Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for

Article pubs.acs.org/IC

Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for Ag+ and Phosphate Ions: Ag+‑Assisted Detection and Imaging of rRNA Sanjoy Kumar Sheet,† Bhaskar Sen,† Romita Thounaojam,‡ Kripamoy Aguan,‡ and Snehadrinarayan Khatua*,† †

Centre for Advanced Studies, Department of Chemistry, North Eastern Hill University, Shillong, Meghalaya 793022, India Department of Biotechnology and Bioinformatics, North Eastern Hill University, Shillong, Meghalaya 793022, India

‡

S Supporting Information *

ABSTRACT: A new bis-heteroleptic Ru(II) complex (1) of benzimidazole-substituted 1,2,3-triazole pyridine ligand has been designed and constructed for the photoluminescent detection of cationic and anionic analytes, Ag+ and phosphate ions. Compound, 1[PF 6]2 was fully characterized by various spectroscopic techniques and the solid-state structure was determined via single-crystal X-ray diffraction. The cation and anion sensing properties in 50% aqueous buffer (pH 9.2) and pure acetonitrile were carefully examined in photoluminescence (PL) spectroscopy. The 1[PF6]2 was found to be highly selective to pyrophosphate; PPi/HP2O73− and H2PO4− ions in CH3CN. It showed ∼10-fold PL intensity enhancement at 583 nm in the presence of only 1 and 2 equiv of PPi and H2PO4− ions, respectively. The PL titrations of 1[PF6]2 with PPi and H2PO4− in CH3CN furnished the association constant (Ka = 3.3 × 103 M−1 and 6.8 × 103 M−1) and the detection limit was as low as 5.73 and 5.19 ppb, respectively. The 1[PF6]2 also selectively detected Ag+ over other competitive cations through the luminescence light up in 50% aqueous buffer (pH 9.2) media. The PL titration of 1[PF6]2 with Ag+ showed ∼8-fold luminescence enhancement at 591 nm and yielded association constant, Ka = 3.5 × 104 M−1 and the detection limit was determined to be 5.05 ppb. A new cation sensing mechanism has been established where the Ag+ ion is detected in photoluminescence spectroscopy through the unique cyclometalated Ag+-triazolide complex formation. The high selectivity of 1[PF6]2 for phosphates and Ag+ was established by PL in the presence of various competing ions. Finally, for biological application, the cytotoxicity study was performed. The probe showed low cytotoxicity and was suitable for intracellular Ag+ imaging. The cell imaging and in vitro photoluminescence study revealed that the probe stained the cell nucleoli and specifically bind with ribosomal RNA (rRNA) and, therefore, it can also serve as a luminescent probe for rRNA in the presence of Ag+.

■

INTRODUCTION Recently, the development of single molecular light-up probes for real-time detection and quantification of multiple analytes has received immense attention, because of its simplicity and low cost.1,2 Several approaches were developed to design single molecular multianalyte probes, such as (a) assembly of multiple receptors with one or more reporter units,3−5 (b) single receptor/reporter in different channel interrogation,6−8 and (c) single receptor/reporter operating in single channel at different experimental condition with different mode of action.9−12 Approaches (a) and (b) are of particular interest but are much more tedious from the synthetic and operational viewpoint.13 Although it is challenging, approach (c) is beneficial from an operating perspective, as several analytes can be quantified in single channel without any interference. The displacement assays and sequential/relay assays to estimate multiple analytes have been reported in large number; however, they are not truly useful in real-world sensing.2,14−16 To date, there have © XXXX American Chemical Society

been few reports on single molecular bifunctional probes for cations17−19 and anions,20−22 but a true fluorescence light up probe capable of the detection of both cation and anion in single channel is hardly reported.2,23−25 Silver is one of the most demanding metal and it has been widely used in the electronic, photographic, and imaging industries. On the other hand, silver is a hazardous metal pollutant and rapidly absorbed and accumulated in the body.26−28 It is known that silver has good antibacterial properties and it can deactivate sulfhydryl enzymes and combine with amine, imidazole, and carboxyl groups of a variety of metabolites.29,30 Because of its bioaccumulation and serious toxicity at high concentration, it is highly desirable to construct a selective probe for Ag+ quantification in environmental and biological systems.31−36 Inorganic phosphate ions Received: September 29, 2016

A

DOI: 10.1021/acs.inorgchem.6b02343 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Synthesis of the Ligand BiPT and the Compound 1[PF6]2a

a Reagents and conditions: (a) CuSO4, 5H2O, sodium ascorbate, H2O/THF (1:1 v/v), reflux, 17 h; (b) aqueous EDTA solution, DCM, stirring, 8 h; (c) cis-[Ru(phen)2Cl2], EtOH/H2O (3:1), Δ, 17 h, N2; and (d) excess NH4PF6.

Scheme 2. Cation and Anion Sensing by the Bifunctional Probe 1[PF6]2 and the Chemical Structure of the Control Probe 2[PF6]2

(H2PO4−, and pyrophosphate; PPi/HP2O73−) play important roles in a range of life processes such as energy storage, signal transduction DNA sequencing and DNA replication catalyzed by DNA polymerase. Consequently, the significant progress has been made in the selective detection of phosphate ions.37−41 In recent years, the live cell imaging and organelle-specific staining using luminescent probes has become an integral part in biomedical research. In contrast to various DNA, Gquadruplex DNA and nucleotide selective fluorescent probes,42−44 a sizable amount of effort has been devoted to develop small-molecule-based fluorescent dyes for RNA detection.45−49 It is obvious that the detection of various RNA elements is of prime importance in unravelling the functions of the myriad RNA world. Among these, ribosomal RNA (rRNA) is of great importance, because it is the factory for protein synthesis and comprises ∼70% of all RNAs in the cell. rRNA is synthesized and assembles in the nucleolar region of the nucleus during telophase and interphase and clearly visible by fluorescence microscopy as dense and dark region of the nucleus. However, the details of rRNA nucleolar dynamic mechanisms of intracellular distribution and trafficking during cell cycle are lacking. Therefore, the development of an rRNAselective probe to stain cell nucleoli is imperative.

In contrast to organic dye and other metal complexes, the ruthenium(II) polypyridyl complex has significant potential for biological imaging, because of its visible excitation wavelength, long emission lifetime, polarized luminescence, pronounced photostability, and large Stokes shifts.50−55 Thomas et al. reported several dinuclear ruthenium(II) complex-based probes for the direct imaging of DNA in cells.56−58 There are several reports on the selective imaging of cellular organelles such as nucleus,59−61 mitochondria,62−64 lysozome,65−67 and endoplasmic reticulum;68−70 however, relatively few examples of rRNAselective probes to stain nucleoli can be found, and among these, ruthenium(II) based rRNA-selective probe for nucleolar imaging is rarely available.71,72 Since the past decade, ruthenium(II) polypyridyl complexes have been extensively studied as luminescent probes for anion73−77 and biochemical analytes,78−85 but only a few ruthenium(II) polypyridine complex-based cation sensors have been reported to date.6,86−88 However, so far, Ru(II) complexes have not been used as bifunctional probes for sensing both cation- and anion- and metal-ion-assisted selective detection and imaging of rRNA. It is highly challenging to design a cation-selective ruthenium(II) polypyridine complex-based probe. For cation sensing, ruthenium(II) complex of a phen/ B


Article

Inorganic Chemistry

Figure 1. (a) ORTEP plot of 1[PF6]2 with 30% thermal ellipsoid probability. Only noncarbon and nonhydrogen atoms are labeled here. (b) View of the 2D packing of the complex cation formed by C−H···N, π−π stacking, and C−H···π interaction among phenanthroline ligands and benzimidazole of BiPT along the crystallographic a-axis. Solvents, counterions, and C−H···F interactions are omitted for the sake of clarity.

to different conformational settings as a function of the technique used for interrogation. Here, we artfully introduced 2-methylbenzimidazole at 1,2,3-triazole pyridine, since, in addition to the C−H···anion hydrogen bonding interaction, it can also bind to the cation through coordination of the benzimidazole nitrogen. Herein, we present the design and synthesis of benzimidazole-substituted 1,2,3-triazole-pyridine (BiPT)-based bis-heteroleptic ruthenium(II) complex, 1 (see Scheme 1), which is a light-up bifunctional probe that allows the quantitative detection of inorganic phosphates (H2PO4− and PPi) and Ag+ ion in CH3CN and 50% aqueous buffer media at two different wavelengths (Scheme 2). The Ag+ detection through the cyclometalated triazolide complex formation is reported for the first time. The Ag+-assisted intriguing nucleoli staining and rRNA binding are also discussed herein.

bpy based ligand with N/O/S donor center is preferred to bind the cation. However, from the synthetic viewpoint, this is problematic as the ruthenium(II) center can form a complex at N/O/S donor sites, as well as with phen/bpy. Post-synthetic modification of the phen/bpy-based ligand in ruthenium(II) complex might be an alternative way to introduce N/O/S donor sites, which is also equally tedious and tricky. Schmittel and co-workers skillfully designed thiaaza crown and azacrown ether-substituted phenanthroline-based ligands and their iridium(III) and ruthenium(II) complexes for multication detection in single or multichannel detection protocol.6,87 We also constructed bis-heteroleptic ruthenium(II) complex carrying two benzothiazole amide-substituted bipyridine ligand for light up sensing of both Hg2+ and Ag+.88 A recently reported complex (2 in Scheme 2, presented later in this work) served as a selective probe for single analyte, i.e., phosphate ions through the hydrogen bonding interaction.89 Our strategy is to use a single recognition site that shows different binding specifics due C


