are
labeled.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Probes, Ru-1 and
Ru-2. The BtPT ligand was synthesized from azide/tetrazole
(A/B) derivatives and 2-ethynylpyridine by a click reaction
and characterized spectroscopically (Scheme 2, Figures S1−
S5). Probe Ru-1, readily prepared from BtPT and cis-
[Ru(phen)2]Cl2 (Scheme 2), was characterized by 1D (1H
and 13C) and 2D (COSY, HSQC, and HMBC) NMR, ESI-MS
(Figures S6−S11), and single-crystal X-ray diffraction (Figure
1 and Tables S2 and S3). Like previously reported Ru(II)
based probes,13,14 here, the Ru(II) center adopts a distorted
octahedral geometry with the trans angles ranging from
170.69(18)° to 172.54(17)°. Additionally, complex Ru-2 of
the methyl substituted pyridyl triazole ligand was synthesized
to support the mechanistic details of the probe analyte reaction
(Scheme 2, inset).
UV−vis and PL Response of Probe Ru-1 toward HOCl.
The UV−vis spectrum of Ru-1 (50 μM) revealed broad
MLCT bands with λmax at 400 and ∼433 nm in PBS buffer/
DMSO (v/v, 9.5:0.5, pH 7.4) solution which are assigned by
TDDFT studies (Supporting Information). Probe Ru-1 emits
weakly at 580 nm (λex = 400 nm; Φ = 0.008) (Figure S12)
13
3
because of nonradiative decay from the MC state. Upon
screening of several ROS/RNS (ONOO−, H2O2, NO•, O2
,
•−
•OH, O2, BuOOH, and HOCl; aq NaOCl as a source of
1
t
HOCl) and anions (F−, Cl−, Br−, I−, AcO−, OH−, CN−, HS−,
B
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Figure 2. (a) PL intensity of Ru-1 (50 μM) with various analytes in PBS buffer (pH 7.4). (A-V: blank, F−, Cl−, Br−, I−, AcO−, OH−, CN−, HS−,
−
−
−
−
HSO4 , S2O32−, H2PO4 , NO2 , NO3 , ONOO−, H2O2, NO•, O2•−, •OH, 1O2, tBuOOH, and HOCl). (Inset) PL selectivity plot and photographs
of Ru-1 with/without HOCl under UV irradiation (365 nm). (b) PL titration of Ru-1 (50 μM) with HOCl (0−20 equiv). (Inset) Plot of PL
intensity vs HOCl concentration.
Scheme 3. Synthetic Route for Ru-1-OH from Probe Ru-1
Figure 3. (a) Compounds Ru-1 and Ru-1-OH with atom labeling scheme in BtPT ligand. (b) 1H and (c) 13C NMR spectra of Ru-1 and Ru-1-OH
in CD3CN.
C
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1
1
Figure 4. (a) H NMR titration of Ru-1 with HOCl (0−10.0 equiv) in DMSO-d6. (b) Plausible mechanism established from the H NMR
titration, H/13C NMR of the Ru-1 and Ru-1-OH.
1
HSO4 , S2O32−, H2PO4 , NO2 , and NO3 ) in UV−vis
(Figures S13−S15) and PL spectroscopy (Figure 2a), probe
Ru-1 (50 μM) solely shows absorbance change, enhanced
emission (at 587 nm), and red luminescence in the presence of
HOCl (1.0 mM). No apparent change in PL has been
accounted in the presence of a 10-fold excess of all other
analytes (10.0 mM), entailing exceptional selectivity to HOCl
(Figure 2a and inset). A titration experiment reveals that the
PL of Ru-1 is gradually increased upon addition of 0−20 equiv
of HOCl (Figure 2b), and a distinct turn-on emission with ∼9-
fold PL enhancement at 587 nm (Φ = 0.053) is observed. A
plot of PL intensity vs HOCl concentration (0−1.0 mM)
shows a steady linear increment (Figure 2b, inset) in the 0−0.4
mM concentration of HOCl, and the detection limit was
calculated as 76 nM, lower than the intracellular HOCl
concentration and other reported probes (Figures S16 and
S17a, Table S1).5−8,17 While a 1:200 mixture of Ru-1 and
ROS, RNS and other competitive anions did not show
remarkable PL enhancement at 587 nm, an immediate
enhancement was observed upon the addition of only 20
equiv of HOCl (Figure S17b).
and Cl− in the neutral pH range, and the maximum
decomposition rate is observed at pH ∼ 6.89.18 HOCl also
decomposes to Cl2 gas at very low pH (below pH 3). Thus,
more HOCl was available in the high pH media to react with
CC of 1,2,3-triazole and a more rapid change in emission
intensity was achieved. To further support this, we did a PL
titration in pure DMSO media, where only 5 equiv of HOCl
was required to attain the saturation (Figure S20b).
Mechanistic Investigation of HOCl Detection by ESI-
MS and NMR Spectroscopy and Control Experiments.
The ESI-MS of the Ru-1 and NaOCl mixture shows a clear
peak at m/z = 770.13, corresponding to [C39H26N9ORuS]+,
which indicates oxidation in Ru-1 (Figure S21). While Ru-1
may undergo HOCl/ClO− mediated S-oxidation of benzo-
thiazole to sulfoxide or sulfonate,19 the possibility of oxidation
in 1,2,3-triazole is considered since our previous work on
Ru(II) based probes attests that the reactive C-H of 1,2,3-
triazole is responsible for the PL enhancement.14
−
−
−
−
To establish the oxidation reaction precisely, we synthesized
the oxidized product, Ru-1-OH, by reacting Ru-1 with NaOCl
in aqueous CH3CN (Scheme 3), and the solution structure
was determined by NMR spectroscopy and ESI-MS (Figure 3,
Figures S22−S25). 1H NMR spectra of Ru-1-OH revealed the
loss of a triazole proton (Hg) signal, observed initially at δ =
9.70 ppm for Ru-1. Also, the pyridine ring protons of BtPT
(Ha, Hb, Hc, and Hd) shifted to the upfield region with Δδ =
0.39, 0.48, 0.30, and 0.30 ppm, respectively (Figure 3b). Most
importantly, the triazole carbon (Cg) signal has been shifted
downfield from 123.6 to 152.1 ppm (Δδ = 28.5 ppm) in Ru-1-
The lifetimes (τavg) measured in PBS buffer were found to
be 14.63 and 79.30 ns for Ru-1 and the Ru-1 + HOCl mixture
(1:20), respectively (Figure S18). The PL intensity of the free
probe Ru-1 was not affected by the pH of the medium, but the
PL intensity of the mixture of the probe and HOCl (i.e, Ru-1 +
HOCl) is affected by the pH of the medium; the PL intensities
of Ru-1 and the NaOCl mixture (1:20) were enhanced above
pH 5 and steadily increased to pH 7 and further slowly above
pH 8 (Figure S19). Further, a time course study in PL reveals
that the faster PL response to HOCl was achieved with
increasing DMSO content in a PBS buffer-DMSO mixture
(Figure S20a). In the 95% PBS buffer medium (pH 7.4), the
available HOCl is comparatively less than that in the 50% PBS
buffer-DMSO medium where buffer pH is not maintained (pH
= 11.19 after addition of NaOCl solution). It is a well-known
1
OH (Figure 3c). Therefore, H/13C NMR together with ESI-
MS designates the hydroxylation at C5 of 1,2,3-triazole in Ru-
1.
Although the UV−vis spectra of probe Ru-2 of a methyl
substituted 1,2,3-triazole pyridine ligand shows a negligible
change in the presence of NaOCl (20.0 equiv), the PL spectra
of Ru-2 with 20.0 equiv of NaOCl shows ∼1.7-fold PL
enhancement at 592 nm (λex = 403 nm) and the less PL
−
fact that the aqueous HOCl normally decomposes to ClO3
D
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enhancement can readily be explained by high luminescence of
the blank sample (Figures S26 and S27). It is noteworthy that
the benzothiazole unit was introduced in 1,2,3-triazole pyridine
(BtPT) to diminish the PL of the analyte free Ru-1 via PET
from the electron rich benzothiazole group. The ESI-MS of the
Ru-2 and NaOCl mixture shows a peak at m/z = 637.16
corresponding to [C32H23N8ORu]+, further supporting hydrox-
ylation in triazole (Figure S28).
To gain mechanistic insight into the hydroxylation, 1H NMR
titration of Ru-1 with HOCl (0−10.0 equiv; aq NaOCl as a
source) in DMSO-d6 (Figure 4a) was performed. The titration
data undoubtedly authenticate the progress of hydroxylation
reaction through the chlorohydrin intermediate, Ru-1-ClOH
(Figure 4b). The highly acidic triazole proton (Hg) signal of
Ru-1 at 10.42 ppm has been shifted downfield (Δδ = 0.26
ppm), weakened gradually (0−5.0 equiv), and vanished
completely after addition of 10.0 equiv of NaOCl. Most
importantly, two new doublets at 4.91 and 4.73 ppm (3J = 11.2
Hz) have appeared which may due to the interaction between
hydroxyl (HY) and methine proton (HX), respectively. The
fading of the Hg signal and the appearance of doublets for
vicinal protons (HX and HY) undeniably confirm the formation
of the chlorohydrin intermediate, Ru-1-ClOH. In contrast to
reported HOCl mediated epoxidation in acyclic CC,8 in Ru-
1, unusual anti-Markovnikov HOCl addition and subsequent
hydroxylation after the β-HXCl elimination (Figure 4b) is
presumably assumed. It is also expected that the chlorohydrin
in Ru-1 may be in an abnormal syn-orientation, so the alkoxide
(O−) cannot attack the backside of the C−Cl bond and thus
the epoxide is not formed. Notably, the unusual regio- and
stereoselectivity extremely depends on the electronic effect of
CC substituents and solvent polarity which was previously
reported for a four- to seven-membered ring system.20
Notably, the C−H hydroxylation was also observed in free
BtPT but was not useful for probing HOCl as it finally
decomposed to picolinic acid (Figures S29 and S30). While
1,2,3-triazole based anion/cation sensors are only known, a
probe has not been designed for HOCl detection.21 Similar
decomposition was also observed for Ru-1, with excess NaOCl
(100 equiv, 24 h), which yielded a nonemissive heteroleptic
Ru-3 of picolinic acid and characterized by UV−vis/PL,
1H/13C NMR, ESI-MS, and X-ray structure (Figures S31−S35,
Tables S3 and S4).
Figure 5. RuII/RuIII based redox wave for Ru-1, Ru-1-OH, and
[Ru(phen)3](PF6)2 in CH3CN.
(Figures S36−S38 and Table S5).13b Like the previously
reported Ru(II) complex by Schubert et al.,13b here, the trans
Ru−Npy bond is elongated from 2.114 to 2.130 Å due to the
influence of the trans effect (Figure S36 and Table S5). The
HOMO of Ru-1-O− is based on hydroxylated BtPT, while it is
based on Ru(dz2) for Ru-1, which once again supports the
increased electron density on the hydroxylated BtPT ligand
(Figures S39−S42). Similar to previous reports,13 and the
calculated energies of principal MOs for the optimized ground-
state geometries (Figure 6a), here, we believe that the 3MC (d-
d*) state in Ru-1 is close to the 3MLCT state and the thermal
3
population of MC states is leading to the nonradiative decay
and weak luminescence. Further, due to the strong σ-donation
3
3
of BtPT in Ru-1-O−, the MLCT is stabilized and the MC
state destabilized, which increases the MLCT−3MC energy
gap and assists to emit from the MLCT exited state.
3
3
The TDDFT calculations at the triplet excited state reveals
that the weak emission of Ru-1 at 580 nm is due to the
nonradiative decay from the 3MC[Ru(dz2)→Ru(dσ*)] state, assigned
as a HOMO-5→ LUMO transition at 559 nm. The
experimental very strong emission band of Ru-1-O− at ∼587
nm arises from 3 MLCT[ R u ( d π ) → p h e n ( L π * ) ] and
3LLCT[BtPT(Lπ)→phen(Lπ*)] transitions, characterized as HOMO
→ LUMO+5 and HOMO → LUMO+6 transitions at 654 nm
(Figure 6b and Table S10).