Article

Inorganic Chemistry

■

RESULTS AND DISCUSSION Synthesis and Characterization. The ligand, BiPT was synthesized by refluxing 2-azidomethyl benzimidazole and 2ethynylpyridine in the presence of copper sulfate and sodium ascorbate in a THF/H2O (1:1 v/v) mixture and isolated in 74% yield (see Scheme 1). The BiPT was fully characterized by various one-dimensional (1D) NMR (1H, 13C) spectroscopy (Figures S1 and S2 in the Supporting Information), electrospray ionization−mass spectrometry (ESI-MS) (Figure S3 in the Supporting Information), and elemental analysis. Compound 1[PF6]2 was synthesized by refluxing cis-[Ru(phen)2Cl2] and BiPT in EtOH−H2O (3:1) under N2, followed by PF6 anion exchange and isolated in good yield (41%) (see Scheme 1). The probe, 1[PF6]2 was fully characterized by various spectroscopies, viz. 1D NMR (1H, 13C) and 2D NMR (1H−1H COSY, 1H−13C HSQC, and 1H−13C HMBC) spectroscopy (Figures S4−S8 in the Supporting Information), ESI-MS (Figure S9 in the Supporting Information), elemental analysis, and the solid-state structure of 1[PF6]2 was determined via single-crystal X-ray diffraction (XRD) (see Figure 1). The 1D and 2D NMR spectra of 1[PF6]2 were recorded in acetone−d6 at room temperature, which clearly shows all expected peaks of phenanthroline and benzimidazole-substituted triazole pyridine ligand. The ESI-MS spectra of 1[PF6]2 clearly shows two peaks at m/z = 883.12 (calcd. 883.08) and 369.07 (calcd. 369.04), which correspond to singly charged 1· (PF6)+ and doubly charged 12+, respectively (see Figure S9). The experimental isotopic distribution patterns of both the singly and doubly charged species are matched perfectly with their calculated patterns. Crystal Structure. Compound 1[PF6]2 was crystallized in the monoclinic space group P21/n (Table S1 in the Supporting Information). The structure reveals that the central ruthenium adopts an octahedral geometry through bidentate coordination of two ancillary phenanthroline and one BiPT ligand (Figure 1). The Ru−N bond distances in 1[PF6]2 are in the range of 2.031(4)−2.073(4) Å, with cis and trans N−Ru−N angles in the range of 78.73(15)°−97.09(17)° and 170.67(16)°− 176.02(16)°, respectively (Table S2 in the Supporting Information). Similar bond lengths and angles were also observed in previously reported ruthenium polypyridyl complexes.90−92 The crystal packing in 1[PF6]2 reveals that the supramolecular 2D networks (Figure 1b) is formed in the solid, which are held together by weak C−H···N and C−H···F hydrogen bonds as well as by π−π stacking and C−H···π interactions of two phenanthrolines and phenanthroline with benzimidazole of BiPT of neighboring complex units. Electrochemical and Photophysical Study. The electrochemical properties of 1[PF6]2 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using a Pt working electrode in dry and degassed CH3CN under N2 atmosphere with ferrocene as internal standard (Eox 1/2 = +0.400 V vs Ag wire). Compound 1[PF6]2 shows a single quasi-reversible (ΔEp = 84 mV) Ru2+/Ru3+ redox couple at E1/2ox = +0.941 V (Epa = 0.983 V and Epc = 0.889 V) vs Fc+/Fc (Figure S10a in the Supporting Information). The redox wave is anodically shifted by 30 mV in comparison to [Ru(phen)3]2+ + (Eox 1/2 = +0.911 V vs Fc /Fc) (Figure S10c), which suggests the stronger π-acceptor ability of the BiPT ligand than phen. Since the well-defined reduction waves were not found in CV analysis, the DPV was carried out to acquire the ligand-based reductions under the similar experimental conditions. The

compound 1[PF6]2 shows three ligand-based reduction waves (Ered 1/2) at −1.85, − 2.10, and −2.20 V, in comparison to [Ru(phen)3]2+ (Ered 1/2 = −1.61, − 1.78, and −2.13 V) (see Figures S10b and S10d). Absorption and photoluminescence spectral profiles of complex 1[PF6]2 in CH3CN are presented in Figure 2. The

Figure 2. Ultraviolet−visible light (UV-vis) (red line) and photoluminescence (PL) (blue line) spectra of 1[PF6]2 in acetonitrile at room temperature.

ultraviolet−visible light (UV-vis) spectrum of 1[PF6]2 in CH3CN displays sharp bands at λ = 225 nm (ε = 2.0 × 104) and 262 nm (ε = 2.7 × 104), which are assigned to intraligand (IL) π−π* transitions within phen and BiPT ligands. In addition, a moderate intense broad metal-to-ligand chargetransfer (MLCT) absorption is observed in the 355−500 nm range consisting of two or more MLCT bands. For 1[PF6]2, a band at λmax = 401 nm (ε = 2.3 × 103) and a shoulder at λ = 445 nm (ε = 3.2 × 103) are observed. A time-dependent density functional theory (TD-DFT) calculation was performed to assign those bands (vide inf ra). Compound 1[PF6]2 shows a rather poor luminescence at 575 nm upon excitation at 400 nm both in degassed and air-saturated CH3CN. It is notable that the PL maxima (λem) and shape are independent of the excitation wavelength (from 400 nm to 470 nm), which suggests that the emission occurs from the same MLCT excited state. Electrochemical data of 1[PF6]2 were used to calculate the transition energies and are compared with the transition energies for the experimental MLCT bands of 1[PF6]2 at 445 nm (3.01 eV) and 401 nm (2.78 eV). The difference between the potential of the first reduction and the first oxidation (ΔE(1) 1/2 ox 1st L red = E1st ) is matched well with lowest energy MLCT 1/2 − E1/2 band at 445 nm (E = 2.78 eV; ΔE(1) 1/2 = 2.79 eV). Also, the highest energy MLCT band at 401 nm (3.09 eV) in the absorption spectra is matched reasonably with the electroanalytical data (ΔE(3) 1/2 = 3.14 eV) that was obtained directly from the difference between the potential of the third reduction 1st ox 3rd L red and the first oxidation (ΔE(3) ). 1/2 = E1/2 − E1/2 Anion and Cation Sensing in Ultraviolet−Visible Light (UV-vis) and Photoluminescence (PL) Spectroscopy. At first, 5.0 equiv of various anions, namely, F−, Cl−, Br−, I−, HO−, AcO−, NO3−, HSO4−, CN−, H2PO4−, and HP2O73−, and 10.0 equiv of cations (Na+, K+, Mg2+, Ca2+, Al3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, and Ag+) were screened in CH3CN and aqueous buffer of 1[PF6]2, respectively (see Figures S11 and S12 in the Supporting Information). The D


Article

Inorganic Chemistry

Figure 3. PL spectra of 1[PF6]2 (50 μM) upon addition of (a) various anions (2.0 equiv) in CH3CN and (b) various cations (5.0 equiv) in CH3CN/ carbonate buffer (v/v, 1:1; pH 9.2), (λex = 459 nm) at 25 °C.

Figure 4. PL titration of 1[PF6]2 (50 μM) (a) with PPi (0−1 equiv) and (b) with H2PO4− (0−2 equiv) in CH3CN at room temperature. (Insets in panels (a) and (b) show plots of PL intensity as a function of PPi and H2PO4− concentration. λex = 459 nm, λem = 583 nm.)

respectively, only after the addition of Ag+ (5.0 equiv) and phosphates (2.0 equiv) in their respective media. As shown in Figure 3, a natural competitor of Ag+ (i.e., Hg2+, Cd2+, Pb2+, and other competitive anions) did not trigger any significant enhancement or interrupt the response toward Ag+ and phosphates. It is assumed that the hydrogen-bonding interaction with phosphates and Ag+-triazolide complex formation (vide inf ra) increase the rigidity of the methyl benzimidazole group at the 1,2,3-triazole pyridine. As a consequence, nonradiative decay from MLCT excited state is inhibited and PL is enhanced. During the PL titration of 1[PF6]2 with H2PO4− and PPi, the emission band at 575 nm is red-shifted to 583 nm. The intensity increases gradually up to ∼10-fold with the progressive addition of PPi (0−1.0 equiv) and H2PO4− (0− 2.0 equiv) (see Figures 4a and 4b). The linear PL intensity enhancement at 583 nm with PPi/H2PO4− amount potentially allows PPi quantification in an unknown sample (see insets in Figures 4a and 4b). The PL response of 1[PF6]2 toward PPi (2 equiv; see Figure 5a) and H2PO4− (2 equiv; see Figure 5b) in

MLCT band at 445 nm was red-shifted only in the presence of H2PO4−, HP2O73− (PPi), and Ag+ in their respective mediums. During absorption titration of 1[PF6]2 with the incremental amounts of PPi (0−2.0 equiv), H2PO4− (0−4.0 equiv) and Ag+ (0−5.0 equiv), the band at 401 nm gradually decreased and the ∼5−10 nm red shift of the MLCT band at 445 nm was detected with isosbestic points at 293 and 459 nm (Figures S13−S15 in the Supporting Information). While the ∼5 nm red shift of the absorption band at 401 nm is detected immediately by UV-vis spectroscopy during selectivity experiments, it is virtually unusable, because no distinct color change was observed by the naked eye. Complex 1 itself emits faintly at 575 and 580 nm (λex = 459 nm) in CH3CN and aqueous buffer (pH 9.2) respectively. Because of the structural flexibility at benzimidazole-substituted triazole pyridine ligand in solution, the nonradiative decay from MLCT excited state diminishes the photoluminescence (PL). To inspect the selectivity profile, 1[PF6]2 was tested with various anions and cations (see Figures 3a and 3b). Significant PL enhancement was registered with 11 and 8 nm red shifts, E


Article

Inorganic Chemistry

Figure 5. (a) PL of 1[PF6]2 (λem = 583 nm) in the presence of competing anions (10 equiv) with 2 equiv PPi (green) and without PPi (brown). (b) The PL response of 1[PF6]2 in the presence of competing anions (10 equiv) with 2 equiv H2PO4− (red) and without H2PO4− (black).

Figure 6. (a) PL titration of 1[PF6]2 (50 μM) with Ag+ (0−5 equiv) in CH3CN/carbonate buffer (v/v, 1:1; pH 9.2). (Inset shows a plot of PL intensity as a function of Ag+.) (b) PL of 1[PF6]2 (λem = 591 nm) in the presence of various cations: with Ag+ (red bar) without Ag+ (black bar).

1:1 model shows good fit and furnishes a binding constant of Ka = 3.5 × 104 M−1 (error of ca. 8.2%) for Ag+ to 1 (Figure S22 in the Supporting Information). The detection limit of Ag+ was calculated to be as low as 5.05 ppb from the PL titration data (Figure S23 in the Supporting Information), which is lower than many other reported Ag+ probes and the maximum permissible level stipulated by WHO (50 ppb in drinking water).32,33,36 While a 1:30 mixture of 1[PF6]2 and competitive cations did not show any PL enhancement at 591 nm, an immediate enhancement was observed upon the addition of only 5.0 equiv of Ag+ (Figure 6b). The Ag+ detection is strongly dependent on the pH and works above pH 8 (Figure S24 in the Supporting Information). Basic media is required to deprotonate the benzimidazole N−H and triazole C−H activation and to form the Ag+-triazolide complex, which induces rigidity and enhances the PL intensity. To check the necessity of benzimidazole moiety in Ag+ detection, the PL spectra of control probe 2[PF6]289 (Scheme 2) were recorded in the presence of Ag+. The excess of Ag+ (20.0 equiv) did not influence the PL intensity in CH3CN/ carbonate buffer (v/v, 1:1; pH 9.2) (Figure S25 in the Supporting Information). Evidently, the benzimidazole is

the presence of other competitive anions (10 equiv) were measured to examine the possible interference. The tested anions did not interfere in phosphate ions detection. From the Benesi−Hildebrand (B−H) plot analysis, the binding constants (Ka) are calculated as 3.3 × 103 M−1 and 6.8 × 103 M−1 for PPi and H2PO4−, respectively (see Figures S16 and S17 in the Supporting Information). The detection limits of PPi and H2PO4− are calculated to be as low as 5.73 and 5.19 ppb, respectively, which is lower than many other reported PPi and H2PO4− probes (see Figures S18 and S19 in the Supporting Information).38,39,41 For practical use of 1[PF6]2, PL titration with PPi was carried out in aqueous solution. Similar to acetonitrile, the weakly luminescent band of 1[PF6]2 at 575 nm in CH3CN/H2O (97:3 v/v) was enhanced ∼13-fold upon the addition of 2.0 equiv of PPi (see Figure S20 in the Supporting Information). PL titration of 1[PF6]2 with Ag+ (0−5.0 equiv) shows a gradual red shift and ∼8-fold enhancement of the initially weak PL band at λmax = 580 to λmax = 591 nm (Figure 6a). The Job plot analysis shows the inflection point at 0.5, indicating a 1:1 stoichiometry of the Ag+/1 association (Figure S21 in the Supporting Information). The nonlinear curve fitting for the F