Electrochemical Study. To gain deeper understanding of
the PL enhancement in Ru-1-OH, cyclic voltammetry (Figure
5) studies were performed. Both Ru-1 and Ru-1-OH show a
quasi-reversible (ΔEp = 83 mV) Ru2+/Ru3+ redox couple at
Exogenous and Endogenous Imaging of HOCl. For
biological application of Ru-1, we evaluated its cytotoxicity in
HEK293T cells. An MTT assay using of Ru-1 (0−100 μM)
suggested low cytotoxicity of Ru-1 (Figure S43). The cell
viability gradually decreased with increasing amount of Ru-1
from a concentration range of 10−100 μM. More than 88% of
the cells survived at ≤25 μM of Ru-1 after 24 h of treatment.
During cell imaging, the confocal laser scanning microscopy
(CLSM) images showed no luminescence from the cells,
incubated with only Ru-1 (50 μM) (Figure 7a). A bright red
luminescence throughout the cell except in the nucleus region
was observed when Ru-1 (50 μM) loaded cells were incubated
with NaOCl (50 μM), which indicates the ability of Ru-1 to
detect HOCl in living cells (Figure 7b). For endogenous
HOCl imaging, cells were treated initially with LPS (1 μg/
mL)22 for 2 h and with Ru-1 (25 μM) for a further 15 min.
The observed red luminescence from the extranuclear region
of the cell designates the endogenous HOCl generation
(Figure 8a). Paraquat, a widely used herbicide in agriculture,
enhances the oxidative stress in humans and results in
E1/2 = +1.427 V and +1.166 V vs Fc/Fc+, respectively. The
ox
113 mV anodic and 148 mV cathodic shifts for Ru-1 and Ru-1-
OH in comparison to [Ru(phen)3]2+ (E1/2 = +1.314 V) are
ox
readily explained by the weak and strong σ- as well as π-
donation of BtPT before and after hydroxylation, respectively.
Theoretical Study. Density functional theory (DFT) and
time dependent-density functional theory (TD-DFT) calcu-
lations (Tables S5−S10) were performed to obtain insight into
the electronic transitions responsible for the absorption spectra
and luminescence spectra of Ru-1 and Ru-1-OH. It is expected
that the Ru-1-OH in 95% aqueous buffer solution exists as
enolate, so the deprotonated form, Ru-1-O−, was used for all
computation. As shown in the ground-state optimized
structure, the Ru−NTriazole bond lengths are shortened in Ru-
1-O− (2.068 Å) compared to Ru-1 (2.084 Å), which indicates
stronger σ- and π-donation of the hydroxylated BtPT ligand
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Figure 6. (a) Energy level diagram for the molecular orbitals of Ru-1 and Ru-1-O− with corresponding graphical plots of HOMOs, LUMO, and
dσ* orbitals shown at the ground-state optimized geometry. (b) Representative plots (isovalue = 0.03) of selected MOs for Ru-1 and Ru-1-O− at
the triplet excited state optimized geometry.
Figure 7. CLSM images of HEK293T cells, (a) treated with Ru-1 (50 μM, 15 min) and (b) pretreated with HOCl (50 μM, 15 min) and then
incubated with Ru-1 (50 μM, 15 min). Nucleus marker DAPI was used in all experiments. Images were taken using 405 nm (for DAPI) and 488
nm (Ru-1) excitation and emission windows of 420−510 nm (blue) and 510−630 nm (red).
neurodegeneration.23 However, paraquat assisted HOCl
generation is rarely reported in the literature.24 Similar red
emission from cells treated with 1 mM of paraquat for 1.5 h
and successive incubation with Ru-1 (25 μM) for another 15
min indicates the aptness of Ru-1 for endogenous HOCl
imaging (Figure 8b).
F
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Figure 8. Endogenous HOCl imaging: Cells pretreated with (a) LPS (1 μg mL−1) for 2 h and (b) paraquat (1 mM) for 1.5 h and then Ru-1 (25
μM) for 15 min. Nucleus marker DAPI was used in all experiments. Images were taken using 405 nm (for DAPI) and 488 nm (Ru-1) excitation
and emission windows of 420−510 nm (blue) and 510−630 nm (red).
fluorescence images of stained HEK293T cells were acquired with a
confocal laser scanning microscope (Leica, TCS SP5, Germany).
(Caution! Covalent azides are potentially hazardous and can decompose
explosively under various conditions. It should be handled with care).
CONCLUSIONS
■
In summary, an abnormal regio/stereoselective syn-addition of
HOCl to triazole CC and subsequent β-elimination make
the Ru-1 a HOCl specific probe through unique C−H
Synthesis. Synthesis of 2-Azido-4-methylbenzo[d]thiazole/
methylbenzo[4,5-d]thiazolo[3,2-d]tetrazole, A/B. 2-Amino-4-methyl
benzothiazole (5.0 mmol, 0.819 g) was dissolved in 80% phosphoric
acid (32 mL), and the solution was placed in an ice bath to maintain
the reaction temperature at 0 °C. After that, a conc. nitric acid (18
mL) was added, followed by the dropwise addition of aqueous sodium
nitrite (50 mmol, 3.530 g) over 10 min. After 30 min stirring, an
aqueous solution of sodium azide (25 mmol, 1.624 g) was added.
After that, the ice bath was removed and stirring was continued for 2
h at room temperature. Afterward, the reaction mixture was poured
into 50 mL of ice-cold water; a yellow precipitate was obtained
immediately. The precipitate was filtered and washed with distilled
water until the pH of the filtrate reached 7. The crude product was
purified by 60−120 mesh Silica gel column chromatography using 5%
ethyl acetate/hexane (v/v). The desired azide/tetrazole [A/B]
yellowish compound was obtained in a good yield (0.781 g, 84%)
(Scheme 2). Anal. Calcd for C8H6N4S (Mw = 190.22): C, 50.51; H,
3.18; N, 29.45; S, 16.86. Found: C, 50.48; H, 3.12; N, 29.35; S, 16.76.
FTIR in KBr disc (ν/cm−1): 3450, 2128 (NNN stretching),
1650, 1456, 1336, 1215, 1081. Melting point = 98−100 °C. 1H NMR
(400 MHz, CDCl3): δ (ppm) = 7.46 (d, J = 7.0 Hz, 1H), 7.37 (d, J =
7.4 Hz, 1H), 7.30−7.24 (m, 2H), 7.07−6.99 (m, 2H), 2.79 (s, 3H),
2.46 (s, 3H).13C NMR (100 MHz, CDCl3): δ (ppm) = 157.8, 150.1,
133.5, 132.7, 131.7, 129.6, 128.2, 127.9, 127.7, 127.2, 124.6, 122.5,
122.3, 118.9, 18.5, 18.2.
1
hydroxylation which has been supported by ESI-MS and H
NMR titration. The hydroxylation in triazole amplifies the σ-
donation ability of the BtPT ligand in Ru-1, manipulates the
3
3MC vs MLCT energy gap, and is crucial for luminescence
light-up. The MTT assay on HEK293T cells shows that the
probe is less cytotoxic and can efficiently permeate the cell
membrane. The bioimaging experiments on HEK293T cells
reveals rapid staining of the extranuclear region and indicates
the presence of cytoplasmic HOCl. The endogenous HOCl
generation and imaging, stimulated by lipopolysaccharides
(LPS) and paraquat in the HEK293T cells, is also
demonstrated. This unusual, catalyst free C−H hydroxylation
in 1,2,3-triazole may provide a practical method to perform C−
H to C−O bond functionalization which may be beneficial to
design an organic and metal complex based HOCl probe with
exceptional selectivity.
EXPERIMENTAL SECTION
■
Materials and Physical Measurements. All chemicals used for
synthesis and sensing studies were purchased from commercial
suppliers (Aldrich, Alfa Aesar, and Spectrochem India) and were used
as received without further purification. All 1D and 2D NMR spectra
were measured on a Bruker AVANCE II (400 MHz) spectrometer,
and chemical shifts were expressed in ppm using the residual protic
solvent resonance as the internal standard. ESI mass spectra of all
compounds were measured on a Waters ZQ-4000 mass spectrometer.
All the NMR and ESI mass spectral data were processed in a
MestReNova V12.0.0-20080. Infrared spectra were recorded using a
PerkinElmer FT-IR spectrometer with KBr pellets in the range of
4000−400 cm−1. Elemental analysis measurements were done using
the PerkinElmer 2500 series II elemental analyzer. UV−vis and PL
spectra were recorded on a PerkinElmer Lambda 25 UV−vis
spectrophotometer and a Hitachi F-4500 fluorescence spectropho-
tometer with a quartz cuvette (path length = 1 cm), respectively. The
luminescence lifetime measurements were carried out on a time-
correlated single photon counting (TCSPC) spectrometer from
Edinburg Instruments Ltd. (Lifespec II, U.K.). Electrochemical
experiments were performed using a CHI 600C electrochemical
workstation at 25 °C. Excitation and the emission slit for PL data
collection were set to 10 mm and the PMT voltage at 700 V. The
Synthesis of 4-Methyl-2-(4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl)-
benzo[d]thiazole, BtPT. The azide/tetrazole [A/B] derivative (2.10
mmol, 0.399 g) was dissolved in THF (15 mL), followed by the
addition of CuI (2.10 mmol, 0.399 g), DIPEA (12.6 mmol, 2.195 μL),
and 2-ethynylpyridine (2.52 mmol, 255 μL). Then the reaction
mixture was stirred for 24 h at room temperature. After evaporating
the THF, the crude solid was dissolved in an aqueous ammonia and
DCM mixture (50 mL; 1:1, v/v) and stirred at room temperature for
12 h. The organic layer was separated and removed in a rotary
evaporator under reduced pressure. The pure yellowish white BtPT
ligand was obtained by silica gel column chromatography (20% ethyl
acetate/hexane) in a good yield (0.314 g, 51%) (Scheme 2). Anal.
Calcd for C15H11N5S (Mw = 293.35): C, 61.42; H, 3.78; N, 23.87; S,
10.93. Found: C, 61.39; H, 3.70; N, 23.81; S, 10.87. FTIR in KBr disc
(ν/cm−1): 3450, 1597, 1535, 1450, 1420, 1227, 1021. Melting point =
135−137 °C. ESI-MS: m/z calculated for [C15H11N5S + H]+ 294.07;
found: 294.27. ESI-MS: m/z calculated for [C15H12N5S − N2]+
1
266.07; found: 266.25. H NMR (400 MHz, CDCl3): δ (ppm) =
G
DOI: 10.1021/acs.inorgchem.9b01125
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
9.21 (s, 1H), 8.67 (d, J = 4.4 Hz, 1H), 8.27 (d, J = 7.9 Hz, 1H), 7.85
(t, J = 8.4 Hz, 1H), 7.73 (d, J = 7.9 Hz, 1H), 7.38−7.30 (m, 3H), 2.73
(s, 3H). 13C NMR (100 MHz, CDCl3): δ (ppm) = 154.8, 149.9,
149.5, 149.3, 149.2, 137.1, 133.8, 133.2, 127.7, 126.2, 123.6, 120.9,
119.9, 119.3, 18.1.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01125.
■
S
Synthesis of [Bis(1,10-phenanthroline)(BtPT)] Ruthenium(II)
Dihexafluorophosphate], Ru-1. cis-[Ru(phen)2Cl2] was synthesized
according to the reported literature procedure23 and used for the
synthesis of complex Ru-1 (Scheme 2). A mixture of ligand, BtPT
(0.19 mmol, 0. 056 g), and cis-[Ru(phen)2]Cl2 (0.19 mmol, 0.102 g)
was refluxed in 20 mL of degassed aqueous ethanol (ethanol/water =
3:1) at 100 °C for 6 h under a N2 atmosphere. Then, ethanol was
evaporated and an excess NH4PF6 was added. An orange-red color
solid was obtained, which was extracted by DCM, and the solvent was
evaporated. A pure deep red colored complex was obtained using
silica gel column chromatography (DCM:MeOH = 95:5) in a good
(0.160 g, 81%) yield. The diffraction-quality single crystals of complex
Ru-1 were obtained from an acetone and chloroform (3:1) mixture
after 1 week. Anal. Calcd for C39H27F12N9P2RuS·2CHCl3 (Mw =
1283.51): C, 38.37; H, 2.28; N, 9.82; S, 2.50 Found: C, 38.32; H,
2.30; N, 9.86; S, 2.48. FTIR in KBr disc (ν/cm−1): 3436, 1654, 1510,
1402, 1136, 844 (PF6 stretching), 557. Melting point = >300 °C. ESI-
MS: m/z calculated for [C39H27F6N9PRuS]+ 900.08; found: 900.08.