Article

Inorganic Chemistry prerequisite to form chelate and makes 1 a highly selective Ag+ probe. In order to assess the performance of 1 as a bifunctional probe, the cation selectivity study in CH3CN media and anion selectivity study in 50% aqueous buffer was carried out. Since the phosphates have been detected through the hydrogenbonding interaction in pure organic media and Ag+ has been detected through the triazolide complex formation in 50% aqueous carbonate buffer (pH 9.2), the detection and quantification of phosphates is not hampered by the Ag+ and vice versa (see Figures S26 and S27 in the Supporting Information). Therefore, both the phosphates and Ag+ in an unknown mixture will be quantified by using different media in a single spectroscopic channel. The time course of the PL response of 1[PF6]2 upon the addition of 1.0 equiv of of PPi and H2PO4− in CH3CN and Ag+ in CH3CN/carbonate buffer (v/v, 1:1; pH 9.2) at room temperature was monitored. Figure 7 shows that the PL intensity of 1[PF6]2 is enhanced by 88%,

conducted in dry and degassed CH3CN for 1[PF6]2, both in the absence and presence of PPi (2.0 equiv). The experiment shows an ∼40 mV anodic shift of the Ru(II)-based redox wave of 1[PF6]2 (E1/2ox = 0.941 V vs Fc+/Fc) in the presence of PPi (2.0 equiv) (E1/2ox = +0.901 V vs Fc+/Fc). The result clearly suggests the possible interaction of 1[PF6]2 with PPi (see Figure S28 in the Supporting Information). During the 1H NMR titration with Ag+ (0−8.0 equiv), the N−Hi proton vanished instantly and the triazole proton, C−He shifted upfield (Δδ = 0.28 ppm) and disappeared after the addition of 8.0 equiv of Ag+. Unlike 1H NMR titration with PPi, here, two methylene protons (Hf) became magnetically nonequivalent after the addition of Ag+ and the sharp singlet at 5.97 ppm has been shifted upfield and split into two doublets ( fa and f b) with the apparent coupling constants of 15.0 and 13.8 Hz, respectively (Figure 8b). The disappearance of He and Hi signals and appearance of two doublets for magnetically nonequivalent protons (Hfa and Hf b) confirm the Ag+ chelation through triazole carbon and benzimidazole nitrogen.96 In the ESI-MS spectrum, a clear peak is observed at m/z 843.04 (calcd. 843.04), corresponding to [(C39H28N10Ru)2+ − 2H+ + Ag+]+, upon treatment of 1 with excess Ag+ in basic CH3CN (see Figure S29 in the Supporting Information). This result unambiguously confirms the 1/Ag+ = 1:1 stoichiometry and the formation of 1•Ag+ triazolide complex depicted in Figure 8b. Although the C−H activation and triazolide complex formation is already established,97,98 to the best of our knowledge, to date, Ag+ detection through the formation of the Ag+-triazolide complex is not known. Triazolide is sensitive to ambient atmosphere and is used extensively as an intermediate in many catalytic reactions.99−101 Several attempts were unsuccessful to determine the diffraction quality crystal of the 1•Ag+ -triazolide complex. Computational Study. The geometry optimization for the free complex 1, 1·H2PO4−, and 1•Ag+ were performed using DFT in the ground state except for the 1·PPi where the convergence was not achieved. The energy-minimized structures and related bond lengths and angles are given in Figure S30 and Table S3 in the Supporting Information. In the phosphate adduct, stability of 1·H2PO4− is gained as 13.65 kcal/mol free energy is released (Figure S31 in the Supporting Information), because of the hydrogen bonding interaction. Selected calculated molecular orbitals and theoretical UV-vis spectra of 1, 1·H2PO4−, and 1•Ag+ are shown in Figures S32 and S33 in the Supporting Information. For 1, the associated occupied molecular orbitals HOMO, HOMO−1, and HOMO−2 are mainly located on the ruthenium(II) center. The two highest lying molecular orbitals, i.e., HOMO and HOMO−1, are related to the ruthenium(II) dz orbital, whereas the HOMO−2 corresponds to the ruthenium(II) t2g set (Figure S32). The five unoccupied molecular orbitals (LUMO, LUMO +1, LUMO+2, LUMO+3, and LUMO+4) of complex 1 focus on the ancillary phen ligand, except for the LUMO+5 orbital, which is focused on the 1,2,3-triazole pyridine of the BiPT ligand. To gain insight into the electronic transitions responsible for the absorption spectrum of 1, 1·H2PO4−, and 1•Ag+, timedependent DFT (TD-DFT) calculations on optimized geometry in CH3CN were performed. In the visible region between 355 and 500 nm, the transitions are assigned to various metal-to-ligand charge transfer bands in the singlet state (1MLCT). The calculated vertical excitation energies and composition of the related transitions assigned to the

Figure 7. Time course of the photoluminescence response of 1[PF6]2 upon the addition of 1.0 equiv of PPi and H2PO4− in CH3CN and Ag+ in CH3CN/carbonate buffer (v/v, 1:1; pH 9.2) at 25 °C.

64%, and 41%, immediately after the addition of PPi, H2PO4−, and Ag+, respectively. For PPi and H2PO4−, the maximum PL is reached after ∼2 h. While Ag+ reacts slowly with the probe and the maximum PL is reached after ∼3 h, this observation points to a relatively fast reaction of 1[PF6]2 with phosphate ions. Phosphate Ions and Ag+ Detection Studies Via 1H NMR Spectroscopy, ESI Mass Spectrometry, Cyclic Voltammetry (CV), and Differential Pulse Voltammetry (DPV). The interaction of PPi with complex 1 was further investigated by 1H NMR spectroscopy, CV, and DPV, whereas the Ag+ interaction with complex 1 was examined by 1H NMR spectroscopy and ESI-MS. The highly acidic N−Hi proton signal of 1[PF6]2 in DMSO-d6 at δH = 12.66 shifted slightly upfield and broadened gradually during the addition of 0−0.175 equiv of PPi. When 0.2 equiv of PPi was added, the signal vanished completely, indicating extraction by the PPi ion, which is normal for many imidazole-, indole-, and thio−urea-based receptors.93−95 The addition of 2.0 equiv of PPi revealed the downfield shift (Δδ = 0.15 ppm) of triazole proton, C−He (Figure 8a). Therefore, the PPi interact with both the triazole proton and the amine proton of benzimidazole, causing PL enhancement (Scheme 2). CV and DPV experiments were G


Article

Inorganic Chemistry

Figure 8. (a) 1H NMR spectra of 1[PF6]2 (4.5 mM) upon addition of PPi (0−9.0 mM) in DMSO-d6. (b) 1H NMR titration of 1[PF6]2 (4.5 mM) with Ag+ (0−36.0 mM) in the presence of Et3N (0.25 mM) in DMSO-d6 and the resulting 1·Ag+ triazolide complex.

Another band at λmax = 445 nm (2.78 eV) arises from a relatively weak transition characterized as HOMO−1 → LUMO ( f = 0.08) (410 nm, 3.02 eV) (see Table S5 and Figure S32 in the Supporting Information). For 1·H2PO4−, the MLCT band centered at 449 nm (2.75 eV) is due to the ruthenium t2g set to the π*-orbital of the phen ligand i.e., HOMO−1 → LUMO and HOMO−2 → LUMO+2 ( f = 0.15) (413 nm, 3.00 eV). However, the highest energy MLCT band

experimental UV-vis spectrum in CH3CN are displayed in Table S5 in the Supporting Information. Only those transitions with oscillator strength (f) larger than 0.05 are considered. The TD-DFT calculations for 1 indicate that the experimental MLCT band at λmax = 401 nm (3.09 eV) is due to the strong transitions from HOMO−2 → LUMO+4 (f = 0.09) (376 nm, 3.30 eV), HOMO−2 → LUMO+2 (f = 0.05) (377 nm, 3.29 eV) and HOMO → LUMO+3 (f = 0.06) (391 nm, 3.17 eV). H


Article

Inorganic Chemistry

Figure 9. Fluorescence images of (a) fixed HeLa cells treated with only 1[PF6]2 (25 μM) (b−d) fixed HeLa cells treated with DNase and RNase in the presence of Ag+ (50 μM) and 1[PF6]2 (25 μM) in red channel and (e−h) overlay images.

at λmax = 406 nm (3.05 eV) arises from comparatively weak transitions characterized as the ruthenium t2g orbital to the π* orbital of phen and BiPT ligand, i.e., HOMO−1 → LUMO+1 (f = 0.08) (402 nm, 3.08 eV), HOMO−2 → LUMO+4 ( f = 0.06) (394 nm, 3.14 eV), and HOMO−1 → LUMO+4 (f = 0.07) (392 nm, 3.16 eV), respectively (see Table S5 and Figure S32). The absorption band for 1•Ag+ centered at 409 nm (3.02 eV) arise mostly from two dominant MLCT transitions characterized as HOMO−2 → LUMO+2 and HOMO−1 → LUMO+4 (f = 0.11) (396 nm, 3.23 eV). Another absorption band at 455 nm (2.72 eV) is attributed to a MLCT process involving the promotion of an electron from the mixed metal(Ru)-ligand(benzimidazole) HOMO−1, HOMO−3, HOMO−4 to the LUMOs derived from the π*-orbital of the phen ligand (f = 0.06) (412 nm, 3.01 eV) (see Table S5 and Figure S32). Cytotoxicity, RNA Imaging, and RNA Binding Studies. For biological application of 1[PF6]2, we evaluated its cytotoxicity in HeLa cell for 24 h. The cell viability gradually decreased with increasing amount of 1[PF 6]2 from a concentration range of 5−100 μM. More than 75% of the cells survived at ≤25 μM of 1[PF6]2, whereas, with 100 μM of 1[PF6]2, only 69% of the cells survived after 24 h of treatment, suggesting that 1[PF6]2 has a low cytotoxicity at low concentration (see Figure S34a in the Supporting Information). We also tested the cytotoxicity of Ag+ (within a concentration range of 5−100 μM) in HeLa cell for 24 h and observed 82% and 69% cell survivability at 50 μM and 100 μM of Ag+, respectively (Figure S34b). For the cell imaging experiment, 25 μM of 1[PF6]2 and 50 μM of Ag+ was used, since the cell viability was >75% at this concentration. However, we observed 66% cell survivability when we used Ag+ and the compound together at a concentration of 50 μM and 25 μM, respectively (Figure S34c). When the HeLa cells were treated with the probe 1[PF6]2 for 30 min, it did not reveal any staining of live cells in the red channel. Subsequently, in a separate well, the HeLa cells were first treated with Ag+ for 10 min and then incubated with probe 1[PF6]2 for an additional 30 min in PBS buffer (pH 7.4). The probe was found to be cell-permeable and, in the presence of Ag+, it stained the cell nucleoli, as well as the cytoplasm (see Figure S35 in the Supporting Information). It is a fact that the rRNA is synthesized and assembled in the