ESI-MS: m/z calculated for [C39H27N9RuS]2+ 377.56; found: 377.56.
1H NMR (400 MHz, CD3CN): δ (ppm) = 9.70 (s, 1H, Hg), 8.70 (d, J
Experimental procedures; NMR, ESI-MS, and X-ray
data; UV−vis and PL data; theoretical calculation related
files; and associated figures and tables (PDF)
Accession Codes
CCDC 1497233 and 1831199 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.
AUTHOR INFORMATION
Corresponding Author
*E-mail: snehadri@gmail.com, skhatua@nehu.ac.in.
ORCID
■
Snehadrinarayan Khatua: 0000-0003-0992-4800
Notes
= 8.2 Hz, 2H, H4,4′), 8.61 (d, J = 8.3 Hz, 1H, H7′), 8.56 (d,
semicovered, J = 7.6 Hz, 1H, H7), 8.55 (d, J = 7.6 Hz, 1H, H2′), 8.36−
8.33 (m, 2H, H2,d), 8.27 (d, J = 4.8, 2H, H5′,6′), 8.24 (d, J = 6.2, 2H,
H5,6), 8.08−8.03 (m, 2H, H9′,c), 7.97 (d, J = 5.2 Hz, 1H, H9), 7.87−
7.82 (m, 2H, H3,3′), 7.76−7.73 (m, 1H, Hl), 7.65−7.56 (m, 3H,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been financially supported by DST, India (No.
SB/FT/CS-115/2012). We thank the DST Purse program for
the single-crystal X-ray diffraction facility and Sophisticated
Analytical and Instrumentation Facility (SAIF), North Eastern
Hill University (NEHU), for NMR and ESI-MS data. We
thank Dr. B. Banerjee, NEHU, for his help in bioimaging. Dr.
P. N. Chatterjee (NIT, Meghalaya), Dr. A. K. Pal (NEHU),
Dr. P. Pahari (CSIR-NEIST), and Dr. S. C. Pal (Midnapore
College) are acknowledged for useful discussions. B.S, S.K.S.,
and S.K.P thank CSIR (SRF) and RGNF for their fellowships.
Also, we would like to thank the reviewers for their comments
and suggestions. The present work is dedicated to Prof.
H8,a,8′), 7.42−7.37 (m, 2H, Hk,m), 7.26 (t, J = 7.4 Hz, Hb), 2.7 (s, 3H,
Ho). 13C NMR (100 MHz, CD3CN): δ (ppm) = 154.6 (1C, Ch),
154.3 (1C, C9′), 154.1 (2C, C9,2′),154.0 (1C, C2), 153.5 (1C, Ca),
151.2 (1C, Ce), 150.1 (1C, Cf), 149.8 (1C, Ci), 149.3 (1C, C12′),
149.0 (1C, C12), 148.8 (1C, C11′), 148.7 (1C, C11), 139.5 (1C, Cc),
138.2 (1C, C4′), 138.1 (1C, C4), 138.0 (1C, C7′), 137.8 (1C, C7),
134.8 (1C, Cn), 134.0 (1C, Cj), 132.1(2C, C13′,13), 132.0 (1C, C14′),
131.5 (1C, C14), 129.1 (3C, C5′,6′,5), 129.0 (1C, C6), 128.9 (1C, Cm),
128.1 (1C, Ck), 127.6 (1C, Cb), 127.2 (1C, C3′), 127.1 (1C, C3),
127.0 (1C, C8′), 126.3 (1C, C8), 124.3 (1C, Cd), 123.6 (1C, Cg),
120.8 (1C, Cl), 17.9 (1C, Co).
Synthesis of [Bis(1,10-phenanthroline) (3-(4-Methylbenzo[d]-
thiazol-2-yl)-5-(pyridin-2-yl)-3H-1,2,3-triazol-4-ol)] Ruthenium(II)
Dihexafluorophosphate], Ru-1-OH. The complex Ru-1 (0.07
mmol, 0.073g) was dissolved in a 1:1 acetonitrile/water mixture
(10 mL). To this stirred solution was added an aqueous NaOCl (0.7
mmol, 3 mL) dropwise. After 3 h stirring, the organic solvent was
evaporated and treated with an excess NH4PF6. The crude product
was then collected as a DCM extract and dried under vacuum. Finally,
the crude product was purified by silica gel column chromatography
(5% CH3CN/DCM as an eluent) to afford brick red colored Ru-1-
OH in a moderate yield (0.038g, 51%) (Scheme 3). Anal. Calcd for
C39H27F12N9OP2RuS (Mw = 1060.75): C, 44.16; H, 2.57; N, 11.88; S,
3.02. Found: C, 44.19; H, 2.54; N, 11.83; S, 3.05. FTIR in KBr disc
(ν/cm−1): 3446, 2923, 2848, 1628, 1532, 1431, 841(PF6 stretching),
559. Melting point = >300 °C. ESI-MS: m/z calculated for
[C39H26N9ORuS]+ 770.10; found: 770.09. 1H NMR (400 MHz,
CD3CN): 8.74 (d, J = 6.3 Hz, 1H, H4′), 8.64 (d, J = 9.3 Hz, 1H, H4),
8.57 (d, J = 8.3 Hz, 1H, H2′), 8.46 (d, J = 8.3 Hz, 1H, H7′), 8.39−8.34
(m, 2H, H2,7), 8.24−8.17 (m, 2H, H5′,6′), 8.09−7.99 (m, 4H,
̈
Michael Schmittel (Universitat Siegen) on the occasion of his
62th birthday.
REFERENCES
■
(1) Dickinson, B. C.; Chang, C. J. Chemistry and Biology of Reactive
Oxygen Species in Signaling or Stress Responses. Nat. Chem. Biol.
2011, 7, 504−511.