nucleolar region of the nucleus. Since the total cellular RNA consists of rRNA, tRNA, mRNA, and miRNA, and 75%−80% of the total cellular RNA is rRNA, we therefore speculate that probe 1[PF6]2 binds rRNA in the presence of Ag+ during imaging. To establish whether the probe 1[PF6]2 binds to cellular DNA or RNA, the DNase and RNase digestion tests were performed. A bright red luminescence was observed from the nucleoli of the fixed HeLa cell treated with both the Ag+ and 1[PF6]2. The DNase is known to hydrolyze only DNA without affecting RNA in the cells whereas only RNA substrates are hydrolyzed in the RNase digest test. As expected, the cell nucleoli stained with probe 1[PF6]2 and Ag+ shows significant red luminescence after the DNase treatment. However, the bright luminescence of the nucleoli diminished significantly in the RNase-treated cells (Figure 9). It has been amply reported that the Ag+ forms G-Ag+-G and C-Ag+-C duplex structures with guanine (G) and cytosine (C) of single-strand RNA or DNA preferably and G-G/C-C mismatch of mutated doublestranded DNA.102−105 In eukaryotes, nucleotide sequence of rRNA is very rich in GC bases.106−108 Eukaryotic cells contain more than 75% rRNA and due to its high demand rDNA locus actively continues to synthesize a greater amount of rRNA in the nucleus, and therefore, at any given time, there would be a million-fold more copies of rRNA in the nucleus, compared to any other RNAs, including mRNAs, which are only 5%−10% of total RNA of the cell. Therefore, Ag+ will bind more predominantly in the nucleolar rRNA and very lightly in the cytoplasm where rRNA is also diffusely distributed in a larger space.109 However, the Ag+-triazolide complex formation is unfeasible at the cellular pH (7.4), but the observation from cellular fluorescence imaging study leads us to presume that G-Ag+-G/ C-Ag+-C duplexes are formed with rRNA104−107 and the bright luminescence is generated due to the rigidity induced by the interaction of benzimidazole-substituted triazole pyridine ligand of 1 with G-Ag+-G/C-Ag+-C duplex, although the detailed molecular interaction is unclear at present (see Figure S36 in the Supporting Information). Using the PL spectroscopy, we further investigated the interactions of 1[PF6]2 with ctDNA, ssDNA (21 BP), Gquadruplex DNA, bovine serum albumin (BSA), and RNA I


Article

Inorganic Chemistry

Figure 10. (a) PL spectra of 1[PF6]2 (50 μM) upon the addition of RNA, ctDNA, ssDNA, BSA, and G-quadruplex DNA (20-fold) in the absence of Ag+ in CH3CN/PBS buffer (v/v, 1:5; pH 7.4). An ∼2.7-fold PL enhancement is observed in the case of RNA in the presence of Ag+. (b) PL spectra of 1[PF6]2 (50 μM) upon the addition of a mixture of Ag+ (10-fold) and RNA, ctDNA, ssDNA, BSA, and G-quadruplex DNA (22AG1, 22AG2, 22AG3) (20-fold) in CH3CN/PBS buffer (v/v, 1:5; pH 7.4) at 25 °C. (c) PL titration of 1[PF6]2 with Ag+ and RNA mixture (0−20 fold).

confirmed the mode of phosphate ion interaction. The Ag+ detection is extremely selective over its frequent competitors (the Hg2+, Cd2+, and Pb2+ ions). For the first time, it has been shown that the Ag+ is detected in PL through the formation of the Ag+-triazolide complex. The Ag+ to 1 binding has been established explicitly by the 1H NMR titration and the ESI-MS. Two different sensing mechanisms were involved in the detection of phosphate and Ag+ ions. The phosphates are sensed through the formation of hydrogen bond in pure organic media and the Ag+ is detected through the formation Ag+-triazolide complex in a mixed aqueous buffer media (pH 9.2); accordingly, the detection and quantification of phosphates are not hampered by the Ag+ and vice versa. The probe has low cytotoxicity and is suitable for intracellular Ag+ imaging. The cell imaging and in vitro photoluminescence study shows that the probe stains the cell nucleoli via the interaction with nucleolar RNA and it can serve as a luminescent probe for rRNA in the presence of Ag+.

(from S. cerevisiae; contains >70% of rRNA) in mixed buffer media. However, in the absence of Ag+, the luminescence intensities of 1[PF6]2 remain unchanged, implying that 1[PF6]2 did not interact with RNA and other bioanalytes (Figure 10a). However, significant PL enhancement at 603 nm (λex = 459 nm) was observed upon the addition of Ag+ in the presence of RNA only (Figure 10b). The PL titration of 1[PF6]2 with 20fold RNA and Ag+ mixture shows a gradual blue shifting of the initial band, from 615 nm to 603 nm, with an ∼2.7-fold PL enhancement (Figure 10c). The in vitro PL and in vivo imaging results collectively suggest that bright luminescence originates from the interaction of probe 1[PF6]2 and Ag+ with rRNA in the nucleoli of HeLa cells.

■

CONCLUSION In conclusion, a new bis-heteroleptic Ru(II) complex (1) of a benzimidazole-substituted 1,2,3-triazole pyridine ligand, has been synthesized. We have shown that 1 acts as a turn-on luminescent bifunctional probe and quantitatively detects both Ag+ and phosphate ions (H2PO4− and HP2O73−) in aqueous buffer and organic media, respectively. The calculated detection limit and interference study suggest that 1 can detect phosphate ions at the submicromolar level, even in the presence of many other anions. A substantial downfield shifting of the triazole C− H proton during the 1H NMR titration of 1[PF6]2 with PPi

■

EXPERIMENTAL SECTION

Materials and Physical Measurements. All chemicals were used as received from commercial suppliers (Aldrich, Alfa Aesar, and Spectrochem India). The control probe, 2[PF6]2, and its corresponding ligand was synthesized according to the reported literature procedure.109 The 1H and 13C NMR spectra were measured on a Bruker Avance II (400 MHz) spectrometer and chemical shifts were J


Article

Inorganic Chemistry

the 1[PF6]2 (50 μM) are titrated with aliquots of RNA solution PerkinElmer LS55 fluorescence spectrophotometer with a 1 mL quartz cuvette (path length = 1 cm). Concentration of RNA in working solutions was 1.0 mM. The phosphate buffered saline (PBS) (pH 7.4, 20 mM) was prepared using the doubly purified water. Cytotoxicity Study. The cytotoxicity of the compound 1[PF6]2, silver perchlorate, and the 1:2 mixture of 1[PF6]2 and silver perchlorate against HeLa cells was determined by colorimetric cell cytotoxicity assay kit - ab112118 (abcam) in a 96-well cell culture plate. HeLa cells were seeded in a 96-well plate at a density of 5 × 103 cells/well and incubated at 37 °C, 5% CO2 incubator. At 70% confluency, cells were treated with different concentration of 1[PF6]2 (5 μM, 10 μM, 25 μM, and 100 μM) and silver perchlorate (5 μM, 10 μM, 25 μM, 50 μM, and 100 μM) and the 1:2 mixture of 1[PF6]2 and silver perchlorate and incubated for 24 h. An assay solution was thawed and warmed at 37 °C, and 20 μL (1/5 volume) of the solution was added into each well. The reagents were mixed by shaking the plate gently for 30 s and incubated at 37 °C, 5% CO2 incubator. The change in absorbance was monitored at 570 and 605 nm, using a microplate reader. The ratio of OD570 to OD605 was calculated to determine the cell viability in each well. The cell viability is proportional to increases in OD570 and decreases in OD605. Readings were taken in quadruplet. The percentage of cell viability was calculated for samples and controls based on the following formula:

expressed in ppm using residual solvent as internal standard. ESI-MS were performed with a Waters ZQ-4000 mass spectrometer. 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 scanning spectrophotometer and Hitachi F-4500 and PerkinElmer LS55 fluorescence spectrophotometer with quartz cuvette (path length = 1 cm). All spectroscopic measurements of 1[PF6]2 were performed in CH3CN for anion and 50% aqueous buffer solution (CH3CN: 0.2 M carbonate buffer solution; pH 9.2; 1:1; v/v) for cation. All metal salts were used as their perchlorate salt and anions were used as their tetra-n-butylammonium salt. Excitation and the emission slit were set to 10 mm and the PMT voltage was set at 700 V. Electrochemical experiments were performed at 25 °C using a CHI 600C electrochemical workstation (CH Instruments) and Metrohm Autolab B.V. instrument. The cell contained a Pt working electrode, a Pt wire auxiliary electrode, and an Ag wire as a pseudo-reference electrode. Experiments were carried out on a 1.0 mM solution of 1[PF6]2 in a dry and degassed acetonitrile with 0.1 M tetra-nbutylammonium perchlorate (Bu4NClO4) as the supporting electrolyte. For comparison, the electrochemical data of [Ru(phen)3]2+ was also collected under the same experimental conditions. After each experiment, the electrochemical potential window was calibrated using ferrocence as the internal standard. The redox potential of the ferrocene/ferrocenium (Fc/Fc+) couple was taken as +0.400 V vs Ag wire electrode.110 All the reported potentials were measured at a scan rate of 100 mV s−1. DFT Calculations. All geometry optimizations were performed with the Gaussian 09 program package, using denisty functional theory (DFT). The B3LYP/6-31G(d) exchange correlation functional111 was used for C, H, N, together with the LANL2DZ112 for ruthenium and silver. The geometry was fully optimized in the ground states. Timedependent density functional theory (TD-DFT) calculations using the polarizable continuum model (PCM) nonequilibrium version113 were performed with a spin-restricted formalism to examine low-energy excitations at the ground-state geometry in acetonitrile at the same level of calculation, as employed for geometry optimizations. To address the nonbonding interaction properly, the Grimme’s-D3 dispersion is utilized in our computation. General Method for In Vitro RNA Binding Study. All oligonucleotides, calf-thymus DNA (ctDNA), ssDNA, bovine serum albumin (BSA), and RNA (ribonucleic acid from baker’s yeast) used in this study were purchased from Integrated DNA Technologies, Merck, and Alfa Aesar, respectively. (See Table 1.) Stock solutions of ctDNA,

% cell viability = 100 ×

name

sequence

structure

5′-CCAGTTCGTAGTAACCCGACC-3′ from calf thymus 5′-AG3TTAG3TTAG3TTAG3-3′ 5′-AG3TTAG3TTAG3TTAG3TTAG3-3′ 5′-AG3TTAG3TTAG3TTAG3TTAG3TTAG3-3′ ∼70% of 16S-and 23S-Ribosomal from baker’s yeast

single-strand double-strand hybrid-type G4 hybrid-type G4 hybrid-type G4 single-strand

R ctrl − R 0

where Rsample is the absorbance ratio of OD570/OD605, in the presence of the test compound; Rctrl the absorbance ratio of OD570/OD605, in the absence of the test compound (vehicle control); and Ro the averaged background (noncell control) absorbance ratio of OD570/ OD605. Cell Culture and RNA Imaging. A fluorescence inverted microscope (Leica DMI4000B) was used to visualize the fluorescence of the cells following the addition of the respective compound with a 20× objective lens. Fluorescence detection was carried out using an excitation filter (Model BP 515-560) for complex 1. HeLa cells were cultured in DMEM media containing low glucose (Invitrogen) with 10% FBS (Invitrogen) at 37 °C in 5% CO2 incubator chamber. One day before imaging, cells were seeded in 24-well flat-bottomed plates. After 24 h cell growth, cells washed with PBS (phosphate buffer saline) and fresh PBS (500 μL) were added in two successive wells. One well was treated with 25 μL aqueous solution Ag+ (1.0 mM) and incubated for 10 min. Afterward added 25 μM of 1[PF6]2 (10.0 mM in DMSO) and incubated for 20 min. The other well was treated with only 25 μM of 1[PF6]2 and incubated for 30 min. For a fixed-cell experiment, cultured cells grown on a special confocal microscope dish were fixed by precooled methanol (−20 °C) for 15 min and then washed twice with PBS for 5 min. For DNase and RNase digest test, three sets of pretreated HeLa cells were stained with 25 μM of 1[PF6]2 and 50 μM of Ag+ for 15 min. Cells washed with PBS (phosphate buffer saline) and fresh PBS (500 μL) then were added in two successive wells. A total of 100 μL of clean PBS (as control experiment), 30 μg/mL DNase (Thermo-Fisher Scientific, USA), or 25 μg/mL DNase-Free RNase (Thermo-Fisher Scientific, USA) was added into the three adjacent wells and incubated at 37 °C in 5% CO2 for 1 h. Cells were rinsed by clean PBS twice before imaging. For each test, the fluorescent imaging pictures were obtained with an equal parameter for control. Synthesis. Synthesis of 2-(4-Pyridin-2-yl-[1,2,3]triazol-1-ylmethyl)-1H-benzimidazole (BiPT). 2-azidomethyl benzimidazole (A) was synthesized according to reported literature procedure114 and was used for the synthesis of ligand, BiPT (Scheme 1). 2-Azidomethyl benzimidazole (0.303 g, 1.75 mmol) was dissolved in 10 mL of a THF/H2O (1:1 v/v) mixture. Then, 2-ethynylpyridine (0.216 g, 2.10 mmol), sodium ascorbate (0.208 g, 1.05 mmol), and copper sulfate (0.026 g, 0.105 mmol) were added to the solution. The mixture was refluxed for 17 h and an off-white solid was found after evaporation of the solvent. To the precipitate, DCM (50 mL) and the aqueous

Table 1. Sequences of the Oligonucleotides Used in This Work ssDNA ctDNA 22AG1 22AG2 22AG3 RNA

R sample − R 0

bovine serum albumin (BSA), and RNA were prepared by dissolving them in DNase- and RNase-free Millipore water. The concentration of ctDNA and RNA were determined spectrophotometrically, using the molar absorption coefficients of ε260 nm = 6600 M−1 cm−1 and 7800 M−1 cm−1, respectively. All the oligonucleotides were dissolved in Millipore water. To obtain G-quadruplex formation, oligonucleotides were annealed in relevant buffer containing KCl (100 mM) by heating to 95 °C for 5 min, followed by gradual cooling to room temperature. The 1.0 mM stock solutions of 1[PF6]2 was prepared in CH3CN for the PL measurements. In the emission titration study, the solution of K


Article

Inorganic Chemistry solution of EDTA (0.390 g, 1.05 mmol, 50 mL) was added and the solvent mixture was stirred for 8 h. The DCM part was extracted and evaporated in rotary evaporator to obtain the dark beige BiPT ligand. The pure BiPT was obtained after the recrystallization from DCM. Yield: 358 mg (74%). Anal. Calcd for C15H12N6 (molecular weight (Mw) of 276.11): C, 65.21; H, 4.38; N, 30.42. Found: C, 65.38; H, 4.42; N, 30.46. FTIR in KBr disc (ν/cm−1): 3429, 2913, 1595, 1447, 1205, 1107, 847, 785, 738. UV−vis in CH3CN: λmax/nm (ε/L M−1 cm−1) = 282 (14 917), 275 (14 310), 243 (19 660), 210 (22 580). PL in CH3CN: λex/nm = 275; λem/nm = 360, 300. ESI-MS [C15H12N6 + Na]+: Calcd: m/z = 299.10; Found: m/z = 299.13; [C15H12N6 + H]+: Calcd: m/z = 277.12; Found: m/z = 277.11. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 12.67 (s, 1H, Hi), 8.73 (s, 1H, He), 8.61 (d, J = 3.2 Hz, 1H, Hd), 8.05 (d, J = 7.6 Hz, 1H, Ha), 7.90 (t, J = 7.6 Hz, 1H, Hb), 7.59 (d, J = 7.6 Hz, 1H, Hm or Hj), 7.50 (d, J = 7.6 Hz, 1H, Hm, or Hj), 7.36 (t, J = 6.4 Hz, 1H, Hc), 7.23−7.15 (m, 2H, Hk,l), 5.96 (s, 2H, Hf). 13C NMR (100 MHz, DMSO-d6): δ = 149.7 (2C), 149.6 (2C), 148.3, 147.3, 137.2, 124.1, 123.0, 122.6, 121.5, 119.4, 118.8, 111.5, 47.5. Synthesis of [Bis(1,10-phenanthroline) 2-(4-Pyridin-2-yl-[1,2,3]triazol-1-ylmethyl)-1H-benzimidazole)] Ruthenium(II) Dihexafluorophosphate, 1[PF6]2. A mixture of cis-[Ru(phen)2Cl2] (0.119 g, 0.225 mmol) and 2-(4-pyridin-2-yl-[1,2,3]triazol-1-ylmethyl)-1H-benzimidazole (BiPT) (0.062 g, 0.225 mmol) were dissolved in 30 mL of welldegassed ethanol−water mixture (3:1 v/v). The mixture was heated to reflux under N2 atmosphere for 17 h. Thereafter, the reaction mixture was cooled to room temperature and ethanol was evaporated in the rotary evaporator. The dark red aqueous solution was treated an excess of NH4PF6 (0.400 g). A dark red solid precipitate was formed, which was dissolved in dichloromethane (DCM) (50 mL). The DCM solution was washed by water and the organic layer was separated, evaporated under rotary evaporator, and dried under vacuum. The compound was purified by silica gel column chromatography packed in DCM using a mixture (CH3CN:H2O:saturated KNO3 ratio = 88:9:3) as the eluent and the dark red band was collected as the nitrate salt of Ru(II) complex. The solvent was reduced and excess amount of NH4PF6 was added to the collected portion in the presence of water. The compound was extracted by DCM and evaporated under rotary evaporator to obtain the reddish brown crystalline solid product. Subsequent crystallization from a CH3COCH3:CHCl3 (6:1) mixture provided 1[PF6]2 as shiny, dark red, diffraction-quality crystals. Yield: 0.098 g (41%). Melting point (MP): > 300 °C. Anal. Calcd for C39H28F12N10P2Ru·0.4CHCl3 (Mw = 1075.45) C, 44; H, 2.66; N, 13.02 found: C 44.16, H 2.70, N 13.03. FTIR in KBr disc (ν/cm−1): 3421, 2922, 2340, 1630, 1428, 1314, 1269, 1221, 1096, 1051, 841, 746, 716, 557. ESI-MS [C39H28F6N10PRu]+: Calcd: m/z = 883.12; Found: m/z = 883.08. ESI-MS [C39H28N10Ru]2+: Calcd: m/z = 369.07; Found: m/z = 369.04. 1H NMR (400 MHz, acetone-d6): δ (ppm) = 9.40 (s, 1H, He), 8.87 (t, J = 7.2 Hz, 2H, H4,4′), 8.77 (d, J = 8.0 Hz, 1H, H9′), 8.68−8.67 (m, 3H, H2,2′,7), 8.49 (d, J = 8.0 Hz, 1H, Hd), 8.45− 8.33 (m, H6,6′,5,5′,7′), 8.24 (d, J = 5.2 Hz,1H, H9), 8.12 (t, J = 8.0 Hz,1H, Hc), 8.07- 8.01 (m, 2H, H3,3′), 7.93 (d, J = 6.4 Hz,1H, Ha), 7.79 (dd, J = 8.0 Hz, 5.7 Hz, 1H, H8′), 7.66 (t, J = 7.2 Hz, 1H, H8), 7.59 (br, 2H, Hm,j), 7.36 (t, J = 6.4 Hz, 1H, Hb), 7.27−7.25 (m, 2H, Hk,l), 6.01 (s, 2H, Hf). 13C NMR (100 MHz, acetone-d6): δ = 155.1, 150.0 (4C, C9,9′,7,7′), 154.2 (1C, Ca), 153.2 (1C, Cg), 150.3, 150.3, 150.0, 149.9, 149.9 (6C, C10,10′,11,11′,h,p), 140.3 (1C, Cc), 138.9 (2C, C4,4′), 138.8 (1C, C2), 138.4 (1C, C2′), 133.0, 132.7, 132.4 (5C, C12,12′,13,13′,n), 130.1, 129.9, 129.8 (4C, C6,6′,5,5′), 129.1 (1C, Ce), 128.2, 128.2, 128.1, 128.0 (4C, C3,3′,b,8′), 127.4 (1C, C8), 125.1 (1C, Co), 124.7 (2C, Ck,l), 124.0 (1C, Cd), 121.2 (1C, Cm), 113.5 (1C, Cj), 51.4 (1C, Cf).

■

■

All 1D and 2D NMR, ESI-MS, CV, UV-vis, and PL data for 1[PF6]2 and associated figures (PDF) Crystallographic information (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail addresses: [email protected], [email protected]. ORCID

Snehadrinarayan Khatua: 0000-0003-0992-4800 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was financially supported by DST, India (No. SB/ FT/CS/115/2012). We thank the DST Purse program for use of the single-crystal X-ray diffraction facility at NEHU and Sophisticated Analytical and Instrumentation Facility (SAIF), North Eastern Hill University for the NMR data. Dr. D. Samanta of JNCASR, Bangalore, India is gratefully acknowledged for useful discussions regarding the computational study. S.K.S. and B.S. thank RGNF and North Eastern Hill University for their research fellowship. Also we would like to thank the reviewers for their critical comments and suggestions.