(2) Ow, Y.-L. P.; Green, D. R.; Hao, Z.; Mak, T. W. Cytochrome c:
Functions Beyond Respiration. Nat. Rev. Mol. Cell Biol. 2008, 9, 532−
542.
(3) Yap, Y. W.; Whiteman, M.; Cheung, N. S. Chlorinative Stress:
An Under Appreciated Mediator of Neurodegeneration? Cell.
Signalling 2007, 19, 219−228.
(4) (a) Andersen, J. K. Oxidative Stress in Neurodegeneration:
Cause or Consequence? Nat. Med. 2004, 10, S18−S25. (b) Soo, C.
C.; Haqqani, A. S.; Hidiroglou, N.; Swanson, J. E.; Parker, R. S.;
Birnboim, H. C. Dose-Dependent Effects of Dietary α- and γ-
Tocopherols on Genetic Instability in Mouse Mutatect Tumors. J.
Natl. Cancer Inst. 2004, 96, 796−800.
H5,6,d′,9′), 7.91−7.82 (m, 3H, H9,3′,3), 7.78−7.73 (m, 2H, Hc′,l), 7.54
(dd, J = 5.2, 8.2 Hz, 1H, H8′), 7.34−7.31 (m, 1H, H8), 7.23−7.19 (m,
2H, Ha′,m), 7.11 (d, J = 7.0 Hz, 1H, Hk), 6.78 (t, J = 7.3 Hz, 1H, Hb′),
2.08 (s, 3H, Ho). 13C NMR (100 MHz, CD3CN): δ (ppm) = 156.8,
155.8, 155.1, 153.8, 153.3 (2C), 152.1, 151.2 (2C), 149.1, 148.9,
148.6, 148.4, 148.3, 138.0, 137.4, 137.3, 136.8 (2C), 133.2, 131.8,
131.7, 131.6, 131.2, 131.1, 128.8, 128.7, 128.0, 127.9, 127.8, 126.8,
126.7, 126.4, 126.3, 125.6, 125.4, 121.5, 119.8, 17.7.
(5) For review: (a) Chen, X.; Wang, F.; Hyun, J. Y.; Wei, T.; Qiang,
J.; Ren, X.; Shin, I.; Yoon, J. Recent Progress in the Development of
Fluorescent, Luminescent and Colorimetric Probes for Detection of
Reactive Oxygen and Nitrogen Species. Chem. Soc. Rev. 2016, 45,
2976−3016. (b) Yue, Y.; Huo, F.; Yin, C.; Escobedo, J. O.; Strongin,
R. M. Recent Progress in Chromogenic and Fluorogenic Chemo-
sensors for Hypochlorous Acid. Analyst 2016, 141, 1859−1873.
H
DOI: 10.1021/acs.inorgchem.9b01125
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(6) Organic fluorophore based: (a) Zhu, H.; Fan, J.; Wang, J.; Mu,
H.; Peng, X. An “Enhanced PET”-Based Fluorescent Probe with
Ultrasensitivity for Imaging Basal and Elesclomol-Induced HClO in
Cancer Cells. J. Am. Chem. Soc. 2014, 136, 12820−12823. (b) Zhu,
B.; Li, P.; Shu, W.; Wang, X.; Liu, C.; Wang, Y.; Wang, Z.; Wang, Y.;
Tang, B. Highly Specific and Ultrasensitive Two-Photon Fluorescence
Imaging of Native HOCl in Lysosomes and Tissues Based on
Thiocarbamate Derivatives. Anal. Chem. 2016, 88, 12532−12538.
(c) Li, K.; Hou, J.-T.; Yang, J.; Yu, X.-Q. A Tumor-Specific and
Mitochondria-Targeted Fluorescent Probe for Real-Time Sensing of
Hypochlorite in Living Cells. Chem. Commun. 2017, 53, 5539−5541.
(d) Dong, X.; Zhang, G.; Shi, J.; Wang, Y.; Wang, M.; Peng, Q.;
Zhang, D. A Highly Selective Fluorescence Turn-On Detection of
ClO− with 1-Methyl-1,2-Dihydropyridine-2-thione Unit Modified
Tetraphenylethylene. Chem. Commun. 2017, 53, 11654−11657.
(e) Pak, Y. L.; Park, S. J.; Wu, D.; Cheon, B.; Kim, H. M.;
Bouffard, J.; Yoon, J. N-Heterocyclic Carbene Boranes as Reactive
Oxygen Species-Responsive Materials: Application to the Two-
Photon Imaging of Hypochlorous Acid in Living Cells and Tissues.
Angew. Chem., Int. Ed. 2018, 57, 1567−1571. (f) Pak, Y. L.; Park, S. J.;
Song, G.; Yim, Y.; Kang, H.; Kim, H. M.; Bouffard, J.; Yoon, J.
Endoplasmic Reticulum-Targeted Ratiometric N-Heterocyclic Car-
bene Borane Probe for Two-Photon Microscopic Imaging of
Hypochlorous Acid. Anal. Chem. 2018, 90, 12937−12943. (g) Pak,
Y. L.; Park, S. J.; Xu, Q.; Kim, H. M.; Yoon, J. Ratiometric Two-
Photon Fluorescent Probe for Detecting and Imaging Hypochlorite.
Anal. Chem. 2018, 90, 9510−9514. (h) Halle, M. B.; Yudhistira, T.;
Lee, W.-H.; Mulay, S. V.; Churchill, D. G. Diels−Alder and Stille
Coupling Approach for the Short Protecting Group-Free Synthesis of
Mycophenolic Acid, Its Phenylsulfenyl and Phenylselenyl Analogues,
and Reactive Oxygen Species (ROS) Probing Capacity in Water. Org.
Lett. 2018, 20, 3557−3561. (i) Jiao, X.; Xiao, Y.; Li, Y.; Liang, M.; Xie,
X.; Wang, X.; Tang, B. Evaluating Drug-Induced Liver Injury and Its
Remission via Discrimination and Imaging of HClO and H2S with a
Two-Photon Fluorescent Probe. Anal. Chem. 2018, 90, 7510−7516.
(j) Xie, X.; Wu, T.; Wang, X.; Li, Y.; Wang, K.; Zhao, Z.; Jiao, X.;
Tang, B. A Two-photon Fluorescent Probe for Ratiometric Visual-
ization of Hypochlorous Acid in Live Cells and Animals Based on a
Selenide Oxidation/ Elimination Tandem Reaction. Chem. Commun.
2018, 54, 11965−11968.
(7) Metal complex based: (a) Zhang, K. Y.; Zhang, T.; Wei, H.; Wu,
Q.; Liu, S.; Zhao, Q.; Huang, W. Phosphorescent Iridium(III)
Complexes Capable of Imaging and Distinguishing Between
Exogenous and Endogenous Analytes in Living Cells. Chem. Sci.
2018, 9, 7236−7240. (b) Zhang, K. Y.; Zhang, J.; Liu, Y.; Liu, S.;
Zhang, P.; Zhao, Q.; Tang, Y.; Huang, W. Core−Shell Structured
Phosphorescent Nanoparticles for Detection of Exogenous and
Endogenous Hypochlorite in Live Cells via Ratiometric Imaging
and Photoluminescence lifetime imaging microscopy. Chem. Sci.
2015, 6, 301−307.
(8) (a) Park, J.; Kim, H.; Choi, Y.; Kim, Y. A Ratiometric
Fluorescent Probe Based on a BODIPY−DCDHF Conjugate for the
Detection of Hypochlorous Acid in Living Cells. Analyst 2013, 138,
3368−3371. (b) Xiao, H.; Li, J.; Zhao, J.; Yin, G.; Quan, Y.; Wang, J.;
Wang, R. A Colorimetric and Ratiometric Fluorescent Probe for ClO−
Targeting in Mitochondria and Its Application in vivo. J. Mater. Chem.
B 2015, 3, 1633−1638. (c) Wu, Y.; Wang, J.; Zeng, F.; Huang, S.;
Huang, J.; Xie, H.; Yu, C.; Wu, S. Pyrene Derivative Emitting Red or
Near-Infrared Light with Monomer/Excimer Conversion and Its
Application to Ratiometric Detection of Hypochlorite. ACS Appl.
Mater. Interfaces 2016, 8, 1511−1519.
Synthesis. Nat. Commun. 2017, 8, 14227. (b) Maji, A.; Bhaskararao,
B.; Singha, S.; Sunoj, R. B.; Maiti, D. Directing Group Assisted meta-
Hydroxylation by C−H Activation. Chem. Sci. 2016, 7, 3147−3153.
(11) Shang, M.; Shao, Q.; Sun, S.-Z.; Chen, Y.-Q.; Xu, H.; Dai, H.-
X.; Yu, J.-Q. Identification of Monodentate Oxazoline as a Ligand for
Copper Promoted Ortho-C−H Hydroxylation and Amination. Chem.
Sci. 2017, 8, 1469−1473.
(12) Yang, Y.; Lan, J.; You, J. Oxidative C−H/C−H Coupling
Reactions between Two (Hetero)arenes. Chem. Rev. 2017, 117,
8787−8863.
́
́
́
(13) (a) Fernandez-Hernandez, J. M.; Yang, C. H.; Beltran, J. I.;
̈
Lem-aur, V.; Polo, F.; Frohlich, R.; Cornil, J.; De Cola, L. Control of
the Mutual Arrangement of Cyclometalated Ligands in Cationic
Iridium(III) Complexes. Synthesis, Spectroscopy, and Electro-
luminescence of the Different Isomers. J. Am. Chem. Soc. 2011, 133,
10543−10558. (b) Schulze, B.; Escudero, D.; Friebe, C.; Siebert, R.;
̈
Gorls, H.; Sinn, S.; Thomas, M.; Mai, S.; Popp, J.; Dietzek, B.;
́
Gonzalez, L.; Schubert, U. S. Ruthenium(II) Photosensitizers of
Tridentate Click-Derived Cyclometalating Ligands: A Joint Exper-
imental and Computational Study. Chem. - Eur. J. 2012, 18, 4010−
4025. (c) Schulze, B.; Schubert, U. S. Beyond Click Chemistry−
Supramolecular Interactions of 1,2,3-triazoles. Chem. Soc. Rev. 2014,
43, 2522−2571. (d) Scattergood, P. A.; Ross, D. A. W.; Rice, C. R.;
Elliott, P. I. P. Labilizing the Photoinert: Extraordinarily Facile
Photochemical Ligand Ejection in an [Os(N∧N)3]2+ Complex.
Angew. Chem., Int. Ed. 2016, 55, 10697−10701. (e) Scattergood, P.
A.; Elliott, P. I. P. An unexpected journey from highly tunable
phosphorescence to novel photochemistry of 1,2,3-triazole-based
complexes. Dalton Trans. 2017, 46, 16343−16356.
(14) (a) Sheet, S. K.; Sen, B.; Thounaojam, R.; Aguan, K.; Khatua, S.
Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for
Ag+ and Phosphate Ions: Ag+-Assisted Detection and Imaging of
rRNA. Inorg. Chem. 2017, 56, 1249−1263. (b) Sheet, S. K.; Sen, B.;
Aguan, K.; Khatua, S. A cationic Organoiridium(III) Complex-Based
AIEgen for Selective Light-up Detection of rRNA and Nucleolar
Staining. Dalton Trans. 2018, 47, 11477−11490.
(15) (a) Mauro, M.; Aliprandi, A.; Septiadi, D.; Kehr, N. S.; De
Cola, L. When Self-Assembly Meets Biology: Luminescent Platinum
Complexes for Imaging Applications. Chem. Soc. Rev. 2014, 43, 4144−
̈
4166. (b) Mede, T.; Jager, M.; Schubert, U. S. Chemistry-on-the-
Complex”: Functional RuII Polypyridyl-Type Sensitizers as Divergent
Building Blocks. Chem. Soc. Rev. 2018, 47, 7577−7627.