■ ■

DEDICATION The present work is dedicated to Prof. Michael Schmittel (Universität Siegen) on the occasion of his 60th birthday. REFERENCES

(1) Magri, D. C.; Brown, G. J.; McClean, G. D.; de Silva, A. P. Communicating Chemical Congregation: A Molecular AND Logic Gate with Three Chemical Inputs as a “Lab-on-a-Molecule” Prototype. J. Am. Chem. Soc. 2006, 128, 4950−4951. (2) Chen, K.; Shu, Q.; Schmittel, M. Design Strategies for Lab-on-amolecule Probes and Orthogonal Sensing. Chem. Soc. Rev. 2015, 44, 136−160. (3) Tulyakova, E.; Delbaere, S.; Fedorov, Y.; Jonusauskas, G.; Moiseeva, A.; Fedorova, O. Multimodal Metal Cation Sensing with Bis(macrocyclic) Dye. Chem.Eur. J. 2011, 17, 10752−10762. (4) Bhaumik, C.; Das, S.; Maity, D.; Baitalik, S. A Terpyridylimidazole (tpy-HImzPh3) Based Bifunctional Receptor for Multichannel Detection of Fe2+ and F− Ions. Dalton Trans. 2011, 40, 11795−11808. (5) Yuan, L.; Lin, W.; Xie, Y.; Chen, B.; Zhu, S. Single Fluorescent Probe Responds to H2O2, NO, and H2O2/NO with Three Different Sets of Fluorescence Signals. J. Am. Chem. Soc. 2012, 134, 1305−1315. (6) Schmittel, M.; Lin, H.-W. Quadruple-Channel Sensing: A Molecular Sensor with a Single Type of Receptor Site for Selective and Quantitative Multi-Ion Analysis. Angew. Chem., Int. Ed. 2007, 46, 893−896. (7) Schmittel, M.; Qinghai, S. A Lab-on-a-molecule for Anions in Aqueous Solution: Using Kolbe Electrolysis and Radical Methylation at Iridium for Sensing. Chem. Commun. 2012, 48, 2707−2709. (8) Chen, K.; Schmittel, M. An Iridium(III)-based Lab-on-a-molecule for Cysteine/homocysteine and Tryptophan Using Triple-channel Interrogation. Analyst 2013, 138, 6742−6745. (9) Dong, M.; Wang, Y.-W.; Peng, Y. Highly Selective Ratiometric Fluorescent Sensing for Hg2+ and Au3+, Respectively, in Aqueous Media. Org. Lett. 2010, 12, 5310−5313. (10) Kumar, S.; Luxami, V.; Kumar, A. Chromofluorescent Probes for Selective Detection of Fluoride and Acetate Ions. Org. Lett. 2008, 10, 5549−5552. (11) Zhang, J. F.; Zhou, Y.; Yoon, J.; Kim, Y.; Kim, S. J.; Kim, J. S. Naphthalimide Modified Rhodamine Derivative: Ratiometric and

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02343. L


Article

Inorganic Chemistry Selective Fluorescent Sensor for Cu2+ Based on Two Different Approaches. Org. Lett. 2010, 12, 3852−3855. (12) Neupane, L. N.; Park, J.-Y.; Park, J. H.; Lee, K.-H. Turn-On Fluorescent Chemosensor Based on an Amino Acid for Pb(II) and Hg(II) Ions in Aqueous Solutions and Role of Tryptophan for Sensing. Org. Lett. 2013, 15, 254−257. (13) Yuan, M.; Zhou, W.; Liu, X.; Zhu, M.; Li, J.; Yin, X.; Zheng, H.; Zuo, Z.; Ouyang, C.; Liu, H.; Li, Y.; Zhu, D. A Multianalyte Chemosensor on a Single Molecule: Promising Structure for an Integrated Logic Gate. J. Org. Chem. 2008, 73, 5008−5014. (14) Dong, M.; Peng, Y.; Dong, Y.-M.; Tang, N.; Wang, Y.-W. A Selective, Colorimetric, and Fluorescent Chemodosimeter for Relay Recognition of Fluoride and Cyanide Anions Based on 1,1′-Binaphthyl Scaffold. Org. Lett. 2012, 14, 130−133. (15) Santos-Figueroa, L. E.; Moragues, M. E.; Climent, E.; Agostini, A.; Martínez-Máňez, R.; Sancenón, F. Chromogenic and Fluorogenic Chemosensors and Reagents for Anions. A Comprehensive Review of the Years 2010−2011. Chem. Soc. Rev. 2013, 42, 3489−3613. (16) Sheet, S. K.; Sen, B.; Thounaojam, R.; Aguan, K.; Khatua, S. Highly Selective Light-up Al3+ Sensing by a Coumarin Based Schiff Base Probe: Subsequent Phosphate Sensing DNA Binding and Live Cell Imaging. J. Photochem. Photobiol., A 2017, 332, 101−111. (17) Maity, D.; Govindaraju, T. A Differentially Selective Sensor with Fluorescence Turn-On Response to Zn2+ and Dual-mode Ratiometric Response to Al3+ in Aqueous Media. Chem. Commun. 2012, 48, 1039− 1041. (18) Maity, D.; Kumar, V.; Govindaraju, T. Reactive Probes for Ratiometric Detection of Co2+ and Cu+ Based on Excited-State Intramolecular Proton Transfer Mechanism. Org. Lett. 2012, 14, 6008−6011. (19) Maity, S. B.; Banerjee, S.; Sunwoo, K.; Kim, J. S.; Bharadwaj, P. K. A Fluorescent Chemosensor for Hg2+ and Cd2+ Ions in Aqueous Medium under Physiological pH and Its Applications in Imaging Living Cells. Inorg. Chem. 2015, 54, 3929−3936. (20) Kumari, N.; Jha, S.; Bhattacharya, S. Colorimetric Probes Based on Anthraimidazolediones for Selective Sensing of Fluoride and Cyanide Ion via Intramolecular Charge Transfer. J. Org. Chem. 2011, 76, 8215−8222. (21) Fu, L.; Tian, F. F.; Lai, L.; Liu, Y.; Harvey, P. D.; Jiang, F. L. A Ratiometric “Two-in-one” Fluorescent Chemodosimeter for Fluoride and Hydrogen Sulfide. Sens. Actuators, B 2014, 193, 701−707. (22) You, G. R.; Park, G. J.; Lee, S. A.; Choi, Y. W.; Kim, Y. S.; Lee, J. J.; Kim, C. A Single Chemosensor for Multiple Target Anions: The Simultaneous Detection of CN− and OAc− in Aqueous Media. Sens. Actuators, B 2014, 202, 645−655. (23) He, X.; Yam, V. W. A Highly Selective Bifunctional Luminescence Probe for Potassium and Fluoride Ions. Org. Lett. 2011, 13, 2172−2175. (24) Wang, H.; Xue, L.; Jiang, H. Ratiometric Fluorescent Sensor for Silver Ion and Its Resultant Complex for Iodide Anion in Aqueous Solution. Org. Lett. 2011, 13, 3844−3847. (25) Liu, Y.; Sun, Y.; Du, J.; Lv, X.; Zhao, Y.; Chen, M.; Wang, P.; Guo, W. Highly Sensitive and Selective Turn-On Fluorescent and Chromogenic Probe for Cu2+ and ClO− Based on a N-picolinyl Rhodamine B-hydrazide Derivative. Org. Biomol. Chem. 2011, 9, 432− 437. (26) Ratte, H.-T. Bioaccumulation and Toxicity of Silver Compounds: A Review. Environ. Toxicol. Chem. 1999, 18, 89−108. (27) Wang, H.-H.; Xue, L.; Qian, Y.-Y.; Jiang, H. Novel Ratiometric Fluorescent Sensor for Silver Ions. Org. Lett. 2010, 12, 292−295. (28) Huang, H.; Chen, R.; Ma, J.; Yan, L.; Zhao, Y.; Wang, Y.; Zhang, W.; Fan, J.; Chen, X. Graphitic Carbon Nitride Solid Nanofilms for Selective and Recyclable Sensing of Cu2+ and Ag+ in Water and Serum. Chem. Commun. 2014, 50, 15415−15418. (29) Chatterjee, A.; Santra, M.; Won, N.; Kim, S.; Kim, J. K.; Kim, S. B.; Ahn, K. H. Selective Fluorogenic and Chromogenic Probe for Detection of Silver Ions and Silver Nanoparticles in Aqueous Media. J. Am. Chem. Soc. 2009, 131, 2040−2041.

(30) Chernousova, S.; Epple, M. Silver as Antibacterial Agent: Ion, Nanoparticle, and Metal. Angew. Chem., Int. Ed. 2013, 52, 1636−1653. (31) Kim, J. M.; Lohani, C. R.; Neupane, L. N.; Choi, Y.; Lee, K. H. Highly Sensitive Turn-On Detection of Ag+ in Aqueous Solution and Live Cells with a Symmetric Fluorescent Peptide. Chem. Commun. 2012, 48, 3012−3014. (32) Dessingou, J.; Mitra, A.; Tabbasum, K.; Baghel, G. S.; Rao, C. P. Benzimidazole Conjugate of 1,1′-Thiobis(2-naphthol) as Switch-On Fluorescence Receptor for Ag+ and the Complex as Secondary Recognition Ensemble toward Cys, Asp, and Glu in Aqueous Methanolic Solution: Synthesis, Characterization, Ion and Amino Acid Recognition, Computational Studies, and Microscopy Features. J. Org. Chem. 2012, 77, 371−378. (33) Zhou, Y.-P.; Liu, E.-B.; Wang, J.; Chao, H.-Y. Highly Ag+ Selective Tripodal Gold(I) Acetylide-based “Off−On” Luminescence Chemosensors based on 3(ππ*) Emission Switching. Inorg. Chem. 2013, 52, 8629−3637. (34) Zhu, M.; Zhou, Y.; Yang, L.; Li, L.; Qi, D.; Bai, M.; Chen, Y.; Du, H.; Bian, Y. Synergistic Coupling of Fluorescent “Turn-Off” with Spectral Overlap Modulated FRET for Ratiometric Ag+ Sensor. Inorg. Chem. 2014, 53, 12186−12190. (35) Singha, S.; Kim, D.; Seo, H.; Cho, S. W.; Ahn, K. H. Fluorescence Sensing Systems for Gold and Silver Species. Chem. Soc. Rev. 2015, 44, 4367−4399. (36) Gao, R.; Xu, G.; Zheng, L.; Xie, Y.; Tao, M.; Zhang, W. A Highly Selective and Sensitive Reusable Colorimetric Sensor for Ag+ Based on Thiadiazole-Functionalized Polyacrylonitrile Fiber. J. Mater. Chem. C 2016, 4, 5996−6006. (37) Khatua, S.; Choi, S. H.; Lee, J.; Kim, K.; Do, Y.; Churchill, D. G. Aqueous Fluorometric and Colorimetric Sensing of Phosphate Ions by a Fluorescent Dinuclear Zinc Complex. Inorg. Chem. 2009, 48, 2993− 2999. (38) Ni, X.-L.; Zeng, X.; Redshaw, C.; Yamato, T. Ratiometric Fluorescent Receptors for Both Zn2+ and H2PO4− Ions Based on a Pyrenyl-Linked Triazole-Modified Homooxacalix[3]arene: A Potential Molecular Traffic Signal with an R-S Latch Logic Circuit. J. Org. Chem. 2011, 76, 5696−5702. (39) Roy, b.; Rao, A. S.; Ahn, K. H. Mononuclear Zn(II)- and Cu(II)-Complexes of a Hydroxynaphthalene-Derived Dipicolylamine: Fluorescent Sensing Behaviours Toward Pyrophosphate ions. Org. Biomol. Chem. 2011, 9, 7774−7779. (40) Das, P.; Chandar, N. B.; Chourey, S.; Agarwalla, H.; Ganguly, B.; Das, A. Role of Metal Ion in Specific Recognition of Pyrophosphate Ion under Physiological Conditions and Hydrolysis of the Phosphoester Linkage by Alkaline Phosphatase. Inorg. Chem. 2013, 52, 11034−11041. (41) Nadella, S.; Sahoo, J.; Subramanian, P. S.; Sahu, A.; Mishra, S.; Albrecht, M. Sensing of Phosphates by Using Luminescent EuIII and TbIII Complexes: Application to the Microalgal Cell Chlorella vulgaris. Chem.Eur. J. 2014, 20, 6047−6053. (42) Zhou, Y.; Xu, Z.; Yoon, J. Fluorescent and Colorimetric Chemosensors for Detection of Nucleotides, FAD and NADH: Highlighted Research During 2004−2010. Chem. Soc. Rev. 2011, 40, 2222−2235. (43) Ma, D.-L.; He, H.-Z.; Leung, K.-H.; Zhong, H.-J.; Chan, D. S.H.; Leung, C.-H. Label-Free Luminescent Oligonucleotide-Based Probes. Chem. Soc. Rev. 2013, 42, 3427−3440. (44) Xu, Z.; Xu, L. Fluorescent Probes for the Selective Detection of Chemical Species Inside Mitochondria. Chem. Commun. 2016, 52, 1094−1119. (45) Han, K. Y.; Leslie, B. J.; Fei, J.; Zhang, V.; Ha, T. Understanding the Photophysics of the Spinach−DFHBI RNA Aptamer−Fluorogen Complex To Improve Live-Cell RNA Imaging. J. Am. Chem. Soc. 2013, 135, 19033−19038. (46) Wang, J.; Sun, S.; Mu, D.; Wang, J.; Sun, W.; Xiong, X.; Qiao, B.; Peng, X. A Heterodinuclear Complex OsIr Exhibiting NearInfrared Dual Luminescence Lights Up the Nucleoli of Living Cells. Organometallics 2014, 33, 2681−2684. M


Article

Inorganic Chemistry (47) Liu, Y.; Jun, E. J.; Kim, G.; Lee, A.-R.; Lee, J.-H.; Yoon, J. A Bispyrene Derivative as a Selective Fluorescent Probe for RNA. Chem. Commun. 2014, 50, 2505−2507. (48) Lu, Y.; Deng, Q.; Hu, D. P.; Wang, Z. Y.; Huang, B. H.; Du, Z. Y.; Fang, Y. X.; Wong, W. L.; Zhang, K.; Chow, C. F. A Molecular Fluorescent Dye for Specific Staining and Imaging of RNA in Live Cells: A Novel Ligand Integration from Classical Thiazole Orange and Styryl Compounds. Chem. Commun. 2015, 51, 15241−15244. (49) Guo, L.; Chan, M. S.; Xu, D.; Tam, D. Y.; Bolze, F.; Lo, P. K.; Wong, M. S. Indole-based Cyanine as a Nuclear RNA-Selective TwoPhoton Fluorescent Probe for Live Cell Imaging. ACS Chem. Biol. 2015, 10, 1171−1175. (50) Ozawa, H.; Haga, M.-A.; Sakai, K. A Photo-Hydrogen-Evolving Molecular Device Driving Visible-Light-Induced EDTA-Reduction of Water into Molecular Hydrogen. J. Am. Chem. Soc. 2006, 128, 4926− 4927. (51) Wong, K. M.-C.; Yam, V. W.-W. Luminescence Platinum(II) Terpyridyl ComplexesFrom Fundamental Studies to Sensory Functions. Coord. Chem. Rev. 2007, 251, 2477−2488. (52) Dixon, I. M.; Lebon, E.; Sutra, P.; Igau, A. Luminescent Ruthenium−Polypyridine Complexes and Phosphorus Ligands: Anything but a Simple Story. Chem. Soc. Rev. 2009, 38, 1621−1634. (53) Zhao, Q.; Li, F.; Huang, C. Phosphorescent Chemosensors Based on Heavy-Metal Complexes. Chem. Soc. Rev. 2010, 39, 3007− 3030. (54) Hirahara, M.; Masaoka, S.; Sakai, K. Syntheses, Characterization, and Photochemical Properties of Amidate-Bridged Pt(bpy) Dimers Tethered to Ru(bpy)32+ derivatives. Dalton Trans. 2011, 40, 3967− 3978. (55) Tsubonouchi, Y.; Lin, S.; Parent, A. R.; Brudvig, G. W.; Sakai, K. Light-Induced Water Oxidation Catalyzed by an Oxido-Bridged Triruthenium Complex with a Ru−O−Ru−O−Ru Motif. Chem. Commun. 2016, 52, 8018−8021. (56) Gill, M. R.; Garcia-Lara, J.; Foster, S. J.; Smythe, C.; Battaglia, G.; Thomas, J. A. A Ruthenium(II) Polypyridyl Complex for Direct Imaging of DNA Structure in Living Cells. Nat. Chem. 2009, 1, 662− 667. (57) Ahmad, H.; Wragg, A.; Cullen, W.; Wombwell, C.; Meijer, A. J. H. M.; Thomas, J. A. From Intercalation to Groove Binding: Switching the DNA-Binding Mode of Isostructural Transition-Metal Complexes. Chem.Eur. J. 2014, 20, 3089−3096. (58) Wragg, A.; Gill, M. R.; Turton, D.; Adams, H.; Roseveare, T. M.; Smythe, C.; Su, X.; Thomas, J. A. Tuning the Cellular Uptake Properties of Luminescent Heterobimetallic Iridium(III)−Ruthenium(II) DNA Imaging Probes. Chem.Eur. J. 2014, 20, 14004−14011. (59) Johnson, J. R.; Fu, N.; Arunkumar, E.; Leevy, W. M.; Gammon, S. T.; Piwnica-Worms, D.; Smith, B. D. Squaraine Rotaxanes: Superior Substitutes for Cy-5 in Molecular Probes for Near-Infrared Fluorescence Cell Imaging. Angew. Chem., Int. Ed. 2007, 46, 5528− 5531. (60) Peng, X.; Wu, T.; Fan, J.; Wang, J.; Zhang, S.; Song, F.; Sun, S. An Effective Minor Groove Binder as a Red Fluorescent Marker for Live-Cell DNA Imaging and Quantification. Angew. Chem., Int. Ed. 2011, 50, 4180−4183. (61) Zhang, S.; Fan, J.; Li, Z.; Hao, N.; Cao, J.; Wu, T.; Wang, J.; Peng, X. A Bright Red Fluorescent Cyanine Dye for Live-Cell Nucleic Acid Imaging, with High Photostability and a Large Stokes Shift. J. Mater. Chem. B 2014, 2, 2688−2693. (62) Dickinson, B. C.; Srikun, D.; Chang, C. J. MitochondrialTargeted Fluorescent Probes for Reactive Oxygen Species. Curr. Opin. Chem. Biol. 2010, 14, 50−56. (63) Neto, B. A. D.; Corrêa, J. R.; Silva, R. G. Selective Mitochondrial Staining with Small Fluorescent Probes: Importance, Design, Synthesis, Challenges and Trends for New Markers. RSC Adv. 2013, 3, 5291−5301. (64) Xu, Z.; Xu, L. Fluorescent Probes for the Selective Detection of Chemical Species Inside Mitochondria. Chem. Commun. 2016, 52, 1094−1119.

(65) Kim, H. M.; An, M. J.; Hong, J. H.; Jeong, B. H.; Kwon, O.; Hyon, J.-Y.; Hong, S. C.; Lee, K. J.; Cho, B. R. Two-Photon Fluorescent Probes for Acidic Vesicles in Live Cells and Tissue. Angew. Chem., Int. Ed. 2008, 47, 2231−2234. (66) Zhang, X.; Wang, C.; Han, Z.; Xiao, Y. A Photostable NearInfrared Fluorescent Tracker with pH-Independent Specificity to Lysosomes for Long Time and Multicolor Imaging. ACS Appl. Mater. Interfaces 2014, 6, 21669−21676. (67) Wu, Z.; Tang, X. Visualizing Fluoride Ion in Mitochondria and Lysosome of Living Cells and in Living Mice with Positively Charged Ratiometric Probes. Anal. Chem. 2015, 87, 8613−8617. (68) Lin, W.; Buccella, D.; Lippard, S. J. Visualization of Peroxynitrite-Induced Changes of Labile Zn2+ in the Endoplasmic Reticulum with Benzoresorufin-Based Fluorescent Probes. J. Am. Chem. Soc. 2013, 135, 13512−13520. (69) Yang, Z.; He, Y.; Lee, J. H.; Chae, W. S.; Ren, W. X.; Lee, J. H.; Kang, C.; Kim, J. S. A Nile Red/BODIPY-Based Bimodal Probe Sensitive to Changes in the Micropolarity and Microviscosity of the Endoplasmic Reticulum. Chem. Commun. 2014, 50, 11672−11675. (70) Xu, W.; Zeng, Z.; Jiang, J.-H.; Chang, Y.-T.; Yuan, L. Discerning the Chemistry in Individual Organelles with Small-Molecule Fluorescent Probes. Angew. Chem., Int. Ed. 2016, 55, 13658−13699. (71) O’Connor, N. A.; Stevens, N.; Samaroo, D.; Solomon, M. R.; Martí, A. A.; Dyer, J.; Vishwasrao, H.; Akins, D. L.; Kandel, E. R.; Turro, N. J. A Covalently Linked Phenanthridine−Ruthenium(II) Complex as a RNA Probe. Chem. Commun. 2009, 2640−2642. (72) Sun, S.; Wang, J.; Mu, D.; Wang, J.; Bao, Y.; Qiao, B.; Peng, X. A Heterodinuclear RuIr Metal Complex for Direct Imaging of rRna in Living Cells. Chem. Commun. 2014, 50, 9149−9152. (73) Cui, Y.; Niu, Y.-L.; Cao, M.-L.; Wang, K.; Mo, H.-J.; Zhong, Y.R.; Ye, B.-H. Ruthenium(II) 2,2′-Bibenzimidazole Complex as a Second-Sphere Receptor for Anions Interaction and Colorimeter. Inorg. Chem. 2008, 47, 5616−5624. (74) Berni, E.; Gosse, I.; Badocco, D.; Pastore, P.; Sojic, N.; Pinet, S. Differential Photoluminescent and Electrochemiluminescent Detection of Anions with a Modified Ruthenium(II)−Bipyridyl Complex. Chem.Eur. J. 2009, 15, 5145−5152. (75) Bhaumik, C.; Saha, D.; Das, S.; Baitalik, S. Synthesis, Structural Characterization, Photophysical, Electrochemical, and Anion-Sensing Studies of Luminescent Homo- and Heteroleptic Ruthenium(II) and Osmium(II) Complexes Based on Terpyridyl-imidazole Ligand. Inorg. Chem. 2011, 50, 12586−12600. (76) Khatua, S.; Samanta, D.; Bats, J. W.; Schmittel, M. Rapid and Highly Sensitive Dual-Channel Detection of Cyanide by Bisheteroleptic Ruthenium(II) Complexes. Inorg. Chem. 2012, 51, 7075−7086. (77) Shu, Q.; Birlenbach, L.; Schmittel, M. A Bis(ferrocenyl)phenanthroline Iridium(III) Complex as a Lab-on-a-Molecule for Cyanide and Fluoride in Aqueous Solution. Inorg. Chem. 2012, 51, 13123−13127. (78) Martí, A. A.; Puckett, C. A.; Dyer, J.; Stevens, N.; Jockusch, S.; Ju, J.; Barton, J. K.; Turro, N. J. Inorganic−Organic Hybrid Luminescent Binary Probe for DNA Detection Based on SpinForbidden Resonance Energy Transfer. J. Am. Chem. Soc. 2007, 129, 8680−8681. (79) Cook, N. P.; Torres, V.; Jain, D.; Martí, A. A. Sensing Amyloid-β Aggregation Using Luminescent Dipyridophenazine Ruthenium(II) Complexes. J. Am. Chem. Soc. 2011, 133, 11121−11123. (80) Cook, N. P.; Kilpatrick, K.; Segatori, L.; Martí, A. A. Detection of α-Synuclein Amyloidogenic Aggregates In Vitro and in Cells using Light-Switching Dipyridophenazine Ruthenium(II) Complexes. J. Am. Chem. Soc. 2012, 134, 20776−20782. (81) Gill, M. R.; Thomas, J. A. Ruthenium(II) Polypyridyl Complexes and DNAfrom Structural Probes to Cellular Imaging and Therapeutics. Chem. Soc. Rev. 2012, 41, 3179−3192. (82) Cook, N. P.; Ozbil, M.; Katsampes, C.; Prabhakar, R.; Martí, A. A. Unraveling the Photoluminescence Response of Light-Switching Ruthenium(II) Complexes Bound to Amyloid-β. J. Am. Chem. Soc. 2013, 135, 10810−10816. N