(16) (a) Khatua, S.; Schmittel, M. A Single Molecular Light-up
Sensor for Quantification of Hg2+ and Ag+ in Aqueous Medium: High
Selectivity toward Hg2+ over Ag+ in a Mixture. Org. Lett. 2013, 15,
4422−4425. (b) Leung, M.-Y.; Leung, S. Y.-L.; Wu, D.; Yu, T.; Yam,
V. W.-W. Synthesis, Electrochemistry, and Photophysical Studies of
Ruthenium(II) Polypyridine Complexes with D−π−A−π−D Type
Ligands and Their Application Studies as Organic Memories. Chem. -
Eur. J. 2016, 22, 14013−14021. (c) Poynton, F. E.; Bright, S. A.;
Blasco, S.; Williams, D. C.; Kelly, J. M.; Gunnlaugsson, T. The
development of Ruthenium(II) Polypyridyl Complexes and Con-
jugates for in vitro Cellular and in vivo Applications. Chem. Soc. Rev.
2017, 46, 7706−7756. (d) Du, Z.; Song, B.; Zhang, W.; Duan, C.;
Wang, Y.-L.; Liu, C.; Zhang, R.; Yuan, J. Quantitative Monitoring and
Visualization of Hydrogen Sulfide In Vivo Using a Luminescent Probe
Based on a Ruthenium(II) Complex. Angew. Chem., Int. Ed. 2018, 57,
3999−4004.
(17) (a) Zhang, R.; Ye, Z.; Song, B.; Dai, Z.; An, X.; Yuan, J.
Development of a Ruthenium(II) Complex-Based Luminescent Probe
for Hypochlorous Acid in Living Cells. Inorg. Chem. 2013, 52,
10325−10331. (b) Liu, F.; Gao, Y.; Wang, J.; Sun, S. Reversible and
Selective Luminescent Determination of ClO−/H2S Redox Cycle in
vitro and in vivo Based on a Ruthenium Trisbipyridyl Probe. Analyst
2014, 139, 3324−3329. (c) Cao, L.; Zhang, R.; Zhang, W.; Du, Z.;
Liu, C.; Ye, Z.; Song, B.; Yuan, J. A Ruthenium(II) Complex-Based
Lysosome-Targetable Multisignal Chemosensor for in vivo Detection
of Hypochlorous Acid. Biomaterials 2015, 68, 21−31.
(9) (a) Bag, S.; Jayarajan, R.; Mondal, R.; Maiti, D. Template-
Assisted meta-C-H Alkylation and Alkenylation of Arenes. Angew.
Chem., Int. Ed. 2017, 56, 3182−3186. (b) Ping, L.; Chung, D. S.;
Bouffard, J.; Lee, S.-G. Transition Metal-Catalyzed Site- and Regio-
Divergent C−H Bond Functionalization. Chem. Soc. Rev. 2017, 46,
4299−4328.
(10) (a) Wu, Q.; Yan, D.; Chen, Y.; Wang, T.; Xiong, F.; Wei, W.;
Lu, Y.; Sun, W.-Y.; Li, J. J.; Zhao, J. A Redox-Neutral Catechol
I
DOI: 10.1021/acs.inorgchem.9b01125
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
́
́
(18) (a) Adam, L. C.; Fabian, I.; Suzuki, K.; Gordon, G.
Hypochlorous Acid Decomposition in the pH 5−8 Region. Inorg.
Chem. 1992, 31, 3534−3541. (b) Takikawa, H.; Takada, A.; Hikita,
K.; Suzuki, K. Formation of a-Hydroxy-b-diketones through
Hydroxylation of Isoxazolium Salts: Stereoselective Approach to
Angular cis-Diols in Polycyclic Systems. Angew. Chem., Int. Ed. 2008,
47, 7446−7449.
(19) (a) Koide, Y.; Urano, Y.; Hanaoka, K.; Terai, T.; Nagano, T.
Development of an Si-Rhodamine-Based Far-Red to Near-Infrared
Fluorescence Probe Selective for Hypochlorous Acid and Its
Applications for Biological Imaging. J. Am. Chem. Soc. 2011, 133,
5680−5682. (b) Jing, J.; Zhang, J.-L. Combining Myeloperoxidase
(MPO) with Fluorogenic ZnSalen to Detect Lysosomal Hydrogen
Peroxide in Live Cells. Chem. Sci. 2013, 4, 2947−2952.
(20) (a) Traynham, J. G.; Pascual, O. S. Effects of Ring Size on the
Reactions of Cyclic Olefins: Halohydrins from Methylenecycloal-
kanes. Tetrahedron 1959, 7, 165−172. (b) Carey, F. A.; Sundberg, R.
J. Advanced Organic Chemistry. Part A: Structure and Mechanisms, 5th
ed.; Springer: New York, 2007; pp 473−577.
(21) Lau, Y. H.; Rutledge, P. J.; Watkinson, M.; Todd, M. H.
Chemical Sensors that Incorporate Click-Derived Triazoles. Chem.
Soc. Rev. 2011, 40, 2848−2866.
(22) Haegens, A.; Heeringa, P.; van Suylen, R. J.; Steele, C.; Aratani,
Y.; O'Donoghue, R. J. J.; Mutsaers, S. E.; Mossman, B. T.; Wouters, E.
F. M.; Vernooy, J. H. J. Myeloperoxidase Deficiency Attenuates
Lipopolysaccharide-Induced Acute Lung Inflammation and Subse-
quent Cytokine and Chemokine Production. J. Immunol. 2009, 182,
7990−7996.
(23) (a) Mandel, J. S.; Adami, H.-O.; Cole, P. Paraquat and
Parkinson’s Disease: An Overview of the Epidemiology and a Review
of Two Recent Studies. Regul. Toxicol. Pharmacol. 2012, 62, 385−392.
(b) Hou, J.-T.; Li, K.; Yang, J.; Yu, K.-K.; Liao, Y.-X.; Ran, Y.-Z.; Liu,
Y.-H.; Zhou, X.-D.; Yu, X.-Q. A Ratiometric Fluorescent Probe for In
Situ Quantification of Basal Mitochondrial Hypochlorite in Cancer
Cells. Chem. Commun. 2015, 51, 6781−6784.
(24) Hartshorn, R. M.; Barton, J. K. Novel Dipyridophenazine
Complexes of Ruthenium(II): Exploring Luminescent Reporters of
DNA. J. Am. Chem. Soc. 1992, 114, 5919−5925.
J
DOI: 10.1021/acs.inorgchem.9b01125
Inorg. Chem. XXXX, XXX, XXX−XXX