Article

Inorganic Chemistry (83) Baggaley, E.; Gill, M. R.; Green, N. H.; Turton, D.; Sazanovich, I. V.; Botchway, S. W.; Smythe, C.; Haycock, J. W.; Weinstein, J. A.; Thomas, J. A. Dinuclear Ruthenium(II) Complexes as Two-Photon, Time-Resolved Emission Microscopy Probes for Cellular DNA. Angew. Chem., Int. Ed. 2014, 53, 3367−3371. (84) Stimpson, S.; Jenkinson, D. R.; Sadler, A.; Latham, M.; Wragg, D. A.; Meijer, A. J. H. M.; Thomas, J. A. Tuning the Excited State of Water-Soluble IrIII-Based DNA Intercalators that are Isostructural with [RuII(NN)2(dppz)] Light-Switch Complexes. Angew. Chem., Int. Ed. 2015, 54, 3000−3003. (85) Wragg, A.; Gill, M. R.; McKenzie, L.; Glover, C.; Mowll, R.; Weinstein, J. A.; Su, X.; Smythe, C.; Thomas, J. A. Serum Albumin Binding Inhibits Nuclear Uptake of Luminescent Metal-ComplexBased DNA Imaging Probes. Chem.Eur. J. 2015, 21, 11865−11871. (86) Watanabe, S.; Ikishima, S.; Matsuo, T.; Yoshida, K. A Luminescent Metalloreceptor Exhibiting Remarkably High Selectivity for Mg2+ over Ca2+. J. Am. Chem. Soc. 2001, 123, 8402−8403. (87) Schmittel, M.; Lin, H. Luminescent Iridium Phenanthroline Crown Ether Complex for the Detection of Silver(I) Ions in Aqueous Media. Inorg. Chem. 2007, 46, 9139−9145. (88) 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. (89) Chowdhury, B.; Khatua, S.; Dutta, R.; Chakraborty, S.; Ghosh, P. Bis-Heteroleptic Ruthenium(II) Complex of a Triazole Ligand as a Selective Probe for Phosphates. Inorg. Chem. 2014, 53, 8061−8070. (90) Pyo, S.; Pérez-Cordero, E.; Bott, S. G.; Echegoyen, L. Crystal Structure of [Ru(Terpy)2](0): A New Crystalline Material from the Reductive Electrocrystallization of [Ru(Terpy)2]2+. Inorg. Chem. 1999, 38, 3337−3343. (91) Derossi, S.; Adams, H.; Ward, M. D. Hydrogen-Bonded Assemblies of Ruthenium(II)-Biimidazole Complex Cations and Cyanometallate Anions: Structures and Photophysics. Dalton Trans. 2007, 33−36. (92) Bhaumik, C.; Das, S.; Saha, D.; Dutta, S.; Baitalik, S. Synthesis, Characterization, Photophysical, and Anion-Binding Studies of Luminescent Heteroleptic Bis-Tridentate Ruthenium(II) Complexes Based on 2,6-Bis(Benzimidazole-2-yl) Pyridine and 4′-Substituted 2,2′:6′,2″ Terpyridine Derivatives. Inorg. Chem. 2010, 49, 5049−5062. (93) Boiocchi, M.; Del Boca, L.; Esteban-Gomez, D.; Fabbrizzi, L.; Licchelli, M.; Monzani, E. Anion-Induced Urea Deprotonation. Chem.Eur. J. 2005, 11, 3097−3104. (94) Shiraishi, Y.; Maehara, H.; Hirai, T. Indole-Azadiene Conjugate as a Colorimetric and Fluorometric Probe for Selective Fluoride Ion Sensing. Org. Biomol. Chem. 2009, 7, 2072−2076. (95) Pathak, R. K.; Hinge, V. K.; Mondal, P.; Rao, C. P. Ratiometric Fluorescence Off−On−Off Sensor for Cu2+ in Aqueous Buffer by a Lower Rim Triazole Linked Benzimidazole Conjugate of Calix[4]Arene. Dalton Trans. 2012, 41, 10652−10660. (96) Silverstein, R. M.; Bassler, G. C.; Morrll, T. C. Spectrometric Identification of Organic Compounds, 5th Edition; Wiley: New York, 1991; pp 195−196. (97) Liu, S.; Müller, P.; Takase, M. K.; Swager, T. M. “Click” Synthesis of Heteroleptic Tris-Cyclometalated Iridium(III) Complexes: Cu(I) Triazolide Intermediates as Transmetalating Reagents. Inorg. Chem. 2011, 50, 7598−7609. (98) Sinn, S.; Schulze, B.; Friebe, C.; Brown, D. G.; Jäger, M.; Altuntas, E.; Kübel, J.; Guntner, O.; Berlinguette, C. P.; Dietzek, B.; Schubert, U. S. Physicochemical Analysis of Ruthenium(II) Sensitizers of 1,2,3-Triazole-Derived Mesoionic Carbene and Cyclometalating Ligands. Inorg. Chem. 2014, 53, 2083−2095. (99) Krasiński, A.; Fokin, V. V.; Sharpless, K. B. Direct Synthesis of 1,5-Disubstituted-4-magnesio-1,2,3-triazoles, Revisited. Org. Lett. 2004, 6, 1237−1240. (100) Chuprakov, S.; Chernyak, N.; Dudnik, A. S.; Gevorgyan, V. Direct Pd-Catalyzed Arylation of 1,2,3-Triazoles. Org. Lett. 2007, 9, 2333−2336.

(101) Zhou, Y.; Lecourt, T.; Micouin, L. Direct Synthesis of 1,4Disubstituted-5-alumino-1,2,3-triazoles: Copper-Catalyzed Cycloaddition of Organic Azides and Mixed Aluminum Acetylides. Angew. Chem., Int. Ed. 2010, 49, 2607−2610. (102) Ono, A.; Cao, S.; Togashi, H.; Tashiro, M.; Fujimoto, T.; Machinami, T.; Oda, S.; Miyake, Y.; Okamoto, I.; Tanaka, Y. Specific interactions between silver(I) ions and cytosine−cytosine pairs in DNA duplexes. Chem. Commun. 2008, 4825−4827. (103) Guo, W.; Yuan, J.; Dong, Q.; Wang, E. Highly SequenceDependent Formation of Fluorescent Silver Nanoclusters in Hybridized DNA Duplexes for Single Nucleotide Mutation Identification. J. Am. Chem. Soc. 2010, 132, 932−934. (104) Schultz, D.; Gwinn, E. Stabilization of fluorescent silver clusters by RNA homopolymers and their DNA analogs: C,G versus A,T(U) dichotomy. Chem. Commun. 2011, 47, 4715−4717. (105) Swasey, S. M.; Leal, L. E.; Lopez-Acevedo, O.; Pavlovich, J.; Gwinn, E. G. Silver (I) as DNA glue: Ag+-mediated guanine pairing revealed by removing Watson-Crick constraints. Sci. Rep. 2015, 5, 10163. (106) Schaak, J.; Mao, J.; Söll, D. The 5.8S RNA gene sequence and the ribosomal repeat of Schizosaccharomyces pombe. Nucleic Acids Res. 1982, 10 (9), 2851−2864. (107) Nazar, R. N.; Wong, W. M.; Abrahamson, J. L. A. Nucleotide Sequence of the 18−25 S Ribosomal RNA Intergenic Region from a Thermophile, Thermomyces lanuginosus. J. Biol. Chem. 1987, 262 (16), 7523−7527. (108) Lodish, H.; Berk, A.; Zipursky, S. L.; Matsudaira, P.; Baltimore, D.; Darnell, J. Molecular Cell Biology, 4th Edition; W. H. Freeman: New York, 2000; Chapters 4, 11. (109) Felici, M.; Carballada, P. C.; Vida, Y.; Smits, J. M. M.; Nolte, R. J. M.; Cola, L. D.; Williams, R. M.; Feiters, M. C. IrIII and RuII Complexes Containing Triazole−Pyridine Ligands: Luminescence Enhancement upon Substitution with β-Cyclodextrin. Chem.Eur. J. 2009, 15, 13124−13134. (110) Pavlishchuk, V. V.; Addison, A. W. Conversion Constants for Redox Potentials Measured Versus Different Reference Electrodes in Acetonitrile Solutions at 25 °C. Inorg. Chim. Acta 2000, 298, 97−102. (111) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (112) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299−310. (113) Cossi, M.; Barone, V. Time-Dependent Density Functional Theory for Molecules in Liquid Solutions. J. Chem. Phys. 2001, 115, 4708−4717. (114) Wang, T.; Wang, M. D.; Ding, C. D.; Fu, J. J. MonoBenzimidazole Functionalized β-Cyclodextrins as Supramolecular Nanovalves for pH-Triggered Release of p-Coumaric Acid. Chem. Commun. 2014, 50, 12469.

O


Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for

Recommend Documents